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<br />Plllnnlng And Preliminary Dealgn <br /> <br />e <br /> <br />Construct on surveys should be made to control feature project location in the field. <br />Stakes should be set to mark the limits of work, locate stroctures. establish final grade <br />and a1igmBents, and so on. (Peterson, 1986) <br /> <br />Post-cons ruction surveys made for preparation of as-built drawings immediately <br />following completion of construction and later for general operation and maintenance <br />work, such as maintenance dredging and repair of structures. are recommended. <br />(peterson, 1986) <br /> <br />5.3.2 Aerial Photography. <br /> <br />Aerial photos are very helpful for de1ineating floodplain features, geologic historY, <br />physiographic features, and structural features such as faulting. They are also useful for <br />comparing channel conditions and meandering of a river over time and for noting the <br />extent of ,:hannel changes, extent of flooding and flood damage, low.water conditions, <br />bank ems Ion and deposition, and changes in land use on the overbank. <br /> <br />5,3,3 Geologll:. <br /> <br />Geologic investigations define the underlying rock line and provide basic information <br />on channd morphology, characteristics of alluvial deposits, bank stability, suitability of <br />sites for major structures, availability of construction materials, and so on. Geologic <br />bistory impacts a stream both directly and indirectly through influence on other <br />streambarik variables. Geologic conditions are responsible for the quantity and quality <br />of sedimfnt available for transport. Streambank and bed material dictates the location <br />and rate)f bank failure. Geologic conditions influence stream slope, entrenchment, <br />aggradati'JII, and degradation. (peterson, 1986) <br /> <br />A geolo~ic and seismologic assessment program might include field borings and <br />surveys to determine general geologic characteristics of the site and in the area, <br />including locations and characteristics of active faults. The extent of the exploration <br />program depends on the geological complexity of the site and the size and type of <br />project willer study. (Peterson, 1986) <br /> <br />5.3.4 Bank REtC8sslon Rates . <br /> <br />To develop an effective program for bank stabilization and channel rectification, an <br />understanding of the complex historical pattern of channel migration and bank recession <br />of the strl:am is essential. A relationship between channel changes and streamflow can <br />be formulated with this information. Studies of bank caving, based on survey data and <br />aerial photographs, provide information on the progressively shifting alignment of a <br />stream ar,d are basic to laying out a rectified channel alignment. <br /> <br />5.3.5 Sedlmelll SUrveys. <br /> <br />Knowledge of sediment transport, in terms of both quantity and quality, is <br />recommended for design of river engineering works on alluvial streams. Appendix B <br /> <br />e <br /> <br />58 <br /> <br />Colorac:to Erosion Control Manual <br />