Rainfall event-based surface runoff and erosion in small watersheds under dairy and direct-seeding grain production

A 3-year study on erosion and streamflow was conducted in two adjacent paired watersheds that flow into the Passo Real reservoir, one of the largest and most important reservoirs for human water supply and power generation in southern Brazil. The watersheds have similar land use and soil management, but different size and riparian vegetation. The first objective of the study was to monitor and evaluate hydrosedimentological dynamics and effects of riparian vegetation, over a range of rain events, in the two watersheds; the second was to assess the ability of the Limburg Soil Erosion Model (LISEM) to represent these small watersheds in hydrosedimentological terms (runoff and erosion) under individual rain events, in the context of better understanding the role of riparian vegetation and land cover. LISEM is a hydrological model structured on physically based equations that can be used for planning and conservation purposes. Studied rainfall events between 2016 and 2018 had a wide range in total rainfall (10-170 mm), rainfall intensity in 1 h (3-66 mm h(-1)), stream peak flows (4-5741 L s(-1)), runoff volume (0.02-40 mm), runoff coefficient (0.1-32%), maximum suspended sediment concentration (20-19 611 mg L-1), and sediment yield (0.002-33.790 Mg km(-2)). Both watersheds showed a rapid response to rain events with significant runoff generation. Abundance of unpaved roads (often parallel to the slope) promoted high runoff due to channelization effects. South Watershed has 59% more riparian vegetation than North Watershed, but this greater riparian vegetation was not effective in reducing surface runoff and erosion. Furthermore, local adoption of no-tillage was insufficient to control runoff and sediment yield.