Title: Second, the levee system itself proved faulty
Author: Jeremy Hodgkin
Company: National Science Foundation

Second, the levee system itself proved faulty. Whether or not flood waters actually overtopped the west side levee (it was a matter of inches), the fairgrounds area behind the levee was completely inundated. This resulted from inadequate project analysis and possibly from human error in the withdrawal of pumps at a fairly early point in the flood fight.
The most provocative question involving performance of the levees is that of why the flood crested above the projected ^11standard project flood" despite a considerably smaller discharge (130,000 vs. 207,000 cfs). As in 1961, the works of man in the form of bridges, buildings., and highways impeded the flow of the river. Yet, the levee system was designed to accommodate a greater discharge than actually occurred.
There also may have been overconfidence in the ability of Ross Barnett Dam to control floodwaters. The anomaly between the statutory purpose of providing "flood control" and the actual operation of the dam to promote recreation has been noted. It is likely that the general public considers that "a dam is a dam" and a dam means flood control. In any event, there was much acrimony after the flood as to why the dam did not restrain the floodwaters.
2. Failure to Restrain Floodplain Encroachment - Concomitant to the misplaced trust in the dam and levees has been a virtual abdication of public responsibility on both sides of the Pearl for floodplain management. Jackson^1s Zoning Map of 1969 designated all land bordering the Pearl as suitable for development. That "invitation" was widely accepted as residential and commercial structures have been erected in areas known to be flood prone.
Jackson's only token bow to floodplain management was a city council resolution of April 1973 instructing the director of the building department to "...review all building permit applications to determine if the proposed construction is consistent with the need to minimize flood damage." This permitted the city to participate in the "emergency phase" of the National Flood Insurance Program. Although interpreted to mean that new construction should be elevated above the 100-year flood level, enforcement is by visual inspection only.
Floodplain management has been nonexistent on the east side of the Pearl River. Development both within and outside the levee has proceeded unrestrained by any zoning or flood considerations. Construction of an office park outside the levee in Flowood continued in December 1979 despite the "Easter Flood."
The result of this pattern of neglect clearly has been a substantial magnification of the investment and lives at risk due to floods. Although the east side levee was saved, the effort was lengthy, dangerous, and very costly.
3. Location of Vital Public Facilities - Public services and facilities were seriously damaged by the Pearl River flood. Only through heroic efforts did the city of Jackson manage to avert the loss of electricity, water, telephone, and other services. Its new $70,000,000 sewage treatment plant was totally disabled. Several electrical substations were flooded out and a key facility serving downtown Jackson was saved only by erection of an emergency earthen dike at a cost of $1,000,000. Even the city^1s Emergency Operations Center was located in the basement of a downtown building and was flooded out.
This experience highlights the importance of Executive Order 11988 Guidelines which require '^1critical actions" to be taken outside the 500-year floodplain.
4. Need for Pre-Disaster Contingency Planning - Although the city of Jackson rose to the occasion very courageously, there was a notable lack of specific contingency planning on either side of the Pearl River. Perhaps the most serious lack was an emergency plan for operation of the Ross Barnett Dam. Such a plan should have provided for drawing down of the reservoir pool in anticipation of oncoming floodwaters from upstream. Another deficiency was inadequate flow of communications and mode of coordination among various public authorities involved, particularly the municipalities, the levee district, and officials at the Ross Barnett Dam. Downstream parties had no idea when and to what extent discharges from the dam were being varied. There was no overall official in charge of the flood fight on both sides of the Pearl. The COE and the National Guard viewed their roles as supportive to state and local authorities. In the case of this flood, important decisions were required regarding allocation of resources to each side of the river.
Pre-disaster planning also should identify those structures or parcels of land which should not be rebuilt in the event of a major flood. These would logically include property in the designated floodway or property which has suffered multiple flood losses. Similarly, contingency plans also should identify those structures which should be floodproofed or elevated in the event of flood damage.
