The Conejohela Flats are a group of islands in the flooded Conejohela Valley, a large floodplain along the southernmost 30 miles (50 km) of the
Susquehanna River in
Pennsylvania
Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...
and
Maryland
Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean to ...
in the United States. The valley was flooded primarily during the early 1900s by the construction of the
Holtwood,
Conowingo, and
Safe Harbor dams from 1910 to 1931.
Geography and history
Before the twentieth century, the Conejohela Valley was a marshy floodplain, with extensive wetlands. The Susquehanna River flooded annually in the spring, and there were more damaging floods approximately once per decade. Thick forests surrounded a mixture of small waterfalls, rapids, and marshes. A wide, flat valley formed; the frequently wide river was a substantial barrier to crossing, both for Native Americans and for colonists.
The varied terrain created many nurturing biological habitats, but human passage across the valley and river was extremely difficult. The Susquehanna is very wide in this area, as it nears its mouth on the
Chesapeake Bay
The Chesapeake Bay ( ) is the largest estuary in the United States. The Bay is located in the Mid-Atlantic (United States), Mid-Atlantic region and is primarily separated from the Atlantic Ocean by the Delmarva Peninsula (including the parts: the ...
. This stifled trade across the lower Susquehanna in colonial
Pennsylvania
Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...
and
Maryland
Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean to ...
. In 1730, the
Wright's Ferry
Wright's Ferry was a Pennsylvania Colony settlement established by John Wright in 1726, that grew up around the site of an important Inn and Pub anchoring the eastern end of a popular animal powered ferry (1730–1901) and now a historic part of ...
was established to cross the river. Later the first
Columbia-Wrightsville Bridge was built, once believed to be the longest covered bridges in the world. It was replaced by bridges built of structural steel, large enough to carry a range of vehicles. The modern bridge opened in 1930; it was dedicated in 1980 as the Veterans Memorial Bridge.
Flooding
Three dams were built across the Conejohela Valley during the first four decades of the 20th century to provide hydroelectric power for southern Pennsylvania (including
electrical power for Amtrak and SEPTA Regional Rail) and to control the annual flooding. It was intended to keep sediment from the flats out of the
Chesapeake Bay
The Chesapeake Bay ( ) is the largest estuary in the United States. The Bay is located in the Mid-Atlantic (United States), Mid-Atlantic region and is primarily separated from the Atlantic Ocean by the Delmarva Peninsula (including the parts: the ...
. The first dam across the lower Susquehanna, the
Holtwood Dam, was completed in 1910 as McCalls Ferry Dam. The
Conowingo Dam
The Conowingo Dam (also Conowingo Hydroelectric Plant, Conowingo Hydroelectric Station) is a large hydroelectric dam in the lower Susquehanna River near the town of Conowingo, Maryland. The medium-height, masonry gravity dam is one of the large ...
followed in 1928.
The
Safe Harbor Dam
The Safe Harbor Dam (also Safe Harbor Hydroelectric Station) is a concrete gravity dam, with an associated hydroelectric power station, on the lower Susquehanna River. It is the most northerly and last of three Great Depression- era public elect ...
had the largest effect on the river ecosystem. When it first closed its gates on September 29, 1931, it flooded more than 10 miles of the upper Conejohela Flats, creating the artificial
Lake Clarke. Most of the valley was flooded. The few islands that remain in Lake Clarke are a gathering of low, marshy flats about five miles north of Safe Harbor Dam.
Habitat
The remaining Conejohela Flats provide habitats for a number of species. The varying depths of inundated islands on the bottom of Lake Clarke support numerous fresh water feeder fish, pan fish, and large predatory
game fish
Game fish, sport fish or quarry refer to popular fish pursued by recreational anglers, and can be freshwater or saltwater fish. Game fish can be eaten after being caught, or released after capture. Some game fish are also targeted commercial ...
species. The Safe Harbor Dam has become a popular area for local fishing.
The low-lying islands and
riparian
A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the terrestrial biomes of the Earth. Plant habitats and communities along the river margins and banks a ...
ecosystem also support dozens of species of birds; the flats are popular among birders.
See also
*
Cresap's War
Cresap's War (also known as the Conojocular War, from the Conejohela Valley where it was mainly located along the south bank) was a border conflict between Pennsylvania and Maryland, fought in the 1730s. Hostilities erupted in 1730 with a serie ...
*
List of dams and reservoirs of the Susquehanna River
The Susquehanna River, in the Mid-Atlantic States of the United States, has a collection of dams. These dams are used for power generation, flood control, navigation and recreation. These dams have local and regional environmental impacts on ...
*
Susquehanna River dams
**
Safe Harbor Dam
The Safe Harbor Dam (also Safe Harbor Hydroelectric Station) is a concrete gravity dam, with an associated hydroelectric power station, on the lower Susquehanna River. It is the most northerly and last of three Great Depression- era public elect ...
**
Holtwood Dam
**
Conowingo Dam
The Conowingo Dam (also Conowingo Hydroelectric Plant, Conowingo Hydroelectric Station) is a large hydroelectric dam in the lower Susquehanna River near the town of Conowingo, Maryland. The medium-height, masonry gravity dam is one of the large ...
*
Thomas Cresap
Colonel Thomas Cresap (17021790) was an English-born settler and trader in the states of Maryland and Pennsylvania. Cresap served Lord Baltimore as an agent in the Maryland–Pennsylvania boundary dispute that became known as Cresap's War. Lat ...
References
External links
Safe Harbor Water Power Company
{{authority control
Susquehanna River
Crossings of the Susquehanna River
Landforms of Lancaster County, Pennsylvania
Landforms of York County, Pennsylvania
Islands of Pennsylvania