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L4~n h1athews - 3 - 14arch 11, 1983 Alluvial Valley Floors The applicant has made a negative alluvial valley floor determination based upon an alluvial valley floor reconnaissance investigation. A copy of the reconnaissance investigation was provided to the Division in September 1980, and a portion of the investigation (the t~vo page text) is included in the application. The investigation identifies potential alluvial valley floors along Sage Creek and Fish Creek. These areas, however, are not hydrologically adjacent to the proposed operations and do not need to be considered at this time. Upper Grassy Creek would not be identified as an alluvial valley floor because the valley is narrow, steep, and would not be useful for either flood irrigated or subirrigated agricultural activities. A lower area along Grassy Creek adjacent to the county road, includes approximately 20 acres of alluvium. This area has not been flood irrigated, and only about two acres of it are subirrigated. The applicant indicates that no known irrigation is practice in similar valleys within a two- mile radius, that irrigation would create erosion problems, and that irrigation would be economically unsound. Based upon this information the applicant concludes that the area along Grassy Creek is not an alluvial valley floor. The Division does not necessarily disagree with this conclusion. However, in order for the Division to make its own negative alluvial valley floor determination, some additional information should be incorporated into the permit application. 1. The AVF reconnaisance man showing areas of flood irrigation and areas of unconsolidated streamlaid deposits must be include in the permit application. 2. The assessment of the capability for flood irrigation is based upon regional flood irrigation practices. Therefore, the applicant must expand his discussion of flood irrigation beyond the two-mile radius to include an assessment of the capability for flood irrigation based upon regional practices. Ttiis assessment should describe the flood practices in the region in valleys the same size or smaller than Srassy Creek. If flood irrigation is not practiced in such valleys or if the area of concern is physically different from those valleys in some way that makes the area unsuitable for irrigation then the area ~vould be found to be not capable for flood irrigation. (Capability should be assessed on the basis of physical water supply, water quality, soil suitability, size of the area capable for flood irrigation as practiced regionally, or some other physical consideration. The capability for flood irrigation is not based upon direct economic considerations.) If you or the applicant have any questions concerning this review let me know. cc: Jim Pendleton Brian 1.lunson