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Subp lc. Bluff Impact Zone: This definition is needed to describe the extent of the bluff impact <br /> zone; an area that is proposed to be managed for the protection of vegetation, soil and aesthetic <br /> resources within shoreland areas. It is reasonable to manage these areas to ensure that <br /> development activities will not involve significant vegetative clearing and soil disturbance or <br /> disruption of scenic vistas as viewed from the surface of a waterbody.Vegetation is important <br /> to bluff stability in four ways: it directly removes water from the soil layers;the root systems <br /> hold soil in place; vegetation softens the impact of raindrops which otherwise can jar loose soil <br /> particles; and, vegetation slows runoff and filters out suspended sediments. (4)Therefore, <br /> defining the bluff impact zone as the bluff plus 20 feet from the top of the bluff will reasonably <br /> achieve the objective of managing the bluff feature for soil and vegetation protection in <br /> shoreland areas. <br /> Subp. 18b and 18c. Toe of the Bluff and Top of the Bluff: These definitions are needed to aid <br /> in the definition and field location by shoreland managers and surveyors of the bluff and bluff <br /> impact zone as defined and discussed earlier in this document.The text of" 50-foot segment" <br /> and " an average slope exceeding 18%" were derived after detailed discussion by members of <br /> the Shoreland Committee to refine the definition of a bluff as proposed in earlier rule revision <br /> drafts. The definitions are reasonable because professional surveyors and planners (Minnesota <br /> Land Surveyors Association and Minnesota Planning Association)participating on the <br /> committee felt that these definitions in combination with the definitions for bluff and bluff <br /> impact zone will enable the accurate location and mapping of bluff features in shoreland areas <br /> for planning and development activities. <br /> *References for bluff discussion: <br /> 1. Drexhage,T. and Calkin P.E. (1981), "Historic Bluff Recession Along the Lake Ontario <br /> Coast,New York," New York Sea Grant Institute. Albany New York. <br /> 2. Personal communication with Dr.Tuncer Edil,Department of Civil and Environmental <br /> Engineering, University of Wisconsin-Madison son. Spring 1986 <br /> 3. Yanggen,D.A. (1981), "Regulations to Reduce Coastal Erosion Losses",pg. 89 IN: Bluff <br /> Slumping,Proceedings of the 1982 Workshop,Romulus,Michigan,February, 1982. <br /> 4.Tainter, Suzanne P. (1982) "Bluff Slumping and Stability: A Consumer's Guide",pg. 6. <br /> Michigan Sea Grant Program, Ann Arbor,Michigan. <br /> Item B, which addresses requirements for elevation of structures to prevent flood •amag-, <br /> contains several proposed rewordings of existing requirements, a new provision for lakes with <br /> extreme water level fluctuations,and a new provision for water-oriented accessory structures. <br /> The introductory language under this item has been rewritten to make it briefer and clearer. It <br /> requires structures to elevated consistent with local flood plain ordinances where. they exist. As <br /> with the current rules, where local ordinances do not exist several approaches are presented <br /> (Subitems 1-3)for determining the appropriate structure elevation. A new phrase has been <br /> added to reference the possibility of floodproofing certain structures rather than elevating them <br /> on fill,as an introduction to the specific requirements for water-oriented accessory structures <br /> under subitem (3), as explained below. <br /> Subitem(1) has also been also been rewritten. A statement has been added to authorize local <br /> officials, when they deem it prudent, to require structures to be elevated higher than the <br /> standard elevation requirements on lakes that have a history of extreme water level fluctuations. <br />