Chapter 17.90
STORM AND SURFACE WATER MANAGEMENT
Sections:
17.90.030 Stormwater management plans.
17.90.040 General requirements.
17.90.050 Surface water conveyance standards.
17.90.060 Pollution reduction and flow control standards.
17.90.010 Purpose.
Detention of stormwater collected from impervious surfaces on a given property, or within the public right-of-way, is essential to the management of stormwater in Rogue River. This chapter includes standards for conveyance of surface water to streams, creeks and channels. It also addresses pollution reduction and flow control for stormwater generated from new development and redevelopment. For the purpose of this chapter, “new development” and “redevelopment” refer to any manmade change to improved or unimproved real estate including but not limited to the placement of buildings or other structures, dredging, filling, grading, or paving. [Ord. 23-418-O § 124 (Exh. A-4)].
17.90.020 Applicability.
No permit for construction of new development or tenant improvements that result in impervious cover greater than 500 square feet within the city and urban growth boundary shall be issued until effects on stormwater management are evaluated. The stormwater plan shall be reviewed by the public works director and city engineers. All additional fees for this review shall be paid by the applicant. The level of review varies according to the affected area:
A. Level 1: 500 to 1,999 square feet. No stormwater management measures beyond any mitigation measures for pollution reduction or flow control are required.
B. Level 2: 2,000 to 4,999 square feet. Conceptual plans that conform to the stormwater management best practices shall be submitted and approved.
C. Level 3: 5,000+ square feet. A stormwater management plan that conforms to the stormwater management manual shall be submitted and approved.
Areas smaller than 500 square feet may require review, and a greater level of review for properties between 500 and 4,999 square feet may be necessary when the site is identified as having especially sensitive conditions, including but not limited to wetlands and steep slopes.
Separate applicability thresholds for pollution reduction and flow control standards are listed in RRMC 17.90.040. Development projects shall not be phased or segmented in such a manner to avoid the requirements of these rules and regulations. [Ord. 23-418-O § 124 (Exh. A-4)].
17.90.030 Stormwater management plans.
A. Site plans shall include the following analyses and descriptions:
1. A description of stormwater mitigation strategies to increase infiltration and evapotranspiration (use of water by plants) and reduce the amount of stormwater runoff generated from the site.
2. Calculations of the amount of impervious surface before development and the amount of impervious surface after development. “Impervious surface” refers only to strictly impervious surfaces including roofs of buildings, impervious asphalt and concrete pavements, and other specifically impervious pavement materials such as mortared masonry and gravel.
3. An analysis of vegetative and other treatment methods used to reduce pollutants.
4. An analysis of flow reduction methods including infiltration and detention techniques.
5. Statement of consistency with city stormwater management objectives and/or requirements of a pollutant load reduction plan for a water quality limited stream.
B. Postconstruction plans shall include the following information:
1. As-built plans, stamped by a qualified professional, indicating all stormwater mitigation and management strategies are installed per approved plans and approved changes.
2. Maintenance plans for all stormwater treatment facilities installed to comply with this chapter. The maintenance program shall be subject to a recorded agreement with the city that outlines the stormwater treatment facility responsibilities of property owners and the city. [Ord. 23-418-O § 124 (Exh. A-4)].
17.90.040 General requirements.
A. All development shall be planned, designed, constructed and maintained to:
1. Provide a system by which storm/surface water within the development will be managed without causing damage or harm to the natural environment, or to property or persons.
2. Protect property from flood hazards.
B. Criteria.
1. Plans shall be submitted to the jurisdiction for review. If required by the city, all plans and calculations for areas 5,000 square feet or larger shall be stamped and signed by a qualified professional. Plan approval will be based on the criteria in this subsection.
2. Design, construction and maintenance of proposed stormwater management plan will result in postconstruction stormwater volumes flowing off site which are substantially the same as preconstruction volumes for all storms less than or equal to the water quality design storm.
3. All culvert installations must allow fish passage in accordance with Division of State Lands (DSL) and the U.S. Army Corps of Engineers (COE) and any other authorized federal, state, or local agency.
4. Installation of culverts, spans or stormwater outfalls along natural water features shall be designed to emphasize preservation of natural flow conditions, allow for natural obstructions and pursue stream enhancement opportunities.
5. Stormwater mitigation strategies, such as retention of existing trees, and use of porous paving surfaces, as well as stormwater treatment and flow control facilities used to meet the requirements of this code must be included in the plans.
6. Stormwater management plan shall be consistent with the city’s stormwater management plan and design manual.
7. In areas of high pollutant load, stormwater infiltration shall incorporate, or be preceded by, treatment as necessary to prevent siltation of the infiltration facility, protect groundwater, and prevent toxic accumulations of pollutants in the soil.
8. All vegetation used for the installation and landscaping of stormwater facilities shall be selected from an approved plant list. Planting schedule and maintenance of vegetation shall be approved by the city.
9. All storm conveyance pipes, vaults and stormwater infiltration, treatment and detention facilities shall be built to specifications of the city, as described in the stormwater management plan.
10. The plan shall demonstrate compliance with the surface water conveyance standards of RRMC 17.90.050.
11. The plan shall demonstrate compliance with the pollution reduction and flow control standards of RRMC 17.90.060.
C. The city reserves the right to restrict the use of infiltration facilities in high risk areas including those with steep slopes, unstable soils, high water tables, or sites known to be contaminated by hazardous substances.
1. Infiltration facilities which fall under the jurisdiction of DEQ’s underground injection control (UIC) program must be registered with the state and meet the requirements of the UIC program.
