A. Adequate provisions for stormwater drainage shall be provided in accordance with requirements specified by this title and the standards of the Columbia Falls public works department. Those areas where a trunk storm sewer does not exist may require design and installation of drainage facilities for connection to a future storm sewer system. A waiver of protest against a future storm sewer special improvement district may be required to be executed by the subdivider and filed with the final plat when recorded. The grading and drainage plan shall be submitted to and meet the approval of the Columbia Falls public works department.

B. Drainage Analysis. Unless otherwise waived by the city council, an analysis shall be made, and documents submitted by a professional engineer, of the stormwater conditions as it affects and is affected by any subdivision having five or more lots. The analysis shall include:

1. Location of intermittent streams or drainage courses which are within the subdivision boundaries and a determination of their water surface elevation for a twenty-five-year storm;

2. Volume of stormwater entering the subdivision on a ten-year storm;

3. Volume of stormwater contributed by the subdivision before development and after development, based on a ten-year storm;

4. Analysis of the effects of the stormwater discharging from the site after development for a distance of one thousand feet downstream from the subdivision boundary at the point(s) of discharge;

5. In areas where groundwater may be a factor, the analysis shall include the effects of the groundwater on the total storm drainage system proposed for the subdivision.

C. Temporary Erosion and Sedimentation Control. During construction of improvements in the subdivision, the developer shall control the surface runoff by the installation of temporary erosion and sedimentation control facilities. No silt-laden waters or excess surface runoff caused by the development shall flow to downstream areas. (Ord. 588 § 1(part), 1996)