Lake Chaweva - a case of dam and reservoir rim failure, lawsuit and innovative design rehabilitation

Lake Chaweva was constructed in 1935. The dam is an earth embankment, 30 feet high and 288 feet crest length. It has a reinforced concrete core wall, a rectangular concrete channel spillway located at the right abutment, and a reservoir drainpipe with a downstream shutoff valve. In 1995, surface holes were observed on the downstream face of the dam. The open channel spillway had a history of problems with erosion beneath the spillway slabs, concrete cracking and leaning walls. In 1997, West Virginia Dam Safety program issued an order to lower the water in the reservoir to its lowest practical level. Recommended rate for lowering the level was no more than one foot per day. During lowering of the reservoir level, the upstream slope of the dam failed. At about the same time, sections of the reservoir rim slipped, causing damage to some homes, the road, and utilities. The slide from the dam covered the inlet to the reservoir drain pipe with several feet of mud. Efforts to locate and clean the inlet proved futile. A V notch breach was cut into the dam, and a square hole cut into the concrete core wall to keep the reservoir drained. Homeowners filed a lawsuit against the Lake Chaweva Club (homeowners association), the homeowners association's engineer, and the State of West Virginia. As a result of an out-of-court settlement, limited funds became available to reconstruct the dam. Due to the limited funds, construction costs had to be kept to a minimum. The final accepted design consists of constructing a principal spillway capable of passing a 100 year design storm, and designing the dam to safely pass the PMP storm by overtopping. The principal spillway riser utilizes 6 foot diameter precast manhole sections with a 10 foot diameter section on the top. A concrete fillet in the 10 foot diameter section forms a funnel shape to improve the hydraulic efficiency. The 10 foot diameter also increases the flow due to a longer weir length. The outlet pipe for the riser is 4 foot diameter, corrugated, HDPE with a smooth inner liner. The pipe has bell and spigot locking joints with a polyisoprene gasket. The pipe is rated for 10.8 psi. Overtopping design incorporates use of layers of large rock placed on a flattened downstream face. The slope and rock sizing is in accordance with studies and experiments performed by Henry Olivier as presented to the Institute of Civil Engineers in 1967 in a paper titled "Through and Overflow Rockfill Dams - New Design Techniques. 9 pp.