U.S. Geological Survey Water-Supply Paper 2375
National Water Summary 1988-89--Floods and Droughts:
Mississippi has a humid climate. Annual precipitation ranges from about 50 inches in the northern part of the State to about 68 inches near the gulf coast in southeastern Mississippi. The principal source of moisture is the Gulf of Mexico (fig. 1); tropical airmasses bring moisture inland from the gulf, particularly during summer and fall. At times, moisture from the eastern Pacific Ocean reaches Mississippi. Precipitation generally is the result of convective showers from surface heating of moist air or the frontal lifting of moist air over polar continental airmasses moving into the State from the north. Tropical storms and hurricanes also can produce intense rainfall when moisture-laden air is blown inland by strong winds.
In addition to the oceans, important moisture sources include local and upwind land surfaces, as well as lakes and reservoirs, from which moisture evaporates into the atmosphere. Typically, as a moisture-laden ocean airmass moves inland, it is modified to include some water that has been recycled one or more times through the land-vegetation-air interface.
Precipitation that results from frontal systems occurs as general, widespread rain associated with warm fronts and as intense showers, squall lines, thunderstorms, and severe weather associated with rapid convergence of cold fronts with moist, tropical airmasses. Frontal systems are most common in late winter and spring. When frontal systems stall or move slowly across the State, they can produce large quantities of rainfall and cause severe flooding. Floods associated with frontal systems are most common in March and April.
Tropical storms and hurricanes occur frequently from June through October. These systems can produce rainfall rates of 2 inches per hour. Flooding associated with these storms can be serious, particularly when the storm systems move slowly or become stalled.
Precipitation can vary substantially from year to year. State-wide rainfall totals averaged less than 37 inches in 1889 but more than 85 inches in 1983. Extremely wet years and extremely dry years commonly are produced by anomalous shifts in the jetstream, variations in the strength of the Bermuda High, or some other unusual global air-circulation pattern. The extremely large rainfall total in 1983 resulted from circulation patterns in the western Gulf of Mexico in conjunction with an anomaly called El Niņo-a southern oscillation (Enfield, 1989) that occurs in the Pacific Ocean. Extremely dry years in Mississippi often are produced by high atmospheric pressure associated with the semipermanent Bermuda High, which is located in the Atlantic Ocean off the southeastern coast of the United States. Downward motion within a high-pressure ridge in the upper atmosphere limits convection and inhibits the formation of clouds, and thus of convective showers and thunderstorms.
MAJOR FLOODS AND DROUGHTS
Floods and droughts have plagued Mississippians since the territory was first settled. As early as 1543, a great flood on the Mississippi River was recorded in a history of Hemando De Soto's expedition to the North American Continent (U.S. Weather Bureau, 1923). However, it was in the last one-half of the 19th century that collection of hydrologic data began on a systematic basis. The floods and droughts discussed herein are the most recent and most severe in Mississippi since systematic records have been collected. The most significant floods and droughts are listed chronologically in table 1; rivers and cities are shown in figure 2. The flood or drought severity (recurrence interval) given in table 1 is the maximum calculated for each event from streamflow records. Records from six streamflow-gaging stations have been selected to portray the severity and areal extent of historic floods (fig. 3) and droughts (fig. 4) in Mississippi. Data from these gaging stations are collected, stored, and reported by water year (a water year is the 12-month period from October 1 through September 30 and is identified by the calendar year in which it ends). These gaging stations are located in five of the six major river basins in the State and monitor streamflow in basins having drainage areas ranging from 180 to 620 mi2 (square miles) (fig. 3). Upstream from these gaging stations, streams are largely unaffected by regulation, diversion, or channelization.
Five extensive and damaging floods have occurred in Mississippi during the past 35 years. Frontal storms caused record floods in 1955, 1973, 1974, 1979, and 1983; hurricanes also have caused flooding and extensive property damage along the coast.
The 1543 flood on the Mississippi River was described by De Soto (U.S. Weather Bureau, 1923, p. 10) as follows:
A hurricane during October 1-2, 1893, was one of the most devastating natural disasters in the history of the United States. The hurricane, which had 130-mi/h (mile per hour) winds and created a 15-foot storm surge, caused the loss of more than 1,800 lives along the gulf coast and about $1 million in damage in Mississippi and Louisiana (Sullivan, 1986).
