Land and Watershed Management - Practices of Irrigation and On-farm Water Management - page 210

Fig. 6.2 Schematic of grid
method

80.5 90

85 88.5

to squares of 3, 6, 15, 30, or more meter depending on the project size and the accu-
racy desired. For each grid square, final elevations are established for each corner
of every grid square (Fig. 6.2 ) . These are subtracted from the existing elevations at
the same location to determine the depth of cut or height of fill at each corner. For
each grid square an average of the depths/heights of the four corners is multiplied by
the area of the square to determine the volume of earthwork associated with the grid
area. The total earthwork volume for the project is calculated by adding the volumes
of each grid square in the excavation area. Volumes are calculated as follows:

V = (( D 1 + D 2 + D 3 + D 4 ) / 4) × A (6.3)

where

volume (m 3 )

V =

area of the grid square (m 2 )

A =

depth of cut/fill at each grid corner (m)
Total volume, V T = V i

D =

End Area Method
The End Area Method (EAM) utilizes the areas of parallel cross-sections at regular
intervals through the proposed earthwork volume. The cross-sections can be spaced
at intervals of 10, 20, 50, or 100 m depending on the size of the site and the required
accuracy. They are aligned perpendicular to a baseline that extends the entire length
of the excavation area (Fig. 6.3 ) . There are several types of cross-sections, which
can be drawn by hand or generated by CADD. For flat terrain or level excavation,
a level section is suitable. Irregular sections are used for most excavations in rough
terrain. Cross-sectional areas are calculated with either the triangular area method
described above (if the cross-sections are geometrically simple) or by the Length
Interval Method for more complicated cross-sections. Unit volumes are calculated
as follows: