Evaluating environmental flows for the targeted fish habitats in selected rivers

Area of Science:

• Environmental Science
• Hydrology
• Fisheries Management

Background:

• Padma, Karnafuli, and Halda rivers are vital water sources for Dhaka and Chattogram, supporting significant Hilsha and Carp fisheries.
• Maintaining adequate environmental flow (EF) is essential for aquatic habitats and water supply, balancing human needs with ecological requirements.
• Specific water depth and Dissolved Oxygen (DO) levels are critical for the survival and growth of Hilsha and Carp fish populations.

Purpose of the Study:

• To assess the environmental flow (EF) requirements for fish habitats and drinking water supply in the Padma, Karnafuli, and Halda rivers.
• To determine the Mean Annual Flow (MAF) and simulate water quality parameters for these critical river systems.
• To provide data supporting Decision Support Systems (DSS) for effective water resource management in Bangladesh.

Main Methods:

• Long-term field sampling and analysis of historical secondary data.
• Onsite and laboratory testing for water quality parameters, including Dissolved Oxygen (DO).
• Hydrologic Engineering Centre's River Analysis System (HEC-RAS) simulations for flow and water quality.

Main Results:

• Padma River flow drops below 20% of MAF during the dry season, potentially harming aquatic life; DO levels remained above 6.0 mg/L.
• Halda and Karnafuli rivers maintained minimum water surface levels of 2.35-2.40 m in the dry season.
• DO levels in Halda-Karnafuli rivers fell below acceptable limits annually; Halda River flow decreased to less than 10% of MAF, degrading aquatic life and hindering carp spawning.

Conclusions:

• Environmental flow in the Halda River is critically low during the dry season, posing a severe threat to its aquatic ecosystem and carp spawning.
• While DO levels are generally adequate in the Padma, flow reduction poses a risk; Halda-Karnafuli rivers face significant DO deficits.
• The study provides essential EF data for Hilsha and Carp habitats, crucial for developing sustainable water management strategies and supporting DSS.