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, ,..~,., ~) U I ::..' assumed that the canals would be constructed and maintained so that they would leak except along reaches that were very close to the river, In these areas, it was assumed that the canal would be earth-lined to keep losses to a minimum. Table 3 indicates the recharge and conveyance facility requirements for the four test areas. To ascertain whether or not the development of ground-water mounds beneath the recharge ponds would be a problem, equations developed by Hantus~ (1967) were used to estimate the position of the mound at the end of the 30-day recharging period. These calculations showed that each individual spreading site may be sized to minimize the mounding problem. Obviously, the lithology of the unsaturated zone will have a controlling effect on the formation of ground-water mounds, and would require detailed onsite geologic investigations. Alternative Recharge Plans for the Total Study Area Three schemes to convey water to the recharge areas have been considered. Each scheme requires a series of shallow infiltration ponds. All infiltration ponds are considered as new facilities. Originally, the existing conveyance facilities were assumed to be diverting at capacity during the irrigation season. This led to the development of the first alternative which consists of an entirely new system of diversion structures, canals, and recharge ponds. This scheme minimizes drain- out losses and river diversion requirements by recharging as far away from the river as possible. After review of diversion data, it became evident that the existing conveyance facilities were not diverting to capacity during the entire irrigation season. Therefore, the possibility of using the existing conveyance system to get the water to the recharge areas was considered. Further study indicated that excess canal capacity in some of the existing canals did not exist when the water supply was available. This led to the formulation of a third alternative consist- ing of a combination of new and existing conveyance facilities. The combination system uses existing conveyance facilities in test areas I, II, and III, and uses new canals for the remainder of the study area. These areas were selected because they lie at sufficient distances from the river so that drain-out from year to year is anticipated to be low and carryover storage is expected. It appears that existing canals in these areas do have sufficient unused capacity during the early part of the irrigation season to be used in this manner. Therefore, the combination system of new and existing conveyance facilities forms the basis of the economic evaluation which follows, 42