(A) Intent. The intent of these requirements is to guide development in the flood prone area consistent with the flood threat in order to minimize adverse effects on the public health, safety, and general welfare.
(B) Definitions. For the purpose of this section, the following definitions shall apply unless the context clearly indicates or requires a different meaning.
DRAINAGEWAY, NATURAL. Any naturally occurring watercourse, trench, ditch, swale or similar depression in which surface water or groundwater is collected and flows during any part of a year.
FLOOD LEVEL, MAXIMUM. The elevations at which flooding is recorded by the flood prone soils in a natural drainageway, for example, or the elevation of flood prone soil boundaries in undeveloped watersheds.
FLOOD PRONE SOILS. Based on the U.S.D.A. Soil Conservation Service Soil Survey of Olmsted County, Minnesota, alluvial soils or soils deposited by surface water runoff that indicate areas of land that are flooded temporarily. Any land area on which the following soils are located are subject to flooding and are flood prone soils:
Map Symbol | Soil Name |
19 | Chaseburg |
467 | Sawmill |
468 | Otter |
1846 | Kato
|
(C) Uses in the flood prone area. All uses located within the flood prone area shall be permitted only after a conditional use permit has been issued by the city.
(D) Development standards. The deposition of any fill or spoil from dredging or sand and gravel operations, the construction of any structure or the grading or paving of any area shall require certification by a registered professional engineer or hydrologist that the following conditions have been met. The City Engineer also shall review all permit applications to determine that the following conditions have been met:
(1) Fill deposited in the flood prone area shall be no more than the minimum amount necessary to conduct the use. Where any permanent building or structure is planned to be located fill shall be at a minimum of one foot above the maximum flood level;
(2) No net loss of capacity for surface storage of flood waters shall result from the activity. The cumulative effect of fill within the flood prone area shall cause no increase in upstream flood levels. Compensatory storage shall be provided to offset the storage lost through filling;
(3) The cumulative effect of fill shall not cause an increase in the velocity of flood waters;
(4) The effect of such activities in the flood prone area shall not result in an increase in erosion potential on the site or in the flood prone area downstream of the fill site;
(5) In no event shall an increase in the maximum flood level be permitted if it would affect any existing building;
(6) Fill shall consist of soil or rock materials only;
(7) All fill areas shall be stabilized with material which will ensure and protect against erosion, undercutting and undermining.
(E) Engineering studies. In developing proper hydrologic and hydraulic studies, the following conditions shall be addressed:
(1) Consideration of the effects of a proposed use shall be based on a reasonable assumption that there will be an equal degree of encroachment extending for a significant reach on both sides of the natural drainageway;
(2) The maximum flood level is calculated based on the location of alluvial soils and is therefore an historic record, not a reflection of the potential flooding once urban development occurs in the watershed or a portion thereof. Engineering studies shall address this difference, and, where the studies indicate that the maximum flood level, as defined, is at a lower elevation than the flooding elevation based on hydraulic studies of a developing watershed, then the flooding elevation of the hydraulic studies shall be used to determine all further development standards under this section of this chapter.
(F) Flood prone soils location. The location of flood prone soils shall be determined by the Zoning Administrator by scaling the location from the soils map covering the Byron area in the Soil Survey of Olmsted County, Minnesota. Otherwise, the applicant shall be given the opportunity to determine flood prone soils locations as part of the required engineering study carried out by a registered professional engineer or hydrologist.
(Ord. 2023-02, passed 5-9-23)