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TRANSCRIPT
UNIVERSITY OF NAIROBI
SCHOOL OF CONSTRUCTION, ARCHITECTURE & ENGINEERING
DEPARTMENT OF CIVIL ENGINEERING
Hydrological Study of the Upper Athi River Basin
BY: FRANCIS WANJOHI KANYI
(F16/28857/2009)
A project submitted as a partial fulfillment for the requirement for the
award of the degree of Bachelor of Science Degree in Civil Engineering.
2014
DECLARATION
I declare and affirm to the best of my knowledge that this research is my original work and has
not been presented for a degree or any other award in this or any other university.
Signed: ……………………................. (Author); date…………………………………
FRANCIS WANJOHI KANYI - F16/28857/2009
I confirm that the work reported in this research was carried out by the candidate under my
supervision.
Signed: ……………………................. (Supervisor); date………………………………
MR.CHARANIA
ABSTRACT
This report deals with the water resources and the usage of water in the Upper Athi River
Catchment Basin. A detailed study of the hydrology of the area has been made using the data at
present available, together with the results of such detailed studies as were made during the
period of the investigation.
The area investigated includes the tributary catchments on the upper area of the Athi River
upstream of the outlet regular gauging station, which lies just above Fourteen Falls near. The
Athi River and its upper tributaries drain south east slopes of the southern end of the Aberdare
Range, and part of the eastern slopes of the Ngong Hills, with major Counties like Nairobi
,Thika, Kiambu and Machakos present within the Catchment Basin.
Statistical analysis of the available records collected was done. An assessment of the low flows
was done and expected flood flows at the outlet were determined. The required storage was also
determined at specific points in the river. Rainfall data was collected and analysis done for the
catchment. This included the seasonal rainfall in the area, the average rainfall in the catchment
and the available water for water resources development.
The river has high flows thus experience flooding. The river has a good potential for storage of
excess water.
DEDICATION
To almighty God for the life and strength He has granted me. To my parents, brothers and sisters,
thank you for your love, emotional and financial support.
And especially to my Mother, the ‘Late’ Hellen Njeri Kanyi, all would be lost without
responsible parenthood. Thank you for your relentless sacrifices and confidence so that I can be
who I am today. May your soul Rest in Peace.
ACKNOWLEDGEMENT
I wish to sincerely acknowledge the contributions of all those who assisted me either directly or
otherwise towards the undertaking of this project.
Special thanks to Eng. Sadrudin Hassanali Charania my supervisor, for rigorously guiding me
through the research process.
The Civil engineering department for technical and material support throughout the entire
project.
To all my classmates especially Muna B.W thanks for your creative criticism and ideas and also
for your friendship and assistance.
To all my friends, who have in one way or another contributed to the completion of this project, I
am entirely grateful for all your support.
Table of Contents Page
TITLE ............................................................................................................................................ i
DECLARATION ........................................................................................................................... i
ABSTRACT .................................................................................................................................. ii
DEDICATION ............................................................................................................................. iii
ACKNOWLEDGEMENT ............................................................................................................ iv
TABLE OF CONTENTS .............................................................................................................. v
LIST OF ABBREVIATIONS .................................................................................................... viii
LIST OF TABLES ........................................................................................................................ ix
LIST OF FIGURES ...................................................................................................................... x
Chapter One……………………………………………………………………………………...1
Introduction…………………………………………………………………………...….…1
1.1 Introduction……………………………………………………………….......…..1
1.2 Research Objectives……………………………………………………..…….…..1
1.3 Problem Statement……………………………………………………..................2
1.4 Scope of Study..……………………………………………………………....…...2
Chapter Two…………………………………………………………………………...…………3
Literature Review………………………………………………………………...……….3
2.1 Description of the Catchment..……………………………………………...…….3
2.1.1 Extent...…………………….……....…….…………………………………..4
2.1.2 Topography………………………………………………………........……..5
2.1.2.1 The Athi Plain………………………………………………………..……5
2.1.2.2 The Low Ridge……………………………………………………………6
2.1.2.3 The Middle Ridge…………………………………………………………6
2.1.2.4 The Headwater Zone……………………………………………………...6
2.1.2.5 The Rift Valley Fault Sytem……………………………………………...6
2.1.3 Soils………………………………………………………………………….6
2.1.4 Climate………………………………………………………………………7
2.1.5 Ground Water……………………………………………………………….7
2.1.6 Catchment Degradation……………………………………………………..8
2.2. Network of Stations…..…………………………………………..………….......9
2.2.1 Rainfall………………….............................................................................9
2.2.1.1 Rainfall Gauges…………………………..………………....................9
2.2.1.2 Recording Rain Gauge…………….………………………...………....9
2.2.2 Stream Flows…………………………………………………….….……11
2.2.2.1 River gauging Stations..…………………………………………...…12
2.2.2.2 The Instruments…………………………………………………..….12
2.2.2.3 Recorders…………………………………………………..……..….13
2.2.2.4 The Pressure type recorders…….…………………………..…….....13
2.2.2.5 Artificial Controls…………………………………………………....13
2.3 Sedimentation…...……………………………………………………...…..…...14
2.4 Evaporation…………………………………………………………………..…15
Chapter Three……………………………………………………………………………..…16
Methodology and Results……………………………………….………..…………16
3.1 Rainfall ………………………………………………………..…………..……16
3.1.1 Preparation of Missing Data………………………..………………..…16
3.1.2 Estimation of data …………………………………………………....…17
3.1.3 Thiessen Polygon………………………………………….....………….18
3.1.4 Isohyetal Method…………………………………………...…...............19
3.1.5 Arithmetic Mean Method……………………………………..…………19
3.1.6 Trend of Rainfall…..……………………………………………….…….20
3.1.7 Moving Average…….……………………………………………….......20
3.2. Stream Flow Analysis ……………………………………………………….…..21
3.2.1 Processing of raw data…………………………………………………...21
3.2.2 Flow Duration Analysis………………………………………………….21
3.2.2.1 Analysis period.………………………………………………….22
3.2.2.2 Flow Duration Curve…………….………………………………22
3.2.3 Low-Flow Analysis……………………………………………………....22
3.2.4 Mass Curves……………………………………………………...………23
3.3 Results and Analysis……………………………………………………………25
Chapter four…………………………………………………………………………………….50
Discussion and analysis……………………………………………………………………...…50
4.1 Rainfall Analysis and Discussion………………………………………………..50
4.1.1 Seasonal Variation………………..……………………………………...51
4.1.2 Volume of Water…………………………………………………………51
4.2 Stream flow Analysis…………………………………………………………….52
4.2.1 Flow Hydrograph………………………………………………………...52
4.2.2 Flow Duration Curve…………………………………………………….53
4.2.3 Mass Curve……………………………………………………………....54
4.2.4 Low Flow Curve…………………………………………………………55
4.3 Evaporation………………………………………………………………………57
4.4 Sedimentation Analysis………………………………………………………….59
Chapter five…………………………………………………………………………………..…60
Conclusion and recommendations……………………………………………......60
5.1 Conclusions……………………………………………………………………....60
5.2 Recommendations………………………………………………………………..61
References……………………………………………………………………………………….62
Appendix .................................................................................................................................... 40
Appendix A: Rainfall Data.......................................................................................................... 40
Appendix B: Stream Flow Data................................................................................................... 41
List of Acronyms
MoW Ministry of Water
RGS River Gauging Station(s)
FDC Flow Duration Curve
List of Illustrations
List of Tables Page
1.0 Rainfall Stations showing relevant details …………………….………………...…..……5
1.1 The Sub-Drainage Area….……..………………………………………………..…........10
