California’s four-year drought is the worst in the state’s history and wide-ranging restrictions on water use came into effect at the start of June. In the longer run Californians will need to find new ways of managing their water supply.
Rainwater can be captured with dams to create reservoirs, but there is an alternative approach, that of groundwater banking. River water is diverted into shallow pools, known as recharge ponds, where it soaks through the ground and replenishes aquifers. Recharge ponds have proved successful in the San Joaquin valley, with banked water being extracted from the aquifers, below ground level, via wells.
San Joaquin county is extending the scheme, to catch rain water directly by surrounding flat areas of farmland with an earth wall or berm about 60cm (2ft) high. Winter storms are an important source of water, and such walls stop the water from escaping and turn the field into a recharge pond.
Known as the Dream project (demonstration, recharge, extraction and aquifer management) the scheme is starting with a series of two-acre trial plots. These require the right sort of porous soil, but the project need not interfere with other activities, such as growing grapes.
Aquifers do not lose water through evaporation like reservoirs, and the technique is far cheaper than desalination. Climatologists suggest that Californian rainfall is increasingly likely to arrive in short intense bursts. The existing infrastructure may not be ideal for handling these, but a system of recharge ponds should work like a dream.
