386 ANNUAL REPORT SMITHSONIAN INSTITUTION, 196 2 



Even if this proved to by hydrologically feasible, which is not likely, 

 care would have to be taken to ensure that the ground water did not 

 become polluted. 



The sixth major water problem, that of floods, probably gains the 

 greatest public attention because floods are often of disaster propor- 

 tions. Floods are a normal part of a river's life. The flow of a river 

 generally ranges from the low flow, which is maintained principally 

 by ground-water seepage into the stream, to a bank-full stage which 

 occurs on the average of about twice a year. Higher flows, which may 

 occur about every 10, 50, or 100 years, depending upon local condi- 

 tions, can only be carried outside the channel of the river on the flood 

 plain. Floods can be controlled by the construction and use of water- 

 storage reservoirs, which tend to even out the annual fluctuation to a 

 more or less steady flow. However, the construction of reservoirs 

 solely for flood control is not always economically practical, and for 

 that reason multipurpose reservoirs must be designed. These can be 

 partly emptied and used for storage of flood water, which is later re- 

 leased for hydroelectric power generation, navigation, irrigation, water 

 supply, and the dilution of waste reaching the river downstream from 

 the reservoir. 



The extent to which floods can endanger life and damage property 

 is well illustrated by the floods of August 13-19, 1955, on the eastern 

 and northeastern coasts of the United States. Hurricane Connie 

 crossed the coast of North Carolina at about noon on August 12, 

 moved north along the coast, across eastern Virginia, northeastward 

 across central Maryland, Pennsylvania, and the southwestern tip of 

 New York, and entered Ontario on August 14. Scattered floods oc- 

 curred as a result of this hurricane, but its most dangerous effect was 

 to saturate the soil to its capacity, which meant that further heavy 

 rains would cause high runoff. Three days later hurricane Diane 

 crossed the southern North Carolina coast, moved northward across 

 southeastern Pennsylvania, crossed New Jersey, and swept out to sea 

 south of Long Island on August 19. Heavy rains occurred in a broad 

 band along the coast, an area that includes the most industrialized and 

 densely populated part of the United States. The ground, still wet 

 from the rains of August 12-14, could absorb only a small part of the 

 rain ; consequently, the rest ran off in the stream channels and flood 

 plains, causing disastrous floods. In spite of flood-control reservoirs, 

 property damage amounted to almost $500 million, and some 200 

 persons were killed or injured. The floods reached new record maxi- 

 mum discharges at 129 of the 287 stream-gaging stations in the flood 

 area (Bogart, 1960). Predictions of maximum expected floods are 

 based on statistical analyses of the frequency and magnitude of pre- 

 vious floods, and the recorded data on such record-breaking floods as 

 those of 1955 will make possible wiser planning of future flood control. 