2.0 Regular Gauging Stations showing ID number and period of records…….…………….12
3.0 Summary of Sedimentation Rates on the major Athi tributaries…..…………………….54
4.0 An illustration of the Thiessen Polygon Method………………...…………………........16
5.0 Rainfall Data for Muguga Station ID.9136043…………………...……………………...48
6.0 Rainfall Data for Kabete Agromet Station ID.9136208………….……………………...48
7.0 Rainfall Data for Katende Station ID.9137102…………………...……………………...48
8.0 Rainfall Data for Machakos Station ID.9137089………………...……………………...48
9.0 Streamflow Data of Upper Athi River at R.G.S.3DA2 ……….………….…………..….44
10.0 Streamflow Data of Ndarugu River at R.G.S.3CB05 ……….……..…….…….……….44
11.0 Streamflow Data of Thiririka River at R.G.S.3BD08……….………….……………….44
12.0 Streamflow Data of Nairobi River at R.G.S.3BA32……….……………………...…….44
13.0 Flow Duration Analysis Curve of Upper Athi River at R.G.S.3DA2 …………………...54
14.0 Flow Duration Analysis Curve of Nairobi River at R.G.S.3BA32.. …….……………...54
15.0 Flow Duration Analysis Curve of Ndarugu River at R.G.S.3CB05 …….……………...54
16.0 Flow Duration Analysis Curve of Thiririka River at R.G.S.3BD08 …….……………...54
17.0 Flow Duration Analysis Curve of Thiririka River at R.G.S.3BD08 …….……………...54
18.0 Trend of Rainfall Analysis of Kiambu D.C office at ID.913628……...….……………...54
19.0 Weighted Mean Monthly Rainfalls…………………………….……...….……………...54
20.0 Application of the Thiessen Polygon Method on various Stations…………………........16
21.0 Thiessen Polygon Weights on various Stations……………………………….……........16
22.0 Mass Curve Method (1963-1964) dry period……….…………………………………...23
23.0 Stream Flow Data of RGS 3AA4 Mbagathi River………………………………………45
List of figures Page
1.0 Showing the extent of the Athi River Basin….............……………………………...……4
2.1 An illustration of a standard Rain Gauge………………….……..…………….………...53
2.2 Tipping Bucket Rain gauge.……...…………………………………………………...…54
2.3 Weighing Type rain gauge..………...……………………………………………………56
2.4 Float Type Rain gauge……………...……………………………………………………56
2.5 The Gauging Scale types… ………………………..………………………………....…38
2.6 A Recording Casing …………...………………………………...………………………42
2.7 An installation of the two types of recorders ………………………………………........46
2.8 Illustration of the Staff Gauges……………..……………………..………………..……71
2.9 The Rectangular Crest Weir………..……………………………………...…..…………75
3.0 An illustration of the Parshall Flume…..………………………………………...………45
3.1 Illustration of the Theissen Polygon Method…………………………………………….34
3.2 An illustration of the Isohyetal Method………………………………………………….45
3.3 An illustration of the Mass Curve Diagram……………………………………………...23
3.4 Bargraph of Rainfall Station ID.9136043 Muguga……………………………………...56
3.5 Line Graph of Rainfall Station ID.9136043 Muguga…………………………………...56
3.6 Bargraph of Rainfall Station ID.9136208 Kabete Agromet..…………………………...56
3.7 Line Graph of Rainfall Station ID. 9136208 Kabete Agromet. ………………………...56
3.8 Bargraph of Rainfall Station ID.9137102 Katende Forest.....…………………………...56
3.9 Line Graph of Rainfall Station ID. 9137102 Katende Forest. ……..…………………...56
List of Maps Page
1.0 Catchment map showing its boundaries, rivers, river gauging stations and contours…….3
2.0 Catchment map featuring rainfall stations, contours and rivers…………………………52
3.0 Sketched map of contour lines……………………………………………………..…….42
List of Plates Page
1.0 Athi Catchment at Regular Gauging Station 3DA2……..…………………………….…12
2.0 Low stream flows in drought periods……………………………………………..……..13
CHAPTER 1
1.0 INTRODUCTION
Athi River being the only major river traversing the basin is approximately 591 km long with an
average width of 44.76 m, mean depth of 0.29m and average flow rate of 6.76 m3/sec. The Athi
river basin with an estimated population of 8,500,127 people, covers an area of 58,636
km2 (approximately 10% of land surface in Kenya) comprising the southern part of the country,
east of the Rift Valley draining the southern slopes of the Aberdare Ranges and the flanks of the
Rift Valley, to form the Athi River, and finally flowing into the Indian Ocean.
The Upper Athi catchment being the main part of this investigation is bounded by
latitudes 1°
to 4.5°
South and Longitudes 37° to 40
° East, and ranges in altitude from 2600 m to
1,500 m mean sea above level. It extends from the Ngong Hills and parts of Aberdares in the
North West. It abuts the Rift Valley to the west, the Yatta Plateau to the east and the Indian
Ocean to the south east.
Athi Catchment extends across four administrative provinces – Central, Nairobi, Eastern,
Rift Valley with the following pre-2007 Districts within the catchment: Nairobi, Makueni and
44.8% of Thika, 77.7% of Kajiado, 60.2% of Machakos and 75% of Kiambu. The main
economic activity in the catchment area is agricultural farming in the central districts area and
nomadic pastoralists‘ in the lower part of the catchment.
Upper Athi has a number of tributaries; the main ones being Nairobi River, Ruiru,
Thirika and Ndarugu River. Mbagathi to the south of the catchment joins Athi River just before
3DA2. The catchment is characterized by significant economic activity, principally in the large
urban centre of Nairobi, Machakos and Thika; however there are a large number of other
significant urban centres in the catchment.
1.1 RESEARCH OBJECTIVES
1.1.1 General objective
The general objective of the study is the hydrological characteristic features in the Upper Athi
River basin.
1.1.2 Specific objectives
A description of the catchment area and status of the Upper Athi river basin.
To study the river and stream flows, high flows and low flows of the river discharge.
To conduct probability analysis and determine the flow duration analysis of the river flow
discharge.
To analyze the rainfall data of the area through the data recorded and collected by the
gauging stations through hydrographs and other various methods.
To determine the relevant information will be essential to determine the water resource
availability and hydrological response of the area.
To determine the need for storage of water for domestic and commercial use of the
community within the area.
1.2 PROBLEM STATEMENT.
Athi catchment is a water scarce catchment subject to low flows which are required to be
analyzed, thus threatening to the reliability of supply and sustainable exploitation of
water resources.
1.3 SCOPE OF THE STUDY
This report deals with the hydrological study and analysis of rainfall and river flows, through the
analysis of the data collected by the Ministry of Water, Water Management Authority (WRMA)
and the Metrological Department.
CHAPTER 2
LITERATURE REVIEW
2.1 DESCRIPTION OF THE CATCHMENT
Map 1. Map showing the Upper Athi Catchment Area boundaries
2.1.1 Extent
The Athi Catchment altitudes ranges from 2600 m to 1500 m above mean sea level in the upper
zone. The Athi River flows in a north-easterly direction from Athi River Township and the Athi
plains south of Nairobi until it reaches the hill of Ol Donyo Sapuk, where it turns south-
eastwards. The left bank tributaries of the Arberdare drainage system run in a south-easterly
direction, joining ten streams crossing the Nairobi-Thika road, and later into the two main
tributaries, the Nairobi and Ndarugu Rivers, which join the Athi River. The streams north-east of
the Katamayu rise in the escarpment forest, and many of the streams have their sources from
springs and swamps associated with the faulting of the eastern edge of the Rift Valley.
The Upper Athi Region‘s key catchment assets include the major water tower of the
Aberdares; however, there are numerous less well-known features that act as water towers such
as the Ngong Hills, National parks, the most prominent of which are the two Nairobi National
parks, also comprise important catchment assets.
The Ngong Hills catchment area, which may be approximately the area bounded on the
north-east by the Nairobi-Athi River Road, and on the north-west by a line from Nairobi to
Ngong, is open, almost treeless plain, the larger part of the large part of the Nairobi National
Park, and has black cotton type of soils and comparatively low rainfall.
The Area of the Aberdare drainage is roughly rectangular in shape, bounded by the Athi
River in the south and south-east, by the Ndarugu River in the North-east, by the crest of the
Aberdares in the north and north-west and by the edge of the Rift Valley in the west and south-
west. The Rift valley fault system runs almost north to south and the escarpment of the Rift has
truncated the headwaters of the streams lying to the south-west of the Katamayu River in the
Ruiru sub-drainage area.
