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Home My WebLink About5.a. Stormwater Management Plan Discussion - ENG 0089 �OJ�I�IOt.Il r 1 EXECUTIVE SUMMARY UTILITY COMMISSION Utility Commission Meeting: March 12, 2012 AGENDA ITEM: Stormwater Management Plan AGENDA SECTION: Discussion — ENG 0089 Ole ktc 11i t S5 PREPARED BY: Andrew J. Brotzler, PE, Director of Public AGENDA NO. ' /; A Works /City Engineer " ATTACHMENTS: Memorandum and Exhibits APPROVED BY: lq* RECOMMENDED ACTION: Discussion BACKGROUND At the last Utility Commission meeting, a preliminary review of the City's storm water area charges and utility rates was discussed. During this discussion, the City's current Comprehensive Surface Water Management Plan (SWMP) and strategies were also discussed along with alternative methods for overall management of storm water and flood protection within the city. Since this time, Mayor Droste, staff and Pete Willenbring have met to discuss various options for storm water management then constructing an overflow to the Mississippi River. The attached memorandum highlights the existing components of the current SWMP and includes a comparison of options and impacts for discussion and evaluation. Additionally, the two attached exhibits highlight the impact of a critical event based on the current storm water system. Pete Willenbring with WSB & Associates, Inc. will be in attendance at the meeting to review the options that may be considered as a change to the City's current SWMP. C:\ Users \ajd \AppData \Local \Microsoft \Windows \Temporary Internet Files \Content.Outlook \ONLP97EA \20120312 UC Stormwater Management Plan Update.doc WSB &Assoc- Engineering • Planning • Environmental • Construction 701 Xenia Avenue South Suite 300 Minneapolis, MN 55416 Tel: 763 - 541 -4800 Fax: 763 - 541 -1700 Memorandum To: Rosemount Utility Commission From: Pete Willenbring, PE Date: March 8, 2012 Re: Review of Options Available to Accommodate Stormwater Runoff Generated from the City of Rosemount WSB Project No. 1916 -24 INTRODUCTION/BACKGROUND This memorandum has been prepared as a follow up to the request by the Utility Commission to review the feasibility of converting to a stormwater plan that would develop storage and infiltration systems within eastern Rosemount instead of using the currently proposed pipe and/or open ditch overflow system to the Mississippi River. The Cities stormwater plan currently anticipates the construction of a pipe or open ditch overflow to the Mississippi River to accommodate runoff from rainfall exceeding a 100- year /24- hour duration event (6 inches in 24- hours). The piped overflow system would accommodate the additional runoff volume generated by longer duration events such as a 10 -day snowmelt event which creates approximately two times the runoff volume from a 100 -year 24 -hour duration event. It has been determined that the 100 - year /10 -day runoff event (snowmelt condition) is the critical event for flooding within the City of Rosemount. The Commission is also advised that should a 100 -year runoff event occur, because we have not yet constructed a pump that would provide a positive outlet from Shannon Pond and the outlet from the Bloomfield development is not yet complete, if no overflow is provided it is anticipated that approximately 50 structures could be inundated in and around Shannon Pond, and up to 135 structures could be inundated in the Bloomfield development (Figure 1A and 1B). Minneapolis • St. Cloud Equal Opportunity Employer CdUsers tajbVsppDato\LocalUticrosofl\Windows \Temporary Inland Files \ContatlOutlook\RTQJIJOI\MEMO utility commission 030612.doc Rosemount Utility Commission March 8, 2012 Page 2 Outlined below please find a listing of the various features associated with the two systems. These systems will be discussed in more detail during the Utility Commission meeting on Monday March 12, 2012. Storage /Infiltration System capable of Storm Sewer Overflow to Mississippi River handling 10 day runoff volume with no discharge • Pipe outlet from basin 1864 (Bloomfield • Pipe outlet from basin 1864 (Bloomfield development) would be finished and outfall development) would be finished, outfall to to the Flint Hills property and be the Flint Hills property and be operational operational (Figure 2). (Figure 2). • Pipe overflow conveyance system • A storage /infiltration system capable of constructed to river with capacity of 800 handling a 10 -day runoff overflow volume cfs at outfall into river. This system would with no discharge would need to be be capable of overflowing 16,000 acre feet developed. It would need to create storage to the river over a 10 day period. for approximately 8,000 acre feet of water within the community. • Approximately 30 acres of permanent • To accommodate the 10 -day runoff volume easements would be required to facilitate overflow, if the average depth of installation of the pipe outfall downstream stormwater storage was 5 feet, 1,600 acres of Bloomfield to the river of land would need to be reserved for this purpose. This could be provided as part of development