MOBILE, Ala. – While no single major storm system has occurred, successive storm events over a period of three months caused by a polar weather stream crossing from the north into the United States have led to historic flooding along the Black Warrior and Tombigbee Rivers (BWT). According to the Southeast River Center of the National Weather Service, this was the wettest December to February in the U.S. and wettest December to February in parts of North Alabama since 1895.These high flows caused the U.S. Army Corps of Engineers Mobile District to close multiple locks as well as execute dredging operations in response to unprecedented shoaling and formation of sandbars obstructing watercraft along the Tennessee-Tombigbee Waterway (TTWW) and lower Tombigbee River.
Beginning in the first week of December 2018, and continuing through early March 2019, the watershed containing the TTWW experienced multiple back-to-back storm events in the form of low pressure and frontal systems. These weather systems, occurring on a near weekly basis, have caused conditions on the rivers to gradually deteriorate due to the cumulative rainfall amounts. The total rainfall in the watershed over the last 90 days has been approximately 25 – 30 inches, deviating from the historical normal of 15 – 20 inches. The precipitation over the watershed is 150 – 200 percent above normal.
This has translated to extreme, long duration, high flows and river stages on the TTWW, as well as significant flooding on the Black Warrior River. The continuous back-to-back events occurring from December and into March have caused conditions to get progressively worse, saturating soils and providing no time for water levels to recede in between weather events.
Daily flows at Bevill Lock and Dam (L&D), located at the southern end of the TTWW on the Tombigbee River, reached 126,000 cubic feet per second (cfs) in late February — the third highest daily flow recorded at that location since 1980. The monthly average flow for February reached 41,000 cfs, which is the fourth highest monthly average flow since 1980 — typically, monthly average flow rate this high should take place at this location no more than once in 10-year cycles.
Downstream of Bevill L&D, flooding was further compounded by extreme flows from the Tombigbee River joining with flood flows from the Black Warrior River. At Demopolis L&D, located just below the confluence of the Black Warrior and Tombigbee Rivers (BWT), the U.S. Geological Survey data shows flows reached 308,000 cfs on March 2. While still considered a preliminary measurement, this flow rate would be the second highest flow at that location since 1929. River stages all along this stretch of the lower Tombigbee River have reached levels not seen since 1991.
While navigation conditions have recently begun to improve, additional forecast rainfall over the next 1 to 3 months may return the rivers to high water conditions quickly. Due to the unusual, wetter-than-normal, continuous rainfall this winter, the watershed is saturated and primed for all future rainfall to run off into the rivers.
Currently, all the locks on the BWT and TTWW are open. The locks, including Demopolis and Coffeeville, had been previously closed due to high flows at each facility. Also, water traffic is moving normally again on the Black Warrior River.
USACE Mobile District has already begun executing its dredging plan to ensure that navigation mission requirements are met on the TTWW. District dredging operators have already opened a navigation channel restricted to 150' width at Mile 410. Initial hydrographic surveys are complete on the TTWW and scheduled to start on the lower BWT within the next two weeks, depending on water levels below Demopolis and Coffeeville Locks. Other navigation obstructions remain nearby the Aberdeen Lock (mile 357), which continue to block river traffic along the TTWW. There are also a number restricted channel areas, marked by buoys, at the following river mile markers: mile 326, mile 362.6, mile 423.1, mile 431, mile 433, mile 436.6 and mile 440.3.
USACE Mobile District continues to meet the challenges brought on by the ongoing weather event impacting the Southeastern United States, and appreciates the public’s patience as it continues aggressively executing its mission to clear the navigation impacts across the region.
For the latest updates, call 251-690-2505 or visit the following pages:
USACE Mobile District website: www.sam.usace.army.mil
USACE Mobile District Facebook: https://www.facebook.com/USACEMOBILE/
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