Heat Flux Processes in Streams and Their Impact on Coldwater and Coolwater Fishes

The deluge of rain that soaked the lower Susquehanna watershed during last week is now just a memory.  Streams to the west of the river, where the flooding courtesy of the remnants of Hurricane Debby was most severe, have reached their crest and receded.  Sliding away toward the Chesapeake and Atlantic is all that runoff, laden with a brew of pollutants including but not limited to: agricultural nutrients, sediment, petroleum products, sewage, lawn chemicals, tires, dog poop, and all that litter—paper, plastics, glass, Styrofoam, and more.  For aquatic organisms including our freshwater fish, these floods, particularly when they occur in summer, can compound the effects of the numerous stressors that already limit their ability to live, thrive, and reproduce.

(Environmental Protection Agency image)

One of those preexisting stressors, high water temperature, can be either intensified or relieved by summertime precipitation.  Runoff from forested or other densely vegetated ground normally has little impact on stream temperature.  But segments of waterways receiving significant volumes of runoff from areas of sun-exposed impervious ground will usually see increases during at least the early stages of a rain event.  Fortunately, projects implemented to address the negative impacts of stormwater flow and stream impairment can often have the additional benefit of helping to attenuate sudden rises in stream temperature.

Stream Subjected to Agricultural Runoff
While a row of trees along a creek can help provide protection from the thermal impact of the sun, a vegetative riparian buffer must be much wider to be effective for absorbing, cooling, and treating runoff from fields, lawns, and paved surfaces.  This buffer is too narrow to prevent surface runoff from polluting the water.

Of the fishes inhabiting the Lower Susquehanna River Watershed’s temperate streams, the least tolerant of summer warming are the trouts and sculpins—species often described as “coldwater fishes”.  Coldwater fishes require water temperatures below 70° Fahrenheit to thrive and reproduce.  The optimal temperature range is 50° to 65° F.  In the lower Susquehanna valley, few streams are able to sustain trouts and sculpins through the summer months—largely due to the effects of warm stormwater runoff and other forms of impairment.

Blue Ridge Sculpin
Sculpins, including the Blue Ridge Sculpin (Cottus caeruleomentum) seen here, are native coldwater fishes which, during the 11,000 years since the last glacial maximum, have had the availability of their favored habitat sharply reduced by warming water temperatures and a rising Atlantic.  During this interval, seawater has inundated the path of the “Late” Pleistocene lower Susquehanna which passed through the section of flooded river watershed we now call Chesapeake Bay and continued across the continental shelf to what was, during the glacial maximum, the river’s mouth at Norfolk Canyon.  Today, cut off from neighboring drainage basins, sculpins survive exclusively in cold headwaters, and only in those where human alterations including pollution, dams, channelization, and reduced base flow haven’t yet eliminated their isolated populations.  Formerly believed to be composed of two widespread North American species, the Slimy Sculpin (Cottus cognatus) and the Mottled Sculpin (Cottus bairdii), study in recent decades is discovering that sculpin populations in the present-day lower Susquehanna and neighboring Potomac headwaters consist of at least three newly delineated species: Blue Ridge Sculpin, Potomac Sculpin (Cottus gerardi), and Checkered Sculpin (Cottus sp.), the latter an as yet undescribed species found only in the refugium of limestone springs in the Potomac drainage in West Virginia; Frederick and Washington Counties, Maryland; and Franklin County, Pennsylvania.  (United States Geological Survey image)
Ice Age Susquehanna
Stare at this for a little while, you’ll figure it out…………More than 11,000 years ago, during the last glacial maximum, when sea level was about 275 feet lower than it is today, there was no Chesapeake Bay, just a great Susquehanna River that flowed to the edge of the continental shelf and its mouth at Norfolk Canyon.  It was a river draining taiga forests of pine, spruce , and fir, and it carried along the waters of all the present-day bay’s tributaries and more.  The section of the river’s watershed we presently call the lower Susquehanna was, at the time, the upper Susquehanna watershed.  Brook Trout and sculpins had the run of the river and its tributaries back then.  And the entire watershed was a coldwater fishery, with limestone and other groundwater springs providing not refuge from summer heat, but a place to escape freezing water.  (United States Geological Survey base image)
Norfolk Canyon, the mouth of the Susquehanna River during the most recent glacial maximum, now lies more than 275 feet below the surface of the ocean and plunges to more than a mile in depth along the finger of out wash from the gorge.  (United States Geological Survey image)
Rainbow. Brown, and Brook Trout
Tens of thousands of trout are raised in state-operated and cooperative nurseries for stocking throughout the lower Susquehanna valley.  These rearing facilities are located on spring-fed headwaters with sufficient flow to assure cold temperatures year round.  While the Rainbow Trout and Brown Trout (Salmo trutta) are the most commonly stocked species, the Brook Trout (Salvelinus fontinalis) is the only one native to American waters.  It is the least tolerant of stream warming and still reproduces in the wild only in a few pristine headwaters streams in the region.  During spring, all three of these species have been observed on rare occasions entering the fish lift facilities at the hydroelectric dams on the river, presumably returning to the Susquehanna as sea-run trout.

Coldwater fishes are generally found in small spring-fed creeks and  headwaters runs. Where stream gradient, substrate, dissolved oxygen, and other parameters are favorable, some species may be tolerant of water warmer than the optimal values.  In other words, these temperature classifications are not set in stone and nobody ever explained ichthyology to a fish, so there are exceptions.  The Brown Trout for example is sometimes listed as a “coldwater transition fish”, able to survive and reproduce in waters where stream quality is exceptionally good but the temperature may periodically reach the mid-seventies.

Eastern Blacknose Dace
The Eastern Blacknose Dace is sometimes classified as a “coldwater transition fish”.   It can be found in headwaters runs as well as in creeks with good water quality.
Longnose Dace
The Longnose Dace is another “coldwater transition fish” known only from clear, clean, flowing waters.

More tolerant of summer heat than the trouts, sculpins, and daces are the “coolwater fishes”—species able to feed, grow, and reproduce in streams with a temperature of less than 80° F, but higher than 60° F.  Coolwater fishes thrive in creeks and rivers that hover in the 65° to 70° F range during summer.

Creek Chubs
The Creek Chub is a familiar species of “coolwater fish” seldom found remaining in waters exceeding 80 degrees Fahrenheit.
The Yellow Perch (Perca flavescens) was perhaps the most frequently targeted coolwater “gamefish” in the Lower Susquehanna River Watershed prior to the introduction of the Northern Pike (Esox lucius) and Muskellunge (Esox masquinongy).  Today’s prevalence of warmwater streams and the dozens of species of non-native predatory fishes now naturalized within them have left the Yellow Perch populations greatly reduced and all but forgotten by anglers.  Out of sight, out of mind.  (National Park Service image)

What are the causes of modern-day reductions in coldwater and coolwater fish habitats in the lower Susquehanna River and its hundreds of miles of tributaries?  To answer that, let’s take a look at the atmospheric, cosmic, and hydrologic processes that impact water temperature.  Technically, these processes could be measured as heat flux—the rate of heat energy transfer per unit area per unit time, frequently expressed as watts per meter squared (W/m²).  Without getting too technical, we’ll just take a look at the practical impact these processes have on stream temperatures.

