Conejohela Flats
Encyclopedia
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
and Maryland
in the United States. The valley was flooded primarily during the early 1900s by the construction of the Safe Harbor
, Holtwood
, and Conowingo
dams.
The varied terrain created many nurturing biological habitats, but rendered passage across the valley nearly impossible. This stifled trade across the lower Susquehanna in colonial Pennsylvania
and Maryland
, spurring the 1730 opening of the historic Wright's Ferry
and the first Columbia-Wrightsville Bridge
s, once believed to be the longest covered bridges in the world.
) and to control the annual flooding, as well as to keep sediment from the flats out of the Chesapeake Bay
. The first dam across the lower Susquehanna, the Holtwood Dam
, was completed in 1910 as McCalls Ferry Dam. The Conowingo Dam
followed in 1928. However, the Safe Harbor Dam
had the largest impact on the river ecosystem. When it first closed its gates on September 29, 1931, it flooded over ten 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.
species. The Safe Harbor Dam has become popular for local fishing.
The low-lying islands and riparian ecosystem also support dozens of species of birds; the flats are popular among birders.
Susquehanna River
The Susquehanna River is a river located in the northeastern United States. At long, it is the longest river on the American east coast that drains into the Atlantic Ocean, and with its watershed it is the 16th largest river in the United States, and the longest river in the continental United...
in Pennsylvania
Pennsylvania
The Commonwealth of Pennsylvania is a U.S. state that is located in the Northeastern and Mid-Atlantic regions of the United States. The state borders Delaware and Maryland to the south, West Virginia to the southwest, Ohio to the west, New York and Ontario, Canada, to the north, and New Jersey to...
and Maryland
Maryland
Maryland is a U.S. state located in the Mid Atlantic region of the United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east...
in the United States. The valley was flooded primarily during the early 1900s by the construction of the Safe Harbor
Safe Harbor Dam
The Safe Harbor Dam is a concrete gravity dam on the lower Susquehanna River with an associated hydroelectric power station. It is the most northerly and last of three Great Depression-era public electrification projects' hydroelectric dams and was constructed between 1 April 1930 and 7 December...
, Holtwood
Holtwood Dam
Holtwood Dam is the oldest of three major dams built across the lower Susquehanna River, and the middle location of the three. It was constructed as the McCalls Ferry Dam between 1905 and 1910 by the Pennsylvania Water & Power Company...
, and Conowingo
Conowingo Dam
The Conowingo Dam is a large hydroelectric dam in the Lower Susquehanna River. The dam, one of the largest non-federal hydroelectric dams in the US, is classified as a medium height, masonry gravity type dam...
dams.
Geography and History
Before the twentieth century, the Conejohela Valley was a marshy floodplain, with smaller annual floods and more catastrophic 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 natives and for colonists.The varied terrain created many nurturing biological habitats, but rendered passage across the valley nearly impossible. This stifled trade across the lower Susquehanna in colonial Pennsylvania
Province of Pennsylvania
The Province of Pennsylvania, also known as Pennsylvania Colony, was founded in British America by William Penn on March 4, 1681 as dictated in a royal charter granted by King Charles II...
and Maryland
Province of Maryland
The Province of Maryland was an English and later British colony in North America that existed from 1632 until 1776, when it joined the other twelve of the Thirteen Colonies in rebellion against Great Britain and became the U.S...
, spurring the 1730 opening of the historic Wright's Ferry
Wright's Ferry
Wright's Ferry was an animal powered ferry established by John Wright in 1730, and the very first means of crossing the wide unfriendly Susquehanna in the counties of the lower half of the state of Pennsylvaniaand directly triggered Cresap's War between the Province of Maryland and Pennsylvania...
and the first Columbia-Wrightsville Bridge
Columbia-Wrightsville Bridge
The Columbia–Wrightsville Bridge, officially the Veterans Memorial Bridge, spanning the Susquehanna River between Columbia and Wrightsville, Pennsylvania, is commonly associated with the name “Columbia–Wrightsville Bridge,” although five other former and present-day bridges share this...
s, once believed to be the longest covered bridges in the world.
