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<br />O ~.. / r" <br />v '_.:" 0') <br /> <br />25 <br /> <br />Hydrologic Areas <br /> <br />Area 1. -- As shown in figure 7, area 1 is in the northeast corner of the <br />State. It has a rolling hilly relief and is characterized by the occurrence of <br />glacial till. The relation between mean annual flood, drainage area, and rnean <br />flow is based on 19 stations in the area. A convenient way of expressing the <br />exponential relation is by the nomograph in figure 10. The use of the nomo- <br />graph will be described in the following section. Statistically the relation has <br />a standard error of estimate of 0.10 log units. The standard error is a meas- <br />ure of the scatter of points about a curve of relation and provides a comparison <br />with other relations or methods. It implies that for two-thirds of the time, <br />Q2.33 is defined within 0.10 log units, which is equivalent to 23 percent. <br /> <br />Area 2. --The terrain in area 2 is gently undulating with occasional pro- <br />nounced escarpments. The relation for mean annual flood is based on 18 sta- <br />tions and it is shown as a nomograph in figure 11. The standard error of esti- <br />mate is 0.075 log units or 18 percent. <br /> <br />Area 3. --This area contains primarily the Chatauqua and Flint Hills. The <br />Flint Hills Upland is gently rolling and merges on the west with a gentle slope <br />toward the Arkansas River Valley but the eastern escarpment probably con- <br />tains the most rugged relief in the State. The relation for mean annual flood <br />is based on 20 stations and it is shown as a nomograph in figure 12. The stand- <br />ard error of estimate is 0.075 log units or 18 percent. <br /> <br />Area 4. - - The terrain in area 4 consists primarily of Dissected High Plains <br />and Arkansas River, Lowlands but the western boundary includes part of the <br />High Plains. Relief in the dissected hills varies from rolling to flat plateau- <br />like surfaces with steep escarpments. The lowlands are characterized by lack <br />of relief or by gently rolling sand dunes. The relation for mean annual flood <br />is based on 45 stations and it is shown as a nomograph in figure 13. The stand- <br />ard error of estimate is 0.112 log units or 26 percent. The relation is not <br />applicable to the main stem of the Arkansas River above Pawnee River. Flood- <br />frequency relations for this reach of Arkansas River are developed in a sub- <br />sequent section entitled "Regulation". <br /> <br />Area 5. - -This area contains the High Plains. It constitutes the most level <br />part of the State. In many portions, the surface is so flat that surface runoff <br />is delayed or even prevented from reaching a major stream. There are also <br />numerous depressions or closed basins scattered throughout the area that pre- <br />vent direct surface drainage to a major stream. The relation for mean annual <br />flood, shown as a nomograph in figure 14, is based on 14 stations exclusive of <br />the main stern of Arkansas River, which is discussed under "Regulation", and <br />of the Sappa and Beaver Creek stations. The standard error of estimate is <br />0.060 log units or 14 percent. Data for Sappa and Beaver Creeks scattered so <br />erratically that they were not amenable to the areal analysis. However, they <br />