In an area with slopes greater than 15%, hillside local street standards may be utilized to encourage better adjustment to the topography of the area. See Exhibit 4 of this Ordinance and Article III, Section 3.05 of this Ordinance for more regulations on the use of hillside local roads. Existing significant topographical features, such as washes, hillsides, boulders and rock outcroppings, and established stands of native vegetation which cannot be re-vegetated, may warrant the approval of alternative engineering designs. Modifications would be considered on an individual basis, with approval by the Town Council. The following are requirements and design alternatives for street construction in the hillside areas.
A. Grading Disturbance. Grading for the construction of public streets or private streets are subject to the cut and fill and land disturbance limitations of this ordinance, and shall be developed as prescribed by the Town Engineer, the International Building Code, and the Department. Furthermore, disturbance as a result of road grading shall reduce the subdivision-wide allowance for hillside disturbance, as prescribed in this Ordinance. Disturbance outside of street rights-of-way or private road street tracts meeting public street right-of-way standards as a result of road grading shall reduce the subdivision-wide allowance for hillside disturbance, as prescribed in this Ordinance. Any subdivision contained within an Area Specific Plan adopted prior September 19, 1996 shall be exempted from this Subsection.
B. Revegetation. Where scarring occurs as a result of street or utility construction, re-vegetation and restoration shall be required of the subdivider. Restored areas shall be graded and landscaped to blend with the natural vegetation and terrain, and stabilized to control erosion. Landscaping and stabilization shall occur concurrently with construction (See Article VI, Section 6.05 of this Ordinance).
C. Retaining Walls. Grade changes that require retaining walls may be used only with the approval of the Town Council. Where approved for use, vertical retaining walls shall be in conformance with Sections 5.06 and 5.07 of this Article. For grade changes of more than eight feet, the use of multiple walls in a series of terraces is required. If two retaining walls are separated by a landscaped terrace of a width at least the height of the taller of the adjacent walls, then each wall shall be considered as a separate retaining wall. The finished surfaces of retaining walls are encouraged to blend into the natural setting by such means as texturing and the use of earth tone coloring. The use of native stone as a veneer is also possible (See Exhibit 30).
For slopes of 50 degrees and less, mortar free stone retaining walls using irregularly shaped native boulders may be used, subject to structural and slope stability design considerations. Landscaping of the slope shall be provided to produce a more natural appearance (See Exhibit 30).
D. Balanced Excavation. Subject to Subsection 5.03.B of this Article, all excess excavated material shall be removed or incorporated as an integral part of the site development so that a natural look is maintained.
E. Drainage. Where drainage ways cross streets, culverts shall be installed to convey ten year frequency storm flows under the pavement, with higher volume storm flows being allowed to flow over the pavement in dip sections (See Exhibits 28 and 29). For washes with low flows, deletion of the culvert may be permitted where a concrete dip section is provided, when approved by the Town Engineer.