SURFACE WATER MANAGEMENT
SURFACE WATER MANAGEMENT
9.02 General Provisions
9.04 Surface Water Runoff Policy
9.08 Surface Water Management Program
9.12 Water Quality See K.C.C. chapter 20.14 for basin plans
9.14 Groundwater Protection
9.20 Fertilizers (Takes effect January 1, 2011) CROSS REFERENCE:
(King County 3-2009)
GENERAL PROVISIONS 9.02.010 - 9.02.020
9.02.010 Relationship to comprehensive plan and growth management act.
9.02.020 Notification to tribes.
9.02.010 Relationship to comprehensive plan and growth management act. This Title is
hereby enacted to be consistent with and implement the comprehensive plan in accordance with RCW
36.70A. (Ord. 11615 ? 1 (part), 1994).
9.02.020 Notification to tribes. The county recognizes that many actions undertaken pursuant to Title 9, as amended, may impact treaty fishing rights of federally-recognized tribes. In order to honor and
prevent interference with these treaty fishing rights and to provide for water quality and habitat preservation,
the county shall provide notice to any federally-recognized tribes whose treaty fishing rights would be affected
by an action undertaken pursuant to this title, including but not limited to: development of wetlands, stream
and river banks, lakeshore habitat of water bodies, or development directly or indirectly affecting anadromous
bearing water bodies, including the promulgation of plans, rules, regulations or ordinances implementing the
provisions of this title, whether or not review of such actions is required under the State Environmental Policy
Act (SEPA) RCW 43.21C. (Ord. 11615 ? 1 (part), 1994).
(King County 3-2005)
SURFACE WATER RUNOFF POLICY 9.04
SURFACE WATER RUNOFF POLICY
9.04.030 Drainage review - when required - type.
9.04.050 Drainage review - requirements.
9.04.060 Critical drainage and/or erosion areas.
9.04.070 Engineering plans for the purposes of drainage review.
9.04.090 Construction timing and final approval.
9.04.095 Vesting period for lots in final short plats.
9.04.100 Liability insurance required.
9.04.105 Financial guarantees authorized.
9.04.115 Drainage facilities accepted by King County for maintenance.
9.04.120 Drainage facilities not accepted by King County for maintenance.
9.04.192 Liberal construction.
9.04.194 Implementation, review and revision.
9.04.196 Agency rules.
9.04.197 Effective date.
(King County 3-2005)
SURFACE WATER RUNOFF POLICY 9.04.005 - 9.04.020
9.04.005 Scope. Compliance with the standards in this chapter and the Surface Water Design
Manual does not necessarily mitigate all probable and significant environmental impacts to aquatic biota. Fishery resources and other living components of aquatic systems are affected by a complex set of factors. While employing a specific flow control standard may prevent stream channel erosion or instability, other factors affecting fish and other biotic resources (such as increases in stream flow velocities) are not directly addressed by the Surface Water Design Manual. Thus, compliance with this manual should not be construed as mitigating all probable and significant stormwater impacts, and additional mitigation may be required to protect aquatic biota in streams and wetlands. (Ord. 13191 ? 22, 1998).
9.04.010 Purposes. The council finds this chapter is necessary in order to promote the public
health, safety and welfare by providing for the comprehensive management of surface and storm waters and erosion control, especially that which preserves and utilizes the many values of the county's natural drainage system including open space, fish and wildlife habitat, recreation, education and urban separation. The council also finds that King County shall conduct programs to reduce flooding, erosion, and sedimentation; prevent and mitigate habitat loss; enhance groundwater recharge; and prevent water quality degradation through the implementation of comprehensive and thorough permit review, construction inspection, enforcement, and maintenance in order to promote the effectiveness of the requirements contained in this chapter. (Ord. 11615 ? 2, 1994: Ord. 9163 ? 1, 1989).
9.04.020 Definitions. The definitions in this section apply throughout this chapter unless the
context clearly requires otherwise.