The flood of April-May 1927 is considered by the U.S. Army Corps of Engineers to be the most severe flood recorded on the Mississippi River at Vicksburg. The discharge was 1,648,000 ft3/s (cubic feet per second) at Vicksburg; however, computations indicate that the discharge would have been 2,278,000 ft3/s had the levees retained all the flow. At the Corps of Engineers gage at the mouth of the Yazoo River, the river reached a stage of 58.4 feet. This flood caused more than 100 breaks in the levee system in Mississippi, Arkansas, and Louisiana; the first was about 18 miles north of Greenville on the east bank. The official death toll was 246; some estimates were as many as 500. About 650,000 people were left homeless. Inundation of 2.3 million acres of flood plain with as much as 18 feet of water caused $230 million in damage (dark, 1982).
The flood of 1937 is the second largest recorded flood on the Mississippi River at Vicksburg, where the river reached a stage of 53.2 feet. The peak discharge of 2,080,000 ft3/s is the greatest ever recorded at that site.
Large floods in the Skuna River and upper Tombigbee River basins in March 1955 resulted from a strong frontal system that produced more than 10 inches of rain in 24 hours in the Skuna River basin on March 20 and 21. The areal extent and severity of this flood are shown in figure 3. The flood was the largest of record for the Skuna River throughout most of its length; the flood on the Tombigbee River at Aberdeen was the largest since April 1892. On March 22, 1955, the peak discharge of Town Creek near Nettleton (fig. 3, site 1) was 151,000 ft3/s, which was more than double any other discharge during the period of record. One person was killed, and damage was about $4 million (U.S. Geological Survey, 1956). Several highways were under water, and some bridges and roadways were washed away.
Hurricane Camille, one of the strongest and most destructive hurricanes ever recorded, struck the Mississippi gulf coast on August 17, 1969. One of the lowest recorded barometric pressures in the Western Hemisphere (26.61 inches) was measured in the eye of this storm. Wind speeds approached 200 mi/h, and winds caused a 25-ft storm surge near Pass Christian. About 8 hours after entering Mississippi, the eye of Hurricane Camille passed over Ross Bamett Reservoir near Jackson and caused the surface of the 30,000-acre lake to tilt and have a 1.0-ft pileup at the dam (Wilson, 1972, p. 2). The hurricane killed 139 people and injured more than 8,900. About 80 boats and ships were sunk, and 9 were washed aground. Some 5,700 homes were destroyed, and 35,000 were damaged. Total damage in Mississippi was an estimated $ 1.3 billion (Wilson and Hudson, 1969), and 33 counties were declared disaster areas.
Torrential rains during March 14-16, 1973, caused severe flooding in Alabama, Georgia, Mississippi, and Tennessee. The flooding resulted in the loss of seven lives in the Tennessee River basin, and total damage, excluding the Yazoo River basin, exceeded $60 million (Edelen and Miller, 1976). In Mississippi, the peak discharge recorded on the Tombigbee River at Bigbee had a recurrence interval greater than 100 years. Flooding was moderate in upstream reaches of the Big Black and Yazoo River basins in north-central Mississippi (fig. 3). At places, rainfall totals for this storm exceeded 12 inches. Flood damage in the Tombigbee.River basin between Fulton and Columbus was about $15 million (Edelen and Miller, 1976, p. 283). In the Yazoo River basin, floodwater passed over the emergency spillways of four flood-control dams. Damage in the Yazoo River basin alone from a combination of the March 14-16 flood and the subsequent April-May flood was about $169 million (U.S. Army Corps of Engineers, 1973, p. 37).
About 3,590 mi2 of farmland was inundated by a combination of the March 14-16 flood along the headwaters of the Yazoo River and backwater from the April-May 1973 flood of the Mississippi River. In the Mississippi River, which was above flood stage for 88 days, the total volume of flow for the first 9 months of 1973 exceeded the total for the same period during 1927 and 1937. As a result of the 1973 floods, 19 lives were lost, 14,000 people were evacuated, and $212 million in damage was sustained in Mississippi (U.S. Army Corps of Engineers, 1973). This flood was rated by the Corps of Engineers as a "project flood," the worst flooding that could be expected in a flood-control project area.