5. Need for Post-Disaster Hazard Mitigation - The Pearl River flood prompted a modest effort by the FEMA to encourage post-disaster hazard mitigation. This was limited to surveys of flood victims to determine their willingness to relocate, organization of seminars on floodproofing and establishment of a hazard mitigation team to determine possible short and long range mitigation measures. In the absence of adequate funding for relocation or acquisition, however, these efforts had limited impact. With encouragement from the Jackson city government and the real estate industry, homeowners generally returned to restore and rehabilitate their homes. An additional activity that mertis attention was the creation of the Governor's Long Range Recovery Committee.
Hazard mitigation also may include regulations to deter further encroachment upon the floodplain. Jackson has been delayed in this process by revision of its Flood Insurance Rate Map by FEMA. Procedures must be developed to provide communities with approximate data for zoning purposes which may be refined later. Due to delays at the federal level, Jackson still had not adopted floodplain zoning six months after the flood.
6. Need for Improved Cooperation Among Public Authorities - The Pearl River flood of 1979 is the example of an absence of communication and cooperation among local public authorities sharing jurisdiction over a common floodplain. The two sides of the river were under the jurisdiction of the city of Jackson to the west and four local governments (including Rankin County) to the east. Important roles also were performed by the Rankin-Hinds Drainage and Flood Control District and the Pearl River Valley Water Supply District responsible for the levees and the dam, respectively. No institutional mechanism exists by which these diverse entities can address their common interest in the Pearl River floodplain. Questions regarding cross-stream effects of filling, levee construction, or other hydraulic changes simply are not raised. The result was the "one-sided flood" of 1979 in which east bank communities of the river received most of the protection and the Jackson side incurred most of the damage (due in part to its own negligence).
Lower Mississippi River Valley
The Mississippi River Commission (MRC) was created in 1879 to try to control the Mississippi. Although many projects have been put into operation since then, the river seems to "have a mind of its own." Attempting to curb the natural processes of this dynamic waterway has resulted in serious consequences all along its course, particularly at and near its termination point, the Gulf of Mexico.
Additional earnest consideration is needed, soon, to address available options for hazard reduction to human life and property and for maintenance of an adequate floodplain providing for natural events and activities of "The Father of Waters."
Setting
The alluvial valley of the lower Mississippi is a broad lowland varying in width from 25 miles to 125 miles and extending for more than 600 miles across the Gulf Coastal Plain from Cape Girardeau, Missouri, to the Gulf of Mexico encompassing 50,000 square miles.
The river changes course constantly, adjusting to erosion and deposition patterns governed by the physics of hydrology and geology. Its primary natural function is to transport water and sediment from upper elevations to sea level in the most direct and favorable gradient available.
Snow melt, spring rains, and saturated aquifers force the river to follow the most expedient route to the sea. When its course is hindered by manmade friction, hydraulic pressure, and volume restraints, backwater becomes floodwater. Thus, the natural processes of the river to build and fertilize land can thwart and destroy human endeavors to habitate and develop the floodplain.
Flooding Incidence and Response
The last major flood (1973) of the Mississippi River was a costly reminder that development along the floodplain coupled with manmade attempts to redesign and constrict the river^ts natural course and function bring serious problems. Economic losses were estimated at more than $1,000,000,000. Although few lives were lost, 69,000 persons were left homeless and 13,000,000 acres of land were inundated.
These losses might have been considerably more extensive had it not been for levees and structures developed by the COE as a result of the Mississippi River and Tributaries Project (MRT) originated in 1928 after the great flood of 1927 which claimed more than 300 lives, The COE estimates that protective structures existing in 1973, as a result of the MRT project, prevented additional economic loss of $15,000,000,000 and flooding of another 10,000,000 acres. The Corps does not estimate how many lives might have been lost in 1973 without the MRT levees and other structures or if they had failed.
Consequences and damages of the 1973 flood to the MRT project facilities were severe. Siltation in the lower Mississippi and at the passes to the gulf was extremely heavy; and revetments, dikes, and levees were critically damaged up and down the stream. Reconstruction is still ongoing to replace and relocate certain portions which were damaged or appear from 1973 problems to be inadequate in future floods.
Most crucial in the 1973 flood was what almost occurred. On April 12 an old wingwall collapsed at the Old River Control Low-Sill Structure near Morganza, Louisiana. This structure is a major element in control of flood waters at a point where the Mississippi may ultimately divert itself to a new course, the Atchafalaya River. A complete break-down was very close, and continued investments in engineering designs and structures must be made to prevent absolute catastrophe in subsequent floods. Should the Mississippi divert its course to the Atchafalaya, implications are that New Orleans would be deprived of its primary economic sustenance; and Morgan City and many othet southern Louisiana communities would be essentially eliminated.
