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APPENDIX A SURVEYING TECHNIQUES This appendix discusses the basic equipment and surveying tech- niques commonly used for hydraulic simulations in instream flow studies. The-techniques described are somewhat abbreviated, and confined to those techniques most often used for instream flow work. For a more complete description of surveying techniques, the reader is referred to a.pro fess.ionai surveying course or to one of the references quoted in this text. Two types of measurements are regularly used in instream flow studies. The first type is called leveling, which is the process of finding the difference in elevation between two points by measuring the vertical distance between the horizontal planes intersecting the two points. The second type is the measurement of linear distances between two points, which may be achieved by taping or use of surveying or electronic devices. USE OF THE LEVEL A level is an instrument combining a telescopic sight having both vertical and horizontal cross hairs, with a level vial which indicates when the instrument is in a level position. The types of levels most commonly used for instream flow work are the American type engineer's level and the self-leveling level. Occasionally, a transit is used as a level, but these are somewhat more difficult to use than a level, and are somewhat less precise for leveling. A line drawing of an engineer's level is shown in Figure A-1 to familiarize the reader with some of the principal components of the instrument. A self-leveling level has many components in common with the engineer's level. Focusing The process of focusing is the most important function to be per- formed with a telescopic sight. The telescope consists of an objective lens (mounted on a sliding tube inside the tube), a reticle (cross hairs), and an eyepiece. The purpose of the negative lens is to focus the object image on the reticle. The focusing pinion for'the negative lens is a large knob on the top or side, near the center of the tube. Since the reticle remains fixed in the telescope tube, the distance between it and the eyepiece must be adjusted to suit the eye of the observer. This is done by focusing the eyepiece on the cross hairs with the eyepiece focusing ring. After the eyepiece has been adjusted, objects are brought into focus with the objective focusing pinion. If the cross hairs appear to travel over the object sighted when the eye is shifted slightly in any direction, parallax exists. Further adjustment of either the objective lens system or the eyepiece is required to eliminate parallax. -7/