HEAT FLUX PROCESSES IN A SEGMENT OF STREAM

Heat Flux Processes on Stream and River Segments.  These processes could be measured as heat flux—the rate of heat energy transfer per unit area per unit time.  (Environmental Protection Agency image)
      • INCOMING TEMPERATURE AND FLOW—The baseline temperature of stream water entering a given segment of waterway is obviously the chief factor determining its temperature when exiting that segment.  Incoming temperature and flow also determine the water’s susceptibility to heat absorption or loss while transiting the segment.  Lower flows may subject the given volume of water to a greater loss or gain of heat energy during the time needed to pass through the segment than the same volume at a higher flow.  Lower flows may also reduce stream velocity and extend a given volume of water’s exposure time to the exchange of heat energy while moving through the segment.  Generally speaking…
        1. …the higher the stream flow, the less a given volume of that stream’s  water may be impacted by the effects of the heat flux processes within the segment.
        2. …the lower the stream flow, the more a given volume of that stream’s water may be impacted by the effects of the heat flux processes within that segment.
        3. …the temperature and flow rate of precipitation entering the segment are factors that determine the impact of its heat energy transfer to or from a given volume of the stream’s waters.
        4. …the temperature and flow rate of runoff and point-source discharges entering the segment are factors that determine the impact of their heat energy transfer to or from a given volume of the stream’s waters.
Stormwater Discharge into Channelized Creek
Stormwater from impervious surfaces including roads, parking lots, roofs, and lawns quickly impacts temperatures in small creeks.  Channelized  streams are availed few of the positive attributes provided by many of the heat flux processes we’re about to see.  They therefore suffer from severe impairment and are exposed to temperature extremes that few aquatic organisms can survive.  Runoff from sun-heated pavement during a summer thunderstorm can often exceed 100 degrees Fahrenheit and can, at sufficient flow rate, quickly raise the temperature of a small stream to well over 90 degrees.
Stormwater Runoff
Stormwater runoff not only poses a thermal threat to waterways, its a significant source of a wide variety of pollutants.
      • GROUNDWATER INPUT—In streams connected to the aquifer, the temperature in a flowing segment can be impacted by the influx of cold groundwater.  With temperatures ranging from about 52° to 60° Fahrenheit, groundwater will absorb heat from the stream in summer, and warm it in the winter.  In warmwater streams, coldwater and coolwater fishes will often seek areas of the substrate where groundwater is entering for use as refugium from the summer heat.  Yellow Perch in the lower Susquehanna are known to exhibit this behavior.
Creeks and rivers connected to the aquifer and receiving supplemental flow from it are known as “gaining streams”. These streams frequently feed water into the aquifer as well. (United States Geological Survey image)
When flowing through an area experiencing drought or an excessive removal of groundwater (lots of wells, etc.), a waterway can become a “losing stream”, one that surrenders a portion of its flow to recharge the aquifer.  Further downstream, the reduced flow can make such a creek or river more susceptible to the effects of heat flux processes.  (United States Geological Survey image)
Seriously depleted aquifers can lead to a “disconnected stream”.  Smaller waterways subjected to these conditions will sometimes lose all their flow to the ground, often causing a catastrophic failure of the aquatic ecosystem supported therein.  (United States Geological Survey image)
Urban Flooding and Dry Streambed
Urban runoff overwhelms this small stream with polluted water than can reach temperatures of 100 degrees or more (left), then lets it high and dry with no baseflow during periods of dry weather (right) as the waterway becomes disconnected from the much-depleted aquifer.
Stormwater Retention Basin
Well-designed and properly constructed stormwater retention basins not only recharge groundwater supplies for wells and streams, they can also help prevent thermal pollution in waterways.  Planted with native wetland species and allowed to thrive, they can become treasured wildlife islands in otherwise inhospitable environs.  The benefits don’t stop there; plants also help sequester nutrients contained in the runoff.
      • HYPORHEIC EXCHANGE—Related to groundwater input, hyporheic exchange is the slow movement of water through the rock, sand, gravel, and soils composing the streambed, saturated shoreline, shallow aquifer, and connected floodplain of a creek or river.  As a heat flux process, hyporheic exchange helps moderate extremes in seasonal water temperatures by conducting energy between the solid materials in the zone and the flowing water.  Hyporheic zones are important habitats for many species of aquatic invertebrates and spawning fish.  Natural chemical processes within these zones convert ammonia-producing wastes into nitrite, then nitrate, allowing it to be absorbed as food by plants growing in the stream or in the alluvium within the zone.  Vegetation removal, channelization, legacy sediments, silt deposits, and man-made walls and dams can negate the benefits of hyporheic exchange.
Exchange of surface and ground water within the hyporheic zone is most directly associated with high-gradient (left) and meandering (right) segments of streams. (United States Geological Survey image)
Legacy Sediments and Fill
Very common on streams in the lower Susquehanna valley are these accumulations of legacy sediments at the sites of former mill ponds.  After the dams were removed, the creeks began eroding their way down through the mire as they tried to reestablish their floodplains and find their native substrate.  These trapped waterways are not only cut off from their hyporheic zones, they’re now a major source of nutrient and sediment pollution.  Misguided landowners like this one frequently dump fill into these sites to “save their land” and “control flooding”.  The fill and materials added to “shore up the banks” do nothing to fix what ails the creek, but instead displace more water to make the impact of flooding even more widespread.
Flooplain and Stream Restoration
Rehabilitation projects that remove legacy sediments help restore hyporheic exchange by reconnecting the stream to its underlying geology, its floodplain, and its wetlands.  Rising waters remain in the floodplain where they get a good bio-scrubbing and help replenish the creek and groundwater supply.  As the experts say, “floodplains are for flooding.”
      • ATMOSPHERIC EXCHANGE (CONVECTION, EVAPORATION)—Primarily a process by which a stream loses heat energy and cools its waters, atmospheric exchange is also a means by which a warm air mass can relinquish heat to cooler waters and thus increase their temperature.  This phenomenon can be dramatically enhanced when a stream passes through a so-called urban heat island where air temperatures remain warm through the night.  Convection, the movement of heat energy through a fluid (liquid or gas), causes warmer, less-dense water to rise to the surface of a stream, particularly where there is minimal turbulence.  When the air above is cooler than the water’s surface layer, the stream will conduct heat energy across the water/atmosphere interface causing the warmed air molecules to rise in a convection column.  If the atmospheric relative humidity is less than 100%, some surface water will vaporize—a process that expends more of the stream’s heat energy.  The rate of convective and evaporative cooling in a given stream segment is directly related to the degree of difference between the water temperature and air temperature, and to the relative humidity in the air mass above the lake, creek, or river.  The mechanical action of stream turbulence including rapids, riffles, and falls increases the contact area between air and water to maximize the atmospheric exchange of heat energy.  The convective air current we call surface wind has a turbulent wave-producing effect on water that can also maximize atmospheric exchange; think of a cold autumn wind robbing heat energy from a warm lake or river or a hot summer wind imparting its heat to a cooler creek.  These exchanges are both conductive in nature (air-to-water/water-to-air) and evaporative, the latter being expedited by the movement of dry air over warm water.
Tessellated Darter
Usually classified as one of the coolwater fishes, the bottom-dwelling Tessellated Darter can thrive in the warmer creeks and in the main stem of the Susquehanna by inhabiting riffles where atmospheric exchange in the form of increased evaporation helps reduce temperatures and convective currents carry the cooler, well-oxygenated water to the streambed.
Three mile Island Unit 1 Cooling Towers
Humans utilize the concept of atmospheric exchange, adopting the phenomena of evaporation and convection to cool the hot waters produced during electric generation and other industrial processes before discharge into a lake or river.
      • STREAMBED CONDUCTIVE EXCHANGE—In the lower Susquehanna watershed, there may be no better natural example of streambed conductive exchange than the Triassic-Jurassic diabase pothole bedrocks of Conewago Falls on the river at the south end of Three Mile Island.
During sunny days, the massive diabase pothole rocks at Conewago Falls absorb solar (shortwave) radiation, then conduct that heat energy into the flowing water, often continuing to pass the accumulated warmth into the river during the night.  On cloudy days, the riverbed collects longwave atmospheric radiation, a heat flux process that yields significantly less energy for conduction into the rapids, riffles, and pools of the falls.  During periods of low river flow, the heating effect of streambed conductive exchange can become magnified.  Compared to conditions that prevail when torrents of turbid water are rushing through the falls, partially exposed bedrock surrounded by clear water collects radiated energy much more efficiently, then conducts the heat to a greatly reduced volume of passing water.  During summer and autumn, this process can create a mix of temperature zones within the falls with warmer water lingering in slow-moving pools and cooler water flowing in the deeper fast-moving channels.  Along the falls’ mile-long course, a haven is created for aquatic organisms including warmwater and some coolwater fishes, oft times attracting anglers and a variety of hungry migrating birds as well.
Fallfish
Classified as one of our coolwater fishes, the Fallfish finds favorable conditions for feeding, growing, and spawning in the well-oxygenated waters of Conewago Falls.
Northern Hog Sucker
Though the lower Susquehanna River is classified as a warmwater fishery, the Northern Hog Sucker (Hypentelium nigricans), another of our native coolwater fishes, finds the fast-moving waters of Conewago Falls to its liking.  Northern Hog Suckers are known to inhabit streams cold enough to host trout.  They exhibit remarkable home range fidelity, sometimes spending their entire lives occupying the same several hundred feet of waterway.  Northern Hog Suckers are often designated an indicator of good water quality, intolerant of many stream impairment parameters.  Their presence in Conewago Falls provides testament to the quality of the warmwater fishery there.
Severely Impaired Channelized Stream
An unnatural example.  The reduced base flow in this channelized and severely impaired creek has been rendered vulnerable to the negative impacts of several heat flux processes including streambed conductive exchange.  Urban stormwater/surfacewater inflow, solar (shortwave) radiation, and heat conducted into the stream from the masonry walls, curbs, and raceway can all conspire to cook aquatic organisms with life-quenching summer water temperatures exceeding 90 degrees Fahrenheit.
      • SOLAR (SHORTWAVE) RADIATION—The sun provides the energy that fuels the earth’s complex climate.  The primary heat flux process that heats our planet is the absorption of solar radiation in the shortwave spectrum, which includes ultraviolet, visible, and infrared frequencies at the upper end of the longwave spectrum.  Streams and other bodies of water absorb the greatest amounts of solar (shortwave) radiation during the weeks around summer solstice when the sun at mid-day is closer to zenith than at any other time of the year.  However, the heating impact of the radiation may be greatest when the volume of water in the creek, river, or lake is at its minimum for the year—often during early fall.
The rate, measured in watts per square meter, at which solar (shortwave) energy is directly radiated to a given area on the earth’s surface (including streams and other waters) is determined by: solar activity, the angle of the sun in the sky, aspect (slope) of the receiving surface, the opacity of the overlying atmosphere, and the distance of the earth from the sun.  The former varies with the year’s seasons, the time of day, and the latitude of a given area.  The latter is currently at its annual minimum when earth is at perihelion during the early days of January, thus providing the northern hemisphere with a little bump in radiation during the shortest days of the year when the sun is at its lowest angle in the sky.  (NASA image)
A varying portion of the solar (shortwave) radiation reaching the earth is reflected back into space by clouds.  A smaller share is absorbed by the atmosphere, thus heating it.  An even lesser quantity is reflected back into space by water and land.  The remainder of the energy is absorbed by the planet’s surfaces, its water and land. (NASA image)
      • INCIDENT SHORTWAVE RADIATION—Also known as insolation (incoming solar radiation), incident shortwave radiation is the sum total energy of both the direct solar radiation that travels to the earth’s surface unaffected by the atmosphere and the diffuse radiation, waves that have been weakened and scattered by constituents of the atmosphere before reaching the planet’s surface.  On a cloudy day, the warming of terrestrial surfaces including streams and other bodies of water is the result of diffuse radiation.  On days with any amount of sunshine at all, both direct and diffuse radiation heat our waters and lands.
Pumkinseed
Warmwater fishes such as the native Pumpkinseed (Lepomis gibbosus) thrive in sun-drenched 70-to-85-degree waters as long as other heat flux processes prevent sudden temperature increases and oxygen depletion.
Mowed Stream Bank
Mowed stream banks offer a waterway no protection from incoming solar (shortwave) radiation, nor terrestrial forms of impairment including nutrient-rich stormwater runoff and silt.
      • REFLECTED SHORTWAVE RADIATION—known as albedo, reflected solar (shortwave) radiation is energy directed away from the earth’s surface before being absorbed.  A surface’s albedo value is basically determined by its color, black having little reflective value, white and silvery surfaces reflecting nearly all solar (shortwave) radiation away.  A surface with no reflective properties has an albedo value of 0, while a totally reflective surface has a value of 1.  Clean snow with a value of about 0.85 to 0.9 (85% to 90%) is a highly reflective surface; yellow snow isn’t as good.  A stream, river, or lake blanketed with ice and snow will absorb very little solar energy and will rely upon other heat flux processes to trigger a melt and thaw.  The surface of open water has a varying albedo value determined mostly by the angle of the sun.  Solar radiation striking the water’s surface at a low angle is mostly reflected away, while that originating at an angle closer to zenith is more readily absorbed.
Forested Stream
To avoid the heating effects of solar (shortwave) and atmospheric longwave radiation, coldwater and coolwater fishes require streams offering protection from full exposure to direct sunlight and cloud cover.  Runs and creeks flowing beneath a closed canopy of forest trees are shielded from 25% or more of incoming radiation and are thus able to better maintain thermal stability during the most vulnerable period of the year for temperature-sensitive fishes, May through October.
      • LONGWAVE RADIATION—Radiation in the longwave spectrum is composed of infrared waves at frequencies lower than those of the shortwave spectrum.  Longwave radiation, sometimes just called infrared radiation, is produced by the earth and its atmosphere and is propagated in all directions, day and night.  It warms mostly the lower atmosphere which in turn warms the earth’s surface including its waters.  Some longwave energy can even be radiated into the waterway from its own streambed—and the stream can return the favor.  Other forms of mass surrounding  a stream such as a rocky shoreline or a man-made structure such as bridge pier can trade longwave radiation with a waterway.  The effect of these latter exchanges is largely trivial and never rivals the heat flux transfer of warm to cold provided by  conduction.
Longwave radiation emissions slow as the temperature of the emitting mass decreases, just as they also increase with temperature of the mass.  Longwave radiation emissions therefore decrease with altitude along with the temperature of the water vapor, carbon dioxide, methane, and other gases that produce them.  As such, the highest reaches of the atmosphere have a greatly reduced capability of shedding longwave radiation into space.  At ground level, lakes, creeks, and streams receive their greatest dose of longwave radiation while beneath the cover of low-lying clouds or fog.  (NASA image)
      • CANOPY RADIATION—Trees emit longwave radiation that may have a limited heat flux impact on waterway temperature.  This radiation is diffuse, of scattered effect, and scarcely detectable, particularly beneath multilayered dense canopies.  Some of the infrared energy transmitted by the tree canopy is radiated skyward as well.
      • WATER RADIATION—Water, like all earthly matter composed of vibrating molecules, emits longwave radiation.  This heat flux process provides an ongoing cooling effect to streams, rivers, lakes, and oceans—warmer ones shedding infrared energy at a faster rate than those that are cold.

Now that we have a basic understanding of the heat flux processes responsible for determining the water temperatures of our creeks and rivers, let’s venture a look at a few graphics from gauge stations on some of the lower Susquehanna’s tributaries equipped with appropriate United States Geological Survey monitoring devices.  While the data from each of these stations is clearly noted to be provisional, it can still be used to generate comparative graphics showing basic trends in easy-to-monitor parameters like temperature and stream flow.

Each image is self-labeled and plots stream temperature in degrees Fahrenheit (bold blue) and stream discharge in cubic feet per second (thin blue).

The West Conewago Creek drains much of the Gettysburg Basin’s Triassic redbeds in Adams and northern York Counties in Pennsylvania and includes a small headwaters area in northern Maryland.  The gauge station is located just a over a mile upstream from the waterway’s mouth on the Susquehanna just below Conewago Falls.  Right through the summer heatwave, this 90-day graph shows a consistent daily pattern of daytime rises in temperature and nighttime cooling.  To the right, a rapid cool down can be seen coinciding with two periods of high water, the first from a series of heavy thundershowers, the second from flooding caused by the remnants of Hurricane Debby.  Notice that the early August downpours were so heavy that they cooled the hot surface runoff and waterway quickly, without creating a rise in stream temperature at the gauging station.  Had this monitoring device been located on a small tributary in an area with an abundance of impervious surfaces, there would probably have been a brief rise in stream temperature prior to the cooldown.  (United States Geological Survey image)

The daily oscillations in temperature reflect the influence of several heat flux processes.  During the day, solar (shortwave) radiation and convection from summer air, especially those hot south winds, are largely responsible for the daily rises of about 5° F.  Longwave radiation has a round-the-clock influence—adding heat to the stream during the day and mostly shedding it at night.  Atmospheric exchange including evaporative cooling may help moderate the rise in stream temperatures during the day, and certainly plays a role in bringing them back down after sunset.  Along its course this summer, the West Conewago Creek absorbed enough heat to render it a warmwater fishery in the area of the gauging station.  The West Conewago is a shallow, low gradient stream over almost its entire course.  Its waters move very slowly, thus extending their exposure time to radiated heat flux and reducing the benefit of cooling by atmospheric exchange.  Fortunately for bass, catfish, and sunfish, these temperatures are in the ideal range for warmwater fishes to feed, grow, and reproduce—generally over 80° F, and ideally in the 70° to 85° F range.  Coolwater fishes though, would not find this stream segment favorable.  It was consistently above the 80° F maximum and the 60° to 70° F range preferred by these species.  And coldwater fishes, well, they wouldn’t be caught dead in this stream segment.  Wait, scratch that—the only way they would be caught in this segment is dead.  No trouts or sculpins here.

The Codorus Creek drains primarily the carbonate valleys of York County to the south of the West Conewago watershed.  This gauge station is located about a mile upstream from the creek’s mouth on the Susquehanna just below Haldeman Riffles.  The graphic pattern is very similar to that of the West Conewago’s: daily heating and cooling cycles and a noticeable drop in stream temperature in early August caused by a day of thundershowers followed by the remnants of Hurricane Debby.  (United States Geological Survey image)

Look closely and you’ll notice that although the temperature pattern on this chart closely resembles that of the West Conewago’s, the readings average about 5 degrees cooler.  This may seem surprising when one realizes that the Codorus follows a channelized path through the heart of York City and its urbanized suburbs—a heat island of significance to a stream this size.  Before that it passes through numerous impoundments where its waters are exposed to the full energy of the sun.  The tempering factor for the Codorus is its baseflow.  Despite draining a smaller watershed than its neighbor to the north, the Codorus’s baseflow (low flow between periods of rain) was 96 cubic feet per second on August 5th, nearly twice that of the West Conewago (51.1 cubic feet per second on August 5th).  Thus, the incoming heat energy was distributed over a greater mass in the Codorus and had a reduced impact on its temperature.  Though the Codorus is certainly a warmwater fishery in its lower reaches, coolwater and transitional fishes could probably inhabit its tributaries in segments located closer to groundwater sources without stress.  Several streams in its upper reaches are in fact classified as trout-stocked fisheries.