Conclusion
"Controlling' the Mississippi River sometimes has proven elusive in many ways. The essential need to protect life and property is costly far beyond dollar investments in flood control structures. Loss of nutrients and sediment in Louisiana coastal wetlands as a result of leveeing, for example, has eliminated natural land-building powers of t~e river; erosion and salt water now gravely threaten Louisiana fishing industries.
For every control effort the river has a response. Constricted water volumes in one place must be displaced elsewhere; and confining flow levels below the river 5 natural capacity and tendency creates greater pressure on the entire protection system. Safety measures are included in the MRT design, and the Morganza and Bonnet Carre spillways can be opened to relieve some of this pressure; but these measures cannot be relied upon for effective long-range management. As siltation continues, despite annual investment of millions of dollars to try to keep the river flowing by human design, river bottom elevations steadily increase as do levee lifts and flood elevations.
The Mississippi River is an alluvial stream and it must have a floodplain. Its basic nature cannot be changed. Before the best, and perhaps only, options for hazard mitigation are foreclosed, it is imperative to scrutinize alternatives and implement viable courses of protection action.
Green Brook Watershed, New Jersey
The Green Brook watershed exemplifies the very damaging flood situation which unrestrained urbanization creates.
Setting and Key Features
Green Brook is a small tributary of the Raritan River in New Jersey, with a total drainage area of 65 square miles. The stream extends southwest along the edge of the Watchung Mountains. About 20 percent of its drainage area is sparsely settled and mountainous, and the balance is a relatively flat plain, ocLupied by virtually uninterrupted housing and related commercial areas.
The headwaters of Green Brook, and one tributary, Stony Brook, originate in the mountainous area. From the east, Ambrose Brook, Bound Brook, and smaller tributaries drain large urbanizing areas. The population averages 2300 per square mile, in spite of the sparsely settled Watchung Mountain area. There are no large cities; Plainfield, with a population of fewer than 44,000, is the most populous. The watershed outside the mountains has a pattern of general development with only scattered open spaces. It is estimated that 59.2 percent of the area of the basin is now developed.
The Flood of 1973
The flood of August 2, 1973, on the Green Brook watershed cost six lives and $38,000,000 in direct damages and resulted in a major disaster declaration from the President. It was not a very unusual flood in the physical sense; on the average, the discharge at its mouth was estimated to be exceeded once in 25 years. The most significant aspect of the flood is that serious damage was due to extensive urbanization of three-fourths of the basin, with extensive occupation of floodplains and creation of impervious surfaces which accentuate flooding.
The flood occurred as the result of a storm lasting about six hours which precipitated about 8 inches of rainfall over the upstream and mountainous portions of the basin At many points the rainfall exceeded the lOG-year probability rainfall for six hours (5.2 inches). Fortunately, no rain had fallen in the preceding five days and the storm occurred during the morning, so daylight was available for evacuation and rescue operations; otherwise, many more lives might have been lost.
The community hardest hit was North Plainfield. Floodwaters surged out of the narrow Stony Brook canyon through the Watchung Mountain and overtopped stream banks by 10 feet~ a record flood height for the area. Five lives were lost and 26 persons were injured because there was almost no warning. A highway bridge over Stony Brook which had been opened to traffic only a day previously, having been destroyed in the preceding 1971 flood, was seriously damaged. Several hundred automobiles were destroyed, and there was other extensive damage.
In Plainfield, the city was divided into two parts by a flood on Cedar Brook and a diversion into it by Green Brook. This diversion isolated one-half of the city from the hospital.
In other communities damage was widespread, particularly in Scotch Plains and Middlesex Borough; but in the lower portion of the basin, damages in the 1973 flood were fewer than they had been in the flood of August 1971.
