Water rotation

Water rotation is the method of rotation of the order of crop watering based on the timetable designed for equitable distribution of irrigation water. Water rotation implies the order of water delivery in accordance with the schedule where water delivery day, time, and duration are specified.

Scheduled water supply at continuous current rate is deemed the main type of water delivery to the water user. In the WUA, water is delivered to so-called water delivery points in farms or to water users’ groups (WUG). In farms (or WUGs), water is delivered alternately to the land plots of one-time watering and cultivation in line with the progress of field works (according to water application–cultivation plans).

Alternating water distribution (water rotation between WUAs) should be carried out only in the case of strongly pronounced water deficit, when water losses in the network remarkably increase because canals are not filled enough.

There are a number of theoretical schemes of water distribution-water rotation. Two- or three-cycle water rotation based on alternating water delivery to water distribution units should be considered to be the simplest and practical scheme of alternating water distribution. With this scheme, main canals operate uninterruptedly, while water is supplied to distribution units by turns.

To establish water supply priority, distribution units of the system are united into two or three groups (turns) and duration of water supply for each turn is set in proportion to the scheduled water delivery to the WUA. At the same time, water is not delivered at all to all nodes shut down; protection is enhanced at the nodes as well as control over their operation. The water users that are put on the waiting list; they are timely warned about canal closing and opening.

At considerable water shortage (with strongly pronounced low water level), special guarding is set at command centers.

Water rotation is widely used in the water apportioning practice both abroad and in Central Asian countries. In Kyrgyzstan (Osh and Djalalabad provinces) water rotation is called avron; in Uzbekistan (Kashkadarya province), avandoz; in Tajikistan (Sogd province), ob gardon.

With normal water availability (without water deficit), water rotation is used only at the lowest levels of water partitioning: between irrigation contours, temporary irrigation ditches, and delivery ditches.

If water deficit deepens, it is reasonable to use water rotation on higher-order canals, including water rotation between main canal’s hydraulic sites.

Water rotation types

Water rotation is established between:

  • irrigation contours;
  • farm canals;
  • farms;
  • water consumers/users’ associations (WCA/WUA); and
  • main canals.

Water rotation efficiency

Water rotation efficiency implies decrease in technical water losses that could be with continuous water supply at lower discharges.

At the same time, operational (organizational) losses considerably decrease. This happens because with water rotation it is easier to mobilize water men and water users for controlling over the water distribution process.

Thanks to the above-mentioned advantages of water rotation, they succeed to a certain extent in solving the “head-tail” problem related to that water users at the end section of the canal are generally restricted in water supply in comparison with the farms located at the canal head section.

Water rotation components

System water availability coefficient is the quota limit (at acute water deficit, it is a.k.a. setting limit) equal to the ratio of the set design ten-day rate of water supply to the system to the planned ten-day rate of water supply.

Alternating units mean the parties of the water rotation process, who are supplied with water by turns (irrigation contour, canal, aggregate of canals in the WUA, district, etc.).

Number of water rotation cycles means the figure indicating the number of alternating units; two-cycle and three-cycle water rotation processes are the easiest and most prevailing.

Water rotation period means the cycle time during which water turns a complete circle between alternating units (as a rule, water rotation period is taken as a ten-day period at most).

Duration of a water rotation cycle for an alternating unit is a part of the water rotation cycle (period) during which water arrives to the zone of the alternating unit.

Design water rotation rate is the rate of (gross) water flow coming by turns to alternating units (to the head of the system (system section) where water rotation is applied).

Water rotation pattern

Irrespective of the level of water apportioning, water rotation pattern is as follows:

  1. A higher-order water delivery canal operates on an uninterrupted basis.
  2. Water from the higher-order water delivery canal is conveyed to lower-order canals in turns.
  3. To setting water supply priorities (scheduling), the lower-order canals are united into alternating units according to the following features:
    • maximum capacity of simultaneously operating canals will allow receiving excess (rotating supply) capacity
    • the effective length of the canals in a given group should be the least
    • the rates of (net) water flow of some groups should be approximately the same.
  4. Transit water flow rate and water supply for industrial and technician purposes.
  5. Design water rotation rate is determined taking into account the lateral inflow to the main canal.
  6. Design rates of water inflow to the canals operating in the same priority group are determined in proportion to ten-day setting limits fixed upon on-the-spot readjustment.

Duration of water supply to each priority group is set in proportion to the setting limits.