Chapter 15.10


15.10.010    Purpose.

15.10.020    Construction – Intent – Definitions.

15.10.030    Storm and surface water utility authority.

15.10.040    Studies and basin plans.

15.10.050    Capital improvement and planning program.

15.10.060    Maintenance of drainage facilities.

15.10.070    Storm and surface water rates.

15.10.080    Liability.

15.10.010 Purpose.

The purpose of this chapter is to separate the existing storm and surface water utility function from the combined sewer utility and to provide for the planning, design, construction, use, inspection and maintenance of the storm water systems; to minimize flooding; and to provide for an effective system for the control and prevention of storm water runoff and water quality problems. This chapter supplements other city regulations regarding protection of the storm and surface water system, including the storm water management program, Chapter 15.09 MICC, and the interim critical area regulations. (Ord. 17C-09 § 2; Ord. 95C-127 § 2).

15.10.020 Construction – Intent – Definitions.

A. This chapter is enacted as an exercise of the police power of the city of Mercer Island to protect and preserve the public health, safety and welfare and its provisions shall be construed accordingly. The obligation of compliance with storm water regulations is upon the owner or operator of each private system, until such time as the city accepts the private system into the city drainage network under the provisions of this chapter. Nothing contained in this chapter is intended to be or shall be construed to create or form the basis of liability on the part of the city of Mercer Island, this utility, its officers, employees or agents, for any injury or damage resulting from the failure of the owner or operator of any private system to comply with the provisions of this chapter, or by reason or in consequence of any act or omission in connection with the implementation or enforcement of this chapter by the city of Mercer Island, its utility, officers, employees or agents.

B. For purposes of this chapter, the following definitions shall apply:


“City or public storm water system” means those elements of the storm and surface water system of the city that are located on property owned by the city or in the public right-of-way, or are located on property on which the city has an easement, license or the right of use for utility purposes.


“Low impact development” or “LID” means a storm water and land use management strategy that strives to mimic predisturbance hydrologic processes of infiltration, filtration, storage, evaporation, and transpiration by emphasizing conservation, use of on-site natural features, site planning, and distributed storm water management practices that are integrated into a project design.

“Low impact development best management practices” or “LID BMPs” means distributed storm water management practices, integrated into a project design, that emphasize predisturbance hydrologic processes of infiltration, filtration, storage, evaporation and transpiration. LID BMPs include, but are not limited to, bioretention, rain gardens, permeable pavements, roof downspout controls, dispersion, soil quality and depth, vegetated roofs, minimum excavation foundations, and water reuse.


“On-site storm water management BMPs” are synonymous with LID BMPs.


“Private system or private storm water facility” means any element of the storm and surface water system which is not part of the public storm water system as defined in this chapter.


“Storm and surface water system” means the entire system within the city, both public and private, naturally existing and manmade, for the drainage, conveyance, detention, treatment and storage of storm and surface waters.

“Storm water treatment and flow control BMPs/facilities” means detention facilities, treatment BMPs/facilities, bioretention, vegetated roofs, and permeable pavements that help meet Minimum Requirement No. 6 (Runoff Treatment), Minimum Requirement No. 7 (Flow Control), or both.


“Utility” means the storm and surface water utility of the city of Mercer Island. (Ord. 17C-09 § 2; Ord. 95C-127 § 2).

15.10.030 Storm and surface water utility authority.

The storm and surface water utility shall have the authority, by and through the city manager or his/her designee, to plan and implement storm and surface water programs and improvements in the areas described below, and to take such other actions as are deemed necessary and are consistent with the intent of this chapter to control and manage storm water runoff and water quality. The utility shall have the authority to determine the priorities for working on each of the programs, based on utility funds available and a determination of which programs require primary attention to protect the public health, safety and welfare:

A. Develop, adopt and carry out procedures to implement this chapter, including the collection and spending of revenue for operations, maintenance and capital improvements. Fund capital project planning, administration, and public education functions of utility. Incur debt and pay debt service for utility functions.

B. Prepare engineering standards to establish minimum requirements for the design and construction of storm water facilities and their maintenance, consistent with the standards established in Chapter 15.09 MICC.

C. Administer and enforce procedures relating to the planning, acquisition, design, construction and inspection of storm water facilities.

