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RESOLUTION 85-8 CITY OF LAKE ELMO WASHINGTON COUNTY, MINNESOTA A RESOLUTION FORMALLY ADOPTING THE "ONE PERCENT RULE" FOR THE CITY OF LAKE ELMO. WHEREAS, the City Council of the City of Lake Elmo has been and is very concerned over increased surface water within the City; and, WHEREAS, the City of Lake Elmo desires to adopt a policy requiring restrictions on both the rate and volume of increased surface runoff due to new constrution; and WHEREAS, the City of Lake Elmo anticipates that the adoption of a policy would help to limit the runoff volume, and to move any increased surface water into the ground water system; and WHEREAS, the City of Lake Elmo desires such a policy because a large portion of the City is landlocked and increased runoff volume, even at low rates, tends to collect at the low points in the Watersheds and to increase flood levels; and WHEREAS, the Lake Elmo City Council has reviewed and considered a policy referred to as the "One Percent Rule" which states that: 1. The annual probability of increased rate and volume of surface runoff, due to new construction shall not exceed one percent. 2.. "Annual probability shall not exceed one percent" d means that a 100 year storm of appropriate duration should be used for design, but that storms of lesser magnitudes should be examined as well. 3. Surface runoff is water leaving the property on or very near the surface. 4. Surface runoff rate is the peak discharge as calculated by appropriate hydrologic method for a. storm of critical duration. 5. Volume is the total volume of water calculated by an appropriate hydrologic method for a storm of critical duration. The rational method is. not appropriate for calculation of runoff volumes unless coefficients are adjusted. New,, THEREFORE, BE 1T RESOLVED ty tne y Councli of the City Q Lake Elmo that the above referred to "One Percent Rule" is hereby formally adopted by the City of Lake Elmo.