It is the purpose of this section to provide supplemental development regulations to underlying zones, which ensure that development occurs in such a manner as to protect the natural and topographic character, environmental resources, aesthetic qualities and restorative value of these areas, as well as the public health, safety, and general welfare, by ensuring that development does not create soil erosion, sedimentation of lower slopes, slide damage, flooding problems, and severe cutting or scarring. It is the intent of these development standards to encourage a sensitive form of development and to allow for a reasonable use that complements the natural and visual character of the city. Hillside protection shall be provided on slopes of 15 percent or greater or unconstrained slopes within 30 feet of the top of escarpments associated with rivers or streams.
A. Hillside Development Standards.
1. Steep Slopes.
a. Steep slope areas include all areas in the city where the slope of the land is 35 percent or greater.
b. Existing parcels where all existing terrain is 35 percent or greater shall be considered buildable for one dwelling unit only.
c. All grading, retaining wall design, drainage, and erosion control plans shall be designed by a geotechnical expert in compliance with subsection (C)(2) of this section.
d. Existing parcels where all existing terrain is 35 percent or greater cannot be subdivided or partitioned.
2. Constrained Slopes.
a. Constrained slope areas include all areas where the slope of the land is between 15 percent and 35 percent.
b. The impervious surface area of any residential lot or commercial or industrial site (including driveways, sidewalks, structures, swimming pools, and any other area not covered by vegetation) shall not exceed 30 percent of the constrained slope area;
c. At least half the constrained slope area shall remain in, or be planted in, approved native vegetation. The existing tree canopy shall be retained wherever possible, and shall be considered in meeting this standard.
B. All Hillside Developments.
1. Specific determination of steep slope and constrained slope areas shall be based on a topographic map and field survey prepared by an engineer or surveyor registered in Oregon, and provided by the applicant or property owner(s).
a. Where development, excavation or vegetation removal is proposed for areas with 15 percent or greater slope, an on-the-ground topographical survey shall be prepared for the entire property. The survey shall show trees or tree clusters and two-foot contours.
b. Areas with between 15 and 35 percent slopes, and areas with 35 percent and greater slopes, shall be specifically indicated on the required survey maps.
2. All newly created lots either by subdivision or partition shall contain a building envelope with a slope of 35 percent or less.
3. Development shall not result in cuts or fills in excess of three feet except for basement construction unless specifically approved by the city.
4. If development is proposed on constrained or steep slope areas, a mitigation plan for disturbed areas on constrained or steep slope areas shall be prepared and implemented. This plan shall provide for the replanting and maintenance of approved native plant species designed to achieve predisturbance conditions.
5. Residential roof lines shall not exceed the natural ridgeline when viewed from the public street providing access to the property.
6. Circulation.
a. The location, alignment design, grade width, and capacity of roads within the development shall conform to city engineering standards. However, the use of public and private lanes shall be encouraged in the hill areas to reduce the disturbance of the natural landscape. The width of these lanes shall be allowed to be as narrow as public safety and traffic generation will permit.
b. Loop and split, one-way street sections, and occasional steep street grades shall be allowed to fit terrain and minimize grading and exposed slopes.
c. Streets and lanes in the hill areas shall be laid out to encourage slow speed traffic and respect the natural topography of the area.
d. Street grades may be permitted up to 15 percent, provided they do not exceed 200 feet in length, whereby they must be reduced to 10 percent or less for a minimum length of 20 feet. The overall grade shall not exceed 10 percent.
e. Culverts, bridges and other drainage structures shall be placed to encourage drainage in established drainage ways and as provided in Chapter
16.15 RRMC. Additional road construction improvements may be required in areas exhibiting poor soil stability.
f. Circulation shall, when feasible, be designed to allow for separation of vehicular, pedestrian, bicycle, and hiking trails. The circulation system shall, when feasible, be developed throughout the hill areas, to provide connections between park areas and scenic easements in order to help maximize leisure opportunities of the hills. Trails may be accepted by the appropriate jurisdiction in fee or easement.
g. Walkways shall be required when determined to be needed for public safety and convenience. When required, walkways shall be of minimum width of four feet unless a greater need is shown. Walkways shall be constructed of a material suitable for use in the particular area and shall be located as necessary to provide maximum pedestrian safety and preservation of the character of the area.
h. Driveways shall be designed to a grade and alignment that will provide the maximum safety and convenience for vehicular and pedestrian use. Collective private driveways shall be encouraged where their utilization will result in better building sites and lesser amount of land coverage than would result if a public road were required.
i. Minimum standards for private easement construction within the steep and constrained slope areas shall be as follows:
i. Minimum travel service width: 12 feet.
ii. Minimum vertical clearance: 14 feet.
iii. Minimum horizontal clearance: 16 feet.
iv. Maximum intermittent grade: 15 percent for 200 feet.
v. Maximum sustained grade: 10 percent.
j. Whenever private drives are permitted, it shall be the responsibility of the benefited property owners to maintain the private easement or driveway established in accordance with this chapter.
