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2.4 Spill Channel Operations Two gates on the Hartland Ditch divert flows into the spill channel by backing water up and forcing excess flows to spill into the channel. Diversion to the spill channel is through a 4.5-foot opening with flashboards to create a weir spill. A second opening adjacent to the flash boards is gated and typically stays closed during normal operations. Water passes over the flashboards into an open concrete box and then into an open channel leading immediately to a 36-inch culvert. From the culvert, flows enter a 350-foot long open channel that slopes . back into the Gunnison River (Drawing 5, Appendix A). 2.5 Dam Structure The dam structure is approximately 300 feet wide and spans the entire Gunnison River. The elevation at the crest of the dam varies between 4952.4 and 4953.0. The channel bed elevations also vary along the toe of the dam and at an approximate elevation of 4948. Scour holes exist along the east bank toe at elevation 4946. The water surface over the top of the dam drops a total of 4.5 feet in low flow conditions and is less than 1 foot when flows in the river reach or exceed the 5-year event. The east bank elevation ranges from 4957 to 4962, where a small berm has been constructed to redirect overtopping flows back into the river when elevations exceed 4957. The west bank rises steeply and is at least 20 feet above the main river channel. The dam consists of railroad iron driven vertically into the riverbed and horizontally placed steel cribbing (Hie 2000). The cribbing is filled with river cobbles and boulders. The structure was repaired in 1942 (HIC 2000). HIC reports that the dam functions very well and they have no immediate or future needs for repair or reinforcing. The only feature of the dam that causes some problems is that the dam snags debris and trees that are floating in the river (HIC 2000). This is a typical maintenance requirement at any low head diversion dam where 5 I I I I I I I I I I I I I I I I I I I