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J-1. Surface Water Management Plan Update0 CITY OF CNANNASSEN 7700 Market Boulevard PO Box 147 Chanhassen MN 55317 Administration Phone 952 2271100 Fax 952 2271110 Building Inspections Phone 952 2271180 Fax 952 2271190 Engineering Phone 952 2271160 Fax 952 2271170 Finance Phone 952 2271140 Fax 952 2271110 MEMORANDUM TO: Kate Aanenson, AICP, Community Development Director FROM: Terry Jeffery, Water Resources Coordinator DATE: January 20, 2015 b SUBJ: Surface Water Management Plan Update With the Riley -Purgatory -Bluff Creek Watershed District's adoption of the rules in August of 2014, all four watershed organizations have completed their local water management plan (LWMP) updates. Under Minnesota Statute we are required to update our plan to be consistent with the various organization LWMPs In anticipation of this, staff began working with Wenck Associates to update our Surface Water Management Plan Minnesota Rules Chapter 8410 dictates what must be included in a local water management plan. These minimum required elements include- 1 Plan purpose, Park & Recreation 2. Water resource management related agreements, Phone 952 2271120 3 Land and water resource inventory, Fax 952 2271110 4. Establishment of policies and goals, Recreation Center 5 Assessment of problems, 2310 Coulter Boulevard 6. Corrective actions; Phone 952 2271400 7 Financial considerations, Fax 952 2271404 8. Implementation priorities, Planning & 9 Implementation program, and Natural Resources 10 Amendment procedures. Phone 952 2271130 Fax 952 2271110 Many of these elements will remain relatively consistent with the two previous plans. Public Works Some of the elements, such as land and water resources inventory, are continuously 7901 Park Place being updated as land uses change. We have recently updated our hydrologic model Phone 952 2271300 for the entire City of Chanhassen This will be used to help identify and assess Fax 952 2271310 problems Our next step is to begin review of the current policies and goals and Senior Center update as necessary Staff will meet with the Environmental Commission in February Phone 952 2271125 to go over the existing policies and goals, offer suggestions for revisions and schedule Fax 952 2271110 an open house to open a dialogue with residents and stakeholder groups Website www ci chanhassen mn us Chanhassen is a Community for Life - Providing for Today and Planning for Tomorrow Kate Aanenson Surface Water Management Plan Update January 20, 2015 Page 2 Goal Number Goal Goal Statement I Water Quantity Provide 100-year (1% chance) flood protection for all structures Achieve water quality standards in lakes, 2 Water Quality streams, and wetlands consistent with their designated uses and established classifications 3 Wetlands Protect and rehabilitate wetlands to maintain or improve their function and value. Erosion and 4 Sediment Minimize soil erosion and sedimentation Control 5 Financing Establish and maintain funding sources to finance activities of this Plan Maintain primary responsibility for managing Regulatory water resources at the local level but continue 6 Responsibility coordination and cooperation with other agencies and organizations Public Provide information and educational resources to 7 Education and improve knowledge and promote an active public Information role in management of water resources. Table ES-1. Chanhassen Surface Water Management Plan Goals Concurrent with this, staff will begin updating the implementation program, specifically, local controls that will need to be revised as part of the plan update. Attached to this memorandum you will find a spreadsheet comparing the various watershed rules and our existing code The remainder of this report will be dedicated to summarizing the watershed organization rules and anticipated code changes FLOODPLAIN PROTECTION Our code was first adopted in 1986 and was based upon the 1979 Flood Insurance Rate maps (FIRM) Currently the Federal Emergency Management Agency (FEMA) is updating the FIRM maps but should not alter our overlay district. The only anticipated change to current ordinance will be to require mitigation for any reduction of storage volume Kate Aanenson Surface Water Management Plan Update January 20, 2015 Page 3 EROSION PREVENTION AND SEDIMENT CONTROL This section of the city code is in Chapter 19 and was recently updated In its current form it is consistent with all other rules Staff is reviewing the current top soil requirement as