Specific Water Consumption

(in Russian, gidro-modul’), the average water consumption per hectare of sown area of a crop during a given period of time.

The specific water consumption (q) is expressed in liters per second (l/sec) per hectare (ha). A distinction is made between water consumption from the consumer’s point of view (q′), which is the consumption per hectare of field area, not taking into consideration losses within the irrigation network, and consumption from the point of view of supply (q″), which is the consumption of water with these losses taken into account. Under conditions of an irrigation norm of m m³/ha, an irrigation period of t days, and round-the-clock irrigation,

If the efficiency of the irrigation system during the period t is equal to η, then q″ = q/η/l/sec per ha.

If the specific water consumption and the area in hectares of the section to be irrigated (ω) are known, then the consumption of water by the section (Q′ net) and the supply of water to the head of the irrigation system (Q″ gross) during the time period t may be determined as follows:

Q′ = ω∙q′l/sec Q″ = ω∙q″l/sec

In sowing an irrigated area with several crops that occupy α₁, α a₂, … , α_i percent of the area, respectively, q′₁ = q′(α₁/100)l/sec per ha. The values of q″₁, Q′₁ and Q″ are obtained in the same way—that is, the quantities q″, Q′ and Q″ are multiplied by (α₁/100). In cases of the simultaneous irrigation of several crops, their specific water consumption is combined.

Having determined the irrigation norms for each crop, as well as the periods and specific water consumption for this irrigation, one can draw up a graphic plan for the water utilization of the section to be irrigated throughout the entire growing period; this is known as the specific water consumption graph. For this purpose the time t is plotted on the x-axis, and the specific water consumption q is plotted on the y-axis. If the ordinates are sharply different, reflecting interruptions in the water supply, the graph is completed—that is, the time and duration of the watering periods, as well as the water-supply norms, are changed within permissible limits for each crop, but the irrigation norms are retained. Approximate values for specific water consumption (in l/sec per ha) are 1.05-0.80 for rotated cotton crops in Middle Asia, 0.50-0.40 for rotated cereal-fodder and wheat crops in the southern Ukraine and Transvolga regions, and 0.5-0.3 for vegetable and fodder crops in the Central Chernozem Zone. The specific water consumption for rice-crop irrigation systems is higher: during the initial flooding 2.5-2.0 l/sec per ha is required, and to sustain growth a rate of 2.0-1.0 l/sec per ha must be maintained.