Storm Sewers
Storm Water Management Benefits Everyone
“Why do I have to pay a stormwater fee when there is no storm sewer in front of my house?” is a common question, along with “Why does stormwater management cost so much?” The revenue derived from the stormwater utility fee is used solely for the operation and maintenance of our stormwater collection, conveyance, and treatment facilities.
Storm Infrastructure
Most people are surprised at the extent of the infrastructure required to manage our stormwater. This infrastructure includes 65 miles of storm sewers, 4 miles of tunnels, 250 discharge outfalls, 2,410 storm sewer inlets, 70 treatment/detention ponds, 5 rain gardens, and many miles of roadside ditches, engineered ditches and drainage ravines.
All of these require periodic maintenance and some require fairly extensive repair or rehabilitation. While some of this infrastructure serves individual properties, much of it serves large areas of the city, including common areas such as streets and parks, and is necessary to prevent flooding, severe erosion, and other large scale problems. All parcels in the City are assessed a storm water utility fee as all parcels benefit from comprehensive storm water management, not just those with a storm water sewer in front of their house.
Storm Sewer System Permits
Municipalities are required to obtain a Municipal Separate Storm Sewer System (MS4) permit from the Minnesota Pollution Control Agency. This permit covers all storm water discharges whether they are in a pipe, street gutter or the ditch along a gravel road. The permit contains restrictions on flow volume and water quality, which will continue to become more stringent as the efforts to reduce nutrients and sediment to the Mississippi River and Lake Pepin continue.
A significant portion of the revenue from the storm water utility fee goes towards major projects necessary to maintaining our existing infrastructure. In the past, these have included ravine restoration to minimize erosion and reduce sediment transport, rehabilitation of the large engineered storm water channel from Twin Bluff School to Hay Creek, removal of sediment from storm water treatment ponds, and repair of a collapsed storm sewer that was causing sinkholes in Old West Main Street. Public Works will be undertaking another larger scale project this summer, namely the rehabilitation of a portion of the Bluff Street storm tunnel.
Storm Tunnels
Red Wing’s tunnels represent an interesting component of our history, and like our other historic buildings, parks and infrastructure, are very costly to maintain. The tunnel system was originally constructed as a combined sewer system discharging both sanitary sewage and storm water into the Mississippi River. The sanitary sewage was separated in the 1980’s and 1990’s, and now the tunnels only convey storm water. The storm water tunnels range in size from 3 feet to 10 feet wide, 3 feet to 10 feet high and were constructed from cast-in-place concrete, reinforced concrete pipe, brick, granite blocks, limestone blocks, vitrified clay pipe, wood and various combinations of these materials. The tunnels are relatively shallow, ranging from approximately 2 feet to 25 feet below the ground surface. Some of them are over 100 years old, and many have sections that exhibit serious deterioration. The replacement value of our tunnels exceeds $50,000,000.
Tunnel Evaluation
Public Works contracted with a civil engineering firm specializing in tunnels to conduct a comprehensive evaluation of them, and provide a prioritized list of rehabilitation measures or repairs needed to maintain their structural integrity and functional capacity. Each tunnel segment was inspected, and was rated good, fair, poor or urgent. By definition, an urgent designation means the tunnel segment is “structurally inadequate or has a service-impending defect and requires immediate corrective action’. Likewise, a segment designated as poor means that the tunnel is “structurally inadequate and has defects that are causing deterioration. Rehabilitation is required.” Thirteen segments totaling 1600 feet were rated poor. The estimated cost to rehabilitate these segments is approximately $3.5 million dollars. Five segments totaling 154 feet were rated urgent. The estimated cost to rehabilitate these is $300,000.
Tunnel Rehabilitation
The Public Works Department will be undertaking a project to rehabilitate those tunnel segments with an urgent rating later this spring. These segments are all part of the Bush Street Tunnel, and are located on Fifth Street from Bush Street to East Avenue; on East Avenue from Fifth Street to Seventh Street; and on Seventh Street from East Avenue to Central Avenue. This work will consist of removing the pavement and soil over the tunnel, removing the existing tunnel roof and installing a new reinforced concrete roof. The roadway, curbs and boulevards will also be replaced.
Additional phases will be completed in upcoming years, with the ultimate goal of getting the entire tunnel system to a state where only routine monitoring and maintenance is adequate to keep the system functioning and intact.