Chapter 15.10
DRAINAGE

Sections:

15.10.010    Purpose.

15.10.020    Repealed.

15.10.030    Repealed.

15.10.040    Applicability.

15.10.050    Definitions.

15.10.060    Stormwater drainage requirements.

15.10.070    Adjustment and variance criteria.

15.10.080    Site planning and BMP selection and design criteria.

15.10.090    Low impact development.

15.10.100    Long-term operation and maintenance of post-construction stormwater facilities.

15.10.110    Inspection.

15.10.120    Enforcement.

15.10.010 Purpose.

The purpose of this chapter is to provide for the health, safety, and general welfare of the citizens of Clyde Hill, to manage stormwater drainage, and to enhance the water quality of surface waters through the regulation of non-stormwater discharges from the Clyde Hill municipal stormwater sewer system. This chapter is established to address a community history of drainage issues by controlling discharges into the city’s system and onto neighboring properties. Because of the city’s previous stormwater problems, addressing drainage is a responsibility of those developing or redeveloping property in the city of Clyde Hill. This chapter was also established in compliance with the Federal Clean Water Act and the requirements of the city’s National Pollutant Discharge Elimination System (NPDES) Phase II permit issued by the Washington State Department of Ecology. (Ord. 947 § 1, 2016; Ord. 905 § 2, 2010)

15.10.020 Roadmap to this chapter.

Repealed by Ord. 947. (Ord. 905 § 2, 2010)

15.10.030 Stormwater drainage requirements – Development less than 43,560 square feet or one acre.

Repealed by Ord. 947. (Ord. 905 § 2, 2010)

15.10.040 Applicability.

This chapter applies to all development, redevelopment, and construction site activities where stormwater from the site drains directly or indirectly into the city of Clyde Hill’s municipal storm sewer system, unless specifically exempted by the city. This chapter applies to both private and public development, including roads. (Ord. 947 § 1, 2016; Ord. 905 § 2, 2010)

15.10.050 Definitions.

For all development, redevelopment, and construction site activities the definitions published in the then existing Appendix 1 of the Western Washington Phase II Municipal Stormwater Permit shall govern. (Ord. 947 § 1, 2016; Ord. 905 § 2, 2010)

15.10.060 Stormwater drainage requirements.

A. All new development, redevelopment, and construction site activities will be subject to the thresholds and minimum requirements published in Appendix 1 of the 2013-2018 Western Washington Phase II Municipal Stormwater Permit.

B. All new development and redevelopment shall also be subject to additional stormwater drainage requirements contained in the city’s publication “Storm Water Drainage Guidelines” dated January 1, 2017, or as thereafter amended, provided such additional requirements are not in conflict and do not reduce the minimum requirements published in Appendix 1 of the 2013-2018 Western Washington Phase II Municipal Stormwater Permit. The additional stormwater drainage requirements in the guidelines include the following:

1. Drainage Control Plan Requirement.    All projects that add less than 2,000 square feet of new hard surface and that are therefore not required to submit a stormwater site plan per Minimum Requirement No. 2 must submit two copies of a drainage control plan to the public works director. The required content of the drainage control plan is described in the city of Clyde Hill Storm Water Drainage Guidelines.

2. Small Detention Requirement. All projects that add 750 square feet or more of new hard surfaces, but that due to site conditions are unable to fully implement on-site stormwater management BMPs per Minimum Requirement No. 5 for all new and replaced hard surfaces, and that are also not required to construct a flow control facility per Minimum Requirement No. 7, must install stormwater collection and small detention systems as described in the city of Clyde Hill Storm Water Drainage Guidelines. The intent of the small detention system is to restrict peak stormwater flows to prevent overloading of the city’s storm sewer system. The detention system must be sized for both new and replaced hard surfaces. In calculating the hard surface area, the surface of the water of swimming pools shall not be included, unless the public works director determines that such pool contributes to surface water runoff. For projects where the main structure on a redeveloped lot is deemed “substantially remodeled” as defined in CHMC 17.60.030, the small detention system sizing shall also include existing hard surfaces. (Ord. 947 § 1, 2016; Ord. 905 § 2, 2010)