D. Enter into any contract for the construction of storm water facilities with owners of real estate and to accept the facilities as municipal storm water facilities, with the right to recover costs and expenses, pursuant to Chapter 35.91 RCW.

E. Accept, reject, or take other appropriate action with regard to easements offered to the utility or city.

F. Prepare and enforce standards for the maintenance of storm water facilities, including retrofit measures, consistent with the standards in Chapter 15.09 MICC.

G. Develop a program for inspection of private storm water facilities, consistent with the standards in Chapter 15.09 MICC.

H. Advise commissions, the city council, city manager and other city departments on matters relating to the utility.

I. Prepare comprehensive drainage plans for individual drainage basins for adoption by the city council.

J. Establish and implement programs to protect and maintain water quality and to control the duration of storm water flows.

K. Perform or direct the performance of financial review and analysis of the utility’s revenues, expenses, indebtedness, rates and accounting, and recommend budgets, rates, and financial policy for adoption by the city council.

L. Conduct public education programs related to protection and enhancement of storm water and surface water and the municipal storm water system. (Ord. 17C-09 § 2; Ord. 95C-127 § 2).

15.10.040 Studies and basin plans.

The utility may conduct studies and may develop basin plans for adoption by the city council. Basin plans shall be developed according to the engineering standards in Chapter 15.09 MICC. Once a basin plan has been adopted and implemented, it may be modified as authorized by Chapter 15.09 MICC; provided the basin plan and basin-specific policies and requirements provide an equal or greater level of water quality and runoff-control protection. (Ord. 17C-09 § 2; Ord. 95C-127 § 2).

15.10.050 Capital improvement and planning program.

A. The city manager or his/her designee shall develop a six-year capital improvement and planning program for improvements to or modifications of the public storm water system, including the incorporation or extension of storm water systems and facilities and the acceptance of drainage easements and private drainage facilities.

B. The city manager or his/her designee shall provide the proposed six-year capital improvement and planning program to the city council prior to the adoption of the biennial budget.

C. The city manager or his/her designee shall provide to the city council a draft of storm and surface water rules and regulations on inspection and maintenance, basin planning, and acceptance of private systems for review and comment prior to adoption by the city manager or his/her designee of the rules and regulations. (Ord. 17C-09 § 2; Ord. 95C-127 § 2).

15.10.060 Maintenance of drainage facilities.

A. The utility is responsible for maintaining public storm water systems and facilities.

B. Owners of private storm water systems and facilities, including but not limited to on-site storm water management (low impact development) BMPs, flow control (detention) facilities, treatment facilities and conveyance systems, are responsible for their operation and maintenance.

C. In new subdivisions and short plats, maintenance responsibility for private drainage facilities shall be specified on the face of the subdivision or short plat.

D. If a private drainage facility serves multiple lots, then maintenance responsibility rests with the properties served by the facility, unless there is a legal document placing responsibility on some other entity. (Ord. 17C-09 § 2; Ord. 95C-127 § 2).

15.10.070 Storm and surface water rates.

A. General. The city council shall establish by resolution service rates for use of the storm water system and related drainage services; such rates are in addition to connection charges and fees for specific services. The city may establish classifications of customers or service and rate structures, using any method or methods authorized by law.

B. Rate Basis. Drainage rates shall be based on revenue requirements to cover all costs of the utility, as authorized by the city council by the adoption of the biennial budget and subsequent amendments.

C. Rate Adjustments. The sufficiency of rates shall be evaluated periodically as part of the review and adoption of the annual budget. Rate adjustments shall be recommended as needed to meet revenue requirements. The recommendation shall consider equity, adequacy, costs and other factors allowed by law.

D. Billing and Collection. The utility shall develop and implement procedures and systems pertaining to the billing and collection of drainage service charges and fees in accordance with state law, and shall provide an appeal process for the review of utility bills.

E. Rate Relief. The city council may establish drainage rate relief measures for specific customer classes as authorized by law. (Ord. 17C-09 § 2; Ord. 95C-127 § 2).

15.10.080 Liability.

The city manager, his/her designee, or any other employee charged with the enforcement of this chapter, acting for the utility in good faith and without malice in the discharge of his/her duties shall not be liable personally for any damages which may accrue to persons or property as a result of any act required or by reason of any act or omission in the discharge of such duties. (Ord. 17C-09 § 2; Ord. 95C-127 § 2).