The river and its tributaries drain the south east slopes of the southern end of the
Aberdare Range, and part of the eastern slopes of the Ngong Hills. The areas drained by sub-
catchments are given in the Table 1.1
Table 1.1
Sub-Drainage Areas
Sub-Drainage Area
Principal River
Area sq. miles
3.AA Mbagathi 285
3.AC Athi 329
3.BA Nairobi 314
3.BB Kamiti 102
3.BC Ruiru 205
3.BD Thiririka 136
3.CB Ndarugu 142
Total = 1,513
2.1.2 Topography
The topography of the Upper Athi catchment is very varied but for the purposes of description it
may be divided into five key areas which are described individually below, namely:-
1. The Athi Plain;
2. The Low Ridge;
3. The Middle Reaches;
4. The Headwater Zone;
5. The Rift Valley Fault System;
2.1.2.1 The Athi plain
The Athi plain may be said to lie between the Nairobi-Thika road and the Athi River. It is an area
of generally low relief sloping gently to the south-east, and intersected at intervals by the main
streams such as the Nairobi, Ruiru and Ndarugu. These rivers have curved out narrow steep-
sided valleys 50 – 100 ft. deep. The land lying between the rivers consists mainly of thin murram
or black cotton soils.
2.1.2.2 The Low Ridge
This is an area of medium relief with long ridges of varying width lying between the stream
valleys. Interspersed with the ridges are many low flat areas, usually elongated in the general
direction of drainage, but with poor drainage and filled with dark or black clay soils. The higher
ridges are composed of red kikuyu loam which supports the coffee plantations of the area.
2.1.2.3 The Middle Reaches
These areas have comparatively narrow ridges lying between valleys up to 300 ft. deep. The
lower limit of this area roughly coincides with the upper boundary of the mostly settled area at
about 5,250 ft. O.D. The upper limit is about 8,000 ft. and lies within the forest boundary.
2.1.2.4 The Headwater Zone
This is a relatively small area of high plateau on the Arberdare range. A number of the major
tributaries of the Athi rise in this area.
2.1.2.5 The Rift Valley Fault System
This area is treated separately because it exhibits unique topographical characteristics. The east
Rift valley fault system has truncated the headwater reaches of streams lying south-west of the
Katamayu and severe disruption of original drainage directions has taken place. This has resulted
in swamps and strong springs which now form the source of many of the streams.
2.1.3 Soils
The area has high and medium humic red soils, and red soils with regions of good relief and
drainage and the black cotton soils with the badly drained plains.
Plate 1. View of Athi River at RGS 3DA2
2.1.4 Climate
The climate across the catchment is variable, typically being sub-humid in the upper zone.
There are two distinct rainy seasons in the catchment: March-April-May (the ‗long‘ rains) and
October-November (the ‗short‘ rains). The Appendix shows the mean annual rainfall distribution
across the Upper Athi Catchment and also shows the mean monthly rainfall for certain rainfall
stations (machakos, Kabete, Muguga, Katende).The daily temperatures range from 18°C in the
upper zone of the region to over 29°C.
Plate 2. Pathways flooded during the heavy rainfall season in the Upper Athi Catchment area
2.1.5 Ground Water
The Athi catchment is characterized by varying hydrological conditions which leads to different
aquifers. The upper zone, which is predominately volcanic, has relatively good aquifers, of
considerable value for domestic, community and commercial water supply.
2.1.6 Catchment Degradation
The Upper Athi region is a high potential area which is characterized by catchment destruction
leading to low flows. High population density in these areas is a cause of over-abstraction, both
of ground and surface water. There are pockets in this zone where there are excessive
concentrations of fluoride, iron, manganese etc in ground water. The high number of agro-based
industries and urbanization contribute to substantial pollution to the water resource.
In general, the catchment suffers from past degradation as a result of tree-felling in forest
and reserve areas. Encroachment in and cultivation of wetlands has also exacerbated this
situation further. Inappropriate agricultural practices have endangered our water sources. Sand
harvesting has adversely affected the water-carrying capacity and bank stability of the rivers.
These activities destroy surface cover resulting in reduced recharge, increased surface
run-off, soil erosion and eventually desertification. Eroded soils are carried by the surface run-off
and deposited in rivers, lakes and dams, resulting in reduced storage capacity and poor water
quality.
Plate 2. Drought period of the Athi River, low stream flows.
2.2 NETWORK OF STATIONS
2.2.1 RAINFALL
Whenever we think of constructing a reservoir or a tank or etc, we have to consider the rainfall
pattern over the catchment area or basin of the stream or river. To assess this, we require the
rainfall data of the various rain gauge stations located inside the catchment.
A good network of rain-gauges exists over most of the settled area, but the coverage in
the forest reserves and rural land areas is thin. There are principal stations used for the research
of this project, of which about one third have been established for over 20 years and more. The
table 1 lists these stations, showing their registration number, position and height above sea
level.
2.2.1.1 Rainfall Gauges
A substantial network of rain-gauges exists over the Upper Athi catchment basin. To assess the
rainfall it requires an establishment of well-organized high quality, evenly distributed network of
rain gauges. A brief description of the types of rain-gauges has been illustrated below.
2.2.1.2 Recording Rain Gauge
This is also called self-recording, automatic or integrating rain gauge. This type of rain gauge has
an automatic mechanical arrangement consisting of a clock work, a drum with a graph paper
fixed around it and a pencil point, which draws the mass curve of rainfall. From this mass curve,
the depth of rainfall in a given time, the rate or intensity of rainfall at any instant during a storm,
time of onset and cessation of rainfall, can be determined. The gauge is installed on a concrete or
masonry platform 45 cm square in the observatory enclosure by the side of the ordinary rain
gauge at a distance of 2-3 m from it. The gauge is so installed that the rim of the funnel is
horizontal and at a height of exactly 75 cm above ground surface.
There are three types of recording rain gauges—tipping bucket gauge, weighing gauge
and float gauge.
Fig 2.1 A standard Rain gauge Fig 2.2 Tipping Bucket Rain gauge
Fig 2.3 Weighing type gauge Fig 2.4 The Float type raingauge
2.2.2 STREAM FLOW
The flow of a river represents the integrated basin response to various climatic inputs, with
precipitation and temperature being very important. Changes over time in the hydrology of
unregulated basins with stable land use generally reflect changes in climatic conditions and can
be used as indicators of climate change. In addition to providing an understanding of the effects
of climate change on society and ecosystems, such analyses provide measures of climate change
that are based on river flow data.
The early gauging stations were established for the collection of information on normal
and low flows for use in the allocation of water, and stations were unsuited to record the high
flows occurring in flood periods, hence; the low flows and storage analysis are determined in the
report.
The catchment has 38 regular gauging stations and the table 2 lists these stations,
showing their registration number and some length of records available. Stations closed without
useful records have been omitted from the table.
The map A shows the positions of the gauging stations listed in the table, the boundaries
of the catchments of the larger streams. The distribution of stations is somewhat uneven and the
greatest concentration is in the area immediately around Nairobi. For the missing data due to
short term records, a judicious use of correlation methods on these records has been employed to
fill the gaps in the records used in this report.
2.2.2.1 River gauging Stations
When siting of a station at a point in a river - The following criteria is used:
- Accessibility of the site;
- Availability of an observer
- Straight stretch of channel with a control
2.2.2.2 The Instruments
The equipment used at a river gauging station is either manual gauges for gauge height
observations, runoff recording gauges or Artificial controls.
Manual gauges - The purpose is to observe gauge height manually everyday with respect to a
datum permanently fixed, for a gauge height observation.
Types of Staff gauges either on Posts and Struts or fixed to the banks of the rivers are generally
used. It may be necessary to use wire-weight gauges on columns of bridges or stands on the
banks are used.