15.10.070 Adjustment and variance criteria.

A. Adjustments to the minimum requirements contained in Appendix 1 of the Western Washington Phase II Municipal Stormwater Permit may be granted by the city upon application; provided, that a written finding of fact is prepared addressing the following:

1. The adjustment provides substantially equivalent environmental protections as those required by the Western Washington Phase II Municipal Stormwater Permit;

2. Based on sound engineering practices, the objectives of safety, function, environmental protection and facility maintenance are met.

B. Exceptions or variances to the minimum requirements contained in Appendix 1 of the Western Washington Phase II Municipal Stormwater Permit may be granted prior to permit approval and construction. The board of adjustment may grant a variance following legal public notice of an application for an exception, legal public notice of the decision on the application, and written findings of fact. The application must address each of the factors listed below and must be submitted with the applicable fee, established in the city’s master fee resolution. Exceptions to the minimum requirements may be granted if their application imposes a severe and unexpected economic hardship. To determine whether the application of the minimum requirements imposes a severe and unexpected economic hardship on the applicant, the board of adjustment must consider and document with written findings of fact the following:

1. The current (pre-project) use of the site;

2. How the application of the minimum requirement(s) restrict the proposed use of the site compared to the restrictions that existed prior to the adoption of the minimum requirements;

3. The possible remaining uses of the site if the exception were not granted;

4. The uses of the site that would have been allowed prior to the adoption of the minimum requirements;

5. A comparison of the estimated amount and percentage of value loss as a result of the minimum requirements versus the estimated amount and percentage of value loss as a result of requirements that existed prior to adoption of the minimum requirements; and

6. The feasibility for the owner to alter the project to apply the minimum requirements.

In addition, any exception must meet the following criteria:

a. That the granting of the exception will not be detrimental to the public health and welfare, nor injurious to other properties in the vicinity and/or downstream, and to the quality of waters of the state; and

b. The exception is the least possible exception that could be granted to comply with the intent of the minimum requirements. (Ord. 947 § 1, 2016; Ord. 905 § 2, 2010)

15.10.080 Site planning and BMP selection and design criteria.

The city adopts the site planning requirements, BMP selection, design, and infeasibility criteria, LID competing needs criteria, and BMP limitations contained in the Washington State Department of Ecology’s 2012 Stormwater Management Manual for Western Washington, as amended in December 2014, that, when used to implement the minimum requirements in Appendix 1 of the Western Washington Phase II Municipal Stormwater Permit, will protect water quality, reduce the discharge of pollutants to the maximum extent practicable and satisfy the state requirement under Chapter 90.48 RCW to apply all known, available and reasonable methods of prevention, control and treatment prior to discharge. (Ord. 947 § 1, 2016; Ord. 905 § 2, 2010)

15.10.090 Low impact development.

In order to promote low impact development using creative approaches to site design, habitat and tree retention, significant reduction of impervious surfaces, changes in traditional site features such as roads and structures in favor of natural habitat features, the director may approve, or for those projects requiring review and approval by the city council, recommend approval of deviations from engineering design and the provisions of Clyde Hill’s development regulations for all development, redevelopment, and construction site activities based upon the following factors:

A. The deviations will produce a compensating or comparable result in stormwater flow control and treatment that is in the public interest;

B. The deviations contribute to and are consistent with the goal of achieving low effective impervious surface area within a development;

C. The proposed development project offers reasonable assurances that low impervious surfaces will be achieved and maintained;

D. The deviations do not threaten public health or safety;

E. The deviations are consistent with generally accepted engineering and design practices and are prepared by a registered professional engineer licensed in the state of Washington with experience in LID design;

