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c.., ~... .....-- 5 .-1 ,-.-., ,- Agricultural Research Service (ARS) studies will resL~t in determina- tions of seepage losses from canal reaches, and determine deep perco- lation losses from on-farm water application. They are examining the mechanisms by which the salt load of return flow water is modified after it leaves the farm unit and moves toward the Colorado River. Also being studied by ARS are the mechanism of ground water flow to the river and usefulness of the ratio of calCium/magnesium as a tra~er to apportion mixed waters as to their source, and will be used to '2valuate the sources of surface drain effluent. The effectiveness of small, frequent irriga- tions to reduce the necessary leaching fraction (and .~herefore, reduce ground water flow) and to encourage harmless precipitation of salts is being studied by ARS near Fruita, Colorado. A study is being conducted by Colorado State University for Environ- mental Protection Agency to evaluate the effect of different water management practices on crop yields along with the chemical quality of the deep perCOlation losses after having moved through the soil profile. Besides the CSU-EPA studies defining the surface and subsurface hydro- logy in this study area, investigations have been completed regarding the value of channel lining, irrigation scheduling, and drainage in reducing the salinity in the Colorado River. Present CSU-EPA studies are evaluating benefits to the farmer and from reducing salt loading to the Colorado River by on-farm works of improvement installation. The planned and installed improvements include combining and lining laterals in the distribution and on-farm ditch system, water co~trol structures, and drainage. The effect of water management on fertilizer efficiency and crop yield is being demonstrated. Colorado Water Conservation Board activities include demonstrations of the use of time-operated automatic gates on border and furrow irrigated fields, and the effectiveness of a pump back system and deep percolation loss determinations. Also being demonstrated are two drip irrigation systems for orchards, and seepage losses from a canal ~re being monitored. In 1968 the Colorado Water Conservation Board organized the Grand Valley Purification Project, a group of irrigation companies that obtained an EPA grant to line canals and laterals in the Clifton area. CSU was contracted to do the study. These studies defined both the surface and subsurface hydrology, including the water contributions from channel seepage, channel spills, field tailwater runoff, deep percolation losses, drain outflows, and ground water flows. CWCB also conducted investigations in the Grand Valley to find a sui t- able area where the hydrology could be isolated. It is proposed that the Reed Wash-Peck and Beede Wash be utilized as a stu~r area with the east branch of Reed Wash used as a control area. The two areas are adjoining and bounded by topographic ridges. In the summer of 1973 the CWCB and the Colorado River Di.strict con- tracted with the U.S. Geological Survey to install six >rater quality monitoring stations to measure the inflow and outflow of the salts to the Salt Creek Basin.