The Conservation Commission approved the order of conditions for a project intended to eliminate flooding caused by the drainage system of Mainline Drive.
The current drainage systems collects storm water and dumps it into Little River. The problem is that the elevation of the system is not much higher than the river, which is quick to rise during any significant storm event, causing river water to back up through the two drainage pipes and bubble up out of the storm drains, flooding the street, forcing the city to close the street to traffic.
The flooding and road closure has a significant financial impact for businesses, and employees, because vehicular access is denied along the dead-end industrial road.
Jessica Roberts, PWS, of Tighe & Bond, presented the project last night to the Conservation Commission members, stating that the flooding is caused by storms frequently.
“A 10-year storm event, or less” can cause the flooding incidents, Roberts said.
The project is receiving a $74,000 flooding hazard mitigation grant through the Massachusetts Emergency Management Agency and the Federal Emergency Management Agency and will also address erosion problems along the bank of Little River near the outflow of two drainage pipes. The city is matching 25 percent of that funding.
Roberts said there are two drainage pipes, one 18-inches in diameter and the other a 24-inch line. The larger pipe has no protective head wall, resulting in bank erosion around the pipe that currently hangs out, unsupported, over the river.
The solution to the street flooding is elegant in its simplicity: stop the water from going backward up the pipe.
“An in-line check valve will be inserted into the ends of the pipes, which will allow (storm)water to flow out, but not allow inflow (of river water),” Roberts said. “This is a resource area improvement project because of the bank mitigation and flood control aspects.”
The project will require the contractor to install a cofferdam to protect the bank during construction of a head wall around the 24-inch outflow. Roberts said the design calls for use of Gabion baskets, wire mesh structures filled with rock. The type of basket being used in the project also has pipes holding soil on the top and side, facing the river, that can be planted with grasses to stabilize the head wall into the bank.
The Conservation Commission set a condition that the work, expected to require between 30 and 45 days, be done during “low flow periods” which typically occur during the high summer months. The commission also set a condition for the contractor to coordinate with the Springfield Water Department, pertaining to water release from Cobble Mountain Reservoir, that causes the river water to rise significantly. The commission also requested a number of annual inspections of the system because the technology being used for both the back-flow valve and head wall are relatively new.
Roberts said that other advantages provided by the system will include a reduction of sedimentation caused when the flood water returns to the river, pulling material off the roadway into the river.
The project is one of three now approved by the commission for drainage and bank stabilization along the Mainline Drive section of the Little River.
The commission has approved orders of conditions for two state Department of Transportation projects, one a drainage project of a holding area along East Main Street where plowing and sanding trucks line up while awaiting entry into the DOT yard, and the second to address erosion of the river bank at the rear of the DOT property. That stabilization project will also use a technology, J-hooks, which is new to the New England area, but has been used successfully in other parts of the country to address river bank erosion.
