EXPLORING HYDROLOGICAL CONNECTIVITY IN THE LOWER HIMALAYAN REGION: MAPPING IRES DYNAMICS WITH LOW- COST SOIL MOISTURE SENSORS

Abstract

A comprehensive exploration of streamflow dynamics at the watershed scale in non-perennial rivers is an arduous task. In the lower Himalayan region, the presence of numerous intermittent and ephemeral streams contributes to a high volume of water for a small duration and transports a significant amount of sediment downstream. Fluvial alterations reshape stream geomorphology, triggering flash floods. To map those headwater streams, a comprehensive study within the lower Himalayan watershed of an area of 56.61 𝑘𝑚2 has been done by developing low-cost capacitive soil moisture sensors. This real-time monitoring sensor is a microcontroller-based system and an indirect method for indicating the soil moisture content. These sensors have been strategically deployed across two distinct sub-watersheds within the headwater watershed to capture the continuous soil moisture response during the monsoon period in 2023. For analyzing this study, on-field data was collected from automated weather stations (AWS) to obtain rainfall data, which was complemented by the utilization of stagedischarge curves for a more thorough understanding of discharge fluctuation. During the 2023 monsoon period, 9 rainfall events were recorded and categorised as small, medium, and high to get the rainfall-runoff relationship with the antecedent moisture condition (AMC). From the analysis, different signatures in capacitance value are found to be influenced by several factors, which include slope, % area, stream order and land cover. These thresholds will aid in accurately mapping streams and quantifying discharge capacity. Hydrological modelling using SWAT+ on a daily temporal scale validates field observation for the different category rainfall events. The percentage active drainage length for each category with their AMC conditions during both monsoon and non-monsoon periods is analysed. This study will enhance management strategies for sediment transport and ecological health within high-gradient headwater watersheds.