SWC 211 Soil and Water Conservation Engineering
Department of Soil & Water Conservation Engineering
DUMPY LEVEL
HEIGHT OF COLLIMATION AND RISE & FALL METHOD
Aim:
To determine to difference in elevation between the given points adopting height
of collimation (HC) and rise & fall method.
Instruments required:
Dumpy Level with stand, Telescopic Metric Staff
HEIGHT OF COLLIMATION
Procedure:
Compound leveling in also called as differential or fly leveling. This leveling is
resorted under the following circumstances.
1. When the two stations are quite apart beyond the reach of telescope.
2. Difference in elevation is too great.
3. There is an obstacle between the two stations.
Under the above circumstances, a number of settings of the instrument are
required. We have to start the levels from one station and carry out upto the end station
continuously. Hence we have to conveniently install some change points.
After setting the instruments, the first reading we have to take it on a station of
known elevation, called as Bench Mark and the sight is known as ‘Back Sight’. The
reading taken on the staff held at last point whose elevation is to be determined, just
before shifting the instrument is called ‘Fore Sight’. Normally the back sight distance
and fore sight distance should be approximately equal to eliminate instrumental errors.
The sights that are taken on the intermediate stations are called ‘Intermediate
Sights’ normally. Changed point is a point where we take two readings one fore sight,
from the previous station and one back sight from the successive station.
Suppose we want to determine the difference in elevation between P & Q stations
which are quite apart, we have to select number of change points as required. As shown
in figure first set the instrument at O1, and take a back sight on station P1 of known
elevation. Then keep the staff at CP1 and take a foresight. Then shift the instrument to
station O1 and set it. Then take a back sight to CP2. Similar way repeat the procedure till
