IF YOU WERE GIVEN the task of installing a drainage

Transcription

1 Applying Profile Leveling Techniques IF YOU WERE GIVEN the task of installing a drainage system, how would you determine the slope needed to keep the water flowing? Profile leveling is an option. As part of profile leveling, you must record clear and accurate notes. Learning how to record your thoughts is an excellent skill that can help you in your career and in your personal life. Objective: Explain how to conduct a profile survey. Key Terms: backsight benchmark elevation foresight height of instrument profile leveling station turning point Understanding Profile Leveling Profile leveling is an important technique commonly used for drainage systems, irrigation systems, fences, and roads. Conducting a profile survey involves record keeping as well as leveling techniques. FIELD NOTE RECORDS No aspect of surveying work is more important than keeping accurate records of field notes. Surveying notes must be recorded legibly and accurately in a field book as the work is done. Notes should not be recorded on scratch paper and later transferred to a book. Doing this introduces an opportunity for error. The field notes reflect the quality of the work performed. Professional looking notes indicate professional quality work in measurement and readings. Other surveyors completing later surveys often refer to survey notes. Page 1

2 When making entries in the field book, a 3-H or 4-H pencil should be used. Pen or soft lead pencil markings may become smeared and unreadable over time. In addition, erasures of data should be avoided because this makes the validity of the data questionable. To make corrections, draw a single thin line through the incorrect data and write the correct entry above it. Misspelled words, however, may be erased. Several important sections are included in a field notebook. Each part plays a specific role in the accurate completion of the leveling exercise. The different sections are the table of contents, paging, and form of entries. Table of Contents Leave a few pages blank at the beginning of the book for a table of contents. On this page, the recorder should make a brief description and a page reference for each activity completed. He or she should include enough information so someone examining the table of contents could identify the work, the place, and the date of completion. Table of Contents Page Activity Location Date 1 Taping P. Hermes Farm Aug. 4, 20 2 Profile Leveling T. Smith Farm Sept. 2, 20 3 Waterway Profile I. Jones Watershed Sept. 9, 20 4,5 6 Differential Leveling Tiling Henry Brown 600 Acres Construction Survey House Drain T. Hayes Addition Lot 7 Oct. 21, 20 Nov. 3, 20 FIGURE 1. Field notebook table of contents. Paging A survey activity may require one or more sets of facing pages. Each set is considered one page when pages are numbered. A new day s work should be recorded on a new page. Form of Entries Printed entries are generally more legible than written entries. Field notes should be arranged according to the standard form that has been developed. This form outlines specific information, which should be found on each of the facing pages. Page 2

3 Left-Hand Page The left-hand page includes a legal description of the land, and the type of survey should be written at the top of the page. The recorder should place column headings between the first two horizontal lines at the top of the page. Readings should be recorded and tabulated in these columns. It is important to record figures with the decimal point and digits in line vertically. Readings should be written with significant zeros (i.e., 4.70 compared to 4.7). The column headings, which should be found in the survey notes, are station, backsight, foresight, height of instrument, and elevation. The station (Sta.) is the location of the leveling rod when the reading is being taken. The backsight (BS) is a level reading taken on a point of known or assumed elevation. The foresight (FS) is a level reading taken on a point of unknown elevation. The height of instrument (HI) is the elevation of the level line of sight with respect to the benchmark, as indicated by the cross hairs in the telescope. Height of instrument is calculated by adding the backsight to the elevation of the benchmark or turning point, whichever is being used. The elevation (Elev.) is the height of a point relative to the benchmark location of the survey. Elevation is calculated by subtracting the foresight from the height of instrument. Bob Hofmann Farm NW¼ SW¼ Sect T3N R6W Profile Leveling Tile Drain Sta. BS HI FS Elev. BM TP TP 2 BM Error = April 17, p.m. Cold, Cloudy, Calm Top NE Corner Headwall at SW corner of farm. In ditch, 20 E of BM-1 ROAD BM Line Surveyed Brian Myers Kim Romine Tom Jones Level #372 DITCH 6+35 N FIGURE 2. Left- and right-hand pages with field book notes. Page 3

4 Right-Hand Page On the top left of the right-hand page, the date, time of day, and weather conditions should be recorded. The names and duties of the survey party should be recorded at the top right of the right-hand page. The type and number of the surveying instrument may be recorded there. A sketch of the survey should be included on this page. The sketch should be of general proportions, and north should be indicated using conventional signs and symbols. The recorder should sign the lower right corner of the right-hand page. PROFILE LEVELING Profile leveling is the process of determining the elevations of a series of points at measured intervals along a line. A profile survey is extremely useful for locating drains, roads, dams, and other earth structures. The usual procedure is to determine the profile elevations; choose the grade elevations; and compute cuts or fills. Profile leveling is actually differential leveling with a number of intermediate foresights added between turning points. A turning point is a solid location, usually marked by a temporary stake, on which a foresight is taken, to which the instrument is moved, and from which a backsight is taken to determine a new height of instrument. Each foresight is subtracted from the first height of the instrument until the instrument is moved. Profile Leveling Procedure The procedure for completing a profile survey is relatively simple. The first reading is taken on a benchmark, which is a permanent point of known or assumed elevation from which leveling surveys are started. Then the instrument should be turned and readings should be TF BM FIGURE 3. Readings from a profile leveling circuit. Page 4

5 taken along the stations of the profile until it is necessary to establish a turning point. It is essential to move the instrument, to compute a new height of instrument, and to continue to take readings. After the foresights on stations along the profile have been taken, the survey should not be considered finished until a differential leveling circuit is completed and a final reading is taken on the beginning benchmark. CALCULATING ALLOWABLE ERROR In leveling, errors can and will occur. The final error of closure in a leveling circuit is proportional to the square root of the number of rod readings. The formula assumes a distance of 100 feet for each rod reading. Therefore, divide the total length of the traverse by 100, determine the square root of that dividend, and multiply by the factor of For experienced surveyors, a less tolerant factor of may be used. If the error of the survey is greater than the allowable amount calculated, the survey should be repeated. Summary: No aspect of surveying work is more important than keeping accurate records of field notes. Surveying notes must be recorded legibly and accurately in a field book as the work is completed. Important sections are the table of contents, paging, and form of entries. The column headings, which should be found in the survey notes, are station, backsight, foresight, height of instrument, and elevation. Profile leveling is the process of determining the elevations of a series of points at measured intervals along a line. A profile survey is extremely useful for locating drains, roads, dams, and other earth structures. The procedure for completing a profile survey is relatively simple. In leveling, errors can and will occur. The final error of closure in a leveling circuit is proportional to the square root of the number of rod readings. If the error of the survey is greater than the allowable amount calculated, the survey should be repeated. Checking Your Knowledge: 1. What are some important guidelines for record keeping? 2. What column headings should be found in the survey notes? 3. What is profile leveling? 4. What is the procedure for completing a profile survey? 5. How are leveling errors calculated? Page 5

6 Expanding Your Knowledge: Conduct a profile survey on the school s land lab. Following the procedures discussed in this unit. Report your results to your instructor. Web Links: Profile Leveling SURVEYING/modules/module4/html/52.htm Profile Leveling Profile Leveling Agricultural Career Profiles Page 6