A. General Standards:
1. Construction shall be scheduled to minimize soil disturbance between December 1 and April 15.
2. The county engineer may require the grading operation and/or project schedule be modified if delays occur which result in weather generated problems not anticipated at the time approval was granted.
3. All development shall take into account land use planning, soil mechanics, engineering geology, hydrology, civil engineering, the environment, architectural and landscape design, and related disciplines as applied to hillside areas.
B. Development Of Special Hazard Areas: Any area that presents one or more of the following limiting factors shall not be permitted to develop unless the engineer of record can demonstrate to the county engineer, based on the required engineering reports, that these limitations can be overcome in such a manner as to prevent hazard to life, hazard to property, adverse effects on the safety, use or stability of a public way or drainage channel, and adverse impact on the natural environment:
1. Landslide areas or scarps, or areas of active landslides.
2. Lines of active faults.
3. Soils with a high shrinkage-expansion potential and hydrocompactible soils.
4. Soils with unified classification of ML, CL, OL, MH, CH, OH, and Pt as listed in ASTM.
5. Natural slopes greater than twenty five percent (25%).
6. Water table within six feet (6') of the surface at any time of the year.
7. Any area of hydrologic hazard as determined by the engineering hydrology report.
C. Vegetation:
1. Vegetation shall be removed only when absolutely necessary, such as for the construction of structures, filled areas, roadways, firebreaks, or as required by this title.
2. Every effort shall be made to conserve topsoil that is removed during construction for later use on areas requiring revegetation or landscaping, e.g., cut and fill slopes.
3. Vegetation or a chemical or mechanical stabilization method sufficient to stabilize the soil shall be established on all disturbed areas, except for proposed rights of way, as each stage of grading is completed. Areas not contained within property boundaries shall be protected with adapted, fire resistant species of perennial vegetative cover after all construction is completed.
4. New plantings shall be protected with organic cover unless determined not to be necessary in the slope stabilization and revegetation plan and report.
D. Grading And Stabilization:
1. All retaining walls with a total vertical height of four feet (4') or more, including footing, shall be designed in accord with the regulations of the Ada County building code.
2. All slopes that are stabilized by mechanical or chemical means shall conform to the surrounding terrain and shall be given aesthetic treatment that is consistent with the purpose of this article.
3. Large tracts shall be divided into smaller workable units on which construction can be completed within one construction season so that large areas are not left bare and exposed during the winter-spring runoff period.
4. All disturbed soil surfaces shall be stabilized or covered prior to December 1. If the planned impervious surfaces (e.g., roadways, driveways, etc.) cannot be established prior to December 1, a temporary treatment adequate to prevent erosion shall be installed on those surfaces.
E. Hydrologic Controls:
1. Curb and gutter, pavement, and appurtenant roadway drainage facilities shall be designed to control roadway runoff to such a point that it is contained within the natural watercourse system.
2. Watercourses shall be riprapped or otherwise stabilized below drainage and culvert discharge points for a distance sufficient to convey the discharge without channel erosion.
3. Any material from construction, including soil and other material, shall not be deposited within any floodway or watercourse.
4. Hydraulic structures in major watercourses shall be designed for the 100-year flood. In minor watercourses, such structures shall be designed for the 50-year flood.
5. With the exception of roadway crossings, approved drainage structures, and recreation and open space uses that do not involve the destruction of vegetative cover, development shall be prohibited within the 100-year floodplain for major watercourses, and the 50-year floodplain for minor watercourses.
F. Sediment:
1. Sediment catchment ponds shall be constructed and maintained by the owner at the downstream property line of each development or at other appropriate locations to protect downstream properties and watercourses from the adverse impacts of sediment generated on site due to development construction work. All sediment catchment ponds shall be designed to provide a minimum of forty five (45) minutes' detention time at a velocity not greater than two feet (2') per second and shall provide for the removal of surface debris and surface contaminants.
2. The overall drainage system shall be completed and made operational at the earliest possible time during construction. No certificate of occupancy shall be issued on the property until the drainage system is complete.
3. Alterations of major watercourses shall be prohibited, except for approved roadway crossings and drainage structures.
4. Natural or improved open channels shall be preserved, or provided for, in watercourses, except that at roadway crossings, conduits may be permitted.
G. Roadways And Circulation:
1. Roadway alignments shall be designed to create the minimum feasible amounts of land coverage and the minimum feasible disturbance of the soil.
2. Roadway alignments shall be designed to minimize removal of existing deep rooted perennial vegetation.
3. Roadway alignments shall be designed to follow natural terrain.
4. The width of the graded section shall extend five feet (5') beyond the travel right of way line on both the cut and fill sides of the roadway for slope rounding purposes. If a sidewalk is to be installed parallel to the roadway, the graded section shall be increased by the width of the sidewalk plus five feet (5') beyond the sidewalk.
5. Combinations of collective private driveways, cluster parking areas, and on street parallel parking bays shall be used where possible to attempt to optimize the objectives of minimum soil disturbance and minimum impervious cover.
6. Approval of the applicable transportation authority is required for publicly dedicated streets.
7. Paving shall commence within ninety (90) days of county engineer approval of a drainage study or drainage plan (see section 8-4A-11 of this title) and shall be completed within thirty (30) days of any building permit being issued.
H. Alternatives: The director may approve, or recommend approval of, an alternative development proposal when the overall design, as proposed by the applicant, meets or exceeds the intent and the requirements of this article and shall not be detrimental to the public health, safety, or welfare.
I. Maintenance: The owner of any private property on which grading or other work has been performed pursuant to a grading plan approved subject to the regulations of this article shall maintain in perpetuity and repair all graded surfaces and erosion prevention devices, retaining walls, drainage structures, means, and devices not subject to the jurisdiction of the applicable transportation authority, and plantings and ground cover installed or completed. Such requirements shall be incorporated into the protective covenants for a subdivision and the conditions of approval for development applications. (Ord. 389, 6-14-2000; amd. Ord. 766, 12-8-2010)