An at-grade stabilization structure impact on runoff and suspended sediment

Abstract

Abstract:In recent years, agricultural runoff has received more attention as a major contributor to surface water pollution. This is especially true for the unglaciated area of Wisconsin, given this area's steep topography, which makes it highly susceptible to runoff and soil loss. We evaluated the ability of an at-grade stabilization structure (AGSS), designed as a conservation practice to reduce the amount of overland runoff and suspended sediment transported to the surface waters of an agricultural watershed. Eight years of storm and baseflow data collected by the US Geological Survey-Wisconsin Water Science Center on a farm in west central Wisconsin were analyzed for changes in precipitation, storm runoff volume, and suspended sediment concentration before and after installation of an AGSS. The agricultural research site was designed as a paired watershed study in which monitoring stations were installed on the perennial streams draining both control and treatment watersheds. Linear mixed effects model analyses were conducted to determine if any statistically significant changes occurred in the water quality parameters before and after the AGSS was installed. Results indicated no significant changes (p = 0.51) in average event precipitation and runoff volumes before and after installation of the AGSS in either the treatment (NW) or control (SW) watersheds. However, the AGSS did significantly reduce the average suspended sediment concentration in the event runoff water (p = 0.02) in the NW from 972 to 263 mg L -1 . In addition, particle size analyses, using light diffraction techniques, were conducted on soil samples taken from within the AGSS and adjacent valley and ridge top to determine if suspended sediments were being retained within the structure. Statistical analysis revealed a significantly (p < 0.001) larger proportion of clay inside the AGSS (37%) than outside (30%). These results indicate that the AGSS was successful in reducing the amount of suspended sediment transported to nearby surface waters. The cost of an AGSS can range from US$3,500 to US$8,000, depending on size. Thus, these structures provide a cheap and effective means of improving water quality in highly erosive landscapes.

At-grade stabilization structure impact on surface water quality of an agricultural watershed

“…1) and were the same watersheds studied in Minks et al (2012). The NW is approximately 174 ha, of which 58% is woodland (101 ha), 42% is cropland and pasture (73 ha).…”

“…The USGS-WWSC used linear regressions of runoff volumes, suspended solids, TKN, TP, and total dissolved P loadings where one watershed was the dependent variable (south watershed) and the other was the independent variable (north watershed). They reported the r 2 values as ranging from 0.64 to 0.96, and intercepts and slopes as being significant (P < 0.05) (Minks et al, 2012). Thus, it was assumed that the two watersheds are similar with respect to nutrient and runoff.…”

“…An at-grade stabilization structure (AGSS) can be effective in reducing the amount of suspended sediment being transported to surface waters of the DA (Minks et al, 2012). These structures consist of a large embankment that is designed to retain storm runoff long enough for transported sediments to settle (Fig.…”

“…As previously noted, it has been shown by Minks et al (2012) that AGSS can be used to reduce suspended sediment transport to surface waters, but the impact of this structure on nutrient loading has not been evaluated. Thus, we hypothesized that the same AGSS installed by Minks et al (2012) will reduce the concentration of P and N movement into nearby surface waters. To achieve this objective, a collaborative project was established between the University of Wisconsin Discovery Farms Program and the US Geological Survey (USGS) Wisconsin Water Science Center (WWSC).…”

“…The two watersheds are adjacent to each other, with one being actively farmed with row crops and the other being used primarily for hay/pasture or enrolled in the Conservation Reserve Program (CRP) (Minks, 2010). Minks et al (2012) reported data on basin paring and showed that the two basins were similar. They noted that USGS-WWSC used data from 12 storm events occurring from 1 October 2001 to 4 October 2002 to show that the two basins had similar hydrologic behavior.…”