By the numbers
8.73 - Inches of rainfall during in the Tennessee Valley watershed that drains through Chattanooga, or 76 percent more than normal
47.6 - Inches of rainfall in Chattanooga so far this year, or 46 percent above normal
$44 million - Estimated flood control savings for Chattanooga from TVA dams and flood control program
1.858 - Gigawatthours of electricity generation in July from TVA hydro units, an all-time high
Source: Tennessee Valley Authority
Chattanooga was spared an estimated $44 million of flood damage last month because of TVA's network of dams and storage reservoirs.
With rainfall during July nearly twice its normal level across East Tennessee, the Tennessee Valley Authority projects the rain-swollen Tennessee River and its tributaries would have spilled out of their banks and damaged many developed properties in Chattanooga's low-lying areas without TVA's dams and storage lakes to hold back the floodwaters.
TVA spokesman Duncan Mansfield said July's rainfall in the Tennessee Valley was the highest since 1967 and the fourth highest since precipitation record keeping began in 1890. Combined with heavy rains during the first half of the year, rainfall in Chattanooga so far this year totals nearly 48 inches, or 15 inches above normal, according to the National Weather Service.
Rainfall runoff from 20,000 square miles of land in East Tennessee, Northern Georgia, and western North Carolina and Virginia is funneled into the Tennessee River through Chattanooga. TVA operates 49 dams on the Tennessee River and its tributaries for flood control, hydroelectricity production, river navigation and lake recreation in its 7-state region.
"The performance of our river operations staff managing more than 40 inches of rain across our Valley has been a true highlight," TVA President Bill Johnson said in a conference call earlier this week. "Our integrated system of dams and reservoirs has been setting records for hydroelectric generation and averted flood damage since January of this year."
TVA calculates that without its dams, $800 million of flood damage would have occurred during January, including nearly $700 million of damages in Chattanooga.
Although the flood control savings in July were far less, such savings are highly unusual in July, traditionally one of the hottest and driest months of the year and one in which trees, crops and other vegetation usually soak up any extra rainfall.
The extra rainfall has helped TVA use its 29 power-generating dams to produce about 43 percent more hydro power than normal.
So far this year, TVA has broken hydro generation records in February, May and July, which has helped lower TVA's fuel expenses and resulted in a slight dip in electricity rates last month compared with a year ago.
TVA also has been burning more coal and less natural gas to generate power this year in response to higher natural gas prices this year compared with their 2012 lows. TVA Chief Financial Officer John Thomas said the federal utility has generated 17 percent more power from its coal-fired power plants during the first nine months of its fiscal year, ending June 30. In the same period, gas generation was down 14 percent from a year ago.
Contact Dave Flessner at email@example.com or at 757-6340