(A) Purpose. The City of Jordan requires developments or land disturbing activities to comply with the policies identified in the CSWMP. Activities are required to manage stormwater effectively, either on or off-site. To promote and encourage a reduction in runoff rates, encourage infiltration and promote increased groundwater recharge. Manage stormwater to minimize erosion, with an emphasis on stabilizing flow rates and velocities and prioritizing critical areas based on site characteristics, aesthetic conditions, and existing vegetation. Promote development strategies, land use practices, and surface water management activities that decrease and desynchronize peak runoff rates, lengthen the watershed time of concentration, and raise base flow levels.
(B) Regulation. No person or political subdivision shall commence a land disturbing activity or the development or redevelopment of land, unless specifically exempted by division (C) below, without first developing an approved project-specific SWPPP and obtaining all applicable permits from the city and other governing agencies.
(C) Criteria. Project-specific stormwater management plans shall comply with the following criteria:
(1) A hydrograph method based on sound hydrologic theory and approved by the city shall be used to analyze stormwater runoff for the design and analysis of flows and surface water levels.
(2) Stormwater runoff rates for the proposed activities, development, or redevelopment shall:
(a) Not exceed existing runoff rates for the 2-year, 10-year and 100-year, 24-hour, storm events;
(b) Not accelerate on- or off-site water course erosion, downstream nuisance, flooding or damage as demonstrated by the applicant according to division (C)(3)(d) below; and
(c) Be restricted to less than the existing rates when necessary for the public health, safety, and general welfare of the city.
(3) Runoff rates for the proposed activities in unincorporated areas shall:
(a) Not exceed pre-settlement runoff rates for the 2-year, 10-year, and 100-year, 24-hour storm events for land areas annexed into the city that are currently within unincorporated areas of the Scott WMO (Note: As land is annexed into a city, the land being annexed carries with it the existing condition. Parcels developed after the date of this section within unincorporated areas will be regulated using pre-settlement conditions and this would then become the existing condition for the city once the area is annexed. If agricultural land is annexed, agriculture is the existing condition. If roads or streets are present they are part of the existing condition.)
(b) The following curve numbers shall be used to analyze pre-settlement conditions:
Hydrologic Soil Group | Runoff Curve Number |
A | 30 |
B | 55 |
C | 71 |
D | 77 |
(c) For post-development runoff, drained hydric soils shall be assumed to revert to an undrained condition unless the applicant demonstrates that publicly owned and maintained drainage facilities shall be adequate to maintain the drained condition.
(d) Post-development runoff shall not accelerate on or off-site water course erosion, downstream nuisance, flooding or damage as demonstrated by the applicant according to division (C)(4) below; and
(e) Runoff rates may be restricted to less than the pre-settlement runoff rates when necessary for the public health, safety, and general welfare of the City of Jordan.
(f) In situations where the smallest practical outlet as identified by the city is being used and the site will not meet the 2-year discharge rates as identified in the pre-settlement conditions, the site discharge may exceed the pre-settlement 2-year discharge rate if the volume of the 2-year critical duration event being discharged is less than existing 2-year discharge volume from the site and the assessment required in division (C)(4) below is provided and shows no impacts from the increased discharge rate.
(4) An assessment of the potential for adverse impacts downstream of proposed site improvements, whether on- or off-site, is required except when the proposed activity, development or redevelopment is less than 20 acres and less than 8% of the site is covered by impervious surface, or when the rate control provisions of divisions (C)(2), (3), and (5), as applicable, are met; and the proposed activity, development, or redevelopment does not increase runoff volume for the 2-year, 24-hour, storm event (not including snow melt). To demonstrate that the proposed activity does not accelerate on- or off-site erosion, downstream nuisance, flooding or damage, the applicant shall complete an evaluation downstream to the point where the proposed activity is 10% of the drainage area (e.g. a 10-acre development shall evaluate downstream to the point where the drainage area is 100 acres). The evaluation at a minimum shall consist of and include an assessment of:
(a) Potential impacts to areas surrounding landlocked lakes or ponds, or lakes or ponds with inadequate outlets where flood levels would be increased by added runoff volume;
(b) Water levels in the receiving water bodies resulting from the contributing watershed’s full annual runoff yield during a 100-year wet year using the simplified hydrologic yield method (SHYM), or other approved methods for back-to-back 100-year, 24-hour storm events, for both existing conditions and fully developed watershed conditions; and
(c) The identification of public and private structures (including low floor and entry elevations of residences, and ISTS), and infrastructure (sanitary sewer, stormwater pipes and facilities, and roads) surrounding the receiving water bodies and located within 2 vertical feet of the future conditions water level elevation predicted using the SHYM, or the elevation for the back-to-back 100-year, 24-hour storm event.
