Grasshoppers are perhaps best known for the occasions throughout history when an enormous congregation of these insects—a “plague of locusts”—would assemble and rove a region to feed. These swarms, which sometimes covered tens of thousands of square miles or more, often decimated crops, darkened the sky, and, on occasion, resulted in catastrophic famine among human settlements in various parts of the world.
The largest “plague of locusts” in the United States occurred during the mid-1870s in the Great Plains. The Rocky Mountain Locust (Melanoplus spretus), a grasshopper of prairies in the American west, had a range that extended east into New England, possibly settling there on lands cleared for farming. Rocky Mountain Locusts, aside from their native habitat on grasslands, apparently thrived on fields planted with warm-season crops. Like most grasshoppers, they fed and developed most vigorously during periods of dry, hot weather. With plenty of vegetative matter to consume during periods of scorching temperatures, the stage was set for populations of these insects to explode in agricultural areas, then take wing in search of more forage. Plagues struck parts of northern New England as early as the mid-1700s and were numerous in various states in the Great Plains through the middle of the 1800s. The big ones hit between 1873 and 1877 when swarms numbering as many as trillions of grasshoppers did $200 million in crop damage and caused a famine so severe that many farmers abandoned the westward migration. To prevent recurrent outbreaks of locust plagues and famine, experts suggested planting more cool-season grains like winter wheat, a crop which could mature and be harvested before the grasshoppers had a chance to cause any significant damage. In the years that followed, and as prairies gave way to the expansive agricultural lands that presently cover most of the Rocky Mountain Locust’s former range, the grasshopper began to disappear. By the early years of the twentieth century, the species was extinct. No one was quite certain why, and the precise cause is still a topic of debate to this day. Conversion of nearly all of its native habitat to cropland and grazing acreage seems to be the most likely culprit.
The critically endangered Eskimo Curlew (Numenius borealis), a species not photographed since 1962 and not confirmed since 1963, fed on Rocky Mountain Locusts during its spring migration through the Great Plains. Excessive hunting and conversion of grasslands to agriculture are believed responsible for the bird’s demise. (United States Fish and Wildlife Service image by Christina Nelson)
In the Mid-Atlantic States, the mosaic of the landscape—farmland interspersed with a mix of forest and disturbed urban/suburban lots—prevents grasshoppers from reaching the densities from which swarms arise. In the years since the implementation of “Green Revolution” farming practices, numbers of grasshoppers in our region have declined. Systemic insecticides including neonicotinoids keep grasshoppers and other insects from munching on warm-season crops like corn and soybeans. And herbicides including 2,4-D (2,4-Dichlorophenoxyacetic acid) have, in effect, become the equivalent of insecticides, eliminating broadleaf food plants from the pasturelands and hayfields where grasshoppers once fed and reproduced in abundance. As a result, few of the approximately three dozen species of grasshoppers with ranges that include the Lower Susquehanna River Watershed are common here. Those that still thrive are largely adapted to roadsides, waste ground, and small clearings where native and some non-native plants make up their diet.
Here’s a look at four species of grasshoppers you’re likely to find in disturbed habitats throughout our region. Each remains common in relatively pesticide-free spaces with stands of dense grasses and broadleaf plants nearby.
CAROLINA GRASSHOPPER
Dissosteira carolina
The Carolina Grasshopper, also known as the Carolina Locust or Quaker, is one of the band-winged grasshoppers. It is commonly found along roadsides and on other bare ground near stands of tall grass and broadleaf plants.The Carolina Grasshopper is variable in color, ranging from very dark brown……to a rich tan or khaki shade. These earth-tone colors provide the insect with effective camouflage while spending time on the ground.The Carolina Grasshopper is most readily detected and identified when it flies. The colors of the wings resemble those of the Mourning Cloak butterfly.Carolina Grasshoppers are among the preferred victims of Great Black Wasps (Sphex pensylvanicus). A female wasp stings the grasshopper to paralyze it, then drags it away to one of numerous cells in an underground burrow where she lays an egg on it. The body of the disabled grasshopper then provides nourishment for the larval wasp.
DIFFERENTIAL GRASSHOPPER
Melanoplus differentialis
Differential Grasshopper nymph with small “fairy wings”.An adult female Differential Grasshopper with fully developed wings.An adult female Differential Grasshopper
TWO-STRIPED GRASSHOPPER
Melanoplus bivittatus
An early-stage Two-striped Grasshopper nymph.A Two-striped Grasshopper nymph in a later stage.An adult female Two-striped Grasshopper.An adult female Two-striped Grasshopper. Note the pale stripe originating at each eye and joining near the posterior end of the wings to form a V-shaped pattern.An adult female Two-striped Grasshopper.
