Hydrology for Water Quality Analysis and Design

Focus Area

Water Quality/Wetlands


Natural Resources







Research Idea Scope

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. Most water quality requirements apply to small storm events rather than large flood flow events. Roadway designers lack the tools necessary for the hydrologic design of water quality facilities because most of hydrologic design tools currently available are crude adaptations of methods used for flood flows. To insure that state DOTs are spending their water quality dollars effectively and that water quality is being effectively protected it is necessary to understand what tools are currently available and their known limitations. The outcome of this synthesis is to gain that understanding, which would provide an immediate expansion of the design toolbox for many states and provide the basis for future research. 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 squander valuable resources while not achieving compliance with water quality goals or regulations.

Urgency and Payoff

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. 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.

Suggested By

Becky Humphreys AFB65 6143871125

[email protected]