Aquaculture Engineering

Practical - 5
Experiment No 1 - Determination of elevation of different points

Aim
To find out the elevation (reduced levels (R.L.)) of different points shown on the ground with respect to a given arbitrary bench mark (B.M.) Apparatus: Dumpy level with accessories, Levelling staff etc.

Procedure

• Set up the instrument at a convenient place so that all the points and Bench mark is visible properly.
• Do the “Temporary adjustments” properly and make the line of sight exactly horizontal.
• First take a back sight by focusing the telescope towards the staff held on the bench mark, the R.L. of which can be assumed suitably (50 m, 100m) and enter the staff reading in the back sight (B.S) column of the level book.
• Calculate the elevation of the line of sight as height of instrument (H.I) H.I. = R.L of B.M + B.S
• Now focus the telescope towards the staff held on different points on the ground and note down their corresponding readings and enter them in the intermediate sight (I.S) column of the level book. The reduced levels of these points can be calculated as R.L. of given point. R.L. = H.I – I.S. or F.S.
• The last reading should be entered in the fore sight (F.S) column, so as to have a proper check on the accuracy of the work. However R.L. is calculated in a similar manner.