VOLUME 5, NUMBER I, FEBRUARY 1980

flood

THE PEARL RIVER FLOODAT JACKSON, MISSISSIPPI

APRIL, 1979

PRELIMINARY REPORT

by

Rutherford H. Platt (1)Department of Geology/Geography

University of MassachusettsAmherst, MA 01003

(413) 545-2296

1. INTRODUCTION

This report is a preliminary accountof certain aspects of the Pearl Riverflood at Jackson MS, 12-21 April1979. The report is based on fieldwork conducted by the writer inJackson during the flood, on 18-19April, under the auspices of a grantfrom the National Science Foundationto the Natural Hazards Research andApplications Information Center atthe University of Colorado (Boulder).This project is one of a series of

"quick response" studies of naturalhazard events sponsored by theCenter. Co-Principal Investigator ofthis study is Professor RichardFrancaviglia of Antioch College,Yellow Springs OH.

This study was undertaken with thespecific encouragement of the FederalDisaster Assistance Administration,the Federal Insurance Administration,and the Army Corps of Engineers,Floodplain Management Services. Theobservations and conclusionsexpressed herein are strictly thoseof the writer and are subject torevision in light of furtherinformation. More detailed

(1) Written while on leave at theUniversity of Colorado, Boulder CO80309.

investigation as to the history ofland development in the Jackson areafloodplain is currently in progress.Recommendations concerningpost-disaster flood migration effortswill be offered in a final report.

Information included herein wasgathered by the writer through directobservation (including a helicopteroverflight of the flooded area);attendance at a press briefing by theGovernor of Mississippi and hisstaff; conversations with federal,state and local officials in Jackson;and accounts in local newspapers.

2. GEOGRAPHIC SETTING AND FLOODEXPERIENCE

Jackson, the state capital ofMississippi, is a city of 288,000situated on the west side of thePearl River about 150 miles upstreamfrom its mouth at the Gulf of Mexico.

Above Jackson, the Pearl drains anarea of 3100 square miles, consistingmostly of marginal farmlands andnational forests. Runoff fromupstream areas is largelyuncontrolled, since proposedflood-control structures have notbeen built. The river is partiallycontrolled at Jackson by the RossBarnett Dam, built and operated by astate agency in 1962 to provide watersupply and recreation to Jackson.The reservoir behind this dam is

25

NATIONAL WEATHER DIGESTmaintained at a high level whichprecludes significant flood storage.

Below Ross Barnett Dam, the Pearlnormally meanders past the City ofJackson at a sluggish pace. Thefloodplain at this point broadens toabout three miles in width and thenis "pinched" by bluffs convergingfrom either side. This creates anatural bottleneck holdingfloodwaters in the vicinity ofJackson and its cross-streamneighbors - Flowood, Pearl City, andRichland.

The City of Jackson occupies atopographically diverse site borderedby the Pearl on the east anddissected by numerous tributarycreeks. Older development includingthe State Capitol and its environsoccupies upland sites, well free ofthe vagaries of the Pearl and itstributaries. The Ci ty received majorfloods in 1902, 1913, 1915, 1921, andmany years thereafter. Before April1979, its flood of record occurred on21 December 1961, when the Pearlcrested at 37 feet - 19 feet aboveflood stage.

Since the 1961 flood, commercial andresidential development has widelyencroached upon the lowlandsbordering the Pearl. Several factorsaccount for this phenomenon. First:although not intended or designed forflood control, the Ross Barnett Dam,completed in 1962, apparently createdthe impression that the river wouldno longer flood. Second: levees werecompleted by the Corps of Engineerson both sides of the Pearl in 1967affording a design level ofprotection up to a flood stage of40.5 feet, or three feet above theflood of record. Third: InterstateHighways 55 and 20 were built throughJackson in the late 1960's with amajor intersection in the floodplainjust southeast of the centralbusiness district. Fourth: the Ci tyby 1970 was running out of availablespace for additional urban growthwithin its own taxing jurisdiction.Fifth: a new jetport across the riverthreatened to spawn development inFlowood if Jackson could provide nofurther bUilding space. For theseand other r eas ons, mas s i vedevelopment of the Pearl floodplainin Jackson has occurred.

26

3. OVERVIEW OF THE JACKSON FLOOD

During the week before Easter 1979,massive storm systems rolled acrossthe south-central United States.Thunderstorms, hai I, tornadoes, andrecord rainfalls battered Texas,Louisiana, Oklahoma, Arkansas,Mississippi, and Alabama. In WichitaFalls TX, a series of tornadoeslevelled the city. With the mediafull of reports on natural disasters(including an earthquake inYugoslavia and a volcano eruption inthe Caribbean), Mississippi residentswere perhaps nonchalant about theirown situation. Nearly 20 inches ofrain fell during the week atLouisville in the upper Pearl Riverwatershed. Jackson received 10inches, including 4 inches in an houron 12 April. Flash floodingdeveloped in many of Jackson's creekswith localized damages affecting somehomes and shopping areas. By 14April, these problems receded, and itseemed the worst was over.

