Laserfiche WebLink
<br />e <br /> <br />e <br /> <br />e <br /> <br />2-3 <br /> <br />Survey Procedures <br /> <br />The survey procedure for "Preliminary Surveys" outlined in the National <br />Engineering Handbook Section 16,YChapter 2, is applicable. This procedure <br />should be augmented by "Landscape Architecture Survey and Analysis" <br />as outlined in Chapter 2, Appendix A. Technical Release-62, (TR-62), <br />contains guidance for notekeeping and stationing. <br /> <br />Horizontal Control <br /> <br />Where suitable 8-inch aerial photographs or photo mosaics are available <br />which show sufficient detail to locate and identify an existing channel <br />that can be used as a base line, it will not be necessary to run a transi t <br />traverse in the planning stage to establish a base line. Other existing <br />maps or plans of equivalent accuracy sometimes are acceptable for <br />this purpose. <br /> <br />Horizontal control for the planning and design of stream channel work <br />varies with the survey method selected. In most cases, sufficiently <br />accurate horizontal control can be obtained from semicontrolled photo <br />mosaics for both planning and preliminary design of channel work. <br />The photo mosaic also may be used to show drainage areas, flood plain <br />area, control elevations, channel locations, land ownership, etc. <br /> <br />The following steps are involved in obtaining semicontrolled photo mosaics: <br /> <br />1. Using the latest available aerial photos of the flood plain (preferably <br />the 4" = 1 mi. scale), select two points near the center of each <br />aerial photo, which can be identified on both the aerial photo and <br />on the ground. These points should be at least 500 feet apart and, <br />preferably parallel with the flood plain. Some additional accuracy <br />may be obtained by selecting a second line, approximately perpendicular <br />to the first, on each photo. To facilitate identification and measurement, <br />these lines should be selected along established lines, such as roads <br />or fences. Also, delineate the approximate area of the flood plain <br />on the aerial photos. <br /> <br />2. Measure the distance to the nearest foot between the selected <br />points in the field. Stadia distances may be used for lines up to <br />about 1000 feet long. Identify the points on the photos by a small <br />pin prick at each point. Circle the pin points on both the front <br />and back of the photo. Also, number or letter each point for identifi- <br />cation and mark the distance between the points on the back of <br />each photo. For a permanent reference, record each measurement <br />in a field notebook as follows: <br />