Where the total contributing drainage area of the pavement (A<sub>c</sub>) and total depth of clear stone aggregate needed for load bearing capacity are known (i.e., storage reservoir depth is fixed) or if available space is constrained in the vertical dimension due to water table or bedrock elevation, the footprint area of the water storage reservoir, A<sub>r</sub> can be calculated as follows:<br>
+
Where the total contributing drainage area of the pavement (A<sub>c</sub>) and total depth of clear stone aggregate needed for load bearing capacity are known (i.e., storage reservoir depth is fixed) or if available space is constrained in the vertical dimension due to water table or bedrock elevation, the minimum footprint area of the water storage reservoir, A<sub>r</sub> can be calculated as follows:<br>
Then adjust A<sub>p</sub> accordingly to keep R, the ratio of impervious contributing drainage area to water storage reservoir (i.e., permeable pavement) area, between 0 and 2 to reduce hydraulic loading and avoid premature clogging.