Flooding along the Pearl in Jackson\oIas delayed by two factors. First:several days were required for themajor runoff from the storm in theupper watershed to reach Ross BarnettReservoi r. Second: the Pearl RiverValley Water Supply District, whichoperates the darn, did not immediatelybegin emptying the reservoir toaccommodate approaching floodwaters.By Easter Sunday (IS April), inflowsto the reservoir far exceededoutflows. The latter were hastilyincreased and the Jackson Flood wasunderway. By Tuesday (17 April), theflood crested at 43.2 feet, a level25 feet above flood stage and 6 feetabove the 1961 flood of record. Thiswas approximately the level of the"standard project flood" estimated bythe Corps of Engineers in its 1972Flood Information Report for thePearl River. In terms of probablereturn period, it was somewhatgreater than the SOD-year floodindicated in the Flood Insurance RateMap for the city prepared by theFederal Insurance Administration.

The most visible and costly flooddamage was inflicted upon newdevelopment surrounding theintersection of Interstates 55 and20. Up to fourteen feet of waterinundated major public and private

investments in this area - theMississippi Coliseum (also a casualtyin 1961), Ramada Inn, Motel Six, theState Fairgrounds, the Trailways BusStation, and many otherhighway-oriented businesses. Thehighways themselves were closed by aconsiderable expanse of flooding.Cultural facilities were damaged,including the Mississippi Art Museum,a new planetarium, and the NaturalHistory Museum. Even businesses longestablished on higher ground such asthe Jackson "Daily News" receivedserious basement flooding.

Residential flooding was concentratedin northeastern Jackson where some ofthe City's most expensive homes arelocated. Floodplain encroachment byluxury homes and apartmentdevelopments has occurred heredespite inundation of much of thearea in Jackson's flood of record 21December 1961.

Additional residential floodingoccurred in southeastern Jackson andin tributary ravines throughout theCity. The latter received floodwaters from two sources. First theyexperienced flash flooding from heavyrainfall on 11-12 April. Later theyreceived backwatering from the risingwaters of the Pearl on 15-18 April.In addition to property damage,tributary flooding substantiallyimpaired communications throughoutthe City due to blockage of localstreets and arteries.

A great potential threat to Jackson'shealth and safety was the nearcollapse of its vital publicservices: electrical, water supply,sewage treatment, gas and telephone.All of these services were gravelyaffected by rising floodwaters. Thesewage treatment plant was entirelydisabled and discharged raw sewageinto the floodwaters for severaldays. The water treatment plant wasnarrowly saved by an improvised dike.

Three electrical substations wereflooded out. The loss of two otherswhich would have caused a majorblackout was averted through heroicsandbagging efforts. Gas andtelephone services wereunderstandably disrupted in floodareas but maintained for the rest ofthe City.

Altogether 20 per cent of the land

VOLUME 5, NUMBER 1, FEBRUARY 1980area of Jackson was flooded, some ofit for more than a week. Twochildren lost their lives. Seventeenthousand persons were evacuated fromtheir homes. About 2,000 dwellingswere damaged by flooding, 800 of themsustantially. Preliminary damageestimates for Jackson placed totaldamage to public and private propertyat $500 million. This does notaccount for the costs of emergencyservices such as sandbagging, thepsychic costs incurred by floodvictims, or the loss of income tolocal businesses. Nor does itinclude further losses outsideJackson caused by the same flood.Only a minute portion of these losseswill be compensated by floodinsurance. The City of Jackson hasbeen in the "emergency phase" of theNational Flood Insurance Program forthree years and is due to qualify forthe "regular phase" in January 1980.One thousand four hundred policieshave been purchased by Jacksonproperty owners but these are at thelow levels of coverage allowed in the"emergency phase".

4. PRELIMINARY FINDINGS ANDOBSERVATIONS

It is of course premature to statedefini te findings andrecommendations. These will be madein the final report following furtherfield work and data assembly inJackson. However, the writer aseyewitness to the Jackson Floodformed some strong impressions duringthe event itself. These are brieflynoted below.

5. UNRELIABILITY OF ROSS BARNETT DAM

It is probable that much of thefloodplain development that hasoccurred in Jackson since 1965 hasbeen predicated upon the existence ofthe Ross Barnett Dam completed inthat year. This dam however may haveexacerbated rather than relieved theflood situation in April, 1979.Furthermore, if the dam had failed,as happened in Rapid City, SD in1972, a massive wall of water wouldhave been released upon Jackson andother downstream communities.

