Author(s): Monomoy Goswami; Avijit Paul; M. Ao

Linked Author(s): Avijit Paul

Keywords: Longitudinal connectivity; Environmental Flow; Flow release methods; Weir; Waki hydropower project

Abstract: Ensuring longitudinal connectivity of a river across a storage or a diversion structure of a project is stipulated by approving authorities for sustenance of downstream aquatic ecosystem. This requires releasing environmental flow (e-flow) across the structure by mimicking the timing, frequency, duration and variability of natural flow of the river. However, the demand of eflow is more often than not viewed by project developers as being a factor likely to cut into the project’s commercial interests due to reduced share of the river’s water. As a fallout of this conflict, the regulating and monitoring authorities insist on active monitoring for enforcing flow allocation decisions and for undertaking adaptive management. In a stricter stipulation, such as that in the case of Waki Small Hydropower Project (SHP) in Uganda, the authorities stipulate no or minimal operator control and no possibility of device failure that might interfere or interrupt the mandatory release of e-flow. In this paper, an outline of the types and descriptions of different e-flow release methods/arrangements are provided, and the arrangement for unregulated release of e-flow adopted in Waki SHP is described. In the case of Waki SHP, e-flow is released over a broad-crested weir having its crest at an opening in an intake chamber in the Water conductor system adjoining a Tyrolean weir type diversion structure. With this arrangement, the regulatory requirement was fulfilled and the project was commissioned. The arrangement has since been functioning satisfactorily, and may be incorporated in similar cases of e-flow release in river valley projects, particularly in SHPs.

DOI: https://doi.org/10.3929/ethz-b-000675921

Year: 2024