Flood Discharges and Frequency
As is usual after major floods, it proved difficult to evaluate the frequency of the flood of 1973 with accuracy. From hydrologic analysis it appears that the peak discharge in cf 5 was as follows for the two floods:
1971 1973
Plainfield 2,055 6,380
At Mouth of Green 13,850 10,450
River
Stony Brook 3,050 7,650
For the Green Brook watershed as a whole, the peak flow of 10,450 cfs in 1973 was not an exceptional event; it was materially exceeded in 1971 and is estimated to have a recurrence interval of 25 years. Some of the tributaries had more exceptional flood discharges, particularly Stony Brook, which, with its peak of 7650 cfs in 1973, has an estimated recurrence interval of 200 years. However, Stony Brook has a drainage area of only 7.8 square miles, or 12 percent of the total Green Brook watershed.
Impact of Urbanization
To place the flood situation in perspective, the COE studied the impact of future urbanization in the Green Brook Basin. Applying the land-use plans of the various municipalities, COE analyzed projected increases in flood peaks which may be expected after urban development in the Green Brook drainage basin is complete. Very few future increases are anticipated. At Plainfield, peak discharges of the 2-year flood would be increased by 8 percent, and the 100-year flood by 4 percent. At them outh of Green Brook, corresponding increases would be 12 and 7 percent respectively. It appears that further urbanization will have little impact on increases in flooding in this area.
Conclusion
Analysts can show readily that the peaks of small floods are at least doubled by the impact of complete development; and there is no doubt that this has occurred on the Green Brook basin. Early settlements near the streams of the basin in rarely flooded areas have now become subject to much more frequent damaging floods. The Green Brook watershed clearly shows the consequences of occupation of floodplains and creation of impervious surfaces throughout the basin. These effects will be produced in other urbanizing areas unless preventive programs of stormwater management and floodplain management are adopted early in their development. For the Green Brook area, there are only two alternatives: a program of channel improvement and small dams, made costly by the expensive rights of way; or, even more costly, nonstructural programs of floodplain clearing and evacuation. The time is long past when programs of stormwater management and floodplain management, taken together, would have avoided creation of a major flood hazard in this area.
Houston, Texas
The Houston, Texas, regional flooding analysis illustrates the nature and potential extent of urban flooding. The Houston problem is both unique and typical. Both are important in terms of this report. It is typical in the sense that all metropolitan areas experience flooding problems to some degree; it is unique in that its problems are created by the myriad of events, physical features, hydrological factors, and political realities peculiar to Houston.
Setting
The Houston Metropolitan Area is located in southeast Texas in a semitropical climatic zone with an average annual rainfall of about 47 inches. Physically, the area is very flat; the grade across the area is about 140 feet in 60 miles. The area historically has been drained by bayous (creeks) that lead to Galveston Bay or the Gulf of Mexico.
The Houston Metropolitan Area consists of five counties: Harris, Fort Bend, Brazoria, Montgomery, and Galveston. Other counties interacting to a lesser extent with the metro area are Wailer, Liberty, and Chambers. The approximate area of the eight county metr~o region is 8455 square miles. Within the eight counties are 26 incorporated jurisdictions with a population greater than 5000 and 87 with less than 5000. The population of the eight county area was approximately 2,181,100 in 1970 and is estimated to be approximately 3,334,000 in 1980, an increase of 53 percent. Houston is one of the fastest growing metropolitan areas in the United States.
Prior to urbanization the primary land-use was agriculture with rice as the main crop. Because of the flatness and relatively impervious clay soils, overland flooding has historically occurred, but such flooding had little adverse effect before urbanization. In addition to being relatively slow draining, the area is subject to intense localized rainfall. For example, south Harris County and the city of Alvin experienced over 40 inches of rainfall in 24 hours in July 1979. In September 1979 a regional storm dumped 12 to 16 inches of rainfall over the entire Houston Metropolitan Area. A previous storm in April 1979 had poured over 12 inches of rain on the Montgomery County area, with lesser amounts in northern Harris County. All these storms caused substantial flooding.
More than 400 agencies in the Houston area have responsibility for drainage planning and implementation. In addition to the eight counties and 113 incorporated jurisdictions there are federal and state agencies, river basin authorities, drainage districts, flood control districts, and water districts.
