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The severe constraints associated with the development of steep slopes Include: 1) Subdivision roads with steep gradients which are hazardous under icy conditions, 2) Large cuts and fi I Is which may be unstable, 3) Access roads to lots with even steeper gradients, which may not be accessible, 4) Some lots may have no reasonable access through a large cut or fill on the main subdivision road, 5) I ntercept I on of steep hili s I de dra i nages. Appendix B Topographic Maps and Contours A major element of any subdivision plan or master plan Is a topograph i c map. The d i st i ngu I sh I 09 character i st I c of a topographic map Is Its abl I Ity to portray the position, both horIzontal and vertical, as well as size, shape, and elevation of features in the area. The contour I lnss of a topographic map are imaginary I inss on the land surface at the same elevation above sea level. The contour Interval Is the vertIcal difference between contours and it varies according to the amount of relief and the detai I needed for a particular map's purpose. A map made or used to depict or support a particular land use activity should be of sufficient scale, contour interval, and detaIl to show all pertinent topographic and cultural features related to that development. Using a contour map, it is possible to determine the average slope angle and gradient at any location. The closer the contour lines are together, the steeper the slope be i n9 represented. By measur I ng the e I evat I on change over a measured horizontal distance, the average gradient or slope angle can be determined. In construction plans, slopes are IO:~ A..O:\ 100:\ J?;USl'lllfl ~h~ }'&-reent tl1eor.e, <'ln3le. of ..lope ll'\ i:ibjf't.~, B.l'\d llolopc: ra.tl..o. POCENT 51..Ol':E =.,. It 100 " AKGU. OF SlOJ>~ ~LDPJC: RAt"IO" 'j:X y 56 frequently designated by a ratio such as 2:1 or 5:1. In this Instance the 2 means two feet horizontal distance to one foot of vert i ca 1 measurement. The re I at I onsh I p of these rat I os to percent slope and angle of slope are shown In the diagram. 'S The importance of topography, both natural and m~n-made. to development in Colorado cannot be overemphasized. An understanding of rock types, vegetation, drainage. cl imate, and active earth processes In relationship to topography Is one of the keys to successful development. Some of the planning elements affected directly by topography include: 1) road layout, 2) access to individual lots, 3) need for cut and fi II, 4) sewage disposal system feasibi I ity. 5) surface drainage control and pattern, 6) slope stabi Ilty. 7) lot layout. 8) density of units, 9) need for bui Iding envelopes, 10) visual impact, and 11) wi Idfire hazard. Clearly an essential component of any subdivision plan Is an adequate topographic map which shows the shape and character of the land surface proposed for development. Superimposing the proposed deve I opment on a topograph I c map can revea I unsuspected relationships that are not evident when considered Individually. The developer/bui Ider then can take advantage of desirable natural features and avoid problem areas, especially If a geologic Investigation provides data on subsurface characteristics of a site.