How Legacy Sediment Impacts Streams and Floodplains

What is Legacy Sediment?

The Environmental Protection Agency (EPA) defines legacy sediment as soil “that was eroded from upland areas after the arrival of early settlers and over the centuries of intensive land uses”, such as agriculture. This sediment accumulates along stream corridors, building up higher and higher as the years pass. Pennsylvania’s streams have a lot of it, in large part because of the myriad old mill dams still located along their shores.

What does It Do?

The accumulation of legacy sediment in a stream alters the natural course of the stream and buries floodplains and wetlands. Instead of a gently-sloped stream bank, you end up with a steep, easily eroded bank. Without the natural floodplains and wetlands, the stream flows faster, adding to the erosion problem and removing great habitat for wildlife and plants. One main reason why Pennsylvania contributes so much sediment and nutrient pollution to the Chesapeake Bay is the existence of so much legacy sediment in our waterways.

What can be done?

Thankfully, many organizations now recognize the impact legacy sediment has on water quality and are doing something about it. They are removing tons of it and restoring the floodplain to a more natural, gradually-sloped state. They are planting grasses, trees, and other vegetation along the restored streambanks to prevent erosion and improve wildlife habitat. They are removing antiquated mill dams so that the water can flow free.

Tackling legacy sediment is all about floodplain restoration. A floodplain is the low-lying land on either side of a waterway’s banks. Floodplains allow what would otherwise be potentially dangerous flood waters to slow and spread out. Floodplains are nature’s flood protection policy. Unfortunately, over the years, people have built roads, buildings, and other structures in floodplains, giving the stream or river no place to go but into our way during a flood. Combine the lack of natural floodplains with the build-up of legacy sediment and it is doubly-damaging to us.

Our Involvement

LandStudies is one organization that recognized early on what legacy sediment was and did something about floodplain restoration. The company has worked across Lancaster County, PA and beyond to restore floodplains and wetlands from their buried ways. For instance, they, in partnership with B.R. Kreider & Son, Inc., received two awards from the Associated Builders & Contractors Keystone Chapter organization for the Logan Park – Rife Run Floodplain Restoration Project in Manheim Township. The legacy sediment removed from this stream was used to improve nearby community soccer fields. LandStudies also worked with Franklin and Marshall College to remove 20,000 tons of it from Big Spring Run and restore a functioning wetland ecosystem. To learn about other floodplain restoration work, visit https://landstudies.com/?s=legacy+sediment.

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