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001187 Summary: Lessons to Be Learned The Jackson case history points to a number of lessons that can be learned, although not all of them have taken hold there. Briefly stated, these involve: 1) the danger of overconfidence in structural flood control; 2) the importance of preventing floodplain encroachment; 3) the importance of locating vital public facilities outside the pos- sible flood zone; 4) the need for pre-disaster con- tingency planning; 5) the need for post-disaster hazard mitigation, including appropriate relocation and prevention of ad- verse future development; and 6) the need for improved coopera- tion among public authorities. All of these six points are important, but the first two are especially so. For finally, the question comes down to this: Why did the 1979 Jackson disaster hap- pen? Why did a flood whose discharge was only two-thirds that of a 175-year flood against which the area was sup- posed to be protected by the 1960's im- provements-why did that real flood crest above the hypothetical, larger flood? The answer doesn't lie in a mis- calculation of the theoretical flood lev- els. It lies instead with the fact that the real flood had to contend with a myriad of encroachments, planned and un- plan'1ed, each one seemingly innoc~nt (as with the homes in the floodplam) and well-intended (as with the levees), yet each one constricting the river and raising its level--and the level of poten- tial disaster. 2. HAIKEY CREEK-UPSTREAMI DOWNSTREAM CONFLICfS No one wants floodwater-but where should it go? The Haikey Creek case history is an example of the conflicts that can arise between upstream and downstream neigh- bors over this issue. The Setting: Highlands to Lowlands; City to Suburb Haikey Creek is one of several prairie creeks that rise within the city limits of Tulsa Oklahoma, and flow outward to the Arkansas River. Its 37 square mile basin lies within the fast-developing southeast section of the Tulsa metro- politan area. The creek rises in the Ozark highlands-roliing hills now becoming houses, streets, and shopping centers. But from these busy hills it drops to the still-pastoral bottom lands of the Arkan- sas River. Barns and farmhouses dot the "Bixby Bottoms" and only scattered subdivisions can be seen in this area of rich agricultural soils. However, those scattered lowland sub- divisions are a portent of things to come, and the portent does not bode well. At present there are about 400 structures (most of them single-family homes) in the 100-year floodplain of the Haikey basin (which covers about one-fifth of the basin). There is still plenty of room for development. Today, a 100-year flood would cause an estimated $5.4 million in damages. Who knows what it could cause ten years from now? \ I I The Creek and Its Flood Experience Haikey Creek drops about 275 feet in its total twelve-mile length, partly through channelized and straightened courses but otherwise meandering. The occasional flooding usually found with abrupt elevation drops is made worse in Haikey's case by several factors: (1) the basin's geological underpinnings are mainly an impermeable strata of shale and limestone, preventing ground water absorption; (2) this naturally high sur- face water runoff is increased by the ur- banization upstream; and (3) in the Haikey area, rain comes erratically, in- tensively, often in cloudbursts or torren- tial downfalls. All this means floods- more and more of them and with in- creasingly severe consequences as ur- banization marches on. Before 1960, the Haikey basin housed fewer than 6,000 people, most of them in the upland area, and flood damage was largely confined to agricultural crops. By 1974, the population had tripled, and this meant two things: more surface runoff and more property to be damaged. Floods in 1957 and 1959 had each caused $100,000 in damages; floods in 1974 and 1976 caused damages of $650 000 and $783,000, respectively (Fig.' 16). So again the question arises: 33