2008-02-22_APPLICATION CORRESPONDENCE - C2008086 (42)

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Jurisdictional Wetlands Jurisdictional waters and wetlands in the project area consist of the perennial stream Mack Wash and its associated riparian fringe wetlands. Mack Wash flows year around and is considered a relatively permanent water of the US. The surveyed portion of Mack Wash extended 800 lineal feet up stream starting from just south of the Hwy 6&50 bridge. The area of jurisdictional non- wetland WOUS was 0.6 acres, adjacent riparian fringe wetlands totaled 0.11 acres. Non-Jurisdictional Wetlands Wetlands evaluated in this jurisdictional determination are associated with irrigation ditches, seepage, and irrigation return flows. Wetland characteristics and vegetation are a direct result of irrigation water. Without this source of hydrology these wetlands would cease to exist. Non- jurisdictional wetlands in the project area are associated with water allocated from the Colorado River, TNW, as irrigation water in a series of canals, and lateral ditches constructed by the Bureau of Reclamation in the late 19th century (BOR 1985). Wetlands established and maintained solely by artificial irrigation does not meet the definition of Waters of the U.S. under the criteria contained in the 1987 Corps of Engineers Wetlands Jurisdictional Manual or its regional supplements. Artificially irrigated wetlands that would revert to uplands if irrigation would cease are not generally considered to be jurisdictional waters of the United States under section 404 of the Clean Water Act (Sacramento RBM 2007-O1). The 18 polygons showing wetland characteristics that are likely to be non jurisdictional based on their source of hydrology are A, B, C, D, E, F, G, H, K,L, M, N, O, P, Q, R, S, T, and V (Figures 2 through 6). A description of the progression of water flow through a series of ditches to the project area follows. Flow into the Grand Valley Canal is diverted from the Colorado River east of Grand Junction in Palisade, Colorado. The canal flows west through the City of Grand Junction distributing irrigation water to lateral ditches. Between 12 and 13 Roads the canal turns south, crosses underneath Highway 6&50, and returns flow to the Colorado River near 13 Road. On the south side of the Highway 6&50 crossing, the Grand Valley Canal distributes water into the Mack Lateral. The Mack Lateral conveys water from the canal, via underground pipe, approximately 1.5 miles east to the town of Mack and its associated agricultural lands. The section of the Mack lateral that is piped ends at the Interstate-70 exit to the Town of Mack and is an open ditch from there on. The lateral meanders around the southern portion of Mack until just west of 10 Road where it turns north. The lateral splits into two main irrigation ditches. One ditch feeds two small agricultural ponds, crosses under the railroad tracks and turns west eventually flowing into to Mack Wash 1.5 miles downstream of the Highway 6&50 bridge. The other ditch continues north, crosses under the railroad tracks and divides into two smaller ditches. One of the smaller ditches flows north under Highway 6&50 and into Mack Wash. The other ditch is diverted to the west paralleling Highway 6&50 and ends up flowing through an underground conduit into Mack Wash, just south of the Highway 6&50 bridge (Photo 12 and Figure 5). From the Highway 6&50 bridge, Mack Wash flows southwest to Salt Creek and then into the Colorado River. WestWater Engineering Page 7 of 75 January 2008 DBMS 428