UNIVERSITY OF NAIROBI
DEPARTMENT OF CIVIL AND CONSTRUCTION ENGINEERING
PROJECT TITLE: IMPACT OF CLIMATE VARIABILITY ON DAM LEVELS AND HYDROELECTRIC POWER PRODUCTION: A CASE STUDY OF KAMBURU DAM
Muruki J.R. Mugendi
F16/1330/2010
A project REPORT submitted in partial fulfilment for the award for the degree of Bachelor of Science in Civil Engineering
2016
ABSTRACT
The main objective of this study was to assess the impact of climate variability on both dam levels andhydroelectric production at Kenya’s Kamburu dam. The study explored the relationship between dam levels and hydroelectric power production through statistical analysis of primary data obtained from KenGen and the Kenya meteorological department.The study used both primary and secondary data. The study objectives were achieved by analyzing monthly records of rainfall and temperature dating back at least 30 years to establish the prevailing climatological normal. The effect of climate variability was shown via a comparative analysis of the trends of annual rainfall, inflows, dam levels, and power production.
From the report’s findings, the mean annual rainfall for the Kamburu area is 762.3mmand is bimodal with long rains from March to May and short rains from October to December. The dam receives a steady, controlled inflow inflow from Masinga dam and natural inflowsThiba River. When there is no overspill at Masinga, the flow through Masinga Dam’s turbines are released to flow intothe Kamburu reservoir at a maximum theoretical inflow rate of2*45m3per second. From Thiba River, the mean annual inflows over the 1982-2015 period are 222.4 cumecs per year.
The report found that Dam levels at Kamburu fluctuate across a narrow range between 1000m and 1006m. However, climate variability events such as severe droughts and heavy rainfall fluctuate them across this band and push them beyond this narrow range.The mean annual Power production from 1991-2015 is 405.467Gwhand its trend is highly correlated to Dam levels, inflows, and Rainfall.
The report found that rainfall has a direct effect on inflows and subsequently on dam levels. The report also found that the rise and fall of dam levels across the years is mirrored by arise and fall of annual power production. Overall, the report found that annual rainfall patterns and levels are correlated top power production, thus firmly affirming the study’s hypothesis that climate variability has a big impact on dam levels and power production. The report closed by suggesting practical mitigating solutions to reduce the negative effects of climate variability on power production at Kamburu Dam.
DEDICATION
To my family for their financial and moral support as I strived to complete this project. To all the scientists interested in the impact of climate variability on Hydropower generation in Kenya and around the world, may the findings of this project be a motivation and a revelation to you all.
ACKNOWLEDGEMENT
I would like to express my sincerest gratitude to my supervisor, Dr. S.O. Dulo for his invaluable guidance and direction throughout the process of researching and writing this research project. He has been a flawless advisor and a patient counsellor during the entire period. I deeply thank him for his time, teachings, counsel, and his sacrifice. I shall always be grateful.
I acknowledge and thank all the lecturers throughout my entire undergraduate study period, for the knowledge and the advice they passed to my classmates and me over the period.
My sincerest gratitude to Mr. Willis Ochieng’, Kengen’s chief energy planner, for his cooperation and assistance towards the acquisition of pertinent data.To Mr. Elijah Kibathi, the assistant Manager at Kamburu power station, I am grateful for his cooperation, insights, hospitality and his candid remarks during my interview with him.I would also like to thank Christine Mahonga of the Kenya meteorological Department for her assistance and cooperation in obtaining temperature data records used this project.
I would like to thank my family, friends, and relatives for the moral and financial support accorded to me. Finally, I remain grateful to my classmates for support, criticism, and the information shared as well as the good times we had.
