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• valley floors in the proposed permit and adjacent areas. However, the type of agricultural activities in the above areas is documented in Map 2, Fish Creek Tipple Land Use. Potential Material Damage The determination of the risk of causing material damage to an alluvial valley floor is dependent on four criteria. These criteria are: 1) potential increases in the concentration of total dissolved solids (TDS) of waters supplied to an alluvial valley floor to levels above the threshold value at which crop yields decrease; 2) potential increases in the average depth to water that would reduce the amount of sub-irrigated land; 3) potential decrease in surface flows that would reduce the amount of flood-irrigated land and 4) potential changes in the surface or ground water systems that reduce the area available to agriculture as a result of flooding or increased saturation of the root zone. • The Middle Creek floodplain is flood irrigated and the applicable criteria for determining material damage are: potential TDS concentration as compared with crop salt tolerance; potential surface water availability measured against irrigation requirements; and potential flooding as it impacts agricultural land use. From Table 29, Surface Water Quality Data, the average and maximum TDS concentrations for affected water at sample site 29, in 1983 are 888.2 mg/1 and 2,450 mg/1, respectively. The TDS concentrations of affected water are well within the recommended salt tolerance level (5,000 mg/1) for stock water in the Middle Creek floodplain. Although Sedimentation Pond E will detain runoff from the proposed permit area, there will not be a corresponding reduction in water supply for irrigation, because the ponds will fill during early spring before the annual irrigation season begins, and because the headgates for the irrigation ditches are located either upstream from the . proposed permit area or in other unaffected watersheds. Furthermore, 2.06-29