Levelling and surveying methods are also used for measurements of any type of field survey work. Sometime, less accurate methods can also be used for this survey work than for water-level recording stations, although the techniques are almost common.

Definition  of different Levelling

  • Differential levelling is termed as to such method of measuring directly with a graduated level staff the vertical difference in elevation between two or many points.
  • Precise levelling is a basically authenticate method of differential levelling which actually uses highly accurate levelling machine and with a excessive rigorous observing protocol than general type of engineering levelling process. The target is  to achieve high orders of accurate measurement such as 1 mm per 10000 mm.
  • Level surface is a surface which is anywhere tangential perpendicular to the direction of the gravitational force. The example of the level surface is a completely steady still lake.

  • Datum level is an assumed level surface upon which elevations are referred. The very most common surveying datum is mean sea-level (MSL), at any location of earth but in hydrological work it is basically just concerned with levels in a local surrounding work area, most of the time we use:

a) An assumed datum level , which is established by providing a benchmark of an assumed value ( 100.00 m) to which all levels in the local area will be reduced by measurment.

  • Reduced level is defined as the vertical distance between any survey point and the adopted level datum.