This is a zoomed-in look at the previous graph showing the impact of a rainfall event on the water temperatures in Codorus Creek.  Unlike the sharp declines accompanying the deluge of flood waters during the two events in early August, these lesser storms in late June generated just enough runoff to capture heat energy from impervious surfaces and warm the creek, temporarily breaking the daily heating/cooling cycle.  Upstream in the immediate area of the runoff, the impact on the stream and/or its tributaries was probably much more dramatic, certainly raising temperatures into the nineties or above.  (United States Geological Survey image)
Kreutz Creek drains a carbonate bedrock area of York County and flows parallel to the Lincoln Highway (US 30) to enter the Susquehanna at Wrightsville.  The gauging station is about one mile upstream from the creek’s mouth.   (United States Geological Survey image)

The Kreutz Creek gauge shows temperature patterns similar to those in the West Conewago and Codorus data sets, but notice the lower overall temperature trend and the flow.  Kreutz Creek is a much smaller stream than the other two, with a flow averaging less than one tenth that of the West Conewago and about one twentieth of that in the Codorus.  And most of the watershed is cropland or urban/suburban space.  Yet, the stream remains below 80° F through most of the summer.  The saving graces in Kreutz Creek are reduced exposure time and gradient.  The waters of Kreutz Creek tumble their way through a small watershed to enter the Susquehanna within twenty-four hours, barely time to go through a single daily heating and cooling cycle.  As a result, their is no chance for water to accumulate radiant and convective heat over multiple summer days.  The daily oscillations in temperature are less amplified than we find in the previous streams—a swing of about three degrees compared to five.  This indicates a better balance between heat flux processes that raise temperature and those that reduce it.  Atmospheric exchange in the stream’s riffles, forest cover, and good hyporheic exchange along its course could all be tempering factors in Kreutz Creek.  From a temperature perspective, Kreutz Creek provides suitable waters for coolwater fishes.

Muddy Creek drains portions of southern York County through rolling farmland and woodlots.  There are no large impoundments or widespread urban impacts in the watershed, which may help explain its slightly lower temperature trends.  (United States Geological Survey image)

Muddy Creek is a trout-stocked fishery, but it cannot sustain coldwater species through the summer heat.  Though temperatures in Muddy Creek may be suitable for coolwater fishes, silt, nutrients, low dissolved oxygen, and other factors could easily render it strictly a warmwater fishery, inhabited by species tolerant of significant stream impairment.

Chiques Creek drains mostly limestone farmland in northwestern Lancaster County.  The gauging station is located near the stream’s mouth on the Susquehanna at Chiques (Chickies) Rock.  Oscillations in temperature again resemble the other waterways, but daily highs remain almost entirely below 80 degrees.  (United States Geological Survey image)

A significant number of stream segments in the Chiques watershed have been rehabilitated to eliminate intrusion by grazing livestock, cropland runoff, and other sources of impairment.  Through partnerships between a local group of watershed volunteers and landowners, one tributary, Donegal Creek, has seen riparian buffers, exclusion fencing, and other water quality and habitat improvements installed along nearly ever inch of its run from Donegal Springs through high-intensity farmland to its mouth on the main stem of the Chiques just above its confluence with the Susquehanna.  The improved water quality parameters in the Donegal support native coldwater sculpins and an introduced population of reproducing Brown Trout.  While coldwater habitat is limited to the Donegal, the main stem of the Chiques and its largest tributary, the Little Chiques Creek, both provide suitable temperatures for coolwater fishes.

Limestone Formation on Little Chiques Creek
Streams in the Chiques Creek and similar limestone watersheds often pass through areas with significant bedrock formations.  Heat flux processes including groundwater input, hyporheic exchange, and streambed conductive exchange can have a greater influence on water temperature along these segments.
Eastern Blacknose Dace
A breeding condition Eastern Balcknose Dace, one of the coldwater transition fishes found in the Chiques and its tributaries.
Common Shiner
The Common Shiner (Luxilus cornutus), a fish tolerant of warmwater streams, prefers cool, clear waters for spawning.  For protection from late-spring and summer heat, breeding males may seek a section of creek with a streambed inflow of limestone groundwater to defend as their nesting territory.
A closeup of the Chiques Creek graph showing what appears to be a little bump in temperature caused by surface runoff during a couple of late-May showers.  Stream rehabilitation is an ongoing process and the pressures of land disturbances both old and new present challenges to those who make it their passion to fix the wrongs that have been inflicted upon our local waters.  Even the  exemplary Donegal Creek faces new threats from urbanization in one of its headwater areas several miles to the northwest of the historic springs.  (United States Geological Survey image)
Conewago Creek (East) drains primarily Triassic redbed farmlands in Dauphin, Lancaster, and Lebanon Counties.  Much of the headwaters area is forested but is experiencing an increasing rate of encroachment by housing and some commercial development.  Conewago Creek (East) enters the Susquehanna on the east side of Conewago Falls at Three Mile Island.  The watershed is equipped with three U.S.G.S. gauge stations capable of providing temperature data.  This first one is located just over a mile upstream of the creek’s mouth.  (United States Geological Survey image)

Despite its meander through and receipt of water from high-intensity farmland, the temperature of the lower Conewago (East) maxes out at about 85° F, making it ideal for warmwater fishes and even those species that are often considered coolwater transition fishes like introduced Smallmouth Bass, Rock Bass, Walleye, and native Margined Madtom.  This survivable temperature is a testament to the naturally occurring and planted forest buffers along much of the stream’s course, particularly on its main stem.  But the Conewago suffers serious baseflow problems compared to other streams we’ve looked at so far.  Just prior to the early August storms, flow was well below 10 cubic feet per second for a drainage area of more than fifty square miles.  While some of this reduced flow is the result of evaporation, much of it is anthropogenic in origin as the rate of groundwater removal continues to increase  and a recent surge in stream withdraws for irrigation reaches its peak during the hottest days of summer.

Juvenile Rock Bass
A juvenile Rock Bass.
A juvenile Margined Madtom.
A juvenile Margined Madtom.
A closer look at the Conewago Creek (East) graphic shows the temperature drop associated with a series of thundershowers and the remnants of Hurricane Debby in early August.  Despite the baseflow being below five cubic feet per second, the cooling effect of the downpours as measured in the area of the gauge was significant enough to overwhelm any heating of runoff that may have occurred as precipitation drained across hardened soils or man-made impervious surfaces.  (United States Geological Survey image)

A little side note—the flow rate on the Conewago at the Falmouth gauge climbed to about 160 cubic feet per second as a result of the remnants of Hurricane Debby while the gauge on the West Conewago at Manchester skyrocketed to about 20,000 cubic feet per second.  Although the West Conewago’s watershed (drainage area) is larger than that of the Conewago on the east shore, it’s larger only by a multiple of two or three, not 125.  That’s a dramatic difference in rainfall!

The Bellaire monitoring station on Conewago Creek (East) is located on the stream’s main stem just downstream from the mouth of Little Conewago Creek, a tributary with its origins in farmland and woodlots.  (United States Geological Survey image)

The temperatures at the Bellaire monitoring station, which is located upstream of the Conewago’s halfway point between its headwaters in Mount Gretna and its mouth, are quite comparable to those at the Falmouth gauge.  Although a comparison between these two sets of data indicate a low net increase in heat absorption along the stream’s course between the two points, it also suggests sources of significant warming upstream in the areas between the Bellaire gauge and the headwaters.

Data from the gauge site on the Little Conewago Creek shows a temperature averaging about five degrees cooler than the gauge several miles downstream on the main stem of the Conewago at Bellaire.  (United States Geological Survey image)

The waters of the Little Conewago are protected within planted riparian buffers and mature woodland along much of their course to the confluence with the Conewago’s main stem just upstream of Bellaire.  This tributary certainly isn’t responsible for raising the temperature of the creek, but is instead probably helping to cool it with what little flow it has.

Juvenile Eastern Blacknose Dace (top) and a juvenile Longnose Dace.
A stream like the Little Conewago Creek with daily temperatures that remain mostly below 80 degrees and retreat to 75 degrees or less during the night can be suitable for coldwater transition fishes like these juvenile Eastern Blacknose Dace (top) and Longnose Dace.

Though mostly passing through natural and planted forest buffers above its confluence with the Little Conewago, the main stem’s critically low baseflow makes it particularly susceptible to heat flux processes that raise stream temperatures in segments within the two or three large agricultural properties where owners have opted not to participate in partnerships to rehabilitate the waterway.  The headwaters area, while largely within Pennsylvania State Game Lands, is interspersed with growing residential communities where potable water is sourced from hundreds of private and community wells—every one of them removing groundwater and contributing to the diminishing baseflow of the creek.  Some of that water is discharged into the stream after treatment at the two municipal sewer plants in the upper Conewago.  This effluent can become quite warm during processing and may have significant thermal impact when the stream is at a reduced rate of flow.  A sizeable headwaters lake is seasonally flooded for recreation in Mount Gretna.  Such lakes can function as effective mid-day collectors of solar (shortwave) radiation that both warms the water and expedites atmospheric exchange.

The Conewago Creek (East) Watershed from the Bellaire U.S.G.S. Gauging Station (lower left) upstream to the headwaters in Mount Gretna.  (United States Geological Survey image)

Though Conewago Creek (East) is classified as a trout-stocked fishery in its upper reaches in Lebanon County, its low baseflow and susceptibility to warming render it inhospitable to these coldwater fishes by late-spring/early summer.

River Chub
Despite being considered a warmwater fish, the River Chub (Nocomis micropogon) will ascend streams like the Conewago to seek cooler, gravel-bottomed waters for spawning.  Reduced baseflow has probably rendered the stream currently too small for this species on Pennsylvania State Game Lands in Colebrook where this specimen was photographed in 2018.
Juvenile Golden Shiner
The Golden Shiner, another warmwater fish, often ascends streams to enter cooler water. Juvenile Golden Shiners like this one will move into shallower headwaters not only to seek reduced temperatures, but to escape large predatory fishes as well.
Irrigation using stream water.
Irrigation of agricultural fields using a large portion of the already diminished baseflow in the Conewago Creek (East) just downstream of the Bellaire gauging station.  Despite millions of dollars in investment to rehabilitate this Susquehanna valley stream, the riparian buffers and other practices can have little effect when the creek gets sucked down to just a trickle.  Low baseflow is a hard nut to crack.  It’s best prevented, not corrected.
Hammer Creek, a trout-stocked fishery, originates, in part, within Triassic conglomerate in the Furnace Hills of Lebanon County, then flows north into the limestone Lebanon Valley where it picks up significant flow from other tributaries before working its way south back through the Furnace Hills into the limestone farmlands of Lancaster County.  From there the stream merges with the Cocalico Creek, then the Conestoga River, and at last the Susquehanna.  Note the tremendous daily temperature oscillations on this headwaters stream as it surges about 15 degrees each day before recovering back close to groundwater temperature by sunrise the next day.  (United States Geological Survey image)
Headwaters of Hammer Creek including Buffalo Springs, a significant source of cold groundwater feeding the western leg of the stream.  The large dams on this section that created the Lebanon and Rexmont Reservoirs have been removed.  (United States Geological Survey base image)

The removal of two water supply dams on the headwaters of Hammer Creek at Rexmont eliminated a large source of temperature fluctuation on the waterway, but did little to address the stream’s exposure to radiant and convective heat flux processes as it meanders largely unprotected out of the forest cover of Pennsylvania State Game Lands and through high-intensity farmlands in the Lebanon Valley.  Moderating the temperature to a large degree is the influx of karst water from Buffalo Springs, located about two miles upstream from this gauging station, and other limestone springs that feed tributaries which enter the Hammer from the east and north.  Despite the cold water, the impact of the stream’s nearly total exposure to radiative and other warming heat flux processes can readily be seen in the graphic.  Though still a coldwater fishery by temperature standards, it is rather obvious that rapid heating and other forms of impairment await these waters as they continue flowing through segments with few best management practices in place for mitigating pollutants.  By the time Hammer Creek passes back through the Furnace Hills and Pennsylvania State Game Lands, it is leaning toward classification as a coolwater fishery with significant accumulations of sediment and nutrients.  But this creek has a lot going for it—mainly, sources of cold water.  A core group of enthusiastic landowners could begin implementing the best management practices and undertaking the necessary water quality improvement projects that could turn this stream around and make it a coldwater treasure.  An organized effort is currently underway to do just that.  Visit Trout Unlimited’s Don Fritchey Chapter and Donegal Chapter to learn more.  Better yet, join them as a volunteer or cooperating landowner!