The April 13, 1974, flood caused record, or near-record, peak discharges and stages on many streams in south-central Mississippi (fig. 3). Rainfall totals for the April 12-14 storm exceeded 20 inches near Sanatorium and Magee and 16 inches at Brookhaven. On April 13, 1974, the peak discharge of the Homochitto River at Eddiceton (fig. 3, site 6) was 55,400 ft3/s, which had a recurrence interval slightly greater than 100 years. The peak discharge on the Leaf River at Hattiesburg also had a recurrence interval slightly greater than 100 years and was the largest of record. This flood resulted in the loss of 8 lives, the evacuation of about 9,000 people, and nonagricultural flood damage of about $50 million (U.S. Army Corps of Engineers, 1975). Twenty-seven counties were declared disaster areas.
Table 1. Chronology of major and other memorable floods and droughts in Mississippi, 1543-1988.
[Recurrence interval: The average interval of time within which streamflow will be greater than a particular value for floods or less than a particular value for droughts. Symbol: >, greater than. Sources: Recurrence intervals calculated from U.S. Geological Survey data; other information from U.S. Geological Survey, State and local reports, and newspapers]
The largest and most damaging recent flood in Mississippi (commonly called the Easter Flood) was during April 13-24, 1979 (fig. 3), on the Pearl River. A major storm on April 11-13 produced rainfall totals of 12 inches in much of the upper Pearl River basin and 21 inches at one site near Louisville. This storm caused record flood peaks from April 13 through 24. The peak discharge of the Yockanookany River near Ofahoma (fig. 3, site 4) was 46,500 ft3/s, which exceeded the discharge having a 100-year recurrence interval (32,100 ft3/s). On the main-stem Pearl River, peak discharges and stages were the greatest since at least 1874, and peak-discharge recurrence intervals generally were greater than 100 years. Floodwater crested 6 ft above the previous maximum stage at Jackson, and 17,000 people in the Jackson area were forced to evacuate their homes. Flood damage in the Pearl River basin was about $257 million (Edelen and others, 1986). The storm also produced 8 inches of rainfall and subsequent severe flooding in the upper Tombigbee River basin in eastern Mississippi and western Alabama. Nine lives were lost in Mississippi and Alabama as a result of these floods (Edelen and others, 1986, p. 212). Twenty-five counties in Mississippi were declared disaster areas. Total flood damage was about $344 million in Mississippi, Alabama, and Georgia (Edelen and others, 1986, p. 212).
Hurricane Frederic struck the Mississippi gulf coast near Pascagoula on September 12, 1979, with 128-mi/h winds and 12-ft storm tides. The hurricane spawned many tornadoes and caused extensive damage. This storm resulted in the loss of 11 lives in Mississippi and Alabama. About 60 boats were sunk in Biloxi Bay. Damage was about $500 million in Jackson County, in southeastern Mississippi, and 85 percent of the structures in Pascagoula were damaged (Sullivan, 1986).
Major floods occurred in southern Mississippi and southeastern Louisiana in April 1983. At Columbia, rainfall from a slow-moving cold front totaled about 14 inches on April 7 and 17 inches during April 4-8. This rainfall resulted in large floods on many streams. Peak discharges at 15 gaging stations had recurrence intervals equal to or greater than 100 years. The flood on Black Creek near Brooklyn exceeded the previous maximum stage (flood of 1961) by 4 feet: the peak discharge (42,500 ft3/s), which was almost twice the previous maximum, had a recurrence interval of greater than 100 years (Carlson and Firda, 1983, p. 32).
A few weeks later, in May 1983, widespread rainfall over the northern two-thirds of Mississippi resulted in moderate to severe flooding on many streams (fig. 3). Rainfall during May 18-22 was 8 inches in many areas of central and northeastern Mississippi. The flooding that followed caused one death and damage of about $500 million (David Imy, National Weather Service, oral commun., 1988).
At Jackson, the Pearl River crested 11 feet above flood stage, which was 3.7 feet lower than the peak stage for the April 1979 flood; however, the flood forced the evacuation of about 5,000 people (David lmy, oral commun., 1988).
Information on extreme low flows is important for water-use-management decisions during droughts. To define the areal extent and severity of droughts in Mississippi, streamflow records at 19 continuous-record gaging stations were analyzed. The length of record for these gaging stations ranged from 35 to 58 years. Data from six of these gaging stations-one in the Tombigbee River basin, two in the Pascagoula River basin, one in the Pearl River basin, one in the upper Yazoo River basin, and one in the Homochitto River basin-are presented in figure 4.
