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HomeMy WebLinkAbout10A - Fish Point Park Pond Outlet 16200 Eagle Creek Avenue S.E. Prior Lake, MN 55372-1714 CITY COUNCIL AGENDA REPORT MEETING DATE: AGENDA #: PREPARED BY: MARCH 19, 2007 10A ROSS BINTNER, WATER RESOURCES ENGINEER AGENDA ITEM: CONSIDER APPROVAL OF A RESOLUTION ACCEPTING A FEASIBILITY REPORT FOR IMPROVEMENT OF THE FISH POINT PARK POND OUTLET. DISCUSSION: Introduction The purpose of this agenda item is for the City Council to approve a Feasibility Report for the improvement of the Fish Point Park pond outlet. History The Fish Point Pond outlet channel was scheduled for repair in the 2007 Capital Improvement Program after it was proposed to the City Council last year by a nearby resident. The Fish Point Park outlet channel drains 87 acres of single family residential area. Two ponds in Fish Point Park serve to dampen peak rates from the stormwater runoff from this area. A pipe conveys the water under Fish Point Road to the channel under consideration. Current Circumstances The outlet section under consideration is downstream of a City owned drainage system and has historically been under private ownership. This project proposes to acquire drainage and utility easements from the private owners that border the existing channel, and to improve and stabilize the flow path through one of two options. The options for improvement are described in detail in the attached Feasibility Report, but in summary they are: 1. Improved Open Channel: Consisting of side slope and channel re- grading and stabilization, this option proposes to provide a stabilized, bioengineered ditch section to transmit regular and emergency flows to the Lake. 2. Pipe System: This option consists of a stormwater system made up of concrete pipe and a stabilized overflow channel. This system would be designed to convey most storms. Large storms would flow both through the pipe system and overland in a stabilized channel. Prior to consideration by the City Council, the Engineering Department met with the affected property owners to share its preliminary recommendations contained in the Feasibility Report. The purpose of the meeting was to gain a better understanding of the concerns of the property owners prior to finalizing the report, and to try to gain buy-in for Option 1, an improved open channel. While the meeting was cordial and informative for both sides the residents still prefer Option 2, a pipe network solution. G:\Water Resources\Drainage Issues\Fish Point Park o~~it~W~&gtOOJ;!;genda Report.doc Phone 952.447.4230 / Fax 952.447.4245 ISSUES: For this drainage issue to be solved the City will need permanent easements for the purpose of repair and maintenance of the channel. During the reconstruction project meeting, the property owners were reluctant to give easements because the City viewed them as a prerequisite for proposing a design. Because of this uncertainty of what the solution would look like the parties could not come to an agreement at the time. Through the CIP process, the resident meeting and this Feasibility Report the property owners have been given more information prior to this decision. In the Feasibility Report, the Engineering Department recommends Option 1, an improved open channel. This option was deemed prudent and feasible for the following reasons: . It meets the goal of reducing the risks of property damage. . It is a prudent use of funds. . It addresses the problem at its source, a restriction in the channel. . It uses natural materials to convey even large storm events. The property owners have expressed their preference for Option 2, a pipe system. The property owners stated their reasons for wanting this option include: . It meets the goal of reducing the risks of property damage. . It provides the owners more usable land along their shared property line. . The additional land could be used to relocate an association maintained lake access easement. . It lowers their costs for maintaining aging retaining walls. . It is perceived to reduce a mosquito problem. The Engineering Department did not recommend Option 2 for the following reasons: . A pipe cannot feasibly be designed to convey large storm events. . An overflow channel would have to remain for large storm events. . The costs to construct a pipe system are not justified by the public benefit. FINANCIAL IMPACT: If permanent easements are granted, the City will take responsibility for the drainage path in the future. The financial impact will vary dependent on the option chosen. Option 1, an improved open channel is estimated to cost $9,380.00, while Option 2, an extended outlet pipe and emergency overflow is estimated to cost $31,980.00. The no-build alternative has no immediate financial impact to the City; however, the risk of private property damage will remain. A detailed estimate of costs is included in the attached feasibility report. Option 1 has the ability to be completed as normal maintenance with City maintenance crews. If maintenance crews are used plans and specifications will not be produced and the project will not be bid. G\Water Resources\Drainage Issues\Fish POint Park Outle/"Fish PDint Park Outlet Agenda Reportdoc ALTERNATIVES: 1. Approve a resolution accepting the Feasibility Report and ordering the preparation of plans and specifications for the Option 1, the open channel solution, contingent on gaining easement for construction. 