Trends in Streamflow in Relation to Water Retention Structures: A Case Study in Bharathpuzha River Basin, India

Lack of availability of land, water and other natural resources along with climate change has caused a major threat for increasing the agricultural production on par with the increasing population. Bharathapuzha river is considered as the cradle of civilization in Kerala state, India. The river flow is highly affected by increased water use and reduced recharge caused due to increasing population, urbanization and unscientific management practices. Even though, watershed development activities in river basins help in conserving water in the upstream areas for agricultural, domestic and other uses, very few research have been done to understand its effect on the flow regime in the lower reaches. A number of dams, check dams and other conservation structures have been constructed in Bharathapuzha catchment area during the past and hence its effect on the downstream flow need to be studied. The calibrated and validated SWAT model was applied to Bharathapuzha river basin for studying the impact of watershed interventions on the water balance of the area. The simulated monthly streamflow was analyzed during 2007 to 2011 after addition of Water Retention Structures (WRS) @ 0.05%, 0.1% and 0.2% of the land area. The results indicated that even though the total annual flow decreased, the flow during the summer months (baseflow) increased due to the addition of the conservation structures. The increase in river flow was highest during the period January to April when the river had lean flow. It was found that SWAT model can be used as an effective tool to study the impact of water retention structures in a watershed. The conservation structures help to store water in the upper reaches for irrigation and domestic purpose, and at the same time it helps in increasing the summer flow. This helps to maintain a better environmental flow regime. Hence while planning the conservation measures in a watershed so as to meet the demand of the upstream users, care should be taken to avoid the negative impact that can happen in the downstream.