Basic Information | International Commission on Irrigation & Drainage (ICID)

Regional Bio-Drainage

The most important factor to consider when deciding where to establish bio drainage plantings is the hydrological process underlying the catchment water balance. Accurate identification of recharge (intake) and discharge (seepage) areas in the landscape is a major requirement for the proper planning of bio drainage activities.

In non-irrigated, undulating areas the identification of recharge-discharge relationships is often relatively easy with the lower areas of the landscape generally serving as discharge land units. Exceptions do occur where impermeable layers in the soil profile can cause discharge to occur higher up the slope. Bio drainage plantings in dry land areas where salts are stored in the soil profile should focus on recharge areas and thus prevent the development of saline seeps further down the slope. In non-saline areas, recharge plantings could result in the drying-up of springs or wells further down the slope and thus have negative social impacts.

In relatively flat irrigation areas, recharge-discharge interactions are often less clear. On the same land unit a recharge scenario immediately after irrigation can turn into a discharge situation at the end of the irrigation cycle when vegetation starts to tap the shallow water table.

The planning scale of bio drainage plantings depends on a large number of factors. Where farm holdings are small, obviously landholders are unable to set part of their farm aside for bio drainage activities. Therefore any application of this technique will have to focus on public land. Where farms are large, landholders might be able to integrate bio drainage plantings in their farm layout.

Where large-scale recharge plantings are planned, cost-sharing arrangements might have to be developed to assure that (part of) the implementation costs of the works are carried by the beneficiaries. In Australia, where regional tree-planting activities are widely supported by volunteer community groups, there have been examples of salt-affected irrigation farmers in the bottom-end of catchments actively participating in tree planting activities in the top-end of the catchment, 50 or more kilometres away.