Ross Barnett Dam is an earthenstructure three miles long and fiftyfeet high, at the northeastern edge

27

NATIONAL WEATHER DIGESTof the City of Jackson. It wasdesigned, constructed and has sincebeen operated by the Pearl RiverValley Supply District, astate-created instrumentality. Nofederal money or supervision has beeninvolved in its construction ormaintenance.

Ross Barnett was not designed toprovide flood control although thatis a purpose stated in itsauthorizing legislation. It wasdesigned primarily to afford adependable water supply to Jacksonand to create recreationalopportunities. Its 75-mile shorelineis extensively developed withyear-round and seasonal homes andwater-orientated commercialactivities. To accommodate theseuses, the pool is maintained at aconstant level of 295 feet above meansea level (a depth of about 45 feet).

Since the spillway elevation of thedam is 300 feet mean sea level, thisleaves only five feet to accommodateexcess runoff. The level of thereservoir on April 15 reached 299.79feet, which required rapid discharge(up to 130,000 cubic feet per secondas compared with a normal rate of9,200 cubic feet· per second) toprevent overtopping. The questionnaturally arises as to whether theDistrict took timely action to lowerthe level of the pool reservoir.toaccommodate approaching floodwaters.If the 350,000 acre-feet normallystored in the pool could have beensubstantially discharged before theupstream floodwaters arrived on AprilIS, flooding in Jackson would haveoccurred earlier but would not havereached the record level of 43.2feet.

An even more dire question concernsthe potential failure of the damitself. This would not necessarilyhave resulted from overtopping sincethe dam is designed for emergencydrawdown of pool elevation by tenfeet (which did not in fact occur).However at least one "boil" or leakwas discovered on the downstream sideof the dam during the flood. Thiswas quickly plugged but it indicatedthat the stress limits of the damwere being approached. The Chief ofthe Corps of Engineers MobileDistrict Office denied publicly thatthis leak signified an imminentfailure of the dam.

28

Ironically, a rapid reduction inwater levels against the dam andlevees could itself have caused themto collapse. According to EugeneThomas, consultant to the WaterSupply District, a sudden withdrawalof hydrostatic pressure against asaturated earthen structure couldproduce such a failure. The Districttherefore had to time its releases soas to balance the threat ofovertopping the dam and leveesagainst the threat of too-rapidreduction of water levels. Thiscould cause the dam and levees todissolve (Jackson Daily News, 16April 1979).

It is recommended that an officialinvestigation review the conditionand performance of Ross Barnett Dambefore and during the flood of April1979. The dam is located virtuallyon top of an urban area of a halfmillion people; its integrity isobviously imperative. Furthermore,the operation of the dam with regardto the timing and rate of dischargeshould be carefully examined. Theexperience of Jackson should serve asa warning to communities elsewherenot to rely on structures of thiskind (i.e. earthen dams) for floodprotection.

6. WERE THE LEVEES NEEDED?

Experience with the Pearl Riverlevees raises some additionalquestions. These structures extendtwo miles on the Jackson side, and 13miles on the Flowood-Pearl City side.

They were constructed by the ArmyCorps of Engineers to accommodate aflood stage of 40.5 feet, with athree-foot freeboard. Since theircompletion in 1967, they have beenoperated and maintained by theRankin-Hinds Flood Drainage ControlDistrict.

But what of the property they wereintended to protect? Areas behindthe levee in Jackson were flooded asthough the levee never existed. Thisresulted from inflow through a lowpoint where the levee meetsInterstate 55. On the opposite side,the Flowood-Pearl City levee was moresuccessful in protecting landwardareas from flooding. But much ofthis land was sparsely developed.

The river was denied access to 4,500acres of natural floodplain, so thecrest elevation and therefore thelevel of damage on the west (Jackson)side was increased. This presents anexample of intergovernmentalconflict, because the Pearl river isan inter-jurisdictional boundary.

Finally, it is possible that themanpower and resources devoted to theexpensive and dangerous campaign tosave the levees might have beenbetter used elsewhere; e.g. inevacuating buildings and removingproperty from the reach of floodwaters. It would appear that thelevees became part of the problemrather than of the sOlution.

7. FLOOD WARNING: A CONVENIENTSCAPEGOAT?

With the gradual subsidence offloodwaters following the crest on 16April, the media expressed a generaloutcry that the public had beeninadequately warned about the height,timing, and duration of flood levels.For instance, Jackson Mayor DaleDanks was quoted in the New YorkTimes on 19 April as criticizing theNational Weather Service and the ArmyCorps of Engineers for failure toprovide enough warning to permitpeople to remove belongings fromhomes and businesses.

