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27 ~~ ~ ~ N Sprinkler - 0.4 ac ft/ac x 4.2 tons/ac ft = 1.68 tons/acre Surface 0.2 ac ft/ac x 4.2 tons/ac ft = .84 tons/acre The salt load reduction from installing improved systems and better management for the McElmo Creek unit is: Sprinkler Surface Salt load - 19,700 ac 1,850 ac Reduction - x 1.68 tons/acre = x 0.84 tons/acre = Improved .ystems = 33,100 1.500 34,600 tons/year tons/vear tons/year SEEPAGE REDUCTION: Onfarm earthen ditch seepage loss calculations are necessary to compute a salt load reduction due to lining or piping (Refer to the FIRI manual distributed by Engr, WNTC, 1991, for procedure). Assume silt and clay loam soils with a seepage rate of 0.6 cfd ; flow of 1 to 5 cfs; time flow in the ditch for 3 to 5 irrigations is 45 days; and the wetted perimeter of the ditch is 4 square feet per linear foot. Seepage from earthen onfarm ditches = 0.6 cfd x 1 AF/43,560 cf x 4 sq ft/lin ft x 45 days x 5280 ft Seepage = 13.1 acre feet/mile/year. Assume that 20 \ of the potential seepage is consumed by wetland vegetation and doesn't return to the river. Use by 4,000 acres of wetland habitat mapped during planning would reduce return flow about 6,000 ac ft or 20 percent. About 80\ of the seepage would return to McElmo Creek. 13.1 x 0.8 = 10.5 ac ft/mi/yr. Seepage reduction due to lining or p~p~ng earthen ditches: 10.5 ac ft/mile/year or 0.2 ae ft/100 feet Salt load reduction due to lining or piping earthen onfarm ditches and small laterals: Assume 4.2 tons salt lac ft 10.5 ac ft/mi/yr x 4.2 tns/ac ft = 44 tons salt per mile/year Salt load reduction - lining/pipe 0.83 tons salt/100 ft/year 268 miles of lining or pipe x 44 tons/mile = 11,800 tons/year The impact of substituting pipeline for an additional 335 miles of field earth ditches when installing sprinklers is included with unit reduction per acre in deep percolation due to installation of sprinkler systems.