Surface Water Management (Title 13) | Environment & Sustainability
Historic Plats, no exemption to tightline requirements shall be approved.
b) Siting formal flow control or water quality facilities on site would result in significant increased risk to landslide hazard areas; or c) Sizing a flow control facility is not feasible where the target release rate cannot be matched with a minimum orifice size of one-quarter-inch diameter. iii. No exemptions or exceptions to Core Requirement Nos. 1, 3, and 8 shall be granted when the director deems that granting such exemption/exception request would cause significant impact to downstream properties, natural resources, and/or public infrastructure. Minimum thresholds for core requirements as described in the Surface Water Design Manual shall be met without exemption or exception. f. Where application of this section will deny all reasonable use of a property and a facility or design that produces a compensating or comparable result cannot be obtained, then an adjustment criterion exception may be approved pursuant to the applicable provisions of the Surface Water Design Manual. These standards are in addition to the applicable standards of SDC 21.03.020. g. Drainage Adjustment applications for projects subject to full or large project drainage review or any project subject to drainage review located within a critical drainage area shall be treated as a Type 2 process in accordance with SDC 21.09.010.
c) Where a tightline system is proposed, discharge shall be to a City owned, operated, and maintained system or where the City has or is granted an easement for the inspection, maintenance, repair, and replacement of the tightline system properly sized to convey the cumulative full build-out of flows. Basin transfers may be allowed if downstream wetland hydrology and stream flows are maintained and the risk of landslides, severe erosion, and flooding related property damage will not increase for downslope properties. Pumped systems shall only be allowed where existing structures and access will not be damaged in the event of pump failure.
ii. The director may approve an exemption or exception request from Core Requirement No. 3 (Flow Control) and/or Core Requirement No. 8 (Water Quality), prepared by a Washington
State licensed professional engineer using sound engineering principles and judgment, which can demonstrate that site conditions or strict adherence to the Core Requirements would negatively affect the site’s ability to mitigate its surface water impacts. Such site conditions and adherence to the Core Requirements may include, but are not limited to, the following: a) Significant trees would be damaged or require removal to install such facilities; or
Effective | January 1, 2022 Revisions | June 29, 2022
Title 21: Sammamish Development Code | 147
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