SMALL DAMS PETITS BARRAGES

Fig. 7.2 – Section through an embankment showing rehabilitation with a positive effect
both on stability, piping control and seepage control
Furthermore, to extend an earthfill core a High Density Polyethylene Sheet may be used
to raise the core by anchoring it in a trench excavated in the top of the core. This method is
especially applicable where ice conditions occur where the top of the core can be damaged by
low temperatures.
7.3.1.3 Protection of Embankment from Erosion During Overtopping
Erosion as a result of overflow during flood events is a principal cause of embankment
dam failure. Consequently, the approach to solving this problem has been not to allow
overtopping. Preventing overtopping of existing dams to accommodate today’s current
estimates of inflow floods often requires costly modifications to the spillway or raising of the
embankment. For a large number of potentially unsafe dams with inadequate spillway
capacity, permitting overtopping during large or infrequent floods would result in significant
benefits.
If overtopping of an embankment is allowed, the owner of the dam must ensure that the
downstream slope is sufficiently protected to prevent erosion. Two erosion protection systems
i.e. articulated concrete blocks (ACB) and roller compacted concrete (RCC) are often used
successfully for the protection of the downstream face of embankments during floods.
(a) Articulated Concrete Blocks
An auxiliary spillway constructed with small cable tied concrete blocks system laid on a
geotextile base is capable of withstanding velocities less than 8 m/s and provides a low cost
alternative to reinforced concrete, as can be seen in Figure 7.3 and 7.4. Care should be taken
to design for lower velocities of up to maximum 5 m/s (say) to accommodate deteriorating (or
ageing) conditions during the life of the dam.
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