Remediation of the Limestone Creek Landslide
Central New York,
Madison County Planning Department
Basin Program Funds:
A major, and ongoing slope failure was occurring on the East Branch of Limestone Creek in Madison County, causing severe impairments to aquatic life and stream function in the Class "C(T)" trout stream. The slope failure also could have impact homeowner dwellings and a major power line crossing of the creek adjacent to the ongoing failure.
The landslide along Limestone Creek was first identified in the summer of 2002, and was slowly-propagating and continued to fail during periods of heavy rain and runoff. Located in a relatively steep valley lined with glacial kame moraine deposits, the slide covers approximately 7 acres and has an elevation change of over 440 feet.
Initial investigations by the NYS Department of Environmental Conservation (DEC), the United States Geological Survey (USGS), Madison County, The Natural Resources Conservation Service (NRCS), and Niagara Mohawk Power Corporation (NIMO) suggest that Limestone creek is incising into the toe of the unstable slope causing subsidence from the adjacent hillside. Geologic maps suggest that the surficial unconsolidated deposits are kame moraine. A dense, gray clay is present at the creek level and is currently being incised by the stream. Bedrock in the area is part of the Hamilton Group, and in nearby areas (downstream) the bedrock is seen in the creek channel. Across the slope, fine-grained and coarser-grained sediment layers contribute to groundwater seepage/discharge zones that also contribute to scarp failures seen up-slope of the creek. Subsidence scarps adjacent to the stream channel continue to enter and, at times, entirely block the stream channel. During higher-flow events there are high levels of turbidity in Limestone Creek for several miles downstream. Without further investigation and remediation of this hillside, this problem will continue causing significant threats to aquatic life in the creek and in downstream waters.
Activities Determine the current slope failure extent, growth, and failure mechanisms as related to site geology and hydrology. Determine the stability of nearby slopes in relation to the factors defined above.
Determine the ecosystem impact under the current conditions-- water quality, fishery habitat, spawning, etc.
Design and implement a slope-failure mitigation program for the active slope to reduce mass wasting and prevent future failures on nearby slopes by installation of subsurface drainage which will outlet safely downstream of the failing slope and implementation of preventative toe erosion mitigation projects.
Although the use of all "soft" or bioengineering methods would be most opportune, the magnitude of the slope failure wouldl require some "hard" engineering practices to be implemented in order to utilize the bioengineering practices. It is anticipated that stream alterations was required and as such, the Rosgen principles of natural stream design was utilized when possible. Specific bioengineering practices included: live staking, brushmattressing, rootwads, joint planting, coconut fiber rolls, land shaping in conjunction with vegetative measures, and other techniques deemed appropriate for the site conditions. Emphasis was placed on using native plant materials in the restoration efforts. We anticipated starting date in spring 2003 and a completion date in fall 2004.
The major goals and objectives of this project included:
We were successful in moving and restoring approximately 600 linear feet of stream channel. The stream was moved away from the toe of the landslide and protected to prevent it from impacting the landslide again in the future. The new channel contained a series of 3 pools and 2 riffles with four j-hooks to direct flow to the center of the channel where appropriate. Coir logs and coir erosion control matting were used to stabilize the new channel at the normal water elevation while our planted vegetation takes time to establish. The installation of j-hooks, coir logs, and coir erosion control matting was designed with aesthetics and longevity in mind. (Expected lie time is about 3-5 years depending on rate of decomposition for the coir materials.) We used a mix of native willow, dogwood, and buttonbush species to re-vegetate the new channel. In addition, we planted all native seed mixes specifically designed for seasonally flooded and riparian habitat areas to re-vegetate the newly created channel.
Paramount to the project were efforts to improve trout spawning and macro invertebrate habitat damaged due to the landslide erosion and sediment. We spread appropriately sized gravel and cobble materials within the new channel and placed a number of large boulders to create eddies and backwater refuge for trout in the pool areas of the restored channel.
The collected suspended sediment and discharge data for the area of the stream directly below the landslide has lead to an estimate in a soil loss prevention of potentially 25,000 tons per year or more to the downstream watershed, not to mention the improvements to trout spawning and macro invertebrate habitat. Although no official provisions were made to maintain the restored channel, we do plan to use Finger Lakes-Lake Ontario Protection Alliance (FL-LOWPA) funds (which we obtain from the State annually) to undertake periodic maintenance on the stream channel if needed. We do plan on using the Natural Channel Design process for future stream restoration projects in the County, and in particular, in areas of high priority within the Oneida Lake Watershed.
Contact: Mr. Scott Ingmire, 315-366-2498