- Summary
- Objectives
- Status
- Project Publications
Tropical estuaries are transition zones between freshwater and marine environments; their ecosystem functioning depends critically on the timing, quality, and quantity of upstream inputs such as freshwater and sediments carried by the river. In tropical developing countries, hydropower dams drastically alter downstream flow and sediment regimes. Understanding their effects on estuarine salinity and suspended sediment concentration – two key physical parameters that influence estuarine ecosystem functioning, is important. Estuaries provide livelihoods through reliance on artisanal fisheries and bivavlve collection to millions of people in the tropics. This study also aims to understand how natural resource-dependent communities living downstream of hydropower dams adapt their livelihoods to ecological changes.
1. How freshwater and sediment inputs to the estuary are modified by hydropower dams.
2. How fisherfolk and bivalve collectors adapt to hydropower dam-induced changes to the estuary.
- Data collection in the field has been completed and analysis of this data is ongoing. A participatory GIS map of bivalves created from the data collected during interviews is being prepared.
- The study site included four estuaries, two that were dammed (Sharavati and Kali) and two that were free flowing (Aganashini and Gangavali). For each estuary, data on freshwater level, salinity and suspended sediment concentration (SSC) were collected for the period Feb 2023 – Feb 2024.
- The data highlighted that undammed rivers showed a natural flow regime with the characteristic monsoon flood pulse, while dammed rivers showed hydropeaking. Estuarine salinity data of free-flowing rivers is driven by natural flow and tide and was found to range between 0 during monsoon to 35 during summer. Salinity of the Sharavathi estuary was driven by hydropower releases. Limited data suggests that hydropeaking does not affect the salinity of Kali estuary, which is likely due to the lower percentage of the watershed under the reservoir.
- The free-flowing rivers showed a marked increase in SSC during the monsoon period. SSC is subdued in the Sharavathi because the reservoir captures the monsoon flood pulse. Kali river, on the other hand, showed a peak in SSC that corresponds to the period when the reservoir released a part of the monsoon flows.
- Artisanal bivalve collectors in the Aghanashini and Sharavathi estuaries (30 each) were interviewed to understand how they adapt their livelihoods in response to changes in bivalve distribution and availability.
- In the Aghanashini estuary, bivalves show a strong longitudinal gradient in their distribution driven by their tolerance to salinity. These bivalves constitute an important source of livelihood for people who co-produce this ecosystem service despite local pressures from shell mining, shrimp aquaculture, and small-scale sand mining. In Sharavathi, bivalve collections no longer constitute a significant source of livelihood. Here, locals who were previously dependent on bivalves for their livelihood are now depending on other local sources of income such as estuarine fisheries, aquaculture, tourism, or large-scale, mostly illicit sand mining of the estuary, or by migrating away from the estuary to find other income sources.