Some Instruments Used for Measuring Distance:

Instruments Used for Measuring Distance:

1. Chain 

1. Metric chain
2. Steel band chain
3. Günter’s Chain
4. Revenue Chain
5. Engineers chain

2. Arrows (chain pins)

3. Tapes

1. Cloth or linen Tape
2. Metric Woven Metallic Tape
3. Metric steel Tape
4. Invar tape.
5. Synthetic Tape.
6. Wooden pegs.

5. Ranging Road.

6. Ranging Poles.

7. Offset Rod.

8. Laths

9. Whites

10. Plumb Bob

1. Chain

The chain is composed of 100 or 150 pieces of galvanized mild steel wire 4mm in diameter called links. The end pf each link are bent into a loop and connected together by means of three oval rings. The ends of the chain are provided with brass handles for dragging the chain on the ground. The length of link is the distance between the centers of the two consecutive middle rings. The end links includes the handles. Metallic tags or indicators are fixed at various distinctive of the chain to facilitate quick reading.

a. Metric surveying chains:

The chains are made in lengths of 20 and 30 meters. To enable the reading of factious of a chain, tallies (tags) are fixed at every five meter length and small brass rings are provided at every meter length. To facilitate holding of the arrows in position with the handle, a groove is cut on the out side surface of the handle. The handle joints are flexible. the tallies used for marking the distances in a metric chain are marked with letters ‘Me’ and ‘m’.

b. Steel Band Chain:

It consists of a ribbon of steel with bras handle at each end. It is 20 or 30long and 16 mm wide. It is wound on an open steel cross or on the metal reel in a closed case. The graduations are etched as meters decimeters, centimeters on one side and 0.2 m links on the other. Brass tallies are fixed at every 5 m length of the band.

c. Günter’s Chain:

It is 66 fit long and is divided into 100 links. Each link is 0.66 ft long. It is very convenient for measuring distance in miles and furlongs. Also for measuring area and when the units of area is an acre

d. Revenue Chain:

It is commonly used for measuring fields in cadastral survey. It is 33 ft long and divided into 16 links. Each link is 2.0625 ft long.

e. Engineer’s chain:

It is 100 ft long and it is divided into 100 links. Each link is 1 ft in a length. Used in all Engineering surveys.

2. Arrows (chain pins):

They are also called as marking or chaining pins and are used to mark the end of chain during the process of chaining. They are made up of good quality hardened and tempered steel wire of 4mm in diameter. The arrows are made 400 mm in length. They are pointed at one end of inserting in to the ground. The other end is in to a ring.

3. Tapes:

a. Cloth or Linen Tape:

Used for taking subsidiary measurements, such as offset. It is very light and handy. It is easily affected by damp. If wet it shrinks. It stretches easily and likely to twist.

b. Metric Woven Metallic Tape:

They are available in 2, 10, 30, and 50 meters. The tape is made of yarn and metal wire. A metal ring is attached to the outer end of tapes. The length of the tape includes the metal ring. At every centimeter a black line 8 to 10 mm in height is drown. Every 5 centimeters is marked with an arrow in black. Every decimeter and meter is marked with a back line extending over the full width of the tape/ the graduation marks at every decimeter and meter are numbered with black and red figures, respectively.

c. Metric Steel Tape:

Tape is available in 1, 2, 10, 30, and 50 meters. The tape is of steel or stainless steel. The outer end is provided with a ring. The length of the tape includes the metal ring. The tape is marked with a line at every five millimeters, centimeters, decimeters, and meter. Every decimeter and meter shall be marked with Hindu Arabic numerals in bold. When the button release devised is pressed, the tape automatically rewind in to the case.

d. Invar Tape:

For highest precision work the invar tape in used. It is made of an alloy of steel and nickel (36%).

