Abstract:
Understanding hydrologic connectivity is essential for managing ephemeral headwater streams where upstream land use influences downstream aquatic habitats. This study relies on a field-based approach to evaluate how precipitation and roads affect runoff generation in low-order ephemeral streams of the U.S. Virgin Islands. Logistic regression analyses show that runoff delivery from unroaded catchments agrees with a water storage conceptual model typical for subsurface storm and saturation overland flow-dominated settings. Without roads, runoff occurs only about 4 times per year in response to 10 and 78 mm of storm rainfall, depending on antecedent precipitation. In contrast, maximum 15-min rainfall intensities are a better predictor of runoff generation on unpaved roads than are total rainfall and antecedent conditions. Intensities surpassing ~10 mm/hr lead to road runoff, and this occurs about 40 times per year. Road-influenced streams represent an intermediate setting for which runoff generation depends on storm and antecedent rainfall, as well as the road surface area captured by drains and flow path distance. In our focus area, roads can provoke streams to deliver runoff to coral bearing waters 10 to 13 times every year as a response to 9.3- to 50-mm storms, depending on antecedent rainfall and road drain characteristics. These results highlight the sensitivity of road connectivity to specific road drain characteristics and display the potential for connectivity as a guiding watershed restoration principle.
