salinily conlrol is conducied by modern engineering and melioration
means, verlical drainage among others.

After many years of siudies on experimental plols and large-scale field
fests the Central Asian Irrigation Research Institute has worked out the basic
principles for calculating and drawing up pumping regimens in the vertical
drainage systems belonging to various nalural and economic zones.

In order to @гам ир а scieniifically substantiated regimen of pumping
it is necessary to provide dala on the degree and nature of salinily, the water
and physical properties of the ground, its lithological structure, the hydrogeo-
logical and irrigation conditions, weaiher conditions, the engineering апа
operatfional parametres of the well systems, the power supply and also results
of studies conducled for the given type of drainage on experimental plots
or on analogous sites.

The engineering and melioration description of a territory gives the best
outline of the natural and economic conditions prevailing in the region. The
pumping regimen is based on estimates for the water and salt balance in the
aeration zone, the ground water, and the entire depth of aciive water
exchange. Depending on the purpose of the system and peculiarities of the
land there may be different requirements fo the calculations of the water and
salt balance.

In the case when the drainage well is intended to reduce soil salinity
it is necessary to ensure the following:

— to provide prerequizites for the given rate of desalination which
would correspond to the selected melioration regimen of the ground water
table and pressure water so that in combination with farming methods it
would prevent secondary salination;

— to provide a favourable water and salt regime in the aeration zone of
the ground and throughout the entire zone of active waler exchange.

The pumping regime is drawn up on the basis of the type, date and volu-
me of maintenance of the pumping and power equipment and inslallations in

Mosf of the land in the irrigated zone of the USSR is saline soil. Soil

3