SMALL DAMS PETITS BARRAGES

The homogeneous dam is recommended only where the lack of free-draining materials
make the construction of a zoned embankment uneconomical, with the further qualification
that for storage dams the homogeneous dam must be modified to include internal drainage
facilities.
Even in the construction of a homogeneous embankment, there is likely to be some
variation in the nature of borrow material. It is important that the coarse and more pervious
material be placed at the outer slopes to approach, as much as possible, the advantages of
zoned embankment. It is also important to avoid segregation of the larger particles when the
fill is dumped. Segregation leads to the formation of layers of much greater permeability than
the other embankment; these layers tend to form drainage channels for percolating water and
to increase the possibility of piping.
Because of the possibility of oversights during construction and of cracking, dispersive
soil, etc., as discussed previously, consideration should be given to providing an inclined filterdrain
to intercept any seepage along defects in the embankment.
The recommended slopes for small homogeneous earthfill dams are shown in Table 6
for detention and storage dams on stable foundations with and without rapid drawdown as a
design condition. Where more than one soil classification is shown for a set of slopes, the
table indicates that the dam can be constructed to the slopes shown by using any of the soil or
combinations thereof.
Zoned embankments
The zoned embankment dam consists of a central impervious core flanked by zones of
material that are considerably more pervious. The recommended slopes for small zoned
embankment dams are shown in Table 5.23. An excellent example of a zoned dam from the
1950 era is Carter Lake Dam. An excellent example of a more recent era is Ute Dam Dike.
This type of embankment should always be constructed where there is a variety of soils readily
available because its inherent advantages lead to savings in the costs of construction. Three
major advantages in using zoned embankments are listed below:
� Steeper slopes may be used with consequent reduction in total volume of
embankment materials;
� A wide variety of materials may be used;
� Maximum use can be made of material excavated from the foundation, spillway,
outlet works, and other appurtenant structures.
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