Male Creek Chub
The male Creek Chub, one of our coolwater fishes, develops head tubercles and becomes flushed with color during spawning season.  Hammer Creek not only provides a home for the Creek Chub, its cold headwaters provide refuge for a population of native Brook Trout too.
Like no other example we’ve looked at so far, this closeup of the Hammer Creek graphic shows temperature bumps correlating with the stormwater runoff from early August’s rains.  Because the stream flow is small and the precipitation rate was not as great at this location, the effect of heat flux from runoff is more readily apparent.  (United States Geological Survey image)
Brook Trout adult and juvenile.  (United States Fish and Wildlife Service image by Ryan Hagerty)

For coldwater fishes, the thousands of years since the most recent glacial maximum have seen their range slowly contract from nearly the entirety of the once much larger Susquehanna watershed to the headwaters of only our most pristine streams.  Through no fault of their own, they had the misfortune of bad timing—humans arrived and found coldwater streams and the groundwater that feeds them to their liking.  Some of the later arrivals even built their houses right on top of the best-flowing springs.  Today, populations of these fishes in the region we presently call the Lower Susquehanna River Watershed are seriously disconnected and the prospect for survival of these species here is not good.  Stream rehabilitation, groundwater management, and better civil planning and land/water stewardship are the only way coldwater fishes, and very possibly coolwater fishes as well, will survive.  For some streams like Hammer Creek, it’s not too late to make spectacular things happen.  It mostly requires a cadre of citizens, local government, project specialists, and especially stakeholders to step up and be willing to remain focused upon project goals so that the many years of work required to turn a failing stream around can lead to success.

Riparian Buffer
Riparian buffers with fences to exclude livestock can immediately begin improving water quality.  With establishment of such vegetative buffers, the effects of stressors that otherwise eliminate coldwater and coolwater fishes from these segments will begin to diminish.
Riparian Buffer
Within five to ten years, a riparian buffer planted with native trees is not only helping to reduce nutrient and sediment loads in the stream, it is also shielding the waters from heat flux processes including the solar (shortwave) radiation that raises water temperatures to levels not tolerated by coldwater and coolwater fishes.
Riparian Buffer
A well-established riparian buffer.
Forested Stream
A forested stream.

You’re probably glad this look at heat flux processes in streams has at last come to an end.  That’s good, because we’ve got a lot of work to do.

Add one more benefit to the wildflower meadow, it infiltrates stormwater to recharge the aquifer much better than mowed grass.  And another related plus, it reduces runoff and its thermal pollution.  Besides, you don’t have time to mow grass, because we have work to do!
Potomac Sculpin
Our native coldwater fishes including the Potomac Sculpin will survive only if we protect and expand the scattered few habitats where they have taken refuge.  They have no choice but to live in these seriously threatened places, but we do.  So let’s give ’em some space.  How ’bout it?  (United States Fish and Wildlife Service image by Ryan Hagerty)

Birds Along the River’s Edge

Just as bare ground along a plowed road attracts birds in an otherwise snow-covered landscape, a receding river or large stream can provide the same benefit to hungry avians looking for food following a winter storm.

Here is a small sample of some of the species seen during a brief stop along the Susquehanna earlier this week.

Song Sparrow
Along vegetated edges of the Susquehanna and its tributaries, the Song Sparrow is ubiquitous in its search for small seeds and other foods.  As the river recedes from the effects of this month’s rains, the shoreline is left bare of more recently deposited snow cover.  Song Sparrows and other birds are attracted to streamside corridors of frost-free ground to find sufficient consumables for supplying enough energy to survive the long cold nights of winter.
American Robin
Thousands of American Robins have been widespread throughout the lower Susquehanna valley during the past week.  Due to the mild weather during this late fall and early winter, some may still be in the process of working their way south.  Currently, many robins are concentrated along the river shoreline where receding water has exposed unfrozen soils to provide these birds with opportunities for finding earthworms (Lumbricidae) and other annelids.
Golden-crowned Kinglet
This Golden-crowned Kinglet was observed searching the trees and shrubs along the Susquehanna shoreline for tiny insects and spiders. Temperatures above the bare ground along the receding river can be a few degrees higher than in surrounding snow-covered areas, thus improving the chances of finding active prey among the trunks and limbs of the riparian forest.
Brown Creeper
Not far from the kinglet, a Brown Creeper is seen searching the bark of a Silver Maple (Acer saccharinum) for wintering insects, as well as their eggs and larvae.  Spiders in all their life stages are a favorite too.
American Pipits
American Pipits not only inhabit farm fields during the winter months, they are quite fond of bare ground along the Susquehanna.  Seen quite easily along a strip of pebbly shoreline exposed by receding water, these birds will often escape notice when spending time on mid-river gravel and sand bars during periods of low flow.
An American Pipit on a bitterly cold afternoon along the Susquehanna.
An American Pipit on a bitterly cold afternoon along the Susquehanna.

Piscivorous Waterfowl Visiting Lakes and Ponds

Heavy rains and snow melt have turned the main stem of the Susquehanna and its larger tributaries into a muddy torrent.  For fish-eating (piscivorous) ducks, the poor visibility in fast-flowing turbid waters forces them to seek better places to dive for food.  With man-made lakes and ponds throughout most of the region still ice-free, waterfowl are taking to these sources of open water until the rivers and streams recede and clear.

Common Mergansers
The Common Merganser is a species of diving duck with a primary winter range that, along the Atlantic Coast, reaches its southern extreme in the lower Susquehanna and Potomac watersheds.  Recently, many have left the main stem of the muddy rivers to congregate on waters with better visibility at some of the area’s larger man-made lakes.
Common Mergansers Feeding
Common Mergansers dive to locate and capture prey, primarily small fish.  During this century, their numbers have declined along the southern edge of their winter range, possibly due to birds remaining to the north on open water, particularly on the Great Lakes.  In the lower Susquehanna valley, some of these cavity-nesting ducks can now be found year-round in areas where heavy timber again provides breeding sites in riparian forests.  After nesting, females lead their young to wander widely along our many miles of larger rivers and streams to feed.
Several Common Mergansers Intimidating a Male with a Freshly Caught Fish
The behavior of these mergansers demonstrates the stiff competition for food that can result when predators are forced away from ideal habitat and become compressed into less favorable space.  On the river, piscivores can feed on the widespread abundance of small fish including different species of minnows, shiners, darters, and more.  In man-made lakes stocked for recreational anglers with sunfish, bass, and other predators (many of them non-native), small forage species are usually nonexistent.  As a result, fish-eating birds can catch larger fish, but are successful far less often.  Seen here are several mergansers resorting to intimidation in an effort to steal a young bass away from the male bird that just surfaced with it.  While being charged by the aggressors, he must quickly swallow his oversize catch or risk losing it.

With a hard freeze on the way, the fight for life will get even more desperate in the coming weeks.  Lakes will ice over and the struggle for food will intensify.  Fortunately for mergansers and other piscivorous waterfowl, high water on the Susquehanna is expected to recede and clarify, allowing them to return to their traditional environs.  Those with the most suitable skills and adaptations to survive until spring will have a chance to breed and pass their vigor on to a new generation of these amazing birds.

Photo of the Day

Rising Susquehanna River at Northwest Lancaster County River Trail underpass at Shock's Mill Railroad Bridge, December 18, 2023.
Torrential rains throughout the Susquehanna watershed last night have the river’s main stem on the rise today.  By late this afternoon, the Northwest Lancaster County River Trail’s underpass beneath the Shock’s Mill Bridge was just 18 inches from inundation.  An additional seven feet or more of flood water is expected at this location by the time the river reaches its crest on Wednesday.

The Value of Water

Are you worried about your well running dry this summer?  Are you wondering if your public water supply is going to implement use restrictions in coming months?  If we do suddenly enter a wet spell again, are you concerned about losing valuable rainfall to flooding?  A sensible person should be curious about these issues, but here in the Lower Susquehanna River Watershed, we tend to take for granted the water we use on a daily basis.

This Wednesday, June 7,  you can learn more about the numerous measures we can take, both individually and as a community, to recharge our aquifers while at the same time improving water quality and wildlife habitat in and around our streams and rivers.  From 5:30 to 8:00 P.M., the Chiques Creek Watershed Alliance will be hosting its annual Watershed Expo at the Manheim Farm Show grounds adjacent to the Manheim Central High School in Lancaster County.  According to the organization’s web page, more than twenty organizations will be there with displays featuring conservation, aquatic wildlife, stream restoration, Honey Bees, and much more.  There will be games and custom-made fish-print t-shirts for the youngsters, plus music to relax by for those a little older.  Look for rain barrel painting and a rain barrel giveaway.  And you’ll like this—admission and ice cream are free.  Vendors including food trucks will be onsite preparing fare for sale.

And there’s much more.

To help recharge groundwater supplies, you can learn how to infiltrate stormwater from your downspouts, parking area, or driveway…

Urban Runoff
Does your local stream flood every time there’s a downpour, then sometimes dry up during the heat of summer?  Has this problem gotten worse over the years?  If so, you may be in big trouble during a drought.  Loss of base flow in a stream or river is a sure sign of depleted groundwater levels in at least a portion of its drainage basin.  Landowners, both public and private, in such a watershed need to start infiltrating stormwater into the ground instead of allowing it to become surface runoff.
Rain Garden Model
You can direct the stormwater from your downspout, parking area, or driveway into a rain garden to help recharge the aquifer that supplies your private or public well and nearby natural springs.  Displays including this model provided by Rapho Township show you how.

…there will be a tour of a comprehensive stream and floodplain rehabilitation project in Manheim Memorial Park adjacent to the fair grounds…

Legacy Sediments
Have you seen banks like these on your local stream?  On waterways throughout the Lower Susquehanna River Watershed, mill dams have trapped accumulations of sediments that eroded from farm fields prior to the implementation of soil conservation practices.  These legacy sediments channelize creeks and disconnect them from their now buried floodplains.  During storms, water that would have been absorbed by the floodplain is now displaced into areas of higher ground not historically inundated by a similar event.
Adjacent to the Manheim Farm Show grounds, the Chiques Creek Stream Restoration Project in Manheim Memorial Park has reconnected the waterway to its historic floodplain by removing a dam and the legacy sediments that accumulated behind it.
Legacy Sediments Removed
Chiques Creek in Manheim following removal of hundreds of truck loads of legacy sediments.  High water can again be absorbed by the wetlands and riparian forest of the floodplain surrounding this segment of stream.  There are no incised banks creating an unnatural channel or crumbling away to pollute downstream waters with nutrients and sediment.  Projects similar to this are critical to improving water quality in both the Susquehanna River and Chesapeake Bay.  Closer to home, they can help municipalities meet their stormwater management (MS4) requirements.
Bank-full Bench
Mark Metzler of Rettew Associates guides a tour of the Chiques Creek rehabilitation.  Here, cross vanes, stone structures that provide grade control along the stream’s course, were installed to gently steer the center of the channel away from existing structures.   Cross vanes manipulate the velocity of the creek’s flow across its breadth to dissipate potentially erosive energy and more precisely direct the deposition of gravel and sediment.

…and a highlight of the evening will be using an electrofishing apparatus to collect a sample of the fish now populating the rehabilitated segment of stream…

Electrofishing
Matt Kofroth, Lancaster County Conservation District Watershed Specialist, operates a backpack electrofishing apparatus while the netting crew prepares to capture the temporarily stunned specimens.  The catch is then brought to shore for identification and counting.

…so don’t miss it.  We can hardly wait to see you there!

The 2023 Watershed Expo is part of Lancaster Conservancy Water Week.

Three Mile Island and Agnes: Fifty Years Later

Fifty years ago this week, the remnants of Hurricane Agnes drifted north through the Susquehanna River basin as a tropical storm and saturated the entire watershed with wave after wave of torrential rains.  The storm caused catastrophic flooding along the river’s main stem and along many major tributaries.  The nuclear power station at Three Mile Island, then under construction, received its first major flood.  Here are some photos taken during the climax of that flood on June 24, 1972.  The river stage as measured just upstream of Three Mile Island at the Harrisburg gauge crested at 33.27 feet, more than 10 feet above flood stage and almost 30 feet higher than the stage at present.  At Three Mile Island and Conewago Falls, the river was receiving additional flow from the raging Swatara Creek, which drains much of the anthracite coal region of eastern Schuylkill County—where rainfall from Agnes may have been the heaviest.