TABLE OF CONTENTS
Contents
ABSTRACT
DEDICATION
ACKNOWLEDGEMENT
TABLE OF CONTENTS
List of Tables and Figures
CHAPTER ONE
1.1...... INTRODUCTION
1.1.1...... Kamburu Dam
1.2...... Objectives of the study
1.3. PROBLEM STATEMENT
1.3...... Project scope
CHAPTER 2
2.1. Literature review
2.1.1. Introduction
2.1.2. Hydropower generation and its susceptibility to climate variability
2.1.3. The case of Kenya’s Kamburu dam
2.1.4. The case of climate variability and its impact on Zambezi’s Kariba dam
2.1.5. Experiences from the Chinese HEP industry
2.1.6. Impact of the 2011 drought on hydroelectric production along the Yangtze River and on the Three Gorges Dam.
2.1.7. The disruptive effect of excessive thunderstorms and windstorms
CHAPTER 3
3.1. METHODOLOGY
3.1.1. Research Approach
3.1.2. Data processing
3.1.3. Data collection
3.1.4. Interviews
CHAPTER 4
4.1. Analysis and discussion
4.1.2. Rainfall trend
4.1.3. The trend in temperature
4.1.4. Combined trend of rainfall and temperature
4.1.5. The Trend in Inflows
4.1.7. The trend in power production
4.2.1 Determination of the correlation between rainfall, dam levels, inflows from Thiba, and power production at Kamburu
4.2.1.1. The correlation between Rainfall, Temperature, Inflows from Thiba and Kamburu dam levels.
4.2.1.2. Trends in annual rainfall, mean monthly dam levels, total annual inflows from Thiba, and cumulative annual temperature
CHAPTER 5
5.1. Conclusion
5.2. Recommendations
REFERENCES
APPENDIX
LIST OF ACRONYMS
List of Tables and Figures
Table 1: showing temperature data processing using the average method
Table 2 Kamburu power station rainfall in mm 1976-2014
Figure 1: monthly rainfall at Kamburu in mm (1976-2013) source: KenGen
Table 3 Monthly temperature 1976-2012.
Table 4 average monthly temperature and rainfall
Figure 2 combined graph showing average monthly rainfall and temperature for Kamburu area
Table 5 Test inflows into Kamburu from Thiba River
Table 6 THIBA TEST INFLOWS in cumecs 1983-2015
Table 7 Kamburu end of month reservoir levels in metres 1981-2015
Table 8: Kamburu end of month reservoir level (ordered by single years)
Table 9: Kamburu power station gross energy production in Gwh 1990-2015
Table 10: Aggregated annual variables for rainfall, inflows, dam levels, production and temperature
CHAPTER ONE
1.1.INTRODUCTION
1.1.1.Kamburu Dam
Kamburu dam is a rock filled embankment dam on Tana River in Kenya. It was the second major station in independent Kenya following Kindaruma power station as part of the seven forks cascade hydropower complex. It is found at the border of Embu and Machakos counties, 160km from Nairobi via Nairobi-Thika- Kangonde- Embu highway and approximately 50km from Embu. Its constructioncost USD 47 million, with ground-breaking for the construction work commencing on 29th June 1971 and commissioning taking place four years later on 5th July 1974. Its operations are still managed by the Kenya electricity generating company (KenGen) to date. KenGen manages the dam’s main purpose, hydroelectric power production. It has a power production capacity of 93mw produced by three 31mw, vertical Francis turbines. These are housed in apower station that is located underground just below the left toe of the dam. The spillway is composed of three radial gates and a single flap gate.
The 52m tall dam harnesses a 123 million cubic meter reservoir behind it. The reservoir’s water comes from the Tana River through Masinga Dam and Thiba River that is a tributary injecting water into Tana River between Masinga Dam and Kamburu dam. The difference in elevation between the underground power stations and the reservoirs affords a net hydraulic head of 82m. Water discharged from the plants flows down a 3kilometre (3,040m) tailrace tunnel to Gitaru reservoir further down along the Tana River.
1.2.Objectives of the study
The overall objectives of this study project is to assess the impact of climate variability within the catchment area of Kamburu dam though analysis of rainfall, inflows, their impact on Kamburu dam levels, and the subsequent effects on hydropower productions at the dam’s power station.
