ITEM TITLE:
Approval of Change Order #2 with Harris Sand and Gravel for the 10 Mile Dike Maintenance Project in the Amount of $472,136.00
SUBMITTED BY: Nathan Duval, Capital Facilities Director
FISCAL NOTES:
Expenditure Required: $472,136.00
Unencumbered Balance: $1,223,946.63 ($798,946.63 if CO#1 Approved)
Funding Source: 350-0750-55000.409
RECOMMENDATION:
Approve Change Order #2 with Harris Sand and Gravel for the 10 Mile Dike Maintenance Project in the Amount of $472,136.00
SUMMARY STATEMENT:
Background: The project currently underway on the Lowe River is designed to first be a maintenance project repairing the dikes and adding rip rap for a toe and armoring the existing banks and secondly establish a base for a future dike raise. The design is phased so that a future dike raise can be accomplished on top of the newly renovated dike system without redoing current work. The maintenance is currently underway on groins 1, 2, and 4. Groin 3 does not currently see significant flow from the Lowe River directly contacting its bank; it is protected by yet to erode land in front of the dike.
The proposed change order is the result of additional aggradation at the toe of groins 1,2,&4 resulting in excess gravel needing to be removed for the placement of the new toe. The excess gravel is currently temporarily staged in front of the dikes on the river side.
The approved drawings allow for the excess fill material to be used on top of the dikes; otherwise it will need to be leveled out in the riverbed. Significant concerns exist with the natural rise in the river bed elevation. Leaving excess material in the river only accelerates those concerns.
Working with the Engineers, DOWL, and the contractor we have calculated that we can use the excess material to raise the dikes an average of 3 feet. The dikes would be armored in accordance with the current and future plans and specifications with a 3:1 slope, class 1 filter rock layer, and a class 3 armor rock layer.
The attached graphic illustrates the elevation increase over the project stationing. Additionally, a sketch of the typical section shows the relative elevation change.
The anticipated future phase includes excavating material from the riverbed and placing that material on the dikes to increase the dike elevations 4-5 feet at an estimated project cost of $4-7 Million dollars. Using the available material previously noted, and the already mobilized contractor, we can achieve an average of 3’ in elevation for approximately ten to twenty percent of the total cost of the future project.
It should be noted that a significant cost associated with the future phase ($2-3M) is the excavation of material from the river and that will not specifically be negated with this change order. However, the portion of the work to raise the dikes is value added compared to the potential future expenditure. This change order can achieve 60-70% of the protection for 10-20% of the cost.
Completing this work will also allow the neighborhood and the City a sense of security as we negotiate with the Department of Natural Resources while they continue their lengthy review of our previously submitted Lowe River Flood Mitigation Plan.
The Flood Mitigation Task Force was consulted on this change order and generally agreed with the idea to incrementally raise the dikes at a good value to the City. Savings realized in this phase may allow for rescoping of future phases to ensure the dike system and flood control measures on the Lowe River adequately address current and future risks.
The additional material to be added to the dikes consists of approximately 19,500 cubic yards of gravel fill from the toe, 814 cubic yards of Class 1 rip rap, and 3224 cubic yards of class 3 rip rap. The contractor will have access to use City owned rip rap stored on site but will be responsible for replacing the quantity used no later than May 1st, 2022. Allowing the contractor access to the on site material will help keep the schedule to be complete this winter before the spring flood season and fish windows.