Chapter 21A.85
LOW IMPACT DEVELOPMENT

Sections:

21A.85.010    Intent and goals.

21A.85.020    Applicability.

21A.85.030    Low impact development approaches.

21A.85.040    LID incentives.

21A.85.050    Review.

21A.85.010 Intent and goals.

Low impact development (LID) is an approach to land use planning and project design that seeks to:

(1) Increase the ability of a developed site to effectively emulate predevelopment hydrologic conditions, including without limitation, storm water retention, water quality treatment, and infiltration functions;

(2) Minimize overland storm water runoff from a developed site;

(3) Maximize the retention of trees, native vegetation, understory plants, and native soils;

(4) Minimize soil disturbance;

(5) Minimize the conversion of site surfaces from vegetated to nonvegetated surfaces; and

(6) Maximize the quantity and use of appropriate native plants on site.

The purpose of this chapter is to encourage development proposals to incorporate LID planning and design approaches into project development by providing incentives tied to LID’s use.

This chapter seeks to guide land use planning decisions only and does not replace any federal, state or local storm water flow control and water quality treatment regulations. Applicants are responsible for ensuring that their project proposal complies with all applicable regulations. (Ord. O2016-429 § 7 (Att. G); Ord. O2008-236 § 1)

21A.85.020 Applicability.

All new development subject to drainage review shall be required to comply with the adopted Surface Water Design Manual (SWDM). The SWDM requires low impact development (LID) flow control best management practices (BMPs) to mitigate the impacts of storm and surface water runoff generated by new impervious surfaces, new pervious surfaces, existing impervious surfaces, and replaced impervious surfaces.

In addition to the use of these required BMPs, new development may also have the option to incorporate LID site planning approaches described in SMC 21A.85.030 into project design in order to accumulate sufficient technique points to allow the applicant to take advantage of the incentives identified in SMC 21A.85.040.

The City of Sammamish shall apply this chapter to all City projects and encourage other governmental entities to utilize LID in accordance with this chapter in their projects. (Ord. O2016-429 § 7 (Att. G); Ord. O2008-236 § 1)

21A.85.030 Low impact development approaches.

The following list identifies preferred LID approaches that may be proposed within any zoning designation and the technique points associated with the successful use of each approach. Whether the implementation of any LID approach is sufficient to earn technique points shall be subject to the review and approval of the director.

(1) Retention of Existing Forested Condition – Up to 25 Technique Points.

(a) The applicant may earn up to 25 technique points for retaining up to 50 percent of the subject site’s remaining existing forested area after meeting retention standards in accordance with Development Standards – Trees, Chapter 21A.37 SMC.

(b) Existing forested areas shall be subject to Development Standards – Trees, Chapter 21A.37 SMC, and the maintenance and irrigation requirements of SMC 21A.35.110 through 21A.35.140.

(c) Technique points shall be awarded for retention as follows:

(i) Retention of 10 percent of existing forested condition: five technique points.

(ii) Retention of 20 percent of existing forested condition: 10 technique points.

(iii) Retention of 30 percent of existing forested condition: 15 technique points.

(iv) Retention of 40 percent of existing forested condition: 20 technique points.

(v) Retention of 50 percent of existing forested condition: 25 technique points.

(2) Restoration of Vegetated Area – Up to 20 Technique Points.

(a) The applicant may earn up to 20 technique points for restoring up to 50 percent of the subject site in one or more permanent open space tracts after meeting retention standards in accordance with Development Standards – Trees, Chapter 21A.37 SMC;

(b) Technique points shall be awarded for restoration as follows:

(i) Restoration of 10 percent of vegetated area: four technique points.

(ii) Restoration of 20 percent of vegetated area: eight technique points.

(iii) Restoration of 30 percent of vegetated area: 12 technique points.

(iv) Restoration of 40 percent of vegetated area: 16 technique points.

