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, necessarv, it was bel ieved that such a system could be postponed for several decades. However, the rapId rate at which land was put into production in the early years of the District, the magnitude of the need to leach the salty soils, the water appl ication requIrements made necessary by the high temperatures and 1 ight soils, and the nature of the underlying aquifer itself made the return flow system essential in less than ten years after Colorado River water was first appl ied. DESCRIPTION OF WMIDD's RETURN FLOW SYSTEM Other than a very small amount of seepage (from farmland immediately adjacent) into the normally dry Gila River channel, the District's return flow is made up entirely of pumped water. Tile drainage of District lands has been attempted, but has met with little success. It is no coincidence that the drainage wells resemble irrigation wells. Abandoned wells (dating from pre-Reclamation times) were pressed into service in the initial effort to control the rapidly rising water table. The successful use of these wells made it apparent that the aquifer underlYIng the District was very open, uniform, continuous, and of limited depth. Those same characteristics explained the rapid and widespread effects of the initIal appl ications of development ~ater. Once ~il1ed, this well-defined underground reservoir responded quickly to addItional irrigation appl ications, or removal of groundwater by pumping. The aquifer serves to collect percolated irrigation water and allows it to be pumped out, keeping the level of the groundwater, ~ith its increased sal inlty, for the most part below the root =one of the crops. This responsive aquifer is one of the more unique features of the District, and is ideal for this effort. Wellton-Mohawk is one of the few irrigation projects in the world that can effectively and economically drain itself by pumping. Except during Gila River flooding, the District has total control over the local groundwater table, using a network of approximately 90 wells, at a nominal spacing of about one mile. The wells, of an average depth of about 100 feet, are equipped with 40 to 75 HP motors. Drainage well operation is guided by computer printed graphs of groundwater elevations produced monthly by the District, using readings taken from 480 widely spaced observation wells. Additionally, the observation well data is used in the monthly preparation of a groundwater contour map as a permanent record. DISPOSAL OF RETURN FLOWS All drainage collector channels are now concrete 1 ined; once pumped, return flows are prevented from re-entering the aquifer. After initially discharging the pumped return flows directly into the GIla River, a concrete lined main conveyance channel was constructed, ending just downstream from the Gila