2. Approve a resolution accepting the Feasibility Report and ordering the preparation of plans and specifications for the Option 2, the pipe solution. 3. Approve a resolution accepting the Feasibility Report and ordering plans and specifications for Option 2, the pipe solution, contingent on cost sharing (equal to the difference in cost of options 1 and 2) from the two benefiting adjacent property owners. 4. Deny this item for a specific reason and provide staff with direction. 5. Table this item until some date in the future. RECOMMENDED MOTION: Staff recommends Alternative #1. ReVi1:j Frank Boyles, Ity Steve Albrecht, Public Works Director/City Eng. G:\Water Resources\Drainage Issues\Fish:Joint Park Outlet'Fisll POint Park Outlet Agenda Reportdoc 16200 Eagle Creek Avenue S.E. Prior Lake, MN 55372-1714 RESOLUTION 07-xx A RESOLUTION APPROVING A PRELIMINARY REPORT FOR THE IMPROVEMENT OF THE FISH POINT PARK POND OUTLET Motion By: Second By: WHEREAS, The improvement of the Fish Point Park pond outlet was include in its Capital Improvement Plan, and; WHEREAS, Improvement of this outlet will promote a stable and safe flow path that lessens risk of property damage, and; WHEREAS, The City will attempt to gain permanent easements from nearby residents for the perpetual maintenance of this flow path, and; WHEREAS, The project will proceed only if permanent easements are obtained. NOW THEREFORE, BE IT HEREBY RESOLVED BY THE CITY COUNCIL OF PRIOR LAKE, MINNESOTA as follows: 1. The recitals set forth above are incorporated herein. 2. The Feasibility Report titled "Preliminary Report for the City of Prior Lake Fish Point Park Pond Outlet" and dated March 14, 2007 is hereby approved. 3. Council hereby approves option # 1, an improved open channel. 4. The Staff is directed to obtain easements for said improvements. PASSED AND ADOPTED THIS 19TH DAY OF MARCH 2007. Haugen Haugen Erickson Erickson Hedberg Hedberg LeMair LeMair Millar Millar YES NO Frank Boyles, City Manager www.cityofpriorlake.com Ci:VVlter ~bclJr<esDI:-l;rlage Issu~s\FISli e''Ph6Iikk~~:zr41.423'6lt lilrp~it~5Z:4141.4245 PRELIMINARY REPORT FOR THE CITY OF PRIOR LAKE FISH POINT PARK POND OUTLET MARCH 2007 I hereby certify that this Feasibility Report was prepared by me or under my direct supervision and that I am a duly licensed Professional Engineer under the laws of the State of Minnesota. ~l~ Ross T. Bintner, P.E. Reg. No. 44570 3- li - 2007 Date G:\Water Resources\Drainage Issues\Fish Point Park Outlet\Fish Point Park Feasibility Report.doc Page 1 of 6 INTRODUCTION The City of Prior Lake is responsible for the operation and maintenance of the storm water drainage system within its boundary. This report evaluates the feasibility of providing a safe and stable flow path from the pond at Fish Point Park to Lower Prior Lake. Three options are discussed in this report, they include improvement and repair of the open channel, construction of a pipe network, and a no-build option. BACKGROUND The proposed project area is shown on Exhibit 1. The existing channel location is southwest of Fish Point Road and South of Frost Point Circle. Currently the drainage system includes a pond outlet structure, 45' of 30" culvert, and 220' of unimproved channel. The outlet structure, culvert and channel drain the pond in Fish Point Park. During the design phase of the 2006 Fish Point neighborhood reconstruction project, the Engineering department considered putting in a pipe or drainage channel, but was unable reach agreements with property owners for drainage and utility easements for the project. During the street reconstruction project in this area two flood events occurred that caused damage to the outlet system and private property. Both storms overtopped Fish Point Road causing washout at both the road and near the outlet to the lake. These two overtopping events caused nearby residents to reconsider withholding their approval of easements for this drainage path. After a nearby resident approached the City Council asking that this problem be solved, the Council allocated funds for the improvement and maintenance of this channel. Improvement of this drainage path is included in the Capital Improvement Plan (CIP) for 2007, but for work to proceed, a right of entry agreement and easement will be needed from both adjoining property