Stormwater Projects
The Estuary Partnership secured funding to work with Oregon City, Oregon and Longview, Washington on projects designed to help each city better address stormwater management issues in their local codes and ordinances. Each project had multiple components.
Impervious Surface Mapping
Alternative Development Schemes
Pollutant Loading Analysis
Presentations
Code Analysis and Recommendations
Impervious surfaces such as buildings, roads, parking lots, and sidewalks prevent rain from soaking into the ground There is less vegetation to soak up, store and evaporate water. As a result, stormwater runoff over the land surface greatly increases, even during small rainstorms. Generally, watersheds that have higher levels of impervious surfaces are more likely to have degraded water quality.
To help each city understand its level of imperviousness, a two part series of impervious surface maps was developed for each city. One tracks current impervious surfaces. A second map projected future impervious surfaces based on similar development patters. Each map in the series can be linked below.
OR City Map 1
OR City Map 2
Longview Map 1
Longview Map 2
As part of the Longview project, a series of alternative development schemes were created for three, unbuilt but platted sites. Each scheme aimed at illustrating alternative approaches to stormwater management that emphasized on-site infiltration rather than traditional methods. Each scheme was developed with the following principals in mind:
- Minimize amount of stormwater generated by minimizing effective impervious surface area
- Slow down the runoff or disconnect runoff from immediately entering the storm drainage system by retaining and/or infiltrating it at the site
- Remove pollutants by routing runoff through vegetated areas before discharging to storm system
- Protect the habitat in the most important places, such as buffers along streams
Hard Rock Estates
A steep site in the hills of Longview with 22 lots along 36-ft wide cul-de-sac roadway. The alternative development scheme maintains the same number of lots while incorporating features such as a narrower roadway, bio-swales, dry wells, and shared driveways.
Village at Mt. Solo
An extremely flat site with a high water table and an existing network of drainageways, the existing subdivision plat showed 97 lots and a network or roads. The alternative development scheme maintained the number of dwelling units while significantly enlarging set backs from the drainageways, routing runoff through vegetated swales, and reducing street size and other imperviousness.
Mint Farm
An industrial park complete with roads and facilities but a variety of lots available for large scale projects, the Mint Farm is in a very flat area with a high water table and surrounding ditches listed as water quality limited. The alternative development scenario presents a depicts the on-site stormwater practices that could be utilized in an industrial setting on a large warehouse building. They include an ecoroof, permeable pavers in the parking area, bio-swales, and infiltration swales.
Longview City Hall
To examine the stormwater management possibilities available within a retrofit, the project developed an alternative stormwater management plan for Longivew’s City Hall that incorporated an ecoroof and other features.
In Longview, pollutant loading analyses were conducted to quantify the impact of impervious surfaces on water quality in the City of Longview. The analyses included the following studies: pollutant loads for current impervious surface conditions, pollutant loads based on estimated future conditions, as well as pollutant loading estimates for each alternative development scheme that compared estimated pollutant loads from conventionally and low impact developed areas. The analysis quantified the pollutant loading reductions associated with the low impact, alternative development schemes.
Within each city, a number of presentations on the link between land use, impervious surface, and water quality were given to the City Council, Planning Commission and city staff. Additionally, in Oregon City, approximately 13 presentations were given to Oregon City Neighborhood Associations. Neighborhood Association presentations also included information on home owner best management practices with regard to stormwater and what individuals could do to lesson their stormwater impacts.
The Estuary Partnership received grants from the Oregon Department of Environmental Quality and the Environmental Protection Agency to help fund the projects. Parametrix, a local consulting firm, assisted with many of the project’s technical aspects. Many projects components were based on the nationally renowned NEMO (NonPoint Education for Municipal Officials) Project based at the University of Connecticut.
The project evaluated relevant codes in Longview and Oregon City for how well they protected water quality. Applicable codes were evaluated and rated against a set of water quality criteria developed for the project and identified as adequately addressed, need improvement, or not addressed. When codes did not address water quality, specific code language was proposed to enhance the code’s ability to protect water quality. In addition to providing specific code language, the code recommendations provided a rational for the code recommendation and a code example from another jurisdiction. The recommendations were organized in five sections: parking areas, streets/driveways/rights of way, commercial/industrial development, residential development, and natural resources.
A code recommendation example from Oregon City follows:
Parking Lot Drainage
Current Code Language
Drainage shall be designed in accordance with the requirements of Chapter 13.12 and the city Public Works Stormwater and Grading Design Standards.
Recommended Code Language
Parking lot design and construction must provide for on-site surface water management in accordance with the requirements of Chapter 13.12 and the city Public Works Stormwater and Grading Design Standards. Unless otherwise approved due to slope or soil conditions, grading and curb design shall be used to direct stormwater runoff into vegetated swales, artificial wetlands, tree wells, or other landscape features that will maximize on-site infiltration and processing.
Rationale
Most parking lots direct water toward traditional storm drains designed to remove water from parking areas as quickly as possible. Such traditional approaches contribute to nonpoint source pollution and other water quality problems. Parking lot runoff is often contaminated with auto related pollutants and of a higher temperature than receiving waters.
Specific references to landscaping techniques for water quality treatment facilities are included in Oregon City’s Stormwater Grading and Design Standards. However, the city could do more to encourage natural on-site processing of stormwater through landscape features designed to slow and filter polluted runoff and encourage groundwater recharge. In many cases simply removing or modifying the protective curbing around vegetation islands, depressing the plantings, and using appropriate plants, would result in numerous water quality benefits – including reduced stormwater flows, increased groundwater recharge, and more pollution attenuation. Parking lot infiltration trenches are a common stormwater management practice throughout the Metro area. Infiltration trenches are often more aesthetically pleasing than traditional landscaping elements, require little or no irrigation since they utilize native plants, and can be easily incorporated within traditional parking lot designs or layouts. In some cases, infiltration trenches and other parking lot infiltration strategies may be more costly to engineer, plan and construct and may require more maintenance. They also may not be sufficient to avoid the use of detention ponds, oil-water separation systems, and other traditional engineering methods in certain sites.
Locally, the City of Portland in their Stormwater Manual encourages project applicants to consider parking lot drainage in a variety of ways.
Other Code Examples
From City of Portland, Bureau of Environmental Services Stormwater Manual, 1.6.2. Parking Lot Considerations.
- Design the grading to direct stormwater runoff into landscaped areas. Maximize sheet flow opportunities and, if possible, direct the run off away from high traffic areas towards less used areas of the lot before the runoff drains into the landscaped area.
- Provide numerous curb cuts (one every 10 feet) or use tire stops or other means to protect the landscape areas to allow maximum dispersal of the flows.
- Depress the soil area in landscape areas to allow runoff to enter. See the landscape swale detail in Chapter 4 for proposed cross-section at point where runoff flows into landscape.
- To maximize dispersal of runoff, consider design elements such as berms or manufactured trench drains.
- When possible, situate buildings or fill areas on the high elevations of the site.
- Make certain design includes overflow and appropriate disposal methods per all plumbing and building code requirements.
From City of Olympia Code: Design standards – General. Parking Surfaces.
- All parking lots must be paved and designed to meet drainage requirements. Pervious surfaces (e.g., turf block) or other approved dust free surfaces may be used for parking areas held in reserve for future use, overflow parking (parking area furthest from building entrance), or parking areas approved by the Site Plan Review Committee. A maintenance agreement may be required to ensure such surface is properly maintained.
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