Please Note: This is a first-hand account of inspecting a dam by Wappapello Lake Park Ranger, Aaron Winchester
Since I was young, I have gazed in wonder at the Wappapello gatehouse. I have seen larger structures, but this one was built near my childhood home during the Depression era by locals. I never thought that one day I, too, would step back into time and experience what these men saw during the genesis of this project.
Periodic Inspections are done at Wappapello Lake every five years. The inspection involves the draining or dewatering of the spillway inlet channel, control structure and outlet channel. During this timeframe, engineers and employees of the U.S. Army Corps of Engineers St. Louis District comb the channel and related flood control structures looking for potential maintenance problems.
The process begins and ends with safety. First the public is notified weeks in advance of the inspection and lake levels are reduced. Wappapello Lake’s winter pool is kept at 354.74 National Geodetic Vertical Datum (NGVD), which is five feet lower than the summer pool. During the periodic inspection, the lake is lowered an additional foot to a level of 353.74 NGVD. This exposes the inlet channel’s forebay weir, a concrete structure with five water passages constructed into its wall.
Sluice gates are placed into each water passage turning the weir into a temporary dam. They are sealed with sawdust and bentonite (a type of clay that expands in water) to help stop seepage. The channel from the forebay weir to the baffle block area, and the water channel for the turbine are drained using pumps to allow inspectors to access.
A pipe from the lake to the spillway outlet channel located beneath the highway is opened and water is pumped through at a rate of 10-12 cubic feet per second. This process keeps water flowing into the river channel and oxygenates the water to protect downstream fish and wildlife.
The periodic inspection may take up to 36 hours depending upon weather conditions. The sluice gates are removed once inspections are complete to allow water to flow freely again.
During the inspection I had the opportunity to stand where I captured views generally privy to fish, and I was struck by how much bigger the gatehouse looked from below. A strange feeling came over me as I looked at the forebay weir [with the sluice gates in place] knowing there was a 10-15 foot wall of water waiting to resume its course behind it. Venturing through the channel beneath the gatehouse reminded me of being in a subway. I then traipsed through two feet of mud and silt in the draft tube before capturing photos of the turbine from the tunnel. And who would have thought, I had Internet access so far below.
I treasured the opportunity to take part in something that happens only once every five years. Now that I have seen the gatehouse, like the men who built it so long ago, I find it was well worth the wait.