Genesee River Stability Analysis/ Beards Creek Erosion Control Plan, New York

Mussetter Engineering, Inc. (MEI) performed a geomorphic, hydraulic and sediment transport study of an approximately 20-mile long reach of the Genesee River, and two major tributaries (Beards Creek and Canaseraga Creek) to evaluate the effects of subsidence caused by the collapse of an underground salt mine on the stability and flood-carrying capacity of the streams. The project reach is located in a glaciated valley approximately 25 miles south of Rochester, NY. In March 1994, portions of the mine roof and overlying valley floor collapsed, creating two 50- to 75-foot-deep sinkholes along the lower reach of Beards Creek, a tributary to the Genesee River. Between the initial collapse and late November 1995, significant subsidence occurred in an approximately 4.5 mi2 area of the Genesee River valley due to dissolution of the mine pillars. Maximum subsidence along the mainstem was about 4.5 feet, with the subsidence decreasing progressively back to the original bed elevation approximately 2 miles downstream and 2.5 miles upstream from the mouth of Beards Creek. The two sinkholes captured what was previously a very sinuous reach of Beards Creek and initiated a headcut that began rapidly migrating upstream.

The analytical phase of the study included development and application of HEC-2 hydraulic models of the project reach for pre-subsidence, existing and future subsidence conditions. The model results formed the basis for incipient motion, sediment continuity and bank energy index (BEI) analyses to evaluate the potential channel stability effects. Flood boundaries were delineated to evaluate changes in the flooded area associated with the subsidence. The study results indicated that the subsidence was unlikely to have a significant impact on the vertical stability of the river up- or downstream from the subsidence-affected area, because of the coarse-grained nature of the bed material and the presence of bedrock outcrop in the river. The area that would be flooded by the 10-year flood increased by about 30 percent, but the 100-year floodplain increased in area by less than 2 percent. The most significant impact of the subsidence was caused by an approximately 12-foot drop in baselevel of Beards Creek. An erosion-control plan consisting of low-drop grade control structures, bank protection and flood-control berms was designed and implemented to stabilize the headcut, protecting adjacent property and a bridge located a short distance upstream from the affected area.

Major Project Features

• HEC-2 Hydraulic Analyses
• Fluvial Geomorphic Analyses
• Routing of Floods Through River Channels
• Development of Water Surface Profiles
• Sediment Studies
• Bank Erosion Analysis
• Development of Erosion Control Plans
• Evaluate Flood Potential
• Evaluate Alternative Restoration Measures