Knowledge Base

Return water

Return flow adds substantial volumes to usable reserves. However, its high mineralization makes it a prime source of pollution of water bodies and the rest of the environment. Nearly 95% of return flow comes from irrigated land, with the rest comprised of industrial and municipal effluents (table 5).

Development of irrigation and drainage systems led to a steady increase in volumes of return flow, which peaked in 1960-90. Following 1991, they stabilized and even dropped slightly due to the temporary shrinking of areas under irrigation and a steady decay of drainage systems. Overall, in 1990-99 the return flow was 28.0 -33.5 km3/year. As much as 13.5 -15.5 km3 of the return flow was formed annually in the Syrdarya basin and 16 -19 km3 in the Amudarya basin (table 6). More than 51% of the total return flow is discharged into rivers and another 33% into depressions. Due to pollution only 16% of return flow is recycled for irrigation.

Unrestricted discharge of drainage water into rivers leads to a certain mineralization of the freshwater, making it unsuitable to use for any purposes. As a result of the lack of a systematic approach in the drainage into Water reservoirs in deserts and in the periphery of irrigated lands, fed irregularly by irrigation return flow, have no environmental value. There are several hundred reservoirs of varying size created by return drainage water, e.g. the Aidar Arnasaysk depression with a volume of over 30 km3, the Sarkamysh ( around 100 km3), Dengizkul, Solenoye, Sudochye and a number of smaller ones, each containing a few million cubic metres of water. Most of them are stagnating and cannot be used for fishing, with flora and fauna unable to survive due to unstable water and salinity levels.

Improving the management of the use and environmental maintenance of such water reservoirs and preserving their flora and fauna become, therefore, especially important. Measures to achieve this should seek to restore the ecological balance while providing for additional use of water without causing environmental damage. In this connection Turkmenistan’s decision to divert all drainage water currently discharged into the Amudarya into the “Golden Lake of the Desert” should be noted. The countries of the region reacted differently to this decision, as it would be necessary to take into account a number of factors, such as:

  • The trends in water and salt levels, the stability of the Lake’s salinity, including losses in the drainage networks, and due to evaporation;
  • The need to reach agreement with Uzbekistan on the withdrawal of waters drained from Khoresm Province (about 3 km3) as the alternative would be to divert them into the Aral Sea and its adjoining areas;
  • The changes in the inflow into drainage networks depending on the irrigation efficiency and development of irrigation in Turkmenistan;
  • The future of Lake Sarykamysh.

The problem of return flow and reservoirs formed would need a complex solution and decisions should be taken both at the regional as well as at the national levels. In this connection the national diagnostic reports recommend to:

  • Improve the control of return flow dynamics, and verify water balances in the respective basins, taking into account the impact of return flow;
  • Develop methods to forecast volumes and quality of return flow;
  • Develop principles of allocation of return flow according to the three types of its utilization, namely, its discharge into rivers, use at source of origin, and creation of return flow reservoirs;
  • Develop principles and methodology to limit discharges of return flow into rivers based on water availability in a river and content of pollutants in return flow;
  • Develop optimal models of reservoir conditions to provide for their environmentally sustainable management based on environmental requirements;
  • Develop norms for the use of mineralized return flow for irrigation and soil leaching of irrigated land. Flow regulation by water reservoirs