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Spreading methods
General features
The rate of infiltration is depends on the nature of the top soil. In situations where there is a reliable source of good-quality input water, and spreading infiltration can be operated throughout the year, hydraulic loadings of typically 30 m/yr can be achieved for fine texture soils like sandy loams, up to 500 m/yr for coarse clean sands. Evaporation rates (0.4-2.4 m/yr) form a minor component of the water balance. Where the source of water contains high loads of suspended solids, management of the recharge structure becomes increasingly important in order to minimize clogging to maintain infiltration rates and keep evaporation from open water to a minimum. Basic monitoring of the sedimentation rate and infiltration rate relative to the estimated rate of open-water evaporation will assist in operational management decisions.
In general, smaller scale spreading techniques are suitable for water supply to medium sized communities and agriculture in rural areas. The often complex and expensive large scale systems are mainly used in industrialized countries. Due to the diversity in spreading techniques and the scale of these techniques, management of spreading schemes occurs on practically all levels. Small scale flooding techniques can be implemented by individual farmers, whereas large scale infiltration basins are often funded and managed by water authorities.
A well known advantage of spreading schemes is the possibility to infiltrate large quantities of water at relatively low costs. Also clogging problems are relatively easy to mitigate through construction techniques or operational procedures. Infiltration basins are probably the most favored method of recharge, because they allow efficient use of space, they can be integrated into a site's landscaping or open space, and require only simple maintenance. A disadvantage of water spreading schemes is the requirement of a large surface zone with an unconfined aquifer for infiltration, which is not always available.