| Stormwater Management Program |
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| Overview |
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Highways are one of the sources of polluted stormwater that degrade the quality of Oregon’s rivers, streams and lakes. The Oregon Department of Transportation, committed to a sustainable future for the state, is working to protect and improve Oregon’s water resources. ODOT, in collaboration with the Regulatory and Resource agencies, has developed tools, policies and procedures that will reduce the impact of state highways on water quality and hydrology.
This site contains the following information on ODOT’s Stormwater Management Program:
- Goals and Objectives
- Triggers for Stormwater Management on Highway Projects
- Contributing Impervious Area
- Water Quality Design Storm
- Flow Control Design Storm
- Treatment Techniques and Strategies
- Information on ODOT’s Stormwater Program and Initiatives
The ODOT Stormwater Management Program develops and provides guidance and technical support to planning, design, construction, and maintenance staff on water resources issues. The purpose of the program is to help ODOT enhance project delivery, achieve compliance with state and federal laws and regulations, and improve Oregon’s water quality.
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| Goals and Objectives |
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ODOT has set goals and objectives for projects that, when achieved, will contribute to the protection and improvement of the waters of the state. These goals and objectives are described in detail in Project Development Directive PD-05, and in ODOT Geo/Environmental Bulletin GE08-02b. Stormwater Management Program Technical Bulletin GE09-02 (B) (PD-05 is under revision to bring it into line with current expectations.)
The goals of ODOT’s stormwater management are:
- Meet State water quality standards, programs, and policies.
- Address stormwater from all contributing impervious surfaces associated with the project.
- Ensure the pollutant load discharged to waters of the state is not increased.
- Reduce the pollutant load discharged to waters of the state.
- Manage project hydrology, to prevent adverse changes to the receiving waters and channels.
The primary objectives which support the stormwater management goals are:
- Treat all highway runoff from a project’s
- Infiltrate treated highway runoff.
- Manage highway runoff to maintain the frequency and duration of discharge for the range of the Flow Control Design Storms(link below0
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| Triggers for Stormwater Management on Highway Projects |
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ODOT’s strategy is to progressively improve its stormwater treatment in conjunction with highway projects. The Resource agencies and ODOT have identified types of projects which require water quality treatment. Projects are to provide for the management of stormwater runoff when they either result in a change in the quantity or quality of the stormwater, or have a scope and scale such that it is reasonable to expect the project to address stormwater. Stormwater management is required for projects that contain one or more of the following elements:
- A change in the amount of impervious surface area
- A change in the Contributing Impervious Area
- A change in stormwater drainage (type of conveyance, location of conveyance, or location of outfalls)
- Replacement or enlargement of stream crossing structures (bridges or culverts)
- Complete reconstruction of the roadway (removing the pavement to base grade and replacing it)
- Clean Water Act Section 404 permit where the project actively involves impervious surface area
Projects that consist entirely of preservation, i.e. repaving, grindout and inlay, without adding any additional impervious surface area are not required to address stormwater. Neither are projects with tiny amounts of new impervious surface, such as bases for signs, light poles and the like. The same applies to maintenance activities consisting solely of such as cleaning out ditches and culverts. However, Project Teams and Maintenance crews are encouraged to take steps to improve water quality whenever a good opportunity arises, even when not required.
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| Criteria and Definitions |
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Contributing Impervious Area
Runoff from the Contributing Impervious Area (CIA) must be managed by the project. For ODOT, the CIA consists of all impervious surface within the strict project limits, plus impervious surface owned or operated by ODOT outside the project limits that drain to the project via direct flow or discrete conveyance.
ODOT is not responsible for treating stormwater from adjacent, non-ODOT properties.
Water Quality Design Storm
The Water Quality Design Storm defines the magnitude of the precipitation event that must be managed for water quality. Treatment facilities are to be designed to handle the volume and peak flow rate generated by the CIA during the Water Quality Design Storm.
Because Oregon’s climate varies across the state, each major climate zone has its own Water Quality Design Storm. The same percentage of the annual average precipitation is encompassed by the design storm for all the climate zones.
The water quality design storm is 50 percent of the cumulative rainfall from the 2-year, 24-hour storm for the project site, except as follows:
i. Climate Zone 4: 67 percent
ii. Climate Zone 5: 75 percent
iii. Climate Zone 9: 67 percent
A minimum storm size (0.7 inches during 24 hours) was selected to make sure that the “first flush” of high pollutant concentration is always captured. A maximum storm size has also been set, in recognition that the tail end of large storms usually have low pollutant concentrations and load.