(v) Restoration of 50 percent of vegetated area: 20 technique points;

(c) Restoration of vegetated areas shall be subject to Development Standards – Trees, Chapter 21A.37 SMC, and the maintenance and irrigation requirements of SMC 21A.35.110 through 21A.35.140. Landscaping plans for open space tracts shall be designed consistent with SMC 21A.35.080 and 21A.35.100;

(d) Restoration areas shall be landscaped as part of the site’s development and meet the following requirements:

(i) The site design shall maximize the amount of existing mature vegetation retained on site;

(ii) The revegetation plan shall be designed by a licensed professional or ISA certified arborist;

(iii) The plantings shall provide a multilayer canopy of large trees (50 percent), small trees, shrubs, and ground cover at maturity;

(iv) A minimum of 75 percent of the open space tract shall be planted with trees, shrubs and groundcover. Groundcover does not include pasture or turf;

(v) All invasive plants on the site shall be removed;

(vi) No more than 15 percent of the proposed open space tract shall be pasture or turf;

(vii) Plants shall be selected by a licensed professional based upon site suitability;

(viii) For proposed open space tracts exceeding one-half acre in area, a ratio of two evergreens to one deciduous tree is required;

(ix) Three trees shall be planted per 1,000 square feet of proposed open space tract area;

(x) Trees shall be native to the coastal Pacific Northwest. On planting, deciduous trees shall have a minimum caliper of three-quarters inch and coniferous and broadleaf evergreen trees shall be at least five feet in height;

(xi) Eighty percent of shrubs and 80 percent of groundcover shall be species native to the coastal Pacific Northwest;

(xii) Shrubs shall be spaced a maximum of four feet on center and ground cover shall be spaced a maximum of two feet on center; and

(xiii) Significant trees retained in an open space tract may also be counted towards total tree retention requirements for the parcel.

(3) Restoration of Critical Area Buffers – Up to 20 Technique Points.

(a) The applicant may earn up to 20 technique points for restoring up to 50 percent of the critical area buffers within a development site.

(b) Technique points shall be awarded for restoration as follows:

(i) Restoration of 10 percent of vegetated area: four technique points.

(ii) Restoration of 20 percent of vegetated area: eight technique points.

(iii) Restoration of 30 percent of vegetated area: 12 technique points.

(iv) Restoration of 40 percent of vegetated area: 16 technique points.

(v) Restoration of 50 percent of vegetated area: 20 technique points.

(c) Restoration of critical area buffers shall be subject to mitigation standards in accordance with Chapter 21A.50 SMC and the maintenance and irrigation requirements of SMC 21A.35.110 through 21A.35.140.

(4) Increased Width of Critical Area Buffer – 10 Technique Points.

(a) The applicant may increase the width of a critical area buffer required under Chapter 21A.50 SMC by 35 percent.

(b) Any such increased width may also be included as part of a contiguous critical area tract counting as open space tract under subsection (2) of this section (see Diagram B).

Diagram B

(5) Limited Site Disturbance – 12 Technique Points.

(a) Soil disturbance of the site shall be limited to 50 percent of the site area otherwise unconstrained by environmentally critical areas and associated buffers and tree protection standards during plat and subsequent building construction;

(b) Limited clearing may occur within the area where soil is undisturbed, subject to the following limitations:

(i) The top four inches of soil may be disturbed but not removed from the site or lot, as needed, to allow for removal of unsuitable vegetation; provided, that the disturbed soil is moved to an isolated location where it will not be driven upon and such soil is then returned and respread on the parcel;

(ii) Six inches of arborist chippings are placed on top of in-place soil areas that may be subject to construction activities or operations;

(iii) Soil that is not protected as set forth in subsection (5)(b)(i) or (5)(b)(ii) of this section shall be tilled to a depth of 12 inches upon completion of all site disturbance;

(iv) Stump removal shall consist of grinding the stump in the existing location; and

(v) In no case shall the natural grade of the undisturbed area be modified by more than four inches.

(6) Reforestation – Eight Technique Points.

(a) No storm water facility modeling credits to reduce sizing of required flow control or water quality facilities in accordance with the adopted Surface Water Design Manual shall be provided for reforestation unless reforestation areas are contained within a designated tract as approved by the director;

(b) Residential Development. All of the lots within a residential development shall be reforested prior to final occupancy is issued on the development;

(c) Commercial/Institutional Development. The site shall be reforested;

(d) Reforestation shall consist of:

(i) For lots of 4,000 square feet or less, a minimum of two trees planted per lot;

(ii) For lots greater than 4,000 square feet in area, a minimum of two trees plus one additional tree planted per 1,000 square feet over 4,000 square feet;

(iii) Trees shall be native to the coastal Pacific Northwest. On planting, deciduous trees shall have a minimum caliper of three-quarters inch and coniferous and broadleaf evergreen trees shall be at least five feet in height.

