A low-cost, and simple tool for sampling stormwater surface runoff using a Runoff Collection Unit (RCU)

An innovative, low-cost Runoff-Collection Unit (RCU) was developed to enable in-situ storm surface runoff sampling without disrupting natural sheet flow. Runoff from urban and agricultural lands are primary contributors to stream-water pollution, transporting nonpoint source (nps) pollutants and sediments. The device passively collects discrete runoff samples from target locations during storms, requires no power supply, and can be deployed simultaneously across landscapes to enable comparative analyses at low cost. Field validation was conducted in a Mediterranean agricultural watershed (Neve Ya’ar, Israel) to test its efficacy in evaluating best management practices. The trial evaluated the effectiveness of six species within vegetated buffer strip treatments in reducing total suspended solids (TSS) under natural rainfall. RCUs were installed at buffer influent (0 m) and 5 m downslope positions in 24 replicated plots. Across four winter storm events (n = 176 samples), mean TSS concentrations were significantly lower at 5 m compared to influent locations (p = 0.027), demonstrating measurable sediment retention within the first 5 m of vegetation (∼60%). A significant treatment × location interaction (p = 0.0087) indicated species-specific filtration performance. Barley (p = 0.024) and oat/vetch (p = 0.0015) treatments achieved statistically significant TSS reductions within 5 m. Over 80% of RCUs successfully filled during storm events, confirming reliable passive sampling. The RCU provides a robust tool for identifying runoff pollution hotspots, comparing best management practices, and supporting watershed-scale decision-making. By enabling simultaneous, event-based water quality sampling without expensive infrastructure, the RCU advances practical monitoring of agricultural and urban nps pollution.