Techniques for estimating magnitude and frequency of flood-peak discharges, based on channel geometry parameters, are presented as a method for evaluating Ohio floods in geographic areas deficient in flow data.One hundred and sixty gaging stations were selected on streams with alluvial channels unaltered by man. Exposed bedrock is absent from the channels in the vicinity of the surveyed cross sections. Peak stream discharges at the selected sites were related to channel geometry parameters.Active channel width is the only statistically significant parameter.Channel geometry parameters which were tested and found to be statistically insignificant are active channel average depth, bankfull width, and bankfull average depth.The average standard errors of estimate for the resulting statewide equations, with recurrence intervals of 2, 5, 10, 25, 50, and 100 -years, range from 42 to 55 percent.Four previous reports on Ohio floo^ frequency, by Cross (1916), Cross and Webber (1959), Cross and Mayo (1969), and Webber and Bartlett (1977, were the result of cooperative investigations with the
Hhio is divided, diagonally, from southwest to nortneast D^ the line of glaciation. The northwest corner is a very flat, glaciated, old-lake region; the southwest, central dnd northeast areas are rolling, glacial till plains; the southeast area i.; nilly and unglaciatad. Land elevations ran:re frcn a low of ^z,^ r 4-(137 tn) , in Hamilton County, to 1,550 ft (412 m) at t^e highest point, in Logan County. The climate is temperate. Annual precipitation, whicr. averages about 38 in (960 HI in) is distributed rather u:;iformiy throughout the year. Pecords indicate that floods may occur anytime during the year with streams having large drainage art-cio iiore susceptible from January through April and streams havino small drainage areas more susceptible from Miy through August. Jnowfall is not a significant factor of Ohio floods except alone Lake Erie, in Cuyahoga, Lake, Geauga and Ashtabula Counties. METHODS OF ANALYSTS Methods of flood-frequency analysis at gaging stations a nc he application of the results to a regional analysis die Drainage area (A), in square miles, as planimetered from U.S. Geological Survey 7.5 minute series topographic quadrangle maps and tabulated in Ohio Department of Natural Resources Report 12a (1967). Main-channel slope (Si), in feet per mile, was computed as the difference between th9 elevations at 10 and 85 percent of the channel distance from the gaging station to the basin divide, divided by the channel distance between the two points as determined from topographic maps. Main-channel length (L) , in miles from gagingstation to basin divide, was determined from topographic maps. Average basin elevation index (?), in feet above mean sea level, was computed by averaging the elevations at the 10 and 85 percent distance points along the channel as determined from topographic maps. The reliability of this method is discussed by Benson (1964). The characteristic used in regression analysis was average basin elevation index in 1,000's of feet above mean sea level. Surface-storage index (St), in percent, is rhe percentage of total drainage area occupied ty laices, ponds, and swamps, as determined from topographic maps. The characteristic used in regression was surface storage index plus 1.0 percent. Forest area (F) , in percent, is the percentage of total drainage area occupied by forest cover as determined from green tinted areas on topographic maps. The characteristic used for regression analysis was forest area plus 1.0 percent.
A time-of-travel study was made on a 10.6-mile reach of the Tuscarawas River to determine average velocity and dispersion characteristics between selected points. The reach was divided into five subreaches, and a fluorescent dye used as a tracer material. At about the 50-percent flow-duration level, time-of-travel of the peak concentration was 137 hours.
No abstract
The flood of June 13-15, 1981, in the Blanchard River basin in northwestern Ohio caused major damage in Findlay, Ottawa, and adjacent rural areas. Approximately 25 percent of Findlay and 55 percent of Ottawa were flooded. Estimated crop damage was $12
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