A. The planning commission shall not approve any plat for subdivision which does not make adequate provision for stormwater and floodwater drainage channels and basins. The drainage system shall be separate and independent of any sanitary sewer system.

B. Where a subdivision is traversed by a watercourse, such as a drainageway, channel or stream, there shall be provided a watercourse easement conforming substantially to the lines of such watercourse. Whenever possible, it is desirable that the drainage be maintained by an open channel with adequate width for maximum potential volume of flow. Such area shall not be filled or built upon and a note to this effect shall be placed on the plat. Where topography or other conditions are such as to make impractical the inclusion of drainage facilities within rights-of-way, perpetual, unobstructed easements at least twenty (20) feet in width for such drainage facilities shall be provided in a manner satisfactory to the planning commission. Watercourse easements shall be carried to natural watercourses or to other drainage facilities.

C. The subdivider shall construct facilities required to carry away by pipe or open ditch any spring, flood, storm or surface water that may exist either previously to or as a result of the subdivision. Such drainage facilities shall be located in a right-of-way where feasible, or in perpetual, dedicated, unobstructed easements.

D. Where a watercourse separates the building area of a lot from the street by which it has access, the subdivider shall install a culvert or other structure to provide access across the watercourse or a note shall be placed on the plat prohibiting any development of the lot until an adequate culvert or other structure has been installed.

E. A culvert or other drainage facility shall in each case be large enough to accommodate potential runoff from its entire upstream drainage area, whether inside or outside the subdivision.

F. Where it is anticipated that the additional runoff incident to the development of the subdivision will increase the load on an existing downstream drainage system, the planning commission shall withhold approval of the subdivision until an engineer certifies either that the existing downstream system has adequate capacity to accommodate the increased load that is likely to occur during high water runoff periods when all lots within the subdivision are developed or that specified improvements to the downstream system will be required to accommodate the increased loads. The subdivider shall construct the required downstream system improvements as a condition of final plat approval and shall acquire and dedicate or convey to the city such easements downstream as may be required to assure access to the downstream system and improvements.

G. Whenever a plat is submitted for an area which has been designated as a flood hazard area, the planning commission may approve such subdivision only when it has determined that all the provisions of the city regulations requiring compliance with requirements of the National Flood Insurance Program have been met and that reasonable development of each lot within the flood hazard area may be accomplished without a waiver or variance from the requirements of Chapter 15.08 BMC.

H. When a proposed drainage system will divert water across private land outside the subdivision, appropriate drainage easements or enforceable agreements to convey such easements shall be secured and submitted with the preliminary plat.

I. Drainage and utility easements shall be separate and independent of each other unless a shared easement is agreed to by the city administration and all utilities.

J. The subdivider shall install all culverts and pipes and construct all improvements necessary to ensure that the drainage system for the subdivision will function without overflow during high water runoff periods. Thaw pipes meeting city specifications shall be installed in all culverts that are forty (40) feet or longer. Upon the recommendation of the director of public works, the commission may require the installation of thaw pipes in other culverts. A final plat may not be approved unless, prior to the installation of each culvert required as a part of the subdivision, the director of public works has inspected and approved the ditch and compacted bed excavated and prepared for the culvert. [Ord. 01-05 § 7.]