(7) Reduced Impervious Surface – Up to 12 Technique Points.

(a) Lots created through a development proposal shall qualify for points under this subsection if each lot’s total impervious surface area is less than the applicable maximum allowable impervious surface area pursuant to SMC 21A.25.030 or 21A.25.040, as applicable and after meeting maximum impervious surface standards in accordance with the adopted Surface Water Design Manual;

(b) Technique points shall be awarded for reduced impervious surface as follows:

(i) Each lot total impervious surface is five percent less than the applicable maximum allowable impervious surface area: three technique points.

(ii) Each lot total impervious surface is 10 percent less than the applicable maximum allowable impervious surface area: six technique points.

(iii) Each lot total impervious surface is 15 percent less than the applicable maximum allowable impervious surface area: nine technique points.

(iv) Each lot total impervious surface is 20 percent less than the applicable maximum allowable impervious surface area: 12 technique points;

(c) Impervious surface areas which are public roads or public sidewalks shall be excluded from the calculation of the site’s total impervious surface area hereunder; and

(d) The allowed increases in the maximum permitted impervious surface area for smaller lots pursuant to SMC 21A.25.030 and 21A.25.040 shall not apply to this subsection.

(8) Minimal Foundation Excavation – 12 Technique Points.

(a) All of the structures within a residential development shall be designed with minimal foundation excavation which shall include:

(i) Limited or no disturbance of the natural soil profile within the footprint of all proposed structures. “Limited disturbance” shall have the meaning set forth in subsection (5) of this section;

(ii) Using a foundation that consists of a combination of driven piles and a connection at or above the existing grade of the subject site.

(b) Compliance with this technique shall require review and approval by the building official.

(9) Joint Use Driveway – Six Technique Points.

(a) Sixty-five percent of lots within a proposed residential development shall be accessed from a joint use driveway. A “joint use driveway” is defined by the current Public Works Standards.

(10) Hollywood Driveway – Eight Technique Points.

(a) Sixty-five percent of lots within a proposed residential development shall be accessed from a Hollywood driveway. A Hollywood driveway consists of two paved wheel tracks between two and one-half and three and one-half feet wide separated by a planted strip at least three feet wide. (Ord. O2016-429 § 7 (Att. G); Ord. O2008-236 § 1. Formerly 21A.85.040)

21A.85.040 LID incentives.

Technique points earned by installing one or more of the LID approaches described in SMC 21A.85.030 may be used to obtain the following LID incentives. Technique points are cumulative and may be combined to gain the use of one or more incentives below. Technique points may only be used for obtaining incentives for the development proposal that generates the points and may not be used for other development proposals. Except as otherwise noted in this section, technique points may only be used once.

(1) Twenty Percent Increased Density. Subject to compliance with the provisions of Chapter 21A.50 SMC, Environmentally Critical Areas, this density incentive may be used to increase the site density permitted under SMC 21A.25.030 and 21A.25.040, as applicable, by up to 20 percent.

(a) Thirty Technique Points Required. The applicant may include up to 75 percent of the area within streets within the site density calculations required under SMC 21A.25.080;

(b) Twenty-Seven Technique Points Required. The applicant may include up to 50 percent of the area within streets within the site density calculations required under SMC 21A.25.080;

(c) Twenty-Four Technique Points Required. The applicant may include up to 25 percent of the area within streets within the site density calculations required under SMC 21A.25.080.

(2) Thirty Percent Increased Density Incentive. Subject to compliance with the provisions of Chapter 21A.50 SMC, Environmentally Critical Areas, this density incentive may be used to increase the site density permitted under SMC 21A.25.030 and 21A.25.040, as applicable, by up to 30 percent.

(a) Forty Technique Points Required. The applicant may include up to 75 percent of the area within critical areas and critical area buffers within the site density calculations required under SMC 21A.25.080;

(b) Thirty-Five Technique Points Required. The applicant may include up to 50 percent of the area within critical areas and critical area buffers within the site density calculations required under SMC 21A.25.080;

(c) Thirty Technique Points Required. The applicant may include up to 25 percent of the area within critical areas and critical area buffers within the site density calculations required under SMC 21A.25.080.