RED-LEGGED GRASSHOPPER
Melanoplus femurrubrum
An adult male Red-legged Grasshopper hiding in dense urban vegetation.The Red-legged Grasshopper may currently be our most abundant and widespread species.An adult male Red-legged Grasshopper.An adult female Red-legged Grasshopper.
Protein-rich grasshoppers are an important late-summer, early-fall food source for birds. The absence of these insects has forced many species of breeding birds to abandon farmland or, in some cases, disappear altogether.
During the mid-twentieth century, the Cattle Egret (Bubulcus ibis), a notoriously nomadic species, transited the Atlantic from Africa to colonize the Americas…and they did it without any direct assistance from humans. During the 1970s and early 1980s, a nesting population of Cattle Egrets on river islands adjacent to the Susquehanna’s Conejohela Flats off Washington Boro was the largest inland rookery in the northeastern United States. The Lancaster County Bird Club censused the birds each August and found peak numbers in 1981 (7,580). During their years of abundance, V-shaped flocks of Cattle Egrets from the rookery islands ventured into grazing lands throughout portions of Lancaster, York, Dauphin, and Lebanon Counties to hunt grasshoppers. These daily flights were a familiar summertime sight for nearly two decades. Then, in the early 1980s, reductions in pastureland acreage and plummeting grasshopper numbers quickly took their toll. By 1988, the rookery was abandoned. The Cattle Egrets had moved on. (Vintage 33 mm image)During the summer and early fall, juvenile and adult Ring-necked Pheasants feed heavily on grasshoppers. Earlier and more frequent mowing along with declining numbers of grasshoppers on farmlands due to an increase in pesticide use were factors contributing to the crash of the pheasant population in the early 1980s.To the delight of Wild Turkeys, each of the four species of grasshoppers shown above frequents clearings and roadsides adjacent to forest areas. While changes in grasshopper distribution have been detrimental to populations of birds like pheasants, they’ve created a feeding bonanza for turkeys.Wild Turkeys feeding on an abundance of grasshoppers along a forest road.An American Kestrel feeds on a grasshopper while ignoring the abundance of Spotted Lanternflies swarming the adjacent utility pole. In Susquehanna valley farmlands, grasshopper and kestrel numbers are down. Lanternflies, on the other hand, have got it made.Maintaining areas bordering roads, forests, wetlands, farmlands, and human development in a state of early succession can provide and ideal mix of mature grasses and broadleaf plants for grasshoppers, pollinators, birds, and other wildlife.
Back in late May of 1983, four members of the Lancaster County Bird Club—Russ Markert, Harold Morrrin, Steve Santner, and your editor—embarked on an energetic trip to find, observe, and photograph birds in the Lower Rio Grande Valley of Texas. What follows is a daily account of that two-week-long expedition. Notes logged by Markert some four decades ago are quoted in italics. The images are scans of 35 mm color slide photographs taken along the way by your editor.
DAY EIGHT—May 28, 1983
“Bentsen State Park, Texas”
“Alarm at 6:00 A.M. After breakfast we traveled to Falcon State Park and toured the whole camp area, stopping many places to observe birds. We ran up a good list.”
And so we left what had been our home for the last several days and headed west. In the forty years since our departure that morning, Bentsen-Rio Grande State Park has experienced a number of operational changes. Today, it is a World Birding Center site. For conducting the seasonal hawk census, a tower has been erected to provide counters and observes with an unrestricted view above the treetops. If you wanted to camp in the park now, you would need reservations and would have to hike your gear in to one of only a few primitive campsites. Trailer and motor home accommodations no longer exist. A tram service is now available for touring the park by motor vehicle.
West of Rio Grande City, we exited the river’s outflow delta and entered the Texas scrubland, an area mostly devoid of large trees except in moist soils immediately adjacent to the Rio Grande where the lush vegetation creates a dense subtropical riparian forest in many places. The reservoir itself is known to attract migrating and vagrant waterfowl, waders, shorebirds, gulls, terns, and seabirds. (United States Fish and Wildlife Service base image)
Falcon State Park is located along the east shore of Falcon Reservoir. There are no shade trees beneath which one can escape the scorching rays of the sun on a hot day. This is the easternmost section of the scrubland’s Tamaulipan Saline Thornscrub, a xeric plant community of head-high brush found only on clay soils with a particularly high salinity. Many of the plants look similar to other varieties of shrubs and small trees with which one may be familiar, except nearly all of them are covered with nasty thorns and prickles. And yes, there are cactus. You can’t make your way bushwhacking cross country without obtaining cuts, gashes, and scars to show for it. The Falcon State Recreation Area bird checklist published in 1977 has a nice description of the plants found there—mesquite, ebano, guaycan, blackbrush and catclaw acacia, granjeno, coyotillo, huisache, tasajillo, prickly pear, allthorn, cenizo, colima, and yucca. In the margins between the thornscrub growth, there is an abundance of grasses and wildflowers. On nearby ridges, Tamaulipan Calcareous Thornscrub, a similar xeric plant community, occupies soils with a higher content of calcium carbonate. Together, these communities comprise much of the Tamaulipan Mezquital ecoregion of scrublands in Starr County and western Hidalgo County in the Rio Grande valley of Texas.
