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HomeMy WebLinkAbout7. A. 1. Presentation of Valley View Road and CR 83 Drainage Study (D, E) General Business 7. A. 1. SSHAKO1'EE TO: Mayor and City Council Mark McNeill, City Administrator FROM: Bruce Loney,Public Works Director DATE: 07/22/2014 SUBJECT: Presentation of Valley View Road and CR 83 Drainage Study(D,E) Action Sought A motion accepting the Valley View Road and County Road(CR) 83 drainage study and directing staff to move forward on a comprehensive modeling and preliminary design of improvements in the Blue Lake Channel west of CR 83. Background Earlier this year,staff initiated a drainage study with WSB&Associates for the area south of Valley View Road and west of CR 83. The study was to analyze the channel capacity and what improvements can be made to keep the water from entering on to Valley View Road. In the past spring months with spring snow melt,surface drainage would run toward Valley View Road causing minor flooding on Valley View Road. The study is attached for Council review and a presentation will be made at the July 22,2014 workshop. The main items identified with the study is that the current condition of the watershed has a much high peak flow rate than the channel and the 36" culvert under CR 83 can handle. The City entered into a memo of agreement with SMSC,City of Prior Lake and the Prior Lake-Spring Lake Watershed District in 2006.Runoff rate of developed parcels were agreed upon to curtail the flows into the Prior Lake outlet channel and ultimately Minnesota River. The conclusions of the study is that we need additional modeling of the drainage district to evaluate system storage and to consider channel and culvert improvements. Coordination with the SMSC, Scot County Highway Department,City of Prior Lake and the PLSLWD will be needed to come up with a balanced solution. Coordination with the adjacent property owners will be done as well. Recommendation Staff recommends moving forward on further drainage modeling and meeting with the government bodies associated with the Memo of Agreement for the Prior Lake outlet channel.Also to consider preliminary design options in improving the drainage facilities in the area. Budget Impact The study and any future improvements will be paid out of the Storm Drainage fund. Relationship to Vision This supports Goal D and E: Maintain, improve and create strong partnerships with other public and private sector entities;and deliver effective and efficient public services by a staff of well-trained,caring,and professional employees. Requested Action A motion accepting the Valley View Road and County Road(CR)83 drainage study and directing staff to move forward on a comprehensive modeling and preliminary design of improvements in the Blue Lake Channel west of CR 83. Attachments: Study WSB d.9+srx&ues./nt. engineering.planning•environmental.construction 701 Xenia Avenue South Suite 300 Minneapolis,MN 55416 Tel: 763-541-4800 Fax: 763-541-1700 Memorandum To:Bruce Loney, City of Shakopee From:Bob Barth,Katy Thompson Date: July 15, 2014 Re: Valley View Road and CR 83 Drainage Study WSB Project No. 1381-440 Introduction This memo presents results from WSB and Associates analysis of a portion of the Blue Lake Channel that lies a quarter mile south of Valley View Road and west of County Road 83. The channel flows east toward County Road 83 crossing under the road through a 36-inch culvert. Stormwater runoff from 2,510 upstream acres has historically overwhelmed the channel and the City initiated this analysis in the winter of 2014 to better understand what improvements might help contain this channel flow. The City tasked WSB with the following: • Create an existing conditions hydraulic model of the channel parallel to Valley View Road and at the crossing at County Road 83 • Evaluate impacts from the Shakopee Mdewakanton Sioux Community's water reclamation facility discharge on channel performance • Evaluate impacts caused by the reconstruction of the CSAH 83 culvert • Develop a channel improvements to contain the 10-year flow • Develop culvert improvements to contain the 10-year flow Since the study was initiated a large storm on June 19, 2014 caused runoff to break out and enter the Greenfield and Wyndam Ponds neighborhoods to the north causing flooding in a