(5) If there are public or private structures or infrastructure located within 2 vertical feet of the future conditions SHYM, or back-to-back 100-year, 24-hour storm event elevation, the applicant shall either demonstrate that no adverse impacts to health, safety, welfare, or property damage, would occur; or shall provide corrective actions. Corrective actions shall include the following as necessary to mitigate in proportion to the proposed project impact:
(a) Controlling post-development runoff volumes at existing conditions;
(b) Controlling runoff rates to less than existing conditions;
(c) Protecting or re-locating impacted structures or infrastructure, or securing easements for additional flooded areas; or
(d) Other approved actions necessary to mitigate the impact.
(6) Potential impacts. In the event impacts to public or private structures, downstream infrastructure, and erosion along the drainage path or in downstream public waters are identified, an evaluation shall be required. Evaluations shall include:
(a) The identification of existing public and private drainage easements;
(b) The locations, condition, and dimensions of the existing drainage infrastructure to the nearest regional stormwater facility;
(c) The location and elevation of structures with low floors, or entries within 2 vertical feet of the 100-year flood level;
(d) The location and description of known existing flooding problems;
(e) A hydrologic and hydraulic assessment of flooding impacts of the proposed project on downstream public and private structures;
(f) An assessment of existing and potential watercourse erosion, bank stability, bank protection, and watercourse slope;
(g) An assessment of the hydrologic and hydraulic capacity of the downstream public and private infrastructure;
(h) An assessment of property damages including health, safety, and welfare impacts relative to increased flooding of public and private infrastructure. Minnesota Department of Transportation guidelines shall be used to assess safety of flood levels at downstream driveways and road crossings.
(7) Identified property damage. In the event property damage, erosion, public health, safety, and welfare impacts are identified, the applicant shall provide approved corrective action. Corrective actions shall include the following as necessary to mitigate in proportion to the proposed project impact:
(b) Obtaining easements;
(c) The installation of stream bank stability and protection measures;
(d) The upgrading, protecting, or re-locating impacted infrastructure; or
(e) Other approved actions necessary to mitigate the impact.
(8) Wetlands. Evaluate potential impacts to wetlands with exceptional vegetative diversity or functional value (see § 154.337 for determination of exceptional value wetlands). Evaluations shall include:
(b) A hydrologic and hydraulic analysis of the before and after project water level bounce and period of inundation for wetlands with exceptional vegetative diversity for the 1-year, 2-year and 10-year, 24-hour storm events.
(c) The applicant shall provide corrective actions that mitigate in proportion to the proposed project impacts as specified in this rule; if the water level bounce and period of inundation created by the storms evaluated in this section exceeds the limit specified in Table (9)(a).
(d) Corrective actions shall consist of runoff rate and volume controls necessary to keep the water level bounce and period of inundation within the limits specified in Table (9)(a).
(9) All storm drainage conveyance systems shall have capacity for the runoff from a 10-year, 24-hour, storm event. All storm drainage ponds and related facilities shall be designed to store the runoff from the 100-year, 24-hour, storm event or accumulative antecedent conditions without damage to the system or facility, downstream areas and/or significant risk to public health, safety, and welfare unless waived in accordance with this section.
(a)
Hydroperiod standard | Highly susceptible wetlands* | Moderately susceptible wetlands* | Slightly susceptible wetlands* | Least-susceptible wetlands* |
Storm bounce 1 and 2-year events | Existing | Existing plus 0.5 feet | Existing plus 1.0 feet | No limit |
Period of inundation for 1 and 2-year events | Existing | Existing plus 1 day | Existing plus 2 days | Existing plus 7 days |
Period of inundation for 10-year event | Existing | Existing plus 7 days | Existing plus 14 days | Existing plus 21 days |
*See definitions | ||||
(b) Regional detention basins shall be utilized to manage peak flow rates and runoff volumes, and meet water quality objectives when required by the city. On-site stormwater detention basins, volume control facilities, and permanent sedimentation and water quality ponds shall be utilized for land disturbing activities, the development or redevelopment of land that creates greater than 1 acre of impervious surface when regional basins are not in place or feasible, or would not otherwise meet requirements for the protection of downstream areas according to §§ 154.331 through 154.341 that are located between the project and the regional basin.
