Contents preface (VII) introduction 1—37

(viii) Function of the Reservoir
The function of the reservoir determines the allowable water loss due to seepage through the embankment and foundation. Accordingly, the embankment section may be relatively more impervious (for conservation reservoirs) or relatively more pervious (for flood control reservoirs).
In hydroelectric projects, the upstream face of the dam will be subjected to a ‘‘sudden drawdown’’ condition which may necessitate the provision of a flatter upstream slope.
(ix) Earthquake Activity
In regions of seismic activity, the designer may have to adopt more conservative design features such as better filters, downstream drains of larger capacity, thicker cores of more piping resistant materials, flatter side slopes, longer construction time, and so on.
15.2.2. General Design Criteria for Embankment Dams

The major causes of failure of an embankment dam are overtopping, piping, and earth slides in a portion of the embankment and its foundation (due to insufficient shear strength). Of these, overtopping is the most common cause of complete and catastrophic failure of an

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embankment dam. The design of an embankment dam must meet the following safety requirements (6, 3):

(i) There is no danger of overtopping. For this purpose, spillway of adequate capacity and sufficient freeboard must be provided.
(ii) The seepage line is well within the downstream face so that horizontal piping may not occur.
(iii) The upstream and downstream slopes are flat enough to be stable with the materials used for the construction of embankment for all conditions during construction, op-eration, and sudden drawdown.
(iv) The shear stress induced in the foundation is less than the shear strength of the foundation material. For this purpose, the embankment slopes should be sufficiently flat.
(v) The upstream and downstream faces are properly protected against wave action and the action of rain water, respectively.
(vi) There should not be any possibility of free passage of water through the embank-ment.
(vii) Foundation seepage should not result in piping at the downstream toe of the dam.
(viii) The top of the dam must be high enough to allow for the settlement of the dam and its foundation.
(ix) The foundations, abutments, and embankment must be stable for all conditions of operation (steady seepage and sudden drawdown) and construction.