About this metric

standing water

Standing water is water held by impervious surfaces like asphalt and cement, but also green roofs, bioswales, and cisterns/rain barrels. There is a limit to how much water these kinds of surfaces / features can hold, which we measure with a parameter called the impervious water storage capacity. We estimate the impervious water storage capacity on an area-weighted basis for the impervious surfaces associated with the different ecosystem types within the vision. We assume that at the beginning of the precipitation event the impervious surfaces are filled according to the "proportion of impervious water storage filled- initial conditions" parameter. The difference between the impervious water storage capacity and the current amount of water held is called the impervious water storage deficit. During a precipitation event, the amount of surface inputs (from precipitation and outdoor water use) is compared to the impervious water storage deficit. If the deficit is larger, all the surface water hitting the impervious surface is captured and there is no surface runoff. If the surface inputs are larger than the deficit, then the impervious surfaces fill with water to their capacity, and any excess water runs off becoming stormwater.

Impervious water storage capacity = area of impervious surface * average impervious water storage capacity

Impervious water deficit = impervious water storage capacity * (1 - proportion of impervious surface filled- initial condidtions)

Depends upon:

—Parameters: impervious storage capacity, proportion of impervious surface and proportion of impervious water storage filled - initial conditions

—Other metrics: ecosystem area

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