A. "Adjustment" means a department-approved variation in the application of the requirements of K.C.C. 9.04.050 and the Surface Water Design Manual to a particular project in accordance with K.C.C. 9.04.050C. “Adjustment” replaces "variance," which was used in prior editions of the Surface Water Design
B. "Applicant" means a property owner or a public agency or public or private utility that owns a right-of-way or other easement or has been adjudicated the right to such an easement under RCW 8.12.090, or any person or entity designated or named in writing by the property or easement owner to be the applicant, in an application for a development proposal, permit or approval.
C. "Basin" means a geographic area that contains and drains to a stream or river named and noted on common maps, such as the Cedar river, Sammamish river, Green river, Snoqualmie river, Skykomish river or White river, or a geographic area that drains to a nonflowing water body named and noted on common maps, such as Lake Washington or Puget Sound.
D. "Basin plan" means a plan and all implementing regulations and procedures including, but not limited to, capital projects, public education activities and land use management adopted by ordinance for managing surface and storm water within the basin.
E. "Closed depression" means an area greater than five thousand square feet at overflow elevation that is low-lying and that has no or such a limited surface water outlet that the area acts as a stormwater retention facility.
F. "Construct or modify" means to install a new drainage pipe or ditch or make improvements to an existing drainage pipe or ditch, for purposes other than maintenance, that either serves to concentrate previously unconcentrated surface and storm water runoff or serves to increase, decrease or redirect the conveyance of surface and storm water runoff. “Construct or modify” does not include installation or
maintenance of a driveway culvert installed as part of a single-family residential building permit.
G."Conveyance system" means the drainage facilities and features, both natural and constructed, that collect, contain and provide for the flow of surface and storm water from the highest points on the land down to a receiving water. The natural elements of the conveyance system include swales and small drainage courses, streams, rivers, lakes and wetlands. The constructed elements of the conveyance system include gutters, ditches, pipes, channels and most flow control and water quality treatment facilities.
(King County 9-2009)
9.04.020 SURFACE WATER MANAGEMENT
H. "Department" means the department of natural resources and parks or its successor.
I. "Development" means any activity that requires a permit or approval, including, but not limited to, a
building permit, grading permit, shoreline substantial development permit, conditional use permit, special use
permit, zoning variance or reclassification, subdivision, short subdivision, urban planned development,
binding site plan, site development permit or right-of-way use permit. “Development” does not include a
Class I, II, III or IV-S forest practice conducted in accordance with chapter 76.09 RCW and Title 222 WAC or
a class IV-G nonconversion forest practice, as defined in K.C.C. chapter 21A.06, conducted in accordance
with chapter 76.09 RCW and Title 222 WAC and a county-approved forest management plan.
J. "Director" means the director of the department of natural resources and parks, or any duly
authorized representative of the director.
K. "Drainage" means the collection, conveyance, containment or discharge, or any combination
thereof, of surface and storm water runoff.
L. "Drainage facility" means a constructed or engineered feature that collects, conveys, stores or
treats surface and storm water runoff. “Drainage facility” includes, but is not limited to, a constructed or
engineered stream, pipeline, channel, ditch, gutter, lake, wetland, closed depression, flow control or water
quality treatment facility, erosion and sediment control facility and other structure and appurtenance that
provides for drainage.
M. "Drainage review" means an evaluation by King County staff of a proposed project's compliance
with the drainage requirements in the Surface Water Design Manual. The types of drainage review include:
Small project drainage review, targeted drainage review, full drainage review and large project drainage
N. "Erosion and sediment control" means any temporary or permanent measures taken to reduce
erosion, control siltation and sedimentation and ensure that sediment-laden water does not leave the site or
enter into wetlands or aquatic areas.
O. "Financial guarantee" means a form of financial security posted to do one or more of the
following: ensure timely and proper completion of improvements; ensure compliance with the King County
Code; or provide secured warranty of materials, workmanship of improvements and design. “Financial
guarantees” include assignments of funds, cash deposit, surety bonds or other forms of financial security acceptable to the director of the department of development and environmental services. “Performance
guarantee,” “maintenance guarantee” and “defect guarantee” are considered sub categories of financial
P. “Flood hazard reduction plan” means a plan and all implementing programs, regulations and
procedures including, but not limited to, capital projects, public education activities and enforcement
programs for reduction of flood hazards and prepared in accordance with RCW 86.12.200.