number of homes there. This flooding gives additional urgency to this analysis. Executive Summary This portion of the Blue Lake Channel drains 2,510 total acres with the following breakdown: • SMSC— 1239 acres • City of Prior Lake—435 acres • City of Shakopee—835 acres The Joint Powers Agreement among the Cities, SMSC, and Prior Lake Spring Lake Watershed District would allow a 100-year full-development discharge of 189 cfs. The existing Stormwater Equal Opportunity Employer wsbeng.com Valley View Road and County Road 83 Drainage Study July 16, 2014 Page 2 Management Plan for the City of Shakopee, drafted in 2012, anticipates a full-development peak flow of up to 150 cfs at the 36-inch culvert under County Road 83, relatively close to what the JPA would require. However, current flow and culvert capacity diverges significantly from the numbers above. The hydrologic model used for this analysis calculates a current 100-year flow of 369 cfs and the 36-inch culvert under County Road 83 has a capacity of about 70 cfs. The high flow coming down the ravine into the channel and the 70-cfs restriction at County Road 83 are the primary causes of flooding in this location. Table 1 summarizes flow and capacity comparisons for the 100-year and 10-year events. Table 1—Flow and Capacity Comparisons 100-yr(6.0 inches) 10-yr(4.2 inches) Joint Powers Agreement Flow(cfs) 189 NA Surface Water Management Plan Flow(cfs) 150 55 Current Conditions Flow(cfs) 369 163 Culvert Capacity @ CR 83 70 70 Channel flow for both the 10-year and 100-year rainfalls crosses Valley View Road and enters the Greenfield and Wyndam Ponds neighborhoods. The flood conditions are nearly identical with the only difference being the duration of flooding for the 100-year event. Later in this report we compare 10-year flood extents for various conditions. The similarities between 10 and 100-year flooding mean these improvements are also effective in reducing the 100-year flood extents. A comprehensive solution to this flooding problem may include upstream storage and emergency routing in addition to channel improvements. However,this analysis focuses on the channel only. One option would be to increase culvert capacity along the channel. Increased culvert capacity at the two driveways and under County Road 83 can significantly reduce flood potential. In fact, three 36-inch culverts under County Road 83 can pass a simulated 370 cfs,which is essentially the 100-year flow we simulated coming down the ravine. Another improvement option involves constructing a levee to create a ponding area upstream of County Road 83. Existing culverts would be left in place. The discharge under County Road 83 increases from the current 70 cfs to about 120 cfs due to the higher upstream water elevation. The levee would range from one to ten feet high and would require about 51,000 cubic yards of fill. It would also take significant amounts of agricultural land out of production due to the levee width and construction. These improvement scenarios involve the channel only and do not look at what could be done upstream to reduce flows or within the neighborhoods to the north to route water through emergency overflows toward the gravel mine, for instance. The June 19, 2014 event verifies that the existing condition significantly exceeds the planned full-development flow. Given the events of June 19, 2014 we recommend a more comprehensive modeling effort of this portion of the Blue Lake Channel. This analysis would: Valley View Road and County Road 83 Drainage Study July 16, 2014 Page 3 1. Evaluate upstream storage and outlets and manipulation of these to achieve peak flow reduction. 2. Consider channel and culvert improvements to increase conveyance capacity 3. Evaluate emergency routes through the adjacent neighborhood to prevent a repeat of June 19, 2014. Background The channel drains about 2,510 acres of Shakopee Mdewakanton Sioux Community(SMSC), Shakopee, and Prior Lake land. Figure 1 shows the drainage area. The drainage splits are 1,239 acres for SMSC,435 acres for City of Prior Lake, and 835 acres for the City of Shakopee. City of Shakopee City of Prior Lake Shakopee Mdewakanton Sioux Community(SMSC) mot I Municipal Boundary Figure I—Channel Drainage Area Figure 2 shows the channel and its surrounding topography. Note that the land immediately north of the channel drains away from the channel and that ground rises sharply to the channel's south. When runoff overwhelms the channel, it breaks out over the land to the north and toward Valley View Road. The channel is man-made, constructed to better drain the agricultural land west of County Road 83. The channel does not encompass regulatory floodplain and is not Minnesota DNR Valley View Road and County Road 83 Drainage Study July 16, 2014 Page 4 designated public water, allowing the City of Shakopee more options in modifying the channel cross section and alignment. 