Fig 2.5 Gauging scale types Fig 2.6 Recording Casing
2.2.2.3 Recorders
These are gauges in which the gauge heights are continuously recorded. Thus they can produce
instantaneous gauge height of floods and the lowest heights in a river. They are held on a stilling
well connected to the river by inlet pipes. The recorders are placed on stilling wells for wires
and weights to be contact with water in the river. The recorder has a mechanism for recording of
gauge heights or levels of water in the river on recorder charts or for transfer of the level reading
electronically to computers.
2.2.2.4 The Pressure type recorders
They have no inlet pipes but have a tube from the recorder to the bottom of the river. The levels
are transmitted to the recorder through the tube with a gas under pressure. A Recorder must
always be installed along with a Staff gauge. Problems expected where recorders are installed
e.g. Blocking of inlet pipes
Fig 2.7 Installation of the two types of recorders
Fig 2.8 Staff Gauges
2.2.2.5 Artificial Controls
These are either concrete structures or plates of specific shapes to measure the levels of water in
small rivers. Some of the shapes used are Rectangular Weir and V-Notch Weir. Local
Information and Flood Marks and crest gauges - These are the techniques used to obtain flood
levels in rivers.
Fig 2.9 Rectangular Crest Weir
In the catchment there are artificial controls and there is a partial flume in Ruiru River, Kiambu
River. The Parshall flumes are used especially for small rivers. The figure below shows an
illustration of this.
Fig 3.0 An illustration of a Parshall Flume
2.3 Sedimentation
The sediment production rate over the Aberdare foothills drained by the Athi tributaries varies
with a wide range of factors including the magnitude and frequency of storms, catchment slope,
density of vegetation, type of cultivation and erodibility of the soils. The steepest slopes are to be
found in the upper reaches and density of vegetation and the type of cultivation falls into the
three principal zones of forest, reserve areas and mixed farming and coffee areas. The relative
magnitude and frequency of the peak river discharges increase with the larger drainage areas,
higher rainfall and steeper land slopes of the northern tributaries. A range of data collected from
various R.G.S stations were analysed and a table 3, which shows a summary of sedimentation
rates on the major Upper Athi River tributaries.
The sediment production rate also varies widely from year to year according to rainfall
patern and state of the catchment when rain falls. It is probable that the greatest production of silt
takes place where intensive cultivation takes place on steep slopes, for example tea and coffee
growing areas. As the work of soil conservation proceeds it can be anticipated that soil erosion
will diminish and that the sediment loads of the streams will gradually decrease in the future.
2.5 Evaporation
Knowledge of evaporation rates is essential for the estimation of the losses from any reservoir
under consideration. Water lost by evapo-transpiration from any vegetation and evaporation from
the land surface may account for a great percentage of the amount Precipitation experienced and
vitally affects the water yield of any catchment in the area.
Evaporation from exposed standard open pans has been recorded a several points in the
catchment for periods in the catchment for points up to 10 years with varying degrees of
accuracy. The more reliable of these records have been selected for analysis.
The station at Nairobi Dam has been in use for more than 10 years and accurate past
records are available. It has therefore been chosen as the typical station for analysis.
CHAPTER 3
METHODOLOGY
3.1 RAINFALL
Precipitation is expressed in terms of depth to which rainfall water would stand on an
Area if all the rain were collected on it.
3.1.1 Preparation of missing data
Data that was missing and some that were erroneous could be attributed to the changes at the
site, poor maintenance of the station, poor recording by the junior staff, absence by staff on duty,
damage or fault in a rain gauge during a period and sometimes technical reasons e.g. the eroding
of the river section during the flood and the change of river section unnoticed.
The missing data is estimated by using the data of the neighbouring stations. In these
calculations, the normal rainfall is used as a standard of comparison. The normal rainfall is the
average value of rainfall at a particular data, month or year over a specified 25-year period or so.
The normal rainfall is updated every ten years.
3.1.2 Estimation of missing rainfall data
The following methods are generally used.
1. Comparison method
2. Normal ratio method
1. Comparison method
If the rainfall record of a rain gauge station (say. X) is missing for a relatively long
period, such as a month or a year, it can be estimated by comparing the mean annual rainfall
of the station X with that of an adjoining station A. Thus
where PX and PA are the precipitations of the stations X and A for the missing period, and NX
and NA are the mean annual rainfalls of the stations X and A.
2. Normal Ratio Method
When there is the short break in the precipitation data of a raingauge station, it can
be estimated from the observed data of three adjoining index stations A, B and C, which are
evenly distributed around the station X.
The following two cases are dealt with separately.
(a) When the mean annual rainfall at each of the index stations A,B and C is within
10% of the mean annual rainfall of station X, a simple average of the values of
the index station is taken. Thus
(b) When the mean annual rainfall at each of the index stations differs from the
station X by more than 10% the normal ratio method is used. Thus
where the symbol N is used for the mean annual rainfall (also called average annual
precipitation) and the symbol P is used for the precipitation. When there are M index stations,
The mean rainfall over the basin is computed by a number of methods of which the following
three methods are widely used:
3.1.3 Theissen’s Polygon Method
This is a simple graphical method, often used, on the assumption that the record of any one
station, should be used for the portion of the drainage area nearest that station.
The Upper Athi Catchment basin plan is drawn to scale. Then the position of the rain
gauge stations is marked on the plan. Nearest rain gauges outside the basin are also marked. The
rain gauge stations are joined by straight lines. Perpendicular bisectors are drawn to these lines.
These bisectors cut each other at points making polygons around each rain station. Then the
average rainfall of the catchment is determined as illustrated below. The values in the image
below are merely theoretical and not used anywhere in the project. This is the method adapted in
the analysis of rainfall data in this report.
Fig 3.1. illustration of the Theissen Polygon method
Table 4
Gauge No. Area Rain Proportion Average
1 a1 r1 a1/A R1*(a1/A)
2 a2 r2 a2/A R2*(a2/A)
3 a3 r3 a3/A R3*(a3/A)
4 a4 r4 a4/A R4*(a4/A)
5 a5 r5 a5/a R5*(a5/A)
6 a6 r6 a6/A R6*(a6/A)
Total A ∑ (rn*an/A)
3.1.4 Isohyetal Method
Rainfall contours at suitable intervals are drawn over the basin, based on the mean annual rainfall
of stations inside and outside the basin. For each area between isohyets the average precipitation
is determined. Depths of rainfall over portions of areas are determined. Depth of rainfall for a
range of areas is worked out.
Fig 3.2. illustration of the Isohyetal Method
3.1.5 Arithmetic Mean Method
Simplest method but it‘s the least reliable. This method requires merely taking the arithmetic
mean of all rainfall gauges in the basin under study. The influence of a rain gauge outside the
boundary of the catchment even if it is very near is not considered. If the country is flat and the
gauges are uniformly distributed over the area, the rainfall of the individual stations does not
show much variation from the mean precipitation of the area. In the arithmetic mean method, the
average depth of rainfall ( P ) over an area is taken as the arithmetic mean of the rainfall depths
of all stations. It is obtained by dividing the sum of the depths of rainfall recorded at all the rain
gauge stations by the number of stations. Thus;
Where P1, P2, .....Pn are the depths of rainfall recorded at the rain gauge 1, 2, .......n.
This method does not give accurate results and hence is rarely used in practice, therefore, not
used in this report.
3.1.6 Trend of Rainfall
The trend of rainfall is an indication of the increase or decrease in Rainfall over a long period of
time. This is computed as follows:-
Where B = Trend of Rainfall
= Mean Value
N = Total number of values
K = Rank of Value
= Deviation of mean i.e. ( X - )
3.1.7 Moving Average
Moving Average reduction of Rainfall Values shows the general trend and pattern of the rainfall
recorded over a large number of years. This curve can be conveniently used for prediction of
recurrence of floods in the river. If the values are a, b, c, d, e, f, g the forth moving average
reduction is given by (a+4b+6c+4d+e)/16 the illustration below shows the application:
Rainfall 1st Reduction 2
nd Reduction 3
rd Reduction 4
th Reduction
a
b
c
d
e
3.2 STREAM FLOW ANALYSIS
Various methods of analysis of flow records have been developed to assess the sustainability of
supplies and the development of the area around the Upper Athi region. Although before using
the rainfall records of the stations, it was necessary to first check the data for continuity and
consistency. The data from the stations is the raw data booked by technicians.