there is some ambiguity as to what constitutes "top soil" and how to assure compliance WETLAND AND CREEK BUFFERS This regulatory control has the widest disparity between entities and may prove impossible to reconcile It has long been the practice of Chanhassen to maintain local control to provide a central location for residents, developers and consultants to come to ask questions and procure permits Staff is recommending reviewing how setbacks are applied in an effort to bring buffer rules into compliance with the Minnehaha Creek Watershed District, but not adopting the Riley - Purgatory -Bluff Creek Watershed District (RPBCWD) rules as they are beyond what is required by any other agency. This would require certain groups and individuals to go to RPBCWD for permit acquisition The attached bar graph shows a to -scale representation of the various buffer requirements. Watershed districts do not require setbacks while cities do as there are development implications to not requiring setbacks The biggest concern with not having a setback is the expectation that a secondary structure such as a deck or patio can be installed. If the house is constructed at the buffer edge, then the opportunity to install a secondary structure is no longer present. Chanhassen setbacks are 30 or 40 feet and secondary structures may encroach 50% into the setback DREDGING AND SEDIMENT REMOVAL As these are generally regulated by the DNR and the PCA, Chanhassen does not oversee these activities Minnehaha Creek Watershed District has had a dredging rule in effect for some time now and has administered this permit with no apparent issue Given this, staff does not recommend adding dredging and sediment removal to our local controls. SHORELINE AND STREAMBANK STABILIZATION As these are generally regulated by the DNR and the watersheds, Chanhassen does not oversee these activities aside from requiring a zoning permit to assure that there is no conflict with utilities Minnehaha Creed Watershed District has had a shoreline stabilization rule in effect for some time now and has administered this permit with no apparent issue Given this, staff does not recommend adding dredging and sediment removal to our local controls. Kate Aanenson Surface Water Management Plan Update January 20, 2015 Page 4 STORMWATER MANAGEMENT There will be significant modifications to the stormwater management code and design standards These are found primarily in Chapter 19 but are referenced elsewhere. These modifications are not only a result of changes to watershed plans but changes to the National Pollution Discharge Elimination System/State Disposal System — Municipal Separate Storm Sewer System Permit (MS4). The primary focus of these changes will be to incorporate volume control into the standards and to provide credit to utility fees for compliance with the rule changes ATTACHMENTS 1 Buffer Comparison 2. Watershed Rule Matrix g \eng\terry\surface water management\2014 swmpg3 update\ineetmgs\memo_planningcom_012015 docx WIDTH IN FEET MANAGE CLASS 162 3 4 5 6 7 j 11 12 13 14 15 16 17 18 19 201 .2_1.._2 24 25 26 27 28 29 30 31 32 33 34 411 421 431 411 4_ 5L I 471 8L 491 101 511 _5_2 554[5_5.I_5I_5_8IA] 121 131 141 171 68I 611 711 711 721 711 141 711 711 771 711 791 80II2-1 231_�� CHANHASSEN BUFFER = 40' CHANHASSEN SETBACK = 20' CHANHASSEN SETBACK 2 STRUCTURE = 20 PRESERVE MINNEHAHA CREEK WATERSHED DISTRICT MIN BUFFER=67'AVG BUFFER=75' RILEY PURGATORY BLUFF CREEK WATERSHED DISTRICT MIN BUFF ER=40 ' AVG BUFFER=80' Add up to 15 for slopes and 10' for stormwater not to exceed SO CHANHASSEN SETBACK = 15 CHANHASSEN 2' STRUCTURE = 15 MANAGE 1 3T AVG=40' ' RILEY PURGATORY BLUFF CREEK WD - MIN BUFFER = 30' AVG BUFFER = 60' CHANHASSEN BOF '=20 CHANHASSEN SETBACK = 15 CHANHASSEN 2' STRUCTURE = 15 MANAGE 2 MINNEHAHA CREEK WD- MIN =24 AVG=30' I RILEY PURGATORY BLUFF WD MIN=20' AVG =40' C;_ 0 Add up to 15 for slopes and 10' for stormwater CHAN SETBACK = 15' CHANHASSEN 2' STRUCTURE = 15 MANAGE 3 WM'N= RPBCWD MIN =10 AVG =20' CREEKS I RBCWD STANDARD CHANHASSEN RILEY PURGATORY BLUFF CREEK WATERSHED DISTRICT MINNEHAHA CREEK WATERSHED DISTRICT NPDES MS4 PERMIT NOTES ALTERATIONDPLAIN ALTERATION THRESHOLD These uses shall be permitted within the F000dway District to the extent that they are not prohibited b an other ordinance or watershed district regulations and provided the do p y y g y not require structures, fill, or storage of materials or equipment In addition, no use within a floodway district shall be permitted to adversely affect the capacity of the channels or floodways or any tributary to the mainstream or of any drainage ditch, or any other drains a facility ors stem Any land -disturbing activities or filing of land below the 100-year fllod elevation of a waterbody in the watershed No person shall alter or fill land below the 100-year high water elevation without a permit QFQ �JP� �Q� The RPBCWD rule only applies within Boodplains All of Bluff Creek is already within SCOD and Chanhassen requires a 50 foot setback from top of bank of watercourses already Lakes have a setback of between 50' and 150' On subdivisions it has been our practice to acquire floodplain in outlot. 