Three Mile Island flooding from Agnes 1972.
1972-  From the river’s east shore at the mouth of Conewago Creek, Three Mile Island’s “south bridge” crosses the Susquehanna along the upstream edge of Conewago Falls.  The flood crested just after covering the roadway on the span.  Floating debris including trees, sections of buildings, steel drums, and rubbish began accumulating against the railings on the bridge’s upstream side, leading observers to speculate that the span would fail.  When a very large fuel tank, thousands of gallons in capacity, was seen approaching, many thought it would be the straw that would break the camel’s back.  It wasn’t, but the crashing sounds it made as it struck the bridge then turned and began rolling against the rails was unforgettable.  (Larry L. Coble, Sr. image)
Three Mile Island flooding from Agnes 1972.
1972-  In this close-up of the preceding photo, the aforementioned piles of junk can be seen along the upstream side of the bridge (behind the sign on the right).  The fuel tank struck and was rolling on the far side of this pile.  (Larry L. Coble, Sr. image)
2022-  Three Mile Island’s “south bridge” as it appeared this morning, June 24,2022.
Three Mile Island flooding from Agnes 1972.
1972-  The railroad along the east shore at Three Mile Island’s “south bridge” was inundated by rising water.  This flooded automobile was one of many found in the vicinity.  Some of these vehicles were overtaken by rising water while parked, others were stranded while being driven, and still others floated in from points unknown.  (Larry L. Coble, Sr. image)
2022-  A modern view of the same location.
Three Mile Island flooding from Agnes 1972.
1972-  At the north end of Three Mile Island, construction on Unit 1 was halted.  The completed cooling towers can be seen to the right and the round reactor building can be seen behind the generator building to the left.  The railroad grade along the river’s eastern shore opposite the north end of the island was elevated enough for this train to stop and shelter there for the duration of the flood.  (Larry L. Coble, Sr. image)
2022-  Three Mile Island Unit 1 as it appears today: shut down, defueled, and in the process of deconstruction.
Three Mile Island flooding from Agnes 1972.
1972-  In March of 1979, the world would come to know of Three Mile Island Unit 2.  During Agnes in June of 1972, flood waters surrounding the plant resulted in a delay of its construction.  In the foreground, note the boxcar from the now defunct Penn Central Railroad.  (Larry L. Coble, Sr. image)
2022-  A current look at T.M.I. Unit 2, shut down since the accident and partial meltdown in 1979.

Pictures capture just a portion of the experience of witnessing a massive flood.  Sometimes the sounds and smells of the muddy torrents tell us more than photographs can show.

Aside from the booming noise of the fuel tank banging along the rails of the south bridge, there was the persistent roar of floodwaters, at the rate of hundreds of thousands of cubic feet per second, tumbling through Conewago Falls on the downstream side of the island.   The sound of the rapids during a flood can at times carry for more than two miles.  It’s a sound that has accompanied the thousands of floods that have shaped the falls and its unique diabase “pothole rocks” using abrasives that are suspended in silty waters after being eroded from rock formations in the hundreds of square miles of drainage basin upstream.  This natural process, the weathering of rock and the deposition of the material closer to the coast, has been the prevailing geologic cycle in what we now call the Lower Susquehanna River Watershed since the end of the Triassic Period, more than two hundred million years ago.

More than the sights and sounds, it was the smell of the Agnes flood that warned witnesses of the dangers of the non-natural, man-made contamination—the pollution—in the waters then flowing down the Susquehanna.

Because they float, gasoline and other fuels leaked from flooded vehicles, storage tanks, and containers were most apparent.  The odor of their vapors was widespread along not only along the main stem of the river, but along most of the tributaries that at any point along their course passed through human habitations.

Blended with the strong smell of petroleum was the stink of untreated excrement.  Flooded treatment plants, collection systems overwhelmed by stormwater, and inundated septic systems all discharged raw sewage into the river and many of its tributaries.  This untreated wastewater, combined with ammoniated manure and other farm runoff, gave a damaging nutrient shock to the river and Chesapeake Bay.

Adding to the repugnant aroma of the flood was a mix of chemicals, some percolated from storage sites along watercourses, and yet others leaking from steel drums seen floating in the river.  During the decades following World War II, stacks and stacks of drums, some empty, some containing material that is very dangerous, were routinely stored in floodplains at businesses and industrial sites throughout the Susquehanna basin.  Many were lifted up and washed away during the record-breaking Agnes flood.  Still others were “allowed” to be carried away by the malicious pigs who see a flooding stream as an opportunity to “get rid of stuff”.  Few of these drums were ever recovered, and hundreds were stranded along the shoreline and in the woods and wetlands of the floodplain below Conewago Falls.  There, they rusted away during the next three decades, some leaking their contents into the surrounding soils and waters.  Today, there is little visible trace of any.

During the summer of ’72, the waters surrounding Three Mile Island were probably viler and more polluted than at any other time during the existence of the nuclear generating station there.  And little, if any of that pollution originated at the facility itself.

The Susquehanna’s floodplain and water quality issues that had been stashed in the corner, hidden out back, and swept under the rug for years were flushed out by Agnes, and she left them stuck in the stinking mud.

Pick Up and Get Out of the Floodplain

The remnants of Hurricane Ida are on their way to the Lower Susquehanna River Watershed.  After making landfall in Louisiana as a category 4 storm, Ida is on track to bring heavy rain to the Mid-Atlantic States beginning tonight.

Tropical Depression Ida moving slowly toward the northeast.   (NOAA/GOES image)

Rainfall totals are anticipated to be sufficient to cause flooding in the lower Susquehanna basin.  As much as six to ten inches of precipitation could fall in parts of the area on Wednesday.

Rainfall forecasts from the National Hurricane Center.  (NOAA/National Hurricane Center image)

Now would be a good time to get all your valuables and junk out of the floodways and floodplains.  Move your cars, trucks, S.U.V.s, trailers, and boats to higher ground.  Clear out the trash cans, playground equipment, picnic tables, and lawn furniture too.  Get it all to higher ground.  Don’t be the slob who uses a flood as a chance to get rid of tires and other rubbish by letting it just wash away.

Vehicles parked atop fill that has been dumped into a stream’s floodplain are in double trouble.  Fill displaces water and exasperates flooding instead of providing refuge from it.  Better move these cars, trucks, and trailers to higher ground, posthaste.

Flooding not only has economic and public safety impacts, it is a source of enormous amounts of pollution.  Chemical spills from inundated homes, businesses, and vehicles combine with nutrient and sediment runoff from eroding fields to create a filthy brown torrent that rushes down stream courses and into the Susquehanna.  Failed and flooded sewage facilities, both municipal and private, not only pollute the water, but give it that foul odor familiar to those who visit the shores of the river after a major storm.  And of course there is the garbage.  The tons and tons of waste that people discard carelessly that, during a flood event, finds its way ever closer to the Susquehanna, then the Chesapeake, and finally the Atlantic.  It’s a disgraceful legacy.

Now is your chance to do something about it.  Go out right now and pick up the trash along the curb, in the street, and on the sidewalk and lawn—before it gets swept into your nearby stormwater inlet or stream.  It’s easy to do, just bend and stoop.  While you’re at it, clean up the driveway and parking lot too.

Secure your trash and pick up litter before it finds its way into the storm sewer system and eventually your local stream.  It’ll take just a minute.
This is how straws and other plastics find their way to the ocean and the marine animals living there, so pick that stuff up!  Did you know that keeping stormwater inlets clean can prevent street flooding and its destructive extension into the cellars of nearby homes and businesses?
There’s another straw.  Pick it and the rest of that junk up now, before the storm.  Don’t wait for your local municipality or the Boy Scouts to do it.  You do it, even if it’s not your trash.

We’ll be checking to see how you did.

And remember, flood plains are for flooding, so get out of the floodplain and stay out.

Get Out of the Floodplain…And Get Your Stuff Out Too!

After threading its way through waves of Saharan dust plumes, Tropical Storm Isaias, or the remnants thereof, is making a run up the eastern seaboard toward the lower Susquehanna watershed.

Isaias formed just off the northernmost tip of the South American continent.  It drifted north in a narrow pocket between two waves of the Saharan dust plume and, on July 30, strengthened to tropical storm status while in the vicinity of Puerto Rico.  (CIRA/NOAA image)
In this image taken on Friday, note the position of the fast-moving dust plume that was to the southeast of Isaias just a day earlier.  With the storm now clear of the dry Saharan air, it strengthens to become Hurricane Isaias.  (CIRA/NOAA image)
On Friday, the National Hurricane Center issues advisors expecting the strengthening Isaias to sweep the Atlantic coasts of Florida, Georgia, and South Carolina as a hurricane with winds of 74 miles per hour or greater.  (NOAA/National Hurricane Center image)
Then on Saturday, Isaias appears to be back in the dirt.  Did the counterclockwise rotation of the atmosphere around Isaias draw in Saharan dust and dry air to weaken the storm?  Whatever the cause, Isaias is downgraded to a strong tropical storm with maximum sustained winds of 70 miles per hour.  (CIRA/NOAA image)
The latest image of Tropical Storm Isaias.  (CIRA/NOAA image)
The latest forecast projects Isaias will briefly reach hurricane status later today before making landfall in South Carolina and again weakening.  (NOAA/National Hurricane Center image)
Tropical Storm Isaias is expected to bring heavy rain to the lower Susquehanna valley and the Cheapeake Bay region tomorrow (Tuesday).  (NOAA/National Hurricane Center image)

Heavy rain and flooding appears likely, particularly east of the Susquehanna.  Now might be a good time to clean up the trash and garbage that could clog nearby storm drains or otherwise find its way into your local waterway.  NOW is the time to get all your stuff out of the floodplain!  The car, the camper, the picnic table, the lawn furniture, the kid’s toys, the soda bottles, the gas cans, the lawn chemicals, the Styrofoam, and all that other junk you’ve piled up.  Get that stuff cleaned up and out of the floodway.  And of course, get you and your pets out of the there too!

The Colorful Birds Are Here

You need to get outside and go for a walk.  You’ll be sorry if you don’t.  It’s prime time to see wildlife in all its glory.  The songs and colors of spring are upon us!

Flooding that resulted from mid-week rains is subsiding.  The muddy torrents of Conewago Falls are seen here racing by the powerhouse at the York Haven Dam.
Receding waters will soon leave the parking area at Falmouth and other access points along the river high and dry.
Migrating Yellow-rumped Warblers are currently very common in the riparian woodlands near Conewago Falls.  They and all the Neotropical warblers, thrushes, vireos, flycatchers are moving through the Susquehanna watershed right now.
A Baltimore Oriole feeds in a riverside maple tree.
Ruby-crowned Kinglets are migrating through the Susquehanna valley.  These tiny birds may be encountered among the foliage of trees and shrubs as they feed upon insects .
Gray Catbirds are arriving.  Many will stay to nest in shrubby thickets and in suburban gardens.
American Robins and other birds take advantage of rising flood waters to feed upon earthworms and other invertebrates that are forced to the soil’s surface along the inundated river shoreline.
Spotted Sandpipers are a familiar sight as they feed along water’s edge.
The Yellow Warbler (Setophaga petechia) is a Neotropical migrant that nests locally in wet shrubby thickets.  Let your streamside vegetation grow and in a few years you just might have these “wild canaries” singing their chorus of “sweet-sweet-sweet-I’m-so-sweet” on your property.

If you’re not up to a walk and you just want to go for a slow drive, why not take a trip to Middle Creek Wildlife Management Area and visit the managed grasslands on the north side of the refuge.  To those of us over fifty, it’s a reminder of how Susquehanna valley farmlands were before the advent of high-intensity agriculture.  Take a look at the birds found there right now.

Red-winged Blackbirds commonly nest in cattail marshes, but are very fond of untreated hayfields, lightly-grazed pastures, and fallow ground too.  These habitats are becoming increasingly rare in the lower Susquehanna region.  Farmers have little choice, they either engage in intensive agriculture or go broke.
Nest boxes are provided for Tree Swallows at the refuge.
Numbers of American Kestrels have tumbled with the loss of grassy agricultural habitats that provide large insects and small rodents for them to feed upon.
White-crowned Sparrows (Zonotrichia leucophrys) are a migrant and winter resident species that favors small clumps of shrubby cover in pastures and fallow land.
When was the last time you saw an Eastern Meadowlark (Sturnella magna) singing “spring-of-the-year” in a pasture near your home?
And yes, the grasslands at Middle Creek do support nesting Ring-necked Pheasants (Phasianus colcichus).  If you stop for a while and listen, you’ll hear the calls of “kowk-kuk” and a whir of wings.  Go check it out.

And remember, if you happen to own land and aren’t growing crops on it, put it to good use.  Mow less, live more.  Mow less, more lives.

2018 Migration Count Summary: Rainout

If you were a regular visitor to this website during the autumn of 2017, you will recall the proliferation of posts detailing the bird migration at Conewago Falls during the season.  The lookout site among the Pothole Rocks remained high and dry for most of the count’s duration. 

In the fall of 2018, those lookout rocks were never to be seen. There was to be no safe perch for a would-be observer. There was no attempt to conduct a tally of passing migrants. If you live in the lower Susquehanna River drainage basin, you know why—rain—record setting rain.

