Geomorphological Effects of Sand Dams on Surface Elevation and Stability: A Decadal InSAR Analysis From Semiarid Kenya

Climate change is intensifying aridity and water scarcity in semiarid regions, placing increasing stress on soils, ecosystems and agricultural livelihoods. Sand dams are small structures built across ephemeral riverbeds, which have become a widely adopted adaptation measure, enhancing water availability and groundwater recharge. While their hydrological and socioeconomic benefits are well documented, their geomorphological effects remain poorly understood, despite the fact that erosion and sedimentation critically shape both soil stability and the long‐term effectiveness of these dams. This study investigates whether sand dams induce measurable surface elevation changes in their surroundings, using a 10‐year time series of Sentinel‐1 data analysed with the Small Baseline Subset interferometry approach. A sand‐dam‐bearing river in Makueni County, Kenya, was compared with a nearby control river without such structures. The time series revealed ground elevation changes ranging from −12.3 to +11.2 cm between 2015 and 2025. The study river exhibited a more homogeneous distribution of elevation changes and fewer extreme fluctuations than the control river, suggesting that sand dams moderate erosive dynamics. In the vicinity of 14 of 19 dams, positive elevation changes were detected, which are interpreted as localised sediment deposition. Particularly in mid‐course cascades, stabilising effects were evident, whereas some upper and lower course dams showed less consistent patterns, reflecting site‐specific differences in slope, soil type and sediment supply. The results indicate that sand dams act not only as water harvesting structures but also as sediment traps that contribute to soil stabilisation. However, the reliance on radar interferometry highlights methodological limitations, as erosive and depositional processes may cause signal decorrelation, and the absence of ground validation constrains direct interpretation. Future research should therefore integrate radar time‐series analysis with field‐based sediment and groundwater monitoring to better capture the coupled hydrological and geomorphological effects of sand dams.