SR/SSD 98-9


Technical Attachment


Paul S. Trotter, G. Alan Johnson, Robert Ricks, David R. Smith,

NWSFO, New Oleans/Baton Rouge, Louisiana

Donnel Woods, WSO/COE, Vicksburg, Mississippi

Historically, managing the Mississippi River flow for commerce and public safety has created annual problems for decision makers and public officials. During the late 19th and early part of the 20th centuries, widespread heavy rain created numerous devastating floods on the Missouri, Ohio, and Mississippi basins. Such floods as those of 1912 and 1922 lead up to the Great Mississippi River Flood of 1927 with increasing severity in each succeeding event.

The 1927 flood left a disastrous impact upon the entire 1,250,000 mile2 river drainage. The unprecedented rainfall began over the whole basin in late summer 1926, and didn't abate until the summer of 1927. The flooding began at Memphis in the fall of 1926 and it was late August of 1927 before the last of the flood waters flowed into the Gulf below New Orleans. The levee system was decimated with over 120 crevasses (Fig. 1) and 165 million acres were inundated. There were 246 fatalities and over 600 thousand people were made homeless. The total damage was estimated at $230 million.

John M. Barry in his book Rising Tide has eloquently outlined the social and economic impact of that natural disaster upon the nation. As Barry points out, a major portion of the 600 thousand people made homeless was black tenant farmers which made up the labor force of the agriculture-based Delta. Those refugees were not allowed to leave and were forced to work and live on the levees that year to provide damage control. Up to that time, flood relief and river management was largely driven by economics rather than humane concern for the citizens.

Relations between diverse racial and economic groups were needlessly strained by the lack of planning and flood management procedures. Fearing that a flood in New Orleans would ruin the economic structure and investment stature of that city, bankers and commodities brokers convinced the governor to open the levee at Caernarvon 14 miles downstream. The destruction of the levee and the resulting flood inundated the two lower parishes of Louisiana displacing thousands of people and destroying the trapping, farming, and fishing industries for the following several years. Given the crevasses upstream from New Orleans, the necessity of dynamiting the levee was questionable.

As a result of the devastation, the Flood Control Act of 1928 was passed. Levee and reservoir maintenance and management was placed in the hands of the Army Corps of Engineers (COE), with cooperation among levee boards, river commissions and emergency management officials.

Since 1927 there have been 16 years with major flooding on the Mississippi (Table 1). The most memorable floods were those of 1973, 1983 and 1993. The flood of 1973 was the most severe since 1927 on the lower Mississippi River, with damages over $117 million (adjusted to 1983 price levels). It was in 1973 that the strain of record high volume flow nearly caused failure of the Old River Control Structure, which would have allowed the Atchafalaya system to capture the main flow of the Mississippi River.

Table 1. Years With Major Flooding on the Mississippi River


1718 1735 1770 1782
1785 1791 1796 1799


1809 1811 1813 1815
1816 1823 1824 1828
1844 1849 1850 1851
1858 1859 1892 1893


1903 1907 1908 1912
1913 1916 1920 1922
1923 1927 1929 1932
1936 1937 1945 1950
1957 1958 1973 1974
1975 1979 1983 1984
1993 1997

The second most severe flood on the lower Mississippi since 1927 was that of 1983. Damages were $15.7 million sustained mostly by river industries, docking facilities and widespread agricultural losses. Finally, in the Great Flood of 1993 on the Mississippi above Memphis, 50 thousand homes were damaged or destroyed, 54 thousand people were evacuated and damages have been put at $15 to $20 Billion. As extensive and devastating as 1993 was to the Midwest, the lower Mississippi basin was spared major flooding because the Ohio Valley, the Southern Plains, and basins in the southeastern U.S. did not experience the intense runoff that occurred in the Missouri River and the upper Mississippi River drainage.

Looking at the 1997 spring floods, it seems quite a reach to compare this season with the extent of flooding and the amount of devastation just discussed. However, one must keep in perspective the economic, social, and technological changes that have occurred over the intervening years.

Economic and social changes within the lower Mississippi basin have advanced no less rapidly than over the rest of the globe since 1912. During the early 1900s, damage to railroads alone were in excess of $6 million. The same loss today would be multi-billions due to inflation and growth. Most significantly, the impact of shutting down a port as diverse as New Orleans would be a national disaster, not just a regional economic loss as in 1927.

Just as economic and social changes have evolved over the years, so has the approach to emergency planning and flood mitigation. The Federal and State Emergency Management Agencies, flood preparedness plans of local communities, and those of shipping and industrial plants, were highly effective in dealing with the Mississippi River spring flood threat in 1997, nevertheless, some industrial and civic problems did occur with the increased river flow.

