Outlet Works – How They Work
Water is released from a dam in either a controlled release through the outlet works or through the spillway when the water level reaches the spillway overflow elevation. The outlet works are used to make controlled releases of reservoir water impounded behind the dam. The outlet works consists of an intake structure that has valves openings at various heights that allows reservoir water to flow into the structure at a selected flow rate. Water then flows down the intake tower down to an outlet conduit and through the bottom of the dam back into a river and/or pipeline.
Nichols & McClure Dam & Reservoir Facts
Nichols and McClure dams are located on the Santa Fe River and are fed by runoff from a 17,260 acre (22 square mile) watershed area. McClure dam has a reservoir capacity of 3,257 acre feet (1,061 million gallons) when full. Nichols dam has a reservoir capacity of 684 acre feet (223 million gallons) when full. McClure dam is located about 2.7 miles upstream of Nichols dam. McClure reservoir water is released into the Santa Fe River and flows downstream into Nichols dam.
Water from Nichols reservoir is released through the outlet works in a similar manner. Releases from the Nichols outlet then flow into a 24 inch diameter pipeline that delivers untreated reservoir water to the CRWTP for treatment. Controlled releases from the Nichols outlet are also made to the Santa Fe River.
Nichols & McClure Dams – Existing Outlet Works
McClure Dam was originally constructed in the 1920’s and raised in the 1940’s. The existing concrete intake tower is approximately 100 feet in height. The tower is located several hundred feet from the dam crest and must be access by boat or by foot when the reservoir lake is frozen. The tower is 8 feet in diameter on the outside with an inside diameter of 4 feet. Access to the tower and work inside the tower is difficult.
Nichols Dam was originally constructed in the 1940’s. The existing concrete intake tower is approximately 80 feet in height and the tower is also located a couple of hundred feet from the dam crest. The tower is 10 feet in diameter on the outside with a 6 foot inside diameter. Access to the tower and work inside the tower is difficult.
A preliminary engineering report (PER) was prepared to identify, evaluate, and recommend Reservoir Infrastructure Improvements. The PER recommended that catwalks from the dam crest to the intake tower be constructed to improve personnel safety; and the intake valves be repaired or replaced to improve operations and dam safety; and that maintenance of the concrete outlet conduit be performed and the Acequia Llano feed piping be replaced. However, a detailed structural analysis at the beginning of the engineering design work found that the existing intake towers did not meet current seismic stability requirements.
Inclined Intake Structure Design
An inclined intake structure was designed to replace the existing vertical intake tower. This inclined intake will run along the upstream face of the dam from the dam crest to the outlet conduit. The inclined intake tower will be constructed of reinforced concrete. The tower will be have a square cross section that is 8 feet wide and 8 feet high on the inside with 2 foot thick wall, floor, and roof sections. Access doors will be located on the dam crest and personnel will be able to walk down stairs. The inclined intake will have sufficient space for maintenance of piping, valves, and meters which will be located inside the structure. Reservoir water will be carried in the piping inside the concrete intake tunnel so the tunnel will be dry. The release of water through the reservoirs will be precisely controlled by automatically controlled valves with a metered flow.