This document discusses different types of reservoirs and geological problems associated with them. It describes three main types of reservoirs: storage reservoirs which store river water, flood control reservoirs which accommodate large volumes of water during peak river flows, and distribution reservoirs which hold short-term water supplies. The main geological problems with reservoirs are groundwater conditions, permeable rocks which can cause leakage, and silting from sediment-laden rivers which reduces storage capacity over time. Proper geological investigations consider topography, groundwater, permeability, structures, and weathering to identify appropriate reservoir locations.

1. Reservoirs
By : Eng Ismail Mohamoud Ali

2. Introduction
• Reservoir may be defined as artificially created
water storage basins with storage capacity
that may range from a few thousand cubic
meters to thousands of million cubic meters.
• Depending on the purpose of storage
reservoir are classified in to three main
groups:

3. A. Storage reservoirs :
• Where river water stored by creating dams in
its path and is then released from gated or
ungated outlets.
B. Flood control reservoirs:
• Which have as their main function
accommodating large bodies of water during
peak flow times of river.

4. C. Distribution reservoirs:
• Are small storage reservoirs which hold water
supplies in a water supply system for short
spells time.

8. Problems associted with reservoirs
• The main geological problems connected with
the reservoirs are:
(i) groundwater conditions,
(ii) permeable rocks, and
(iii) silting.

9. (i) Groundwater Conditions:
• The amount of leakage of water from the
reservoir is controlled by the depth of water
table. If the water table is so near the ground
surface that the water level in the reservoir
does not rise above it, no serious loss by
leakage will occur.

10. • On the other hand, if water table lies deep
below the ground surface, the water level in
the reservoir will stand above it.
• As result, leakage will occur and its amount
will depend on the permeability of the rocks.

12. (ii) Permeable Rocks.
• During the geological investigation it is
necessary to locate the highly permeable
rocks that are present in the reservoir area.
The rocks which are highly fissured, intensely
jointed, faulted or have solution channels, are
likely to cause serious leakage from the
reservoir.

14. (iii) Silting of Reservoir :
• The reservoirs built on rivers which carry large
amount of sediment, may silt up very soon and
its water storage capacity may be reduced
considerably. The amount of silt produced and
supplied to the rivers depends mainly upon the
lithological character and topography of the
catchment area. The rivers flowing over the soft
rocks and high gradient areas, carry greater
amount of silt.

16. Geological Investigations
a) Topographically
b) Groundwater conditions
c) Permeability
d) Structural conditions of the area
e) Trend and rate of weathering.