After being greeted by a Greater Roadrunner at the campsite, we took a walk to the nearby shoreline of the reservoir. We spotted Olivaceous Cormorants perched on some dead limbs in the water nearby. Known today as Neotropic Cormorant (Phalacrocorax brasilianus), it is yet another specialty of the Rio Grande Valley. Elsewhere on or near the water—Cattle Egret, Great Egret, Black-bellied Whistling Duck, Osprey, Common Gallinule, Killdeer, Laughing Gull, Forster’s Tern (Sterna forsteri), Least Tern, and Caspian Tern were seen.
The Greater Roadrunner is right at home in the Tamaulipan Saline Thornscrub habitat in and around Falcon State Park. This one came to check us out soon after our arrival at our campsite. Roadrunners prey on insects, rodents, and lizards including the Texas Spotted Whiptail (Aspidoscelis gularis), a species which we found nearby.
In the thornscrub around the campground, which, like Bentsen-Rio Grande State Park, we had pretty much to ourselves, we saw Scissor-tailed Flycatcher, Curve-billed Thrasher, White-winged Dove, Mourning Dove, Ground Dove, Inca Dove, and White-tipped Dove. A single Chihuahuan Raven was a fly by. We saw and smelled several road-killed Nine-banded Armadillos (Dasypus novemcinctus), but never found one alive.
Then, it started to rain. Not just a shower, but a soaker that persisted through much of the day. Rainy days can make for great birding, so we kept at it. Unfortunately, such days aren’t too ideal for photography, so we did only what we could without ruining our equipment.
In the campground at Falcon State Park, a Cactus Wren (Campylorhynchus brunneicapillus) takes shelter from the rain beneath a canopy protecting a picnic table.Looks like a good idea, others soon sought shelter there as well.
“Finally we drove to the spillway of the dam and parked.”
Falcon Dam was another of the numerous flood-control projects built on the Rio Grande during the middle of the twentieth century. Behind it, Falcon Reservoir stores water for irrigation and operation of a hydroelectric generating station located within the dam complex. Construction of the dam and power plant was a joint venture shared by Mexico and the United States. The project was dedicated by Presidents Adolfo Ruiz Cortines and Dwight D. Eisenhower in 1953.
Rainy days aside, the route precipitation takes to reach the Falcon Reservoir and the Lower Rio Grande Valley includes hundreds of miles through arid grasslands and scrublands. Along the way, much of that water is lost to natural processes including evaporation and aquifer recharge, but an increasing percentage of the volume is being removed by man for civil, industrial, and agricultural uses. Can the Rio Grande and its tributaries continue to meet demand?
The Rio Grande’s headwaters can be found in south-central Colorado where spring snow melt is vital to establishing adequate flow to allow the river to recharge aquifers in the hundreds of miles of arid lands through which it flows. Presently, dams in the upper reaches of the river are operated to hold water during the spring thaw, then release it slowly to compensate for base flow lost to withdrawals for irrigation in extensive areas of the middle reaches of the watershed. With everyone wanting their take, is there enough water to go around? Diminishing ground water levels suggest the answer is no. (National Oceanic and Atmospheric Administration base image)Using the streamflow recharge process, the flowing Rio Grande provides water to the aquifers in the arid regions through which it passes. Click the image for a slightly larger version. (United States Geological Survey image)
“On the way in we saw and photographed an apparent sick or injured Swainson’s Hawk. We approached it very close.”
The Swainson’s Hawk (Buteo swainsoni), a bird of prairies and other grasslands, is an abundant migrant through the Lower Rio Grande Valley in both spring and fall. This one was grounded, rain-soaked, and obviously running late. Others of its kind were by now on their breeding grounds in the Great Plains and Rocky Mountains.The bird allowed us to approach without attempting to flee, which isn’t a good sign. We looked for any obvious physical injuries and found none.The continuous rain had the hawk’s feathers matted down and soaked.Was its water-logged plumage the problem, or was it the result of its inability to thrive due to an illness? We had no way of telling, so we let it be and vowed to stop back later to check on it.Steve the hawk whisperer?
