SMALL DAMS

Chapter IV
It can only be completely eliminated for very small dams where H 2 V < 100, provided
that the foundation is sufficiently watertight. The thickness of the layers must be
sufficient to discharge the foreseen flow with a minimum thickness for each horizontal
granular layer of 0.20 metre (drain and filter).
If there is a relatively impermeable surface layer in the foundation, covering a much
more permeable layer with its upper surface at a depth of less than H/3, it is
recommended that decompression 1 wells (in general with piezometers) be drilled at
the downstream base of the dam, spaced 10 to 25 metres apart. The decompression
wells must be protected with a filtering material from the surrounding relatively
impermeable material.
FILL DAM DESIGN
Depending on what usable materials are available, the fill dam will be one of the
three types specified above, (pp. 67 and 70) homogeneous, zoned, or with manmade
watertightening.
CROOS-SECTION, CREST WIDTH, FREEBOARD
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Maximum recommended slopes are 1/2. However, steeper slopes may be designed
when coarse materials without fines are used (gravel, pebbles, boulders).
The crest width L is generally determined by one of the following formulas where H is
the height in metres:
L = 1/3 H
L = 1,65 H 1/2
L = 3,6 H 1/3 - 3
where L = 3 m minimum, in order to permit movement of machinery.
Compacting the last layers may require a larger width.
Crest width also depends on how that crest is to be used, e.g. for a road. For zoned
dams, it may also depend on the number of zones at the crest.
The following minimum widths are proposed:
H 2 V < 100 100 to 300 > 300
L minimum 3 m 4 m 5 m
Table 2 - Minimum crest width
1. Decompression wells must be accessible for cleaning.