It is 6 mm wide and may be obtained in length of 30m and 100m. It is not calibrated through its length but has terminal lines. Each terminal division has ten 1 mm division. It is very expensive.

e. Synthetic Tape:

The tapes are manufactured of glass glass fiber having PVC coating. They are graduated every 10 mm and figured every 100 mm. Meter, figures are shown in red. They are convenient for measuring shorts lengths.

Instruments for marking stations:

1. Wooden Pegs:

These are used to mark the positions. They are made of hard timber and tapered at one end. They are usually, 2.5 cm square and 15 cm long. But in soft ground 40 to 60 cm long and 4 to 5 cm square is suitable. They should be driven in the ground with about 4 cm lengths, projecting above the ground.

2. Ranging rods:

Used for making the positions of stations and for ranging. They are made of seasoned timber of teak, blue pine, sisov or deodar. They are circular or octagonal in cross section of 3 cm diameter. Lower shoe is 15 cm long. They are made in two sizes as 2 meters and 3 meters and are divided in to equal parts each 0.2 m long. They are painted alternatively black and white or red and white. Now a day instead of timber, mild steel hallo pipes are used.

3. Ranging Poles:

Similar to the ranging rods but are heavier, they vary in length from 4 m to 6 m or more. Used in the case of very long lines.

4. Offset Rod:

Similar to the ranging rod, they are usually 3 m long and is divided into parts each 0.2 m length. Top is an provided with an open ring for puling or pushing the chain through a hedge. It has two short narrow vertical slots. It is used for aligning short offsets.

5. Laths:

Useful for ranging long lines, also used over uneven ground where the ranging rod is not visible due to obstructions, they are light, cheap, being white; they are easily visible at a great distance. Unusually 1.0m long

6. Whites:

When the ranging rod is not available or insufficient, whites are used. These are thin strip of bamboo and 40 cm to 1 m in length. One end is sharp and the other end is split for inserting pieces of white papers. They are also useful for temporary marking of counter points.

7. Plumb Bob:

The plumb bob is required when measuring the distance along slopes in order to transfer points to the ground. It is also used for testing the verticality of ranging poles.

Difference between Plane and Geodetic Surveying

Difference between Plane and Geodetic Surveying

Plane Surveying	Geodetic Surveying
Curvature of the earth is not taken in to consideration	In this curvature of earth is considered.
In plane Surveying, line joining any two points of triangle formed by any three points is considered as straight line and plane triangle are assumed to be plane angles.	In geodetic surveying line joining two points of triangle formed by three points is considered as curved line of spherical triangle and angles of triangle are considered as spherical angles.
This survey is done on smaller area less than 250km2	This survey is done on large area greater than 250 km2
Required accuracy is competitively low.	High accuracy is required
Simple methods and instruments can be used as the required accuracy is low.	Very refined methods and instruments are used.

Lesson Note On Cross Staff Survey

Cross Staff Survey
 

This type of survey is undertaken to locate boundaries of a field or a field or plat and determinations of its area.

Principle:

The principle of the survey is to divide the given area in to no of right angled triangles and trapezoids and to calculate and plot the areas of triangles and trapezoids.

Instruments/Material Required:

Two Chains, arrows taps, ranging rods, cross-staff and drawing material

Procedure:

Two chains are usually provided one for measuring distance along the chain line and other for measuring the offsets. The cross staff is used to set out the perpendicular directions for offsets. In this survey, the base line runs through the center of the area, so that the offsets are left or right side of base line are fairly equal. To check accuracy length of the boundary lines may also be measured. After the field work is over, the survey is plotted to a suitable scale.

Calculations of Field Area:

By this method of survey, the field as divided in to right angled triangles and trapezoids are calculated as under:

1. Area of right -angled triangle = ½ base x Height.
2. Area of trapezoid= sum of parallel sides/2 x Height.

Add the areas of all the triangles & trapezoids and sum is equal to the total of a field.

The computations for area should be written in a tabular from as given below.

