Prior to development, grading and erosion control plans conforming to the following requirements shall be submitted and approved by the city. Erosion control measures conforming to best management practices (BMPs) approved by the city, or identified in the DEQ manual entitled "Catalog Of Storm-Water Best Management Practices For Idaho Cities And Counties", shall be required.
A. Plans: All grading and erosion control plans shall include the following:
1. Property boundaries.
2. All existing natural and manmade features and facilities within twenty feet (20') of the area to be disturbed, including, but not limited to, streets, utilities, easements, topography, structures, and drainage channels.
3. Existing and proposed finish contours of the areas to be disturbed, at two foot (2') vertical intervals. However, this requirement can be waived when the finished ground surface elevation does not vary by more than two feet (2') from the ground surface elevation prior to the proposed development.
4. Location of all proposed improvements, including paving, structures, utilities, landscaped areas, flatwork, and storm water control facilities.
5. Existing and proposed drainage patterns, including ridgelines and tributary drainage areas.
6. Storm water control facilities, including invert elevations, slopes, length, cross sections, and sizes. Construction details shall be shown for grassed infiltration areas, and/or detention/retention facilities.
7. Existing and proposed drainage easements.
8. Details for temporary and permanent erosion control measures.
9. Revegetation measures.
10. Plans shall be stamped and signed by a professional engineer or landscape architect, licensed in the state of Idaho. However, plans for public improvements shall be stamped and signed by a professional engineer licensed in the state of Idaho.
B. Review By Geotechnical Engineer: The project geotechnical engineer shall provide written proof of review and compliance to all grading plans. All grading shall conform to the most current adopted building code and the recommendations of the geotechnical engineer.
C. Installation Of Temporary Erosion Control: Temporary erosion control measures shall be installed and functional prior to start of any grading and/or land disturbing activity. They shall be maintained in a functional condition until the permanent measures are installed.
D. Retention In Natural State: All development shall retain an area or areas equal to twenty five percent (25%) of the total parcel plus the percentage figure of the average slope of the total parcel, in its 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 twenty five thousand (25,000) square foot lot with an average slope of twenty nine percent (29%), 25% + 29% = 54% of the total lot area shall be retained in a natural state. In this example a maximum of eleven thousand five hundred (11,500) square feet could be disturbed. Also, see exhibit 17.08.940A of this chapter.
Lots less than twenty five thousand (25,000) square feet, legally created prior to adoption of this article, shall be required to retain an area equal to fifty percent (50%) of the area calculated by the above formula. In the above example, on a lot created prior to this article, a twenty four thousand nine hundred ninety nine (24,999) square foot lot would need to leave twenty seven percent (27%) retained in the natural state. The area that could be disturbed would be a maximum of eighteen thousand two hundred forty nine (18,249) square feet.
E. Grading: All cut slopes shall be constructed in such a manner so that sloughing or raveling is minimized. The maximum allowable vertical height of any cut or fill slope shall be thirty feet (30'). The maximum inclination of fill slopes shall be two to one (2:1) (horizontal to vertical). For public roadways, the maximum allowable vertical height for cut and fill slopes in combination shall be sixty feet (60').
F. Temporary Erosion Control For Slopes With Erodable Surface Materials: All slopes with erodable surface material shall be protected with erosion control netting, blankets, or functional equivalent. Netting or blankets shall only be used in conjunction with 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. Temporary slope erosion control measures shall be installed upon completion of slope grading if permanent erosion control measures are not completed at the same time.
G. Revegetation Requirements: All areas with erodable surface materials that are graded and not paved shall be revegetated. The vegetation used for these areas shall be native or similar species that will reduce the visual impact of the slope and provide long term slope stabilization. All revegetation measures shall be installed, inspected by the city, and approved prior to the issuance of a certificate of occupancy, 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.
H. Maintenance Of Erosion Control Measures: 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 indicate the mechanisms in place to ensure maintenance of these measures.
I. Security: After an erosion control plan for a building site is approved by the city and prior to issuance of a building permit, the applicant shall provide a performance bond or other security in the amount of one hundred fifty percent (150%) of the value of the erosion control measures shown on the approved plan. The city attorney shall approve all security. The financial guarantee instrument shall be in effect for a period of at least one year from the project completion date. All or a portion of the security retained by the city may be withheld for a period up to three (3) 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.
J. Inspections And Final Report: Prior to the acceptance of a subdivision by the city or issuance of a certificate of occupancy for individual structures, the project geotechnical engineer shall provide a final report indicating that the project was constructed in accordance with their recommendations, and that all recommended inspections were conducted by the project geotechnical engineer.
K. Protecting Bare Soil During Development: All surfaces where bare soil is exposed during clearing and grading operations, including spoil piles, shall be covered or otherwise protected from erosion.
L. Construction Ways And Vehicles: Stabilized construction entrances and driveways shall be required for all construction sites to minimize sediment tracking onto roadways. Parking of vehicles shall be restricted to paved or stabilized areas. (Ord. 3160 §3, 2003: Ord. 3091 §6, 2003)