Annual precipitation during 2018 as indicated by radar.  Note the extensive areas in pink.  They received in excess of 70 inches of precipitation during 2018, much of it during the second half of the year.  (NOAA/National Weather Service image)
Average annual rainfall.  Most of the lower Susquehanna drainage basin receives an average of just over 40 inches of rain each year.  (NOAA/National Weather Service image)
Departure from normal annual precipitation totals.  Note the extensive areas of greater than 20 inches of precipitation above normal (pink).  Severe flooding occurred on many streams during numerous events throughout the second half of 2018.  Note the closer to normal totals in central New York in the upper Susquehanna watershed.  The lesser amounts of rain there and the localized pattern of the flooding events in Pennsylvania prevented the main stem of the lower Susquehanna from experiencing catastrophic high water in 2018.  (NOAA/National Weather Service image)   
Though there has been no severe flooding, frequent rain events in the Susquehanna watershed have maintained persistently high river levels in Conewago Falls.  Pothole Rocks seen here on December 9 during an ebb in the flow were soon inundated again as rains fell in the Susquehanna basin upstream. 
Of course, each time the river receded it left behind a fresh pile of plastic garbage.  What didn’t end up on the shoreline found its way to Chesapeake Bay…then on to the Atlantic.  Is that your cooler? 

Put Up the White Flag

It was a routine occurrence in many communities along tributaries of the lower Susquehanna River during the most recent two months.  The rain falls like it’s never going to stop—inches an hour.  Soon there is flash flooding along creeks and streams.  Roads are quickly inundated.  Inevitably, there are motorists caught in the rising waters and emergency crews are summoned to retrieve the victims.  When the action settles, sets of saw horses are brought to the scene to barricade the road until waters recede.  At certain flood-prone locations, these events are repeated time and again.  The police, fire, and Emergency Medical Services crews seem to visit them during every torrential storm—rain, rescue, rinse, and repeat.

We treat our local streams and creeks like open sewers.  Think about it.  We don’t want rainwater accumulating on our properties.  We pipe it away and grade the field, lawn, and pavement to roll it into the neighbor’s lot or into the street—or directly into the waterway.  It drops upon us as pure water and we instantly pollute it.  It’s a method of diluting all the junk we’ve spread out in its path since the last time it rained.  A thunderstorm is the big flush.  We don’t seem too concerned about the litter, fertilizer, pesticides, motor fluids, and other consumer waste it takes along with it.  Out of sight, out of mind.

Failure to retain and infiltrate stormwater to recharge aquifers can later result in well failures and reduced base flow in streams.  (Conoy Creek’s dry streambed in June, 2007)

Perhaps our lack of respect for streams and creeks is the source of our complete ignorance of the function of floodplains.

Floodplains are formed over time as hydraulic forces erode bedrock and soils surrounding a stream to create adequate space to pass flood waters.  As floodplains mature they become large enough to reduce flood water velocity and erosion energy.  They then function to retain, infiltrate, and evaporate the surplus water from flood events.  Microorganisms, plants, and other life forms found in floodplain wetlands, forests, and grasslands purify the water and break down naturally-occurring organic matter.  Floodplains are the shock-absorber between us and our waterways.  And they’re our largest water treatment facilities.

Why is it then, that whenever a floodplain floods, we seem motivated to do something to fix this error of nature?  Man can’t help himself.  He has a compulsion to fill the floodplain with any contrivance he can come up with.  We dump, pile, fill, pave, pour, form, and build, then build some more.  At some point, someone notices a stream in the midst of our new creation.  Now it’s polluted and whenever it storms, the darn thing floods into our stuff—worse than ever before.  So the project is crowned by another round of dumping, forming, pouring, and building to channelize the stream.  Done!  Now let’s move all our stuff into our new habitable space.

Natural Floodplain- Over a period of hundreds or thousands of years, the stream (dark blue) has established a natural floodplain including wetlands and forest.  In this example, buildings and infrastructure are located outside the zone inundated by high water (light blue) allowing the floodplain to function as an effective water-absorbing buffer.

Impaired Floodplain- Here the natural floodplain has been filled for building (left) and paved for recreation area parking (right).  The stream has been channelized.  Flood water (light blue) displaced by these alterations is likely to inundate areas not previously impacted by similar events.  Additionally, the interference with natural flow will create new erosion points that could seriously damage older infrastructure and properties.

The majority of the towns in the lower Susquehanna valley with streams passing through them have impaired floodplains.  In many, the older sections of the town are built on filled floodplain.  Some new subdivisions highlight streamside lawns as a sales feature—plenty of room for stockpiling your accoutrements of suburban life.  And yes, some new homes are still being built in floodplains.

When high water comes, it drags tons of debris with it.  The limbs, leaves, twigs, and trees are broken down by natural processes over time.  Nature has mechanisms to quickly cope with these organics.  Man’s consumer rubbish is another matter.  As the plant material decays, the embedded man-made items, particularly metals, treated lumber, plastics, Styrofoam, and glass, become more evident as an ever-accumulating “garbage soil” in the natural floodplains downstream of these impaired areas.  With each storm, some of this mess floats away again to move ever closer to Chesapeake Bay and the Atlantic.  Are you following me?  That’s our junk from the curb, lawn, highway, or parking lot bobbing around in the world’s oceans.

A shed, mobile home, or house can be inundated or swept away during a flood.  Everything inside (household chemicals, gasoline, fuel oil, pesticides, insulation, all those plastics, etc.) instantly pollutes the water.  Many communities that rely on the Susquehanna River for drinking water are immediately impacted, including Lancaster, PA and Baltimore, MD.  This dumpster was swept away from a parking lot in a floodplain.  It rolled in the current, chipping away at the bridge before spilling the rubbish into the muddy water.  After the flood receded, the dumpster was found a mile downstream.  Its contents are still out there somewhere.

Floodplains along the lower Susquehanna River are blanketed with a layer of flotsam that settles in place as high water recedes.  These fresh piles can be several feet deep and stretch for miles.  Nature decomposes the organic twigs and driftwood to build soil-enriching humus.  However, the plastics and other man-made materials that do not readily decay or do not float away toward the sea during the next flood are incorporated into the alluvium and humus creating a “garbage soil”.  Over time, the action of abrasives in the soil will grind small particles of plastics from the larger pieces.  These tiny plastics can become suspended in the water column each time the river floods.  What will be the long-term impact of this type of pollution?

Anything can be swept away by the powerful hydraulic forces of flowing water.  Large objects like this utility trailer can block passages through bridges and escalate flooding problems.

The cost of removing debris often falls upon local government and is shared by taxpayers.

Here, a junked boat dock is snagged on the crest of the York Haven Dam at Conewago Falls.  Rising water eventually carried it over the dam and into the falls where it broke up.  This and tons of other junk are often removed downstream at the Safe Harbor Dam to prevent damage to turbine equipment.  During periods of high water, the utility hauls debris by the truck-load to the local waste authority for disposal.  For the owners of garbage like this dock, it’s gone and it’s somebody else’s problem now.

Motor vehicles found after floating away from parking areas in floodplains can create a dangerous dilemma for police, fire, and E.M.S. personnel, particularly when no one witnesses the event.  Was someone driving this car or was it vacant when it was swept downstream?  Should crews be put at risk to locate possible victims?

Beginning in 1968, participating municipalities, in exchange for having coverage provided to their qualified residents under the National Flood Insurance Program, were required to adopt and enforce a floodplain management ordinance.  The program was intended to reduce flood damage and provide flood assistance funded with premiums paid by potential victims.  The program now operates with a debt incurred during severe hurricanes.  Occurrences of repetitive damage claims and accusations that the program provides an incentive for rebuilding in floodplains have made the National Flood Insurance Program controversial.

In the Lower Susquehanna River Watershed there are municipalities that still permit new construction in floodplains.  Others are quite proactive at eliminating new construction in flood-prone zones, and some are working to have buildings removed that are subjected to repeated flooding.

Another Wall— Here’s an example of greed by the owner, engineer, and municipality… placing their financial interests first.  The entire floodplain on the north side of this stream was filled, then the wall was erected to contain the material.  A financial institution’s office and parking lot was constructed atop the mound.  This project has channelized the stream and completely displaced half of the floodplain to a height of 15 to 20 feet.  Constructed less than five years ago, the wall failed already and has just been totally reconstructed.  The photo reveals how recent flooding has begun a new erosion regime where energy is focused along the base of the wall.  Impairment of a floodplain to this degree can lead to flooding upstream of the site and erosion damage to neighboring infrastructure including roads and bridges.

The floodplain along this segment of the lower Swatara Creek in Londonderry Township, Dauphin County is free to flood.  Ordinances prohibit new construction here and 14 older houses that repeatedly flooded were purchased, dismantled, and removed using funding from the Federal Emergency Management Agency (F.E.M.A).  A riparian buffer was planted and some wetland restorations were incorporated into stormwater management installations along the local highways.  When the waters of the Swatara rise, the local municipality closes the roads into the floodplain.  Nobody lives or works there anymore, so no one has any reason to enter.  There’s no need to rescue stubborn residents who refused advice to evacuate.  Sightseers can park and stand on the hill behind the barricades and take all the photographs they like.

A new Pennsylvania Turnpike bridge across Swatara Creek features wide passage for the stream below.  Water flowing in the floodplain can pass under the bridge without being channelized toward the path where the stream normally flows in the center.  The black asterisk-shaped floats spin on the poles to help deflect debris away from the bridge piers.  (flood crest on July 26, 2018)

People are curious when a waterway floods and they want to see it for themselves.  Wouldn’t it be wise to anticipate this demand for access by being ready to accommodate these citizens safely?  Isn’t a parking lot, picnic area, or manicured park safer and more usable when overlooking the floodplain as opposed to being located in it?  Wouldn’t it be a more prudent long-term investment, both financially and ecologically, to develop these improvements on higher ground outside of flood zones?

Now would be a good time to stop the new construction and the rebuilding in floodplains.  Aren’t the risks posed to human life, water quality, essential infrastructure, private property, and ecosystems too great to continue?

Isn’t it time to put up the white flag and surrender the floodplains to the floods?  That’s why they’re there.  Floodplains are for flooding.

They Call Me the Wanderer

It’s been an atypical summer.  The lower Susquehanna River valley has been in a cycle of heavy rains for over a month and stream flooding has been a recurring event.  At Conewago Falls, the Pothole Rocks have been inundated for weeks.  The location used as a lookout for the Autumn Migration Count last fall is at the moment submerged in ten feet of roaring water.  Any attempt to tally the migrants which are passing thru in 2018 will thus be delayed indefinitely.  Of greater import, the flooding at Conewago Falls is impacting many of the animals and plants there at a critical time in their annual life cycle.  Having been displaced from its usual breeding sites on the river, one insect species in particular seems to be omnipresent in upland areas right now, and few people have ever heard of it.

So, you take a cruise in the motorcar to your favorite store and arrive at the sprawling parking lot.  Not wishing to have your doors dented or paint chipped because you settled for a space tightly packed among other shopper’s conveyances, you park out there in the “boondocks”.  You know the place, the lightly-used portion of the lot where sometimes brush grows from cracks in the asphalt and you must be on alert for impatient consumers who throttle-up to high speeds and dash diagonally across the carefully painted grids on the pavement to reach their favorite parking destination in the front row.  Coming to a stop, you take the car out of gear, set the brake, disengage the safety belt, and gather your shopping list.  You grasp the door handle and, not wanting to be flattened  by one of the aforementioned motorists, you have a look around before exiting.

It was then that you saw the thing, hovering above your shiny bright hood.  For a brief moment, it seemed to be peering right through the windshield at you with big reddish-brown eyes.  In just a second or two, it turned its whole bronze body ninety degrees to the left and darted away on its cellophane wings.  Maybe you didn’t really get a good look at it.  It was so fast.  But it certainly was odd.  Oh well, time to walk inside a grab a few provisions.  Away you go.

Upon completion of your shopping, you’re taking the long stroll back to your car and you notice more of these peculiar creatures.  Two are coupled together and are hovering above someone’s automobile hood, then they drop down, and the lower of the two taps its abdomen on the paint.  You ask yourself, “What are these bizarre things?”

Meet the Wandering Glider (Pantala flavescens), also known as the Globe Wanderer or Globe Skimmer, a wide-ranging dragonfly known to occur on every continent with the exception of Antarctica.

Wandering Gliders sometimes arrive in the lower Susquehanna River valley in large numbers after catching a ride on sustained winds from southerly directions and will often fly and migrate in storm systems.  Conditions for such movements have been optimal in our region since mid-July.  These dragonflies will often hover above motor vehicle hoods and, after mating, females will deposit eggs upon them, apparently mistaking their glossy surface for small pools of water.

Wandering Gliders travel the globe, and as such are accomplished fliers.  Adults spend most of the day on the wing, feeding upon a variety of flying insects.  Days ago, I watched several intercepting a swarm of flying ants.  As fast as ants left the ground they were grabbed and devoured by the gliders.  Wandering Gliders are adept at taking day-flying mosquitos, often zipping stealthily past a person’s head or shoulders to grab one of the little pests—the would-be skeeter victim usually unaware of the whole affair.