A detailed discussion of the development and rational for the selection of the Water Quality Design storm is in the Water Quality Design Storm Evaluation and Guidance.
Flow Control Design Storms
Changes in hydrology caused by increases in impervious surface area can trigger damage to a stream’s form and processes. Projects can avoid this damage by managing the highway runoff to maintain the frequency and duration of the most geomorphically significant range of flows. For the purpose of managing highway runoff, these flows are correlated with a 24 hour storm event with the same frequency. The low end of the range of flows varies with the USGS Flood Frequency Zone. A detailed discussion of the selection of the Flow Control Design Storms can be found at in the Flow Control Guidance Files.
The criteria for flow control for channel protection is to maintain the duration and frequency of discharges from the project for flow resulting from the range of Flow Control Design Storms. The endpoints are:
Lower Discharge Endpoint
- Western OR - 42 percent of the 2-year, 24 hour event
- Southeast, Northeast, North Central Regions: 48 percent of the 2-year, 24 hour event
- Eastern Cascades Region: 56 percent of the 2-year, 24 hour event
Upper Discharge Endpoint
- Minimally incised streams - Channel bank overtopping event
- Incised Streams -10-year/24-hour storm event
Flow control is not necessary when:
- The receiving water is a large river, lake, reservoir or estuary
- The increase in discharge to surface waters is less than 0.5 cfs for the 10 year 24 hour storm
In addition to the flow control requirements for protection of stream channels, projects may be subject to requirements for flood control. Projects should be designed to meet all flow control and detention requirements.
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| Water Quality Treatment Techniques, Strategies and Tools |
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Preferred Best Management Practices
ODOT highway projects are expected to use water quality Best Management Practices (BMPs) that have been classified as “preferred” by ODOT and the resource and regulatory agencies. Only when project specific conditions preclude the use of a Preferred BMP are other BMPs acceptable. In those cases, the decision rational must be documented, and every effort made to assemble and implement a treatment train of equivalent effectiveness.
Preferred BMPs are those that have been judged to effectively treat highway runoff for a wide range of pollutants. The general categories of Preferred BMPs are:
- Infiltration Facilities
- Bioretention
- Bioslope
- Grass Swale with Soil Amendment
- Vegetated Filter Strip with Soil Amendment
- Constructed Wetlands
Design criteria for these and other, non-preferred BMPs can be found at: ftp://ftp.odot.state.or.us/techserv/Geo-Environmental/Hydraulics/Technical%20Bulletins/Stormwater%20Management%20Tech%20Bulletin/Attachment1_WQGuidance/
Chapter 14 of the ODOT Hydraulics Manual (forthcoming)).
The selection of BMPs that are the most appropriate for a project depends on a number of factors. Physical constraints, other protected resources, target pollutants, construction costs, ease and cost of maintenance, scope and scale of the project and its impacts all play a role. The BMP Selection Tool and Guidance is intended to assist designers and project teams in choosing water quality BMPs.
Low Impact Development
Low Impact Development (LID) is defined as “a decentralized source and treatment control strategy for stormwater management”
(NCHRP 2006: For ODOT’s highway projects, the definition has been refined further to “Stormwater management techniques implemented within the highway’s linear right-of-way that emphasize infiltration and filtration through vegetation and amended soil”. LID BMPs include most of the Preferred BMPs designed to fit into the linear right-of-way.
The use of LID techniques on highway projects has benefits beyond those for water quality:
- Can eliminate the need for hydraulically engineered treatment facilities on many projects,
- Can reduce the size of drainage and hydraulically engineered treatment facilities on many projects, and
- Can frequently reduce maintenance and construction costs compared to hydraulically engineered facilities.
- Supports streamlined permitting.
While LID is not always appropriate for highway projects, in many cases it is the most effective and least costly option available.
Planning for Stormwater Management
Incorporating planning for water quality and flow control from the beginning of project development is vital. The early identification of water resources issues and management opportunities gives a Project Team a great deal of flexibility in determining how to deal with stormwater, and supports regulatory streamlining.
The Project Development Timeline - Provides a graphic superimposing the stormwater management tasks and responsibilities on the PD-02 project development process.
