Strategic placement of emergency check dams to reduce connectivity and mitigate post-fire soil erosion in South-Central Chile

This study assessed the spatial disposition of emergency check dams built in two small watersheds (N01 and N02) of 13 ha and 14 ha in south-central Chile as a post-fire management practice and to evaluate their impact on sediment connectivity and soil erosion control. A maintenance priority index (MPi) was used to assess the conditions of the structures after two years of their installation. Temporal variations in connectivity and soil erosion were mapped by means of the Index of Connectivity (IC) and Revised Universal Soil Loss Equation (RUSLE) model using high-resolution Digital Terrain Models (DTMs). Potential effects of emergency check dams on connectivity were assessed by comparing temporal changes in IC before and after installation between influenced and non-influenced areas, under the hypothesis that effective check dams produce significantly greater positive or negative variations in connectivity than areas without intervention. The positioning of the emergency check dams was assessed within the erosion-connectivity maps and considering the area contributing to each check dam. Finally, to assess spatial variations in delivery efficiency within each catchment, the Sediment Delivery Ratio (SDR) was computed at the outlet level, using gross erosion as the denominator following standard SDR methodology. The maintenance assessment showed that 47–67 % of the structures remained undamaged and fulfilled their primary role as emergency measures to trap sediment, soil, and organic matter during the initial post-fire period. However, these structures are unlikely to remain fully functional beyond two years without maintenance, due to overfilling. The effect of check dams on sediment connectivity was generally minimal at the watershed scale, yet detectable at the local scales, although not different from any other area not influenced by check dams. Many structures were placed in low–erosion, low–connectivity areas where sediment input is minimal. At the same time, the relatively low number of structures in high erosion–high connectivity (he-hc) zones highlight a valuable opportunity for improvement. These results emphasized the importance of adopting a data-driven strategy based on geomorphometric maps to plan and guarantee an efficient displacement of the emergency check dams. Finally, the SDR analysis showed values of 13.45 % and 18.57 % for the two watersheds, indicating a difference in sediment transfer efficiency, with outlet-level SDR values of 4.99 % and 10.91 % for N01 and N02 respectively.