Reservoir sedimentation

1. RESERVOIR
SEDIMENTATI
ON
Seminar On

2. CONTENTS
INTRODUCTION.
SEDIMENTATION IN RESERVOIRS.
INDICATORS FOR RESERVOIR SEDIMENTATION.
RESERVOIR SEDIMENT TRAP EFFICIENCY.
FORMS OF SEDIMENT TRANSPORT IN RIVERS.
LOSS OF STORAGE DUE TO SEDIMENTATION.
GEOLOGICAL INVESTIGATION.
IMPACTS OF RESERVOIR SEDIMENTATION.
CONCLUSION.
REFERENCE.

3. INTRODUCTION
Reservoirs may broadly defined as artificially
created water storage basins.
The storage capacity that may range a few
thousand cubic meter to thousands of million
cubic meter.
Depending on the purpose of storage,
Reservoirs are classified into three main
categories,
1. Storage and conservation reservoirs.
2. Flood control reservoirs.
3. Distribution reservoirs.

5. SEDIMENTATION IN
RESERVOIRS
 Rivers carry different types of sediments down their
riverbeds, allowing for the formation of riverbanks,
river deltas, alluvial fans, braided rivers, oxbow
lakes, and levees.
 The construction of a reservoir blocks the flow of
sediment downstream, leads to increased sediment
build-up in the reservoir.
 While the rate of sedimentation varies for each
reservoir and each river, eventually all reservoirs
develop a reduced water-storage capacity due to the
exchange of storage space for sediment.

6. 1 2
3

7. INDICATORS FOR RESERVOIR
SEDIMENTS
 Reservoir storage capacity relative to the mean annual
volume of rainfall.
 Maximum width of the reservoir relative to maximum
width of the up stream river channel.
 Maximum depth of the reservoir relative to the
maximum depth of the river channel.
 Reservoir storage capacity relative to mean annual
sediment load.
 Concentration of contaminant and heavy metals being
supplied from the water shed.

8. RESERVOIR SEDIMENT
TRAP EFFICIENCY
 Reservoir sedimentation depends upon the trap efficiency
which decides the amount of sediments deposited with in
the reservoir.
 It is the ratio of sediments retained in the reservoir to the
sediment inflow to the reservoir.
 Also depends upon fall velocity of various sediments
particles flow rate and velocity through the reservoir as
well as size, depth, and shape.
 Water viscosity also plays an important role.
 Viscosity of water varies with its chemical composition
and composition of sediments.

9. FORMS OF SEDIMENT
TRANSPORT IN RIVERS
Bed Load – Material that moves along the
bottom of the channel (by saltation and
rolling) as a result of shear stress created by
vertical velocity gradients in the
streamflow.
Suspended load- Material Load that becomes
suspended by action of turbulence.
Wash Load – fine material that is carried by
the flow in suspension, but is not
represented in the bed material.

10. LOSS OF STORAGE DUE TO
SEDIMENTATION

11. Schematic diagram of anticipated sediment deposition
(Bureau of Reclamation, 1987).

12. The geologic conditions that exist in the
vicinity of every proposed dam and reservoir should
be known and understood by those responsible for
its planning and design. The principal elements
that must be considered are,
GEOLOGICAL INVESTIGATION
 Geology.
 Geomorphology.
 Hydrology.
 Hydrogeology.

13. IMPACTS OF RESERVOIR
SEDIMENTATION
 Reduce storage capacity.
 Decreased ability to produce hydroelectric
power.
o Retrogressive deposition
 Reduced availability of water for irrigation.
 Shortening of life of a reservoir.

14. CONCLUSION
 Diminished storage capacity results in decreased
ability to produce hydroelectric power, reduced
availability of water for irrigation, may ultimately result in
the expiration of the reservoir and river.
 The construction of a reservoir blocks the flow of
sediment downstream, leading to downstream erosion of
these Sedimentary depositional environments, and
increased sediment build-up in the reservoir.
 The trap efficiency is the ratio of the deposited
sediments to the total sediments inflow.

15.  African Reservoirs," IAHR Proceedings of' the Symposium on Clzalleizges
in Africa.
 Annandale, G. W. (1 987). Reservoir Sedimerztation, Elsevier Science
Publishers, Amsterdam. ASCE (1975). Sedimerztatior~ Engineering,
American Society of Civil Engineering Manual No. 54, V.A. Vanon
editor.
 Basson, G. (2002). "Mathematical Modelling of Sediment Transport and
Deposition in Reservoirs-Guidelines and Case Studies, "
Inter~zationalCommission on Large Dams Sedimentation Committee
Report.
 Beasley, D.B., L.F. Huggins, and E.J. Monke (1980). "ANSWERS: A
model for watershed planning," Trarzsactions of the ASAE, vol. 23, no.
4’pp. 938-944.
 Bingner, R.L. (1996). "Runoff Simulated from Goodwin Creek Watershed
Using SWAT,”Transactions of the ASAE, vol 39, no. 1, pp. 85-89.
REFERENCES
Websi
tes
 http://ida.water.usgs.gov/ressed/
 http://www.usbr.gov/pmts/sediment/
 www.wikipedia.com