Nature of Problem and Response
The flooding problem in Houston is caused by excessive rainfall overburdening the manmade and man-modified drainage systems. Houston has not experienced a hurricane in 18 years, and coastal flooding due to gulf tidal surges has not been a recent problem. However, hurricanes have occurred in the Houston area in the past and will occur again. Potential flooding in some coastal areas is causing concern about current hurricane evacuation plans. In Clear Lake, for example, it is claimed that only two inches of rainfall will cause flooding that will make evacuation virtually impossible.
Urban drainage systems are generally categorized into a minor system and a major system. The minor system consists of storm sewers, street inlets, streets, and roadside ditches, and in the Houston area is generally designed for storms no greater than the 2-year or 5-year events. The minor systems drain into the major systems which consist mainly of bayous in the Houston area. When improved, the major systems are generally designed for larger storms such as the 25-year to 100-year events. However, in the unimproved state, the 100-year flood generally spills out of the banks and onto the adjacent floodplain.
Significant flooding has occurred frequently in Houston on both systems. When the capacity of the minor system is exceeded the streets are designed to flood. If properly designed, flooded streets generally do not cause much property damage to buildings, but the damage to automobiles can be substantial. A study now being prepared by the Rice Center of a severe storm that occurred in 1976 in Harris County indicated that about 32,000 cars were damaged, which was about 2 percent of the total number of vehicles registered in the county. Based on damages of $355 per vehicle the total loss was estimated to be over $11,000,000 for that one storm_3 for vehicles alone. This particular storm was estimated to be approximately a 100-year storm at the point of maximum rainfall.
Flooding that involves both minor and major drainage system results in property damage to homes, businesses, public facilities, industry, and automobiles. The wcrst flooding (measured by reported losses) experienced in the Houston area occurred in July 1979. The total loss estimated by FEMA was $231,000,000 (excluding automobiles) and included the cost of temporary housing, SBA loans, FIA insurance claims, flood related unemployment claims, temporary shelter, and public facility repair. The FEMA reported 11,000 flood insurance claims totalin~ $130,000,000 which involved less than 1 percent of the homes in the region. The Rice Center Study preliminary estimate is that the 11,000 claims represent about 20 to 25 percent of the number of properties that actually experienced damage. If true, actual home damages from the July 1979 storm could be as high as $650,000,000.
Flooding is a problem where man occupies areas subject to flooding. Typical of all urban areas is that the flooding potential is aggravated by community development; water that formerly percolated into the soil now falls on impervious surfaces and causes additional runoff, thus increasing peak flows. In flat coastal areas the increased peak flows result primarily from increased efficiency in the drainage system which dramatically reduces time to peak. In the Houston area, flood volumes are not increased significantly because of the naturally impervious soils. Urbanization can increase peak runoff rates up to five times predevelopment conditions for small events such as the 2-year storm. The effect of urbanization on larger storms such as the 100-year event is not as great, being in the range of a 50 percent increase of peak flow. For storms larger than the 100-year events urbanization has relatively little effect on the magnitude of the peak flows.
Adding to the flooding problem in Houston is land subsidence (sinking) which is attributed to ground water removal. Because of subsidence, which is as much as 10 feet in some places, areas which previously were not prone to flooding now are. Subsidence is estimated to affect about 80 percent of the Houston area. The major impact of subsidence on flooding is confined to the coastal strip which is subject to hurricane induced inundation.
Response to Flooding
Seven major adjustments are used in varying degrees to cope with flooding: control and protection works, floodproofing buildings, forecast and warning systems, land-use management flood insurance, relief and rehabilitation services, and relocation of floodplain occupants. Each of these areas of adjustment is discussed in terms of how it was or is applied in Houston
Control and Protection Works - Facilities for the minor drainage system are provided by local government and land developers. No figures are available on total investment in the Houston area in the minor drainage system, but it undoubtedly involves hundreds of millions of dollars. Although the minor system causes flooding problems, it is not a problem generally considered at the federal level.