44CFR 60.3(d)( )) Communities must prohibit encroachments within regulatory floodways (44 CFR 59 1) unless it is demonstrated through hydro analyses that it would not result in ANY increase in flood levels _ _ _ _ _ _ _ _ _ _ _ _ _ In Chanhassen the 100 floodplain is concurrent to the floodway Any alteration of surface water flows below the 100-year flood elevation diverting, obstructing or newly outletting FLOODPLAIN ALTERATION CRITERIA Two feet freeboard above 100 year elevation No new impervious surface w/in 10- ear flood > 10% We have no mitigation requirement 1 1 volume mitigation 2-feet freeboard No adverse effect on flood risk, base flow, channel stability No increase in flood elevation 50' setback regardless of flood lain No structure w/in 100 feet of centerline of watercourse excepting bridges and trails 10' width Fill shall not result in a net decrease in storage capacity Mitigation shall occur cement of fill tcannot include expansion of shoreline cionrto e garamg must cormwi a cross-section origin WETLAND AND CREEK BUFFERS THRESHOLD With the creation of any new lot Rule B Flood lain Management Stormwater Management Rule Buffer should be required anytime that a wetaand is impacted or a mitigation area is created Rule E Dredging Water Body Crossings Rule Rule F Shoreline Stabilization New rinci al residential strucure with net increase in hardcover Rule G Watenrlbody Crossings Rule J Stormwater Management Applies to Properties Encompasing or adjacent to a public watercourse, PWI Wetland or other protected wetland Applies to Properties Encompasing or adjacent to any watercourse within a High Risk Erosion Area can provide contrary evidence WETLAND AND CREEK BUFFERS DISTANCES Preserve = 40' MIN 140' SETBACK [80FEETJ Exceptional = 80' AVERAGE 140' MINIMUM Preserve = 75' BASE / 67' MINIMUM Suggest altering setbacks to become consistent with MCWD and letting RPBCWD�nfoLatheirswn tt&rrrtlg.LSoUt redrinq§gjbdc),_ _ _ _ Fxisftq 1_fami 20'AVG/ 10' MIN _ _ _ _ _ _ _ For linear projects it shall be limited to the extent of the right-of-way _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Need to go throw h criteria for classification for each Manage 1 = 25' MIN 130' SETBACK 55 FEET High Value = 60' AVG / 30' MIN Manage 1 = 40' BASE/ 34' MIN Man e 2 = 20' MIN 130' SETBACK 50 FEET Medium Value = 40' AVG / 20' MIN Manage 2 = 30' BASE / 24' MIN Manage 3 = 16.5' MIN 130' SETBACK 146.5 FEET Low Value = 20' AVG / 10' MIN Manage 3 = 20' BASE / 16' MIN NA PW Watercourse = 50' AVG / 30' MIN NA High -risk a ercourse = WETLAND AND CREEK BUFFERS ESTABLISHMENT AND MAINTENANCE Must be planted and maintained with native vegetation of varying percent composition but can't be noxious or invasive species Must be planted and maintained in native vegetation May not cultivate 7o—w or pasture the buffer area. Must rip soils, establish native vegetation and have a maintenance and montioring plan 1fertifize Monuments required 1 per lot no more than 300 feet. May selectively remove noxious, etc and use herbicide/pesticide Monuments required every 100 feet No fill material or structure except boardwalk, sidewalk and stormwater features shall be allowed within buffer No fill material or structure except boardwalk, sidewalk and stormwater features shall be allowed within buffer No fill material or structure except boardwalk, sidewalk and stormwater features shall be allowed within buffer Shall be recorded against the property Recorded against deed Performance Bond 50 CY or 5000 SF 50 CY or 5000 SF EROSION & SEDIMENT When tributa to water of the state THRESHOLD u ree an ig y Erodible lane EROSION & SEDIMENT CRITERIA CONSISTENT DREDGING & SEDIMENT REMOVAL 0�k SOP `?