Gunnison - Paonia Feldman Diversion Reconstruction Project (Part 2 - Construction)_Application

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Water Supply Reserve Account – Grant Application Form Form Revised O ctober 2006 _______________________________________ In 2004, an unusually large volume of water entered the Feldman Ditch and washed it out, causing several thousand dolla rs in damage to the ditch and adding a huge volume of silt and debris to the river. Sediment and gravel losses from eroding bulldozed gravel dams are extremely high. This translates into higher sediment loads in the river and loss of adequate elevation req uired to meet the existing elevation of the ditch. The result is a vertical loss of riverbed and aquatic habitat upstream as the down - cutting process migrates. The two diversions are situated immediately upstream from a previous in - stream gravel mine. As a result of gravel mining, extensive downcutting and headcutting has occurred immediately below the current diversion points. This erosion of the river bed resulted in the need to move the diversion point of the Paonia Ditch upstream in past years. As res ult of these moves, the two diversions are nearly opposite one another on different sides of the river. The magnitude of the downcutting is evidenced by the fact that between 1992 and 1997 the river downcut 5 feet at the highway bridge located less than o ne - mile downstream of these diversions. Since mining in the river ceased in 1998 the downcutting has stopped. Headcutting upstream from the gravel pit has also been measured. At the point of diversion for the Paonia Ditch, approximately 3,000 feet upst ream from the bridge, 30 inches of bank erosion and 24 inches of channel degradation was recorded in one year in 1997. The rock diversion structure for the Paonia Ditch may be slowing the advancement of further headcutting upstream but does exhibit signs of damage from the river headcutting below. In 1997, the N orth F ork R iver I mprovement A ssociation negotiated with the gravel company to quit mining in the channel and work only in the floodplain. The work in the floodplain has since been completed; it wa s reclaimed in March of 2004 and is now inactive. The gravel company has generously donated 19 acres in and along both sides of the river for a community river park. Further degradation of the riparian corridor, including the stream channel appears to be slowing since the cessation of in - stream mining. However, it is very possible that the existing diversion, which is acting as a grade control, could fail in a large runoff event. If this were to happen, the headcut could progress further upstream. With out rehabilitation, the river will likely remain braided with a very high width - to - depth ratio. Annual repairs to the diversion and the associated disturbance to the channel bed are expected to continue in the future if this project is not implemented . T he uncontrolled and inefficient diversion of water at this site results in over - diverting flows which often leaves the downstream reach in a dewatered condition and downstream users without water. This is particularly common in later summer and early fall and during drought conditions. This dewatering of the river leaves fish trapped in pools, usually leading to mortality as result of low oxygen levels and lethal water temperatures. The push - up dam also prevents fish migration 6