Modelling Small-Scale Storage Interventions in Semi-Arid India at the Basin Scale

Abstract

There has been renewed interest in the performance, functionality, and sustainability of traditional small-scale storage interventions (check dams, farm bunds and tanks) used within semi-arid regions for the improvement of local water security and landscape preservation. The Central Groundwater Board of India is encouraging the construction of such interventions for the alleviation of water scarcity and to improve groundwater recharge. It is important for water resource management to understand the hydrological effect of these interventions at the basin scale. The quantification of small-scale interventions in hydrological modelling is often neglected, especially in large-scale modelling activities, as data availability is low and their hydrological functioning is uncertain. A version of the Global Water Availability Assessment (GWAVA) water resources model was developed to assess the impact of interventions on the water balance of the Cauvery Basin and two smaller sub-catchments. Model results demonstrate that farm bunds appear to have a negligible effect on the average annual simulated streamflow at the outlets of the two sub-catchments and the basin, whereas tanks and check dams have a more significant and time varying effect. The open water surface of the interventions contributed to an increase in evaporation losses across the catchment. The change in simulated groundwater storage with the inclusion of interventions was not as significant as catchment-scale literature and field studies suggest. The model adaption used in this study provides a step-change in the conceptualisation and quantification of the consequences of small-scale storage interventions in large- or basin-scale hydrological models.

Extending a Large-Scale Model to Better Represent Water Resources without Increasing the Model’s Complexity

“…Collins et al (2020) [69] demonstrated largely under-simulated groundwater-levels compared to the observed data in the Berambadi sub-catchment of the Cauvery, using a one-dimensional numerical transect model. It was suggested that a poor representation of the India Meteorological Department (IMD) rainfall in this region is a critical part of the poor simulations of both recharge to groundwater and streamflow in this region [33].…”

“…Eye-witness accounts and some literature report drying out of streams in the dry season, which is not reflected in the observed data. Additionally, in reality, rivers downstream of significant urban and agricultural areas are often fed by a perennial stream of human or livestock sewage [33]. Although the model represents return flows from domestic demand, this may be under-estimated compared to the volume of effluent being released into these rivers in reality.…”

“…Each 0.5-degree grid cell contains numerous terrain and gradient increments, and the grid cells may fall over the basin boundary. This results in an inaccurate representation of the distribution and total rainfall, and the distribution of the minimum and maximum temperature in this region of the basin [33,34]. There is a known source of uncertainty within the Western Ghats region, which acts as the headwaters for the larger Cauvery Basin.…”

“…Several hydrological modelling exercises have been conducted in the Cauvery Basin or sub-catchments thereof. Remote sensing methods [32], the artificial neutral network (ANN) model [32], GWAVA model [33,34], VIC model [34], and SWAT model [34,35] have been applied in various sub-catchments of the Cauvery. At a basin-scale, the SWAT [36][37][38][39], Soil Conservation Service Curve Number (SCS-CN) [40,41], and Variable Infiltration Capacity macroscale hydrological model (VIC-MHM) [42] have been used to simulate various components of the hydrological cycle.…”

“…The above-mentioned studies focussing on the Cauvery and the Narmada Basins highlight the minimal representation of anthropogenic influences, groundwater abstraction, and reservoir operations within the existing modelling exercises. GWAVA has been applied in both the Cauvery basin [33,34] and the Upper Narmada basin [52]. These publications highlight the need for a more comprehensive reservoir routine when modelling highly regulated basins, and for the inclusion of a coupled groundwater module to account for the limitations of natural groundwater resources and groundwater abstraction to meet anthropogenic demand.…”