what is storm runoffs
what is storm runoffs
Define conjunctive use of water resources.
What is storage capacity?
Conjunctive use is the combined use of surface water resources and groundwater, in a unified way, to optimise resource use and minimise the adverse effects of using a single source.
It exploits the storage capacity of an aquifer and the ease of transport of water by a river. The aquifer is used to store surface water when there is an excess of it and it would otherwise be wasted, such as in winter.
The river is used to transport water from the aquifer to where it is needed when the river discharge is too low on its own, as often happens in summer. Conjunctive use can also reduce abstraction from rivers when the discharge is low by using groundwater instead.
The storage of excess surface water underground in an aquifer is a type of conjunctive use called managed aquifer recharge. This makes the most of excess water by directing it into the ground where it can be stored for future use. Underground storage has many advantages over surface storage:
• no land is taken up by reservoirs,
• there is no evaporation loss, and
• capital costs are much lower.
However, managed aquifer recharge is not a simple process, and it is difficult to do on a useful scale; it cannot absorb large volumes of flood water in a short time. It involves transferring water from the surface to underground, either by dispersing it over the surface to increase infiltration, or through aquifer injection wells.
Surface dispersal involves diverting the water into an unlined canal or shallow lagoon in permeable sediments or rock so that the water can percolate downwards into the aquifer. It works best in areas with highly permeable soils and unconfined aquifers, and where land is inexpensive. Aquifer injection wells are used to recharge aquifers directly. Direct injection of water through wells is more expensive than basin recharge but is used when there is no suitable land for a recharge basin, or with confined aquifers.
Storm runoff, which would otherwise be lost to the sea, can be used for managed aquifer recharge, especially in arid areas. For example, in the Central Valley of California, storm runoff is trapped in alluvial sediments. On Long Island, New York, aquifers are recharged through sands and gravels, which also help to prevent flooding.
In some areas it is possible to use sewage effluent for managed aquifer recharge, as the polluting substances in the water are removed by biological processes during infiltration. However, it is very easy to pollute an aquifer, especially if the effluent contains industrial waste. Another problem of artificial recharge is that fine sediment in the water can quickly clog the pores in an aquifer, reducing the natural rate of recharge from lakes, lagoons and wells.