Feasibility Study, Enlargement of Julesburg Reservoir

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Dam 4 dike forms the eastern embankment of the reservoir. The dam is approximately 4,000 feet in length with a crest width of approximately 20 feet, and varies in height between 10 to 16 feet. The upstream and downstream slope of the embankment are somewhat irregular. The upstream slope is approximately 3:1. The downstream slope varies between 2.5 to 3:1. Extensive seepage has been observed below the downstream toe of the embankment for a number of years. A weir was constructed at the main` <seepager drainage channels to monitor the seepage flow. We understand that excessive seepage occurs when the storage in the reservoir exceeds Gage 16. To alleviate concerns about the potential piping of foundation materials and to prevent rise of phreatic surface within the embankment, a toe drain was constructed to a minimum depth of 4 feet into the bedrock in 1991. Water seepage has not been observed at the ground surface below the downstream slope of the dam since the toe drain was installed. The northern portion of Darn 4 forms the Main Dam 4 and includes the gate controlled outlet structure. As originally constructed, the main dam was somewhat of an irregular shape with the crest varying between 25 to 3046et.and upstream slope of the embankment approximately 3:1 and downstream slope between 1.5 to 2:1. The original outlet works consisted of 3 concrete conduits, 48 inches wide and 52 inches tall. The steel gates controlling the water discharge leaked excessively. Studies performed by Wheeler & Kumar indicated excessive seepage through the steel gates and deterioration of the concrete conduits due to chemical attack over a period of years. There was also concern about the seepage occurring at interface of the bottom of the head wall and top of outlet conduits, and around the wing walls. DUe to? =the 'concerns of the long -term integrity of the outlet works, it was recommended that the outlet be replaced. 2 \reports \97 -1 -500. nk