"In the early part of the 20th century, the lower Guadalupe River Basin below the current location of Canyon Lake in Texas, USA had been especially subject to serious flooding. Due to the need to lower the flooding issues, Congress authorized the construction of Canyon Dam. The dam and its resulting lake was to serve two purposes: flood control and water conservation.
Construction of Canyon Dam began in 1958 on mile 303 of the Guadalupe River. The dam was finished in 1964 and water impoundment began. The lake was dedicated in 1966. The lake filled to conservation pool level by 1968.
Canyon Dam controls floods originating on the 1,432 square miles of drainage above the dam. Flood protection is provided to 157,250 acres of land downstream from the dam.
The high canyons of the upper Guadalupe have a channel capacity of 40,000-50,000 cubic feet per second. The channel on the lower Guadalupe River has a capacity of only 13,000-30,000 cubic feet per second. Thus the cause of prior flood events before the dam construction.
To date, it has been estimated that millions of dollars in flood damage has been averted from several major flood events in the area.
The construction of Canyon Dam on the edge of the Balcones Escarpment has been very effective in protecting the lower Guadalupe River Basin. One example of this came in August 1978. Within two days' time, 40 inches of rain fell on the upper Guadalupe River. The river flowed into the lake at 115,000 cubic feet per second causing the lake to rise 21.6 feet above the conservation pool level of 909.0 feet above mean sea level. It was estimated that 24 million dollars of downstream damage was averted due to the flood protection of Canyon Dam.
The major flood event of record was in 2002 when the lake overflowed the spillway for the first time in the history of Canyon Lake. The highest recorded elevation was 950.32 ft msl. It is estimated that about two times the lakes volume in water went over the spillway in a very short time. There was still flooding down stream, but because the dam exists, the flooding was not worse. Without the dam, every city between Canyon Lake and the Guld of Mexico would have had severe flooding damage.
At conservation pool level Canyon Lake has a capacity of 382,000 acre-feet. It has a surface area of 8,230 acres and 80 miles of shoreline. At flood control pool level of 943 ft-msl, the lake has an additional capacity of 346,000 acre-feet making total storage 728,400 acre-feet.
The Guadalupe-Blanco River Authority (GBRA) is the local agency with rights to the water in the conservation pool of the lake. The Authority contributed to the construction costs and currently pays the U.S. Government annually for the portion of operation and maintenance costs attributed to the conservation pool water. The water is used to operate several small hydroelectric plants downstream from New Braunfels. It is also used by the GBRA for municipal water supply, irrigation, and industrial uses. GBRA began construction of a hydroelectric facility at Canyon Dam in August 1987; it was first put into service in February 1989.
Here is a list of some of the flood events since the construction and impoundment at Canyon Dam.
* The first major flood event occurred in August 1978 when the lake elevation reached 930.60 ft-msl.
* The next major flood event occurred in July 1987 when the lake level reached 942.67 ft-msl.
* In the floods of 1991-1992, maximum elevation reached 937.77 ft-msl.
* Another major flood event occurred in late June to early August 1997 when the maximum elevation was 937.60 ft-msl.
* The flood of record occured in 2002 when the water crested the spillway and kept on rising to reach a maximum elevation of 950.32 ft-msl.
* The lowest lake elevation recorded was 9th September 2009 at 892.70 ft-msl."
Source:
U.S. Corps of Engineers website.