Due to their nomadic life history, Wandering Gliders are opportunists when breeding and will lay eggs in most any body of freshwater.  Their larvae do not overwinter prior to maturity; adults can be expected in a little more than one to two months.  Repetitive flooding in the Lower Susquehanna River Watershed this summer may be reducing the availability of the best local breeding sites for this species—riverine, stream, and floodplain pools of standing water with prey.  This may explain why thousands of Wandering Gliders are patrolling parking lots, farmlands, and urban areas this summer.  And it’s the likely reason for their use of puddles on asphalt pavement, on rubber roofs, and in fields as places to try to deposit eggs.  Unfortunately, they may be as likely to succeed there as they are on your motor vehicle hood.

At this time a year ago, the airspace above the Diabase Pothole Rocks at Conewago Falls was jammed with territorial male Wandering Gliders.  Each male hovered at various locations around his breeding territory consisting of pools and water-filled potholes.  Intruders would quickly be dispatched from the area, then the male would resume his patrols from a set of repetitively-used hovering positions about six feet above the rocks.  Mating and egg-laying continued into late September.  The larvae, also called nymphs or naiads, were readily observed in many pools and potholes in early October and the emergence of juveniles was noted in mid-October.  The absence of flooding, the mild autumn weather, and the moderation of water temperatures in the pools and potholes courtesy of the sun-drenched diabase boulders helped to extend the 2017 breeding season for Wandering Gliders in Conewago Falls.  They aren’t likely to experience the same favor this year, but their great ability to travel and adapt should overcome this momentary misfortune.

A male Wandering Glider aggressively patrols his territory in the Diabase Pothole Rocks Microhabitat at Conewago Falls.  August 20, 2017.

A mating pair of Wandering Gliders continue flying non-stop above one of thousands of suitable breeding pools among the Diabase Pothole Rocks at Conewago Falls.  September 23, 2017.

A female (bottom)Wandering Glider has deposited eggs in a pool while flying in tandem with a male (top).  They’ll do the same thing on your automobile hood!  Conewago Falls Diabase Pothole Rocks Microhabitat.  September 23, 2017.

Wandering Glider larvae are at the top of the food chain in flooded potholes.  As they grew, these dragonfly larvae decimated the mosquito larvae which were abundant there earlier in the summer.  October 7, 2017.

A juvenile male Wandering Glider emerges from the pool where it fed and grew as a larva.  It remained at water’s edge on the surface of a sun-warmed diabase rock for several hours to dry its wings.  It soon flew away to parts unknown, possibly traveling hundreds or thousands of miles.  Look carefully at the wings for the beige dash marks on the forward edge near the terminal end.  Females lack this marking.  Conewago Falls Diabase Pothole Rocks Microhabitat.  October 14, 2017.

A Wandering Glider exuviae, the shed exoskeleton of a creature gone, but not forgotten.  October 14, 2017.

 

Shocking Fish Photos!

There are two Conewago Creek systems in the Lower Susquehanna River Watershed.  One drains the Gettysburg Basin west of the river, mostly in Adams and York Counties, then flows into the Susquehanna at the base of Conewago Falls.  The other drains the Gettysburg Basin east of the river, flowing through Triassic redbeds of the Gettysburg Formation and York Haven Diabase before entering Conewago Falls near the south tip of Three Mile Island.  Both Conewago Creeks flow through suburbia, farm, and forest.  Both have their capacity to support aquatic life impaired and diminished by nutrient and sediment pollution.

This week, some of the many partners engaged in a long-term collaboration to restore the east shore’s Conewago Creek met to have a look at one of the prime indicators of overall stream habitat health—the fishes.  Kristen Kyler of the Lower Susquehanna Initiative organized the effort.  Portable backpack-mounted electrofishing units and nets were used by crews to capture, identify, and count the native and non-native fishes at sampling locations which have remained constant since prior to the numerous stream improvement projects which began more than ten years ago.  Some of the present-day sample sites were first used following Hurricane Agnes in 1972 by Stambaugh and Denoncourt and pre-date any implementation of sediment and nutrient mitigation practices like cover crops, no-till farming, field terracing, stormwater control, nutrient management, wetland restoration, streambank fencing, renewed forested stream buffers, or modernized wastewater treatment plants.  By comparing more recent surveys with this baseline data, it may be possible to discern trends in fish populations resulting not only from conservation practices, but from many other variables which may impact the Conewago Creek Warmwater Stream ecosystem in Dauphin, Lancaster, and Lebanon Counties.

So here they are.  Enjoy these shocking fish photos.

Electrofishing on the Conewago Creek in Lebanon County, PA
Matt Kofroth, Watershed Specialist with the Lancaster County Conservation District, operates the electrofishing wand in Conewago Creek while his team members prepare to net and collect momentarily-stunned fish.  Three other electrofishing units operated by staff from the Susquehanna River Basin Commission and aided by teams of netters were in action at other sample locations along the Conewago on this day.

Fishes of the Lower Susquehanna River Watershed: Common Carp
Really big fish, such as this Common Carp (Cyprinus carpio), were identified, counted, and immediately returned to the water downstream of the advancing electrofishing team. 

Fishes of the Lower Susquehanna River Watershed: Swallowtail Shiner, Fallfish, Red-breast Sunfish, and suckers.
Other fish, such as the Swallowtail Shiner, Redbreast Sunfish (Lepomis auritus), Fallfish, and suckers seen here,  were placed in a sorting tank.

Fishes of the Lower Susquehanna River Watershed: Fallfish
Fallfish (Semotilus corporalis) are very active and require plenty of dissolved oxygen in the water to survive.  Fallfish, Rainbow Trout (Oncorhynchus mykiss), and Smallmouth Bass (Micropterus dolomieu) were quickly identified and removed from the sorting tank for release back into the stream.  Other larger, but less active fish, including suckers, quickly followed.

Fishes of the Lower Susquehanna River Watershed: Fathead Minnow
Small fish like minnows were removed from the sorting tank for a closer look in a hand-held viewing tank.  This Fathead Minnow (Pimephales promelas) was identified, added to the tally sheet, and released back into the Conewago.  The Fathead Minnow is not native to the Susquehanna drainage.  It is the minnow most frequently sold as bait by vendors.

Fishes of the Lower Susquehanna River Watershed: a breeding male Bluntnose Minnow
A breeding condition male Bluntnose Minnow (Pimephales notatus).

Fishes of the Lower Susquehanna River Watershed: Cutlips Minnow
The Cutlips Minnow (Exoglossum maxillingua) is a resident of clear rocky streams.  Of the more than 30 species collected during the day, two native species which are classified as intolerant of persisting stream impairment were found: Cutlips Minnow and Swallowtail Shiner.

Fishes of the Lower Susquehanna River Watershed: Central Stoneroller
The Central Stoneroller (Campostoma anomalum) is a benthic feeder in creeks over gravel and sand.

Fishes of the Lower Susquehanna River Watershed: Eastern Blacknose Dace
The Eastern Blacknose Dace (Rhinichthys atratulus) is found in clear water over pebble and stone substrate.

Fishes of the Lower Susquehanna River Watershed: Longnose Dace
The Longnose Dace (Rhinichthys cataractae) is another species of pebbly rocky streams.

Fishes of the Lower Susquehanna River Watershed: juvenile Golden Shiner
A juvenile Golden Shiner (Notemigonus crysoleucas).  Adults lack the side stripe and grow to the size of a sunfish.

Fishes of the Lower Susquehanna River Watershed: Swallowtail Shiner
A Swallowtail Shiner (Notropis procne) and a very young White Sucker (Catostomus commersonii) in the upper left of the tank.

Fishes of the Lower Susquehanna River Watershed: Spotfin Shiner
A probable Spotfin Shiner (Cyprinella spiloptera).

Fishes of the Lower Susquehanna River Watershed: Spotfin Shiner
A breeding male Cyprinella shiner, probably a Spotfin Shiner.  Show-off!

Fishes of the Lower Susquehanna River Watershed: Margined Madtom
The Margined Madtom (Noturus insignis) is a small native catfish of pebbly streams.

Fishes of the Lower Susquehanna River Watershed: Banded Killifish
The Banded Killifish (Fundulus diaphanus) is adept at feeding upon insects, including mosquitos.

Fishes of the Lower Susquehanna River Watershed: a juvenile Rock Bass
A young Rock Bass (Ambloplites rupestris).  This species was introduced to the Susquehanna and its tributaries.

Fishes of the Lower Susquehanna River Watershed: Greenside Darter
The Greenside Darter (Etheostoma blennioides) is not native to the Susquehanna basin.  The species colonized the Conewago Creek (east) from introduced local populations within the last five years.

Fishes of the Lower Susquehanna River Watershed: Tessellated Darter
The Tessellated Darter (Etheostoma olmstedi) is a native inhabitant of the Susquehanna and its tributaries.

Fishes of the Lower Susquehanna River Watershed: American Eel
The stars of the day were the American Eels (Anguilla rostrata).

Fishes of the Lower Susquehanna River Watershed: American Eel
After collection, each eel was measured and weighed using a scale and dry bucket.  This specimen checked in at 20 inches and one pound before being released.

Fishes of the Lower Susquehanna River Watershed: American Eel
Prior to the construction of large dams, American Eels were plentiful in the Susquehanna and its tributaries, including the Conewago.  They’ve since been rarities for more than half a century.  Now they’re getting a lift.

Eastern Elliptio
American Eels serve as an intermediate host for the microscopic parasitic glochidia (larvae) of the Eastern Elliptio (Elliptio complanata), a declining native freshwater mussel of the Lower Susquehanna River Watershed.  While feeding on their host (usually in its gills), the glochidia cause little injury and soon drop off to continue growth, often having assured distribution of their species by accepting the free ride.  Freshwater mussels are filter feeders and improve water quality.  They grow slowly and can live for decades.

Fishes of the Lower Susquehanna River Watershed: American Eel
American Eels are a catadromous species, starting life as tiny glass eels in the saltwater of the Atlantic Ocean, then migrating to tidal brackish marshes and streams (males) or freshwater streams (females) to mature.  This 20-incher probably attempted to ascend the Susquehanna as an elver in 2016 or 2017.  After hitching a ride with some friendly folks, she bypassed the three largest dams on the lower Susquehanna (Conowingo, Holtwood, and Safe Harbor) and arrived in the Conewago where she may remain and grow for ten years or more.  To spawn, a perilous and terminally fatal journey to the Sargasso Sea awaits her.  (You may better know the area of the Sargasso Sea as The Bermuda Triangle…a perilous place to travel indeed!)

SOURCES

Normandeau Associates,  Inc. and Gomez and Sullivan.  2018.  Muddy Run Pumped Storage Project Conowingo Eel Collection Facility FERC Project 2355.  Prepared for Exelon.

Stambaugh, Jr., John W., and Robert P. Denoncourt.  1974.  A Preliminary Report on the Conewago Creek Faunal Survey, Lancaster County, Pennsylvania.  Proceedings of the Pennsylvania Academy of Sciences.  48: 55-60.

S’more

The tall seed-topped stems swaying in a summer breeze are a pleasant scene.  And the colorful autumn shades of blue, orange, purple, red, and, of course, green leaves on these clumping plants are nice.  But of the multitude of flowering plants, Big Bluestem, Freshwater Cordgrass, and Switchgrass aren’t much of a draw.  No self-respecting bloom addict is going out of their way to have a gander at any grass that hasn’t been subjugated and tamed by a hideous set of spinning steel blades.  Grass flowers…are you kidding?

Big Bluestem in flower in the Riverine Grasslands at Conewago Falls.

O.K., so you need something more.  Here’s more.

Meet the Partridge Pea (Chamaecrista fasciculata).  It’s an annual plant growing in the Riverine Grasslands at Conewago Falls as a companion to Big Bluestem.  It has a special niche growing in the sandy and, in summertime, dry soils left behind by earlier flooding and ice scour.  The divided leaves close upon contact and also at nightfall.  Bees and other pollinators are drawn to the abundance of butter-yellow blossoms.  Like the familiar pea of the vegetable garden, the flowers are followed by flat seed pods.

The Partridge Pea can tolerate dry sandy soils.

But wait, here’s more.

In addition to its abundance in Conewago Falls, the Halberd-leaved Rose Mallow (Hibiscus laevis) is the ubiquitous water’s edge plant along the free-flowing Susquehanna River for miles downstream.  It grows in large clumps, often defining the border between the emergent zone and shore-rooted plants.  It is particularly successful in accumulations of alluvium interspersed with heavier pebbles and stone into which the roots will anchor to endure flooding and scour.  Such substrate buildup around the falls, along mid-river islands, and along the shores of the low-lying Riparian Woodlands immediately below the falls are often quite hospitable to the species.

Halberd-leaved Rose Mallow is a durable inhabitant of the falls.  Regular flooding keeps competing species at bay.  A taproot helps to safeguard against dislocation, allowing plants to grow in places subjected to turbulent currents.

Halberd-leaved Rose Mallow in bloom.  The similarity to cultivated members of the Hibiscus genus can readily be seen.  It is one of the showiest of perennial wildflowers in the floodplain.  Note the lobed, halberd-shaped leaves, source of its former species name militaris.