TABLE

Serial no.	Figure	Chain age in m	base in m	Offset in m	Mean offset in m	Areas in m2 A=col. 4.xcol.6
1	2	3	4	5	6	7
				Total		m2

Lesson Note On Principle of Leveling:

Principle of Leveling:

1. Simple leveling:

It is the simplest operation in leveling when it is required to find the difference in elevation between two points both of which are visible from a single position of the level. Suppose A and b are two such point and level is set up at 0, approximately mid way between. A and B but not necessary on the line joining them, after finding the reading on point A and point B, let the respective reading on A and B be 2.340 and 3.315 difference between them is 3.315-2.340=0.795 m.

2. Differential leveling:

This method is used in order to find out the difference in elevation between two points.

1. If they too apart.
2. If the difference in elevation between them is too great.

In such cases it is necessary to set up the level in several positions and to work in a series of stages. The method of simple leveling is employed each of the successive stages. The process is also known as compound continues leveling.

Methods of Determination of the Reduced Level of Point from the Staff Reading

1. Collimation Method:

It consist of finding the elevation of the plane of collimation ( H.I.)  for every set up of the instrument, and then obtaining the reduced level of point with reference to the respective plane of collimation.

1. Elevation of plane of collimation for the first set of the level determined by adding back side to R.L. of B.M.
2. The R.L. of intermediate point and first change point are then obtained by starching the staff reading taken on respective point (IS & FS) from the elation of the plane collimation. [H.I.]
3. When the instrument is shifted to the second position a new plane collimation is set up. The elevation of this plane is obtained by adding B.S. taken on the C.P. From the second position of the level to the R.L.  C.P. The R.L. of successive point and second C.P. are found by subtract these staff reading from the elevation of second plane of collimation Arithmetical check

                           Sum of  B.S. – sum of F.S. = last R.L. – First R.L.

2. Rise and Fall Method:

It consists of determining the difference of elevation between consecutive points by comparing each point after the first that immediately preceding it. The difference between there staff reading indicates a rise fall according to the staff reading at the point. The R.L is then found adding the rise to, or subtracting the fall from the reduced level of preceding point.

Arithmetic check

Sum of B.S. – sum of F. S. = sum of rise – sum of fall = last R. L. – first R.L.

Booking the staff readings:

The following points may be kept in mind entering the readings in a level field book.

1. The reading should be entering in the respective columns and in order their observation.
2. The first page is always a back side and the last one is ways a foresight.
3.  It a page finished with an IS reading, the reading is entered in the IS and FS columns on that page and brought forward to the next page.
4. The FS and BS of any change point are entered in the same horizontal line.
5. The RL of the line of the collimation is entered in the same horizontal line.
6. Bench marks and change points should be clearly described in the remark column.

Specimen pages of level field book: Collimation system

Station	Distance (cm)	Reading		RL of plane of collimation [HI]		Reduced level			Remarks
		BS	IS	FS
A								B.M.
B
C
Arithmetic check	Sum of BS-Sum of FS=  Last RL-1st -RI

Specimen pages of level field book: Rise & Fall System

Station	Distance(m)	Reading			Rise	Fall	Reduce level	Remarks
		BS	IS	FS				B.M
A
B
C
	Check :	BS-FS=Rise-fall=last RL -1st-Rl

Classification of leveling

Classification of leveling

1. Different leveling:

It is the operation of leveling to determine the elevations of points. Some distance a part or to establish bench marks.

2. Check leveling:

It is the operation of running levels for the purpose of checking the series of levels, which have been previously fixed. At the end of each day’s work, a line of level is run, returning to the starting point of that day with a view to check the work done on that day.

3. Profile leveling:

It is the operation in which the object is to determine the elevation of points at known distance apart along a given line, and thus to obtain the accurate out line of the surface of the ground. It is called the longitudinal leveling or sectioning.

4. Cross sectioning:

It is the operation of leveling to determine the surface undulation or outline of the ground transverse to the given line and on either side of it.

5. Reciprocal leveling:

It is then method of leveling in which the difference in elevation between two points, accurately determined by two sets of observation when it is not possible to set up the level midway between the two points.

