SU0013451 - Laserfiche WebLink

Home Browse Search

4.6 WATER RESOURCES projects. Since the proposed project intends to obtain water under a riparian right, it is appropriate and necessary for this EIR to evaluate the potential environmental impacts associated with such water use, and to identify suitable mitigation measures for significant impacts. i For the proposed project, the applicant may divert water from the Mokelumne River for direct irrigation (e.g., of the golf course or pasture) under a claim of riparian right. This diversion would occur during the irrigation season only, when streamflows in the river are likely to be low. The preceding water balance has shown the greatest need for such diversions to be toward the end of the dry summer season, coinciding with the time when new diversions would have the greatest effect on in-stream flow conditions and other uses of the Mokelumne River (Tables 4.6-2 and 4.6-3). The applicant could not meet this dry season irrigation requirement by wintertime diversions from the Mokelumne River under a claim of riparian right, since such diversions would require lengthy storage (i.e., several months) beyond that permitted for a riparian right. Therefore,while the right to divert water for irrigation purposes clearly exists under the riparian doctrine,were this right to be exercised for the project it could, from year-to- year,significantly affect dry season streamflow conditions and other established uses of the lower reaches of the Mokelumne River. It should be noted that the riparian rights are not lost due to non-use. Appropriative Rights To divert water for storage and later use, or to take water from a stream for use on non-riparian land, an appropriation of water must be obtained from the State Water Resources Control Board, Division of Water Rights. For the proposed Buckeye Ranch project, an appropriative right would be required for: (a) the diversion and storage (in the Tracy Lakes) of streamflow from the Mokelumne River (for lake maintenance and later irrigation);and(b)capture and storage of runoff from the Jahant Slough watershed to a greater extent than occurs naturally. For the first situation, no new appropriations are possible during the period of June 15 to September 30; but no formal determinations have been made by the Division of Water Rights as to the amount of water that might be available for appropriation from the Mokelumne River during the winter-spring runoff season. Certainly under high streamflow conditions (especially at or near flood stage) water could probably be diverted to the lakes from the Mokelumne River. Unfortunately,high runoff flows are not a reliable source, since they are a function of annual rainfall-runoff conditions, plus the effects of controlled releases (and storage) at Camanche Dam. A review of streamflow records shows that Mokelumne River streamflows (at Woodbridge)have not reached 500 cfs since the winter of 1986-87 and, for the most part, the flows have been less than 100 cfs. It is not a certainty, but it is likely that no appropriative diversions from the Mokelumne River for the project would have been possible during the past four years, given the below average rainfall-runoff conditions in the region. Consequently, winter diversions could not have significantly altered the project water supply to eliminate the need for dry season make-up water from groundwater or riparian diversions, as indicated by the water balance analysis (Tables 4.6-2 and 4.6-3). Also, when streamflow conditions in the Mokelumne River are high 4.6-13