The provisions of this Section establish regulations for City Planning Commission review of development, enlargement or site alteration plans from the standpoint of the adequacy of protection for natural features within a Special Natural Area District. Plans that are deficient in this regard may be rejected or required to be modified, even though they comply with all other applicable regulations of this Chapter.

These regulations are to be used by the Commission in reaching a determination whether to approve development, enlargement or site alteration plans filed pursuant to Sections 105-41 (Certification), 105-42 (Authorizations to Alter Natural Features), 105-43 (Authorizations to Modify Bulk, Parking, Grading and Private Roads Regulations) or 105-44 (Special Permits).

The Commission, where appropriate, shall be guided by the reports from other city agencies involved in land contour work, storm water drainage systems and similar operations affecting natural features.

In determining the necessary alteration of natural features or extent of modifications involved in a development, enlargement or site alteration, the Commission shall be guided by the effect of any alteration of a natural feature on the total ecological process of the surrounding natural environment including the following: the effect of such alteration on the existing topography, soil conditions, erosion, natural flow of water and drainage, water quality, and animal, plant and marine life.

Further guidelines for the protection of natural features are:

(a)        No natural feature shall be moved, removed, covered, diminished, broken or disfigured, unless permitted pursuant to the provisions of Sections 105-30 (PRESERVATION OF NATURAL FEATURES) and 105-40 (SPECIAL REVIEW PROVISIONS). Furthermore, topsoil shall neither be removed from the surface of any zoning lot nor covered with inferior material unless permitted pursuant to Section 105-40. Where existing topography is altered without prior authorization of the Commission, the Commission may require new grading or other topographical modifications or surface improvement to reestablish the viability and function of the soil as a growing medium, and as a drainage surface, in order to permit the site to blend harmoniously with the surrounding area of the Special District.

(b)        Filling, excavating, draining, dredging, grading and contouring shall be staged and controlled so as to minimally impair the function, composition, vitality and existence of natural features. When and where possible, such operations shall be done in a manner so as to maintain or improve the biological system and individual features on the site.

(c)        All filling, excavating, draining, dredging, grading and contouring shall avoid creation of steep slopes or conditions causing erosion, loss of fertility of soil, health or safety hazards, and shall be done in conformance with the limits and nature of the soil involved.

(d)        All land operations including filling, excavating, draining, dredging, grading and contouring shall be limited to those operations which maintain or restore natural drainage, cause a minimum disturbance of the natural features and their setting while providing for the development, enlargement or site alteration or permitted uses.

(e)        No development, enlargement or site alteration shall be such as to impede or change the quality, turbidity, temperature or chemical composition of natural drainage or aquatic features.

(f)        A development, enlargement or site alteration shall be permitted only in areas sufficiently removed from the natural features to avoid impairment of their existence, functions or beauty.

(g)        There shall be maximum preservation of all natural vegetation in and adjacent to the natural features found on the site. Plant communities which have been substantially reduced in area or composition as a result of a development, enlargement or site alteration shall be restored, extended or replaced by alternative plant materials with an adequate maintenance program. In no case shall the site be allowed to be denuded and without vegetational cover upon completion of the development, enlargement or site alteration.

(h)        Replacement of any natural feature and planting of new vegetation on a site in the Special District shall be such as to extend, reinforce, increase the diversity, function and vitality of an association or community in the area. Special attention shall be given to symbiotic relationships between plants and the relationship between vegetation to be planted and animal populations which are dependent upon or related to the proposed vegetation. Where appropriate, planting shall include trees, shrubs, vines, ferns, grasses, herbs, annuals, biennials, perennials, mosses, and other associated vegetation.

(i)        Adequate provision shall be made for proper management and maintenance of natural features and their immediate surroundings to avoid pollution, loss of vigor, reduction in composition or function or other ecological damage.

(j)        Where appropriate, when a portion of a natural feature or its function must be altered, such alteration shall not only reinforce the function, vitality and existence of the remaining portion of the natural feature but also improve conditions for other natural features. This shall apply particularly but not exclusively to the removal and replanting of plant materials.

(k)        Where appropriate, a development, enlargement or site alteration shall be such as to leave natural features intact in their natural setting and, where feasible, visible from public streets or places.

(l)        For a steep slope, these additional requirements apply:

(1)        In all Residence Districts, for residential developments on individual zoning lots substantially within a steep slope area, the lot area per dwelling unit requirement shall not be less than 12,500 square feet. Except in R1 Districts located in Special Natural Area District-1 (NA-1), the Commission may, for a tract of land of at least four acres substantially within the steep slope area, modify, by authorization, the lot area per dwelling unit requirement set forth in this paragraph, (l)(1), for the steep slope area, and may allow development to be concentrated in clusters to preserve the steep slope areas in their natural state, provided that such clusters are located to the extent feasible in areas of comparatively flat topography and will not require unnecessary grading on adjacent slopes or the creation of new steep slopes.

(2)        In no event shall the lot area per dwelling unit requirement be less than the amount required by the underlying district regulations.

(3)        Existing vegetational cover in steep areas shall not be removed, destroyed or damaged except pursuant to development and grading plans approved by the Commission. An objective of such plans shall be to fit street layouts and building designs to the natural terrain, limit grading to a practical minimum and provide for maximum preservation of the natural terrain and vegetational cover.