We Got How Much Rain? Emergency Repairs at East Reservoir Dam Portage Lakes State Park

摘要

East Reservoir Dam is a high-hazard, earthfill embankment located just south of Akron, Ohio that was constructed in the 1820's and 1830's as part of the feeder system for the Ohio and Erie Canal system. The dam is approximately 1,300 feet long, has a maximum height of 25 feet, and lake levels are controlled by two spillways, one uncontrolled 21-foot long weir and one with two 30-inch gates. Portage Lakes Drive runs along the top of the embankment and the crest width is 40 to 50 feet. The embankment was constructed using the natural fine sands at the site and the foundation soils consist of fine sands and silts. In July 2011, several isolated but severe storms crossed the Akron area. The worst of these storms dumped as much as six inches of rain across the region over a 3.5-hour period. Additionally, ODNR had recently solicited a private contractor to perform extensive clearing and grubbing on the downstream embankment face. Due to heavy rainfalls and recent construction disturbance, inspections revealed extensive seepage exiting the downstream slope near the left abutment. Some of the exit points were as high as halfway up the slope. The seepage was clear but, because of the quantity of seepage, ODNR pursued an emergency repair of this embankment section. Tetra Tech mobilized to the site the next day with ODNR representatives. It was decided that a seepage berm was the most cost-effective solution that could be implemented quickly. Tetra Tech designed the seepage berm dimensions using available subsurface information and laboratory testing. Seepage analyses indicated that the relatively high-permeability of the sand embankment resulted in significant flows through the embankment. The berm was designed to mitigate the threat of piping from through-seepage and to reduce the potential for piping from underseepage. ODNR used the local contractor to construct the berm, which took approximately three weeks. No further problems have been noted since the berm was constructed.