Watertable control

In agricultural land drainage, the purpose of water table control is to establish a depth of the water table (Figure 1) that no longer interferes negatively with the necessary farm operations and crop yields (Figure 2, made with the SegReg model, see the page: segmented regression).

Optimization of the depth of the water table is related to the benefits and costs of the drainage system (Figure 3).

Figure 4 shows an example of the effect of drain depth on soil salinity and various irrigation/drainage parameters as simulated by the SaltMod program.

Since 1960, one started using long, flexible, corrugated plastic (PVC or PE) pipes that could be installed efficiently in one go by trenching machines.

The pipes could be pre-wrapped with an envelope material, like synthetic fibre and geotextile, that would prevent the entry of soil particles into the drains.

As a result of large scale developments, many modern drainage projects were over-designed,[5] while the negative environmental side effects were ignored.

Drainage wells have been used extensively in the Salinity Control and Reclamation Program (SCARP) in the Indus valley of Pakistan.

Figure 1. Drainage parameters in watertable control
Figure 2. Crop yield (Y) and depth of water table (X in dm) [ 2 ]
Figure 3. Positive and negative effects of land drainage
Figure 4. Example of effects of drain depth
Figure 5. Controlled drainage
Figure 6. Geometry of a well drainage system
Yield of sugarcane versus depth of the water table, Australia. The critical depth is 0.6 m. [ 8 ] [ 9 ]