Improvements to the major drainage system in the Houston area have been addressed by the COE, flood control districts, local governments, and drainage districts. In 1969 the Corps completed channel improvements to Brays Bayous costing a total of about $52,000,000. In Harris County, four bond issues totalling $195,000,000 were passed in 1969, 1973, 1975, and 1979. The Harris County Flood Control District is currently making channel improvements at a level of $25,000,000 to $30,000,000 per year from the proceeds of these bond issues. Current projects by the Harris County Flood Control district in cooperation with the COE include channel improvements on Vince and Little Vince Bayous and Upper White Oak Bayou at a cost of $17,000,000 and $56,000,000 respectively. Although flood control studies are underway on several other streams, no additional COE construction projects are considered likely in the near future. The total construction cost of improving all major drainageways to adequately handle reasonable floods in the Houston area has not been estimated in detail, but it is believed to exceed $1,000,000,000.
Floodproofing Buildings - Some progress is being made with flood-proofing following the 1979 flooding experiences. For example, the Texas Medical Institute has requested that each building in the complex be floodproofed, and has designed "floodways" within the complex grounds to minimize the impacts of flood waters.
Individual homeowners who experience frequent flooding are likely to take their own measures to minimize future losses, but no figures are available to indicate to what extent such measures have been taken.
Forecast and Warning Systems - Warning and evacuation is a factor in terms of hurricanes but not in terms of overland flooding from the bayous. Because of the multiplicity of governmental jurisdictions, warning and evacuation poses problems. Lack of adequate plans has been recognized and the Clear Lake Council of Cities recently convened a meeting to hear a local appeal to the governor for assistance in finding solutions to local highway flooding. Local concern is that flooded egress routes would prevent evacuation in a hurricane emergency. As a result of the meeting the Texas Division of Disaster Emergency Services will assist local officials in preparing their emergency plans for the area.
Land-Use Management - Land-use management has been utilized to a limited extent in the Houston area to mitigate flood damages. Most communities, with only one or two exceptions, have adopted floodplain regulations. This is a relatively recent development with some communities adopting regulations in the early 1970s and some as recently as December 1979. Need for regulation or control of the floodways seems to be recognized and is reasonably enforced. Regulation is difficult, however, since many floodplains have not yet been defined in detail.
Houston is one of a few large U.S. cities without zoning. Land-use controls in general are not popular in Houston, and measures such as detention of excess stormwater caused by development have not been required. Reasons for not requiring detention include the high cost of land, the flatness of the terrain necessitating large detention basin areas, and the onerous restrictions developers feel it places on them. Building codes in some local jurisdictions do recognize flooding problems and this has a positive but unmeasurable and limited effect on reducing flood damages. Land-use measures such as preservation of natural water storage areas have not been considered.
Flood Insurance - Flood insurance has been used significantly in the Houston area. For example, although detailed statistics are difficult to obtain, it is estimated by the Rice Center that 11,000 reported claims resulted from the July 1979 flooding event for a total of $130,000,000 or about $18,000 per claim.
In some instances, property owners are collecting several times from multiple flood events. In Whispering Oaks, a suburb about 25 miles north of Houston, 22 flooding events have occurred since 1970 and the area was flooded three times in 1979. To preclude such repetitive claims payments, FEMA successfully undertook a project to relocate those consistently damaged structures out of the floodplain, using flood insurance proceeds from constructive total loss declarations and SBA disaster loans.
The insurance program has been effective in providing motivation for floodplain regulation. In view of the anti-zoning attitude in the area it is doubtful that floodplain regulation would have been widely implemented without the incentive provided by the flood insurance program.
Relief and Rehabilitation Services - Houston recently experienced flooding (three large events in 1979 plus other lesser events) and has had to address relief and rehabilitation. The Texas Disaster Act of 1975 (Art. 6889-7) is the legal authorization under which the state functions in disaster relief. An Emergency Operation Plan provides guidance for state activities. The State Division of Disaster Emergency Services has a Houston District Office where requests for the assistance of any state agency can be made in an emergency.
Relief and rehabilitation involves many different groups including federal agencies, state agencies, local governments, and private organizations. The effectiveness of a relief and rehabilitation effort depends largely on the effectiveness of the local government. Of the 121 local governments (counties and cities) in the eight-county region, about 25 currently have no emergency operation plan.
