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<br />-225- <br /> <br /> <br />C f'~ "'! ..-:,"~ / <br />'u ,:~ !"t.~ >:t <br /> <br />CHAPTER 10 <br /> <br />LOWER MISSOURI SUBBASIN <br /> <br />SUBBASIN DESCRIPTION <br /> <br />The Lower Missouri Subbasin, the furthest downstream of the <br />Missouri River Basin subbasins, encompasses a total area of 25.4 <br />million acres (as shown in figure 13). It includes all of the <br />tributaries of the Missouri River from Kansas City, Missouri, <br />downstream to the confluence of the Missouri River with the <br />Mississippi River, 15 miles above St. Louis, Missouri. The <br />subbasin encompasses about one-half of Missouri and small parts <br />of Kansas and Iowa. The subbasin has a maximum east-west and <br />north-south extent of about 300 miles. <br /> <br />The principal northern tributaries of the Missouri River in <br />this subbasin, the Grand and Chari ton Rivers, flow southeastward <br />from southern Iowa where the terrain is rolling and elevations <br />reach 1,450 feet (mean sea level). South of the main stem, the <br />Osage and Gasconade Rivers are the chief tributaries. The Osage <br />River system drains the land eastward from headwaters extending <br />from the Flint Hills of east central Kansas to the Ozark <br />foothills in south central Missouri. The Gasconade River,. which <br />lies southeast of the Osage, originates in the foothills of the <br />Ozarks, and flows northward to the Missouri River. <br /> <br />Mean annual precipitation is 32 inches in south central <br />Iowa, increasing to 42 inches in south central Missouri. About <br />70 percent of the precipitation occurs during the growing season, <br />between the months of May and September. January is normally the <br />coldest month of the year. Mean daily maximum temperatures range <br />from 33 degrees in the north to 46 degrees in the south in <br />January, and in July the mean daily temperature ranges from 90 <br />