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HomeMy WebLinkAbout2B, Valentine Park Drainage Analysis Review EN HILLS Request for Council Review 2B Prepared By: Terry Maurer,Public Works Director Worksession Date: December 20,2010 Valentine Park Drainage Analysis Review Discussion Topic: WSB's Valentine Park Drainage Analysis dated February 2009 has been reviewed by Bolton and Menk. In addition staff will present survey information gathered regarding properties adjacent to Valentine Park and information received from Rice Creek Watershed. Staff will be seeking direction on how to proceed with the 2011 CIP programmed improvements in Valentine Park. Supporting Documents: 1. Memorandum dated December 20, 2010 from Terry Maurer and Kris Giga 2. Review Letter dated November 2, 2010 from Bolton and Menk, Inc. EN HILLS MEMORANDUM DATE: December 20, 2010 TO: Honorable Mayor and City Council Members Patrick Klaers, City Administrator ,yam FROM: Terry Maurer, Public Works Director 1� p Kris Giga, Civil Engineer SUBJECT: Valentine Park Drainage Review Background In February 2009, WSB prepared the Valentine Park Drainage Analysis in anticipation of a future park improvement project. Valentine Park historically has been periodically inundated when Valentine Lake's water level rises in spring snow melt or after large rainfall events. The WSB analysis was undertaken to better understand the options available for investment in the park given the periodic flooding from Valentine Lake. When the analysis was presented to the City, neighborhood concerns regarding its conclusions led to the City Council directing staff to have another consultant review the analysis and render a professional opinion regarding its conclusions. Discussion Staff solicited quotes and Bolton& Menk, Inc. (BMI)was retained to perform the review of the February 2009 WSB drainage analysis. BMI's letter dated November 2, 2010 summarizing their findings is attached. The summary of BMI's findings is that the inputs into the drainage model are accurate, and the conclusions in the WSB report appear to be appropriate. They do question the Normal Water Level (NWL) in the WSB report of 875.5 versus the Ordinary High Water Level (OHWL) they received from the DNR of 878.8. BMI also suggests the drainage model be rerun after a determination is made regarding which is the appropriate elevation so the City will have an accurate representation of a storm event. Staff also had Roseville's surveyor determine the lowest opening on the homes adjacent to the park. The lowest opening was determined to be a walk-out patio door at elevation 8839. BMI's review determined that the DNR's highest recorded lake level is 881.1. Industry standards would have the lowest opening elevation a minimum of 2' above the highest flood elevation. The above information indicates that there is 2.8' between the highest flood elevation and the lowest City Council Meeting = - 11Metro-inetlardenhillslAdmin\CouncillAgendas&Packet Information12010112-20-10 WorksessionTacket Information112- 20 ValentineParkDrainageReview.doe Page 1 of 2 opening. This would indicate that filling of the park to raise improvements out of flood danger should have no adverse effects on adjacent properties if proper drainage is included in the design. Staff met with Rice Creek Watershed (RCW)to discuss the outflow from Valentine Lake. RCW staff provided information regarding which portions of the outflow are controlled by the DNR, and which portions are controlled by the Wetland Conservation Act. Finally, staff met with Mr. Don Messerly to get an historic perspective on the park flooding. Staff also shared briefly with Mr. Messerly our findings from the overall analysis and our general thoughts about improvements to the park including drainage. At the workshop, staff will provide a detailed presentation of these findings. Staff will be looking for direction from the Council on how to proceed with the programmed 2011 CIP improvements to the park. City Council Meeting 11Metro-inetlardenhillslAdminlCounciIlAgendas&Packet Information120IO112-20-10 WorksessionTacket Information112- 20 ValentineParkDrainageReview.doc Page 2 of 2 • E-3C�L.T41'�.,I �. M �N K , ! Nam® • Consulting Engineers &Surveyors 12224 NicolletAvenue•Burnsville,MN 55337 Phone(952)$90-0509 o Fax(952)690-3065 www,bolton-menk.com November 2, 2010 Mr.Terry Maurer, P.E. Public Works Director City of Arden Hills Arden Hills, MN 55112 RE: Engineering Review for Valentine Park Drainage Analysis