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HomeMy WebLinkAbout7D - 16100 Evanston Avenue STAFF AGENDA REPORT DATE: 7D LANOL LEICHTY, WATER RESOURCES COORDINATOR CONSIDER ALTERNATIVES FOR THE MAIN STREET STORM SEWER AFFECTING 161 00 EVANSTON AVENUE OCTOBER 6, 1997 AGENDA #: PREPARED BY: SUBJECT: INTRODUCTION: The purpose of this agenda item is to consider alternatives to address the drainage problem at 16100 Evanston Avenue. The City Council directed that staff prepare and submit this report. BACKGROUND: The owners of 16100 Evanston Road have experienced flooding in their yard during past storm events and their basement was flooded this year. They have approached the city requesting that the drainage system in this area be looked at. The first time the City staff was notified of a drainage problem in this area was in the fall of 1996. At that time the owner, John Leidner, notified the City that his yard between T.H. 13 and the house remained saturated for prolonged periods of time after each rain event. Mr. Leidner again called the City to say that his basement had been flooded from a storm event that occurred in July of this year. City staff visited the site and could see water ponding on his property. When asked what the City would do about this problem he was told that it would be investigated, and a project to improve the situation could possibly be added to this years C.I.P. projects funded through the Storm Water utility fund. Although the City did nothing to convey water onto the property the Council may find this situation is a good candidate for using the Storm Water utility fund. Due to the flooding problem a project to improve the situation for the homeowner was recommended for addition in the 1997 C.I.P. and was considered by Council at the August 4, 1997 Council Meeting. Staff was directed by Council to look at various alternatives to address this issue and to contact MnDOT about possible cost participation. Apparently this house was moved in and set on a concrete block foundation around 1981, though there are no City records including either a home moving permit or building permit to verify this. This home is located near the low spot of a drainage area that requires a 24" culvert under T.H. 13 to operate under pressure conditions in order to convey water in heavy storms to 162~~~ Creek Ave. S.E., Prior Lake, Minnesota 55372-1714 / Ph. (612) 447-4230 / Fax (612) 447-4245 AN EQUAL OPPORTUNITY EMPLOYER the pond on the west side of T.H. 13. Investigation into the storm sewer layout shows that the downstream culvert under Main Street is a 15" pipe, which is smaller than the one under TH. 13. The culvert under TH. 13 was designed to operate as an equalizer pipe. The low areas on both sides of the TH. 13 were intended to act as one ponding area with any excess water draining to the west through the Main Street culvert. At the time of the July storm, in which this property was flooded, the 15" culvert under Main Street was half full of sediment, which only magnified the results of an already intense storm. Maintenance has since cleaned out the 15" culvert under Main Street and will regularly flush it in the future. DISCUSSION: City staff wrote a letter and met with representatives of the MnDOT Water Resources Engineering Department about this issue (see attached letter). In summary, their response regarding cost participation is as follows: 1) The home at 16100 Evanston Avenue did not exist prior to the new TH. 13 construction. 2) There has been new development along both sides of T.H. 13 that has contributed to additional runoff. 3) The natural occurring pond located near Lakefront Park and west of Main is a landlocked pond. 4) The water standing in the yard now is at the same elevation of the natural pond and cannot go anywhere. 5) There is 20 feet of MnDOT right-of-way east of the 24" apron on the east side TH. 13. Part of the underlying problem associated with this issue is that the property owner has been trying to develop a well maintained grassed yard in the low area which includes the 20 feet of MnDOT right-of-way. The owner has reseeded this area several times, but to no avail, since each time it rains significantly the ditch area goes under water long enough to kill the new seed or sediment is washed into the newly seeded area. MnDOT would not participate in the cost of enlarging the pipe under T.H. 13, but would contribute their portion to replace the 15" culvert under Main Street based on the amount of contributing flow from T.H. 13 right-of-way, which has been calculated to be 1'7% of the flow through the Main Street culvert. . The current elevation of the natural pond is such that there is standing water on the east side of T.H. 13. This means that there is no elevation difference between the natural pond and the standing water between TH. 13 and Mr. Leidner's house. The existing conditions were modeled to see the effects of a 2, 10 and 100 year - 24 hour storm. The walkout elevation of the house is MAINST.DOC 925.28. Following are the water elevations adjacent to the house that would result for existing conditions: 2 Year - 24 Hour Storm: Elevation = 923.18 10 Year - 24 Hour Storm: Elevation = 924.91 100 Year - 24 Hour Storm: Elevation = 926.68 As can be seen the flood elevation is within 0.4 feet of the walkout for the 10 year-24 hour storm and floods the basement during a 100 year-24 hour storm. These results will vary according to the starting elevation of the natural pond before a storm begins. The higher the starting elevation, the higher will be the resultant flood elevation and vice-versa. Several options were looked at to try to find a solution to this problem. The options along with the associated costs are as follows: OPTION #1: A hydraulic analysis was done to determine if enlarging the 15" culvert under Main Street to a 36" culvert would prevent future flooding. This improvement would be the least expensive storm sewer replacement alternative and MnDOT would financially participate in their portion of the runoff. The results of this analysis showed that basement flooding would occur during a 100 year - 24 hour storm and would be within one foot of flooding the basement during a 10 year - 24 hour event. The cost for this option is approximately $45,000.00. The largest amount of MnOOTs