05-26-1992 Council Packet - Laserfiche WebLink

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8*. i Memo May 10, 1992 Page 2 The Hennepin County Soil Survey categorizes slopes at breakdowns of 0- 2%, 2-6%, 6-12%, 12-18%, 18-24%, and 24-35%. The soil survey does not Indicate that a specific slope percentage is necessarily limiting for development, but indici tes that construction costs and the need for more attention to grading and soil erosion protection become factors in the use of slopes for development as slope increases. Our 1978 Septic Code limited septic systems to slopes of 6-12% depending on the system type, and from 12-18% suggested the need for additional design consideration. However, the buildability of a lot using septic systems is not necessarily excluded merely because some portion of the lot is steeper than 18% slope. I have not been able to locate any concrete information as to why 18% was chosen as the boundary between buildable and nonbuildable land in the 1984 subdivision code. For unsewered property, if conforming septic sites are available, it can certainly be argued that it is technically feasible to construct a residence on a slope steeper than 18%, and adeguately protect the site from soil erosion and stability problems. Since 1984, staff has rarely if ever invoked the 18% slope dry buildable exclusion, and other than for dealing with septic systems, finds little justification for 1^ ' versus some other percentage slope. In the new Shoreland Ordinance, steep slopes are defined as lands having average slopes <^f 18% or greater as measured over horizontal distances of 50* or more, that are not bluffs. The DNR's proposed definition was primarily to deal with agricultural lands, and reads as follows: "Steep slope" means lands where agricultural activity or development is either not recommended or described as poorly suited due to slope steepness and the site's soil characteristics, as mapped and described in available county soil surveys or other technical reports, unless appropriate design and construction techniques and farming practices are used in accordance with the provisions of this ordinance. Where specific information is not available, steep slopes are lands having average slopes over 12%, as measured over horizontal distances of 50* or more, that are not bluffs. Since the agricultural references have little value to Orono, we just adopted the last sentence, changing 12% to 18% to fit our dry buildable" definition. Only five sections of the Shoreland Ordinance provide performance standards on steep slopes. These are attached as Exhibit C.^ These sections tend to place performance standards on certain activities on steep slopes, prohibit others, but generally do not entirely disallow development merely because of the steep topography.