Measurement of the Remaining Storage and Rate of Siltation in Tagwai Impounding Reservoir, Niger State

Measurement of the Remaining Storage and Rate of Siltation in Tagwai Impounding Reservoir, Niger State.

ABSTRACT

An attempt was made to measure the remaining storage of Tagwai Impounding Reservoir using bathymetric mapping and remotely sensed surface area data.

A field study on the Tagwai reservoir was carried out in Tagwai drainage basin, Niger State, Nigeria. The depths of water accompanied with their corresponding coordinates were measured from which area and storage were calculated based on data acquired from the field and that from satellite images.

The remaining storage was at the time of measurement, in the year 2010, the same as the total storage of the reservoir presently because the dead storage has been already silted up. The remaining storage was in the year 2010, 21,650,648 m3 i.e. 76.5 % of the original storage.

Thus, the rate at which the storage shrunk from 1978 and 2010 is 207,792 m3/ year. Losses to siltation are 6,649,352 m3 during a period of 32 years. This corresponds to the average annual loss to siltation of 0.73%.

The reservoir will be completely silted up in 136 years from the date of its impoundment i.e. in the year 2114, if the rate of siltation is not reduced by upgrading the environment in the drainage basin.

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TABLE OF CONTENT

COVER PAGE……………i

FLYLEAF……………….ii

TITLE PAGE………………iii

DECLARATION……..iv

CERTIFICATION………………….v

ACKNOWLEDGEMENT……………..vi

ABSTRACT…………….vii

CONTENTS……………viii

LIST OF TABLES……….x

LIST OF FIGURES……x

LIST OF PLATES………xi

LIST OF APPENDICES………..xi

ABBREVIATIONS………xi

CHAPTER 1 INTRODUCTION

1.1 Concept of the Remaining Storage………1

1.2 Background to the Study…………….2

1.3 Statement of Problem…………5

1.4 Aim ………………….5

1.5 Scope of the Study…………….6

1.6 Justification of the Study……………6

1.7 The Study Area……………7

1.7.1 Location……………..7

1.7.2 Climate and Vegetation……………8

1.7.3 Relief and Drainage……………………….10

1.7.4 Geology and Hydrogeology………11

CHAPTER 2 LITERATURE REVIEW

2.1 Regional Geology…………..13

2.2 Reservoir Siltation………………16

CHAPTER 3 MATERIALS AND METHODS

3.1 Study approach………………30

3.2 Bathymetric Data Collection………..33

3.2.1 Bathymetric Mapping………..33

3.2.2 Mean Pool Level Adjustment…….33

3.3 Bathymetric Interpretation and Volumetric Calculations…………33

CHAPTER 4 RESULTS AND DISCUSSIONS

4.1 The Bathymetry…………….34

4.2 Onset and Cessation of the Hydrological Dry Season……36

4.3 Area of the Open Water Surface………36

4.4 Position of the Pipes Relatively to the Level of the Spillway…………37

4.5 The Remaining Storage and Rate of Siltation………38

4.6 Losses on Storage to Evaporation and Seepage…….40

4.7 Safe Yield in Dry Season………41

4.8 Rate of Surface Erosion (Sediment Yield) in Tagwai Dam Drainage Basin…….….41

4.9 Remote Sensing Application……………45

CHAPTER 5 SUMMARY, CONCLUSION, AND RECOMMENDATIONS

5.1 Summary…………48

5.2 Conclusion……………50

5.3 Recommendations………………51

CHAPTER 6 CONTRIBUTION TO KNOWLEDGE

CHAPTER 7

REFERENCES……54

APPENDICES72

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INTRODUCTION

1.1 Concept of the Remaining Storage

Water resources planning and management is a major challenge to most developing nations, in their struggle to secure water. However, this depends on the availability of water, which is increasingly becoming a scarce resource. All the sources of water need to be considered in its management.

In this study, the reservoir is the focus. Reservoirs are water storage structures created by the construction of dams across rivers to store and capture runoff water for the purposes of water supply, hydropower generation, irrigation, flood control, tourism, aquaculture, etc.

Environmental impact and long-term morphological changes of the natural watercourse and drainage basin due to human activities are inevitable. Many river basins experience severe and uncontrolled environmental degradation.

This results in enhanced soil erosion in the drainage basin and excessive reservoir siltation which are considered threats. The term “siltation” means the increased deposition and accumulation of sediments in reservoirs.

These sediments originating from erosion processes in the drainage basin are propagated along with the river flow. When the flow of a river is stored in a reservoir, the sediments settle in the reservoirs and reduce their storage capacity. It is the major problem that affects and threatens the performance and sustainability of reservoirs apart from structural stability.

Reduction in the storage capacity of a reservoir beyond a limit hampers the purpose for which it is designed i.e. the gradual loss of storage capacity reduces the effective life of reservoirs and diminishes benefits for its intended uses.

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REFERENCES

Abood, M.M., Thamer, A.M., Abdul Halim, G., Ahmed, R.M. and Lariyah, M.S., (2009). Review study and assessment for sedimentation models applied to impounding reservoirs. Journal of Engineering and Applied Sciences. 4(2) :152-160.
A.B.U. Committee on Protection of the Kubanni Dam Drainage Basin. (2008). Reports on results of measurement of the remaining storage in Kubanni Impounding Reservoir and proposal for upgrading the environment in the Kubanni Drainage Basin.
Adediji, A. (2005). Reservoir Sedimentation: The Case of Opa Reservoir Catchment, Southwestern Nigeria. J. S. Afr. Geogr, 87 (2), 123 –128.
Adediji A., and Ajibade L.T. (2008). The change detection of major dams in Osun State, Nigeria using remote sensing (RS) and GIS techniques. Journal of Geography and Regional Planning Vol. 1(6), pp. 110-115. http://www.academicjournals.org/JGRP ISSN 2070-1845
Adekeye, J. I. D and Ishaku, J. M. (2004). Groundwater Contamination in Shallow Aquifers of Jimeta Metropolis, Adamawa State, N.E. Nigeria. Zuma Journal of Pure and Applied Sciences. 6 (1):150-159.