or redevelopment, through the creation of regional ponding systems, or both. • If ponding was provided as redevelopment takes places, for each 100 acre site approximately 25 acre feet of additional stormwater storage would be required compared to the storm sewer overflow alternative. • Cost to construct trunk line estimated at • The cost to construct storage /infiltration $30 million. system estimated as follows: o Cost for excavation estimated to range from $20 to 65 million dollars o Cost for land (1600 acres) o Cost for regional improvements. See attached for description of regional improvements that were identified to be feasible and cost effective. C AUserstajbWppDataLLocal\Microsoft Wmdows\Temporary Inland Film \Contan.Outlook\RIVJUORMEMO ufilitycommission O30612.doc Rosemount Utility Commission March 8, 2012 Page 3 • Limited loss of tax base anticipated over • Stormwater storage /infiltration areas could easement area as pipe alignment would be not typically have structures placed within typically placed in road right -of -areas or in their footprint and would likely reduce areas as part of development in a way to developable area (See Figure 2). reduce impact on buildable areas. • System will have capability to overflow up to 16,000 acre feet every 10 days. • Construction of trunk system will reduce • Storage /infiltration areas will still require size and need for lateral conveyance system lateral system to direct water to regional in many areas. areas and/or serve as overflow routes. If storage /infiltration systems are provided on each site as they develop, the need for and cost of lateral system could be reduced. • Storm sewer outfall provides draw down • Storage /infiltration system must infiltrate capability following event to provide for runoff at 30 day critical duration runoff flood protection for longer duration events volumes to provide flood protection. (30 days). • Existing plan is approved by the • Updated plan will need to be approved by Vermillion River Watershed Vermillion River Watershed, Empire Township, Ninenger Township, and Flint Hills Resources • If approved by the above agencies, unlikely the City will be given allocation from MPCA for future pollutant or volume discharge to the Mississippi River. • Schedule: To provide flood protection for • Schedule: Regional improvements would residents in and around Shannon Pond and need to be constructed to accommodate Bloomfield developments, downstream overflow from upstream area tributary to outlet improvements will need to pond in Bloomfield development. completed. • Require agreement with UMore to impound water on their property without future discharge. • Require agreement with Flint Hills to impound water within their property without future discharge. C:\ Users\ajb\AppData\Local\Microsoft \Windows \Tanporary Intana Files \Contan.Outlaok\RTQJUOI\MEMO utility comnussion 030612.doc t r c Y t r :� 150T��H STREET s _ �" ' e H Cis i 1 `r .4''..—.1411 ° 11 , ! FTT . `� i � :4 4 I, i APPROX. CTUR 94 TO 1.02 ._ I �. �' , y STRUCTURE [MPACTEDt. 1 "-I � ' AT EL EV• 9 38 ` EEE , 938 Ili .. F . t 2439 '�' `» ' ` r 6 00 STORAGE ELT � , F Al 3. ELEV• 938 2 r * . 9< . r:. 24 Z > M rCb 4 " g 1 liir 0_ . , � t A-, 7. r y Z 7 s ' e ft •• ;� �� ,s� , d . ,...i'.4 ...-4-4 y f ,GFRN ]] ZZ 'r x ►� WACHTER L�. ' 1 �,`` .�- "�� " "'' •. ' c REV 9 40 STRUCTURE I MPACT ' r .,�...�'' . °' N 'ELEV. — 92 4 + "�STRUCTURE l PACT EL 950 0, #' ° E LEV. - 927.0. , 1r ," . WL H E 906' E ,' K r ; PPROx 50 - 57 - , r , . T 3 FLOOD ii t� y STRUCTURES I MPACTED _. _le, 9 . +' — 5 H u� ELEV. 9 18 920 , ii r AT ELEV• 930° r k n ELEy w 1 , .. ' fit 4-4.4„: ' ��'# w 1 ,, . � { .. +, Q r1, a ■err 4, yit -r 0 ' . ORA E � ELEV. '''� �:r.l�*''i w t //fiy '�', - z ELEV• 930 U .160TH STREET �. T fL LEGEND SHANNON POND AREA INUNDATED TO EOF —ELEV 930 A WACHTER LAKE AREA INUNDATED TO ELEV 938 I. m Flood Protection Analysis MB Project Nc 1916.24 Date March 7 2012 ,., 701 Xenra Avenue South. Suite 300 WSB Minneapolis MN 55418 100 - fear 10-Day Runo F:rient �»vw wsbeng corn I u re hter ff Lake Shannon Pond & War 9 • 1 ;45TRJ- F': , Erk;'kEEfio6 %pieeyf • :AV5TRUC1Cn Rosemount, Minnesota • I i • \( iAr: r r „... ,r. f , TPA IL , r,,, . 4 r . �. r Cr r Z f f' t r r , ' f ' , s rt, 0. .. AfflIrFF 1 M r' f • t 1 F. f i f r t t r • IN MINI rrr r T ,V ; gyp , 737 j rrrr k , r / / ? 3 r 1 • ", ),4 - t r ' g : I 1783 4 5 r _ _ � STRUCTURE I PACTS ,_, ,F.,, ' e,. - ELEV. — 922.3 r .. r F _ t' 1 . ' „ ' . 1F, ,, #(_t �, 1816 030-135 STRUCTUF , ,T - / , 1 , r ,14Ft nw r! EV. 938y_,, • • i EMERGE CY OVERFLO r tr ■ :., E L E — 9 38 145TH STREET.__ . , µ„", RO.D LOW PO1 T "�,” ' ELEV. — 922 , 16' DEEP I U DATIO v . ) i ( : f t 1 c r };� -' .err, : _ r, V ,. , -----1-- 2019 i l i 1 t „ r ,vrr.rr rt +,Y -, ,T , * ,-, I ,,, 2097 2104 I Flood Protection :Anal sis WSB Project No 1916.24 Date March 7 2612 - 701 Xenia a Avenue South. Suite 300 WSB Minneapolis. MN 55416 `"`”" "'g`°"' 100-1 car 10 -Dad Runoff 1:vcnt Figure Bloomfield Development '3.5'� ��0nM' 'P Rosemount, Minnesota • INF.3hSTRJCTURE . ENG IEEP op y: .10K5TRUC'T A