(A) Stormwater management criteria.
(1) An applicant must install or construct, on or for the proposed land disturbing or development activity, all stormwater management facilities necessary to manage increased runoff so that the 2-year, 10-year and 100-year storm peak discharge rates existing before the proposed development are not increased and accelerated channel erosion will not occur as a result of the proposed land disturbing or development activity. An applicant may also make an in-kind or monetary contribution to the development and maintenance of the community stormwater management facilities designed to serve multiple land disturbing and development activities undertaken by 1 or more persons, including the applicant.
(2) Escrow account established. Prior to beginning any site work related to the approval of a subdivision, building permit, or excavation permit, the applicant shall provide the city with an erosion control deposit commensurate with the type of activity anticipated. The City Building Official shall set the fee as set forth in the city fee schedule. The deposit shall be held by the city in an escrow account established for that particular project. Thereafter, the applicant shall, on a continuous basis, keep the project site in compliance with each and every provision of this section. Failure to do so may result in the city mobilizing whatever efforts it deems necessary to bring the project into compliance with the city’s erosion control provisions. In such an event, the city shall calculate the actual cost of the intervention including labor, the cost of equipment or materials used and a 10% administrative fee (but not less than $50) and deduct that amount from aforementioned escrow account. Upon completion of the project and the establishment of sufficient turf to make erosion control measures unnecessary, the City Building Official shall notify the City Treasurer who shall return the balance of the escrow account to the applicant. In the event that the escrow balance drops below 50% of the escrowed amount, the applicant shall immediately provide the necessary funds to bring the account back to its original amount. Failure to do so shall result in the issuance of a stop work order by the city.
(3) The applicant must give consideration to reducing the need for stormwater management facilities by incorporating the use of natural topography and land cover such as wetlands, ponds, natural swamps, and depressions, as they exist before development, to the degree that they can accommodate the additional flow of water without compromising the integrity or quality of the wetland or pond.
(4) The following stormwater management practices must be investigated in developing a stormwater management plan in the following descending order of preference:
(a) Infiltrations of runoff on-site, if suitable soil conditions are available for use;
(b) Flow attenuation by use of open vegetated swamps and natural depressions; and
(c) Stormwater retention facilities.
(5) A combination of successive practices may be used to achieve the applicable minimum control requirements specified in division (A) above. Justification shall be provided by the applicant for the method selected.
(B) Detention facilities.
(1) Stormwater detention facilities constructed in the city must be designed according to the National Urban Runoff Program (NURP) wet basin design criteria and the urban best management practices as reflected in the WC publication, Protecting Water Quality in Urban Areas.
(2) The facilities must contain, at a minimum, the following design factors.
(a) A permanent pond surface area equal to 2% of the impervious area draining to the pond or 1% of the entire area draining to the pond, whichever amount is greater;
(b) An average permanent pool depth of 4 to 10 feet;
(An alternative to divisions (B)(1) and (2) shall be that the volume of permanent pool be equal to or greater than the runoff from a 2-inch rainfall for the fully developed site.)
(c) A permanent pool length-to-width ratio of 3 to 1 or greater;
(d) A minimum protective shelf extending 10 feet into the permanent pool with a slope of 10 to 1 beyond which slopes should not exceed 3 to 1;
(e) At the minimum of a 30-foot wide protective buffer strip of, if possible, predevelopment vegetation surrounding the permanent pool (all wetlands). The buffer strip’s width shall be increased at least 4 feet for every 1% of slope of the surrounding land. The city may choose to extend the size of the buffer strip to protect sensitive wetlands from degradation.
Where new buffer vegetation is planted “native” vegetation is preferred, since some non-native plant species cannot compete with native species and create a mono-culture of decreased environmental value. Useful references are the Minnesota Pollution Control Agency’s publications Buffer Zone and Soil Bioengineering.
(f) A device to keep oil, grease and other floatable material from moving downstream as a result of normal operations;
(g) Stormwater detention facilities for the new development must be sufficient to limit peak flows in each sub-watershed to those that existed before the development for the 10-year storm event; and (Also, calculations and hydrologic models used in determining peak flows must be submitted along with the stormwater management plan.)
(h) All stormwater detention facilities must have a fore bay to remove coarse-grained particles prior to discharge into a watercourse or storage basin.
(1) Runoff must not be discharged directly into wetlands without pre-settlement of the runoff.
(2) A protective buffer strip of natural vegetation at least 1 rod (16.5 feet) in width must surround all wetlands.
(3) Wetlands must not be drained or filled, wholly or partially, unless replaced by wetland areas of at least equal public value. Replacement must be guided by the following principles in descending order of priority:
(a) Avoiding the direct or indirect impact of the activity that may destroy or diminish the wetland;
(b) Minimizing the impact by limiting the degree or magnitude of the wetland activity and its implementation;
(c) Rectifying the impact by repairing, rehabilitating, or restoring the affected wetland environment;
(d) Reducing or eliminating the impact over time by preservation and maintenance operations during the life of the activity; and
(e) Compensating for the impact by replacing or providing substitute wetland resources or environments. Compensation including the replacement ratio and quality or replacement must be consistent with the requirements outlined in the rules adopted by the Board of Water and Soil Resources described in the Wetland Conservation Act of 1991.
(D) Steep slopes. No land disturbing or development activities are allowed on slopes of 18% or more.
(E) Catch basins. All newly installed and rehabilitated catch basins must be provided with a sump area for the collection of coarse-grained material. The basins must be cleaned when they are half filled with material.
(1) All newly constructed and reconstructed buildings must route drain leaders to storm sewer facilities or pervious areas wherein the runoff can be allowed to infiltrate.
(2) The flow rate of water from the leaders must be controlled so no erosion occurs in the pervious areas.
(G) Inspections and maintenance. All stormwater management facilities must be designed to minimize the need of maintenance, to provide access for maintenance purposes and to be structurally sound. All stormwater management facilities must have a plan of operation and maintenance that assures continued effective removal of pollutants carried in stormwater runoff. The City Engineer, or designated representative, must inspect all stormwater management facilities during construction, during the first year of operation and at least once every 5 years thereafter. The inspection records will be kept on file at the office of the City Engineer for a period of 6 years. It is the responsibility of the applicant to obtain any easements or property interests to allow needed access to the stormwater management facilities for inspection and maintenance purposes.
(H) Models; methodologies and computations. Hydrologic models and design methodologies used for the determination of runoff and analysis of stormwater management structures must be approved by the City Engineer. Plans, specifications, and computations for stormwater management facilities submitted for review must be sealed and signed by a registered professional engineer. All computations must appear on the plans submitted for review unless otherwise approved the City Engineer.
(I) Watershed management plans; groundwater management plans. Stormwater management plans must be consistent with adopted watershed management plans and groundwater management plans prepared in accordance with M.S. §§ 103B.231 and 103B.255, as they may be amended from time to time, respectively and as approved by the State Board of Water and Soil Resources.
(J) Easements. It is the responsibility of the applicant to obtain from adjacent property owners any necessary easements or other property interests concerning flowage of water.
(Ord. 2011-06-07A, passed 6-7-2011)