F. The deviations promote one or more of the following:

1. Innovative site or housing design;

2. Increased on-site stormwater retention using native vegetation;

3. Retention of at least 60 percent of natural vegetation conditions over the site;

4. Improved on-site water quality beyond that required by current applicable regulations;

5. Retention or recreation of predevelopment and/or natural hydrologic conditions to the maximum extent possible;

6. The reduction of effective impervious surfaces to the maximum extent practicable;

G. The deviations do not allow density greater than what would otherwise be allowed under city regulations then in effect;

H. The deviations do not present significantly greater maintenance requirements at facilities that will be eventually transferred to public ownership;

I. There shall be submitted in conjunction with each such project, covenants, conditions and restrictions which will be binding upon the property all necessary native growth protection easements, impervious surface restrictions and such other critical features as the director may require.

Use of LID facilities shall require approval by the public works director. Prior to plan approval of LID facilities, a soils report must be prepared by a professional engineer, geologist, hydrogeologist, or engineering geologist licensed in the state of Washington and submitted to the public works director for review and approval. If LID facilities are found to be feasible, the final signed/stamped soils report must include a statement that the use of the proposed LID facility will not result in springs, surface flooding, seepage into downstream basements or crawl spaces, or slope instability.

Prior to final approval of the LID facility construction, a registered professional engineer licensed in the state of Washington and experienced in LID design shall submit to the city “as built” plans of the LID facility and certification that the facility has been constructed as shown on the “as built” plans. (Ord. 947 § 1, 2016; Ord. 905 § 2, 2010)

15.10.100 Long-term operation and maintenance of post-construction stormwater facilities.

A. The person or persons holding title to the property shall remain responsible for the facility’s continual performance, operation and maintenance in accordance with the standards and requirements of the most current version of Washington State Department of Ecology’s Stormwater Management Manual for Western Washington and remain responsible for any liability as a result of these duties.

B. The city is authorized to inspect a private stormwater drainage facility at least annually unless there are maintenance records justifying a different frequency pursuant to CHMC 15.10.110. (Ord. 947 § 1, 2016; Ord. 905 § 2, 2010)

15.10.110 Inspection.

A. Authority. Whenever implementing the provisions of this chapter or whenever there is cause to believe that a violation of this chapter has been or is being committed, the city’s inspector is authorized to inspect during regular working hours and at other reasonable times all new development, redevelopment, and construction sites within Clyde Hill to determine compliance with the provisions of this chapter.

B. Inspection Procedures.

1. Prior to making any inspections on private property, the inspector shall present identification credentials, state the reason for the inspection and request entry. Any private landowner engaging in new development, redevelopment, or construction activities as defined under this chapter must, as a condition of the building permit required for such development, consent to the creation of an easement for purposes of ingress and egress for inspection of the site.

2. If the property or any building or structure on the property is unoccupied, the inspector shall first make a reasonable effort to locate the owner or other person(s) having charge or control of the property or portions of the property and request entry.

3. If after reasonable effort the inspector is unable to locate the owner or other person(s) having charge or control of the property, and has reason to believe the condition of the stormwater system creates an imminent hazard to persons or property, the inspector may enter.

4. Unless entry is consented to by the owner or person(s) in control of the property or portion of the property or unless conditions are reasonably believed to exist which create imminent hazard, the inspector shall obtain a search warrant, prior to entry, as authorized by the laws of the state of Washington.

5. The inspector may inspect the stormwater system without obtaining a search warrant provided for in subsection (B)(4) of this section, provided the inspection can be conducted while remaining on public property or other property on which permission to enter is obtained.

C. Inspection Requirements. The public works director is authorized to develop inspection procedures and requirements, including checklists, for all stormwater facilities in the city of Clyde Hill.

D. Inspection Fees. Inspection fees shall be established by the city’s master fee resolution. (Ord. 947 § 1, 2016; Ord. 905 § 2, 2010)

15.10.120 Enforcement.

Any person violating the provisions of this chapter shall be subject to those penalties outlined in Chapter 15.13 CHMC. (Ord. 947 § 1, 2016; Ord. 905 § 2, 2010)