3.2.1 Processing of the raw river flow data
The available Gauge height records can initially be checked by converting the individual gauge
heights to Discharges; the processing thus involves:
(a) Observation and scrutiny the complete records at the station for any corrections required.
(b) Comparison and correlation of the station data with the data from the station upstream,
downstream and in adjacent basins for further amendments if necessary.
(c) Evaluation and interpolation of the discharges for the corresponding gauging stations was
determined.
(d) Checking discrepancy in discharges recorded; correcting the records through
interpolation method.
3.2.2 Flow Duration Analysis
The available records are analyzed to develop a flow duration curve. It is a cumulative frequency
curve that represents the flow characteristics of a stream throughout the range of river flows or
discharges. It is used in determining the percent of time specified discharges are equalled or
exceeded during a given period. The two methods used are:
i. The Calender Year Method
ii. The Total Year Method
The year of record must be complete for analysis; however these may not be in consecutive
years; the physical conditions in the basin such as artificial storage, diversions and other
manmade influences must essentially be the same during the period of flow analyzed.
3.2.2.1 Analysis period for assessment.
The period selected can either be daily, weekly or monthly flows in a given period of record.
The results of analysis can be used to show the characteristics of flows when time unit is very
short, i.e. daily rather than monthly or annual and to estimate the percent of time that a specified
discharge will be equaled or exceeded in the future if a reasonable long record of flows is
available.
3.2.2.2 Flow Duration Curve
A flow duration curve represents the relationship between the magnitude and duration of stream
flows; duration in this context refers to the overall percentage of time that a particular flow is
exceeded. The shape of the curve for any river therefore strongly reflects the type of flow regime
and is influenced by the character of the upstream catchment including geology, urbanisation,
artificial influences and groundwater. In practice, Flow Duration Curves are used mainly in
relation to the setting of environmental flow objectives.
The mid-pts are plotted against Cumulative Probability on Log Probability paper. The
value 95% low flow is obtained using the x value of (100 – 95) % = 5%. This is the value of
flow which will be equaled or exceeded 95% of the Time or if the river used for water supply,
the supply would be available 95% of the time; there is a chance of 5% failure.
3.2.3 Low flow frequency
Low flow conditions in rivers and streams are of fundamental importance to the ecological status
of the watercourse. Any change in the seasonal pattern of flows, for example due to exploitation
of a groundwater source or abstraction of water from the river, may lead to irreversible changes
to the stream ecology. Low flow analysis is also important when considering the construction of
works in rivers and streams (for example, a Weir), and for river restoration schemes for which an
understanding of hydrological variation is important in determining appropriate restoration
works. Methods of low flow analysis are outlined below. Usually for an Urban centre, 99%
probability is used or maximum probable precipitation is used.
It evaluates the probability of flows occurring and remaining below a specified (low)
design threshold for a given length of time. Customarily the analysis is carried out with regard to
the minimum discharge aggregated over a period of d days in each year, annual minimum–
derived from daily flow series. This technique is used to assess the low flows in the source of
water. If adequate and appropriate records are available it provides a very accurate assessment of
low flows.
The analysis requires independent low flow values. Generally the daily, monthly values
are not independent. The daily values should therefore not be used for this analysis; monthly
data may be used but it must be made sure that the values are not dependent. Annual values are
generally acceptable for this analysis. It is very important that the data available is adequate,
generally over 25 values.
The low flow values are arranged in ascending order; they are ranked (m), Probabilities
are assigned using plotting position, (m/N+1) where N is the Total number of values; the flow
data and the corresponding probabilities are plotted on Log probability paper. The low flow with
the accepted probability of failure is obtained from the graph.
3.2.4 Flow Mass Curve
The flow mass curve is a plot of the cumulative discharge volume against time plotted
in chronological order. The ordinate of the mass curve, V at any time t is
Where t0= time at the beginning of the curve
Q = discharge rate
t = time at any instant
The slope of the mass curve at any point represents.
Figure 3.3 an illustration of the Mass curve diagram
Assuming reservoir is full at the beginning of a dry period (i.e., when inflow is less
than withdrawal). The storage S is obtained as the maximum difference in the ordinate between
mass curves of supply and demand. The minimum storage volume required by a reservoir is the
largest of such S values over different dry periods.
CHAPTER 4
ANALYSIS & DISCUSSION
4.1 Rainfall Analysis
4.1.1 Seasonal Variations
The Hydrographs and Bar graphs in figures 3.5 - 4.1, shows there are two distinct wet
seasons during the year, the ‗long rains‘ from March to May and the ‗short rains‘ from October
to December. The total fall in these two periods usually amounts to almost 80% of the mean
annual rainfall. January/ March are usually a dry period, although there is usually a short wet
spell of 10 to 14 days in late January or February. The months of July/October period usually
receives a few scattered showers. The general rainfall pattern is erratic.
The formula for trend of rainfall was applied to the monthly records of rainfall in the Kiambu
DC office station ID.91 36 58, reduced to fourth reduction moving average, given in table 18.
The rainfall data was analyzed for the period of 1908 – 1964 as seen in figure 5.0 shows a
constant pattern of rainfall over the years. With highest rainfall being 65 inches and lowest being
23 inches of rainfall recorded. The moving average shows a decrease in rainall rom 1908 to the
year 1945, and then an increase in rainfall is observed from 1945 to 1970.
Visual scrutiny of the rainfall of the data analysed to determine if there is any trend in the rainfall
was done. Each analysis, without any exception, reveals a decrease in rainfall over the last 20 to
50 years.
4.1.2 Volume of Water
The analysis was done where 15 stations were taken for the catchment. The average weighted
monthly rainfalls were obtained from the Theissen Polygon method. These are totaled to give the
average annual rainfall on the catchment:
Average annual Rainfall = 841.77 mm on the catchment
The total area of the catchment is determined by counting the squares method in fig 6.0
Area of the catchment = 6000 sq. km
The volume of water from rainfall is determined as follows: Volume of water from rainfall =
Area of catchment × Average annual rainfall
=
= 5050.62× m3v
4.2 Stream Flow analysis
In the stream flows, a summary of some of the major gauging stations are given in tables 9 to 11,
which give the computed total discharge in each year together with the mean and extreme
values(max/min). Monthly correlation was done where necessary, and in most cases reasonable
and usable results were obtained.
The station 3DA2 was set up with the intention of measuring the total outflow from the Upper
Athi catchment. The year 1957 was the first full year for which records were available and must
be considered a wet year with rainfall some 150% of the mean.
4.2.1 Flow Hydrograph
Generally, the hydrographs for the various rivers in the catchment are of similar form. The main
features are:-
a) The high peaks, of relatively short duration, caused by long and short rains, and
b) The high ratio of sustained low flow to flood flow.
A study of all the hydrographs reveals that the flood peaks on the rivers close to the north-
east watershed are modified into a large ―spread‖. An inspection of each hydrograph indicates
that the discharge of some rivers tends to fall off more rapidly from peak to low flows than
others.
In the outlet Regular Gauging Station 3DA2, the years 1961- 1962 was the critical period of
flood flows, the catchment experienced high flows evident from the spike in the line hydrograph.
The critical drought period observed in the same station is in the year 1974 and 1996; with
minimum flow of 1.056 cumecs.
The Hydrograph of Ndarugu River (RGS 3CB05) also shows a kink in flow, with high flows
seen in the 1961- 1964 and also high flows in the year 1977 and 1978 showing critical periods of
flooding in the area.
The exception to this broad classification is the lower Mbagathi (RGS 3AA4) which exhibits
flashy floods and negligible low flow. Flash floods are observed in the hydrograph at the years
1961-1962 , with a long period of low flows between 1965 and 1966. Flash floods also
experienced in 1967 during the high rain seasons.
