1986-06-13_GENERAL DOCUMENTS - C1981018

Home Browse Search

-23- Based on the extensiveness of unconsolidated alluvium along Red Wash and the probable existence of water with the stream alluvium, the area qualifies for further consideration as a potential alluvial valley floor. Water Availability Criteria - Artificial Flood Irrigation The permittee estimated the potential average annual water yield from the Red Wash drainage basin using Grunsky's Formula (Grunsky 1908, Sellars, 1965; see bibliography in permit application). The estimate indicates that an average of 2,090 acre feet of water could be made available annually in Red Wash. This corresponds to approximately 0.32 inches of runoff, which is about 3.5 percent of the annual precipitation falling on the area. Actual measurements of flow on Red Wash have been made using a crest stage gage station located at the mouth of the basin. With the crest stage gage approach towards stream monitoring, only peak flows which occur between monitoring intervals are recorded. Flows which occur at less than the peak flow during any one monitoring interval will not be recorded. The crest gage method is therefore useful for recording peak events only; the method has limited application for determining duration of flow and hence flow volumes which occur during the monitoring interval . The results of the crest gage monitoring efforts on Red Wash indicate that flow is almost entirely in response to snowmelt and storm rainfall events. A total of six runoff events'lwere recorded during the two year inventory period conducted by the permittee'. Events which occurred during the fall and summer months resulted from thunderstorm activity; however, peak flows during the year were greatest during the spring as a result of snowmelts. The largest event recorded for Red Wash during the inventory period was 240 cfs, which was generated as a result of late winter snowmelt. Because of the nature and intent of crest gage type flow monitoring, it has limited usefulness for identifying water availability criteria necessary for alluvial valley floor interpretation. Therefore, the most useful information supplied by the permittee for AVF purposes is the estimation of average annual streamflow calculated through Grunskys formula. The amount of water available annually, as estimate"hreugh his method, indicates that Red Wash further qualifies as a potential alluvial valley floor. Subirrigation At the time of issuance of, the initial permanent regulatory program permit, the presence of subirrigation along Red Wash had been investigated by the permittee solely on the basis of vegetation identified along the drainage. Vegetative species indicative of subirrigated conditions were mapped by the permittee and are shown on Map of 129 of Volume 11 of the application. The results indicate that a big sage brush - greasewood community exists along the majority of the streamlaid deposits identified on Map 102. The permittee indicated that water in the alluvium is available to the plant species i identified in the big range brush - greasewood community, as most of the species are deep rooted and xerophytic. Since no evidence was provided by the permittee during the original permit review to support the contention that subirrigation was not occurring, it was concluded that subirrigation is a distinct possibility alonglithe entire length of unconsolidated streamlaid deposits identified on Map,i129.