The Assessment of Irrigated Area Drainage

Drainage area in the arid zone is an important condition of melioration (not currently determined when conducting the cadastre). It is almost impossible to reveal the influence of only one drainage factor on the harvest. The following dependence for Golodnaya steppe was revealed on the basis of mathematical models for the meliorative process and empirical connections of cotton harvest from soil salinization [3, 4] (Fig. 19.2).

For assessing artificial land drainage, it is necessary to divide the actual drainage of the collector network into components: irrigation escape water (CnC3) and ground water drainage (Dg); that is:

Fig. 19.2 The dependence

y

of relative crop capacity on

drainage decreases in com

1.0

parison with "critical"

0.9

value for the Golodnaya

steppe

0.8-

0.7

0.6

0.5

y=fiff)

y=fiff)

The contributions of these drainage collector network components are based on the physical method of Kudelin, hydrochemical method of Engulatov, and empirical method of Ikramov [2].

The following method is suggested to assess drainage. Two cases are provided on the basis of the degree of artificial drainage dependency, and on the technical condition of drainage facilities. In the first case, the efficiency of water supply of irrigated areas is normal; that is

where B^ [B] is the actual and necessary conformity with water abstraction norms, M3/ra. The territory is considered to have enough drainage if

where D, [D] is actual and necessary land drainage, M3/ra; Kd is the coefficient of acceptable drainage decrease. It may also be accepted under conditions of crop capacity decreasing no more than 10% of maximal crop capacity by analogy with Kb . In accordance with Picture 2 Kd = 0,9. In the second case, the efficiency of water supply of irrigated areas is insufficient:

The territory is considered to have enough drainage if

where [D]* is determined as a characteristic of critical meliorative regime by concerned water infiltration.

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