� P O� Permit required to remove 1 CY or more of sedmient No dredging within ny public water Leave with watershed districts Only permitted for maintenance, nutrient reduction or wildife Same as RPBCWD No permit required if an approved DNR permit is procured City can get fast track permit up to 20CY with 48 hour notice DREDGING & SEDIMENT REMOVAL STANDARDS Must be minimal impact solution Must be minimal impact solution Cannot alter original alignment slope or x-section ID spoils disposal site Cannot enlarge natural basin or create new connections Must include plan to remediate sediment source where possible Will not occur above the OHW Remainder same as RPBCWD Cannot occur in channel steeper than 3:1 or lake 101 Ecolo icall sensitive anno cause seepage or resu in su su ce rainage SHORELINE & STREAMBANK STABILIZATION Q VP Q �O�P Permit required for any improvement or stabilization of a streambank or shoreline rip rap, sand blanket, etc Same as RPBCWD Sand blanket may be fastracked Add zoning permit provision for review ofclear cutting and other shoreland requirement but leave with districts and DNR No permit if DNR permit issued No permit to maintain existing if in -kind replacement SHORELINE & STREAMBANK STABILIZATION Must demonstrate need Must provide shoreline erosion intensity calculations to justify Sequencing Bioengineering Sequencing consistent with shoreline EIC Combination hardsca a and bioengineering With shear strees talcs to support can o riprap Used DNR criteria for design Retaining walls generally prohibited Sand blankets follows DNR rules STANDARD CHANHASSEN RILEY PURGATORY BLUFF CREEK WATERSHED DISTRICT MINNF14A11A r:RFFK WATPPRwr-in n1STP1rT AIDIICC UCA DCD111IT These development standards shall be reflected in plans prepared by developers and/or Subdivision of property one acre or larger into or more lots, alteration of New development and re -development projects with one acre or more We need to evaluate our triggers. One (1) acre perhaps too large but STORMWATER project proposers in the design and layout of site plans, subdivisions and water topography to effect runoff from 1 ac or larger lot disurbance This shall include areas less than 1 ac if part of larger commong RPBCWD triggers too low Creation of three or more lots, site plan that MANAGEMENT management features Le no minimum threshold 50CY FILL plan of development disturbs 10,000SF, creation of more than 5,000SF impervious surface, TRIGGER SF Disturbance 3 Lot Subdivision 3 Lot redevelopment that does not result in decrease in hardcover Language 1961 TP 40 Major Facilities desinged based upon 100-YR type II, Minor facilities No distinction desi ned for 1 YR ad evaluate 100-YR Atlas 14 or most recent NWS reference data Atlas 14 or most recent NWS reference data Existing permitees shall revise as necessary current program to implement and No increase in 1 , 10- and 100-year where SW discharges across site enforce a Post -Construction Stormwater management program that reduces No Increase in peak rates from proposed project for 1 or2, 10, and 100 year Variances z Limit peak flow rates to existing for 2 , 10- and 100-year storms for all points boundary For ag land new development shall not increase rates over modeled water pollution after construction related to new development and allowed if computations show no W where stormwater discharges site meadow condition. redevelopment Will need to define "at each discrete outlet" and no variances. ---------------------- No volume requirements Provide for abstraction of 1 1 Inches of runoff from impervious surface. Must No net increase from pre -project from pre -project conditions on annual basis of a- 0 ; Volume required via MS4 MCWD CCWMO and NPDES Construction. oretreat runoff for infiltration and filtration features Must have 3-feet separation. Provide for abstraction of first 10 inch of rain from impervious surface dischar a volume, TSS and TP Recommend MIDs - - - - - - - - - - - - - - - - - - - - - J- New development shall result in no net increase in TP from existing conditions Owners and/or operators of constructgion activities must submit site plans with 60%TP and 90%TSS Removal 60%TP and 90%TSS Abstraction counts to compliance Ag land shall be modeled as meadow conditionpost-con SW management BMPs to permitee for review and approval No BMPs required on existing single family homes Existing single family home sites largely exempt from design standards but No BMPs required on single family homes No BMPs required on single family homes We should set a minimum threshold. Anything below falls to District must install a BMP consistent with some MN guideline. MN WM MID Otherwise we administer. There are several areas