Modelling of environmental flow requirements using hydraulic and habitation models

Abstract

Anthropogenic activities in the Krishna River have altered its flow regime and affected the ecosystems in the river. It is essential to maintain an optimum Environmental Flow (EF) in the river to recover from its deteriorated ecosystem. The present study is to estimate Environment Flow Requirement (EFRs) and the Hydrological Alteration (HA) (Flow changes) that take place on the Krishna River at five dam sites. Pre and post construction impact flow data are collected at five gauge stations which are located downstream of these five dams. The flow data which are impacted by climate variability are removed and the study is focussed on the impact of human activities. These EFRs are estimated using statistical relationships between the Krishna River flow regime and ecological indicator with the help of the Global Environmental Flow Calculator (GEFC). HA is used to analyse how the recommended EFRs are different in the post-impact period (after the dam construction). Hydraulic indicators like water depth and velocity are determined by importing estimated EF values into a Hydrologic Engineering Centre’s - River Analysis System (HEC-RAS) model. The habitation analysis is carried out to check whether the hydraulic indicators are providing an acceptable habitation for aquatic species in the study area. The results from HA analysis showed that the required EFRs in the Krishna River were not maintained for almost 43% of the time in the post impact period. The hydraulic analysis showed that recommended EFR is providing velocity in the range of 0.12 m/s to 1.08 m/s and water depth in the range of 0.23 m to 3.16 m throughout the basin. From the habitation study, it is observed that the results obtained from the GEFC approach is providing excellent habitation under the dams of Srisailam and Nagarjuna Sagar. Good habitation conditions are seen under Narayanapur, Ujjani, and PD Jurala dams.