In preparation for the anticipated occurrence of above normal spring rains, and snowmelt, the Lower Mississippi River Forecast Center (LMRFC) and the New Orleans Area National Weather Service Forecast Office (NWSFO), colocated in Slidell, Louisiana, increased early coordination among Louisiana Emergency Management, Louisiana State Officials, and the area users at large. Early briefings were spearheaded by the LMRFC Hydrologist-in-Charge, the Meteorologist-in-Charge of the NWSFO, and the Service Hydrologist and Warning Coordination Meteorologist of the NWSFO.

A major press briefing on the spring flood outlook was held in early February. The presence of the NWS in coordination with U.S. Representative William Baker gave the office prime time media to alert users of the high water and flow expected that spring. During television interviews shortly after the press conference, emphasis was placed upon value of interagency cooperation in data collection and dissemination as well as the synergy of the public cooperative observer program and modern technology. Consequently, public officials in the lower Mississippi basin were prepared when a series of intense rainfall episodes occurred over the Missouri, Ohio, and Mississippi River basins during February and March of 1997. The record rainfall throughout the Ohio Valley, with some areas exceeding 20 inches, produced record or near record river stages and volume flow. The rain rapidly melted the existing snow cover and sent the Ohio River to stages 250% of normal. During that same time period, the northern plains were experiencing well above normal snowfall. To add to the hydrologic mix, rapid warming of the Missouri River basin caused snowmelt that increased flow on the Mississippi below Memphis.

Throughout the threat of rising water, the Louisiana Office of Emergency Preparedness was briefed continuously about atmospheric and river conditions and forecasts. In addition to keeping state officials apprized of the hydrologic threat to commerce and public safety, the NWS Port Meteorological Officer maintained a communications link with the Port of New Orleans and commercial shipping interests to advise them of high water conditions. In turn, the Port Authority relayed to the NWSFO the shipping conditions at the river's Gulf outlets.

To review the lower Mississippi River flood problems and management, one should be aware of the complex river system involving the Mississippi, Atchafalaya and Red Rivers. Old River, about 50 miles above Baton Rouge was once part of an abandoned loop of the Mississippi that connected it with the Atchafalaya and Red Rivers. Recently, the main channel was attempting to change its course and flow down the Atchafalaya. To prevent a complete capture of the Mississippi by the Atchafalaya, the COE constructed the Old River Control Structure (ORCS) in 1963. The project has a design project flow that maintains a diversion of 30% of Mississippi River volume into the Atchafalaya basin.

During the near record 1973 flood, weaknesses developed in the structure which might have resulted in its failure. Timely action on the part of the COE prevented that failure and improved the structure to its present full function. Throughout the spring 1997 high water season, the COE maintained the ORCS project flow, diverting approximately 30 percent of the Mississippi volume into the Atchafalaya basin. As a result, the lower Atchafalaya remained in flood for four months. Throughout that time, the action of the US Coast Guard Traffic Safety Division, in cooperation with other federal and state authorities, maintained the flow of commerce and river safety. Similarly, although port activity was curtailed in the cities of Morgan City and Berwick, structural damage and personal injury was kept at a minimum during that four-month period.

Red River Landing lies just below the ORCS on the Mississippi River. During the flood of 1945, the greatest volume of water without a levee failure surged through the lower basin. As shown in Table 2, that volume of river discharge in 1945 remains the second greatest on record. Although the spring flood of 1997 created the highest stage of record at Red River Landing, the volume of water passing the gage ranks only fourth. Additionally, because the flow was attributed to routed water from record high stages on the Ohio and not from local rainfall, the flood was the shortest in duration of the top 6 floods of record at the Landing.

Table 2. Comparison of the 7 Greatest Floods at Red River Landing, La 1927-1997
Ranked by Highest Stage, Greatest Volume, and Days in Flood

61.3 1997 1799 1927 135 1927
60.9 1927 1520 1945 115 1983
60.5 1983 1500 1973 99 1973
60.0 1945 1480 1997 90 1974
59.2 1979 1448 1983 79 1975
58.2 1973 1419 1979 76 1945
56.6 1975 1220 1975 69 1997

The State Penitentiary at Angola, Louisiana lies across the Mississippi from Red River Landing. The 20,000 acre plant is surrounded on three sides by a sharp bend in the Mississippi channel. Geologically, that area of the Mississippi basin has beds of sharp sand at points near the foundation of the levee. These pockets of sand allow the levee to be eroded from underneath, forcing water under the levee to the land side and creating sand boils that left unattended can rapidly deteriorate into a crevasse. As expected, the threat of sand boil outbreaks at the prison was of major concern. There are two levees protecting the prison from rising water. The inner levee was built and is maintained by the state and is the only section of the levee system not controlled by the COE.

When the river flow was the greatest and record high stages were sustained at Red River Landing in March (Fig. 2), prison officials aided by the COE battled several sand boils threatening the inner levee. The threat of a levee break necessitated relocation of the 5,000 inmate population to temporary tent quarters on higher ground. The warden and prison staff were literally "jailed" with the inmates. The levee was contained within 36 hours and the inmates returned to the facility without incident. Authorities estimate repairs to the levees, system roadways and to farming acreage will run in excess of $1 million.