24-in RCP EC 41 co En CO €1113 ar2 MO E er >_=..p 4 CO 36-in RCP 36-in CMP 2 x 18-in CMP LEGEND � Modeled X-Sections Existing Topo — CEO E High:1000 Ditch 033a Sit Low:814 OW 0 500 1,000 =EN=Feet Figure 2-Existing topography at Valley View Road and County Road 83 Spring flooding has been the most common and occurs when driveway culverts (shown on figure 2)may still be frozen. The Shakopee-Mdewakanton Sioux Community constructed a new water reclamation facility in 2006 which has since been discharging in the winter to wetlands upstream,possibly contributing to flows in the early spring and this freezing problem. During the summer, SMSC uses the reclaimed water for irrigation. The facility is permitted to treat and discharge up to 1.5 million gallons of water per day, but averages 380,000 to 800,000 gallons per day during the winter. During the review of the County Road 83 improvement project in 2008,the City had WSB create a hydrologic model of the area upstream of County Road 83. WSB used this model to generate flows for the channel hydraulic model created especially for this analysis. Prior to reconstruction of County Road 83,topographic information showed water could move in three directions once it breaks out of the channel banks: 1. North by northwest from the channel bend toward Valley View Road 2. North along County Road 83, crossing Valley View Road, heading north to a low point adjacent to County Road 83 3. Over County Road 83 where the 36-inch culvert is shown The County Road 83 improvement project eliminated the low point at the 36-inch culvert forcing water to move along the two remaining routes. Valley View Road and County Road 83 Drainage Study July 16, 2014 Page 5 Methods and Results WSB developed a HEC-RAS model for the channel and input stormwater flows from hydrologic model created in 2008. The model incorporated current survey and Lidar data from the Minnesota DNR to develop cross-sections and channel profiles. As-built information from the 2009 County Road 83 Improvement project was also used in the development of the present day conditions model. This hydrologic model used TP-40 rainfall so we used these same rainfall events in the HEC-RAS hydraulic model. NOAA had not yet developed the Atlas 14 update, which will eventually replace TP-40 for Shakopee's design rainfall events. Current Conditions The initial model run evaluated the 2-year(2.8 inches), 5-year(3.6 inches) and 10-year(4.2 inches)flooding extents based on the present day conditions. The modeled floodplain extents are shown in Figures 3, 4, and 5. 24-in RCP •c, s .arotlia4 45 t1' s4 z 7165 4S r_< e , ' MO 226 ¢ 4 1 {MLR ® 2 x 18-in CMP CO Reconstructed CSAH 83 culvert: LEGEND 9291 •229'x 36"RCP •Upstream invert el.843.83' 'c` r 2-Year Flood Exents OM •Roadway el.857.49' Modeled X-Sections �� � 00. 01i1 0 500 � Ditch ' Figure 3—Existing Condition 2-year Flood Extents Figure 3 shows that under present conditions,water breaks out of the channel for the 2-year event at the 36-inch driveway culvert near the 90 degree channel bend. This water breaks out through a narrow overflow and then spreads out into the agricultural fields to the northwest. Figure 4 shows the flood extent for the 5-year rainfall event under current conditions. Simulated flooding becomes much more extensive and begins cresting Valley View Road and entering the neighborhoods to the north. Valley View Road and County Road 83 Drainage Study July 16, 2014 Page 6 J' s '4."'"'44'- '4 .0' a 's r .a i "v a4 s 'i r _ } s xF s D n t- 7 i"s 24-in RCP 4 , '""^-=. • r .- _„ .,�. ti4k) � , } 4 r::..