Socio-Hydrology and Sustainable Tank Management: Empirical case from a Mailam Tank Cascade, Tamil Nadu, India

Rengalakshmi Raj^1*Thamizoli Perumal²Nagarajan Rajendiren¹Nandeesa Pasuvanna¹

• ¹M S Swaminathan Research Foundation, Chennai, India
• ²Independant Researcher, Chennai, Tamil Nadu, India

The tank cascade system is an interconnected tanks governed by local norms and informal institutions. These linkages connect people, water and environment for resource management and ecosystem services. However, recently, cascading structures have been disrupted at hydrological and social levels, leading to complex issues aggravated by increasing climate risks and farmers' vulnerabilities. An in-depth study was carried out in a tank cascade system connecting 14 tanks in 4,437 ha in South India to understand its impacts on livelihoods, ecology and social networks. The study adopted a mix of qualitative and quantitative methods and remote sensing data to understand the drivers of tank performance, livelihoods, production, land-use, rainfall and interconnectedness with a study period from 2004 to 2024. The study analysed hydrological, socio-economic dimensions and interconnected human-environmental interactions. The dependence on tanks for irrigation in study area has decreased, ranging from 9 to 54 %. In land-use, 44 % reduction in cropped area (1707 ha to 954 ha), 13 % increase in fallow land (1,607 ha to 1,822 ha) and 43 % in other vegetation, and built-up area from 5 ha to 60 ha. The surface-runoff increased from 2029 to 2489 ha-m, while groundwater level has decreased from 0.03 m below ground level (bgl) at pre-monsoon and 0.73 m bgl at post-monsoon, with an increase in well intensity in ayacut (area irrigated by tank). The tank infrastructures are undergoing severe degradation, with a shift in irrigation source from community-based collective surface water irrigation to groundwater-based individual irrigation. The social capital and interconnectedness among farmers are changing along with declining relevance of community-based governance systems. While functional use of tanks shifts to groundwater recharge, tank cascade system-based infrastructure, knowledge, and ecosystem services are on the verge of disappearance. The hydrological status of tank cascades is closely interconnected with good governance, sustainability of institutions in social and financial dimensions. This requires right policy and translational framework to put tank cascades at core of tank development plans. With the increasing climate risks, changing agrarian relations, coupled with degrading ecosystem services from tanks, the paper delves into socio-hydrological principles in designing sustainable tank management initiatives.