Q “Flow control best management practice” means a method or design for dispersing, infiltrating or otherwise reducing or preventing development-related increases in surface and storm water runoff at, or near,
the sources of those increases. “Flow control best management practice” includes the methods and designs
specified in the Surface Water Design Manual.
R. "Flow control facility" means a drainage facility designed to mitigate the impacts of increased
surface and storm water runoff generated by site development in accordance with the drainage requirements
in this chapter. A “flow control facility” is designed either to hold water for a considerable length of time and
then release it by evaporation, plant transpiration or infiltration into the ground or to hold runoff for a short
period of time and then release it to the conveyance system.
S. "Full drainage review" means the evaluation required by K.C.C. 9.04.030 for any proposed project,
unless the project is subject to small project drainage review, targeted drainage review or large project
drainage review, that:
1. Would result in two thousand square feet or more of new impervious surface;
2. Would result in thirty-five thousand square feet or more of new pervious surface: or
3. Is a redevelopment project on one or more parcels where the total of new and replaced
impervious surface is five thousand square feet or more and when the valuation of proposed improvements
exceeds fifty percent of the assessed value of the existing site improvements, including interior
improvements and excluding required mitigation and frontage improvements.
(King County 9-2009)
SURFACE WATER RUNOFF POLICY 9.04.020
T. "High-use site" means a commercial, industrial or road intersection site that generates a higher than average number of vehicle turnovers or has other characteristics that generate the potential for chronic oil accumulation. “High use site” includes:
1. A commercial or industrial site subject to:
a. an expected daily traffic count greater than one hundred vehicles per one thousand square feet of gross building area;
b. petroleum storage or transfer in excess of one thousand gallons per year, not including routine fuel oil storage or transfer; or
c. use, storage or maintenance of a fleet of twenty-five or more diesel vehicles each weighing over ten tons; or
2. A road intersection with average daily traffic counts of twenty-five thousand vehicles or more on the main roadway and fifteen thousand or more vehicles on any intersecting roadway, excluding pedestrian or bicycle use improvement projects.
U. "Hydraulically connected" means connected through surface flow or water features such as wetlands or lakes.
V. "Impervious surface" means a hard surface area that either prevents or retards the entry of water into the soil mantle as under natural conditions before development or that causes water to run off the surface in greater quantities or at an increased rate of flow from the flow present under natural conditions prior to development. Common impervious surfaces include, but are not limited to, roofs, walkways, patios, driveways, parking lots, storage areas, areas that are paved, graveled or made of packed or oiled earthen materials or other surfaces that similarly impede the natural infiltration of surface and storm water. An open uncovered flow control or water quality treatment facility is not an “impervious surface”.
W. "Improvement" means a permanent, human-made, physical change to land or real property including, but not limited to, buildings, streets, driveways, sidewalks, crosswalks, parking lots, water mains, sanitary and storm sewers, drainage facilities and landscaping.
X. “Land disturbing activity” means an activity that results in a change in the existing soil cover, both
vegetative and nonvegetative, or to the existing soil topography. “Land disturbing activity” includes, but is not limited to, demolition, construction, clearing, grading, filling, excavation and compaction. “Land disturbing activity” does not include tilling conducted as part of agricultural practices, landscape maintenance or
Y. "Lake management plan" means a plan describing the lake management recommendations and requirements adopted by public rule for managing water quality within individual lake basins.
Z. "Large project drainage review" means the evaluation required by K.C.C. 9.04.030 for any proposed project that:
1. Has an urban plan development land use designation in the King County Comprehensive Plan land use map;
2. Would, at full buildout of the project site, result in fifty acres or more of new impervious surface within a drainage subbasin or a number of subbasins hydraulically connected across subbasin boundaries; or
3. Has a project site of fifty acres or more within a critical aquifer recharge area, as defined in K.C.C. Title 21A.
AA. "Licensed civil engineer" means a person registered with the State of Washington as a professional engineer in civil engineering.
