Stormwater and Grading Design Standards
Stormwater management is a key element in maintaining and enhancing livability within the City of Oregon City (City). There is a direct link between stormwater runoff and the City’s surface and ground water quality and quantity. As land is developed, creation of new impervious surfaces and loss of vegetation increases stormwater runoff during rainfall events, altering the natural hydrologic cycle. Without stormwater management, the increase in flows erodes stream channels and limits groundwater recharge. In addition, runoff that flows over roadways, parking areas, rooftops, and other impervious surfaces collects pollutants that are transported within the watershed to streams, rivers, and groundwater resources. Properly managing stormwater is vital to protecting our water resources for a great number of uses, including fish and wildlife habitat, recreation, and drinking water.
Updates to the City’s stormwater management standards, set forth in OCMC 13.12, were adopted by Ordinance No. 15-1006 and became effective August 18, 2015. The Stormwater and Grading Design Standards, emphasize low-impact development (LID) practices, source controls for higher pollutant generating activities, erosion prevention and sediment controls, and operation and maintenance practices designed to properly manage stormwater runoff and protect our water resources. Each of these measures have been or are being implemented as direct requirements under the City’s existing NPDES MS4 permit.
The goal of these updated standards is to provide local engineers, developers, builders, and City staff clear guidance in planning and designing stormwater conveyance and management systems that are appropriate to the local climate, hydrogeology, and geology. These standards apply to public and private projects throughout the City.
Some stormwater LID techniques approved for use by property owners who live in Oregon City include:
- Porous Pavement – Typically a walkable or drivable hard surface that looks similar to a traditional finish but allows water to infiltrate through the surface and into the underlying soil or drainage media.
- Green Roof – A Green Roof is a lightweight vegetated roof system consisting of waterproofing material, a growing medium, and specially selected plants.
- Flow through planter – A planter with an under drain system which is piped downstream. The planter holds some water but acts more like a filter.
- Infiltration planters – Like a flow through planter minus the under drain. Infiltration planters need well drained soils.
- Swales – Typically a long, narrow, gently sloping, landscaped depression that collects and conveys stormwater runoff. Usually swales include specially selected plants.
- Rain gardens – Similar to a swale but larger with more specially selected plants.
- Vegetated filter strips - Gently sloped areas designed to accept sheet (heavy water) flow. Filter strips are usually covered with grasses and groundcovers.
With the approval of these techniques, property owners can reduce the amount of impervious surface on their property, they can retain rainwater close to where it falls, and they can mimic natural drainage (filter) systems.