Hydrothermal Simulation of a Stormwater Detention Pond or Infiltration Basin

Abstract

A numerical simulation model has been developed to simulate the hydraulic and heat transfer properties of a stormwater detention pond. The model is dynamic (unsteady) and based on basic principles of hydraulics and heat transfer. It is driven by hourly climate and weather data. To calibrate and validate the pond model field data were collected on a commercial site (State Farm Insurance Company) in Woodbury, Minnesota. The relationship between pond inflow and outflow rates to precipitation was effectively calibrated using continuously recorded pond level. Algorithms developed for surface heat transfer in lakes were found to be applicable to the pond with some modification. A significant diurnal thermal stratification was simulated and measured in the pond which had 2.4m depth. Temperature differences from top to bottom were as high as 13oC during daytime hours. The outflowing water temperature was essentially equal to the pond surface temperature because the outlet was located near the pond surface. Outflow water temperatures were calculated with a RMSE of 1.4oC. Water clarity had little effect on the pond outflow temperatures but the pond bottom temperature was found to be highly sensitive to water clarity. For pond designs with outlet structures that take subsurface water, water clarity will introduce uncertainty to simulations of the pond temperature profile and the pond outlet temperature. Further work is required to consider other pond designs with alternate outlet structures, significant shading, and wind sheltering. Surface shading should include consideration of terrestrial vegetation (trees), emergent, submerged, and floating leaf aquatic vegetation, Algae need to be included in the water clarity. Wet ponds with subsurface outlet withdrawal and high surface shading from emergent or floating leaf plants may yield significantly lower outlet temperatures than typical wet pond designs.