11-7-6 Storm Drainage

A. Ditches or Canals: No ditch or canal shall be approved as suitable for the use of storm drainage without the written permission of the appropriate ditch or canal company or of the water users for such use. No ditch or canal shall be used for storm water unless adequately improved to handle such water as might be reasonably expected to flow from canal and ditch water, subdivision runoff water, and other water expected to reach such canal or ditch. At the discretion of the city, ditches, canals or other waterways may be prohibited on property dedicated, or to be dedicated, for public use. The applicant shall remove such waterways from property to be so dedicated before approval of the final plat shall be granted. The applicant shall indicate ditches, canals or waterways to be removed on the construction drawings. B. Adequate Structures: Storm drains, cross gutters, dip stone inlets and other appurtenant structures shall be provided by the applicant as required to adequately dispose of the 10-year frequency storm flows developed within the limits of the subdivision along with the existing flows entering the proposed subdivision from adjacent properties. The applicant shall have the responsibility of providing off site storm drain extensions in order to satisfactorily dispose of drainage. An excess storm water passage capable of conveying the peak runoff from a 100-year storm event through the subdivision shall be provided. C. Design of Complete Drainage Systems: Complete drainage systems for the entire subdivision area shall be designed by a professional engineer, licensed in the state and qualified to perform such work, which shall be shown graphically. All existing drainage features which are to be incorporated in the design shall be so identified. If the subdivision is to be platted in phases, a general drainage plan for the entire area shall be presented with the first phase, and appropriate development stages for the drainage system for each section, indicated. All proposed surface drainage structures shall be indicated on the plans. All appropriate designs, details and dimensions needed to clearly explain proposed construction materials and elevations shall be included in the drainage plans. D. Design Requirements: The drainage and flood plan systems shall be designed to: 1. Permit the unimpeded flow of natural watercourses; 2. Ensure adequate drainage of all low points; and 3. Ensure applications of the following regulations regarding development in designated floodplains: a. Construction of buildings shall not be permitted in a designated floodway with a return frequency more often than a 100-year storm. b. Building construction may occur in the portion of the designated floodway where the return frequency is between a 100-year and a maximum probability storm, provided all usable floor space is constructed above the designated maximum probable flood level. c. Where floodway flows are generally determined to be under five feet per second (5 fps) and maximum flood depth will not exceed three feet (3'), such uses as cultivated agriculture, nurseries, parks and recreation facilities and accessory parking may be permitted. d. Any use of land is prohibited where flooding would create a public health hazard or problem. This includes shallow wells, uncased deep wells, sanitary landfills, septic tanks and on lot sewage disposal systems, water treatment plants, and sewage disposal systems not completely protected from inundation. e. Any contemplated floodplain encroachment or channeling shall be thoroughly analyzed and its effect on stream flow determined before such encroachment is undertaken. Any construction, dumping and filling operations in a designated floodway constitutes an encroachment and must be approved by the ALUA before beginning operation. f. All lots shall be located at an elevation of at least two feet (2') above the elevation of the 100-year recurrence interval flood, or, where such data is not available, above the elevation of the maximum flood of record. (Ord., 8-12-2003)