A recent report by the U.S. Army Corps of Engineers and the Maryland Department of the Environment attempts to answer that question. Sediment (dirt) and nutrients (mainly nitrogen and phosphorus from animal and human waste) from the land, floodplain, and streams in the watershed have been carried downstream and stored behind the Conowingo Dam and other dams on the river. Historically, the dams acted as traps, reducing the amount of sediment and nutrients reaching the Chesapeake Bay but, over time, the dams have “filled up” with sediment and, consequently, their trapping capacity has been greatly reduced.
Presently, these dams are in a state of "dynamic equilibrium," meaning nutrients and sediment will accumulate behind the dams until a flood event scours out some of the sediment, carrying that sediment into the Bay while simultaneously increasing the dams' storage capacity in the short term. Over the long term (years to decades), this dynamic equilibrium means that the amount of sediment carried to the dams from upstream sources will equal the amount of sediment that reaches the waters of the Chesapeake Bay.
Presently, these dams are in a state of "dynamic equilibrium," meaning nutrients and sediment will accumulate behind the dams until a flood event scours out some of the sediment, carrying that sediment into the Bay while simultaneously increasing the dams' storage capacity in the short term. Over the long term (years to decades), this dynamic equilibrium means that the amount of sediment carried to the dams from upstream sources will equal the amount of sediment that reaches the waters of the Chesapeake Bay.
During a major storm event (one that occurs every 4 to 5 years), approximately 20 to 30 percent of the sediment that flows into the Bay from the Susquehanna River is scoured of material stored behind Conowingo Dam, and the rest is from the upstream watershed. This means stored sediments are part of the problem, but they’re not the only problem. The main problem is pollution from farms, sewage plants, septic systems, and urban and suburban runoff throughout the Bay watershed. This type of pollution is in everyone’s backyard and addressing these sources of pollution is the best way to restore the Bay and our local streams and rivers.
The good news is that plans to address pollution in our local waters already exist and are being implemented. Each state in the Bay watershed has a Watershed Implementation Plan that will improve their local waters and meet the Bay clean-up goals.
A holistic approach that stops pollution at its source is a far better bet for clean water than focusing on just one part of the problem.
Jennifer Quinn is central Pennsylvania outreach coordinator for PennFuture and is based in Harrisburg. She tweets @QuinnJen1.
The good news is that plans to address pollution in our local waters already exist and are being implemented. Each state in the Bay watershed has a Watershed Implementation Plan that will improve their local waters and meet the Bay clean-up goals.
A holistic approach that stops pollution at its source is a far better bet for clean water than focusing on just one part of the problem.
Jennifer Quinn is central Pennsylvania outreach coordinator for PennFuture and is based in Harrisburg. She tweets @QuinnJen1.
