Section 116.17. Levees, floodwalls and channel improvements.

 

(1)   General. The following standards shall apply to municipal floodplain zoning regulations for areas landward of levees, floodwalls and channel improvements.

(2)   Levees or floodwalls.

(a) A levee or floodwall shall be considered adequate if all of the following criteria and the requirements of par. (b) are met:

1. The minimum top elevation of the levee or floodwall shall be calculated using whichever of the following provides the greater protection from floods:

a. The profile of the regional flood with that regional flood confined riverward of the proposed levee or floodwall, plus 3 feet of freeboard; or

b. The standard project flood and/or the 500 year flood confined riverward of the proposed levee or floodwall.

c. Exceptions to the standards in subd. 1. a. and b. may be granted by the department on a case-by-case basis for levees and floodwalls not used to protect human life.

2. U.S. army corps of engineers standards for design and construction of levees and floodwalls shall be the minimum standard for levees and floodwalls.

3. Interior drainage shall be provided using designated ponding areas, pumps or other similar means, in accordance with U.S. army corps of engineers standards.

4. An emergency action plan, concurred in by the division of emergency government and approved by the department, shall be in effect for the area behind the levee or floodwall that would be in the floodplain without the proposed levee or floodwall in place.

5. The municipality shall provide notification to all persons receiving construction permits in the area behind the proposed levee or floodwall that would be in the floodplain without the proposed levee or floodwall in place that they are in an area protected by a levee or floodwall which is subject to flooding if the levee or floodwall is overtopped.

6. The levee or floodwall shall be annually inspected and certified, by a professional engineer registered in Wisconsin, that the levee or floodwall meets the standards in subds. 1. to 5. Annual reports of the inspection and certification shall be sent to the department for review.

7. The department reviews and approves the material submitted under subds. 1. to 5.

(b) No obstruction to flood flows caused by construction of levees or floodwalls may be allowed unless amendments are made to the floodway lines, regional flood profiles, floodplain zoning maps and floodplain zoning ordinances in accordance with the provisions of ss. NR 116.11 , 116.12 (3) and 116.21 (6) . Calculations of the effect of the levee or floodwall on regional flood heights shall compare existing conditions with the condition of the regional flood confined riverward of the proposed levee or floodwall.

(c) Floodplain areas protected by the adequate levee or floodwall shall be designated as flood fringe but may be regulated as areas outside of the floodplain unless the department determines that the levee or floodwall is no longer adequate.

(3)   Inadequate levees or floodwalls. If the department determines that an existing levee or floodwall does not meet the criteria of sub. (2) (a) , all floodplain areas landward of the inadequate levee or floodwall shall be regulated as if the levee or floodwall does not exist.

(4)   Channel improvements.

(a) Channel improvements shall be considered to reduce flooding potential provided the following criteria are met:

1. The channel improvements are designed and constructed in accordance with acceptable standards.

2. Velocities resulting from the channel improvements will not increase downstream erosion.

3. An engineer registered in Wisconsin certifies that the criteria in subds. 1. and 2. are met.

4. The municipality submits a plan detailing how the channel improvements will be maintained.

5. The department reviews and approves the material submitted under subds. 1. to 4.

6. The necessary permits under ch. 30 , Stats. , are obtained for construction of the channel improvements.

(b) Floodplain areas adjacent to channel improvements approved under par. (a) shall be zoned and regulated in accordance with the reduced regional flood profile provided the channel improvements are maintained in accordance with the plan submitted by the municipality under par. (a) 4.

(c) If the department determines that the channel improvements are not being maintained in accordance with the plan submitted by the municipality under par. (a) 4. , the floodplain zoning map shall be amended to reflect existing channel conditions.

(5)   New construction of levees, floodwalls or channel improvements. No anticipated changes in the flood protection elevations or floodplain and floodway limits, based upon proposed levees, floodwalls or channel improvements, may be effective until the improvements are constructed, operative and approved by the department.

(6)   Agricultural levees.

(a) Municipalities may permit agricultural levees which meet all applicable provisions of this subsection. For purposes of this subsection, an agricultural levee is one constructed to protect agricultural lands from floods that occur on a 10-year frequency or more often.

(b) Agricultural levees shall be designed and constructed so that the levees will overtop upon the occurrence of the 10-year frequency flood.

(c) Increases in flood heights in the area upstream from agricultural levees may not exceed 0.5 foot (15 cm.) for the 10-year frequency flood. No increase is allowed unless the written consent of the affected property owners is obtained prior to construction.

(d) Agricultural levees shall be designed and constructed to be overtopped and to cause no increase in flood elevation during the occurrence of the regional flood.

(e) The municipality's zoning administrator shall notify the department of the construction of any agricultural levees.

History: Cr. Register, February, 1986, No. 362 , eff. 3-1-86.