The most significant problem with high volume flow on the Mississippi, aside from public safety and welfare, is the peril to commercial traffic in treacherous currents and the sharp bends in the river. Barge traffic is essential to life support systems such as public utility plants. The coal-fired electric generating plant operation at New Roads, Louisiana, just downstream from Red River Landing, is normally supplied by coal barges. In 1997, the river landing at New Roads became inaccessible for two weeks when the loading facility went under water. Had the flooding been as prolonged as in 1927 or 1983 the coal supply would have been exhausted.

With the current increasingly treacherous around the bends in the river below Red River Landing, the Coast Guard Traffic Safety Division enforced strict regulation upon the length of barge tows and the number of securing lines from the onset of the record volume flow. Even with those precautions, there were 35 traffic incidents between March 13 and April 24 involving 502 barges!

On March 17 25 barges escaped from the pilot tug while negotiating a 100 degree turn just upstream of the US 190 bridge. Although 24 of the barges contained grain and coal, one barge contained benzene and toluene. That barge overturned and came to rest on the left bank near the state capital and Southern University campus, creating a toxic hazard that lasted 18 days. About 20 homes were evacuated and the campus of Southern University and the state capitol offices were closed twice by the threat of toxic fumes from the barge.

Of major concern to civic planners and emergency management officials are the 28 petrochemical plants and the nuclear power plant on a 13 mile stretch of the river in St. Charles Parish. That concern took on very real consequences as the river crest moved through that area during the night of March 19. While authorities were battling the overturned barge at Baton Rouge, 42 barges broke loose near La Place, narrowly missing the Waterford Three nuclear power plant intake valves. Runaway barges tore up wharves, intake facilities and loading platforms on their escape from captivity. In the middle of this wild chase, the release of amonia from a ruptured pipeline necessitated the evacuation of a dozen homes along the river.

Before the night was over 134 barges were running loose in the swift current. Coast Guard crews who were on the river enforcing safety regulations and assisted by industrial tugs were able to secure all of the barges within a few hours avoiding a disaster of unprecedented proportions.

On March 17 the Bonnet Carre Spillway was opened, diverting about 16% of the river volume from the main channel into Lake Pontchartrain. That measure was undertaken under project design to stop the rise at New Orleans to just below the flood stage of 17 ft. The hydrographs in Fig. 3 illustrate the damping effect of the spillway opening upon the rise at Reserve, 36 miles upstream from New Orleans. The action had little effect on the crest at Donaldsonville, approximately 72.5 miles upstream.

As always, the opening of the spillway was not without controversy. Although the action reduced the volume and lowered river stages along the lower river, the threat to the estuarine ecology, salt water fish population, and the blooming of oxygen-depleting algae remains a concern. Each of those threats was realized to some degree with the high volume of silt-bearing river water replacing that of normally high-saline content found in the estuary. For example, the lake's brown shrimp production was reduced by about 80 percent in the summer of 1997 which had an unwelcome effect on the regional economy. In addition, the blue-green algae bloom lasted for approximately four months and presented a health hazard as well as affecting aquatic life. Nevertheless, the interaction of a series of late spring cold fronts and Hurricane Danny moving west to east across the Gulf just below the river's outlets helped reduce the harm to the ecology.

To close the chapter on economic effect of flooding we will have to await the final report from the Corps of Engineers concerning the full effect of the silt deposit at the mouth of the River. During the flood, silt deposits increased to the point where only one ship at a time could navigate the channel at the passes. Five hoppers, two cutters and one dust pan were operating full time to keep the channel open for shipping during the spring. Dredging operations, which were near budget levels at the start of the flood, will need additional appropriations to maintain full port facility operations.

Finally, with all of the potential hazards to public health, economy, and the threat to infrastructure along the lower Mississippi, the planning and community action during the 1997 flood season can be termed a success. But with that good feeling in mind, we must also realize that the nation must maintain the good cooperation, communication and trust currently in place among federal, state and local agencies, levee boards, and the industrial community to successfully combat disastrous floods in the future.


Smith, David T. and David B Reed, 1990: A Centennial Survey of American Floods, Fifteen Significant Events in the United States, 1890-1990. NOAA Technical Memorandum NWS SR-133. NWS Southern Region Headquarters, Fort Worth, TX.

Barry, John M., 1997: Rising Tide. Simon & Schuster. New York.

Frankenfield, H. C., et al. 1927: The Floods of 1927 in the Mississippi Basin. Mon. Wea. Rev., Supplement No. 29. U.S. Department of Agriculture, U.S. Weather Bureau.

Fox, John A., 1915: Mississippi River Flood Problem. The Mississippi River Levee Association, Memphis.