Stormwater Detention Pond Water Temperature Data Collection and Interpretation

This report summarizes a field study that was conducted for the MPCA to collect the data necessary to support the formulation and validation of a temperature simulation model for urban stormwater detention ponds. The urban stormwater detention pond simulation model is included in the MINUHET (MINnesota Urban HEat Transfer) model that computes (simulates) runoff temperatures for typical residential and commercial watersheds. The model simulates single rainfall events or continuous periods of several months. The simulated runoff temperatures and volumes are used to estimate the heat loading from urban surface runoff to coldwater streams. To support these simulations, weather data and urban runoff temperature data had to be collected to serve as model inputs and to validate model outputs. In this report, a subset of the data collection effort is summarized. This report deals with stormwater detention ponds. The study was conducted in 2005 and 2006. Before a pond was chosen for detailed study, it was necessary to obtain an overview of typical stormwater detention ponds in an urban area. Eighteen stormwater detention ponds in Bloomington and Woodbury in the Twin Cities Metropolitan Area were documented, and are described in this report. Then a pond was selected for detailed instrumentation and data collection. That pond was on the former property of the State Farm Insurance Company Headquarters, near I94 and Radio Drive in Woodbury. The pond is a wet pond with an outflow structure and one major stormsewer inflow from two parking lots and the roof. Instrumentation was installed to measure and record weather data, temperature stratification data in the pond, surface inflow and outflow data, pavement temperature and pavement runoff temperature data. In support of another study on the fate of road salt in the Twin Cities area, additional data were collected to document salinity profiles in urban stormwater detention ponds. These data are also presented in this report.