Multi-Station Trend Analysis for Assessing Hydrological Alterations and Environmental Flow Requirements in the Malaprabha and Ghataprabha River Basins, India

The ecological integrity of riverine ecosystems in semi-arid areas is largely affected by variations in the natural flow regime as these flows are increasingly disturbed by anthropogenic activities, particularly the construction of dams, diversion weirs and storage structures. The current study examines the basins of the Malaprabha and Ghataprabha rivers, which are two primary tributaries of the Krishna River in southern India. The water management in these rivers is significantly influenced by the Hidkal and Navilatirtha dams, which serve as large reservoirs for storage. The study's goal is to delve beyond the antiquated concept of "minimum flow" and to develop a comprehensive assessment of Environmental Flow (EF) requirements based on long-term data trends.

            The methodology adopted a comprehensive trend analysis of hydrological and ecological data collected from multiple gauging stations, namely, Bagalkot, Gokak Falls, Cholachaguda, Mudhol, and Navalgund. The daily discharge data from the Central Water Commission (CWC) and Water Resources Department (WRD) of Karnataka are analysed using the Mann-Kendall test and Sen’s slope estimator for monotonic shifts in flow patterns. To measure the extent of the changes, the study applied the Indicators of Hydrologic Alteration (IHA) and the Range of Variability Approach (RVA) for determining 33 ecologically relevant parameters, including the magnitude, frequency, and duration of flow events.

            To understand the notable differences between pre-dam (natural) and post-dam (controlled) situations, a preliminary assessment of the hydrological data is being carried out. These patterns are expected to show a significant dampening of natural flow frequency and magnitude, enabling the data-driven basis required to precisely forecast EF thresholds for the basins.

            The study highlights the need to integrate hydrological data from multiple stations to understand the cumulative effects of interventions at the basin level. The study establishes the thresholds necessary to support native aquatic species and maintain the overall ecological health of these river systems by identifying variations in flow magnitude, frequency, and duration.

 

Keywords: Environmental Flows, IHA/RVA, Mann-Kendall Trend Analysis, Hydrological Alteration, Multi-station Analysis.