Assessment of environmental flow release from Deduruoya reservoir to mitigate possible impacts on downstream ecosystem

Abstract

River ecosystems are interlinked with river hydrology. However, construction of dams can modify the natural flow patterns which can lead to unpredictable consequences. Environmental flow (EF) releases can restore ecosystems or reverse the already occurred degradation. Having understood the importance of EF, large number of methods has been developed to estimate the EF. The objective of this study was to make a comparison between these methods to identify the most comprehensive method and to develop a novel approach to estimate EF based on the concept of minimum information requirement. Among the EF calculation methods studied, holistic method was identified as the most reliable category and the building block methodology (BBM) was identified as the best holistic method which requires more resources or data. The new methodology developed to assess EF basically based on BBM but efforts were taken to identify minimum data requirement approaches to calculate individual water uses. It consists of the flow requirement of riverine flora and fauna, social and cultural water requirement, wetland water requirement, longitudinal connectivity, flushing flow requirement, groundwater recharge and coastal water requirement. The EF requirement of downstream of DeduruOya reservoir was estimated using the developed method. The results were compared with the EF calculated using the Sri Lanka Environmental Flow Calculator model developed by IWMI. There was a significant difference between the EF calculated using new method and the results obtained using model developed by IWMI. Hence, it is recommended to further improve and verify the findings of the new method.

Keywords

• deduru oya reservoir, ecosystems, downstream water requirement, environmental flow, environmental flow assessment methods