Terrain assessment, drainage and erosion - Geotechnical Investigation and Design Tables - page 196

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Compacted Clay linings at the bottom of a channel typically 0.5m thick can
reduce the seepage by 80% to 50% for very gravelly soils to fine sand materials,
respectively.

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Geosynthetic Clay Liners (GCLs) and Geomembranes can also be used with
250mm minimum soil cover.

Figure 15.3 Canal issues to be assessed during investigation.

15.17 Comparison between open channel flows and seepages
through soils

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Hydraulic Gradient of 0.01 in all cases.

Table 15.17 Comparisons between flows in open channels and pipes and seepage through soils and
aggregates, Cedergren (1989).

Flow medium Effective channel Flow (m 3 /s) Area (m 2 ) for discharge

diameter of 50 mm pipe

Smooth channel 24 m 2R 12,000

=

Smooth pipe 2.4 m d 20 =

0.30 m d 0.1 =

50 mm d 4 10 − 4 50 mm pipe (0.2 m 2 ) = ×

25 mm to 40 mm gravel 5 mm # 4 10 − 4 0.1 ×

12 mm to 25 mm gravel 2.5 mm # 1 10 − 4 0.3 ×

5 mm to 10 mm gravel 0.75 mm # 2 10 − 5 2.0 ×

Coarse sand 0.25 mm # 3

×

10 − 6 17

10 − 8 10 3

Fine sand, or graded filter aggregate 0.05 mm # 3

×

1.7

×

10 − 11 10 6

Silt 0.006 mm # 3

×

1.7

×

10 − 13 10 8

Fat clay 0.001 mm # 3

×

1.8

×

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10 − 3 square metre area. # Per 0.93 ×