Offsetting Allochthonus Salinity Increases Threatening Irrigated Agriculture with Managed Recharge
Balance Hydrologics, Inc.
Where the salinity of master streams is increasing, recharge may also become more saline. The choices and yields of crops are becoming more limited in numerous agricultural basins in central and southern California, requiring management of recharge quality to keep high-value agriculture sustainable. Dilution with waters of lower salinity is often the simplest and preferred alternative. Four sources of fresher water are available in many such basins: 1.Low salinity storm runoff captured in reservoirs; 2. Low salinity storm runoff captured in recharge facilities, such as former quarries; 3. Deeper groundwater of lower salinity, typically available from clastic continental deposits of Pleistocene or recent age; 4. Treated effluent, which often is of substantially lower salinity in subarid California than is the master stream, due to water imports or selection of lower-salinity local sources for drinking water quality. As salinity of master streams continues to increase, planning recharge for salinity control will also become increasingly necessary, and should be incorporated in many groundwater basin planning efforts. The Pajaro Valley is used as one example of how low-salinity dilution from each of these sources - singly or in combination - can lead to maintaining the high-value agriculture for which the region is known. Pajaro Valley results suggest that it may be necessary to respond sooner than we think to inhibit salinity increases in at least some alluvial valleys.