County restores degraded streambank
A stream stability demonstration project in Greene County, N.Y., was completed last November, correcting 1,100 feet of degraded stream banks in Broadstreet Hollow. The project was part of a broader plan led by the Ulster County (N.Y.) Soil and Water Conservation District (UCSWCD) to develop a stream management program.
In 1996, the Catskill Region (where Broadstreet Hollow is located) experienced extensive flooding that caused degradation of the stream’s clay banks. A flood in 1999 caused the high bank of the stream to slide into the channel, exacerbating the bank erosion and murky water condition of the stream. With 30 to 40 feet of clay piled on top of four to five feet of sand, the pressure created an artesian mud boil, which forced sand and clay to the surface of the stream and clouded the water.
In June 2000, the Greene County Soil and Water Conservation District (GCSWCD) partnered with UCSWCD, the New York City Department of Environmental Protection (NYCDEP), the U.S. Army Corps of Engineers (ACOE) and the Catskill Mountain chapter of Arlington, Va.-based Trout Unlimited to analyze the entire Broadstreet Hollow. The agencies helped GCSWCD address changes in the channel path that were caused by construction, investigate the artesian mud boil and examine ways to prevent further erosion.
Prior to designing a new stream path, GCSWCD conducted a flood analysis of the existing conditions. Using data from an assessment by the NYCDEP and historical aerial photos, GCSWCD identified stable areas and mapped a new path for the stream.
In September, the district began the stream restoration. During the project, water was diverted from the area in two stages with a 10-foot electric pump and several hundred feet of aluminum piping moving the upstream flow around the work area.
About one-third of the stream was moved one-and-a-half stream widths away from its previous location. The district excavated and relocated more than 2,700 cubic yards of pure clay material from the streambed and stream banks. A coarse cobble/gravel material was placed in the bottom of the new streambed, and a finer material was placed on the banks and flood prone areas.
The district constructed a 90-foot steel, sheet pile wall along part of the stream to protect a nearby private residence from future floods. Additionally, a drilling rig was set up to complete three wells that relieved the artesian condition. Willow trees and other plant materials were introduced to the area to help stabilize the banks.
The majority of the restoration project was completed in six weeks, for a total cost of $355,000. The project was funded by the NYCDEP Stream Management Program and the Army Corp of Engineers Water Resource Development Act.
