Low Impact Development in Western Oregon: A Practical Guide for Watershed Health
Why use this template?
This document will help your jurisdiction address MS4 and TMDL regulatory requirements for water quality during the “post-construction” phase. Once you adapt this to your jurisdiction, the resulting document will be one component of meeting your post-construction stormwater management goals.
- Was reviewed in detail by Oregon DEQ staff, has the support of EPA Region 10 to be used to help meet TMDL and MS4 Phase I and Phase II water quality regulations and aligns with National Marine Fisheries Service programmatic Biological Opinion stormwater requirements for federal permits.
- Will save time and money. Developing a manual template that multiple jurisdictions can use will eliminate inefficiencies and save costs incurred when each city or county attempts to develop a manual from scratch.
- Can be tailored to any city in Western Oregon. Eliminates problems caused when jurisdictions simply refer to the City of Portland manual, which may be inappropriate for their climate or geology and too complex for their needs.
- Allows you to pick and choose from an array of best management practices that most closely meet your development and community needs.
- Provides greater watershed health by focusing on runoff prevention and reduction techniques, not just treating water and sending it downstream.
- Helps maintain clean, more abundant water.
- Lowers the cost of practices appropriate for natural conditions and stakeholders.
- Helps prevent flooding and reduces the cost of associated damage.
- Lowers installation and maintenance cost of streets, curbs, gutters and other infrastructure.
- Improves the aesthetics of neighborhoods.
- Reduces costs associated with long-term maintenance and replacement.
The problem of stormwater runoff and water quality
Oregonians depend on clean water for drinking, agriculture, industry and recreation. Stormwater runoff, the portion of rainfall that flows over the land, carries a variety of pollutants from roofs, sidewalks, driveways, roads, and landscapes to downstream waterways. Without managing stormwater runoff, pollutants from land surfaces in our communities will continue to pollute our waterways.
In undeveloped areas, very little rainwater or snowmelt runs off the land like it does in cities. Trees, plants and soil capture much of the precipitation, and some of it evaporates back into the air. Most of the precipitation that doesn’t evaporate or get captured by vegetation soaks into the ground where soil and microbes remove pollutants naturally. The water slowly recharges streams, wetlands and groundwater. Very little runs off, except in very large storms.
This natural hydrologic cycle is radically changed when land is developed in the way it has been for most of the last century: vegetation is removed, soils are compacted and hard surfaces such as roads, parking lots and rooftops are created. Even landscaped areas can generate unnaturally high runoff volumes. Storm drains are installed to get water out of the way as quickly as possible by sending it into local streams or injecting it underground without treatment. Development dramatically increases runoff volumes that, even when controlled by detention basins, causes flooding, damages fish and wildlife habitat, and delivers urban pollutants such as oils and pesticides to local waterways. Decreased infiltration means that less cool, clean groundwater is recharged into streams during dry summer months.
LID addresses this problem
LID reduces runoff volumes and improves the water quality of any stormwater that does still run off. Runoff is captured close to where it falls, and plants, soil and microbes infiltrate, evapotranspire, and treat runoff, restoring natural function within the city. Whereas a forest acts like a green sponge soaking up water, a city acts like a grey funnel, conveying polluted runoff. Low impact development reintroduces and/or protects spongy pockets of green within the city to mimic natural hydrology and protect water quality.
The technical advisory committee
This guidance was developed with an interdisciplinary technical advisory committee of private industry and public agency staff with expertise in engineering, landscape architecture and design, horticulture, wetland science, wildlife biology, GIS, riparian restoration, erosion control, urban forestry, and stormwater regulation and implementation. This technical advisory committee guided the content of the document from beginning to end, contributing their expertise and deciding the level of appropriate detail needed for a variety of audiences to adequately implement LID. Each section and standard was reviewed and discussed by members of the technical advisory committee for completeness and correctness. A final completeness review was performed of the entire document.
Adapting this template to create an LID-focused Post-Construction Stormwater Manual for your jurisdiction, in combination with any needed conventional stormwater treatment methodologies, satisfies DEQ’s TMDL program Guidance for Including Post-Construction Elements in TMDL Implementation Plans.