The reclamation of an area that is high in soluble salts and the maintenance of the productivity of potentially saline areas involve the same basic principle. The removal of salts from the root zone of the soil must exceed the quantity of salts deposited by the irrigation water. That can be accomplished by good drainage and proper control of irrigation unless the amount of sodium in the soil or the irrigation water is high.

Good drainage is essential. That means that the water table should be at least 5 to 6 feet below the surface. In order to observe variations in the water table throughout the year, an efficient observation well was developed that consists of lengths of 3/8-inch pipe terminating at different depths in the soil and a device for measuring the distance to water. With it, the pressure and direction of movement of ground water and information regarding soil permeability can be determined. The drainage engineer can use the information in selecting the most practical methods of drainage, improving drainage design, and evaluating the effectiveness of drainage systems already in operation.

Where artificial drainage is necessary, three methods are used tile systems, open drains, and pumped wells.

In many irrigation projects, deep open drains are installed and tile drains are frequently used as an adjunct to them. If the surface soil is permeable and is underlain with gravel deposits, wells of satisfactory capacity can be developed, and pumping from them may be the most feasible and cheapest method of controlling the water table. The water collected by these methods is usually removed by large outlet drains, which discharge into the river system. In many places drainage water pumped from wells is mixed with irrigation water and used over. Proper management of irrigation water is as important as good drainage.

Assuming that water of satisfactory quality is available, the amount Of water applied in irrigation is a primary consideration in saline or Potentially saline areas. The total amount of water required under non-saline conditions is the quantity of water, expressed in acre-feet per cropped acre per year, used by the crop in the formation of plant tissue or transpired through the leaves, plus the water that evaporates from the soil surface. To this requirement, sometimes called consumptive use, must be added irrigation losses during water conveyance (seepage, leakage, wasteways, and evaporation) and losses during application (surface runoff and deep percolation).

In saline areas, besides the requirements just noted, sufficient water must be supplied to leach the soil and carry excess salts down below the root zone. Both underirrigation and overirrigation must be avoided. Salts will accumulate if a salty soil is underirrigated, and all the water applied is used by the plant or evaporated. For example, Colorado River water (a class 2 water) contains 1.1 tons of salt per acre-foot. Continued use of water of that degree of salinity in amounts insufficient to" cause leaching and drainage will eventually make the soil too saline for use. Over-irrigation is also dangerous, especially where drainage is poor, since the excess water passing into the subsoil may cause a rise in the water table and bring about an increased accumulation of salts in the root zone.