owners. HYDROLOGY The Fish Point Park outlet channel drains 87 acres of single family residential area. Two ponds in the park function to dampen peak rates draining from the subwatershed. The outlet pipe from the downstream pond drains under Fish Point Road and has capacity to carry the 25-year storm (Runoff from a 4.8" rainfall in normal conditions, over 24 hours). The outlet channel from the pipe outlet to Lower Prior Lake is a natural channel with miscellaneous vegetation ranging from grasses, to shrubs, to trees. A flow constriction exists at the mouth of the channel where it meets the Lake, this feature is primarily made up of sandy soil and is well vegetated with tall shrubs. It is this flow constriction that is responsible for much of the risk to private property. In the two runoff events in 2005, this restriction in the channel remained in place due its vegetation. Taking the path of least resistance, the floodwater washed out the nearby sand beach because it did not have an extensive root system to hold the soils together. A photo showing the constriction and resulting damage from water flowing around is presented in Exhibit 2. DISCUSSION OF AL TERNA TIVES Each option is discussed below. A summary of the options is presented followed by a discussion of engineering feasibility, regulatory requirements, and benefits and downsides of the alternatives. Option 1: Regrade and Stabilize Open Channel Summary: Consisting of side slope and channel re-grading and stabilization, this option proposes to provide a stabilized, bioengineered ditch section to transmit regular and emergency flows to the Lake. Engineering feasibility: Option I consists of modification of the existing open channel. There is a significant sediment deposit at the mouth of the channel where it meets Lower Prior Lake. This deposit has been built up by wave and ice forces on the lake and has created a dike over the mouth of the outlet channel with a small flow path cut through it. It was this flow restriction that caused flows to divert and wash out the beach at 5331 Frost Point Circle S.E. during flood events in late 2005. This alternative proposes to remove the dike restricting large flow events by re- grading the end of the channel. In restoring and stabilizing the channel, a mixture of natural stone, soil reinforcement and native plantings will be used. Regulatorv requirements: This alternative is required to meet DNR requirements, and State and Federal wetland rules. A DNR permit will be required for the work proposed under this alternative and it is likely to be approved. A wetland determination will need to be done to determine if wetland exists in this area, the area of impact is small enough that the project may fall under the de minims exemption. A permit will be required under Federal wetland rules administered by the Army Corp. Pros/Cons: Pros: This alternative would meet the objectives of providing a safe flow path and minimize risks to health, safety and property of nearby residents. This alternative is least costly and is considered a prudent utilization of funds. Details on costs of each option are presented in the "cost estimate" section below. This option is limited enough in scope that the City has the option to use City equipment and personnel to complete the project. If City personnel were utilized, additional savings could be gained if maintenance activity takes place on the nearby Fish Point Park pond when equipment is mobilized. This alternative is preferred by State and Federal officials and permits are likely to be granted. Cons: This is not the preferred alternative of the neighboring residents. Residents may withhold permission to access property and may not grant permanent easement for the City to maintain this flow path. Option 2: Construct Pipe to Prior Lake Summary: This option consists of a stormwater system consisting of concrete pipe and a stabilized overflow channel. This system would be designed to convey most storms. Large storms would flow both through the pipe system and overland in a stabilized channel. Engineering feasibility: This option consists of partial filling of the existing channel and placement of one of more pipes from the current outlet location to Lower Prior Lake. Because the Fish Point Park pond is at nearly the same level as the lake, pipes would be designed to flow under pressure. The difficulties in this alternative are maintaining a safe and effective emergency overflow path, and providing capacity in a pipe that will be underwater during high lake levels. A grassed swale would remain in place along side the pipe alignment, designed to transmit flood flow overland to the lake. Significant fill material will be required to cover the pipe and partially fill the existing channel. Riprap rock, or articulated concrete block would be placed at the end of pipe to provide a stable outlet into the