The seeds of Halberd-leaved Rose Mallow are contained in bladders which can float to assist in their distribution.  Some of these bladders cling to the dead leafless stems in winter, making it an easy plant to identify in nearly any season.

A second native wildflower species in the genus Hibiscus is found in the Conewago Falls floodplain, this one in wetlands.  The Swamp Rose Mallow (H. moscheutos) is similar to Halberd-leaved Rose Mallow, but sports more variable and colorful blooms.  The leaves are toothed without the deep halberd-style lobes and, like the stems, are downy.  As the common name implies, it requires swampy habitat with ample water and sunlight.

Swamp Rose Mallow in a sunny wetland.  This variety with solid-colored flowers (without dark centers) and pale green leaves and stems was formerly known as a separate species of  Swamp Rose Mallow, H. palustris.  Note that the flowers are terminal on the stems.

A few scattered specimens of a more typical variety of Swamp Rose Mallow are found on the shoreline and in the Riverine Grasslands of Conewago Falls.  The blooms are bright pink with darker centers and the leaf stems are robust and reddish.  This one is seen growing among Halberd-leaved Rose Mallow, with which it shares the characteristic of having flower stems growing from some of the upper leaf axils.  A variety with red-centered white flowers is often found throughout the plant’s range.

In summary, we find Partridge Pea in the Riverine Grasslands growing in sandy deposits left by flood and ice scour.  We find Halberd-leaved Rose Mallow rooted at the border between shore and the emergent zone.  We find Swamp Rose Mallow as an emergent in the wetlands of the floodplain.  And finally, we find marshmallows in only one location in the area of Conewago Falls.  Bon ap’.

Here’s S’more

SOURCES

Newcomb, Lawrence.  1977.  Newcomb’s Wildflower Guide.  Little, Brown and Company.  Boston, Massachusetts.

Summer Grasses

It has not been a good summer if you happen to be a submerged plant species in the lower Susquehanna River.  Regularly occurring showers and thunderstorms have produced torrents of rain and higher than usual river stages.  The high water alone wouldn’t prevent you from growing, colonizing a wider area, and floating several small flowers on the surface, however, the turbidity, the suspended sediment, would.  The muddy current casts a dirty shadow on the benthic zone preventing bottom-rooted plants from getting much headway.  There will be smaller floating mats of the uppermost leaves of these species.  Fish and invertebrates which rely upon this habitat for food and shelter will find sparse accommodation…better luck next year.

Due to the dirty water, fish-eating birds are having a challenging season as they try to catch sufficient quantities of prey to feed themselves and their offspring.  A family of Ospreys (Pandion haliaetus) at Conewago Falls, including recently fledged young, were observed throughout this morning and had no successful catches.  Of the hundred or more individual piscivores of various species present, none were seen retrieving fish from the river.  The visibility in the water column needs to improve before fishing is a viable enterprise again.

Ospreys competing for a suitable fishing perch.  Improving water conditions in the coming week should increase their success as predators.

Versatile at finding food, adult Bald Eagles are experienced and know to be on the lookout for Ospreys with fish, a meal they can steal through intimidation.

While the submerged plant communities may be stunted by 2017’s extraordinary water levels, there is a very unique habitat in Conewago Falls which endures summer flooding and, in addition, requires the scouring effects of river ice to maintain its mosaic of unique plants.  It is known as a Riverine Grassland or scour grassland.

The predominant plants of the Riverine Grasslands are perennial warm-season grasses.  The deep root systems of these hardy species have evolved to survive events which prevent the grassland from reverting to woodland through succession.  Fire, intense grazing by wild herd animals, poor soils, drought, and other hardships, including flooding and ice scour, will eliminate intolerant plant species and prevent an area from reforesting.  In winter and early spring, scraping and grinding by flood-driven chunk ice mechanically removes large woody and poorly rooted herbaceous growth from susceptible portions of the falls.  These adverse conditions clear the way for populations of species more often associated with North America’s tall grass prairies to take root.  Let’s have a look at some of the common species found in the “Conewago Falls Pothole Rocks Prairie”.

Big Bluestem (Andropogon gerardi), seen here growing in the cracks of a pothole rock. High water nourishes the plant by filling the crevices with nutrient-loaded sediment. This species evolved with roots over three feet deep to survive fires, trampling by bison, and drought.

Freshwater Cordgrass (Spartina pectinata) does well with its roots in water.  It creates exceptional bird habitat and grows in the falls and on ice-scoured small islands in free-flowing segments of the Susquehanna River downstream.

Switchgrass (Panicum virgatum), like Big Bluestem, is one of the tall grass prairie species and, like Freshwater Cordgrass, grows in near pure stands on ice-scoured islands.  It takes flooding well and its extensive root system prevents erosion.

Though not a grass, Water Willow (Justicia americana) is familiar as a flood-enduring emergent plant of river islands, gravel bars, and shorelines where its creeping rhizome root system spreads the plant into large masses.  These stands are often known locally as “grass beds”.  This member of the acanthus family provides habitat for fish and invertebrates among its flooded leaves and stems.  Its presence is critical to aquatic life in a year such as this.

The Conewago Falls Riverine Grassland is home to numerous other very interesting plants.  We’ll look at more of them next time.

SOURCES

Brown, Lauren.  1979.  Grasses, An Identification Guide.  Houghton Mifflin Company.  New York, NY.

The Wall

It was one of the very first of my memories.  From the lawn of our home I could look across the road and down the hill through a gap in the woodlands.  There I could see water, sometimes still with numerous boulders exposed, other times rushing, muddy, and roaring.  Behind these waters was a great stone wall and beyond that a wooded hillside.  I recall my dad asking me if I could see the dam down there.  I couldn’t see a dam, just fascinating water and the gray wall behind it.  I looked and searched but not a trace of a structure spanning the near to far shore was to be seen.  Finally, at some point, I answered in the affirmative to his query; I could see the dam…but I couldn’t.

We lived in a small house in the village of Falmouth along the Susquehanna River in the northwest corner of Lancaster County over fifty years ago.  A few years after we had left our riverside domicile and moved to a larger town, the little house was relocated to make way for an electric distribution sub-station and a second set of electric transmission wires in the gap in the woodlands.  The Brunner Island coal-fired electric generating station was being upgraded downstream and, just upstream, a new nuclear-powered generating station was being constructed on Three Mile Island.  To make way for the expanding energy grid, our former residence was trucked to a nearby boat landing where there were numerous other river shacks and cabins.  Because it was placed in the floodplain, the building was raised onto a set of wooden stilts to escape high water.  It didn’t help.  The record-breaking floods of Hurricane Agnes in June of 1972 swept the house away.

The view through the cut in the woodland, a little wider than in the early 1960s with the addition of the newer electric transmission wire towers. The “Wall” is the same.

During the time we lived along the Susquehanna, the river experienced record-low flow rates, particularly in the autumn of 1963 and again in 1964.  My dad was a dedicated 8mm home-movie photographer.  Among his reels was film of buses parked haphazardly along the road (PA Route 441 today) near our home.  Sightseers were coming to explore the widely publicized dry riverbed and a curious moon-like landscape of cratered rocks and boulders.  It’s hard to fathom, but people did things like that during their weekends before Sunday-afternoon football was invented.  Scores of visitors climbed through the rocks and truck-size boulders inspecting this peculiar scene.  My dad, his friends, and so many others with camera in hand were experiencing the amazing geological feature known as the Pothole Rocks of Conewago Falls.

Conewago Falls on the Susquehanna River and several exposed York Haven Diabase Pothole Rocks.  Lancaster (foreground) and Dauphin (center) Counties meet along a southwest to northeast borderline through the rapids.  Lands on the west shoreline in the background are in York County.  Three Mile Island is seen in the upper right.

The river here meets serious resistance as it pushes its way through the complex geology of south-central Pennsylvania.  These hard dark-gray rocks, York Haven Diabase, are igneous in origin.  Diabase sheets and sills intruded the Triassic sediments of the Gettysburg Formation here over 190 million years ago.  It may be difficult to visualize, but these sediments were eroded from surrounding mountains into the opening rift valley we call the Gettysburg Basin.  This rift and others in a line from Nova Scotia to Georgia formed as the supercontinent Pangaea began dividing into the continents we know today.  Eventually the Atlantic Ocean rift would dominate as the active dynamic force and open to separate Africa from North America.  The inactive Gettysburg Basin, filled with sediments and intruded by igneous diabase, would henceforth, like the mountainous highlands surrounding it, be subjected to millions of years of erosion.  Of the regional rocks, the formations of Triassic redbeds, sandstones, and particularly diabase in the Gettysburg Basin are among the more resistant to the forces of erosion.  Many less resistant older rocks, particularly those of surrounding mountains, are gone.  Today, the remains of the Gettysburg Basin’s rock formations stand as rolling highlands in the Piedmont Province.

Flooded from the heavy rains of Tropical Storm Lee, the sediment-laden Susquehanna River flows through the Gettysburg Basin just south of Harrisburg, PA, September 10, 2011.  The “Wall” as seen from space.  (NASA Earth Observatory Image)

The weekend visitors in 1963 and 1964 marveled at evidence of the river’s fight to break down the hard York Haven Diabase.   Scoured bedrock traced the water’s turbulent flow patterns through the topography of the falls.  Meltwater from the receding glaciers of the Pleistocene Ice Ages thousands to tens of thousands of years ago raged in high-volume, abrasive-loaded torrents to sculpt the Pothole Rocks into the forms we see today.  Our modern floodwaters with ice and fine suspended sediments continue to wear at the smooth rocks and boulders, yet few are broken or crumbled to be swept away.  It’s a very slow process.  The river elevation here drops approximately 19 feet in a quarter of a mile, a testament to the bedrock’s persisting resistance to erosion.  Conewago Falls stands as a natural anomaly on a predominantly uniform gradient along the lower Susquehanna’s downhill path from the Appalachian Mountains to the Chesapeake Bay.

Normally the scene of dangerous tumbling rapids, the drought and low water of 1963 and 1964 had left the falls to resemble a placid scene—a moonscape during a time when people were obsessed with mankind’s effort to visit earth’s satellite.  Visitors saw the falls as few others had during the twentieth century.  Dr. Herbert Beck of Franklin and Marshall College described an earlier period of exposure, “…pot holes…were uncovered during the third week in October, 1947, for the first time in the memory of man, when the drought parched Susquehanna River retreated far below its normal low stage”.  Then, as in 1963 and on occasions more recent, much of it was due to the presence of the wall.  I had to be a bit older than four years old to grasp it.  You see the wall and the dam are one and the same.  The wall is the York Haven Dam.  And it is responsible for channeling away the low flow of the Susquehanna during periods of drought so that we might have the opportunity to visit and explore the Pothole Rocks of Conewago Falls along the river’s east shore.

The initial segment of the dam, a crib structure built in 1885 by the York Haven Paper Company to supply water power to their mill, took advantage of the geomorphic features of the diabase bedrock of Conewago Falls to divert additional river flow into the abandoned Conewago Canal.  The former canal, opened in 1797 to allow passage around the rapids along the west shore, was being used as a headrace to channel water into the grinding mill’s turbines.  Strategic placement of this first wall directed as much water as possible toward the mill with the smallest dam practicable.  The York Haven Power Company incorporated the paper mill’s crib dam into the “run-of-the-river” dam built through the falls from the electric turbine powerhouse they constructed on the west shore to the southern portion of Three Mile Island more than a mile away.   The facility began electric generation in 1904.  The construction of the “Red Hill Dam” from the east shore of Three Mile Island to the river’s east shore made York Haven Dam a complete impoundment on the Susquehanna.  The pool, “Lake Frederic”, thus floods that portion of the Pothole Rocks of Conewago Falls located behind the dam.   On the downstream side, water spilling over or through the dam often inundates the rocks or renders them inaccessible.

During the droughts of the early 1960s, diversion of nearly all river flow to the York Haven Dam powerhouse cleared the way for weekend explorers to see the Pothole Rocks in detail.  Void of water, the intriguing bedrock of Conewago Falls below the dam greeted the curious with its ripples, cavities, and oddity.  It was an opportunity nature alone would not provide.  It was all because of the wall.

York Haven Dam and powerhouse. The “Wall” traverses Conewago Falls upstream to Three Mile Island to direct water to the powerhouse on the west shore of the Susquehanna River.

SOURCES

Beck, Herbert H.  1948.  “The Pot Holes of Conewago Falls”.  Proceedings of the Pennsylvania Academy of Science.  Penn State University Press.  22: pp. 127-130.

Smith, Stephen H.  2015.  #6 York Haven Paper Company; on the Site of One of the Earliest Canals in America.  York Past website www.yorkblog.com/yorkpast/2015/02/17/6-york-haven-paper-company-on-the-site-of-one-of-the-earliest-canals-in-america/  as accessed July 17, 2017.

Stranahan, Susan Q.  1993.  Susquehanna, River of Dreams.  The Johns Hopkins University Press.  Baltimore, Maryland.

Van Diver, Bradford B.  1990.  Roadside Geology of Pennsylvania.  Mountain Press Publishing Company.  Missoula, Montana.