City of Arden Hills,Minnesota Mr. Maurer: We have reviewed the drainage analysis prepared by WSB&Associates on February 9,2009 for the Valentine Park sub-watersheds of the City of Arden Hills (City). In addition, we performed a site visit on September 22, 2010 to compare the hydrologic model assumptions with the existing conditions observed within the Valentine Park sub-watersheds. The drainage analysis,completed by WSB,provided three options for mitigating the localized flooding within Valentine Park. Per our scope of services we reviewed: "Option#1 —Maintain Park Facilities with Improved Drainage and Storm Water Treatment", found on page 8 of the drainage analysis,the data and results of the XPSWMM model, the practicality of the proposed stormwater system layout,and the apparent cost to value relationship of the overall improvements. Bolton &Menk, Inc. only reviewed the XPSWMM model results. The model itself was not provided for review. THE XPSWMM MODEL Based on the hydrologic model information that was provided in the drainage analysis it appears that the model parameters and assumptions were properly identified using the standard of care appropriate for an analysis of this type and scale_ When we compared the model assumptions with the existing conditions observed within the sub-watersheds it appears that the existing conditions are accurately reflected in the hydrologic model. The model identified localized flooding within the Glenview Avenue and the Crystal Avenue drainage networks for the 5-, 10-,and 100-yr, 24-hr storm events. This flooding was identified in the report, but we believe it is important to note that given that the area has been identified in the City's Pavement Management Program(PMP) for reconstruction, there are options available to the City,within the PMP, that will have a significant impact on downstream(Valentine Park)flooding. It is widely accepted that on urban sites,controlling stormwater at the source is more efficient,cost- effective,and sustainable than the alternative,end of pipe treatment. The City has the opportunity to implement street reconstruction Best Management Practices(BMPs)such as reduced pavement width, biofiltration, bioinfiltration, and other means of volume control and water quality in the PMP that would significantly reduce the downstream flooding at Valentine Park and meet the Rice Creek Watershed District abstraction requirements. This approach would be similar to Option#3 in the drainage analysis accompanied with additional hydrologic model evaluation. City of Arden Hills November 2,2010 Page 2 Finally, the hydrologic model that has been created for this project is a powerful tool that the City can and must utilize to efficiently evaluate the downstream effects of various BMPs installed in the upper sub- watersheds. The goals of this analysis would be reduced downstream flooding in Valentine Park,and increased water quality for stormwater flowing to Valentine Lake. DRAINAGE ANALYSIS The conclusions drawn in the drainage analysis appear appropriate given the input parameters,storm events modeled,and the results of the model. During our site visit we observed lake water approximately 15-in to 20-in deep in the Snelling Avenue 36"RCP culvert extending into the park,adjacent to the parking area,and backing up the park outlet ditch approximately 25-ft. This water level roughly corresponds to a lake elevation of 877.0. This elevation is approximately 1.5-ft higher than the stated Normal Water Level(NWL). This elevated lake water level creates a"tail water"condition at the culvert that increases the localized flooding within Valentine Park- One discrepancy we identified during the site visit may be related to the condition of the outlet for Valentine Lake. The report states that a recent lake level of 879.0,recorded on 10/14/08,is higher than the stated NWL of 875.5 likely due to beaver dams,within the lake's outlet channel,which have since been removed. We understand that the City and Ramsey County currently monitor and maintain the lake's outlet channel condition. We recommend that effort continue in order to keep the lake's outlet channel clear of debris and invasive species and control the Ordinary High Water Level(OHWL). It is our understanding that the 875.5 elevation was obtained from the Rice Creek Watershed District. However,the watershed district now recommends that Valentine Lake water level data be obtained from the Minnesota Department of Natural Resources(Mn/DNR). Our review of current