7. Disturbed areas shall be replanted in approved native vegetation and tree cover.
8. The applicant's engineering plans shall certify that runoff and sedimentation from the site will not increase more than 10 percent above conditions present on the site as of the effective date of the ordinance codified in this section.
9. The applicant's engineer shall provide a construction erosion control plan and water quality plan, consistent with the provisions of RRMC §
17.95.010 through §
17.95.080.
C. Required Reports.
1. Geotechnical Studies. Where division or development is proposed for areas with 15 percent to 35 percent slope, and development is proposed for areas with slopes of 35 percent or greater, a geologic assessment and a geotechnical report, prepared by a geotechnical expert, shall be provided by the applicant, indicating that the site is stable for the proposed use and development. These studies shall include the following information:
b. Project description to include location, topography, drainage, vegetation, discussion of previous work and discussion of field exploration methods.
c. The geologic assessment shall include:
i. Site geology, based on a surficial survey, to include site geologic maps, description of bedrock and surficial materials, including artificial fill, locations of any faults, folds, etc., and structural data including bedding, jointing and shear zones, soil depth and soil structure.
ii. Discussion of any off-site geologic conditions that may pose a potential hazard to the site, or that may be affected by on-site development.
iii. Suitability of site for proposed development from a geologic standpoint.
d. The geotechnical report shall also include:
i. Specific recommendations for cut and fill slope stability, seepage and drainage control or other design criteria to mitigate geologic hazards.
ii. If deemed necessary by the engineer or geologist to establish whether an area to be affected by the proposed development is stable, additional studies and supportive data shall include cross-sections showing subsurface structure, graphic logs with subsurface exploration, results of laboratory test and references.
iii. Signature and registration number of the engineer and/or geologist.
iv. Additional information or analyses as necessary to evaluate the site.
v. Inspection schedule for the project as required in subsection
(G) of this section.
vi. Location of all irrigation canals and major irrigation pipelines.
2. Hillside Grading and Erosion Control Plan. All development shall provide plans conforming with the following items:
a. All grading, retaining wall design, drainage, and erosion control plans for development on hillside lands shall be designed by a geotechnical expert.
b. All cuts, grading or fills shall conform to Chapter 70 of the International Building Code. Erosion control measures on the development site shall be required to minimize the solids in runoff from disturbed areas.
c. For development other than single-family homes on individual lots, all grading, drainage improvements, or other land disturbances shall only occur from May 1st to October 31st. Excavation shall not occur during the remaining wet months of the year.
d. Erosion control measures shall be installed and functional by October 31st. Up to 30-day modifications to the October 31st date and 45-day modification to the May 1st date may be made by the city planner, based upon weather conditions and in consultation with the project geotechnical expert. The modification of dates shall be the minimum necessary, based upon evidence provided by the applicant, to accomplish the necessary project goals.
e. Grading – Cuts. On all cut slopes, the following standards shall apply:
i. Cut slope angles shall be determined in relationship to the type of materials of which they are composed. Where the soil permits, limit the total area exposed to precipitation and erosion. Steep-cut slopes shall be retained with stacked rock, retaining walls, or functional equivalent to control erosion and provide slope stability when necessary. Where cut slopes are required to be laid back (1:1 or less steep), the slope shall be protected with erosion control netting or structural equivalent installed per manufacturer's specifications and revegetated.
ii. Exposed cut slopes, such as those for streets, driveway accesses, or yard areas greater than seven feet in height, shall be terraced. Cut faces on a terraced section shall not exceed a maximum height of five feet. Terrace widths shall be a minimum of three feet to allow for the introduction of vegetation for erosion control. Total cut slopes shall not exceed a maximum vertical height of 15 feet. The top of cut slopes not utilizing structural retaining walls shall be located a minimum setback of one-half the height of the cut slope from the nearest property line. Cut slopes for structure foundations encouraging the reduction of effective visual bulk, such as split pad or stepped footings, shall be exempted from the height limitations of this subsection.
iii. Revegetation of cut slope terraces shall include the provision of a planting plan, introduction of topsoil where necessary, and the use of irrigation if necessary. The vegetation used for these areas shall be native or species similar in resource value which will survive, help reduce the visual impact of the cut slope, and assist in providing long-term slope stabilization. Trees, bush-type plantings and cascading vine-type plantings may be appropriate.