To investigate this allegation, thewriter obtained copies of the JacksonDaily News beginning with the issueof 12 April. On that day, afront-page article stated:

"The National WeatherService said the worst isyet to come. Flooding willincrease as water continuesto rise above normal riverlevels."

And on Friday, 13 April:

"By Easter, the Pearl Riveris predicted to reach anall-time high, pouringwater into lOW-lying areasof the city that haven'tseen flood waters indecades.

VOLUME 5, NUMBER I, FEBRUARY 1980"At 11 a.m. today the riverhad reached a threateninglevel of 35 feet.Officials at Ross BarnettReservoir say upstate rainshave not even begun tofilter into the Jacksonportion of the river."

It is true that the level of theultimate flood crest wasunderestimated by several feet,partly due to the unknown rate atwhich water would be released fromRoss Barnett. But it would appearthat the criticism of inadequatewarning was unfounded. Rather, thecity by 12 April was alreadyexperiencing flash floods unrelatedto the eventual Pearl River crest.This confused the situation.Further, there appears to have beenlittle preparation on the part of thecity to translate warnings of "recordflooding" into specific evacuationplans for affected areas of the cityuntil the waters were actuallyrising. The lack of such planning isin turn related to Jackson's failureto deter new development from beinglocated in the floodplain in thefirst place.

8. VITAL SERVICES: JACKSON'SACHILLES HEEL

Once the flood was in progress, theresponse of the city, county, stateand federal authorities in copingwith the emergency was exemplary.Nowhere was this more evident than inthe heroic efforts to save the city'svital public services, particularlyits water supply and electricalservice. These required constructionof emergency dikes andround-the-clock repair activities toprotect and restore affectedfacilities. The water treatmentplant was saved although the city'stotal water supply was cut in halfduring the crisis. Five of Jackson's42 substations were flooded out orclosed down. The Jefferson Streetsubstation, serving the downtownbusiness district, was protected by amassive dike-building effort. Thecity's $50-million sewage treatment

29

from downed

and emotional

NATIONAL WEATHER DIGESTplant, however, was flooded out, anddischarged raw sewage directly intothe floodwaters. Telephone and gasservices were maintained throughoutmost of the non-flooded areas.

However: it is apparent that thepossibility of flooding was notconsidered in locating many ofJackson's vital service facilities.Shutdown of water and electricalservice (which was narrowly averted)would have crippled the entire city,not just the flooded areas.

9. ASSOCIATED HAZARDS

The danger of drowning, while by nomeans unimportant, is but one.o~ ma~y

hazards to human safety arising inthe midst od a flood. For therecord, this observer noted thefollowing sources of real danger fromthe rising floodwaters to theunfortunate residents of Jackson:

Contamination of public andprivate water supplies

Electrocutionpower lines

Snakes and vermin

Looting of structures andvehicles

Traffic accidents due toovercrowded streets andmalfunction of traffic-control equipment

Aviation accidents due toovercrowded airspace

Boating accidents

Spoilage of food in homesand stores withoutelectrical power

Collapse of structures fromwater damage

Exhaustiontrauma

subject of public warnings.

10. THE NEED FOR FLOODPLAINMANAGEMENT

At a press briefing on 18 April, theGovernor of Mississippi asked anofficer of the Corps of Engineers howthis kind of disaster could beprevented from occurring again. Theanswer was "hi gher 1evees , ifeconomically justified." Jackson'sexperience, however, is a sadcommentary on the effectiveness ofstructures to protect urbancommuni ties from flood losses. It isapparent that most of the damagedstructures have been built on thefloodplain since the last flood ofrecord, in 1961. It is nocoincidence that Ross Barnett Dam andthe Pearl River Levees were completedjust in time for the wave of buildingon the floodplain. The very existenceof flood-control structures invitesunwise development in the "protected"floodplain. When a flood exceeds thedesign limits of the structures,catastrophic losses occur which mayexceed the total of minor losses thatwould otherwise have happened in anunprotected but less developedfloodplain. Preliminary observationsuggests that this is exactly thecase in Jackson.

The Jackson experience thusunderscores the necessity offloodplain management, with orwithout flood control structures.Floodplain management involves arange of adjustments: floodplainzoning, building restrictions, landacquisition and relocation, andemergency evacuation planning.Section 406 of the Federal DisasterRelief Act of 1974, and the NationalFlood Insurance Act of 1968 asamended, require these and relatedmeasures to be applied by communitiesreceiving federal disaster assistanceand flood insurance. Theimplementation of this policy shouldbe first priority in the planning ofpost-flood recovery in Jackson,Mississippi.

Luckily,materialize;

30

these did not allbut most were the

NOTE: a draft final report isavailable directly from the authorfor a fee of $2.00 for reproduction.Include your complete address.