Clackamas Stormwater laws & regulations
Clackamas County has jurisdiction over areas within CCSD#1, SWMACC, and jurisdictional areas with post construction program oversight by the Clackamas County Department of Transportation and Development. Clackamas County regulations are compliant with the National Pollutant Discharge Elimination System (NPDES) through municipal regulation Clackamas County Code 1006.06. The county's portion of the Clackamas County Group Municipal Separate Storm Sewer System (MS4) requires Clackamas to administer and enforce compliance with stormwater discharge permits in an effort to decrease stormwater pollutants and increase overall water quality. The Department of Water Quality Services has been given authority in administering Clackamas’s stormwater program. Clackamas County requires all privately owned storm drain structures to be inspected annually and submit the report electronically to Water Quality Services.
EXCERPT- Clackamas County Zoning and Development Ordinance, May 2018
1006 UTILITIES, STREET LIGHTS, WATER SUPPLY, SEWAGE DISPOSAL, SURFACE WATER MANAGEMENT, AND EROSION CONTROL
1006.06 SURFACE WATER MANAGEMENT AND EROSION CONTROL
The following surface water management and erosion control standards apply:
A. Positive drainage and adequate conveyance of surface water shall be provided from roofs, footings, foundations, and other impervious or near-impervious surfaces to an appropriate discharge point.
B. The requirements of the surface water management regulatory authority apply. If the County is the surface water management regulatory authority, the surface water management requirements of the Clackamas County Roadway Standards (Chapter 4) apply.
C. Approval of a development shall be granted only if the applicant provides a preliminary statement of feasibility from the surface water management regulatory authority. The statement shall verify that adequate surface water management, treatment and conveyance is available to serve the development or can be made available through improvements completed by the developer or the system owner.
1. The surface water management regulatory authority may require a preliminary surface water management plan and report, natural resource assessment, and buffer analysis prior to signing the preliminary statement of feasibility.
2. The statement shall be dated no more than one year prior to the date a complete land use application is filed and need not reserve surface water treatment and conveyance system capacity for the development.
D. Development shall be planned, designed, constructed, and maintained to:
1. Protect and preserve existing natural drainage channels to the maximum practicable extent;
2. Protect development from flood hazards;
3. Provide a system by which water within the development will be controlled without causing damage or harm to the natural environment, or to property or persons within the drainage basin;
4. Ensure that waters drained from the development are substantially free of pollutants, including sedimentary materials, through such construction and drainage techniques as sedimentation ponds, reseeding, and phasing of grading; and
5. Ensure that waters are drained from the development in such a manner that will not cause erosion to any greater extent than would occur in the absence of development.
E. Where culverts cannot provide sufficient capacity without significant environmental degradation, the County may require the watercourse to be bridged or spanned.
F. If a development, or any part thereof, is traversed by any watercourse, channel, stream, creek, gulch, or other natural drainage channel, adequate easements for surface water management purposes shall be provided to the surface water management regulatory authority.
G. Channel obstructions are not allowed, except as approved for the creation of detention, retention, or hydropower facilities approved under this Ordinance. Fences with swing gates may be utilized.
H. The natural drainage pattern shall not be substantially altered at the periphery of the subject property. Greatly accelerated release of stored water is prohibited. Flow shall not be diverted to lands that have not previously encountered overland flow from the same upland source unless adjacent downstream owners agree.
I. A surface water management and erosion control plan is required for significant residential, commercial, industrial, and institutional development. The plan shall include:
1. The methods to be used to minimize the amount of runoff siltation and pollution created from the development both during and after construction; and
2. Other elements required by the surface water management authority.
EXCERPT-Stormwater Standards, July 2013
Section 5 – Stormwater Management Plan
5.1 PLAN REVIEW REQUIREMENT THRESHOLDS
5.1.1 Stormwater Management Plan ≥ 5,000 sqft of Impervious Area
All development that results in 5,000 square feet or more of new impervious surface and/or a modification of existing impervious surfaces is subject to these Standards including: stormwater management, natural resource protection, and erosion control requirements.
5.1.2 Stormwater Management Plan ≤ 5,000 sqft of Impervious Area
All development that results in less than 5,000 square feet of new impervious surface and/or a modification of existing impervious surfaces which is not being phased or segmented in such a manner to avoid the requirements of these Standards is required to meet all provisions herein, including Section 4 – Natural Resources and Vegetated Buffers. All development per Section 5.1.2 that results in less than 5,000 square feet are exempted from the following Sections:
a) Section 5.3 - Stormwater Water Quality Treatment Standards;
b) Section 5.4 - Stormwater Infiltration Standards;
c) Section 5.5 - Stormwater Quantity / Flow Control Standards.
5.1.3 Erosion Control Plan and NPDES 1200-C Permits
Within the boundaries of the District, any grading or soil disturbance associated with a development activity which disturbs 800 square feet or greater is required to obtain an Erosion Control permit from the District. For erosion control requirements see Section 6 of these Standards.
Any development activity in unincorporated Clackamas County not governed by a local authority will be required to obtain a National Pollutant Discharge Elimination System (NPDES) 1200-C Permit for any grading or soil disturbance associated with a development activity which disturbs 1 acre or greater area. The District has an agreement with DEQ to serve as the Agent of DEQ for these permits in the unincorporated area of Clackamas County. This includes plan review, permitting, inspection and enforcement of NPDES 1200-C permit requirements.
5.3 STORMWATER INFILTRATION STANDARDS
Infiltration systems are required for all new developments and redevelopments to infiltrate all runoff from storm events up to one-half inch of rainfall in 24 hours. Treatment shall occur prior to or concurrent with infiltration systems in accordance with Section 5.2. Infiltration system capacity may be incorporated into the detention system design, in order to reduce the required detention volume with appropriate professional on-site infiltration rate testing. Infiltration facilities shall be sized to infiltrate the design runoff volume within a maximum of 96 hours for the one-half inch requirement and 36 hours for the detention requirement.
Infiltration requirements may be waived, or reduced, if it can be demonstrated by a registered professional engineer that infiltration will destabilize the soil, cause adverse structural or environmental impacts, or due to site constraints such as high groundwater, springs, or impermeable soils.