Identifying the Cause of Stream Impacts — The West Fork Case Study

The West Fork of the East Branch of the Black River, outside of Lodi, Ohio, was experiencing increased sediments within the river during moderate to high flows, which was of concern to the Medina County Park District and other land owners along an 8000 If stretch of river just south of Highway 224. Local landowners commented about increased velocities, frequency of flooding, and rates of bank erosion. Field investigations, maps and aerial photos indicated a moderately sinuous "C" type channel with gravel riffles and bars and silty sands in pools. The 40 square mile drainage area consists mostly of farm fields and undeveloped wooded areas with a small commercial/industrial area on the west side of Lodi. A 1 to 2 year flow rate of 430 cfs resulted in a bankfull depth of about 4 feet, width of 50 to 60 feet and a velocity of 2–3 f/s, which was consistent with field observations of gravel bars and vegetation. The existing eroding bank heights were not consistant with this data though. They varied from 5 to 6 feet at the upstream end and 10 to 12 feet at the downstream end. Initial conclusions were that much of the floodplain vegetaion had been cleared and farming operations had deposited significant sediment onto the floodplain raising elevations as much as 4 to 5 feet. The valley side slopes also narrowed which may have contributed to the rising floodplain to stream bed difference. But some observations, such as 100+ year old trees along the stream bank and soil cross sections not showing significant deposition, indicated something else. Then we found the 1937 aerial photographs, used for creation of the Medina County Soil Survey, for the area now crossed by Highway 224 and our whole perspective regarding man's impact on this river changed along with our recommendations for mitigation.