Mn/DNR lake data conflicts with the elevations listed in Figures 3 and 4 of the drainage analysis and presumably the values entered into the hydrologic model (see Figure 1). According to Mn/DNR the OHWL of Valentine Lake is 878.7, the highest recorded water level is 881.1 taken on 07/03/78,and the latest reading taken on 10/01/10 was 879.58. The Mn/DNR defines the OHWL as: ...an elevation delineating the highest water level that has been maintained for a sufficient period of time to leave evidence upon the landscape,commonly the point where the natural vegetation changes from predominantly aquatic to predominantly terrestrial." The Mn/DNR makes no mention of a NWL of 875.5,and in general does not use that term. In addition, the lowest elevation recorded for the lake during the past 10 years was approximately 876.7 during the summer of 2002. We have included the Mn/DNR water level graph showing Lake Valentine water Ievels from the year 2000 to 2010(see Figure 1), which identify the elevation of 878.7 as the overall average elevation of the lake. We recommend that the lake OHWL and the 100-yr high water(881.1)level,as recorded by the Mn/DNR, be utilized to calibrate the XPSWMM model as a verification of the model's accuracy_ FA-CivillARDRU16120645\T16.120645 Report RevieW_FINAL.dorx City of Arden Hills November 2,2010 Page 3 Valentine — 62007100 679.75 6 $76.5 � 4,J Ui 877.25 676 2001 2002 200 2004 2005 2006 2007 2008 2009 2010 Figure L -Valentine Lake Water Level Graph(Jan 2000—Nov 2010) We understand that based on data that the City has collected on lowest structure opening for the residences adjacent to Valentine Park, the lowest opening recorded was 883.92,effectively three feet - above the 100-yr high water level(HWL)of Valentine Lake. The state minimum for lowest opening above HWL's is two feet. We believe that the current standard of three feet of free board provides an acceptable level of safety for residences adjacent to water bodies within the City. The tail water condition at the Snelling Avenue culvert that was identified in the drainage report as a "...contributing factor to the flooding in the park"may be mitigated,in part,with the installation of a tidal valve on the culvert outlet within Valentine Lake. If this approach is considered,the City will need to coordinate with,and obtain approvals from,the Mn/DNR and the Rice Creek Watershed District prior to installation. Although, if the average lake surface elevation is 878.7,no amount of mitigation with water quality and volume control BMPs in the Valentine Park sub-watershed areas will address the localized flooding in the park. This observation is based solely on the recorded OHWL of Valentine Lake and the ground surface elevation of Valentine Park. A tidal valve may represent a cost effective solution that would isolate the tail water effect created by the current OIIWL of Valentine Lake while still allowing the Valentine Park sub-watersheds to discharge through the culvert. PROPOSED STORMWATER SYSTEM LAYOUT The stormwater system layout identified in Option#1 appears to have been configured in the appropriate manner given the space constraints and park programming identified during the public meeting and recommended by the Park,Trails,and Recreation Committee. F:1_CiviHARDMT1 6 1 206451T]6.120645 Report Review_FINAL.docx City of Arden Hills November 2,2010 Page 4 When designing a stormwater treatment train,the most efficient use of space and money dictates that the rate control pond be the first BMP in the train. It has the capacity to absorb the incoming peak flows and discharge water in a more controlled manner. All of the BMPs downstream of the rate control pond can then be designed based on the discharge rate of the pond and not the incoming peak flow rates,thereby increasing efficiency and decreasing required space. The recommendations included adding fill material to Valentine Park to bring the mean elevation up from approximately 880.0 to 882.0. According to the XPSWMM model,those two feet of fill would protect the park amenities from flooding up to the 100-yr storm event. One alternative that was not evaluated in the drainage analysis was adding less fill to the park to protect it from a smaller storm, i.e. a 10-, 20-, or 50-yr storm and accept more frequent localized flooding as a result of construction cost savings. We do not believe that additional fill within Valentine Park will ultimately affect the OHW or the HWL of Valentine Lake. The area of the park proposed to