The specific objectives of this study are:
1. Establish the impact of rainfall and temperature fluctuations on inflows from Thiba River and Kamburu dam levels.
2. Determine the impact that variability of inflow, rainfall, and dam levels have on power generation at Kamburu dam.
1.3. PROBLEM STATEMENT
Kenya has made commendable strides to diversify the sources of power that areinfusedinto the national grid. For instance, there has been increased investment into securing more and more renewable power such as geothermaland wind power. However, there is still a heavy reliance on hydropower on the national grid. As of Dec 2014, hydropower generation had an installed capacity of 821MW which was equivalent to 38% of the total installed capacity on the national grid.(Ministry of Energy, 2015). This reliance on Hydropower is exacerbated by the fact that nearly all of the country’s Hydropower is generated from the Tana SevenForks dams cascade. Concisely, 38% of the country’s power is derived from one river (Tana) and its tributaries on the upper Tana catchment area.
Consequently, the nation’s power production capacity has remained highly vulnerable to climate variability.For instance, after the massive El nino rains of 1998, the 1999/2000 drought that ensued lowered electricity production and causedLosses in the Kenyan industries. The World Bank estimates that the Kenyan economy lost around 2 billion US dollars in the resultant power cuts (Andambi and Mbuthi, 2004).In 2007, up to 52% of Kenya’s electric power came from hydropower generation. However by 2009, that figure had dropped to 32% due to drought (Torrie, 2014).
This report explores this tenuous relationship between climate variability, dam levels, and hydropower energy production at Kamburu dam. It highlights the susceptibility of dam levels and power production at Kamburu to climate variability.
1.3.Project scope
The project report includes analysis of rainfall and temperature records spanningat least 30 years. In this study, the monthly rainfall and temperature records for Kamburu area from 1976 to 2013 are analysed to establish a climatological normal for the area and establish periods with climate variability. The study also involves analysis of monthly inflows from Thiba River in cumecs for the period 1982-2014 , end of month reservoir levels (1982-2015), and monthly power generation in Gwh from 1991-2015. In line with the study objectives, the impact of climate variability on dam levels is established by showing the relationship between rainfall, inflows and dam levels. To show how climate variability affects power production, the link between dam levels and power generation is established and highlighted.
CHAPTER 2
2.1. Literature review
2.1.1. Introduction
Climate, unlike weather that varies from day to day, varies over years and seasons. Some seasons have more rainfall, others have less rain. Some years have more precipitation, some have very little precipitation. From a scientific perspective, climate variability is the manner in which climate fluctuates yearly below or above a long-term average value. When dealing with climate, scientists typically track climate through 30-year intervals. The data through that period is averaged to produce climatological normal (Michigan sea grant, 2003). These 30-year averages of a weather variable are called climatological normal.
These normal are calculated from variety of weather variables mainly precipitation and temperature sourced from data derived from weather stations in the region of interest. There exists substantial year-to-year variability over and above these 30–year averages.This year-to-year fluctuation from the chronological normal is called climate variability. Thus, concisely, climate variability is the way climate fluctuates every year, swinging above or below a long-term average value. Climate change is the long-term continuous change i.e. increase or decrease, to the average weather conditions.
2.1.2. Hydropower generation and its susceptibility to climate variability
The global supply and distribution of water resources are erratic and unreliable. Consequently, human beings have come up with innovative measures to harness available surface water resources through dams to create water reservoirs that store vast amounts of water. Saleh et al., (2005) approximates that the global water volume confined by built reservoirs totals to about 3,400km3. Dam projects bring great positive socioeconomic changes in countries by providing water for domestic and industrial purposes, hydropower generation, flood control, fisheries, irrigation, and hydroelectricity (hydropower) generation.
With the global population predicted to grow to 10 billion by 2050, the demand for hydropower will increase while the water withdrawal rates go up by up to 18 percent in developed countries. Since hydropower production is heavily reliant on water resources, each region in the globe will face challenges as climate changes in the long term and due to climate variability in the short term.
