River restoration is the act of working with a degraded river or stream in order to return it to a pre-disturbed condition. A disturbance is anything that disrupts a stream and knocks it out of equilibrium. Common disturbances in Lancaster County result from suburban sprawl and agriculture. These land use practices cause excess sediment, nutrients, and chemicals to run into the water. Restoration projects work on different scales. A reach is a small section of a stream, while a corridor is the entire length of the stream.
A watershed is an area of land that contributes water to a common network of streams. Watershed boundaries or "divides" occur along high points in the landscape that separate different stream networks. Large watersheds are composed of many smaller watersheds upstream of the primary river in the network. All streams in the Little Conestoga watershed flow into the Conestoga River, then into the Susquehanna River which flows into the Chesapeake Bay. Each stream or river in the watershed is called a tributary of the larger river downstream.
Types of Restoration
There are many components to stream restoration. Most common efforts focus on stream bank stabilization, enhancing riparian buffers by adding trees and natural grasses, the removal of dams and other man-made structures, adding meanders, and stocking the river with fish or other living organisms.
Basic streambank stabilization may involve placing large cobbles or boulders along banks and replanting native vegetation. More sophisticated stabilization procedures include "vegetated geogrids," where alternating layers of live branches, called fascines, are buried along the stream bank. These can be installed along with "live stake" cuttings inserted upright into the soil. Banks can further be stabilized using "biologs" (bundles of coconut fibers) placed at the bottom of a stream bank to hold the bank in place. "Rootwads" are uprooted trees installed into the stream bank with the roots facing into the channel. These structures encourage different speeds of water flow where different organisms can live. They also serve to trap sediment, stop erosion, and prevent damaging effects from pollution.
Planting trees and grasses creates a "green sponge" that filters water flowing into the stream and traps excess sediment. Sediment is problematic because it blocks light to underwater vegetation and lowers the water oxygen levels that fish and other organisms need to survive. These sponges are called riparian buffers. Riparian buffers are planted next to streams and are ideally 20 to 30 feet wide on either side of the river.
Species of Trees and Shrubs used by LCWA for Riparian Buffers
Small dams and other structures were put into place around Lancaster to power mills. However, most dams are unnecessary today. Dams harm streams by blocking fish from their native spawning grounds. They also make stream channels wide and narrow because they prevent different sizes of bedrock from traveling downstream. Many times, dam removal is the first step in restoration because other efforts are useless without it.
Meander Bend Replacement
Meanders are natural stream bends. Streams are "lazy" and want to do the least work possible. Meanders distribute energy equally and allow the stream to move water and sediment while doing a minimum amount of work. Meanders include areas of different water depth and speeds, called pools and riffles. Pools are deeper, with slow moving water, while riffles are shallower, with faster moving water. Pools and riffles provide different habitats that are important to organisms. When streams are straightened to convenience humans, they lose their pools and riffles, and ultimately their diversity of habitat. Meanders are crucial to stream health and are a necessary component in restoration projects.
The last step in restoration projects is to actually stock restored streams with fish. Many of the leaders of the stream restoration efforts in Lancaster are fishermen who want to bring trout back to Lancaster streams. Without the physical types of restoration described here, this would not be possible. Streams need to be able to provide habitat and food before they can support living organisms.
Contact us by e-mail at email@example.com