f. Grading – Fills. On all fill slopes, the following standards shall apply:
i. Fill slopes shall not exceed a total vertical height of 20 feet. The toe of the fill slope area not utilizing structural retaining shall be a minimum of six feet from the nearest property line.
ii. Fill slopes shall be protected with an erosion control netting, blanket or functional equivalent. Netting or blankets shall only be used in conjunction with an organic mulch such as straw or wood fiber. The blanket must be applied so that it is in complete contact with the soil so that erosion does not occur beneath it. Erosion netting or blankets shall be securely anchored to the slope in accordance with manufacturer's recommendations.
iii. Utilities. Whenever possible, utilities shall not be located or installed on or in fill slopes. When determined that it is necessary to install utilities on fill slopes, all plans shall be designed by a geotechnical expert.
iv. Revegetation of fill slopes shall utilize native vegetation or vegetation similar in resource value and which will survive and stabilize the surface. Irrigation may be provided to ensure growth if necessary. Evidence shall be required indicating long-term viability of the proposed vegetation for the purposes of erosion control on disturbed areas.
g. Site Grading. The grading shall be reviewed considering the following factors:
i. No terracing shall be allowed except for the purposes of developing a level building pad and for providing vehicular access to the pad.
ii. Hazardous or unstable portions of the site shall be avoided.
iii. Building pads should be of minimum size to accommodate the structure and a reasonable amount of yard space. Pads for tennis courts, swimming pools and large lawns are discouraged. As much of the remaining lot area as possible should be kept in the natural state of the original slope.
h. Design Standards. The required reports shall include design standards necessary for the engineer and landscape expert to certify that development on slopes of 15 percent or greater, when combined with impacts from development of lesser slopes, will not increase runoff, sedimentation to affected streams or wetlands, erosion, or landslide potential more than 10 percent above base conditions. These requirements shall be incorporated as conditions into the final decision approving the proposed development.
D. Retention in Natural State. All partitions, subdivisions and existing lots with an area greater than one-half acre, an area equal to 25 percent of the total project area, plus the percentage figure of the average slope of the total project area, shall be retained in a natural state. Lands to be retained in a natural state shall be protected from damage through the use of temporary construction fencing or the functional equivalent. For example, on a 25,000-square-foot lot with an average slope of 29 percent, 25 percent plus 29 percent equals 54 percent of the total lot area shall be retained in a natural state. Retention in a natural state of areas greater than the minimum percentage required here is encouraged.
E. Revegetation Requirements. Where required by this chapter, all required revegetation of cut and fill slopes shall be installed prior to the issuance of a certificate of occupancy, signature of a required survey plat, or other time as determined by the city. Vegetation shall be installed in such a manner as to be substantially established within one year of installation.
F. Maintenance, Security, and Penalties for Erosion Control Measures.
1. Maintenance. All measures installed for the purposes of long-term erosion control, including but not limited to vegetative cover, rock walls, and landscaping, shall be maintained in perpetuity on all areas which have been disturbed, including public rights-of-way. The applicant shall provide evidence indicating the mechanisms in place to ensure maintenance of measures.
2. Security. Except for individual lots existing prior to January 1, 1998, after an erosion control plan is approved by the city and prior to construction, the applicant shall provide a performance bond or other financial guarantees in the amount of 120 percent of the value of the erosion control measures necessary to stabilize the site. Any financial guarantee instrument proposed other than a performance bond shall be approved by the city attorney. The financial guarantee instrument shall be in effect for a period of at least one year, and shall be released when the city planner and public works director determine, jointly, that the site has been stabilized. All or a portion of the security retained by the city may be withheld for a period up to five years beyond the one-year maintenance period if it has been determined by the city that the site has not been sufficiently stabilized against erosion.
G. Inspections and Final Report. Prior to the acceptance of a subdivision by the city, signature of the final survey plat on partitions, or issuance of a certificate of occupancy for individual structures, the project geotechnical expert shall provide a final report indicating that the approved grading, drainage, and erosion control measures were installed as per the approved plans, and that all scheduled inspections, as per subsection (C)(1)(d)(ii) of this section, were conducted by the project geotechnical expert periodically throughout the project.
H. Approval Procedure. The city shall approve new development or redevelopment on constrained slope areas only if the proposed use or structure meets all of these conditions:
1. Development standards are met as prescribed under subsection
(C) of this section.
2. Adequate protection is utilized to minimize landslide and erosion hazards, consistent with RRMC §
17.95.010 through §
17.95.080.
3. Notwithstanding the provisions of Chapter
17.105 RRMC, Article I, Variances, an adjustment of up to 20 percent from any dimensional standard in the underlying zoning district may be approved where necessary to avoid construction on slopes of 35 percent or greater or to meet the standards of subsection
(C) of this section.
(Ord. 23-418-O § 124 (Exh. A-4))