eChapters

Aim

To measure the irrigation water by using weirs

a) Weirs

A weir is a notch or opening of some definite shape installed on a channel or a stream through which waterfalls (Fig.59.1). Materials like wood, concrete, mild steel, rigid PVC etc. can be used for construction of a weir. Mainly a cut on a sheet metal is used for fabrication of weirs, to be installed at various locations in a channel. Advantages of weirs are (i) capable of accurately measuring a wide range of flows (ii) easy to construct, portable and adjustable (iii) tends to provide more accurate discharge rating than flumes and orifices.

Aim

To measure irrigation water by area-velocity method by using (i) float and (ii) current meter

Apparatus required

Float

Current meter

Theory

The rate of flow of water in open channel can be determined by multiplying the cross sectional area of the flow section at right angles to the direction of flow by the average velocity of water. In area-velocity method, the water can be measured at motion. The water is measured in motion by means of rate of flow or discharge and is expressed in litre per second (lps), litre per minute (lpm), cubic metre per second (m³/s), etc. Litre per second: A continuous flow amounting to 1 litre passing through a point each second. Cubic metre per second: A flow of water equivalent to a stream of 1 m long, 1 m wide and 1 m deep flowing at a velocity of 1 metre per second. In area-velocity method, the velocity of water is measured either by float or current-meter

Aim

To measure irrigation water by volumetric method

Apparatus required

Siphon tube

Stop watch

Measuring bucket

Aim

To determine the contours by radial line method using dumpy level.

Materials required

Dumpy level
Leveling staff
Measuring tape
Wooden pegs/chain pins
Field book

Aim

To determine the contours by cross-section method using dumpy level.

Materials required

Dumpy level

Leveling staff

Measuring tape

Wooden pegs/chain pins

Field book

Aim

To determine the contours by grid method using dumpy level.

Materials required

Dumpy level

Leveling staff

Measuring tape

Wooden pegs/chain pins

Field book

Aim

To prepare a contour map by direct method using dumpy level.

Materials required

Dumpy level

Leveling staff

Measuring tape

Wooden pegs/chain pins

Field book

Theory

For locating a point on the ground on a contour, its position and elevation in a horizontal plane should be known. In direct method, the contours to be plotted are located on the ground with a level by making various points on each contour, and these points are surveyed and plotted on plan. This method is more accurate but slow and tedious, and is suitable for contouring small areas where great accuracy is required. For locating the points of the same elevation, the instrument is set in such a commanding position from where maximum number of points can be covered. The bench mark is established near the site of survey. The height of the instrument (H.I) is determined after taking a back sight (B.S) on the established bench mark.

Aim

To determine the reduced levels on various points on the road

To plot the profile of the road

Materials required

Dumpy level

Levelling staff

Theory

Profile leveling is the process of leveling along a fixed line to determine the elevations of the ground surface along that line. The fixed line is generally the centre line of a highway, railway, canal, sewer, etc. The profile leveling is done to determine the undulations of the ground surface. Cross-sectioning is required to determine the levels across the line along which profile leveling is done. Profile leveling should be commenced from a bench mark and should end at a bench mark, as far as possible. When the ground surface does not have many undulations, the intermediate points are fixed at a uniform interval. If the ground surface is irregular and there are abrupt changes in the ground surface, the interval may be non-uniform.

Aim

To determine the reduced level of various points

To find out difference of elevations of two points

Materials required

Dumpy level

Levelling staff

Aim

To study the levelling instruments

To practice the simple leveling

Leveling

Leveling is a method of surveying used for determination of the difference of elevations or levels of various points on the surface of the earth. The elevation of a point is its vertical distance above or below a reference level, called datum. Most commonly used datum is the mean sea level (M.S.L). Leveling is required to determine the undulations of the earth’s surface for topographic mapping. Leveling is needed for the design of highways, railways, canals, sewers, etc. Leveling is essential for the layout of construction projects, locating the excavation levels and for the control of various elevations in buildings, bridges, dams etc. The results of the leveling can be used to determine the catchment area, volume of the reservoir and the area submerged by a reservoir.

Aim

To determine the area of given field by intersection method of plane table survey.

Materials required

Tripod

Plane table

Plumbing fork

Level tube

Magnetic compass

Alidade

Measuring tape

Ranging rods

Drawing sheet

Pins, pencil and eraser

Aim

To determine the area of given field by intersection method of plane table survey.

Materials required

Tripod

Plane table

Plumbing fork

Level tube

Magnetic compass

Alidade

Measuring tape

Ranging rods

Drawing sheet

Pins, pencil and eraser

Aim

Studies on plane table survey instruments

To determine the area of given open field by radiation method of plane table survey.

Plane table survey

Plane table surveying is a simple method of surveying for determination of area of field. The plane table survey is quite suitable for plotting small-scale and medium scale mappings directly in the field where great accuracy is not required. It is also used for plotting the topographical maps in the field. The plane table survey is generally more rapid and less costly than other types of survey.

In this survey, a plane table is used for taking the measurements and for plotting the plan in the field. Plane table surveying is a method in which the field observations and plotting of the plan proceed simultaneously. The plotted map can be compared with the actual features in the field. Errors in measurements and plotting can be easily detected in the field by taking suitable check lines.

Aim

To determine the area of the field by intersection method using a prismatic compass.

To determine the included angle of the closed polygon.

Materials required

Prismatic Compass

Tripod

Measuring tape

Arrows

Ranging Rods

Aim

To determine the area of the given field by radiation method using a prismatic compass.

Materials required

Prismatic Compass

Tripod

Measuring tape

Arrows

Ranging Rods

Aim

To identify different parts of prismatic compass and to know their functions.

To practice of taking the angular measurement.

Compass survey principle

Compass surveying is a branch of surveying in which directions of survey lines are determined with a compass and the lengths of the lines are measured with a chain or tape. In practice, the compass is generally used to run a traverse. In compass surveying, a traverse consists of a series of straight lines connected together to form an open or closed polygon as shown in Fig.44.1. The points A, B, C, D and E defining the ends of the traverse lines are called traverse station or traverse points. The lengths of the traverse lines are measured with a chain or tape. At each traverse station, where the traverse lines meet, the angle is measured with a compass.

Theory

Area computation is an important part of surveying. The term ‘Area’ is meant the projected area on a horizontal plane. The area is computed from the following methods: (i) Graphical method (ii) Instrumental method and (iii) Use of formulae. In graphical method, the area can be computed by dividing the whole area either into triangles or squares. The area of individual triangle is computed from base and the altitude and summation of individual area gives the total area. A tracing paper is divided into number of small squares is placed over the plan. The number of complete squares within the boundary is counted. The squares more than half are counted as full squares and those less than half are neglected. The total number of squares multiplied by the area of each square gives the total area of the field. In instrumental method, the planimeter is used to measure the area of a plotted plan. In use of formulae, computation of area by formulae depends on the shape of the field.

Aim

To find out the area of given field by cross-staff survey method

Materials required

Cross-staff

Metric chain

Measuring tape

Ranging rods

Chain pins

Aim

To determine the area of given field by triangulation method of chain survey

Materials required

Metric chain

Measuring tape

Ranging rods

Chain pins

Aim

To measure horizontal distance on the level ground using chain

Materials required

Chain

Ranging rods

Chain pins

Field note book