Story by Jeff Kolkey, Rockford Register Star • 9h ago
A more than decade-long effort to protect nearby Rockford neighborhoods from flooding by modernizing the 81-year-old Alpine Dam at Reuben Aldeen Park should be done this year.
Here is what you need to know.
What is Alpine Dam?
Built in 1942, Alpine Dam is a high mound of earth that contains and slows floodwaters along the northern branch of Keith Creek. Failure of the dam during a severe storm would be catastrophic to homes and businesses downstream.
What's its history?
Alpine Dam was built as part of President Franklin D. Roosevelt’s New Deal-era public works program, which put 8.5 million people to work across the country to combat the Great Depression.
Where is it?
The earthen dam is located in a park east of Alpine Road.
How does the dam work?
Alpine Dam includes a swampy water basin, a gate that controls how much water is released into Keith Creek, a tall hill that holds back flood waters and a graffiti-encrusted concrete spillway. If enough water during a torrential rainstorm overflowed the basin enough to reach it, the spillway would direct the water into a stilling basin meant to calm the water before it leaves the park and floods nearby neighborhoods.
What is happening now?
Plans for this year are to complete the rehabilitation of the dam and to build an additional $1.6 million auxiliary spillway that would provide another way to slow down storm water in the event of a massive storm.
How will they do it?
Crews will shave up to 5-feet from the top of the earthen dam and carve out a 200-foot wide auxiliary spillway west of the current spillway. In addition, construction crews will bolster the concrete spillway by adding an additional foot of depth to increase its capacity, improve the stilling basin and build an access road to the site. The project will go out to bid this summer.
Why is the work needed?
The improvements will bring Alpine Dam into compliance with modern standards for dams under Army Corps of Engineers regulations. It is believed to have been out of compliance since the 1980s. In a 2007 report after severe flooding in Rockford, the Army Corps of Engineers said the dam is “in poor condition due to its age and does not meet federal design standards.”
Will the work improve the dam's capacity?
When complete, the improvements at Alpine Dam are expected to make it capable of withstanding anything up to a terrible storm that has a chance of occurring once every 5,000 years.
How will it be paid for?
A state grant for $800,000 and proceeds from the local 1% road and infrastructure sales tax will pay for the latest upgrade.
What other steps have been taken to modernize the dam?
A $2 million first phase of work included the modernization of the gate and reinforcement of the spillway. The improvements allow Rockford Public Works officials to monitor the dam via video cameras and raise and lower the gate remotely.
How is that better than in the past?
Large storm events before the improvements forced public works crews to drive out to the dam every 30 minutes to check on how much water had filled the detention basin and then brave dangerous weather to cross a gangway and manually crank the gate further open or closed as needed.
Was it ever near capacity?
Alpine Dam neared its capacity in August 2007 during a downpour that brought 5-inches of rain in a single day and caused massive flooding along the creek. Although there were no indications that the dam would fail, engineers refused to guarantee the earthen structure would hold, and a voluntary evacuation was initiated downstream in case of a breach.
Jeff Kolkey can be reached at (815) 987-1374, via email at jkolkey@rrstar.com and on Twitter @jeffkolkey.
This article originally appeared on Rockford Register Star