(c) The city may approve alternative BMPs instead of permanent sedimentation and water quality ponds if it finds that the water quality performance of the proposed alternative BMPs is equivalent to that of a permanent sedimentation and water quality pond designed according to the criteria set forth for permanent sedimentation and water quality ponds in division (C)(11) below. The generally accepted performance of permanent sedimentation and water quality ponds designed to these criteria is 80% total suspended solids removal on an annual average basis. The assumed performance for the proposed BMPs shall be based on information from independent laboratory work, studies, or reference materials including the Minnesota Urban Small Sites BMP Manual (Metropolitan Council 2001), as such manual may be amended, revised, or supplemented. The city may require monitoring of alternative practices and contingency plans similar to the requirements for the general permit authorization to discharge stormwater associated with construction activity under the NPDES/SDS permit program permit MN RI 00001 (NPDES/SDS general construction permit) issued by the Minnesota Pollution Control Agency, August 1, 2003, as amended.
(d) Analysis of flood levels, storage volumes, and flow rates for downstream water bodies and detention basins shall be based on the range of rainfall and snow melt durations producing the critical flood levels and discharges.
(10) Landlocked water basins may be provided with outlets if an outcome based analysis and resource oriented management review regarding downstream impacts is completed that demonstrates:
(b) Dead storage is provided to retain the fully developed future conditions SHYM predicted water volumes, or the back to back 100-year, 24-hour storm event volume, above the highest anticipated groundwater elevation to the extent possible while preventing damage to property adjacent to the basin;
(c) The outlet does not create adverse downstream flooding or water quality conditions, or materially affect stability of downstream watercourses according to the criteria in division (C)(4) of this section;
(d) Proposed development tributary to the land-locked basin has incorporated runoff volume control practices to the extent practical;
(e) There is a demonstrated need for an outlet to protect existing structures and infrastructure; and
(f) The outlet design is part of an approved project-specific SWPPP.
(11) Detention ponds and other permanent stormwater quality management basins shall be designed to provide:
(b) An identified overflow spillway and downstream route sufficiently stabilized to convey the 100-year, 24-hour storm event;
(c) A normal water elevation above the ordinary high water (OHW) of adjacent water bodies or normal water level (NWL) where an OHW is not established; and
(d) Ten-foot wide vehicular access road to the outlet control structure for future maintenance.
(12) Permanent stormwater quality management must be provided in accordance with the NPDES general construction permit no: MN RI 00001 (as amended).
(13) Any new residential, commercial, industrial, and other habitable structures shall be constructed with the following minimum low floor elevations:
(a) Where the 100-year flood level has been established, low floor elevations shall be at least 1 foot above the 100-year flood level. Where the HWL of an adjacent basin has been established, low floor elevations shall be at least 1 foot above the HWL. Elevation of the lowest opening of a structure shall be a minimum of 1 foot above the emergency overflow elevation, or 2 feet above the HWL of the adjacent pond or waterbody, whichever is higher.
(b) For public waters and public water wetlands (DNR protected water bodies) where the 100-year flood level has not been established, low floor elevations shall be at least 3 feet above the ordinary high water level (OHW).
(c) The city shall require a minimum of 3 feet of freeboard above the 100-year back to back 24-hour rainfall event elevation for landlocked basins or ponds where emergency overflows cannot be provided.
(d) In all other cases, the low floor elevation shall be at least 3 feet above the highest known water level.
(e) The lowest exposed floor or opening elevation of structures that are adjacent to ponds shall be indicated on the site grading plan to ensure adequate freeboard. All new structures must have a certificate of survey supplied by the applicant for the city that clearly identifies the as-built low floor elevation and lowest opening elevations. Low floor elevations and lowest opening elevations must comply with the approved development plans, where applicable.
(14) Exhibits. The following represents the City of Jordan stormwater management project submittal checklist. The following exhibits shall accompany the project review application.
(a) Property lines and delineation of lands under ownership of the applicant.
(b) Existing and proposed site contour elevations at a minimum of 2-foot intervals.
