II. THE RALSTON CREEK DRAINAGE BASIN
Drainage Basin Description
This section of the warning plan will be completed in more detail at a later date. Until this is accomplished, refer to the following documents for additional hydrologic data and floodplain information:
Leyden Dam was constructed in 1902 and the existing concrete flume spillway was completed in 1938. Leyden Reservoir stores irrigation and municipal water for the Farmer's High Line Canal and Reservoir Company. The dam and reservoir are located on Leyden Creek approximately three miles northwest of downtown Arvada just west of Indiana Street (Colo. Hwy 72). The reservoir's source of water is runoff from the Leyden Creek watershed and controlled discharge from the Church Ditch.
Leyden Dam is an earthfill structure with a maximum height of approximately 43 feet, a crest length of 1500 feet and a general crest elevation of 5572 feet (NGVD or MSL). The reservoir has a maximum capacity of 1152 acre-feet with a surface area of approximately 69 acres. The outlet works consists of a concrete intake box which discharges through 260 feet of 36-inch steel pipe and empties into the concrete flume spillway which then discharges into the Farmers High Line Canal.
On May 29, 1974, the Colorado State Engineer's Office declared the dam unsafe and placed a storage restriction on the reservoir corresponding to a gage height of 35 (Elevation 5573.4). This restriction level is eight feet below the lowest spot on the dam crest. The concerns of the State Engineer are listed as follows:
Mitigative measures are being considered, but until proper remedial repairs have been made, Leyden Reservoir should be recognized as a HIGH RISK facility. A dam failure would be catastrophic for many developed properties and residents downstream.