Written approval of the proposed stormwater drainage plan, or applicable stormwater management plan shall be obtained from the Lewiston City Engineer. No new or additional stormwater drainage that results from the development of a site shall be allowed to flow from any portion of the subdivision site to any adjacent lots, properties, ditches, canals, or waterways without the prior written authorization from the affected parties, with a note on the subdivision plat identifying a proposed and recordable drainage easement, provided by the adjacent property owner, ditch or canal company. The City Engineer shall approve the subdivision's stormwater management plan prior to recordation of the final plat.
A. No ditch or canal shall be approved as suitable for the use of storm drainage water without the written permission of the appropriate canal company or water user. No ditch or canal shall be used for stormwater unless adequately improved to handle the expected increase in flow.
B. The drainage plan shall be designed to:
1. Permit the unimpeded flow of natural watercourses.
2. Ensure adequate drainage of all low points.
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. Any use of land is prohibited where flooding would create a public health hazard or problem. This includes shallow wells, uncased deep walls, sanitary landfills, septic tanks and on lot sewage disposal systems, water treatment plants, and also sewage disposal systems not completely protected from inundation.
d. Recreational coach or mobile home parks and similar uses shall not be permitted in any designated floodway.
e. No lot one acre or less in area shall include flood lands. All lots more than one acre shall contain not less than forty thousand (40,000) square feet of land which is at an elevation at least two feet (2') above the elevation of the 100-year recurrence interval flood, or, where such data is not available, five feet (5') above the elevation of the maximum flood of record. (Ord. 13-01, 4-16-2013)