The source of errors observed high flows during the storms may be subject to an error of
50%, even on the larger rivers such as the Ndarugu. Some weirs are also known to drown to an
unknown extent at the higher flows, causing an over-estimate to be made of flood flow in the
above cases.
Source of errors in the low flows, the rivers are affected to an unknown extent by the
abstractions upstream of each gauging site. Although the total abstraction sanctioned may be
determined there are no records of what abstraction is usually taking place at the times that
would influence each gauge reading. Another source of error is the present system of reading the
gauges once per day only, and in the case of more inaccessible stations where there is no resident
population to undertake the ask, less frequently than that. Only in the case of very large rivers
free from rapid variations in flow is this method really satisfactory.
4.2.2 Total Flows
The station R.G.S. 3DA2 was set up with the intention of measuring the total outflow from the
Upper Athi catchment. 1961 has the highest flow in the catchment showing flood period at a
total of 848.6 cumecs and a maximum flow of 489.9 cumecs.
4.2.3 Mass Curve
Storage requirements were calculated through the drought periods in the catchment were selected
to interpret the storage capacity. It was found that the most critical storage period on the stream
varied for the gross yield required. The mass curves of RGS 3DA2 has 2 troughs that point to
possible storage of a good amount of water were there a reservoir to store the water. The required
storage (S1)that meets demand of the catchment was 4.5 , which is observed
between November and December. And the second storage (S2) recorded is 8.75 ,
during March and April.
4.2.4 Flow Duration Curve
The 50, 95 97.5, 98 and 99 percentiles for the flow duration curves were obtained as follows:
Table 22
PERCENTILES
CLASS MID POINT VALUE(m3/s)
STREAMFLOW STATIONS (RGS)
3DA2 3BA32
50% 8.75 6.4
90% 2.4 1.9
95% 1.85 1.45
99% 1.3 1.0
Thus the mean stream flow is 8.75 cumecs for RGS 3DA2 and 6.4 cumecs for RGS 3BA32.
Otherwise while accommodating a 10%, 5% and 1% percent error the above results are obtained.
The 5% error is commonly used for rural areas estimation of streamflow to allow for the high
amounts of infiltration of rainfall into the soil, while the 1% is used in urban areas where the
amount of infiltration is low due to the impermeability of pavements and buildings in towns and
cities. The 95% low flows is 2.7 cumecs for RGS 3DA2 as determined from the low flow curve.
4.3 Evaporation
The evaporation rates from a free water surface will be less than that from the standard pans of
shallow depth and it is usual to apply a correction factor of from 0.80 to 0.90 to the pan figures to
arrive at the free water values. In view of the short period for which records are available it was
suggested that a factor of 0.95 be used in this case to give conservative estimates of the
evaporation likely in critical periods.
The table 23 shows the average total monthly and quarterly evaporation measured and
from this it can be seen that the quantity of evaporation is high in the 1st quarter, low in the 2
nd
and 3rd
quarters and intermediate in the 4th
quarter of the year. This classification is sufficiently
accurate for the preliminary estimation of the evaporation loss from reservoirs.
TABLE 23
Average Monthly and Quarterly Pan Evaporation in feet - Nairobi Dam (5,500 ft)
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
0.68 0.7 0.74 0.48 0.35 0.32 0.33 0.34 0.46 0.59 0.47 0.53
2.12 1.15 1.13
1.59
1st quarter 2nd quarter 3rd quarter 4th quarter
4.3.1 Extreme Values
No firm calculations of the extreme values of the evaporation can be made from the short period
of data available. Estimated values are 7½ ft. per year in an extremely hot, dry year and 4 ft. per
year in an exceptionally wet and cloudy year at Nairobi Dam.
4.3.2 Variation with Altitude
The table 24 lists the monthly evaporation in four stations at various altitudes in the catchment.
The figures below show there is a general decrease in evaporation as the altitude increases.
TABLE 24
Measured Evaporation in Inches from Standard Pans
Nairobi Dam Kabete Ruiru Dam Tigoni (5,500 ft.) (5,970 ft.) (6,500 ft.) (7,200 ft.)
January 9.61 8.12 5.91 6.33
February 9.43 8.26 5.62 6.24
March 10.44 7.82 5.03 6.39
April 4.52 3.97 3.45 2.50
May 3.69 3.96 3.09 2.57
June 3.84 3.80 3.57 2.69
July 4.15 3.44 3.01 3.02
August 3.30 2.95 2.56 2.49
September 6.54 6.00 4.08 5.15
October 5.15 5.66 2.87 3.97
November 4.81 5.80 3.59 4.07
December 4.72 5.43 3.84 3.55
Total 70.2 65.2 46.6 49.0
4.4 Sedimentation
The table 3 shows the estimated average sediment load per year and total over a 50 year period
for the major Athi tributaries, also shows the sediment production rates which have been
calculated from rough sediment rating curves. The estimated average production rate varies
considerably from less than 0.016 acre-ft/sq mile/year, for small catchments such as the Kamiti
to more than 0.65 acre-ft/sq.mile/year for the large Thiririka and Ndarugu catchments. This
heavy sedimentation rates on the larger rivers, taking up over 1,000 acre-ft.of storage capacity in
50 years, will restrict the storage works which can be developed on the main streams of the
Ruiru, Thiririka and Ndarugu, although measures to reduce the sediment load could be taken
where stream flow is diverted to off-stream storage.
Chapter 5
5.0 Conclusion & Recommendation
The Upper Athi River Basin has the Capital city of Nairobi, and a major agricultural district of
Kenya. The catchment has potential agricultural development, the area lies generally above the
7,000 ft. contour and receives an average annual rainfall over the area of approximately 50
inches. The soils of this area usually humic, very leached thus an advantage in the growing of
coffee in the area.
The assessment of surface water resources is useful in the planning for further development. The
Upper Athi area has been found to have great potential for further development.
The rainfall in the basin as analysed varies from 600 -1500 mm p.a. The pattern of rainfall being
two rainy seasons: long rains from March to May, Short rains from October to December. The
records show an increasing trend in rainfall since the year 1957. The total volume of rainwater
within the Upper Athi Basin has been estimated to be 5000×106
m3 per annum.
The
major tributaries of the Upper Athi Basin are Mbagathi, Nairobi river, Thiririka, Ruiru,
Kamiti, Ndarugu river and Ngong River. All these join to form the main Athi River. The Ngong
and Mbagathi rivers, which flow from the south, have insufficient water supply, but are subject
to flash-flooding. The Nairobi river, which flows down the Aberdare-ranges, provides almost
8×106 m
3. It has a consistent flow. The volume of water assessed at the outlet of the Athi River is
28×106 m
3.
The 95% Low Flow Duration is accepted in Kenya as Low Flow value of a river particularly
useful for water supply
There lies a great potential for conservation of flood waters in the Upper Athi Basin. The best
possible site for development of a dam is at 3DA2 (outlet). The flow here varies from 3.2 to
50×106 m
3.
References
Alnashir Charania, (1997/1998), Determination Of Parameters Of Upper Athi River Basin,
Kenya, 50 p.
Bear, J., (1979), Hydraulics of Groundwater, McGraw-Hill, New York, 569 p.
Bras, R. L., (1990), Hydrology, an Introduction to Hydrologic Science, Addison-Wesley,
Reading, MA, 643 p.
Burn, D.H. and M.A. Hag Elnur. 2002. “Detection of Hydrologic Trends and Variability.
Journal of Hydrology 255 (2002), 107-122.
Chow, V. T., D. R. Maidment and L. W. Mays, (1988), Applied Hydrology, McGraw Hill, 572p.
Dingman, S. L., (2002), Physical Hydrology, 2nd Edition, Prentice Hall, 646 p.
Dunne, T. and L. B. Leopold, (1978), Water in Environmental Planning, W H Freeman and Co,
San Francisco, 818 p.
E.D Dudley, J.O Robertson (1958), Upper Athi River Investigation, Kenya, Hydraulic Branch,
Ministry of works, 11-79 p.
