Tyler C. Ladd and Dr. Robert Traver, Villanova University

Evaluation of a Porous Concrete BMP: The Hydrologic Perspective

Funding and Acknowledgments: Funding for this project was provided by the Pennsylvania Department of Environmental Protection and Villanova University. Special thanks to Dr. Andrea Welker, Clay Emerson, Michael Kwiatkowski, Matthew Prokop, and Matthew Rea for their help and support.

AbstractThere is an increasing concern about the environmental impacts of urbanization. Impervious coverage such as rooftops and roadways are replacing wooded natural areas. Impervious cover prevents infiltration and creates excess runoff from storms by not allowing rainfall to come in contact with the natural soil. It is this infiltration that replenishes the groundwater which in turn provides baseflow for streams. Impervious systems like gutters and storm sewers channel rain water directly to streams and rivers. While paved areas decrease baseflow, they increase flood flows causing erosion and sedimentation downstream. Innovative stormwater management practices are being developed to help mitigate these problems. Best Management Practices (BMPs) are techniques that can be both aesthetically pleasing and cost effective with the purpose of protecting and improving water resources.

IntroductionThe focus of this study is to evaluate the effectiveness of a Porous Concrete BMP from a water quantity standpoint. In the summer of 2002, the common area between two dormitories, which was formerly an asphalt paved area, was reconstructed and outfitted with three infiltration beds overlain with porous concrete. The site is designed to collect stormwater from the surrounding buildings and grass areas. The runoff is then diverted to three infiltration beds. The site is instrumented to record rainfall, soil moisture levels, and the amount of water leaving the site. A computer model of the site was created using HEC-HMS, a hydrologic model developed by the Army Corps of Engineers. The effectiveness of the BMP is a measure of its ability to infiltrate runoff. The site will be monitored for long-term performance. The results of this study will hopefully encourage the implementation of these BMPs.

Pre-Construction

Research Objectives- To determine the percent of annual rainfall infiltrated by the BMP

- To compare pre-construction functionality with new design functionality

- To monitor the effects of antecedent dry days on infiltration

- To create a computer model to predict the effects of future storms

- To monitor long-term site effectiveness

March 20, 2003 Storm – 1.81 inches

March 26, 2003 Storm – 0.32 inches

March 28, 2003 Storm – 0.59 inches

Preliminary Model Results:

V-Notch Weir in Stormdrain used for measuring site outflow

Instrumentation

Water Content Reflectometers used for measuring soil moisture content

Moisture Fronts vs. Rainfall

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A11 W ater Content Reflectom eter - O ne Foot Down

A12 W ater Content Reflectom eter - Two Feet Down

A13 W ater Content Reflectom eter - Four Feet Down

Rainfall

Weir Outflow vs. Rainfall

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57652.15 ft2Total Drainage Area

5998.21 ft2Pervious Area Draining to Upper Infiltration Bed

17149.57 ft2Impervious Area Draining to Upper Infiltration Bed

13656.55 ft2Pervious Area Draining to Middle Infiltration Bed

15707.74 ft2Impervious Area Draining to Middle Infiltration Bed

5140.08 ft2Impervious Area Draining to Lower Infiltration Bed

57652.15 ft2Total Drainage Area

5998.21 ft2Pervious Area Draining to Upper Infiltration Bed

17149.57 ft2Impervious Area Draining to Upper Infiltration Bed

13656.55 ft2Pervious Area Draining to Middle Infiltration Bed

15707.74 ft2Impervious Area Draining to Middle Infiltration Bed

5140.08 ft2Impervious Area Draining to Lower Infiltration Bed

Areas Draining to Infiltration Beds

Post-Construction

Porous Concrete in action Porous Concrete (foreground) during a rain storm

Losses - 0 .33 inches

U pper Bed Infiltra tion - 0 .12 inches M iddle Bed In filtra tion - 0 .1 inches

Low er Bed Infiltra tion - 0 .04 inches

O bserved O utflow - 0 .01 inches

Losses - 0 .65 inches

U pper Bed Infiltra tion - 0 .51 inches

M iddle Bed Infiltration - 0.51 inchesLow er Bed Infiltra tion - 0 .15 inches

O bserved O utflow - 0 .05 inches

Conclusions-The BMP appears to be extremely efficient at infiltrating stormwater

-The BMP is exceeding hydrologic design expectations

-More storms required for better model calibration

-The BMP can effectively handle storms with 2 inches of precipitation

Losses - 0.21 inches

U pper Bed Infiltra tion - 0 .05 inchesM iddle Bed Infiltra tion - 0 .05 inches

Lower Bed Infiltra tion - 0 .01 inchesO bserved O utflow - 0 .00 inches