To determine the extent and severity of droughts, streamflow records were analyzed to identify extended periods of less than normal flow. Annual departures of discharge from average streamflow at six selected gaging stations are shown in figure 4. Bars below the line of zero departure in the graphs denote years when runoff was less than normal. A hydrologic drought is indicated by 2 or more years of negative departure. Bars above the line of zero departure indicate greater than normal runoff. A drought was considered to have ended when the period of greater than normal streamflow was of sufficient length to have substantially alleviated the drought conditions. Droughts began and ended at different times at each gaging station, but for purposes of making statewide comparisons, common drought periods were used. Five major droughts were identified: 1940-44, 1951-57, 1962-71, 1980-82, and 1983-88. The approximate areal extent and severity of each drought are indicated on the maps in figure 4.
In addition to the five major hydrologic droughts identified by analysis of streamflow records, rainfall records indicate that a meteorological drought occurred in Mississippi during 1930-34. Rainfall quantities were less than average for most of this period and were particularly small in 1930. This drought was very damaging; however, available streamflow records are not adequate to analyze the duration and severity. The Red Cross reported expenditures of almost $11 million for drought relief to 600,000 families in Mississippi and adjacent States in 1930-31 (Hoyt, 1936).
The drought of 1940-44, which affected all of Mississippi, was especially severe in the northern two-thirds of the State. On the basis of streamflow deficits at several sites, the drought was determined to have a recurrence interval exceeding 50 years. Recurrence intervals of streamflow deficits in the southern part of the State ranged from about 15 to 25 years. Statewide, the minimum recorded runoff was 8.24 inches on the Little Tallahatchie River at Etta (fig. 4, site 5), considerably less than the average for the period of record of 22.28 inches.
The drought of 1951-57 was widespread throughout the southeastern United States and was severe in all but northwestern and extreme southern Mississippi. Minimum streamflows of record for most gaging stations then in operation occurred during this drought. Streamflow recurrence intervals exceeded 40 years at Bowie Creek near Hattiesburg and Chunky River near Chunky (fig. 4, sites 2 and 3). This drought marked the beginning of substantial irrigation in the State.
The drought of 1962-71 was severe in most of the State. During this drought, streamflows receded to minimum or near-minimum discharges of record at several gaging stations in 1963-64 and again in 1971. Although the duration and runoff deficit combined to make this drought as severe in Mississippi as the drought of the 1950's, the 1950's drought was probably more severe in other parts of the southeastern United States.
The drought of 1980-82 was moderate and affected only the northern part of the State; however, the drought was significant because of the agricultural losses sustained. Rainfall deficits primarily during the growing season had a devastating effect on crop production.
The 1983-88 drought was moderate in the east-central and north-central parts of the State and severe in a small area of the northeast. Streamflows at several gaging stations receded to or below the 7-day Q10 value (lowest average flow for 7 consecutive days expected every 10 years on average).
Droughts in Mississippi have contributed substantially to changes in patterns of water use. The 1951-57 drought marked the beginning of a substantial increase in the use of water for irrigation. Irrigation-well construction increased from about 10 wells per year to a peak of about 450 wells in 1955 (Harvey, 1956, p. 29). Water used for irrigation decreased slightly from 1960 to 1965, then increased from about 200 to 800 million gallons per day from 1970 to 1980 (Callahan and Barber, 1990). Withdrawals from surface- and ground-water sources totaled 2,310 million gallons per day in 1985. Thirty-eight percent was used for irrigation, and 17 percent was used for aquaculture and livestock production.
From 1956 to mid-1985, only surface-water resources of the State were managed under a permitting system based on the prior-appropriation doctrine. Statutes passed in 1956 provided for the permitting and regulating of surface-water withdrawals and discharge of wastewater effluent. The Statutes also empowered the Department of Environmental Quality, Bureau of Land and Water Resources, to administer and enforce regulations regarding all surface-water withdrawals. The Department of Environmental Quality, Bureau of Pollution Control, is charged with permitting and enforcing rules regarding all wastewater discharge into the surface waters and aquifer systems of the State.
