Stormwater & Grading Design Standards

Stormwater management is a key element in maintaining and enhancing livability within Oregon City. There is a direct link between stormwater runoff and the Oregon City's surface and groundwater 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 Oregon City Municipal Code (OCMC) 13.12, were adopted by Ordinance 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 National Pollutant Discharge Elimination System (NPDES) Municipal Separate Storm Sewer System (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 Oregon 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 or ecoroof is a lightweight vegetated roof system consisting of waterproofing material, a growing medium, and specially selected plants.
• Filtration planters: 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 draining soils.
• Swales: Gently sloping, landscaped depression that collects and conveys stormwater runoff.
• Rain gardens: Similar to planters but does not have vertical walls and is completely constructed by grading the earth.

These techniques mimic natural drainage systems by keeping rainwater close to where it falls and attenuate stormwater runoff.