Helsel, D.R. and Hirsch, R.M., 1991. Statistical Methods in Water Resources. Book 4,
Hydrologic Analysis and Interpretation.
Hirsch, R.M., Slack, J.R. and Smith, R.A., 1982. Techniques of trend analysis for monthly
water quality data, Water Resources. Res. 18, 107–121.
Linsley, R. K., M. A. Kohler and J. L. H. Paulhus, (1982), Hydrology for Engineers, 3rd Edition,
McGraw-Hill, New York, 508 p.
Richter, B.D., Baumgartner, J.V., Powell, J., and Braun, D.P., 1996. A method for assessing
hydrologic alteration within ecosystems. Conservation Biology, 10: 1163-1174.
Richter, B.D., Baumgartner, J.V., Wigington, R., and Braun, D.P., 1997. How much water does a
river need? Freshwater Biology, 37: 231-249.
Richter, B.D., Baumgartner, J.V., Braun, D.P., and Powell, J., 1998. A spatial assessment of
hydrologic alterations within a river network. Regulated Rivers: Research & Management, 14:
329-340.
Shahin M., van Oorschot H.J.L., and de Lange S.J., 1993. Statistical Analysis in Water
Resources Engineering. Balkema Publishers, Rotterdam, Netherlands.
APPENDIX
Appendix A: Rainfall Data
0
50
100
150
200
250
JAN FEB MAR APR MAY JUNE JULY AUG SEP OCT NOV DEC
m
o
n
t
h
l
y
m
e
a
n
motnhs
Fig. Bargrapgh of Rainfall Station 9136043 Muguga
Series1
0
50
100
150
200
250
0 2 4 6 8 10 12 14
m
o
n
t
h
l
y
m
e
a
n
months
Fig LINE GRAPH OF RAINFALL STATION 9136043 MUGUGA
Series1
YEARS JAN FEB MAR APR MAY JUNE JULY AUG SEP OCT NOV DEC ANNUAL
1990 51.6 47.8 219.7 284.2 309.7 6.5 13.6 21 32.8 90 126 76.1 90.59
1991 33.9 0.4 79.7 158.3 282.5 12.5 13.3 40.3 2.8 21.6 199.1 50.7 80.43
1992 5 70.2 3.9 400.9 216.5 20.6 29.4 3.8 14.9 70.5 112.6 87 75.57
1993 200.1 53.1 61.4 45.9 41.4 61.1 3.5 3.9 0 19.3 108.8 179.8 73.21
1994 4.9 35.5 56.3 237.2 92.2 44.4 19.5 33.9 1 87.8 301.4 64.7 97.61
1995 8.6 87.4 165.6 259.3 244.4 124.3 19.2 30.8 51.4 155.7 149.7 67.5 86.58
1996 12.9 36.4 110.1 91.1 89.2 51.5 35.6 36.6 37 1.3 209.7 2.6 98.95
1997 2.7 0 29.2 541.2 106.1 23.1 21.5 85.4 0 322.9 308.8 219.8 123.40
1998 315.5 137.1 101.3 151.8 326.7 63.1 22.6 21.3 33.4 54.8 62.1 11.3 98.01
1999 16 0.9 180 150.6 31.2 2.7 11.9 29.6 26.1 21.4 352.9 228 78.83
2000 5.4 0 41.7 254.4 100.1 57.9 4.1 6.1 53.5 18.4 187.7 111.3 84.35
2001 371.6 3.2 180.3 106.5 85.7 79.4 16.2 23.4 19.5 95.3 189.5 13.3 95.52
2002 52 69.1 90.2 278.7 134.3 1.6 6.6 6.4 22.3 59 157.4 230.9 72.89
2003 28.4 12 51.6 219.2 28.4 30.2 3.1 54.3 27.8 54.7 117.1 14.1 72.07
2004 60.1 45.3 89 411.6 191.3 10.4 6.2 0.2 16.1 82 118.4 58.1 83.00
2005 76.8 45.7 104.7 210.4 253.9 27.2 26.5 8.5 28.2 32.3 88.7 0.5 84.43
2007 51.4 98.6 52.9 349.3 184.2 83 25.4 52.6 89.1 25 69.1 42.4 92.34
2008 42.8 151.9 199.3 173.7 19 5.7 64.3 9.1 47.4 165.1 209.6 5.3 81.01
2009 42.8 18.1 76.6 75.7 141.4 43.3 6.8 2.3 6.3 141.8 110.2 185.7 90.88
2010 143.5 73.8 250.3 252.8 273.8 51.9 2 29.9 19.9 64.3 93.3 74.5 99.03
2011 4.2 66.3 147.7 80.7 93.9 4.7 14.3 26.9 32.5 154.3 175.7 245.5 105.52
2012 0 16 5 352.6 262 39.9 23.4 42.4 8.9 241.7 249.2 244.6 107.52
2013 45.4 0 175.2 508.8 53.4 20.3 5.4 51.7 25.9 48.5 53.5 106.6 91.23
MONTHLY 68.5043 46.4696 107.465 243.257 154.839 37.6217 17.1478 26.9739 25.9478 88.1609 163.065 100.883
Table RAINFALL DATA FOR STATION ID 9136208 KABETE AGROMET STATION
0
50
100
150
200
250
300
JAN FEB MAR APR MAY JUNE JULY AUG SEP OCT NOV DEC
m
o
n
t
h
l
y
m
e
a
n
months
FIG. Bargraph of Rainfall Station 9136208 Kabete Agromet
Series1
YEARS JAN FEB MAR APR MAY JUNE JULY AUG SEP OCT NOV DEC ANNUAL
1990 42.8 23.2 217.3 251.5 64.9 5.1 0 3.4 0 48.8 208.5 110.2 81.31
1991 29.3 13.3 43.5 80.5 57.5 3.1 1.4 8.9 3.4 46.5 119.9 156.7 47.00
1992 12 6.1 5 192.9 32 1.1 6.8 0 0.7 31 141.2 186.2 51.25
1993 256.5 84.9 60.9 20.8 13.7 6.3 0.5 3.1 0.6 26 150.8 67.3 57.62
1994 0 103.5 75.3 82.4 29.8 8.2 3.3 9.9 4.3 110.9 406.3 143.7 81.47
1995 28.5 83.3 150.1 49.6 33.1 0.9 4.1 3.2 5.1 103.7 46 87.6 49.60
1996 22.4 56.5 73.7 96.4 42.8 19.3 2.2 2.2 0.7 0 187.7 1.5 42.12
1997 3.8 0 46 208.5 21.2 0.5 1.2 4.3 0 83.2 270.3 177.3 68.03
1998 295.4 219.4 118 123 162.6 38.7 15.4 2.9 1.8 3.3 113.9 15.8 92.52
1999 16.1 2.2 121 113.8 9.8 5 2.4 4.9 0 20.6 257 108.6 55.12
2000 7 0 52.5 68.5 15.6 6.2 0.3 1.8 2.3 41 189.8 98.8 40.32
2001 244.8 0 113 88.9 15.3 4.3 4.3 2.5 0 7.3 169 43.6 57.75
2002 79.5 7.5 98.9 120.4 126.6 1.4 0 0.2 8.8 21.2 144.3 182.4 65.93
2003 31.6 17.2 115.2 153.2 133.8 0 0 26.3 21.5 31.8 121.1 24.1 56.32
2004 45.1 47.9 83.1 121.5 59.8 0.7 0 0 1 47.6 161.3 89.5 54.79
2005 12.2 19.2 101.7 165.1 100.5 79.4 16.2 23.4 19.5 95.3 189.5 13.3 69.61
2007 61.4 44.8 20.5 143.9 41.7 2.7 26.8 5.2 4.3 18.3 127.9 82.4 48.33
2008 117.4 7.3 73 129.3 4.5 0.3 1.3 0.2 9.1 23.9 122.8 44.9 44.50
2009 74.2 26.3 3.2 145.4 29.7 5.2 0 0 1.2 41.3 34.4 127.1 40.67
2010 51 64.1 241.9 107.9 120.9 1.7 2.7 1.3 0.6 32.1 116 59.6 66.65