“At the spillway we sat in the camper, except when the rain slackened, then we stood out and watched in vain for the Green or Ringed Kingfisher, which we never did see.”
At the spillway House Sparrows, Rough-winged Swallows, and Cliff Swallows were nesting on the dam, the latter two species grabbing flying insects above the waters of the Rio Grande.
Despite the rain, anglers were fishing along the spillway walls where this young man caught a Longnose Gar (Lepisosteus osseus). The reservoir has been stocked with Alligator Gar (Atractosteus spatula), Spotted Gar (Lepisosteus oculatus), and a variety of bass, catfish, and other species to establish a trophy sport fishery. Many specimens grow to become trophy-size there due to the warm water temperatures. These guys though were fishing for food, not trophies.
“I made dinner here at this spillway and we continued to watch. The rain almost stopped, so we walked down the road about 1 1/2 miles, during which time we saw a lifer for Harold — Hook-billed Kite. We followed Father Tom’s directions to a spot for the Ferruginous Owl — no luck.”
A Red-billed Pigeon in a willow tree in the subtropical riparian forest along the banks of the Rio Grande below Falcon Dam. Prior to this trip, neither Steve nor I had ever seen this tropical species before.
“Back at the spillway we had supper and then repeated the hike — no Ferruginous Owl, but a Barn Owl and Great Horned Owl. Back to our #201 campsite and wrote up the day’s log.”
Trees along the river provided habitat for orioles and other species. Since the rain had subsided, we decided to see what might come out and begin feeding. Soon, we not only saw an Altamira Oriole, but found Hooded Oriole (Icterus cucullatus) and the yellow and black tropical species, Audubon’s Oriole (Icterus graduacauda), formerly known as Black-headed Oriole. Three species of orioles on a backdrop of lush green subtropical foliage, it was magnificent.
Along the dirt road below the dam, the mix of scrubland and subtropical riparian forest made for excellent birding. We not only found a soaring Hook-billed Kite, one of the target birds for the trip, but we had good looks at both a Great Horned Owl, then a Barn Owl (Tyto alba) that we flushed from the bare ground in openings among the vegetation as we walked the through. Both had probably pounced on some sort of small prey species prior to our arrival. Because there are seldom crows or ravens to bother them, owls here are more active during than day than they are elsewhere. The subject of this afternoon’s intensive search, the elusive and diminutive Ferruginous Pygmy Owl (Glaucidium brasilianum), is routinely diurnal. Other sightings on our two walks included Turkey Vulture, Black Vulture, White-tailed Kite, Northern Bobwhite, Yellow-billed Cuckoo, Golden-fronted Woodpecker, Ladder-backed Woodpecker, Couch’s Kingbird, Brown-crested Flycatcher, Green Jay, Black-crested Titmouse, Mockingbird, Long-billed Thrasher, Great-tailed Grackle, Bronzed Cowbird, Northern Cardinal, and Painted Bunting.
The day finished as so many others had earlier during the trip—with insect-hunting Common Nighthawks calling from the skies around our campsite.
During the spare time you have on a rainy day like today, you may have asked yourself, “Just how much water do people collect with those rain barrels they have attached to their downspouts?” That’s a good question. Let’s do a little math to figure it out.
First, we need to determine the area of the roof in square feet. There’s no need to climb up there and measure angles, etc. After all, we’re not ordering shingles—we’re trying to figure out the surface area upon which rain will fall vertically and be collected. For our estimate, knowing the footprint of the building under roof will suffice. We’ll use a very common footprint as an example—1,200 square feet.
40′ x 30′ = 1,200 sq. ft.
By dividing the area of the roof by 12, we can calculate the volume of water in cubic feet that is drained by the spouting for each inch of rainfall…
1,200 ÷ 12 = 100 cu. ft. per inch of rainfall
Next, we multiply the volume of water in cubic feet by 7.48 to convert it to gallons per inch of rainfall…
100 x 7.48 = 748 gallons per inch of rainfall
That’s a lot of water. Just one inch of rain could easily fill more than a single rain barrel on a downspout. Many homemade rain barrels are fabricated using recycled 55-gallon drums. Commercially manufactured ones are usually smaller. Therefore, we can safely say that in the case of a building with a footprint of 1,200 square feet, an array of at least 14 rain barrels is required to collect and save just one inch of rainfall. Wow!
Why send that roof water down the street, down the drain, down the creek, or into the neighbors property? Wouldn’t it be better to catch it for use around the garden? At the very least, shouldn’t we be infiltrating all the water we can into the ground to recharge the aquifer? Why contribute to flooding when you and I are gonna need that water some day? Remember, the ocean doesn’t need the excess runoff—it’s already full.
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.
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.