Relocation of Floodplain Occupants - One way to solve a flooding problem is to relocate it. This plan has been discussed widely on a national basis but has been implemented in only a few cases. It has occurred in Whispering Oaks, previously discussed, and in Baytown, just east of Houston, under a Corps of Engineers authorization. This is an isolated event nationally and in the Houston area but perhaps indicates that relocation will become a more accepted flood hazard mitigation measure in the future. In fact, relocation of some homes in the 100-year floodplain of Clear Creek in Galveston, Harris and Brazoria Counties, along with channel widening and deepening, and the provision of a second outlet from Clear Lake to Galveston Bay, is being considered as the preferred flood control plan for Clear Creek.
Big Thompson Canyon, Colorado
Setting
Big Thompson Canyon is perhaps the best known of the many canyons which interlace the Front Range of the Rocky Mountains. Before July 1976, the 25-mile-long canyon was familiar as a scenic and convenient route from Loveland, Colorado, and points east to Estes Park, the Gateway to Rocky Mountain National Park. The steep winding canyon has provided countless visitors with their first glimpse of Rocky Mountain terrain and ecology. Since July 31, 1976, Big Thompson also has been known as the scene of one of the nation's worst flash flood disasters. On that single summer night, at least 139 lives were lost.
Geologically, the canyon was created by Big Thompson Creek which rises in the high mountains near the Continental Divide and flows eastward and downward to the plains near Loveland. The creek is impounded by a small dam and reservoir at the city of Estes Park before it begins its downward plunge through the canyon. This reservoir retains spring snow melt but provides little protection against sudden flash floods due to summer thunderstorms. Such events occurred in the canyon regularly up to 1951 and then, for some reason, ceased until 1976. As it courses through the canyon, Big Thompson Creek is joined by several tributaries and it eventually joins the South Platte River east of Loveland.
The July 31, 1976, flash flood occurred at the height of the Bicentennial summer tourist season. It is estimated that the population of the canyon that evening included about 600 full-time residents, 1200 seasonal residents~ and 700 tourists, plus an unknown number of persons driving within the canyon on Route 34 which follows the creek between Loveland and Estes Park. Most of this population at risk was residing in vacation cottages, cabins, motels, or campgrounds on the narrow floor of the canyon on either side of the creek. In some parts of the canyon, the steep sides preclude construction outside the reach of floodwaters. Structures across the creek from Route 34 were dependent upon private bridges for egress; many were low and flimsy in construction.
The Flood and Public Response
The storm which produced the Big Thompson flash flood resulted from the convergence of moist, warm air from the Gulf of Mexico with colder air from the Canadian prairies. The thunderstorm system reached 60,000 feet in height and hovered over the drainage basin of Big Thompson Creek for four hours. Rain began in the upper and central portions of the basin around 6:30 p.m., in places leaving as much as 12 inches in a few hours. The lower end of the canyon received little or no rainfall, a fact which delayed public response.
At narrower points within the canyon, the flood took the form of a "wall of water" which swept down at an average speed of 25 feet per second. Peak discharge at the canyon mouth was later estimated to have reached 31,500 cfs~ a once in 300-year event. Depending upon the width of the canyon, the depth of water reached as much as 20 feet above grade level. It has been estimated that as much as 40 percent of the flow volume consisted of debris: boulders, trees, houses, and vehicles. Along the way, the flood in the main canyon was joined by secondary crests from side canyons. The physical impact of this high velocity flood was profound. At least 316 homes and cabins, 45 mobile homes, and 52 business structures were destroyed. Numerous sections of Route 34 were washed away. Landslides were common as the floodwaters scoured the base of steep canyon walls. Boulders as large as 22 feet in diameter were moved. It is probable that many structures were destroyed and deaths resulted from such indirect consequences of the flood.
The only immediate, feasible response to this disaster was flood warning and evacuation. The National Weather Service (NWS) radar station at Limon, Colorado, did detect the cloud formation. It lacked the capacity, however, to measure the rainfall in any single canyon or narrowly defined drainage basin. Hence, while NWS issued a flash flood watch at 7:30 p.m., a flash flood warning was not issued until 11:00 p.m. -- after most of the destructive waters had passed through the lower end of the canyon.
Despite this failure, however, warnings were issued by state and county police after flood conditions were reported by police in Estes Park. Much research has been performed upon the effectiveness of this warning effort and the succeeding actions of individual victims.
