Spokane Municipal Code

Title 17D City-wide Standards

Chapter 17D.060 Stormwater Facilities

Section 17D.060.140 Runoff and Infiltration Controls

1. Runoff and infiltration controls apply in all areas of the City except where exempt or modified.

2. Unless otherwise specified, street and alley paving projects funded by local improvement districts are exempt from the provisions of SMC 17D.060.130 and SMC 17D.060.140.

3. Drainage plans shall be prepared and submitted for review and acceptance for all proposed plats and land disturbing activities prior to issuance of any permits for site disturbance, including but not limited to grading permits and building permits. The Director of Wastewater Management has authority to waive requirements to the necessity for a drainage plan, but must do so in writing. Factors considered in the evaluation of a waiver request include, but are not limited to:

1. soil characteristics and depth,

2. number of lots,

3. infill development,

4. percent impervious area,

5. pass-through drainage,

6. history and trends of runoff-related problems,

7. depth to ground water.

4. With respect to drainage plans required under subsection (C) of this section:

1. the volume and rate of surface water runoff after new development shall be no greater than the runoff volume and rate leaving the site prior to development, unless the Director of Engineering Services approves the discharge of additional runoff based on a comprehensive drainage plan and down gradient impact study;

2. drainage plans for development proposals in SDDs shall not rely upon infiltration to accommodate the additional runoff resulting from the proposed development. However, approval to use infiltration in part or in whole may be granted by the Director of Engineering Services upon a showing, after assessing new, existing, and cumulative impacts from prior developments, that no adverse impact to the side, adjacent, or down gradient properties would occur;

3. drainage plans submitted for development proposals shall comply with the Spokane Regional Stormwater Manual and the City of Spokane Design Standards, as approved by and on file with the Director of Engineering Services, for the design of onsite stormwater facilities, including any limitations applicable to any specific SDD;

4. drainage plans shall include identification of all properties to be reserved for onsite stormwater facilities and the location of all natural drainage systems.

5. The developer, property owner, or other responsible, authorized and designated entity acceptable to the Director of Wastewater Management (e.g., a homeowners association) shall be responsible for accepting and maintaining onsite stormwater facilities. The developer shall provide a perpetual maintenance plan, including funding mechanisms and appropriate financial security for such onsite stormwater facilities acceptable to the Director of Wastewater Management.

1. 1. Any private stormwater facilities that receive post-construction stormwater runoff from new development or redevelopment projects which (a) were approved in 2011 or later, and (b) whose disturbance was one acre or more, or projects that were less than one acre and are part of a larger common plan of development or sale, shall be inspected annually by a qualified stormwater professional. Private property owners, or other responsible person, authorized and designated entity shall provide annual certification by a qualified third party that adequate maintenance has been performed and the facilities are operating as designed to protect water quality.

6. New plats shall expressly identify tracts of land devoted to the conveyance and/or disposal of stormwater flows. The location of all on-site stormwater facilities shall meet the requirements of the Spokane Regional Stormwater Manual.

Date Passed: Monday, October 25, 2021

Effective Date: Thursday, December 2, 2021

ORD C36116 Section 3