Chapter 13.32
STORMWATER MANAGEMENT REQUIREMENTS

Sections:

13.32.010    Minimum requirements for drainage improvements.

13.32.020    Drainage plan – Submission.

13.32.030    Drainage plan – Contents.

13.32.040    Development in environmentally sensitive areas or impacting ESAs.

13.32.050    Review and approval of the plan.

13.32.060    Establishment of regional facilities.

13.32.070    Applicability to government entities.

13.32.080    Protection of public/private rights.

13.32.010 Minimum requirements for drainage improvements.

A. All developments shall comply with the Department of Ecology’s February 2005 Stormwater Management Manual for Western Washington (“2005 SWMM-WW”), except for the following: Section 2.6 – Optional guidance, relating to financial liability and off-site analysis and mitigation, city engineering design standards, city stormwater master plan, and adopted drainage basin plans for all clearing and grading activities, for erosion control during construction and for permanent drainage system improvements.

B. Surface water entering the subject property shall be received at the naturally occurring locations and surface water exiting the subject property shall be discharged at the natural locations with adequate energy dissipaters within the subject property to minimize downstream damage and with no diversion at any of these points.

C. All developments shall do the necessary analysis and install the necessary mitigations to ensure that stormwater exiting their property is discharged at a safe location which will not impact other property owners.

D. All structures shall be built such that finished floor elevations are in conformance with the International Building Code as adopted or hereafter amended.

E. Building plans shall clearly show locations of drainage system and stormwater controls within property limits and any off-site drainage improvements.

F. Considerations for the discharge of water off-site include but are not limited to the following:

1. Sufficient capacity of downstream facilities under design conditions;

2. Maintenance of the integrity of the receiving waters;

3. Possibility of adverse effects of retention/detention;

4. Utility of regional retention/detention facilities;

5. Capability of maintenance of the system; and

6. Structural integrity of abutting foundations and structures.

G. All developers not providing permanent stormwater control facilities will be required to sign a no-protest agreement for future participation in a stormwater-related LID. (Ord. 2915 § 1, 2006; Ord. 2867 § 2, 2004; Ord. 2579 § 1, 1997).

13.32.020 Drainage plan – Submission.

A. All developers applying for any of the following permits and/or approvals may be required to submit for approval a drainage plan with their application and/or request:

1. Grading permit;

2. Street development permit;

3. Substantial development permit required under Chapter 90.58 RCW (Shoreline Management Act);

4. Subdivision approval;

5. Short subdivision approval;

6. Commercial, industrial or multifamily site plan approval;

7. Rezones;

8. Conditional use permits;

9. Planned unit developments;

10. Building permits, where the permit either (a) authorizes or is for new construction totaling 40 percent or more of developmental coverage within the subject property; or (b) authorizes or is for new construction which, together with pre-existing developmental coverage, would result in 40 percent or more developmental coverage within the property or (c) is for development in an environmentally sensitive area or which has the potential to impact an environmentally sensitive area;

11. Building permits, where the new development does not involve a change in impervious coverage of a site but where one of the following conditions exist:

a. The stormwater from the existing development is connected to the sanitary sewer system.

b. The drainage system serving the existing development is inadequate to prevent impacts to neighboring properties.

c. Water quality issues are a concern either from the existing development or from the proposed development.

B. In addition, a drainage plan may be required for creation of impervious area, not covered by a permit, which exceeds either:

1. Five thousand square feet; or

2. Forty percent developmental coverage within the subject property.

C. Construction work done under any of the above permits or applications shall not begin until such time as final approval of the drainage plan is obtained in accordance with PTMC 13.32.050.

D. The same plan submitted during one permit/approval process may be subsequently submitted with further required applications. The plan shall be supplemented with such additional information that is requested by the public works department or required by the provisions of the engineering design standards manual and/or DOE Stormwater Management Manual for the Puget Sound Basin.

E. Temporary erosion and sediment control measures may be required under Chapter 5 of the engineering design standards at the discretion of the director for:

1. Site preparation and/or construction of any development; or

2. Creation of impervious area which exceeds either:

a. Five thousand square feet; or

b. Forty percent of the subject property. (Ord. 2687 § 1, 1999; Ord. 2579 § 1, 1997; Ord. 2126 § 1, 1988; Ord. 1957 § 3, 1983).

