Title 17E Environmental Standards
Chapter 17E.040 Spokane Geologically Hazardous Areas
Section 17E.040.100 General Performance Standards
The following standards must be met for all development within geologically hazardous areas and associated buffers as classified in this chapter.
The development shall not increase surface water discharge or sedimentati on to adjacent properties beyond pre-development conditions unless approved by the department of engineering services.
The development shall not create adverse impacts on surrounding properties. These impacts include but are not limited to increases or decreases in water characteristics, deposition or removal of earth material, or changes that would harm the growth of existing vegetati on.
Alterati ons to the site shall not adversely impact other critical areas occurring on- or off-site.
The proposed development shall not decrease the factor of safety for landslide occurrences below the limits of 1.5 for stati c conditions and 1.2 for dynamic conditions. Analysis of dynamic conditions shall be based on a minimum horizontal accelerati on as established by the current version of the Internati onal Building Code.
Structures and improvements shall minimize alterati ons to the natural contour of the slope and the foundati on shall be tiered where possible to conform to existing topography. Terracing of the land shall be kept to a minimum to preserve natural topography where possible. Structures and improvements shall be located to preserve the most critical portion of the site and its natural landforms and vegetati on. All development should be designed to minimize impervious lot coverage.
Roads, walkways and parking areas shall be designed parallel to topographic contours with considerati on given to maintaining consolidated areas of natural topography and vegetati on.
Unless otherwise provided or as part of an approved alterati on, removal of vegetati on from an erosion or landslide hazard are or related buffer shall be prohibited. Removal of vegetati on, including trees, shrubs, grasses and forbs shall be the minimum required for construction. Any replanting that occurs shall consist of trees, shrubs and ground cover that is compati ble with the existing surrounding vegetati on, meets objectives of erosion prevention and site stabilizati on and does not require permanent irrigati on for long term survival.
Structures and improvements shall be clustered where possible. Driveways and utility corridors shall be minimized through the use of common access drives and corridors where feasible. Access shall be in the least sensitive area of the site.
Point discharges from surface water facilities and roof drains onto or upstream from an erosion or landslide hazard area shall be prohibited except as follows:
Conveyed via continuous storm pipe downslope to a point where there are no erosion hazards areas downstream from the discharge.
Discharged at flow durati ons matching predeveloped conditions, with adequate energy dissipati on, into existing channels that previously conveyed stormwater runoff in the predeveloped state; or
Dispersed discharge upslope of the steep slope onto a low-gradient undisturbed buffer demonstrated to be adequate to infiltrate all surface and stormwater runoff, and where it can be demonstrated that such discharge will not increase the saturati on of the slope.
On-site sewage disposal systems, including drain fields, shall be prohibited within erosion and landslide hazards areas and related buffers when sewer is available within two hundred feet or as otherwise provided by chapter 13.03 SMC
Date Passed: Monday, December 3, 2007
Effective Date: Sunday, January 6, 2008
ORD C34149 Section 8