financial participation would be approximately 17% or roughly $7,700.00. The City cost would be $37,300.00. OPTION #2: Next, an analysis was done to see if enlarging both culverts under TH. 13 and Main Street to a 36" pipe would work. Even with this scenario the basement would flood during a 100 year - 24 hour storm. The cost for this option is approximately $121,000.00. OPTION #3: This analysis was done to see what size equalizer pipes would need to be installed to do away with flooding during a 100 year - 24 hour storm. The pipes needed would be a 36" culvert under TH. 13, in addition to the existing 24" culvert, and a 60" culvert under Main Street to provide 0.5 feet of flood protection. The approximate cost for this option is $165,000.00. OPTION #4: Since the natural pond is a land-locked pond, an analysis was run to see if providing an outlet would eliminate flooding at the house. This option also included enlarging the pipe under Main Street to a 36" culvert, but leaving the 24" culvert under TH. 13 intact. The results showed that the basement MAlNST.DOC ISSUES: ALTERNATIVES: RECOMMENDATION: MAlNST .DOC would receive water in a 100 year - 24 hour storm. The cost for this alternative is approximately $76,000.00. From the above four options it can be seen that it is quite expensive to construct a pipe system that will provide significant flood protection during a 100 year - 24 hour storm. Given this information, another alternative was looked at which would allow for additional elevation difference between the 100 year flood and the low opening of the home. This alternative, which is practical, should be at no cost to the City is as follows: OPTION #5: This residence has a full-basement with a walkout on the south side. If the walkout was closed up with block and mortar, 3.67 feet of elevation could be gained between the door opening and the next lowest opening which is a basement window. This analysis was done with the existing pipe system in place with no improvements. The outcome of this analysis would provide approximately 2 feet of protection between the 100 year storm elevation and the lowest window opening of the house. The cost for this alternative is approximately $5,000.00 which would include regrading of the side yard to eliminate the walkout basement. None of the Engineering solutions described will completely eliminate the flooding problems on this property. There is no feasible economical option to accomplish this. During any potential storm event or due to the pond elevation rising through several incremental smaller rainfalls, flooding will always be a possibility on this property given the existing conditions. Alternatives to provide some level of relief can be provided, but the property cannot be kept completely dry. Based on these facts, the City Attorney indicated the City is under no legal requirement to do anything to improve this situation (cause a trespass), because it did not divert the water onto the . property. As a matter .of policy, it could decide to authorize the use of the Storm Water utility fund to contribute towards a solution. Staff's recommendation is that option #5 be chosen. There are three alternatives for the City Council to ~onsider: 1. Approve the recommended option. 2. Deny this item for a specific reason and provide staff with direction. 3. Table this item until some date in the future. Alternative No.1. ACTION REQUIRED: MAlNST.DOC A motion and second to approve the recommended alternative. ~ REVIEw!;;J .:,.'''''''ISo>:O ... '9 q ~ .. ~ ~ \" ~~~ 0"""" Minnesota Department of Transportation Metropolitan Division Golden Valley Office 2055 North Lilac Drive Golden Valley, MN 55422 September 8, 1997 Telephone No. 797-3054 Fax No. 797-3181 Mr. Lanol Leichty Water Resources Coordinator City of Prior Lake 16200 Eagle Lake Avenue S.E. Prior Lake MN 55372-1714 RE: TH 13 at Jon Leidner Property 16100 Evanston Avenue Dear Mr. Leichty: I am writing this letter in response to the letter you wrote to Joe Thomas about the Jon Leidner property at 16100 Evanston A venue. I have reviewed aerial photos, of this area, that were taken in 1967, 1972, and 1995. I took a field trip to review the areas that drain to the culverts in question, and I have reviewed the plan sheets for the construction of TH 13 in 1960. From this information r have made the following conclusions: 1) The property in question did not have a house there when new TH 13 was constructed. 2) There has been new development along both sides of TH 13 that has contributed additional runoff to these culverts. 3) The pond on the west side of TH 13, that this water drains to, is a landlocked pond. 4) The water that is in the yard now is there because the pond on the west side of the roadway is at the same elevation and the water cannot go anywhere. 5) There is 20 feet of Mn/DOT right of way east of the 24" apron on the east side of new TH 13. When this pipe was installed, it was Mn/DOT policy to install a minimum of a 24" pipe under a mainline roadway. The original plan sheet shows the 24" pipe, under new TH 13, should have been an equalizer pipe. Because of the fall to the east that exists today, this pire must have been installed improperly or the east end of the pipe has settled more than the west end of the pipe. Any water that sits in the ditch on the east side of TH 13, . because of the slope of the pipe, will be on Mn/DOT right of way. If it is determined that an additional culvert is needed under new TH 13 it would be Mn/DOTs policy not to contribute because this would be considered as over sizing a pipe, at the time the roadway was constructed. If the city was to replace the 15" pipe, or add an additional pipe from TH 13 to the west, Mn/DOT would contribute based on the amount of contributing flow from Mn/DOT right of way, because this would be considered a system that would carry water contributed from Mn/DOT right of way. An equal opportunity employer If you have any questions or need any further information please call. Sincerely, p~ f! ~ I ames E. Wiczek Water Resources Engineering Project Manager Mn/DOT Metro Division cc: Ion Leidner 16100 Evanston Avenue Prior Lake, MN 55372 ", POND MAIN ST. EL,"922.13 9/25/97. ""}?'''''H?' -------== 919.~ - . 921." / L 922.01 EXHIBIT T .H. 13 16100 EVANSTON 24" CULVERT Lu. L WALKOUT ....2.