13.32.030 Drainage plan – Contents.

All persons applying for any of the permits and/or approvals contained in PTMC 13.32.020 shall provide a drainage plan for surface and pertinent subsurface water flows entering, flowing within, and leaving the subject property both during and after construction. The detailed form and contents of the drainage plan shall be described in procedures established by the public works department, or in the engineering design standards manual and/or DOE Stormwater Management Manual for the Puget Sound Basin. The engineering design standards manual, and the DOE Manual, will set forth the manner of presenting the required information which may include but is not limited to the following:

A. Background computations for sizing drainage facilities:

1. Depiction of the drainage area on a topographical map of approved scale and contour interval, with acreage of the site, development, and developmental coverage indicated;

2. Indications of the peak discharge and volume of surface water currently entering and leaving the subject property due to the design storm;

3. Indication of the peak discharge and volume of runoff which will be generated due to the design storm within the subject property if the development or proposed activity is allowed to proceed; and

4. Determination of the peak discharge and volume of water that will be generated by the design storm at various points on the subject property;

B. Proposed measures for handling the computed runoff at the detail level specified in the engineering design standards manual and/or DOE Stormwater Management Manual for the Puget Sound Basin:

1. The design storm peak discharge from the subject property may not be increased by the proposed development; and

2. Retention/detention facilities must be provided in order to maintain surface water discharge rates at or below the existing design storm peak discharge; and

C. Proposed Measures for Controlling Runoff During Construction. The requirements of this section may be modified at the discretion of the city public works department in special cases requiring more information. (Ord. 2579 § 1, 1997; Ord. 2444 § 2, 1995; Ord. 1957 § 4, 1983).

13.32.040 Development in environmentally sensitive areas or impacting ESAs.

Development in environmentally sensitive areas (ESAs) or development which has the potential to impact ESAs must meet the requirements of Chapter 19.05 PTMC or other requirements as determined necessary for the protection of the ESAs as determined by the public works director. (Ord. 2579 § 1, 1997; Ord. 1957 § 6, 1983).

13.32.050 Review and approval of the plan.

All storm drainage plans prepared in connection with any of the permits and/or approvals listed in PTMC 13.32.020 shall be submitted for review by and approval of the public works department in accordance with the procedures established in the engineering design standards manual and/or DOE Stormwater Management Manual for the Puget Sound Basin. (Ord. 2579 § 1, 1997; Ord. 2444 § 3, 1995; Ord. 1957 § 7, 1983).

13.32.060 Establishment of regional facilities.

In the event that public benefits would accrue due to modification of the drainage plan for the subject property to better implement the recommendations of the comprehensive drainage plan, the public works department may recommend that the city should assume responsibility for the further design, construction, operation and maintenance of drainage facilities on the subject property. Such decision shall be made concurrently with review and approval of the plan as specified in PTMC 13.32.050. In the event that the city decides to assume responsibility for design, construction, operation, and maintenance of the facilities, the developer will be required to contribute a pro rata share to the construction cost of the facilities. The developer may be required to supply additional information at the request of the public works department to aid in the determination by the city. Guidelines for implementing this section will be defined in the engineering design standards manual and/or DOE Stormwater Management Manual for the Puget Sound Basin. (Ord. 2579 § 1, 1997; Ord. 1957 § 8, 1983).

13.32.070 Applicability to government entities.

A. All municipal corporations and governmental entities shall be required to submit a drainage plan and comply with the terms of this chapter when developing and/or improving land including, but not limited to, road building and widening within the areas of the city.

B. It is recognized that many other city, county, state and federal permit conditions may apply to the proposed action and that compliance with the provisions of this chapter does not constitute compliance with such other requirements. (Ord. 2579 § 1, 1997; Ord. 1957 § 12, 1983).

13.32.080 Protection of public/private rights.

Implementation of any provision of this chapter shall not cause nor be construed as an infringement of the rights of individuals, municipalities, or corporations other than the developer seeking a permit or approval as described in PTMC 13.32.030. (Ord. 2579 § 1, 1997; Ord. 1957 § 14, 1983).