be raised is very small when compared to the overall surface area of Valentine Lake. This can be evaluated within the XPSWMM model to provide a reasonable prediction of the change,if any. In addition the most current FEMA Flood Insurance Study (.tune 2010)lists a 500-yr high water elevation for Valentine Lake of 881.3. A second possible alternative would include modifying the PMP to incorporate volume control and water quality at the source,as described above, and then address the remaining flooding problem,if any, at Valentine Park through future hydrologic model evaluations. COST TO VALUE RELATIONSI41P VALUE OF THE IMPROVEMENTS The OPTION#1 stormwater management treatment train appears to have been appropriately sized,the proposed park elevation corresponds to the modeled 100-yr storm event,and the cost estimate included in Appendix C appears reasonable for the identified improvements. As mentioned above, there may be a more cost effective solution to the Iocalized flooding experienced at Valentine Park. The solution will require additional time to be realized as the PMP improvements are - constructed. It is very likely the most cost-effective solution will require a combination of integrating volume control and water quality BMPs into the PMP in the upper Valentine Park sub-watersheds. Based on the results of the XPSWMM model, implementing source control BMPs into the Glenview Avenue and Crystal Avenue sub-watersheds may have the greatest impact in reduced localized street flooding and downstream flooding within Valentine Park. Once the volume of stormwater flowing from the upper sub-watersheds to Valentine Park is reduced,the Valentine Lake outlet continues to be monitored and maintained by the City and Ramsey County,and the OHWL of the lake is verified at the appropriate elevation,the hydrologic model should be modified to reflect these improvements. With a revised and updated model the City can verify the need,if any,of additional park improvements to alleviate localized flooding. CONCLUSIONS There may be additional cost savings available to the City to address the localized flooding at Valentine Park. Portions of the approach will require additional time to evaluate,model, plan,and implement,but a _ number of the possibilities are straight-forward and simple, i.e. monitor the condition of the outlet of F:1_CiviIV"ffiT1 6 1 2 05451T16.120645 Report Rcview_F1NAL.docx City of Arden Hills November 2,2010 Page 5 Valentine Lake or evaluate the installation of a tidal valve on the Snelling Avenue culvert. However, if lake levels,as recorded by Mn/DNR,are accurate,the implementation of upstream BMPs will have a reduced benefit at Valentine Park. The addition of fill material to the park, to effectively raise the park out of the floodplain of Valentine Lake, becomes the primary solution to reduce localized flooding within the park. Our recommended next steps for further investigation of the Valentine Park flooding issues and potential mitigation efforts include the following: • Continued monitoring of the condition of the Valentine Lake outlet • Review Valentine Lake surface elevations(i.e. NWL,HWL,and OHWL)relative to any potential outlet modifications • Identify likely BMP improvements in the Valentine Park upper sub-watersheds • Update XPSWMM model with Mn/DNR OHWL level as well as potential BMP improvements in the Glenview Avenue and Crystal Avenue sub-watersheds • Utilize the Mn/DNR 100-yr HWL and the FEMA 500-yr HWL to calibrate the XPSWMM model. • Use the model as a tool to review multiple possible solutions to mitigate the Valentine Park and upper sub-watershed flooding • Based on model predictions select the best volume control and water quality BMPs and locations that result in decreased park and street flooding The City may want to account for a public comment period associated with the volume control and water quality BMPs in the upper Valentine Park sub-watersheds. If the BMPs are on or near private property it has been our experience that property owner buy-in is essential to project success. If the BMPs are in the city Right-of-Way it will be less of an issue,but getting public acceptance remains an important part of a successful project. Bolton&Menk is available to discuss possible alternatives and assist with planning and modeling if needed. Sincerely, BOLTON&MENK, INC. Douglas Carter,P.E., LEED AP Water Resources Engineer cc: Marcus Thomas, P.E.,Bolton&Menk, Inc. File F:1_Civil\ARDMT161206451T16.120645 Report Review_FINAL.docx