AASHTO STANDING COMMITTEE ON RESEARCH
AMERICAN ASSOCIATION OF STATE HIGHWAY AND TRANSPORTATION OFFICIALS
Subcommittee on Design
Technical Committee on Hydrology and Hydraulics
Spring 2012
NCHRP Problem Statement Outline
I.
PROBLEM NUMBER
To be assigned by NCHRP staff.
II.
PROBLEM TITLE
Hydrology for Water Quality Analysis and Design
III.
RESEARCH PROBLEM STATEMENT
State, county, and other departments of transportation are increasingly subjected to water quality
requirements specifying reduction of stormwater flows and their associated pollutants from new and
existing roads. The United States Environmental Protection Agency (U.S. EPA) is engaged in national
rulemaking scheduled for completion by the end of 2012 to strengthen post-construction stormwater
rules with the objective of improving surface water quality. The proposed rulemaking may have a
significant impact on transportation agency stormwater programs by requiring changes in the objectives
and methods for managing stormwater on highways and other facilities or land owned by transportation
agencies.
Substantial work has been completed or is ongoing to characterize the constituents of stormwater
runoff for roadways and to evaluate the effectiveness of best management practices (BMPs). However,
little work has been completed justifying the hydrology tools needed to analyze the runoff from existing
and proposed roads and to design BMPs. This has resulted in the application of a variety of approaches,
many with questionable technical foundations.
Historically, hydrologic design has been concerned with estimating and managing large flows. These
techniques are based on identifying an appropriate design storm for a selected return period or annual
exceedance probability. In contrast, water quality analysis and design requires assessment of small
flows that may occur several times a year. One erroneous approach has been to attempt to extend the
exceedance probability concept to smaller flows. Other approaches have included data intensive
continuous simulation or identification of design storms that generate a prescribed amount of runoff,
for example 0.5 or 1.0 inches. The lack of good guidance for appropriate hydrologic techniques is
resulting in questionable implementation of BMPs that may waste money and may not comply with
water quality goals or regulations.
The objectives of this synthesis are to:
1. Catalog recommended hydrologic methods for water quality found in state and other agency
drainage design and stormwater manuals available online.
2. Catalog general stormwater quality requirements for the jurisdictions from which manuals have
been acquired and summarize proposed USEPA regulations as they affect highways.
3. Perform a literature search for international application of techniques for water quality
hydrology.
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4. Categorize and evaluate the identified techniques and methods based on the type of
methodology (e.g. design storm versus continuous simulation), technical foundation,
applicability, and other considerations.
5. Identify and interview representatives from 5 to 10 organizations that use broadly applicable,
appropriate, and effective techniques to gain further insight into the source of these techniques
and their experience with them.
6. Document the findings of this synthesis effort including recommendations for further research,
if needed.
IV.
LITERATURE SEARCH SUMMARY
Sources include recently completed or ongoing allied research efforts such as:
 NCHRP 25-31 “Guidelines for Evaluating and Selecting Modifications to Existing Roadway
Drainage Infrastructure to Improve Water Quality in Ultra-urban Areas.”
 “Evaluation and Updates of FHWA Pollutant Loadings Model for Highway Stormwater Runoff.”
(Joint project with USGS)
 NCHRP 20-68A (Scan 08-03). “Best Practices in Addressing NPDES and Other Water Quality
Issues in Highway Systems Management.”
 NCHRP 25-41 “Guidance for Achieving Volume Reduction of Highway Runoff in Urban Areas,”
Contractor selected in early 2012 with project completion 18 months later.
Other sources include:
 State, county, and other agency stormwater and water quality design manuals.
 EPA Stormwater rulemaking website http://cfpub.epa.gov/npdes/stormwater/rulemaking.cfm
 Proceedings from the conference “International Perspectives on Water Resources and the
Environment” to be held in Morocco in January 2012.
V.
ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD
$75,000
VI.
CONTACT
Andrea Hendrickson
State Hydraulic Engineer
MnDOT Bridge Office
3485 Hadley Avenue North
Oakdale, MN 55128
Office: 651-366-4466
Email: andrea.hendrickson@state.mn.us
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