Saturday, May 23, 2020

A delicate balance of a few billons tons of water!

Forsyth MO. - For whatever reason (although I'll get into some in future blogs), the two bodies of impounded water controlled by the Army Corps of Engineers could just possibly get into trouble due to both recent and forecast rainfalls. First, some factual information;

[Source – Wikipedia] 'The original purpose of the reservoir was for flood control on the White River. The dam had been authorized a month earlier under the Flood Control Act of September 3, 1943. The reservoir has a fluctuation of 16 feet (4.9 m). When the reservoir is above the maximum flood pool, excess water goes over the auxiliary overflow spillway at the north end of the dam.

Table Rock Dam’s spillway capacity was evaluated as a result of a dam safety program in the 1990s. Using improved weather data and more modern technology and safety requirements, engineers determined that the lake would rise ten feet higher during the worst-case flood than previously calculated. An event of this magnitude would over top the earthen embankment and destroy Table Rock Dam with catastrophic losses in downstream areas, including Branson. To prevent the potential loss of life and property damages, congress approved and authorized construction of the Dam Safety Project. After considering several options and gathering considerable public input, an auxiliary spillway was determined to be the best solution. The auxiliary spillway was completed in 2005 at a cost of approximately $65,000,000.

The worst case scenario of a catastrophic floodwater discharge from Table Rock Lake using the auxiliary floodgates would roughly resemble this:

At elevation 931 Table Rock Lake is at full flood capacity. The ten Tainter gates are opened to accommodate additional lake inflow from the White River Basin including the James River and Beaver Lake discharge.

At elevation 937 Table Rock Lake is 6 feet above flood capacity. The ten Tainter gates are opened wider in an effort to stabilize reservoir rise. Outflow from the Lake under these circumstances will be nearing 200-300 thousand cubic feet per second (CFS).

At elevation 942 Table Rock Lake is 11 feet above flood capacity and at its "design pool", or the maximum elevation that the reservoir is engineered to reach, under "probable maximum flood" scenarios. The dam’s ten Tainter gates will be fully raised to their maximum height of approximately 30 feet letting loose 550 thousand CFS into Lake Taneycomo. This scenario would effectively submerge and destroy the powerhouse, power transmission grid, hatchery, and wreak serious destruction down stream.

At elevation 947 Table Rock Dam would be at its maximum capacity and water would be at the very top of the dam. The auxiliary spillway would be brought online, in concert with Table Rock’s fully opened floodgates. This catastrophic or "last resort" protocol releases 1 million CFS of lake waters into Taneycomo and deals dreadful destruction to Branson, Hollister, Point Lookout and possibly the Powersite Dam. At this point there is a danger of water over-topping the concrete dam and breaching the earthen structure, which imminently leads to cataclysmic structural failure and the uncontrolled release of the Table Rock Lake impoundment—nearly 3 million CFS of water.

Historical facts: Table Rock Lake has a record crest of 935.47 feet, which occurred on April 27, 2011.

In December 2015, the dam released 72,000 CFS at its peak. This is the highest amount ever released.'

As of May 23rd, the water levels were at;

Click to enlarge
Now while the smallest impounded Lake (Beaver) was doing OK, her two downstream neighbors were carrying a bit of a load. The biggest worry being Bull Shoals, currently at 693 feet or just two feet below flood pool levels. Note that 'flood pool' as defined by Law Insider reads;

30 (24) “Flood pool elevation” means the maximum water surface elevation of a reservoir, equal to the elevation of the spillway.

This is the point at which a dam would be forced to start discharging 'against the will of those in control'. (Note that the Table Rock Dam level is at 926 feet with their flood pool set at 931 feet - That's 4 feet away)! Also note that when were are talking about the height of a body of water, we are referring to msl or height above mean sea level.

So, even though the coming week of rain only equals about an inch, the water game is certainly getting a bit dicey, to say the least!

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