Stormwater Source Control Design Guidelines 2005 - Waterbucket

Stormwater Source Control Design Guidelines 2005Design, Construction and Maintenance Process− Proposed Stormwater Source Controls - users mayselect from Absorbent Landscape, Infiltration Swale,Rain Garden, Infiltration Trench, Pervious Paving andGreen Roof, and input the size and generalcharacteristics of these practices.Output from the Water Balance Model includes:− Proportion of Annual Rainfall that is infiltrated,evaporated, or becomes surface runoff or drainflowfrom subdrains.− Hydrograph showing the annual runoff pattern.− Water level fluctuations within stormwater sourcecontrols.Limitations of the Water Balance Model include:− It is not yet calibrated with field test data.− Surface flow is not modelled within the WBM. That is,infiltration swales and rain gardens are assumed to beflat, so that surface ponding will remain up to theallowable depth that is input by the user, until suchtime as the surface pond can infiltrate. This couldresult in standing surface water for an unacceptablylong period in winter months in parts of the GVRD.Users should review the water level output, andconsider use of Source Controls with Reservoir (andperhaps Subdrain) if surface water ponding durationsare too high.− Groundwater flow is also not modelled in the WBM.Site conditions where groundwater flow or interflowenter the stormwater source control from upstream arenot considered. Designers should be aware that suchgroundwater flow may reduce the available infiltrationcapacity of a proposed stormwater source control.Greater Vancouver Sewerage & Drainage District99