presented at public meeting
A public meeting was held as part of a FEMA grant application process by the City of Cottonwood Thursday, Oct. 12.
The meeting was to inform the public of the city’s options with regard to repairing the failing culvert that carries Cottonwood Creek under part of the city and to look into fixing flooding problems with the Creek.
Mountain Waterworks did a study for the City and presented 4 options.
Option 1 was to abandon the current culvert and run a new 10 foot by 5 foot culvert about 1700 feet from the entrance to the current culvert at Lewiston and Front Streets under Main Street down to Goldstone St. and then route it up Goldstone and connect back with the Creek bed.
Advantages would be the best alternative for flood control, allows new storm water drains to be connected and the Idaho Transportation Department has expressed interest in partnering with the City to either fund or assist with construction and does not require rehab of existing aging and failed infrastructure.
Disadvantages are the high capital cost, the significant disruption to Main Street and there would be no flow remaining in Cottonwood Creek through town.
Estimated cost range is $4.2-4.7 million.
Option 2 is to rehab the current culvert and also add a 48” culvert under Main Street along the 1700’ path described for the much larger culvert in option 1.
Advantages would be that flow continues through the Cottonwood Creek channel, allows new storm water drains to be connected and ITD has expressed interest in partnering with the City to either fund or assist with construction.
Disadvantages would be a significant disturbance of Main Street, risk associated with rehabilitating existing culvert and associated useful life, existing culvert runs beneath existing buildings and higher flood potential than Option 1.
Estimated cost is $2.8-$3.2 million.
Option 3 is to abandon the existing culvert and run a new 10’x5’ culvert under Front Street and then turn south behind The Habit and Rieners and join up with the current Creek bed. This would be about 750 feet of new culvert.
Advantages are it does not require rehab of existing, aging and failed infrastructure, allows new storm water drains to be connected, relatively short culvert length.
Disadvantages include limited ITD involvement potentially reducing available grant funding, significant disturbance of Front Street, site topography requires deep excavations, does not mitigate flooding potential downstream of proposed culvert, higher risk of flooding compared to Option 2.
Due to the high risk associated with construction and flooding, this option was not recommended for further consideration.
Option 4 would be to install Cottonwood Creek Flow Control Structure. This would be a structure built upstream of the City to store and regulate the flow discharged into the creek. The city would need to acquire property that could essentially be flooded during periods of high flow similar to a reservoir.
Due to the significant amount of planning, environmental permitting, high costs and likelihood of high operation and maintenance requirements, this alternative is not considered viable.
It was pretty much decided due to costs, flood control and environmental concerns of using the current creek bed, Option 2 is the one they are likely to pursue.