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| ODOT Stormwater Initiatives |
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Stormwater management has increased in complexity and importance for ODOT, the Federal Highway Administration (FHWA), and the natural resource agencies. An increasing understanding of the deleterious effects of stormwater and a tightening regulatory environment, among other factors, have been met by ODOT with several stormwater specific initiatives. These include:
- The Stormwater Action Team (SWAT)
- ODOT-DEQ Streamlining of Stormwater Management Plan (SWMP) Approvals for CWA Section 401 Water Quality Certification
- ODOT Hydraulics Manual Chapter 14 (Water Quality) development
- Asset Management: Inventory of ODOT owned engineered water quality BMPs, and development of Operations and Maintenance Manuals.
- Water quality focused monitoring and research
Stormwater Action Team
The SWAT is the focus of ODOT’s and the Resource and Regulatory agencies efforts to develop a consistent program for management of highway runoff In May 2006, ODOT, FHWA, and the natural resource agencies embarked on a collaborative venture to promote improved management of stormwater, to ensure that all parties are in alignment on permitting requirements and to enhance streamlined permitting. The natural resource agencies involved were the National Marine Fisheries Service (NMFS), Oregon Department of Environmental Quality (DEQ), the U.S. Fish and Wildlife Service (USFWS), the U.S. Environmental Protection Agency (EPA), and the Oregon Department of Fish and Wildlife (ODFW).
A comprehensive literature review was used to inform and direct the development of the technical guidance. Discipline experts were also consulted during the development of the water quality and flow control (water quantity) design storm definitions. The final selections of the design storms and elements of the BMP Selection Tool and User’s Guide and BMP Summary Reports were consensus decisions by ODOT, FHWA, and the natural resource agencies. The products of the SWAT are used in both the Stormwater Management Plan Approval Streamlining and in the ODOT Hydraulics Manual.
Stormwater Management Plan Approval Streamlining
Highway projects that require Clean Water Act Section 404 permits need to receive CWA Section 401 Water Quality Certification from the Oregon DEQ. Approval of the project’s Stormwater Management Plan (SWMP) is usually a condition of the 401 Certification. Streamlining the SWMP approval process was seen by both ODOT and DEQ as a way to reduce permitting delays, provide consistency in expectations and ensure water quality standards were met by projects. The original MOA was signed in 2007(?), and a revision is being developed to take into account the efforts and products of the SWAT.
ODOT Hydraulics Manual
The Water Quality Chapter of the ODOT Hydraulics Manual provides the design criteria for a wide range of water quality treatment facilities, including those than can be used in a LID context. The chapter is in final development, and will include guidance and specifications for water quality soil amendments. In the mean time, the draft chapter can be viewed at: ftp://ftp.odot.state.or.us/techserv/Geo-Environmental/Hydraulics/Technical%20Bulletins/Stormwater%20Management%20Tech%20Bulletin/Attachment1_WQGuidance/
Because new treatment techniques are being developed it is not possible for the Hydraulics manual to contain them all. New BMPs or modification of the design of ones in the manual are accommodated by the Hydraulic Design Deviation Process.
New types of BMPs proposed for projects are subject to a higher level of review within ODOT. This ensures that there is enough supporting information on treatment effectiveness, that the design criteria are well thought out, and that the BMP can be monitored and evaluated for future inclusion in the Hydraulics Manual.
Asset Management of Water Quality Facilities
ODOT began installing engineered water quality treatment facilities in the mid 1970’s. In the mid 1990’s the pace of construction picked up and by now has over 150 engineered BMPs on the ground and counting. (Engineered BMPs are those that require a hydraulic analysis to support the size and design of the facility.) In 2007 ODOT commissioned an inventory of the facilities as part of an effort to make sure that maintenance obligations and requirements are being met. Maintaining the database of engineered BMPs is an ongoing effort.
Not included in the inventory are the innumerable non-engineered elements of the highway system that contribute to improving the quality of highway runoff. Among these are vegetated shoulders and side slopes, vegetated flat bottomed roadside ditches, and sediment traps to capture sanding material on mountain highways.
Water Quality Focused Monitoring and Research
Ongoing improvement of water quality management of highway runoff depends on information about runoff and treatment techniques. Over the years ODOT has funded several research projects associated with water quality. ODOT has one current water quality research project examining copper speciation in highway runoff. Reports on completed projects can be accessed at the ODOT Research Unit Website.
ODOT is conducting a characterization study of highway runoff quality at three sites: I-5 in Portland, Highway 26 at Wemme and Highway 20 in Bend. This will provide updated information on runoff in high traffic urban areas, and new information on runoff from low-medium traffic highways and from central Oregon (dry side) urban traffic.
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