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<br />\ <br />----4, <br />\ <br />,c~.c.J. <br />~-~~-_.~ <br /> <br />CHAPTER 4. BASIC DATA <br /> <br />Hydraulic theory is well established for channels with rigid <br />boundaries and produces consistent and accurate results when properly <br />applied. Major sources of error when applying hydraulic theory are <br />inaccuracies in data or improper modeling of flow conditions and cur- <br /> <br />" <br />, <br /> <br />rent patterns. <br />Basic data are grouped into three categories: geometric data, <br />hydraulic roughness values, and the water discharge and corresponding <br />water surface elevation. The accuracy required in this data depends <br />upon the accuracy needed in final results. At times, it is more <br />economical to compensate for inaccurate data by safety factors such <br />as providing liberal amounts of freeboard, and in rural areas such <br />procedures are acceptable. However, in urban areas both property <br />damage and loss of life can result from designs based on inaccurate <br /> <br />data. <br /> <br />Section 4.01. The Geometric Model <br /> <br />It is customary to establish the boundary geometry for flow in <br /> <br /> <br />natural rivers by measuring ground surface profiles perpendicular to <br /> <br /> <br />the direction of flow at intervals along the streams and measuring <br /> <br />the distances between these profiles. The profiles themselves are <br /> <br />called cross sections, and the distances between cross sections are <br /> <br />4.01 <br />