(c) Delineation of the subwatershed contributing runoff from any/all off-site sources. Proposed and existing subwatersheds on-site. Emergency overflows and watercourses.
(d) Proposed and existing stormwater facilities location, alignment, and elevation.
(e) Delineation of existing on-site wetland, marsh, shoreland, and floodplain areas.
(f) For applications proposing infiltration as volume control; the identification, description, permeability, hydrologic soil group (HSG) classification and approximate delineation of site soils in both existing and proposed post-development conditions.
(g) The existing and proposed OHW and 100-year high water elevations on-site.
(h) Construction plans and specifications for all proposed stormwater management facilities, including design details for outlet controls.
(i) Stormwater runoff volume and rate analysis for the 2-year, 10-year, and 100-year, 24-hour storm events for existing and proposed conditions.
(j) All hydrologic, water quality, and hydraulic computations made in designing the proposed stormwater management facilities.
(k) Narrative addressing incorporation of infiltration BMP’s.
(l) Delineation of all ponding flowage, drainage easement, or other property interest to be determined for stormwater management purposes.
(15) Maintenance. All stormwater management structures and facilities shall be maintained in perpetuity to assure that the structures and facilities function as originally designed. The responsibility for maintenance shall be assumed either by the City of Jordan, or by the applicant entering into a compliance agreement with the city.
(16) Easements. The applicant shall establish, in a form acceptable to the city, dedicated easements and/or outlets, for ponding, flowage, and drainage purposes over hydrologic features such as water bodies and stormwater basins. The outlets and/or easements shall include the right of ingress and egress for inspection, monitoring, maintenance, and enforcement purposes.
(17) Outlots. The City of Jordan may require that the land be placed in an outlet or a conservation easement, in form acceptable to the city, to prevent the future expansion of impervious surface and the loss of infiltration capacity.
(18) Exceptions. No surface water management permit or stormwater management plan shall be required under this rule for the following land disturbing activities:
(a) Minor land disturbing activities such as home gardens, repairs, and maintenance work, including reseeding or sodding as necessary.
(b) Construction, installation and maintenance of ISTS other than those on steep slopes, on riparian lots within a Shoreland District or in a bluff impact zone.
(c) Construction, installation and maintenance of public utility lines or individual service connections unless the activity disturbs more than 1 acre, in which event division (G)(4) of this section below shall apply.
(d) A land disturbing activity that does not cause off-site erosion, sedimentation, flooding, or other hazards or damage, and disturbs:
1. In the Shoreland District, an area less than 10,000 square feet or less than 100 linear feet of shoreline; in conformance with the City of Jordan Shoreland subchapter for requiring erosion prevention and sediment control BMPs with building permits in a manner consistent with this rule and applicable city ordinances, as amended; or
2. Outside of the Shoreland District, an area of less than 1 acre in conformance with the City of Jordan Subdivision Ordinance for requiring erosion prevention and sediment control BMPs with building permits in a manner consistent with this rule and applicable city ordinances, as amended.
(e) Construction of any structure or associated land disturbing activity on an individual parcel in a subdivision with a stormwater management plan approved by the city, so long as any land disturbing activity complies with the approved plan.
(f) Development or redevelopment of, or construction of a structure on, an individual parcel with a land disturbing activity that does not cause off-site erosion, sedimentation, flooding, or other damage.
(g) Installation of any fence, sign, telephone, or electric poles, or other kinds of posts or poles.
(h) Emergency activity necessary to protect life or prevent substantial harm to persons or property.
(i) Redevelopment projects are exempt from criteria in divisions (C)(2) and (12) of this section. Note: For the purposes of this rule if an activity creates more than 1-acre of new or additional impervious surface the activity is considered new development and the exception shall not apply.
(k) Minor wetland impacts that have received a "Certificate of Exemption or No Loss Determination" by the City of Jordan in the capacity of administering the Wetland Conservation Act, as amended.
(l) All maintenance, repair, resurfacing, and reconditioning activities of existing roads, bridges, and highway systems which do not involve land disturbing activities outside of the existing surfaced roadway.
(m) Land disturbing activities associated with the construction of conservation practices by the SWCD or the Natural Resources Conservation Service (NRCS) provided that erosion prevention and sediment control practices are used in a manner consistent with this rule and applicable city ordinances, as amended.
(Ord. 2013-05, passed 5-20-2013; Am. Ord. 2022-01, passed 2-28-2022)