Apparently many persons in the lower canyon did not receive advance warnings due to lack of communication (e.g., their radio or television was not turned on). Some of those who received warning by broadcast or house-to-house visits by police failed to act quickly, in part because of the lack of rainfall in the lower canyon. Some attempted to drive out of the canyon in their cars and in several cases were overtaken by floodwaters. Others climbed the sides of the canyon, which is now the procedure recommended by signs appearing in many canyons throughout the west. Some remaining indoors were washed away with the structure. Structures located on the inner bends of the creek survived, but most others were demolished or damaged severely.
Post-Flood Response and Recovery
The Big Thompson catastrophe triggered a complex series of actions by decision makers at each level of government: federal, state, and county. Additional decision makers included those from several water and irrigation districts, the city of Loveland (which owns a power plant and two parks in the canyon outside its corporate limits), and private owners. The total cost of the recovery effort has been placed at $56,000,000, the federal government providing about $51,000,000. This federal commitment was rendered under the auspices of at least 29 different programs administered by about 19 agencies and departments. Nonfederal actions were taken principally by the Colorado Legislature, various state agencies, and Larimer County.
The recovery effort was characterized from the outset by diversity in public objectives. On the one hand, business interests in Loveland, Estes Park, and within the canyon itself, called for rapid and complete restoration of roads and other facilities, both public and private, so that tourism would not decline. Reflected in a survey taken at the time, most residents concurred, although about one-third indicated a willingness to sell to the government at pre-flood values. Nearly all wanted highway 34 restored quickly in its pre-flood location. The rarity of this particular flood event supported their position.
On the other hand, a small minority expressed the view that the entire canyon should be set aside for open space, even to the extent of not rebuilding the road system at all. Proponents of that view pointed to the lives lost and the extent of physical devastation. These and other competing objectives were expressed with varying intensities through the recovery process.
Today, the Big Thompson Canyon has regained its peaceful, scenic appearance and serves once again as an important corridor to the Rocky Mountain National Park. Route 34 has been floodproofed to the 100-year floodplain designation and considerable land within the canyon has been acquired for public open space by Larimer County and the U.S. Forest Service. Although some groups who favored complete abandonment of the canyon for residential purposes may view the recovery process as simply having put things back as they were, the mitigation measures achieved go far toward a balanced solution.
Several important lessons may be drawn from the Big Thompson recovery experience for application elsewhere. These will be considered under three headings: Direction of the Recovery Response, Need for Adequate Coordination, and Restoration versus Mitigation.
Direction of the Recovery Response
Within a week after the disaster, Colorado Governor Richard Lamm established the Big Thompson Recovery Council consisting of state, county, and local representatives to plan and coordinate nonfederal activities. Federal representatives also participated. This measure was a key mechanism insuring that these diverse units might work together closely. A Big Thompson Recovery Planning office, funded through HUD, was subsequently opened in Loveland with a full-time staff whose principal function was to coordinate the necessary efforts. During its three-year period of existence, this office had considerable success in identifying key needs and obtaining financial support -- including in some cases special Congressional legislation and appropriations. The value of such a coordinating office close to the scene of the disaster, but having strong contact through the governor's office with Washington and regional federal officials, is an important contribution of the Big Thompson experience to the state of the art of disaster recovery.
Need for Adequate Coordination
As noted above, federal response to ttle Big Thompson disaster involved some 29 different programs and 19 agencies. These involved a spectrum of services and assistance ranging from social welfare benefits to physical debris clearance and land acquisition. Coordination of such diversity is a difficult and complex task.
In accordance with the procedures activated upon designation of this flood as a Presidentially declared disaster, a Federal Coordinating Officer was appointed. This individual, working directly with the Big Thompson Recovery Council, established and maintained contacts with the myriad of federal agencies participating in the recovery effort. In addition, coordination was done with the Office of the Governor, the State Coordinator, the appropriate local officials, and with volunteer agencies so as to include the Interfaith Task Force.
Commenting on the coordination among federal and state layers of government from the county viewpoint, the Assistant County Flood Coordinator indicated that the directors and staffs of both agencies (i.e., the FCO and SCO) merited special praise since they were aware of the disaster assistance programs and the way in which they applied to the specific situation, knew the procedures for expediting programs, understood the needs of disaster victims, and served as advocates for the county in