Porous Pavements. By Michael Drennan, P.E. Weston Solutions, Inc.

Transcription

1 Porous Pavements By Michael Drennan, P.E. Weston Solutions, Inc.

2 Overview What are porous pavements? Why are they used? Types of porous pavements. Applications of porous pavements and site constraints. Benefits of porous pavements. Obstacles to porous pavements.

3 What are porous pavements? Porous pavements are a method of infiltrating stormwater runoff into the ground while simultaneously providing a stable load-bearing surface.

4 Why is Porous Pavement Used? Urban development significantly increases the imperviousness of a watershed. Imperviousness consists of two primary components: Rooftops Transportation system Transportation-related imperviousness composes approximately 70 percent of total impervious cover.

5 Why is Porous Pavement Used? Rainfall is a valuable resource that falls out of the sky for free. Los Angeles and San Gabriel Rivers Watershed = ~1600 square miles. Average rainfall = 12 inches. Annual volume of rainfall = 1,024,000 acre-feet. Value of water in Los Angeles County = $332/af. Value of rainfall in LA/SG Watershed = $340 billion. (LA County DPW currently recharges 220,000 af of stormwater each year.) Porous pavement can help increase the amount of stormwater recharged into groundwater and reduce the amount of rainfall that is lost in runoff.

6 Why is Porous Pavement Used? Increased imperviousness causes three environmental problems: Increased stormwater runoff resulting in increased flood peak flows. Increased stormwater pollutant discharge to creeks and oceans. Reduced infiltration of stormwater into the underlying groundwater aquifer.local regulations and policies are beginning to encourage the use of porous pavements to address these environmental problems.

7 Why is Porous Pavement Used? City of Santa Monica Stormwater Ordinance» Requires 20 percent reduction in runoff from predevelopment. Encourages porous pavements. City of Los Angeles Guide to Stormwater Pollution Control.» Encourages porous pavements. County of Los Angeles Standard Urban Stormwater Mitigation Plans.» Requires a minimum ratio of pervious to impervious; encourages porous pavements.

8 Types of porous pavements? Four main categories of porous pavements 1) Pervious concrete and porous asphalt. 2) Unit pavers. 3) Grass paving systems. 4) Granular materials.

9 Pervious concrete Portland cement pervious pavement. Most commonly used in Florida where it was developed in the 1970s. Also used in several European countries. Primary reason for its use is to provide a superior driving surface during wet weather conditions. Results are better traction, and reduced hydroplaning.

10 Open-graded asphalt concrete Created by using no fine aggregate in the mix. The resulting concrete mixture is characterized as having approximately 16 percent voids as opposed to conventional asphalt concrete which has 3 to 5 percent voids.

11 Chapter 600 of the Caltrans Design Manual provides the standard specification for the materials and construction of opengraded asphalt concrete. Caltrans has specified open graded asphalt concrete throughout Los Angeles County including the on-ramps and off ramps to the 118 Freeway. Industrial Asphalt Company is the largest asphalt supplier with 21 plants in Southern California. They have supplied much of the OGAC for Caltrans. Call Terry Prentiss at 626/ or 800/

12 Where most people normally look Conventional Pavement Highway 118 Freeway on ramp. Porous Pavement

13 Typical cross section of porous pavement installation.

14 Unit Pavers

15 CONCRETE INTERLOCKING PAVING STONES ANGELUS BLOCK COMPANY Sun Valley, CA /

16 PERMA CONCRETE INTERLOCKING PAVERS TURFSTONES FOR PLANTABLE DRIVING SURFACES Day Street Moreno Valley CA /

17 Grass Paving Systems

18 ORANGE BOWL STADIUM, MIAMI FLORIDA GrassPave2 Invisible Structures, Inc. Aurora, CO /

19 GEOBLOCK POROUS PAVING SYSTEM PRESTO PRODUCTS COMPANY Geosystems Products Appleton, WI 800/

20 GrassPave2 Invisible Structures, Inc. Aurora, CO /

21 Applications of Porous Pavements Parking lots Roads and freeways Fire lanes Courtyards, patios Playgrounds (depending on type of use)

22 Applications of Porous Pavements - Site Constraints Use in areas where there is low traffic, such as fire lanes, overflow parking lots, parking stalls, courtyards, patios, etc. Don t use in areas of high groundwater or clay soils. Don t use in areas where potential for significant fuel and/or oil spills. (Fuels can cause premature degradation.) Parking Lots - Use porous asphalt in parking stalls, minimize use in high traffic areas. Install behind tire blocks, grade site to drain towards porous areas. Consider thicker layer in areas of high traffic. Roads - Use on roads where direction of traffic is primarily one direction. (Shear stresses from tire turning can cause degradation.) Playgrounds - Evaluate the activity in the playground. Rougher surface may not be acceptable for certain activities.

23 Benefits of Porous Pavement Allows stormwater to recharge underlying groundwater aquifer. Reduces stormwater pollutant discharge to creeks and ocean. Reduces flood peak flows and volumes. High capability to remove both soluble and fine particulate pollutants in urban runoff.

24 Benefits of Porous Pavement (continued) When properly designed and carefully installed, porous pavement has load bearing strength, longevity, and maintenance requirement similar to conventional pavement. Reduction or elimination of the need for curb and gutters, and storm drains. Preservation of the natural water balance at the site. Safer driving surface which offers better skid resistance, and reduced hydroplaning.

25 Obstacles to Porous Pavement Site-specific data required for design. soil type bedrock groundwater characteristics Special care needed during construction. Special maintenance may be helpful. Limited applications. Slightly higher initial cost. (Although may be offset by reduced costs of storm drains, curbs and gutters.) Initial resistance from the traditional engineering and regulatory community.

26 Porous Pavements - Conclusions Benefits to installing porous pavements in many instances. Costs of porous pavements comparable to conventional pavements, and savings are created as a result of additional benefits. Addressing the single-most significant watershed impact: imperviousness. Helping to accomplish three significant environmental objectives.

27 Porous Pavement - Conclusions Allows stormwater to recharge underlying groundwater aquifer. Reduces stormwater pollutant discharge to creeks and ocean. Reduces flood peak flows and volumes.

28 Porous Pavements By Michael Drennan, P.E. Weston Solutions, Inc