A. Purpose. To establish standards that protect water quality from pollutant loadings of sediment, nutrients, bacteria, and other contaminants, and maintain the stability of bluffs, shorelines, and other areas prone to erosion.
B. Land Alteration.
1. Within the bluff impact zone (BIZ), land alteration is prohibited, except for the following, which are allowed only by permit.
a. Erosion control consistent with a plan approved by the City and consistent with Section 12-3-10.F.
b. The minimum necessary for development that is allowed as an exception under Section 12-3-15; and
c. Repair and maintenance of existing buildings and facilities.
2. Within the water quality impact zone, land alteration that involves more than ten (10) cubic yards of material or affects an area greater than one thousand (1,000) square feet requires a permit.
C. Rock Riprap, Retaining Walls, and other Erosion Control Structures.
1. Construction, repair, or replacement of rock riprap, retaining walls, and other erosion control structures located at or below the OHWL must comply with Minnesota Rules, part 6115.0215, Subp. 4, item E, and 6115.0216, Subp. 2. Work must not proceed until approved by the commissioner, permitted by the US Army Corps of Engineers and all other permits are obtained. [See Figure 9 - below].
FIGURE 9: RIPRAP GUIDELINES DIAGRAM
2. Construction or replacement of rock riprap, retaining walls, and other erosion control structures within the bluff impact zone and the water quality impact zone are allowed with a permit consistent with the provisions of Section 12-3-10.F provided that:
a. If the project includes work at or below the OHWL, the commissioner must approve or permit the project.
b. The structures are used only to correct an established erosion problem as determined by the City.
c. The size and extent of the structures are the minimum necessary to correct the erosion problem and are not larger than the following, unless a professional engineer determines that a larger structure is needed to correct the erosion problem:
(1) Retaining walls must not exceed five feet (5') in height and must be placed a minimum horizontal distance of ten feet (10') apart; and
(2) Riprap must not exceed the height of the regulatory flood protection elevation.
3. Repair of existing rock riprap, retaining walls, and other erosion control structures above the OHWL does not require a permit provided it does not involve any land alteration.
D. Stormwater Management.
1. In the bluff impact zone, stormwater management facilities are prohibited, except by permit if:
a. There are no alternatives for storm water treatment outside the bluff impact zone on the subject site;
b. The site generating runoff is designed so that the amount of runoff reaching the bluff impact zone is reduced to the greatest extent practicable;
c. The construction and operation of the facility does not affect slope stability on the subject property or adjacent properties; and
d. Mitigation based on the best available engineering and geological practices is required and applied to eliminate or minimize the risk of slope failure.
2. In the water quality impact zone, development that creates new impervious surface, as allowed by exemption in Section 12-3-15, or fully reconstructs existing impervious surface of more than ten thousand (10,000) square feet requires a storm water permit. Multipurpose trails and sidewalks are exempt if there is down-gradient vegetation or a filter strip that is at least five feet (5') wide.
3. In all other areas, storm water runoff must be directed away from the bluff impact zones or unstable areas.
E. Development on Steep Slopes. Construction of structures, impervious surfaces, land alteration, vegetation removal, or other construction activities may be allowed on steep slopes, except for those areas in the BIZ, and only if:
1. The applicant can demonstrate that the proposed development can be accomplished without increasing erosion or storm water runoff;
2. The soil types and geology are suitable for the proposed development; and
3. Vegetation is managed according to the requirements of Section 12-3-9.
F. Conditions of Land Alteration Permit Approval. No permit for land alteration shall be approved unless:
1. Temporary and permanent erosion and sediment control measures to retain sediment onsite are consistent with the best management practices in the Minnesota Stormwater Manual, as it may be amended or revised from time to time;
2. Natural site topography, and soil and vegetation conditions are used to control runoff and reduce erosion and sedimentation;
3. Construction activity is phased when possible;
4. All erosion and sediment controls are installed before starting any land disturbance activity;
5. Erosion and sediment controls are maintained to ensure effective operation;
6. The proposed work is consistent with the vegetation standards in Section 12-3-9; and
7. Best management practices are used for protecting and enhancing ecological and water resources as identified in Best Practices for Meeting DNR General Public Waters Work Permit GP 2004-0001, as it may be amended or revised from time to time.
G. Compliance with Other Plans and Programs. All development must:
1. Be consistent with Minnesota Statutes, chapter 103B, and local water management plans completed under Minnesota Statutes, chapter 8410;
2. Meet or exceed the wetland protection standards under Minnesota Rules, chapter 8420; and
3. Meet or exceed the floodplain management standards under Minnesota Rules, sections 6120. 5000 - 6120.6200. (Ord. 568, 9-23-2021)