deficient on treatment and storage (town center) o---------------------- wRedvelopmenl with <50% disturbance only treat new impervious and disturbed Nospecific requirement. Has been practice to address new impervious o >50% then all area Requirements vary depending upon size of site the percent of the site NET REDUCTION ON ANNUAL BASIS Volume, TSS and TP Should adopt policy for redevelopment anyway disturbed and whether impervious surface is reduced or increased, Limit peak flow rates to existing for 2 10- and 100-year storms for all points Maximum extent practicable and must make "reasonable attempt" to purchase w where stormwater discharges site New road or trail > 10,000 SF must meet all requirements additional R/W o Projects between 5000SF and 1AC provide 1 1" abstraction from new Road recon wl>10,000SF and <1ac new impervious must meet P and rate No specific requirements for linear projects Ofimpervious control a z Projects >1AC new impervious must provide abstraction of larger 0.55" runoff from new impervious surface or, 1 1" from net increase HC Road recon > lac new impervious must meet all requirements Applicant must provide narrative listing and explaining variables that limit feasibility of 1 inch. Narrative and concept plan discussing how reasonalble There are conditions in which infiltration is prohibited - contaminated soils, less Applicant must demonstrate to the satisfaction of district engineer that above modifications to project would influnce feasibility of meeting 1" An explanation than 3 feet to ground water, etc Must achieve volume reduction to max extent We have no vooume requirement so hence no restricted site sequencing and exceptions r— cannot be met Then followingsequencing of efforts undertaken b applicant to accomodate or remove constraints practicable MEP usingother techniques reuse, green roofs, etc Xu Abstraction of at least 0.55 inches from applicable impervious surfaces, or Must achieve abstraction of greatest amount feasible and at least 0.5 inches STORMWATER Abstraction of runoff on-ste to greatest extent practicable, or Must treat full Inch for P They offer unique credits trees MANAGEMENT Off -site abstraction and treatment. CRITERIA Adopt MIDs and MN SW manual sequencing and prohibited infiltration areas. All scenarios must meet 60%TP 90%TSS requirements 2 feet of free board 2 feet of freeboard landlocked 2 feet above back to back 100 year events or 10 day snowmelt Landlocked basins designed to hold back to back 100-YR whichever is greater Landlocked must hold back-to-back 100 year events 0 w Requirements for outletting landlocked dead storage requirements, review oE downstream impacts, demonstrate need May not increase volume draining to land locked receiving area Modeling Stormwater volume and rate analysis for 1, 10 and 100 Site plan w/ property lines, all contributing subwatersheds proposed BMPs, delineation of existing waterbodies, existing and proposed NWL of OHW, 2-foot Site plan with property lines, contrours and NAIL & 100-YR contours, construction plans for stormwater BMPs Geotech analysis at all proposed SW management locations soils sampling Ian to at least 5 feet at proposed facility locations as built drawings showing that compliant with approved plans Soil ammendment plan following MN SW Manual guidance All hydrologic hydraulic & water quality calcs used in the design All hydrologic, hydraulic & water quality calcs used in the design Create 0&M plan and declaration All facilities designed with maintenance access All facilities designed with maintenance access U In perpetuity maintenance In perpetuity maintenance Facilities maintenance inspection and monitoring Ian Facilities maintenance inspection and monitoring Ian az Eu Identifies schedule of activities & Responsible a ies Identifies schedule of activities & Responsible a ies z Provides for inspections and maintenance in perpetuity with records available at district's request The plan must be recorded against the deed The plan must be recorded against the deed Construction or reconstruction of a single-family home New development with less than 20% impervious or less than one acre area o ?5 �O Redevelopment of a site less than 5 acres that will result in 10% or greater X decrease in impervious surface or a site greater than 5 ac where less than 40% � disturbed & 10 /o reduction impervious LU Linear transportation projects with less than 10,000 SF of new impervious Sidewalks and trail 12 feet or narrower with an impervious downslope buffer at least 50% as wide