Sediment and Nutrient Yield from Residential Construction Sites

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Abstract
Runoff from three residential construction site watersheds in southeastern Wisconsin was monitored for a 2‐year period. Automatic water quality monitoring equipment was established which sampled each event proportional to flow. Loading rates for sediment and nutrients were developed on an event basis and summed to produce annual loads.Concentrations for suspended solids (SS), organic plus exchangeable N [(Or + Ex)‐N], and total P preceded and paralleled the flow rate during runoff events. With the exception of nitrate plus nitrite nitrogen (NO3 + NO2)‐N, the soluble water quality parameters were independent of flow. Commonly, the (NO3 + NO2)‐N concentration was 1.0 mg/liter and varied inversely proportional to flow. The most common concentrations of dissolved phosphorus and ammonium were 0.05 and 0.10 mg/liter, respectively.Average sediment yield for the three single land use watersheds was 19.2 metric tons /ha per year. Concentrations of 60,000 mg/liter SS were observed for major events; 15,000 to 20,000 mg/liter were common for moderate events. Regression analyses of several independent variables identified flow (Q) as the single most important variable examined for explaining sediment load. Considered in combination, the product of flow and flow rate (Qqp) best explained sediment yield (r2 = 0.62).Yields of contaminants from residential construction sites are inherently variable and site dependent. Strict extrapolation or comparison of results to other areas or existing literature values is difficult. However, when compared to runoff data from a simultaneous agricultural watershed investigation, the yield of contaminants from construction sites is considerably higher (19.2 vs. <1 metric ton/ha per year of sediment).

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