lake that is able to withstand ice forces. Regulatory requirements: This alternative is required to meet DNR requirements, and State and Federal wetland rules. Due to fill being placed under 904.00, this alternative results in a reduction of flood storage for Lower Prior Lake and results in a marginal increased risk of flood events around the lake. Due to the potential for wetland fill and reduction of flood volume permitting may be more difficult. Pros/Cons: Pros: This alternative would meet the objectives of providing a safe flow path and minimize risks to health, safety and property of nearby residents. This is the preferred alternative of neighboring residents. This alternative uses high quality materials and would provide more useable land to nearby homeowners. Cons: The cost of this option is more than three times the cost of the alternate solution, is not considered a prudent use of funds, and is not recommended by the City Engineer. This alternative marginally decreases flood storage in the lake. This alternative will be more difficult to permit with the DNR and Army Corp of Engineers. This alternative does not utilize natural features. Option 3: No build Summary: The no-build alternative considers the feasibility of making no improvements to the existing system. Engineering feasibility: This option is not engineered. Regulatorv requirements: No permits are required. Pros/Cons: Pros: There are no immediate costs. Cons: The risk of private property damage remains due to the constnctlOn in the eXIstmg channel. The City's access rights remain limited to access and maintain this channel because the City currently does not have easement rights for access. ESTIMA TED COST The estimated costs of these three options are explored below. O' lOCh 'OtIOn : Ipen anne ITEM UNIT UNIT COST QUANTITY COST Design Survey Hour $110 4 $440 Design (staff time) Hour $50 16 $800 Construction Survey Hour $110 7 $770 Riprap CY $100 20 $2000 Channel Excavation CY $10 135 $1350 Stabilization and seeding SY $7 360 $2520 Erosion Control LS $1500 1 $1500 ESTIMA TE $9,380 O' 2 P' Jptlon : me ITEM UNIT UNIT COST QUANTITY COST Design Survey Hour $110 4 $440 Design (staff time) Hour $50 16 $800 Construction Survey Hour $110 7 $770 42" Concrete Pipe Foot $70 220 $15400 66" Manhole Each $2800 2 $5600 Fill material CY $9 550 $4950 Stabilization and seeding SY $7 360 $2520 Erosion Control LS $1500 I $1500 ESTIMA TE $31,980 Option 3: No Build The cost of the no build alternative has zero up front cost, instead the cost of doing nothing is a comparison of expected future maintenance cost. This drainage channel was repaired during the 2005 street reconstruction project for the cost of approximately $3,250. PROJECT SCHEDULE Upon approval of this Feasibility Report and a recommendation of which alternative to pursue, the Engineering Department will move forward with survey and design of the chosen alternative in effort to maintain the following schedule: Work item Obtain Easements Survey Design Advertise Bid Bid A ward Contract Construction Start Date April May May June July July July - October If work were done using City equipment and personnel, this project schedule would not include bid or contract work and construction would take place based on staff availability. CONCLUSION AND RECOMMENDED AL TERNA TIVE The engineering department recommends alternative 1, a stabilized open channel, as the preferred alternative. This option represents a prudent expenditure to minimize risk of potential future property damage. The open channel alternative is also recommended for being the least impact to property and environment and the possibility to complete the project using city equipment and personnel. The open channel solution addresses the problem directly by removing the flow restriction that is causing risk to private property. If this alternative is approved by the City Council the property owners may still decide to withhold access and not grant easements. This would result in the no-build alternative. While both open channel and pipe alternative are technically feasible from an engineering perspective, considering costs, the open channel solution also represents a prudent use of funds. EXHIBIT 1 N w-<:>- E FISH POINT PARK OUTLET This drawing is neither a legally recorded map nor a survey and is not intended to be used as one. This drawing is a compilation of records, information and data from various city, county and state offices and other sources. This document should be used for reference only. No representation is made that features presented accurately reflect true location. The City of Prior Lake, or any other entity from which data was obtained, assumes no liability for any errors or omissions herein. If discrepancies are found, please contact the City of Prior Lake. AERIAL IMAGERY IS FROM A SPRING 2003 FLIGHT FOR SCOTT COUNTY. 100 o 200 400 I Feet