BB. "Maintenance" means those usual activities taken to prevent a decline, lapse or cessation in the use of currently serviceable structures, facilities, equipment or systems, if there is no expansion of the structure, facilities, equipment or system and there are no significant hydrologic impacts. "Maintenance" includes the repair or replacement of nonfunctional facilities or the replacement of existing structures with different types of structures, if the repair or replacement is required by one or more environmental permits or to meet current engineering standards and the functioning characteristics of the original facility or structure are not changed.
(King County 12-2008)
9.04.020 SURFACE WATER MANAGEMENT
CC. "Master drainage plan" means a comprehensive drainage control plan intended to prevent significant adverse impacts to the natural and constructed drainage system, both on- and off-site.
DD. "Native vegetated surface" means a surface in which the soil conditions, ground cover and species of vegetation are like those of the original native condition for the site, as more specifically set forth in the Surface Water Design Manual.
EE. "Natural discharge location" means the location where runoff leaves the project site under existing site conditions as defined in the Surface Water Design Manual.
FF. "New impervious surface" means the creation of a hard or compacted surface such as roofs, pavement, gravel or dirt or the addition of a more compacted surface such as the paving of existing dirt or gravel.
GG. "New pervious surface" means the conversion of a native vegetated surface or other native surface to a nonnative pervious surface, including, but not limited to, pasture land, grassland, cultivated land, lawn, landscaping or bare soil or any alteration of existing nonnative pervious surface that results in increased surface and storm water runoff as defined in the Surface Water Design Manual.
HH. "Pollution-generating impervious surface" means an impervious surface considered to be a significant source of pollutants in surface and storm water runoff. “Pollution-generating impervious surface
includes those surfaces subject to vehicular use or storage of erodible or leachable materials, wastes or chemicals and that receive direct rainfall or the run-on or blow-in of rainfall. A covered parking area would be included if runoff from uphill could regularly run through it or if rainfall could regularly blow in and wet the pavement surface. Metal roofs are also considered pollution-generating impervious surface unless they are treated to prevent leaching.
II. “Pollution-generating pervious surface" means a nonimpervious surface considered to be a
significant source of pollutants in surface and storm water runoff. “Pollution-generating pervious surfaces”
include surfaces subject to the use of pesticides and fertilizers, to the use or storage of erodible or leachable materials, wastes or chemicals or to the loss of soil. “Pollution-generating pervious surface” includes, but is
not limited to, the lawn and landscaped areas of a residential or commercial site, golf course, park sports field and county-standard grassed modular grid pavement.
JJ. "Project" means any proposed action to alter or develop a site that may also require drainage review.
KK. "Project site" means the portion of a site and any offsite areas subject to proposed project activities, alterations and improvements including those required by this chapter.
LL. "Redevelopment project" means a project that proposes to add, replace or modify impervious surface for purposes other than a residential subdivision or maintenance on a site that:
1. Is already substantially developed in a manner that is consistent with its current zoning or with a legal nonconforming use; or
2. Has an existing impervious surface coverage of thirty-five percent or more.
MM. "Replaced impervious surface" means an existing impervious surface proposed to be removed and reestablished as impervious surface, excluding impervious surface removed for the sole purpose of installing utilities or performing maintenance. For purposes of this definition, "removed" includes the removal of buildings down to bare soil or the removal of Portland cement concrete slabs or pavement or asphaltic concrete pavement.
NN. "Runoff" means that portion of water originating from rainfall and other precipitation that flows over the surface or just below the surface from where it fell and is found in drainage facilities, rivers, streams, springs, seeps, ponds, lakes, wetlands and shallow groundwater as well as on ground surfaces. For the purpose of this definition, groundwater means all waters that exist beneath the land surface or beneath the bed of any stream, lake or reservoir, or other body surface water, whatever may be the geological formation or structure in which such water stands or flows, percolates or otherwise moves.
OO. "Salmon conservation plan" means a plan and all implementing regulations and procedures including, but not limited to, land use management adopted by ordinance, capital projects, public education activities and enforcement programs for conservation and recovery of salmon within a water resource inventory area designated by the state under WAC 173-500-040.
(King County 12-2008)