The US Bureau of Reclamation (USBR) has awarded Delhur Industries of Port Angeles, Washington, a contract for the second phase of renovations at Horsetooth Reservoir.
Phase Two work involves the rehabilitation of the reservoir’s three east-facing dams. Delhur’s bid of US$22 million was the lowest of the six bids received, which ranged as high as US$31.19 million. The company is also the contractor for Phase One of the proposed renovations at Horsetooth dam.
For some time water had been seeping through the Lykins limestone formation underneath the Horsetooth dam. Sonar tests done in 1999 indicated places in the reservoir bed that had collapsed or developed internal erosion, leading to the formation of sinkholes and erosion gullies. The 9km-long Horsetooth reservoir is located west of Fort Collins in Colorado, between two hogback ridges, where the Horsetooth dam closes the gap at one end. Soldier, Dixon, and Spring Canyon dams and Satanka dike close the remaining gaps. These dams have heights of 46.5m, 68m, 72m, and 66m respectively and contain more than 7.5m3 million of earthfill. Horsetooth furnishes the main supply for the Poudre Valley, where 50% of the project water is used. The reservoir is operated by the Northern Colorado Water Conservancy District.
Reclamation design engineers and construction specialists on the Horsetooth project determined that the safest and most efficient way to complete all the repairs to the dams was to do it in three stages. The first stage involves the construction of a filter and drain and a stabilising earth berm at Horsetooth dam to deal with underseepage and improve stability. Delhur began work on this phase in March 2001.
The second stage will involve the construction of 5m-thick filters and drains at each of the three east-facing dams and adding buttressing berms. It is scheduled to begin in the late summer of 2001 and take approximately two years. The third and final stage will see the construction of a cut-off wall at Horsetooth dam to prevent foundation seepage. Planned construction of the third stage is from summer 2002 until the end of 2003.