Sedimentation and Runoff
in the Finger Lakes

The photographs at the right were taken by Bill Hecht during a fly- over of Cayuga and Skaneateles lakes watersheds on April 5, 2005. Climate patterns bringing winter thaw in March and heavy April showers dowsed the Finger Lakes region with large amounts of water causing lake levels to rise and plumes of sedimentation to form off tributary streams. A lot of what we see as sedimentation is from hydrologically overloaded streams.

After winter thaw, the soils are damp, only a few centimeters below the surface. As rain events occur, the water table – the point at which all the pores between soil particles are filled with water – rises. When the soil is saturated it takes very little rainfall to start a runoff event. In a runoff event, gravity and water work together to detach, remove and deposit materials, such as soil, cobbles, and even large boulders, as they are added to the sediment load traveling downslope.

Sediment carries with it a host of additional pollutants, such as nutrients, herbicides and antibiotics, when it enters lakes in large quantities. The soil itself smothers the lake bottom, making it unsuitable for fish to spawn or other aquatic life to maintain itself. Phosphorus sticks to soil particles and is carried along into the lake where it fertilizes aquatic plants and algae. Algae blooms are more frequent during summer months of high runoff. Pathogens from manure, pet feces or failing septic systems may enter the lake with sediment plumes.

Factors affecting erosion include climate, soil type, topography, and land use. During a runoff event there are a number of non-point sources of sediment, such as construction sites, onsite wastewater systems, agricultural land, pastures, and cropland, lawns and gardens, disturbed forest land, surface mine reclamation, parks, and waste disposal landfills. After heavy rains, as experienced in April 2005, large amounts of sediment washed into the Finger Lakes causing increased turbidity in lake water. In addition to effecting lake water quality, stream bank erosion, failed drainage ditches, sheet and rill erosion, and overland flow surface runoff may cause extensive damage to occur throughout the upper reaches of the watershed.

Links

National Sedimentation Laboratory

Natural Resource Conservation Service: Soil Quality website

Environmental Protection Agency: Erosion, sediment and Runoff control for Roads and Highways