6. Barometric leveling:

It is the method of leveling in which the altitudes of points are determined by means of a barometer, which measures atmospheric pressure.

7. Hypsometry:

It is the method of leveling in which the heights of mountains are found by observing the temperature at which water boils.

8. Trigonometric leveling:

It is then process of leveling in which the elevations of points are computed from the vertical, angles and horizontal distance measured in the field.

Steps in Leveling:

When the level is set up and correctly leveled, the lines of collimation will be horizontal. When the telescope is rotated about its vertical axis, it will revolve in a horizontal plane known as the plane of collimation. Therefore all staff readings taken with the telescope will be vertical measurements made downwards from this plane. There are two essentials steps in leveling.

1. To find the elevation or R.L. of the plane of collimation (H.I) of the level by taking a back sight on a bench mark.
2. To find the levitation of R.L. of any other point by taking a reading on the staff held at the point.

Height of Instrument (H. I.) = R.L. of the plane of collimation
                                         = R.L. of B.M. + B.S.
                R. L. of point    = H.I.-F.S.
                                         = H. I. – I.S.

It is the necessary that after every back side. [However many intermediate sight may be], there must be a foresight. Leveling should always commence from a permanent common bench mark and end on a permanent bench mark.

Lesson Note On Introduction to Runoff

Introduction to Runoff

Over the land surface, for the generation of runoff, the primary source of water is Rainfall. A part of rainfall that intercepted by the vegetation, buildings and other objects and prevented to reach them on grand surface is called as interception. Part of rainfall stored in the surface depressions which in due course of time gets infiltrate or evaporated is referred as depression storage [ Initial detention).

When these entire loses are satisfied then excess rainfall moves over land surface is known as overland flow and draining the same into channel or stream is termed as “Runoff”.

Definition:

Runoff:

Runoff is that portion of the rainfall or irrigation water [or any other flow]. Applied which leaves a field either as surface or as subsurface flow.

When rainfall intensity reaching the soil surface is less than the infiltration capacity, all the water is absorbed in to the soil.  As rain continues soil becomes saturated and infiltration capacity is reduced, shallow depression begins to fill with water, then the over flow starts.

Surface detention/ Detention storage:

The amount of water on the land surface in transit to words stream channels is called detention storage/surface detention.

Surface Runoff:

The runoff which travels over the ground surface to the channels of watershed

Subsurface Runoff:

The portion of unfiltered water which penetrated to shallow depth travels laterally and is intercepted by channels.

Runoff Cycle:

It is that part of hydrological cycles which galls between the phase of precipitation and its subsequent discharge in the stream channels or direct return to the atmosphere through evaporation and evapotranspiration.

Conditions Associated With Runoff Cycle:

1. This refers to the end of day period and beginning of the intense and isolated storm.
2. It is the stage after beginning of rainfall causes the overland flow, base flow, and development of channel storage.
3. It refers to the condition approaching the end of all isolated intense storm.
4. This is the stage indicating after end of rainfall where rainfall causes the overland low, base plot and development of channel storage.

Types of Runoff:

1. Surface runoff
2. Sub-surface runoff
3. Base flow

a. Surface Runoff:

That portion of rainfall which enters the stream immediately after the rainfall. It occurs when all loses is satisfied and rainfall is still continued and rate of rainfall [intensity] in greater than infiltration rate.

b. Sub-Surface Runoff:

That part of rainfall which first leaches into the soil and moves laterally without joining the water table, to the stream, rivers or ocean is known as sub-surface runoff. It is usually referred is inter-flow.

c. Base flow:

It is delayed flow defined as that part of rainfall, which after falling on the ground the surface, infiltrated into the soil and meets to the water table and flow the streams, ocean etc. The movement of water in this is very slow. Therefore it is also referred a delayed runoff.

Total runoff = Surface runoff + Base flow (including subsurface runoff)