(3) Recognition – 24 Technique Points Required. The applicant may request that the City generate a featured LID development article in the City newsletter covering the development which has earned the technique points. Technique points used for this incentive may be reused to obtain additional incentives.

(4) Increased Signage – 12 Technique Points Required. The applicant may increase the allowed signage pursuant to Chapter 21A.45 SMC by:

(a) Adding one additional monument sign; or

(b) Increasing the size of the allowed sign by 10 percent.

(5) Attached Housing – 12 Technique Points Required. One hundred percent of the lots within a proposed residential development may be designed to accommodate attached housing consistent with SMC 21A.30.020. (Ord. O2016-429 § 7 (Att. G); Ord. O2008-236 § 1. Formerly 21A.85.070)

21A.85.050 Review.

(1) Process. The use of preferred LID approaches or full LID design shall be reviewed concurrently with a primary proposal to consider the proposed site plan and methods used to earn the incentives as follows:

(a) For the purpose of this section, a “primary proposal” is defined as a proposed subdivision, binding site plan, conditional use permit, or commercial site development permit;

(b) The applicant shall identify the proposed techniques and incentives at the time of the first permit application for the primary proposal;

(c) When the primary proposal requires a public hearing under this chapter or SMC Title 19 or 20, the public hearing on the primary proposal shall serve as the hearing on the LID approaches proposed, and the reviewing authority shall make a consolidated decision on the proposed development and use of techniques and the resulting incentives;

(d) When the primary proposal does not require a public hearing under this chapter or SMC Title 19 or 20, the LID approach proposal shall be subject to the decision criteria for conditional use permits outlined in Chapter 21A.100 SMC and to the procedures set forth in SMC Title 20;

(e) All notices required by Chapter 20.05 SMC for the proposed development shall include a brief description of the proposed LID approaches and associated incentives;

(f) A notice on title and conditions on the face of final plat or equivalent recorded document shall be required documenting the use of LID approaches and identifying limitations on future development; and

(g) A maintenance plan shall be prepared and distributed to all property owner(s) that addresses structural and drainage maintenance, vegetation management, establishment and appropriate long-term irrigation. The applicant shall obtain written agreement from all property owners to comply with the maintenance plan and to maintain and retain all LID approaches employed on the site and credited for incentives for a period of not less than 15 years from the date of construction. The agreement must include wording that if all or part of any LID approach ceases to function, is removed, or in the case of reduction in impervious surface limits exceeds the limit as approved as part of this chapter, equivalent LID approach(es) must be installed and all other storm water management requirements met prior to removal. The applicant shall provide the City with a copy of the maintenance plan and all written agreements with property owners obtained under this section.

(2) Review. In evaluating the feasibility of a preferred LID approach proposal or Sammamish comprehensive LID proposal, the director shall have the authority to request additional technical information prepared by a certified professional to:

(a) Determine whether the development proposal is consistent with this chapter;

(b) Determine if a proposed approach is consistent with the standards of the current Surface Water Design Manual, City of Sammamish Stormwater Comprehensive Plan, or the Low Impact Development Technical Guidance Manual for Puget Sound, or other suitable reference, as determined by the director;

(c) Determine whether the proposed combination of techniques adequately work together toward meeting the goals of this chapter;

(d) Determine if the monitoring plans and bonding measures proposed by the applicant are sufficient to protect the public benefit, health, safety, and welfare, consistent with this chapter; and

(e) Determine that the proposed LID approaches shall function as intended.

(3) Health and Safety. Approval of all proposed LID approaches, Sammamish comprehensive LID, and incentives grants shall be subject to the review of the City to determine that the proposed development does not pose an unreasonable threat to the public health, safety, or welfare on or off the development proposal site and is consistent with the general purposes of this chapter and the public interest.

(4) Adjustments.

(a) Minor. When reviewing and issuing construction permits in an approved development, the department may allow minor adjustments in the approved approaches and incentives used by the development proposal involving the location and site-specific approaches or incentives.

(b) Major. Changes to a development proposal that result in significant adjustments to the project shall require resubmittal of the development proposal pursuant to subsection (1) of this section. Significant adjustments include, but are not limited to, elimination of proposed LID approaches, increases in the number of dwelling units generated, or additional reduction of proposed street improvements. (Ord. O2016-429 § 7 (Att. G); Ord. O2008-236 § 1. Formerly 21A.85.080)