SMALL DAMS PETITS BARRAGES

3.1 INTRODUCTION
3. SAFETY OF SMALL DAMS
In this chapter are discussed the peculiarities and conditions affecting the safety of small
dams. In comparison with large dams most dam engineering criteria and practices apply to
small dams. The following differences between large and small dam practices are applicable:
Lower water, sedimentation and gravitational loads are applicable and therefore
lower stresses and strains in the structures and on the foundation are to be taken
into consideration in the design;
Economics play a very important role because decisions are taken with financial
constraints as background. This could lead to design criteria and construction
methods with higher risk, more maintenance problems and in some cases to
catastrophic failure.
The time required by engineers for small dam design and construction monitoring is
as time consuming as for large dam activities, although due to cost constraints
significantly less time is approved for technical services by clients of small dams.
This leads to savings in investigation, design and site monitoring costs, which leads
to substandard designs and construction quality achieved during construction.
Proper designs must therefore be done and construction monitoring ensuring quality
must not be limited.
Foundation and construction materials investigations are normally limited due to
financial constraints, with normally higher cost to the structure due to unknown
conditions. Proper investigations tailored to the specific foundation and construction
materials for the required dams are therefore necessary.
Flood Hydrological investigations are sometimes limited with catastrophic
consequences if the dams are overtopped.
Normal seepage rates may impact on the yield of small dams. And low water depth
makes small reservoirs more sensitive to evaporation. Higher care must therefore be
taken to seepage control (reduction) measures.
Often inexperienced small contractors are used to construct small dams. These
contractors have limited resources and sometimes use “farm dam” practices to
construct with a low quality structure and poor performance.
Dambreak floods caused by smaller dams are lower in size due to the lower water
head and water volume in the dams. The potential loss of life and damages are
lower. Due to this, lower design standards are applied for many aspects e.g. spillway
sizing. Despite this fact, the number of victims is generally significant as a
consequence of the great number of small dams and the large number of failures
during extreme floods.
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