� <. � � X3516 ,, ` ...... ■ a a7s y� 1/Irif 5 <, i - �' 3105 E� 1 ! i' ,• 1 36-in CMP 2 x 18-in CMP * �. s}•' . • ei Reconstructed CSAH 83 culvert: LEGEND �" ' 9291 229'x 36"RCP r'or - •Upstream invert el.843.83' ei / 5-Year Flood Exents • •Roadway el.857.49' Modeled X-Sections WV 0 500 ,e 0b a 4i) ;Bet } Ditch Figure 4—Existing Condition 5-year Flood Extents Figure 5 shows the flood extents for the 10-year event. The 100-year event was also simulated. However, it looks very similar to the 10-year event in its extent and its breakout over Valley View Road, so it is not presented here. ,}x" ^ i.0 € . t •i r 24-in RCP iak �:tx a.kwc. s µ s 7165 ° � s�. , „ fit, it',4. S.i r A-, e tt 4. a f r —� ! J 8700 , v I ® _ 3 ' t-,e ..r Reconstructed CSAH 83 culvert: LEGEND ' « ` 929i •229'x 36"RCP i •Upstream invert el.843.83' ?• t 10-Year Flood Exents Roadway el.857.49' �° Modeled X-Sections '` yr€ OM Ditch Figure 5—Existing Conditions 10-year Flood Extents Valley View Road and County Road 83 Drainage Study July 16, 2014 Page 7 Pre 2009 Conditions Using the model built for the existing conditions,the historical conditions were evaluated by revising the culvert crossing at County Road 83 to the pre-2009 design. The reconstruction of County Road 83 raised the roadway elevation 8.4 feet at the channel and,by extending the 36- inch culvert, raised the culvert elevation 0.3 feet(according to the plans). The 10-year flood extents in Figure 6 are slightly less than the existing conditions due to a lower culvert and roadway. However, flooding still occurs, notably through the same northwest breakout at the 36- inch driveway culvert and channel bend. 4-in RCP SID ro ' `1 36-in CMP 2 x I8-in CMP CED .117,1111111r 'r Old CSAH 83 culvert LEGEND 168'x36"RCP Upstream invert eI.843.51' •, 10-Year Flood Exents Roadway el.844.11' Modeled X-Sections Ditch Figure 6—Pre 2009 10 year Flood Extents The results shown in Figure 6 tell us that capacity restrictions at both the first driveway and County Road 83 create the breakouts that flow north to Valley View Road. To further evaluate the impacts of County Road 83,we simulated the channel without the obstruction presented by the road and its culvert. Obviously,this eliminates any capacity constraint associated with the County Road and clearly points to the role the first driveway crossing has in diverting water to the northwest. L Valley View Road and County Road 83 Drainage Study July 16, 2014 Page 8 NO CULVERT l CD 2 i' , 111 ."_"_ �- • E in �.h. _ M a Okir ,JA it a ,: w'i.-. '" NO CULVERT 36-in CMP 2 x 18-in CMP ,�' � h -.., LEGEND [9291 4" ►+ 10-Year Flood Exents CD *' << Modeled X-Sections ii OW 0 500 . z,0 ; + ,. Ditch Figure 7-10 year Flood Extents without County Road 83 Restriction The results, shown in Figure 7, show that while the fields immediately upstream of County Road 83 are no longer underwater,the channel flows continue to break out at channel station 7764 and flow north to Valley View Road. This clearly shows the role played by the first driveway in causing water to break out to the north. SMSC Water Reclamation Facility Winter flows were evaluated by using the present day model and assuming the culverts were 98%blocked with ice. In Figure 8,the maximum SMSC water reclamation facility discharge (1,500,000 gallons per day)was run through the model and shows the same flooding pattern as the no County Road 83 results (Figure 7). This flooding points out the need to improve capacity at the first driveway crossing and potentially lower the driveway's overflow elevation. The current model accounts for a base flow from the SMSC Water Reclamation Facility and for summer rainfall events we find that this base flow has no effect on flood potential. Flood potential for large rainfalls is strictly a function of culvert and channel capacity. However,the Water Reclamation Facility base flow has the potential to fill upstream storage over a long period of time and thus increase the peak flow coming down the ravine into this portion of the Blue Lake Channel. The City of Shakopee needs more detailed analysis of the upstream areas under SMSC control to determine whether the base flow has this effect. Valley View Road and County Road 83 Drainage Study July 16, 2014 Page 9 24-in RCP i C j 226 $' Eaz tat CEO) * - 36-in RCP 36-in CMP k LEGEND 19291 CED * m, a.. f Winter/Spring Flood 1i Modeled X-Sections 0 500 X40 Ditch Figure 8—SMSC Facility Winter Flows with Blocked Culverts along Channel Proposed Channel Improvements A