Design of environmental flow regimes to maintain lakes and wetlands in regions with high seasonal irrigation demand

•Efficiency of EF regimes depends on high seasonal irrigation demand.•A monthly based assessment of water demand, allow to target EF accurately and increase the efficiency of allocated EF.•A monthly flow alteration function was developed, taking various water demands into consideration.

In arid regions, the construction of dams has led to an increase in irrigated agriculture, resulting in the desiccation of vulnerable lakes and wetlands. In many arid mountainous regions, such as in the Middle East, upstream dams typically feed rivers that flow into lowland terminal (closed) lakes or wetlands. The release of water for environmental purposes is a widely recognised option for reducing such impacts. The present study used monthly hydrological data from the Kor river in southern Iran, its main reservoirs and data above and below the Korbal irrigation system. The Kor river is a major source for feeding the Bakhtegan and Tashk lakes, which have recently started to disappear. An analysis of the water resource system before the dam construction (before 1973) showed that the monthly lake inflow depended on available water in river above the irrigation system (for eight months) and, during the irrigation season, water consumed for irrigation as well (for four months). However, in the post-development period (after 1997), the flow rate to the lake depended almost entirely on the Korbal irrigation system, except during some winter months when little irrigation was needed. Environment flow release has not been effective as it has led to greater water availability in the river, which results in more water being consumed for irrigation, as demonstrated here. To overcome this management mismatch, a new environmental flow release strategy (regime) was designed in which water is released from the upstream reservoirs during periods of low irrigation demand (e.g. winter months).