Impact assessment of anthropogenic interpositions on hydrological regimes of Godavari and Krishna River Basins, India

The rivers around the world have been transformed due to various anthropogenic activities and have led to the altered natural flow regime, which is crucial for controlling the essential environmental conditions within the river which in turn forms the biotic diversity. This study quantifies the adverse impacts due to the construction of dams on the hydrology of the Godavari and Krishna River Basins over the last half a century. The quantification of hydrologic alteration at five representative gauging stations of both the rivers has undertaken using Indicator of Hydrological Alteration (IHA) and the Flow Health (FH) methods based on the Range of Variability approach. To evaluate the alterations of flow regime due to the impact of dams (anthropogenic) only, the data for wet and dry years were excluded from the analysis as these represent the impact of climate variability. The IHA results reveal that the average monthly flow (especially from June to September), annual extreme streamflow indices (1-, 3-, and 7-day maxima flow), and rise and fall rates were among the most affected ones when compared to the pre-impacted period. The improved overall hydrologic alteration values for the Dhalegaon, Nowrangpur, K. Agraharam, and Vijayawada stations were found approximately 75.5%, 73.2%, 76.9 %, and 67.9 % respectively, suggesting a significant impact on the overall riverine ecosystem. The flow health (FH) analysis scores for high flow (HF) (K.Agraharam and Yadgir) highest monthly (HM) (Dhalegaon, K.Agraharam, and Yadgir), Low Flow (LF) (Dhalegaon) and flood flow intervals (FFI) (Dhalegaon and Vijayawada) during the test period were in the very high alteration range and these all hydrological indicator represents important ecological functions in both the rivers. The results showed in this study may guide in strategizing the multi-step process needed to improve the riverine ecosystems of Godavari and Krishna Basins and their ecological functioning.

Keywords: Hydrological alteration; Krishna River; Godavari River; Ecosystem