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Diameter

in metres

Depth in metres

1,2 m

1,5 m

1,8 m

2,1 m

2,4 m

3

8 600

10 760

12 900

15 000

17 200

3,6

12 200

15 300

18 300

21 800

24 400

4,2

16 650

20 800

25 000

29 200

33 300

4,8

21 700

27 200

32 600

37 900

43 400

6

34 000

42 500

51 000

59 400

68 000

7,5

53 000

66 000

75 600

92 700

108 000

9

76 500

95 500

114 700

134 000

150 200

10,5

104 000

130 000

155 800

182 000

207 900

12

126 000

170 000

203 500

237 000

271 000

13,5

172 000

241 000

257 500

300 000

344 000

15

212 000

266 000

318 200

372 000

425 000

16,5

257 000

321 000

385 000

450 000

514 000

18

306 000

382 000

458 000

534 000

610 000

ESTIMATED CAPACITY OF RESERVOIRS (IN LITRES)

Example: 1 500 (m

2

) x 5 (m) x 0,4 = 3 000 m

3

To calculate the capacity of your dam in mega litres (ML), divide the volume in m

3

by 1 000

e.g. 3 000 m

3

/ 1 000 = 3 ML

Gully dams

You can estimate the capacity of small gully storages using this formula:

Example: Water level height up bank = 2 m

Length = 20 m, width = 10 m

Volume of excavation = 100 m

3

Volume = (2 x 20 x 10 + 100)/5 = 100 m

3

Width and depth are measured at the embankment site and length is the distance water will

back-up (you will need to add the volume of any excavations made below water level to give

the total storage capacity). If the excavation volume is not known, substitute the depth of water

at the deepest point as an approximation for the depth.

Depth

One way to determine dam depth is to row out into the dam and lower a weighted line over the side.

When the line is vertical, measure the length of the line needed to reach the bottom. Alternatively,

use a pole with distances marked on it. You will need to do this at a number of places across the

dam to find the deepest point.

An alternative for smaller dams, or if no boat is available, use a fishing line with a sinker on the

bottom with a float attached. The line is cast out repeatedly, with the float gradually adjusted until it’s

not quite floating on the surface. The distance between the float and the sinker will be the depth at

that point in the dam. Again, you will need to do this at a number of places across the dam.

Reference:

Rob Dimsey. December 2006.

Vegetable-matters-of-fact

, Number 43

Volume = (width x maximum depth x length) / 5 (where 5 is the correction factor)

7

Conversion tables and formulae

8

GRAIN GUIDE

2018

Relevant