SHORELINE FAILURE PROCESSES, BERLIN LAKE, NORTHEASTERN OHIO

Berlin Dam was constructed on the Mahoning River in northeastern Ohio by the Pittsburgh District, Corps of Engineers, in the early 1940’s. The dam impounds Berlin Lake, a multipurpose reservoir with a surface area of 4 sq. mi. (10.36 sq. km) and 64 mi. (103 km) of shoreline. As a result of war-time expediency, land acquisition for the project included only the minimum considered necessary for flood control operations. Since WW II, private developments have extended virtually to the water’s edge around much of the lake.

Slope failures, erosion, and bank retreat have occurred at many locations since the lake was impounded in 1943. These processes extended beyond Government property onto private property at some locations. In 1985, I was retained by the Pittsburgh District to investigate causes and probable progression of bank failure and erosion at 17 sites around the lake.

Soil conditions around Berlin Lake are extremely complex because ice lobes advanced and retreated along the Mahoning River during the Wisconsin Glacial Stage. My field investigations classified bank soils into three categories: Gray Clay (laminated glacial lake deposit, overlies deeper bedrock, prone to landsliding and erosion); Till (overlies bedrock or Gray Clay, varies widely in thickness, composition, and consistency, prone to weathering and shallow slab sliding as well as deep seated landsliding where underlain by Gray Clay); and Silt (several feet thick to top of bank, overlies Gray Clay or Till at all study sites, shallow water pond or lake deposit, highly prone to frost heave, surface and subsurface erosion, and earthflows).

Two main classes of bank failure processes were observed. Surface Processes included weathering, surface and subsurface erosion, and shallow earthflows in top of bank Silt along with weathering and shallow sliding of cohesive upper bank Till. Deep Seated Failures involved retrogressive slumping in Gray Clay and overlying Till, where Till was present, with or without Surface Processes. Observations on 1935 aerial photographs indicated that deep seated slump masses pre-dated impoundment of Berlin Lake. Initial slumping probably occurred at the end of the Pleistocene Epoch when ice remnants adjacent to the valley walls melted and the Mahoning River began actively eroding glacial soil deposits along its banks.