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2-8 Channels. - - Channel sections are required to make reliable estimates of quantities and to determine easement requirements. They should extend far enough to permit improved channel alignment without additional surveys or at least 50 feet beyond the expected right-of-way, whichever is greater. The allowable distance between cross sections will vary with channel and valley conditions. Normally, 300 to 1000 feet are sufficient for work plan estimates. These sections should be tied into the same basic datum as the other sections in the watershed. e Structures The condition and serviceability of all structures should be recorded. Adequate survey data are needed for all bridges and culverts in order to compute the carrying capacity for each. A minimum of three cross sections is needed at each structure; i.e., an inlet or approach section, a section perpendicular to the direction of flow through the structure, and an exit section. The entrance and exit sections usually are taken approximately 50 feet from the respective ends of the structure. The section through the structure should include the size of the opening, size of bridge piers, abutment footing elevations, and elevations of the bottom of bridge girders and the road surface. This section should be extended along the centerline of the road on either side of the structure beyond any probable overflow elevations. The grade and length and invert elevations of all bridges and culverts also should be obtained. See National Technical Release 14. The three sections described for bridges and culverts also should be taken for all grade control structures along the channel. Similarly, cross sections are needed for all rock ledges which act as grade or hydraulic control sections. e Visual Resources The data necessary to identify, plan, and design the visual resources will vary considerably among projects and may vary among parts of the same project. For example, given a flat terrain covered solely by a crop pattern with only stream way trees, the needed data may include only recording the possible road viewsheds and noting how the treetop edges contribute visual variety or a visual sense of space. However, in an urban landscape it may be necessary to pinpoint the locations of landscape elements such as large trees, accoustical and visual screen shrub masses, and landforms. Landscape architecture survey outline including a visual resource survey appears in Chapter 2, Appendix A. A more detailed discussion of visual resources and landscape architectural design appears in Chapter 8. Plotting Data General. - - Plan, profile, and cross section data obtained during the planning stage should be neatly plotted for use in preparing preliminary drawings. The scales used for plotting the data should be selected so that the information can be clearly shown on as few sheets as practical e