comprehensive solution to this flooding problem may include upstream storage and emergency routing in addition to channel improvements. However,this analysis focuses on the channel only. Figure 9 shows 10-year model results for culvert improvements to increase capacity at both driveways and at County Road 83. The three 36-inch culverts under County Road 83 pass a simulated 370 cfs,which is essentially the 100-year flow we simulated coming down the ravine. Valley View Road and County Road 83 Drainage Study July 16, 2014 Page 10 24-in RCP RIM 1411 \ is 3 x 36-in RCP 3x30-in PE 3x36-in PE CM) e_ it LEGEND CEM 10-Year Flood Extents Modeled X-Sections 0 500 Ditch Figure 9—Proposed Culvert Improvement and 10 year Flood Extents Figure 10 presents a different improvement scenario whereby a levee creates a ponding area upstream of County Road 83. Existing culverts are left in place. The discharge under County Road 83 increases from the current 70 cfs to about 120 cfs due to the higher upstream water elevation. The levee shown Figure 10 ranges from one to ten feet high and would require about 51,000 cubic yards of fill. It would also take significant amounts of agricultural land out of production due to the levee width and construction. Again,these improvement scenarios involve the channel only and do not look at what could be done upstream to reduce flows or within the neighborhoods to the north to route water through emergency overflows toward the gravel mine, for instance. Valley View Road and County Road 83 Drainage Study July 16, 2014 Page 11 4 2 , ';',4, : c,.^Z: ,, 24-in RCP 5806 c .. — 226 A. „.. 3516 1475 �� «` AP 36-in RCP 1 36-in CMP 2 x 18-in CMP ,, .., - 'V', , CO LEGEND 10-Year Flood Extents V 9291 Proposed Levee Modeled X-Sections Ditch Figure 10—Proposed Levee Improvement and 10 year Flood Extents Next Steps The existing Stormwater Management Plan for the City of Shakopee, drafted in 2012, anticipates a full-development peak flow up to 150 cfs at the 36-inch culvert under County Road 83. The hydrologic model used for this analysis calculates a 100-year flow of 369 cfs and the 36-inch culvert under County Road 83 has a capacity of about 70- cfs. Clearly,the discrepancies between capacity,projected flow, and current flow requires closer coordination among the SMSC, City of Shakopee, and Scott County to determine the right mix of storage and conveyance to reduce the flood risk in this portion of the Blue Lake Channel. The cities of Shakopee and Prior Lake and the SMSC restrict their discharge to the Prior Lake Outlet Channel according to a Joint Powers Agreement that includes the Prior Lake Spring Lake Watershed District. Though this restriction pertains to discharge at the channel it is reasonable to expect that the three entities could achieve this same level of rate control upstream of County Road 83. If such were the case the flow in table 2 would occur under County Road 83. Table 2—JPA Flow Restrictions at County Road 83 (100-yr) Entity Drainage Area Allowable Discharge Total Discharge (ac) (cfs/ac) (cfs) SMSC 1,239 0.05 62 City of Prior Lake 435 0.10 44 City of Shakopee 835 0.10 84 Totals 2,510 -- 189 Valley View Road and County Road 83 Drainage Study July 16, 2014 Page 12 Notably the 189 cfs is close to the Stormwater Management Plan 100-year flow of 150 cfs assumed at the 36-inch County Road 83 culvert. Both are significantly lower than the 369 cfs currently calculated as coming down the ravine and into the channel and both are significantly more than the 70 cfs culvert capacity under CR 83. The June 19th event verifies that the existing condition significantly exceeds the planned full- development flow. Given the events of June 19, 2014 we recommend a more comprehensive modeling effort of this portion of the Blue Lake Channel. This analysis would: 1. Evaluate upstream storage and outlets and manipulation of these to achieve peak flow reduction. 2. Consider channel and culvert improvements to increase conveyance capacity 3. Evaluate emergency routes through the adjacent neighborhood to prevent a repeat of June 19, 2014. The analysis summarized here, initiated and nearly complete prior to the June 19''event, looks at the channel alone. It is an adequate start but not comprehensive enough to consider all the options available to alleviate this flooding problem.