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2.1.3. The case of Kenya’sKamburu dam
Kenya uses a lot of power and 82% of it is generated through hydropower. The others are geothermal (8%), thermal (8.7%) and wind (0.01%) (Bunyasi, 2012). The current installed hydropower capacity in Kenya is at 677.3MW. Hydropower relies directly on climatic factors. Water that is essential in the production of the electricity determines run off, the amounts or capacities of the water in the reservoirs and thus the potential for both the baseline and the projected period's provision of power. Hydropower has for long been considered to provide ‘clean energy'. There are so many socio-economic benefits associated with power including industrial growth, improving domestic energy supply, enhancing security services, stimulating economic development among others. What is most significant is that unlike energy from fossil fuels and nuclear energy, it is renewable besides being considered as ‘clean' energy. In Kenya, the bulk of this power is found on the Upper Tana River Basin, which has the following power stations with their respective power production capacities; Gitaru (225 MW), Masinga (40 MW), Kindaruma (44 MW), Kamburu (94.2 MW), and Kiambere (156 MW). These are commonly known as the Seven Forks Dams.
However, just like hydroelectric dams across the globe, there are production challenges highly related to environmental factors. Unlike other sources of energy, and especially thermal which can heavily be determined by human factors including political stability and financial ability, hydropower generation heavily relies on nature and in particular, precipitation. Within the tropics, the main precipitation is rainfall. Rainfall is the factor that determines the availability of water within the reservoirs to enable generation of hydroelectric power. Climatic fluctuations heavily determine the availability and the amount of rainfall and the consequent water levels in the reservoirs. The rate of evapotranspiration is determined by other climatic factors such as temperature, rainfall, and the speed of the wind. Wind affects the amount and the duration over which the volumes of water are stored in the reservoirs, and thus directly affecting electricity generation (Oludhe, 2014).
The Seven Forks, and especially Kamburu power station, are situated within a semi-arid area. Most years the rainfall is fairly well distributed within the bimodal rainfall periods of between September and December and the March to June duration. The two are distinct rainy seasons punctuated by a short dry spell in January and February and some parts of March and a relatively longer drier period spanning July to September. Of these durations, temperature varies too between 25 degrees during wet weather and in most times of June-July and extremes of even above 31 degrees Celsius in drier August, September and at times parts of October. These high temperatures lead to very heavy evapotranspiration with very noticeable impacts on the dam levels with in depth and surface area reduction. Catchment evapotranspiration is at around 500mm annually so far although this has continued to increase with the increase in mean temperatures. Mean temperatures both monthly and annual have increased steadily at approximately 0.15 and 0.26 degrees respectively. This does not factor in the huge differences in climatic conditions that affect the catchment area from time to time. For instance, there are excessive rains and sometimes excessive and prolonged droughts.
This makes the generation of hydropower extremely dependent and sensitive to climatic fluctuations and especially extremities that affect the availability of water. These extremities mainly are floods and droughts. Notably, in 1997/1998 season and 2008/2009 there were El-Niño related floods and in the almost immediate subsequent seasons of 1999/2000 and 2009/2010, there were droughts that led to severe socio-economic constraints on the country. In relation to power production, the water level among the seven forks dams was so low that that there was power rationing across the country. This rationing led to interruptions of power supply due to limitations in the amounts of HEP that could be produced. This was due to the severe water scarcity that occurred in the seasons immediately after El-Nino. Losses in the Kenyan industries that came about because of the low electricity generated in the 1999/2000 drought were estimated by the World Bank to have been around 2 billion US dollars (Andambiand Mbuthi, 2004). During the excessive precipitation, there was increased reservoir sedimentation. Notably, in the flood plains especially on the tail end of the dam where the Thiba River enters the reservoir, irrigation has continued unabated over the last decade. This explains the expansiveness and volume of the amount of the dam that is taken over by the silting and sedimentation. .