Stormwater Design: Quantity Control

Case 1 - Existing Imperviousness Is Less Than or Equal To 50%:
  • Prevent the post-development peak discharge rate and quantity from exceeding the pre-development values for the one- and two-year 24-hour design storms.
OR
  • Protect receiving stream channels from excessive erosion by protection and quantity control strategies.
Case 2 - Existing Imperviousness Is Greater Than 50%:
  • Achieve a 25% decrease in the volume of stormwater runoff from the two-year 24-hour design storm.
Rating Systems and Code Applicable Products/Systems
LEED NC LEED S LEED CS LEED H LEED R LEED ND CHPS CALGreen
SSc6.1
1 Pt.

PC 16 **		 SSc6.1
1 Pt.

PC 16 **		 SSc6.1
1 Pt.

PC 16 **		 SSc6.1
1 Pt.		 SSc6.1
1 Pt.

PC 16 **		 GIBc8
1-4 Pts.		 SS3.1
1 Pt.		 A4.106.4 *

A5.106.2.1

A5.106.3
Direct support of technical goals.
  • Substantial water storage capability
  • Reduces runoff to zero for typical storms
  • Functions as infiltration trenches but with vehicular or pedestrian surfaces
  • PICP are aesthetically superior to any other pervious pavement material, finely finished, and allowing creative design flexibility

Permeable interlocking concrete pavement (PICP) is a type of pervious pavement that can meet both cases. A typical design consists of pavers with openings that allow for infiltration. Small, open-graded crushed stone is used in openings and bedding layer, with various open-graded aggregates used in the base and sub-base. Geotextiles may be used for filtering or containment.

The pervious surface and base structures create typical water storage capacity 30% to 40% of the total volume of the base and sub-base. This water is allowed to infiltrate into the soil usually within 24 to 36 hours. Water that does not infiltrate can be filtered through the base and drained through perforated pipes in the sub-base.

The ICPI manual on permeable pavement notes that the long-term conservative pavement surface infiltration rate is approximately 3 in. /hour (210 l/sec/ha).

This rate will easily accommodate 2-year, 24-hour rainfall intensities given sufficient base storage and soil infiltration. Permeable interlocking concrete pavements can reduce runoff to zero for the most frequent storms.



PICP can maximize the percentage of pervious surface area by combining parking with runoff detention and by utilizing grid pavements for auxiliary parking and fire access lanes.

For illustrations of the basic permeable pavement designs, see Permeable Paver Systems

* CALGreen A4.106.4 Water permeable surfaces. A non-performanced-based residential voluntary measure for permeable paving in parking, walking, and patio surfaces: Tier 1, minimum 20% of total, Tier 2, minimum 30% of total. Primary driveways or walkways, and disabled access routes are excluded.

** LEED Pilot Credit 16: Rainwater Management. This pilot credit is based on SSc6.1 and SSc6.2, but it is intended to encourage natural best practices instead of structural practices. It is focused on restoring or maintaining the natural hydrology and water balance of the site by managing runoff on-site.

Green Credits & Strategies : Stormwater Design: Quantity