The National Academies

NCHRP 25-12 [Completed]

Wet Detention Pond Design for Highway Runoff Pollution Control

  Project Data
Funds: $580,218 (Includes $180,218 from FHWA)
Research Agency: Washington State University
Principal Investigator: David Yonge
Effective Date: 4/15/1996
Completion Date: 2/2/2002
Comments: Report not published.

Background: Research has identified pollutants normally found in highway runoff. Among the sources of these pollutants are vehicles using the highway and land use adjacent to the highway. Regulations, both current and proposed, typically require some type of on-site storm water control to reduce the amount and concentration of potential pollutants from these sources in storm water runoff.

There is an assortment of best management practices (BMPs) that provide various degrees of contamination control as well as other environmental benefits in different highway settings. Currently, the most often recommended control systems are dry or wet detention ponds and vegetative strips. Vegetative strips have shown some effectiveness in decreasing the pollutants in storm water runoff, but existing land area and topography, particularly slope, do not always meet design requirements. Dry detention pond design has not proven satisfactory; ponds designed for large storms do not effectively treat runoff from small storms and those designed for small flows are subject to clogging. The use of wet detention ponds has proven effective to a limited degree.

However, wet detention ponds are one of the less documented pollutant control systems in highway settings. Although wet detention ponds have proven useful for reducing the amount and concentration of potential pollutants in some highway applications, they have exhibited widely varying degrees of efficiency.

Research is needed to quantify the effectiveness of wet detention ponds and to compare their performance to that of dry ponds; to update and verify design methodologies, especially in areas where right-of-way is limited; and to provide a reliable database for designing efficient, low-maintenance wet detention ponds in the highway environment. Wet ponds in this research project will be those having a permanent pool of water.

Objective: The objective of this research is to develop a methodology for designing efficient wet detention ponds in the highway environment. This methodology shall include performance characteristics, design guidelines, conditions, limitations, and applications for use. A comparison will be made between wet detention ponds and dry detention ponds in order to show the advantages and disadvantages of each system.

Tasks: To accomplish the project objective, the following phases and tasks are envisioned.

Phase I: (1) Critically review the published and unpublished literature to document the performance of detention pond systems in achieving reductions of pollutants found in highway runoff. Where available, document the capital and maintenance costs of wet ponds. Also identify methodologies available for designing wet detention ponds and describe their applicability for use in highway storm water runoff treatment. (2) Analyze the Task 1 data to correlate the varying effectiveness of wet detention ponds with methodology, design variables, and sampling program design, as they would apply to a highway setting and under highway regulations. Outline the strengths and deficiencies of wet detention ponds and compare to dry detention ponds. (3) Identify existing wet detention pond sites suitable for gathering additional performance data during Phase II. Specify the deficiencies in existing data that would be addressed by these field studies. (4) Prepare an interim report documenting Tasks 1 through 3 within 6 months. Include a detailed work plan for Phase II as an appendix to the interim report. The cost for Phase I shall not exceed $100,000.

Phase II: (5) Gather and analyze new data from selected test sites to compensate for the deficiencies identified in Phase I. (6) Evaluate existing methodologies with data gathered in this project and from the literature. Establish design guidelines and procedures for wet pond systems in a highway setting. (7) Submit a final report that documents the entire research effort and includes the Task 6 guidelines as a stand-alone document.

Status: Research is complete.

Product Availability: The unedited final report for NCHRP Project 25-12 as prepared by the University of Washington is available at https://onlinepubs.trb.org/onlinepubs/nchrp/docs/NCHRP25-12_FR.pdf .

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