The Construction of Check Dams on the Loess Plateau Has Prolonged Water Transmission Times and Altered Recharge Relationships

Background: As a key structure for gully control on the Loess Plateau, check dams are designed to intercept sediment and reduce flood peaks without intentional water storage. However, persistent ponding zones have often formed upstream of dams in the Niejia River Basin, exceeding their intended functionality. Methods: This study examines the basin using hydrogen and oxygen stable isotopes to trace hydrological processes. Based on 251 water samples, mixing models and exponential fitting were applied to quantify water sources and transmission times. Results: Results show that precipitation (47.07%) and groundwater (34.48%) are the main sources of channel water. Check dams extended water transmission time in dammed tributaries to 489 days—2.8 times longer than in undammed ones. Conclusions: This delay enhances watershed storage capacity, providing insight into the hydrological impacts of check dams on the Loess Plateau.