Crest passes Delta, but flooding river still a threat
by For the MBJ
Published: May 18,2011
MISSISSIPPI DELTA — The Mississippi River at Greenville at 6 a.m. today was 64.04 ft, down 0.14 feet, according to a statement from Mayor Heather McTeer. But officials continue to watch the levee for problems.
The river level at Greenville is forecasted to fluctuate at or below 64.20 ft for the next several days.
“We will remain at a relatively high level for the next several weeks,” McTeer said. “Seepage is evident near the Mississippi River levee system throughout Washington County and is expected to continue.
“Sand boils continue to develop but are being mitigated by the Mississippi Levee Board. There are currently no situations with the levee system. The levee is holding back the water just as it was designed.”
The Delta Council, which is based in Stoneville just east of Greenville, said as floodwaters make their way south down the Mississippi River, the Flood of 2011 has left its mark along the way. The economic impact will take time to assess.
“Although the Mississippi River has reached (or is nearing) crest elevations throughout the region known as the Mississippi Delta, the road ahead is still relatively long,” the Delta Council wrote.
At the present, there is a tremendous volume of water flowing down the Mississippi River, approximately 2 million cubic feet per second. At that flow, it would fill the Ross Barnett Reservoir once every 2 1/2 hours. The Mississippi River at Vicksburg is projected to remain above 2008 flood levels for nearly five weeks.
“This extended period of high water will continue to place a strain on the Mainline Mississippi River Levee,” the Delta Council wrote.
“The economic disruption that has occurred due to the mainstem Mississippi River system is still ongoing. In addition to the loss and degradation of private property, homes and both farm and timber land, the economic loss due to minimal port activities, inundated and/or stranded manufacturing and distribution facilities and the loss of revenue and job interruption to the resorts in Tunica, Lula, Greenville and Vicksburg located adjacent to the Mississippi River. In Tunica, the first two resorts are scheduled to be opened today, but there will be a long period of time before full economic recovery in all of these sectors can be achieved.”
Concerning the Yazoo backwater area, the Delta Council reports: “The projected Vicksburg crest of 57.1 translates to 103.3 feet in relation to ground level (i.e. feet above mean sea level). One of the most common questions regarding this may be ‘how can the Mississippi River overtop the Backwater Levee which is built to 107 feet.’ The simple answer being, the Backwater Levee is located approximately 12 miles upstream of the Vicksburg gauge. At high stages, the slope of the water surface on the Mississippi River over this length is approximately three feet. The Yazoo River’s headwater effects are overshadowed by the volume of the Mississippi River backwater that is moving back up the Yazoo. Near the Steele Bayou structure, the projected crest elevation at the Vicksburg gauge with the additional slope added for the upstream location yield an approximate elevation of 106.7 feet. This would not overtop the Backwater Levee.
“Given no overtopping of the Backwater Levee and below average rainfall it is likely the Yazoo Backwater Area crest will be lowered from 95 feet with normal rainfall from this point forward until Steele Bayou can be open it will probably crest about 92 to 92.5 feet. However, in the event of a levee failure in the Backwater Area, which is very unlikely, the flood elevation is estimated to reach 106 feet. It is projected that if such a failure occurs, the waters of the Mississippi River would take three days to reach Rolling Fork and approximately five days to cover more than one million acres in the South Delta extending to Highway 12 between Belzoni and Hollandale.
“Delta areas on the east side of the Whittington Auxiliary Channel (Satartia, Wolf Lake, Carter and property extending to the upper end of the auxiliary channel in the vicinity of Silver City) are not protected by levees. Therefore, these areas are projected to experience flood elevations of 106.5 feet.
“Currently, water surface elevations are 105.8 feet near Satartia, 105.1 feet near Highway 149 and the Whittington Auxiliary Channel and 104.1 feet near Carter. There is a noticeable slope in water surface elevations moving northeast as it takes time for backwater to fill available storage and equalize. Given prolonged crest elevations of the current flood event, it is likely that backwater flooding will ‘level out’ from the Steele Bayou Structure through the Wolf Lake/Carter area. As storage areas (i.e. low spots) are being filled and the amount of slope in water surface elevation is reduced, the rate of floodwater rise will likely be reduced as well. For example, on May 12 the Wolf Lake area was experiencing approximately two feet of rise per 24 hours. This was due to roughly four feet of head pressure (i.e. higher slope) backing up from the Steele Bayou Structure. As water levels equalize, head pressure is less and we are observing water level rises of approximately 0.25 feet/day currently.
Preliminary projections for water falling in the Wolf Lake area: It could be June 10-12 before water levels drop below 102 feet. This will be revised as the Mississippi River crests at Vicksburg later in the week.
The Silver City/Belzoni area east of the Yazoo River (Tchula/Bee Lake) is projected to see floodwaters up to 107.5 feet. Current water surface elevation of the Yazoo River at Belzoni is 106.53 feet.”
Source: Mayor Heather McTeer; Delta Council
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