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.

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 recording-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 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.

The scene of dangerous tumbling rapids during high flows, 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.  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.

The initial segment, a crib dam constructed 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

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.