2. Bonds. Applicants shall provide a performance bond or similar surety acceptable to the city to assure successful installation and initial maintenance of surface pollution reduction and flow control facilities. During construction and for a period of two years thereafter, the bond shall be in favor of the city and in an amount of the anticipated construction cost.
3. Contingency for System Failure. If the storm drainage system fails due to lack of maintenance or breakage, and there are impacts to downstream water quality or quantity as a result of the failure, the city may perform the maintenance or repair and charge the owner of the facility. [Ord. 23-418-O § 124 (Exh. A-4)].
17.90.050 Surface water conveyance standards.
The following measures are designed to efficiently convey stormwater:
A. Culverts in and spans of streams, creeks, gulches and other natural drainage channels shall maintain a single channel conveyance system.
B. Culverts and/or spans are to be sized for the 24-hour post-developed tributary conditions of the 100-year storm.
C. Conveyance calculations shall use the following methods for analysis:
1. Projects smaller than 20 acres: the rational method, Santa Barbara Urban Hydrograph, SCS TR-55, HEC-1, or SWMM.
2. Projects 20 acres or larger: any of the methods except the rational method.
Exceptions must be documented and approved by the city.
D. Credit will not be given for in-stream and in-line detention.
E. It shall be the responsibility of the owner that the new drainage system shall not negatively impact any natural water conditions. The owner is responsible for providing a drainage system for all surface water, springs, and groundwater on site and for water entering the property as well as management of springs and groundwater that surface during construction. [Ord. 23-418-O § 124 (Exh. A-4)].
17.90.060 Pollution reduction and flow control standards.
A. Applicability.
1. Pollution reduction and flow control standards shall apply to all subdivisions or site plan applications creating greater than 500 square feet of impervious surface or redevelopment footprint area, unless eligible for an exemption or granted a waiver by the city. Additionally, these standards apply to land development activities that are smaller than the minimum applicability criteria if such activities are part of a larger common plan of development that meets the applicability criteria, even though multiple separate and distinct land development activities may take place at different times and at different schedules.
2. Waivers. The city at its discretion can waive in whole or in part minimum requirements for stormwater management; provided, that at least one of the following conditions applies:
a. It can be demonstrated that the proposed development is not likely to impair attainment of the objectives of this plan or the city’s stormwater management program.
b. Alternative minimum requirements for on-site management of stormwater discharges have been established in a stormwater management plan that has been approved by the city.
c. Provisions are made to manage stormwater by an off-site facility. The off-site facility is required to be in place, to be designed and adequately sized to provide a level of stormwater control that is equal to or greater than that which would be afforded by on-site practices and there is a legally obligated entity responsible for long-term operation and maintenance of the stormwater practice.
d. The city finds that meeting the minimum on-site management requirements is not feasible due to the nature or existing physical characteristics of a site.
e. Nonstructural practices will be used on the site that reduce the generation of stormwater from the site, the size and cost of stormwater storage and the pollutants generated at the site. These nonstructural practices are explained in detail in the current design manual and the amount of credit available for using such practices shall be determined by the city.
B. Infiltration, Treatment and Detention. Proper management of stormwater includes a combination of infiltration, treatment, and detention. This section establishes the review standards for each method.
1. Infiltration.
a. Infiltration systems are to infiltrate a minimum of one-half inch of rainfall in 24 hours.
b. Stormwater treatment, in accordance with subsection (B)(2) of this section, shall occur prior to or concurrent with infiltration.
c. Infiltration systems shall be designed to overflow to conveyance systems in accordance with subsection (D) of this section.
d. Infiltration may be waived, or reduced, if it can be demonstrated by a registered professional engineer that infiltration will destabilize the soil, cause structural problems, or provide negative impacts to the environment, or is due to site constraints such as high groundwater or soil contamination.
2. Treatment.
a. Water quality facilities shall be designed to capture and treat runoff for all flows up to the eightieth percentile storm event. In lieu of an adopted stormwater manual, use a two-year, 24-hour storm.
b. The water quality system shall use vegetation for treatment. Accepted types of vegetated treatment facilities and sizing criteria are described in the stormwater design manual. Alternative systems may be used with approval of the city engineer and shall be designed to provide equivalent treatment as is provided with a vegetated system.
c. Systems treating stormwater from over 5,000 square feet of impervious area and all systems that deviate from the sizing and design criteria in the stormwater design manual must be designed by a registered engineer and be approved by the city engineer.
3. Detention. On-site storm quantity detention facilities shall be designed to capture and detain runoff as follows:
a. Two-year, 24-hour, postdeveloped runoff rate to a two-year, 24-hour predeveloped discharge rate;
b. Sites with infiltration systems designed to handle storms in excess of that specified by subsection (B)(3)(a) of this section will be permitted to reduce on-site detention requirements by a volume equal to 100 percent of the excess infiltration capacity.
C. Combined stormwater infiltration, treatment and detention facilities receiving stormwater from impervious areas less than 5,000 square feet and designed in accordance with the sizing and construction standards contained in the stormwater master water design manual are presumed to comply with the infiltration, treatment and detention requirements of this code.
D. Conveyance. Infiltration, treatment and detention facilities shall be constructed to convey stormwater that exceeds their design capacity. Conveyance systems shall be sized to meet the following conditions:
1. Stormwater drain pipes draining less than 640 acres, 25-year, 24-hour design storm.
2. Stormwater drain pipes draining greater than 640 acres, 50-year, 24-hour design storm. [Ord. 23-418-O § 124 (Exh. A-4)].