01/25/2010) Later that same day: When the December snow melted, it saturated the ground. All day yesterday and all last night, heavy rain fell -- as much as 5 inches in the watershed of the upper Catawba. The highest water levels since 2004 sent the river into our yards and over Rhodhiss Dam. Rhodhiss Dam is 65 feet high and 1,500 feet long. Put a few feet of water over the top and it makes a considerable sight and a mighty roar:

[Ray's Weather Photo of the Day, Jan 27, 2010. Thank's Ray]

The dam is usually bone dry on this, the downriver side, with a small amount of water at the base of those rocks. Everything is different when the lake is several feet above full pool. It was at 100.0 (feet? percent?) at 3 AM and rising fast. These photos were made about twelve hours later. Duke Energy estimated the lake could peak at 105. It was spectacular.

A note about lake levels: Duke Energy assigns the point at which water begins to spill over each of its dams the arbitrary but convenient level "100 feet" and reports lake levels with respect to that datum. A lake whose level is 102 is sending two feet of water over the dam. Under the influence of Hurricane Frances, Lake Rhodhiss reached 107.4 on September 8, 2004. It was near 103.24, it's highest level since then, when I made these photos.

Here are the four historical crests (the floods of 1916 and 1940 predate record keeping):

1) 107.41 ft on 09/09/2004 (Hurricane Frances)
2) 103.24 ft on 01/25/2010
3) 103.01 ft on 09/18/2004 (Hurricane Ivan)
4) 101.91 ft on 04/11/2003

From NOAA data describing the Catawba at Rhodhiss Dam.

Comparisons to Niagara are irresistable and not inapt. Assuming the water is moving 4 mph as it crosses the top of the dam (a guess, and one I was not tempted to go out to check in person), then peak flow over the dam was about 28,000 cubic feet per second. A typical flow over Niagara Falls is 85,000 cfs.

Rhodhiss Dam has no flood gates and a spillway that runs from bank to bank. The Rhodhiss Hydro Station has three generators with a total capacity of 26 megawatts. The only way to lower the lake level is to spin the generators. Here's a nice assignment for a physics class: assume the available head is 55 feet and that the generators work at 50% efficiency. How much water can a wood chuck chuck if... no, how many cubic feet per second can the station release? If the dam can keep up with rainfall of 2 inches per day, how many square miles does the watershed contain? Etc.

The middle part of the span: the sign usually stands on a rocky island, high and dry. It reads, "Danger. Remotely controlled plant. Water subject to sudden rise and violent turbulence without advance warning." Indeed.

Stitched panorama of the full length of Rhodhiss Dam with the Catawba spilling over. The full-size image is 20,000 x 4,000 pixels. You don't want to mess with that. This and all photos on this page were made from the site of the destroyed Burlington mill on the north bank of the river, Rhodhiss's claim to fame.

:: back to the slow blog ::