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<br />e <br /> <br />e <br /> <br />e <br /> <br />Z-7 <br /> <br />Stationing <br /> <br />Main channel, - - The base line should be stationed in conformance <br />to Engineering Memorandum SCS-39. <br /> <br />Where semicontrolled aerial mosaics are used to show the location of <br />channels, mark the stationing on the centerline with a short dash at <br />each ZOO-foot point. <br /> <br />Determine the stations at all cross sections and the pertinent features <br />noted during the field reconnaissance by scaling the distances between <br />points on the aerial mosaic. Although the points and the cross sections <br />may be numbered both on the mosaic and in the notebook, these points <br />also should be stationed in the field notebook as a permanent record. <br />Thus, complete profile notes are obtained without actually measuring <br />the distances in the field. <br /> <br />Where preliminary location surveys are obtained by means of an instrument <br />survey, stationing is accomplished by measuring with a chain or stadia <br />in the field. <br /> <br />Tributary channels. - - Base lines on tributary channels should be tied <br />into the main channel base line. <br /> <br />Reaches <br /> <br />The length of design reaches normally is governed by the distance between <br />points where a change of elements of the channel occurs, such as the <br />entry of a side tributary or a change in gradient, depth, width, etc. <br />Where the elements of a channel are constant for relatively long distances, <br />the reach should be subdivided so that no design reach will exceed about <br />Ill. mile in length. <br /> <br />Cross Sections <br /> <br />Valley flood plain. - - The survey of valley cross sections used to develop <br />water surface profiles for damage evaluation should be extended on <br />each side of the valley to be above the maximum high water mark to <br />permit computation of flood plain storage and to establish the vertical <br />relationship between viewers and the channel work. Normally, this <br />work is done in sufficient detail in the planning stage to serve for both <br />the planning and final design requirements. <br /> <br />Sufficient points should be surveyed to represent adequately the hydraulic <br />and visual characteristics of the cross section. Elevations should be <br />established at all significant changes in slope. The distance between <br />points on the cross section should not exceed 300 feet where the slopes <br />are relatively tmiform. <br />