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<br />Section 4.09. Minimum Data Requirements <br /> <br />While it is desirable to have all of the data mentioned in the <br />previous section, prel iminary estimates can be made with a minimum <br />amount of data. For example, cross sections may be taken by a hand <br />level and bridge data may be collected with a measuring tape. Esti- <br />mated roughness coefficients can be obtained by visually comparing <br />the natural ground cover with calibrated photographs from standard <br />textbooks. Topographic maps can sometimes be used to obtain cross <br />sections where field data are not available. However. such informa- <br />tion should be verified by spot checking a few elevations in the <br />fi e 1 d. <br /> <br />Section 4.10. Preparing Field Data for Use <br /> <br />Natural channels are usually irregularly shaped. and consequently <br />the required geometric properties of area and wetted perimeter are <br />not easily expressed. The first step is to plot each cross section <br />in graphic form. It is usually convenient to establish some basic <br />policy to follow every time field data is collected. This permits <br />the bits and pieces of one or several field surveys to be fitted <br />together easily and without a major effort. For example, it is con- <br />venient to establish a common scale to which all cross sections will <br />be plotted. and if cross-section sheets are to be filed in flat files, <br />the size of paper available. and therefore the plotting scale, is <br />determined by the length and .lidth of the drawer. However. it is <br /> <br />4.18 <br />