SMALL DAMS

Chapter III
!"economic, as the viability of the project must be studied according to its purpose, or
possibly purposes (irrigation, increased dry weather river flow and pollution control,
flood routing and protection from flooding, tourism and recreation);
!"local development, as a dam project is sometimes an opportunity to initiate reflection
on the future of rural areas in difficulty (revival of the local economy by attracting
vacationers, etc.).
Although it may seem logical to conclude on the geological feasibility of the project
before initiating these studies, their growing importance and the time needed to carry
them out often mean that they must be initiated simultaneously and sometimes even
that geological studies must be suspended until these other feasibility studies have
reached a favourable conclusion.
This last point reinforces the importance of the surface geology study mentioned above
(see Geological Surface Study, p. 49) and is the reason behind the recommendations
made concerning the potential consequences of an overly optimistic diagnosis in
case of any doubt.
It is in this stage of study (feasibility) that the essential characteristics of the site should
be known and, as far as possible, major problems that could lead to a decision
against the project should be detected.
Although there is generally a technical solution to any problem encountered, the cost
may in some cases be disproportionate versus the dam's economic advantages and
thus render it unfeasible.
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Methodology of the geological feasibility study
Geological feasibility studies require the use of various techniques according to the
size of the dam, the nature of the geological context and/or the habits of the geologist.
The methodology recommended hereafter for geological feasibility study of dams of
the type addressed in the present volume therefore does not pretend to be universal
and must often be adapted to the specific features of the case at hand.
A typical feasibility study could be conducted in whole or in part in the following stages:
STAGE 1: Desk study
For any dam, even the smallest, it is of great interest to consult existing geological
maps and the accompanying documentation. For dams about twenty metres
high or more, it can be of interest to search within regional geological literature
(articles in specialised journals, theses, monographs, notes to geological maps)
for any previous studies done on the region of the site under study or simply
mentions of details that could be useful in understanding the context and the
geological history of the area (location and description of outcroppings, of fossilbearing
formations, borrow areas for various useable materials, particular structures,
cavities, springs or watershed leakage, etc.).
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