Heejun Chang

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Urban runoff -- Mathematical models, Hydrologic models, Urban runoff -- Management


Stormwater runoff quality is affected by a multitude of factors including surrounding land characteristics, human activities, and antecedent precipitation amounts. We explore how seasonal and variable precipitation affect E. Coli, total suspended solids, nitrogen-nitrate, orthophosphate, lead, and zinc concentrations in Portland, OR, USA. Correlation analysis was conducted between the pollutant concentrations and antecedent rainfall each sample site received for the previous 1, 3, 5, 7, and 30 days from when the sample was taken. We ran Mann-Whitney tests to determine if the levels of the pollutants were statistically different between the wet season and the dry season. We found that the nutrients nitrate and orthophosphate saw the most instances where there were statistically significant different levels of their concentrations in the wet season versus the dry season. Additionally, we found that the heavy metals demonstrated the most statistically significant correlations with up to 7 days of antecedent precipitation. For lead, we see that as the surrounding land percent imperviousness increases there is less association of lead concentration explained by antecedent precipitation. Further exploration is needed to understand the relationship between antecedent precipitation and pollutant concentration with respect to how the surrounding level of urbanization affects them. Understanding how pollutant concentrations respond temporally to these events can give city officials insights into how to adjust stormwater management systems to best treat stormwater runoff coming from urban regions.

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