In mid-1985, two comprehensive water statutes were passed by the Mississippi Legislature. The statutes restructured the basic water laws and amended existing statutes that regulated the use of surface water. The new statutes provided for the permitting and regulating of ground- and surface-water use and eliminated several exceptions and exclusions from the regulatory authority. The statutes also provided for the creation of a Central Water Management Data Base and a State Water Management Plan, and authorized creation of local governmental water-management districts.
Basinwide water-management districts were already in existence in Mississippi before the passage of the 1985 water statutes. Some of these districts were active in developing water resources, primarily recreational facilities, within their respective basins. However, passage of the 1985,statutes, which authorized the creation of water-management districts at the city and county level, has increased the potential for development and management of the surface-water and ground-water resources of the State.
Flood-Plain Management.--Flood-plain management in Mississippi has been emphasized almost since passage of the National Flood Insurance Act (P.L.90-448) in 1968. This Act established the National Flood Insurance Program (NFIP), a component of the Federal Emergency Management Agency, which is administered by the Federal Insurance Administration. Following the devastation caused by Hurricane Camille in 1969, counties and municipalities in the coastal area enacted ordinances in 1970 regulating coastal and flood-plain development.
In 1979, the Mississippi Legislature passed an act to require the Commission on Budget and Accounting to purchase flood insurance on State-owned buildings and their contents, as required by Federal law, and to adopt flood-plain-management criteria, particularly those applicable to the construction of State buildings in flood-plain areas. The Commission on Budget and Accounting appointed the State Highway Department to administer and enforce the provisions of this act as applied to State-owned roads and bridges.
At present (1989), 264 political subdivisions in Mississippi participate in the NFIP. These political subdivisions encompass 85 percent of the population in Mississippi that resides within the limits of the 100-year flood plain (Willard Inman, State Coordinator, National Flood Insurance Program, oral commun., 1989).
Flood-Warning Systems.--The National Weather Service operates a flood-warning network in Mississippi that includes 54 sites on large streams and 6 sites on large reservoirs. Rainfall information collected by the National Weather Service is used in conjunction with stream stage and discharge data from gaging stations operated by the U.S. Geological Survey and the U.S. Army Corps of Engineers to forecast peak stages during large floods. River forecasts and flood warnings are based primarily on runoff models maintained and operated by the National Weather Service River Forecast Center in Slidell, La. The Corps of Engineers, the city of Jackson, and the Pearl River Valley Water Supply District also use runoff models for predictive evaluation of flood peaks on the Pearl River and for assistance in the management of Ross Barnett Reservoir during large floods.
Several Civil Defense offices, in cooperation with the Corps of Engineers, have installed or are installing local flood-warning systems. The cities of Hattiesburg and Laurel have systems that monitor stream stage and rainfall at several locations and transmit data by radio frequency to computers located in the respective Civil Defense offices.
Water-Use-Management During Droughts.--Water-use management during droughts has been vested in the Department of Environmental Quality, Bureau of Land and Water Resources. The Bureau is responsible for administering and enforcing the water statutes passed by the Mississippi Legislature in 1985. Permits for surface-water use allow streamflow withdrawals, but each user must allow at least the 7-day Q10 flow to remain in the stream. Only under severe conditions and for public use is a municipality allowed to withdraw water when the streamflow is below the 7-day Q10 flow. Ground-water use is regulated for all wells 6 inches in diameter or larger. Pumpage from these wells must be decreased when the "safe yield" of the aquifer system is reached.
Hydrologic droughts currently have less effect on water use in Mississippi than in States that are more dependent on surface-water supply. Only three municipalities in Mississippi augment their ground-water supply with surface-water withdrawals; however, several other communities are investigating the use of surface water as a source of supply.
At present (1989), water-resources investigations in Mississippi are conducted cooperatively by the U.S. Geological Survey and the Mississippi Department of Environmental Quality, the Mississippi State Highway Department, local agencies and municipalities, and two other Federal agencies.
Prepared by Rodney E. Southard and E.J. Tharpe, U.S. Geological Survey; "General Climatology" section by Charles L. Wax, State Climatologist; "Water Management" section by Charles A. Branch, Mississippi Bureau of Land and Water Resources
FOR ADDITIONAL INFORMATION: District Chief, U.S. Geological Survey, 100 W. Capitol Street, Suite 710, Jackson, MS 39269