Why is Unmanaged Stormwater Runoff a Problem?

Unmanaged stormwater runoff can cause excessive erosion, flooding, and contamination of lakes, rivers, and surface water supplies of drinking water.

Reduce Peak Runoff & Discharge with Permeable Pavers

Traditional site design has focused on estimating the peak runoff rate from large, but less frequent, extreme storm events (or how much stormwater runoff is leaving the site under worst case conditions) to ascertain if the receiving body, be it a river or stormwater collection system, can handle the anticipated flow.

Detention facilities are built to slow down the rate of runoff to levels the receiving body can handle, with the outflow from the pond being controlled by the diameter and number of outlet pipes; the discharge rate can be calculated using a standard orifice equation.
Runoff PICP System Outflow Graph
As shown previously, for full and partial infiltration systems, most outflow is eliminated from the PICP area until the system design is exceeded. However, where the native soils do not drain well a no infiltration system can be used.

No infiltration systems can also be used with an impervious liner for sites where infiltration could have adverse impacts such as over contaminated soils or soils with high swell potential. In this case, the PICP system functions more like a traditional detention system with the available storage volume provided by the voids in the aggregate base/subbase.

As the native subgrade soils are not exposed to moisture, there are no structural limitations on how long the water can be stored.
Reduce Peak Runoff Rate with Permeable Pavers at a Slope Diagram