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 SEPTA Regional RailSEPTA's 25 Hz Traction Power System
SEPTA operates a 25 Hz traction power system in the vicinity of Philadelphia, Pennsylvania that it inherited from the Reading Railroad. This system is separate but similar to the system designed by the Pennsylvania Railroad which is now operated by Amtrak. SEPTA's trains can run over either...
) and to control the annual flooding, as well as to keep sediment from the flats out of the Chesapeake Bay
Chesapeake Bay
The Chesapeake Bay is the largest estuary in the United States. It lies off the Atlantic Ocean, surrounded by Maryland and Virginia. The Chesapeake Bay's drainage basin covers in the District of Columbia and parts of six states: New York, Pennsylvania, Delaware, Maryland, Virginia, and West...
. The first dam across the lower Susquehanna, the Holtwood Dam
Holtwood Dam
Holtwood Dam is the oldest of three major dams built across the lower Susquehanna River, and the middle location of the three. It was constructed as the McCalls Ferry Dam between 1905 and 1910 by the Pennsylvania Water & Power Company...
, was completed in 1910 as McCalls Ferry Dam. The Conowingo Dam
Conowingo Dam
The Conowingo Dam is a large hydroelectric dam in the Lower Susquehanna River. The dam, one of the largest non-federal hydroelectric dams in the US, is classified as a medium height, masonry gravity type dam...
followed in 1928. However, the Safe Harbor Dam
Safe Harbor Dam
The Safe Harbor Dam is a concrete gravity dam on the lower Susquehanna River with an associated hydroelectric power station. It is the most northerly and last of three Great Depression-era public electrification projects' hydroelectric dams and was constructed between 1 April 1930 and 7 December...
had the largest impact on the river ecosystem. When it first closed its gates on September 29, 1931, it flooded over ten miles of the upper Conejohela Flats, creating the artificial Lake Clarke
Lake Clarke, Pennsylvania
Lake Clarke, Pennsylvania is a man-made lake along the Susquehanna River formed by the Safe Harbor Dam, a public works project of the 1930s Great Depression and one of the electrification projects of the New Deal. It is approximately long centered within the Conejohela Valley approximately ...
. 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 fishGame fish
Game fish are fish pursued for sport by recreational anglers. They can be freshwater or marine fish. Game fish can be eaten after being caught, though increasingly anglers practise catch and release to improve fish populations. Some game fish are also targeted commercially, particularly...
species. The Safe Harbor Dam has become popular for local fishing.
The low-lying islands and riparian ecosystem also support dozens of species of birds; the flats are popular among birders.
See also
- Cresap's WarCresap's WarCresap's War was a border conflict between Pennsylvania and Maryland, fought in the 1730s...
- List of dams and reservoirs of the Susquehanna River
- Susquehanna river damsSusquehanna river damsThe Susquehanna River, in the Mid-Atlantic States of the USA, 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 the river and the Chesapeake Bay, both positive and negative.-...
- Safe Harbor DamSafe Harbor DamThe Safe Harbor Dam is a concrete gravity dam on the lower Susquehanna River with an associated hydroelectric power station. It is the most northerly and last of three Great Depression-era public electrification projects' hydroelectric dams and was constructed between 1 April 1930 and 7 December...
- Holtwood DamHoltwood DamHoltwood Dam is the oldest of three major dams built across the lower Susquehanna River, and the middle location of the three. It was constructed as the McCalls Ferry Dam between 1905 and 1910 by the Pennsylvania Water & Power Company...
- Conowingo DamConowingo DamThe Conowingo Dam is a large hydroelectric dam in the Lower Susquehanna River. The dam, one of the largest non-federal hydroelectric dams in the US, is classified as a medium height, masonry gravity type dam...
- Safe Harbor Dam
- Thomas CresapThomas CresapColonel Thomas Cresap was an English-born pioneer settler in the state of Maryland, and an agent of Lord Baltimore in the Maryland-Pennsylvania boundary dispute. During the dispute, Cresap became a notorious figure in the Conejohela Flats areathe Susquehanna Valley in the area south of Wright's...