2011 9.1 71.8 209.8 1 37.7 0 3.4 0.7 5.9 50.2 180.3 28.2 49.84
2012 0 4.6 1.6 286.4 112.5 36.9 0 11.8 0 22.3 119.7 73.2 55.75
2013 50.4 0 113.1 209.3 37.7 0.3 2.7 0.6 2.5 24.5 256.8 78.2 64.68
MONTHLY 64.8043 39.2652 92.9696 128.704 56.6826 9.88261 4.13043 5.07826 4.05652 40.4696 166.717 86.9652
Table RAINFALL DATA FOR STATION ID.9137089 MACHAKOS STATION
0
20
40
60
80
100
120
140
160
180
JAN FEB MAR APR MAY JUNE JULY AUG SEP OCT NOV DEC
m
o
t
n
l
y
m
e
a
n
months
Fig. Bargraph of Rainfall Station 9137089 Machakos
Series1
0
20
40
60
80
100
120
140
160
180
0 2 4 6 8 10 12 14
M
O
N
T
H
L
Y
M
E
A
N
MONTHS
Fig LINE GRAPH OF RAINFALL STATION 9137089 MACHAKOS
Series1
YEARS JAN FEB MAR APR MAY JUNE JULY AUG SEP OCT NOV DEC ANNUAL
1962 172.6 5.7 86.7 235.2 170.3 12.2 17.4 39.2 20.1 166.7 197.6 191.6 109.61
1970 139.3 0 146 251.4 47.7 10.2 10.5 32.6 10.5 7.1 123.2 60.5 69.92
1971 36.6 19.5 32.8 274.8 92.2 64.3 37.3 16.4 7.7 13 121.5 221.9 78.17
1972 50.7 7.8 69.9 101.1 101.6 18.3 8.9 5 50.2 258.5 222.9 37.6 77.71
1973 120.5 118.2 43 292.7 18.8 2.8 3.2 18.2 2.7 49.3 300.7 49.1 84.93
1974 65.8 50.5 136.1 313.4 35.1 41.2 69.1 13.1 30.6 35.7 142.1 59.5 82.68
1975 17.1 7.6 61.9 268.9 39.6 3.3 21.4 9.9 58.6 33.5 225.8 64.2 67.65
1976 0.4 34.2 60.6 265.5 67.2 39.9 0.7 6 37.9 13.8 303.5 143.9 81.13
1977 58.3 60.3 110.6 423.1 168.7 6.4 6.4 36.2 52.3 12.4 544.8 173 137.71
1978 185.5 185.5 185.5 185.5 185.5 16.1 6 4 13.6 63 308.6 263.9 133.56
1979 114.9 50.3 196.2 308.7 193 44.7 32.7 13 4.7 120 246.7 104.8 119.14
1980 0 21.4 89.1 166.4 75.8 0 0 43.2 10.5 9.9 307.4 54.8 64.88
1981 47.1 2.1 484 297.6 306.9 9.8 1.5 10.3 17.4 169.8 185.8 89.7 135.17
1982 16.2 0 8.2 346.3 168.1 9.1 27.1 3.2 53 279.4 387.3 127.1 118.75
1983 0 122.3 138.6 197.1 75.5 3.2 8.7 16.1 27.5 7.8 133.9 336.5 88.93
1984 30.2 0 34.4 115.1 3.2 0 25.9 0 10.1 341.2 458.8 61.5 90.03
1985 6.3 175.5 205.3 359.5 103.6 5.3 15.6 3.1 9.9 191.2 283.6 138.4 124.78
1986 54.5 6.5 58.9 521.7 115.4 5.8 3.7 13.9 7.7 72.2 516.7 184.4 130.12
1987 10.5 13.4 0 216.7 69.5 82.7 0 48.5 4 11.4 267.3 23 62.25
1988 68.2 12.7 234.4 596.5 22.8 0 45.9 38.6 87 285.4 418.9 302.9 176.11
1989 125 16.8 221.4 331.2 103 17.3 4 19.9 14.3 169.8 439.1 258.8 143.38
1990 77 33.4 365.4 387.4 133.2 2.9 3 1.4 43.1 235.5 427.8 352.9 171.92
1991 28.2 0 40.6 107.3 154.8 19.3 0 58.5 3.2 89.6 325.5 234.2 88.43
1992 18.5 0 8.5 175.6 73.1 0 9.5 22.3 16.3 57.4 257.1 188 68.86
1993 389.3 81.3 10.5 140.1 91.1 7.2 0 24.2 0 42.8 162.4 127.9 89.73
1994 0 55.3 111.9 144.6 44.2 10.5 8.5 36.4 0 111.8 350.9 145.4 84.96
1995 29.2 48.2 64.9 165.9 51.4 1.5 11.7 12.5 0 184.2 212.7 178.7 80.08
1996 46.7 2.1 116.3 28.3 111.5 29.7 25 22.2 3.8 0 426.8 0 67.70
MONTHLY 68.1643 40.3786 118.632 257.771 100.814 16.5607 14.4179 20.2821 21.3107 108.3 296.407 149.079
Table RAINFALL DATA FOR STATION ID.9137102 KATENDE FOREST STATION
0
50
100
150
200
250
300
350
JAN FEB MAR APR MAY JUNE JULY AUG SEP OCT NOV DEC
m
o
n
t
h
l
y
m
e
a
n
months
Fig. Bargraph of Rainfall Station 9137102 Katende Forest
Series1
0
50
100
150
200
250
300
350
0 2 4 6 8 10 12 14
Fig LINE GRAPH OF RAINFALL STATION 9137102 KATENDE
Series1
YEAR JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ANNUAL MAX MIN
1957 11.463 12.271 2.545 30.205 150.714 59.288 16.401 10.792 7.351 5.363 10.822 15.776 332.991 150.714 2.545
1958 4.101 20.227 17.110 15.043 244.643 35.475 23.640 15.261 9.863 6.868 5.858 5.231 403.319 244.643 4.101
1959 3.495 2.510 3.328 6.031 19.248 9.569 4.917 4.684 3.883 2.722 9.892 7.682 77.963 19.248 2.510
1960 3.007 2.296 6.817 19.913 17.365 7.498 5.462 4.055 3.438 4.064 9.143 4.028 87.087 19.913 2.296
1961 2.650 2.091 2.143 7.492 13.284 4.453 3.400 3.351 4.389 17.235 489.994 298.176 848.658 489.994 2.091
1962 226.031 27.022 20.891 27.291 103.811 40.617 26.633 16.430 12.980 12.008 13.521 14.465 541.699 226.031 12.008
1963 16.850 10.475 8.389 65.495 235.861 68.337 31.758 20.915 11.367 8.393 19.256 93.332 590.427 235.861 8.389
1964 35.942 11.089 20.305 115.397 91.122 35.523 20.652 19.785 12.881 11.033 9.331 13.822 396.883 115.397 9.331
1965 12.055 5.454 4.165 16.026 22.583 11.419 7.221 5.522 3.639 4.717 18.426 12.673 123.899 22.583 3.639
1966 6.832 5.964 15.036 56.366 68.738 21.621 11.737 8.024 7.223 4.067 19.155 5.203 229.967 68.738 4.067
1967 2.653 2.062 1.731 26.830 182.597 47.973 25.128 16.028 12.382 13.034 25.580 22.792 378.789 182.597 1.731
1968 8.995 6.530 46.496 108.313 96.233 44.398 25.516 16.730 9.563 8.514 68.530 109.078 548.897 109.078 6.530
1969 23.643 19.176 16.004 9.480 32.195 14.213 8.495 7.441 4.735 3.939 8.272 3.530 151.123 32.195 3.530
1970 6.213 2.902 9.116 80.187 58.318 35.222 16.552 10.871 7.330 5.384 6.429 3.567 242.090 80.187 2.902
1971 2.910 2.018 1.188 22.863 85.844 22.340 11.628 9.248 5.840 3.765 2.453 6.033 176.131 85.844 1.188
1972 15.927 5.108 2.263 1.900 7.318 11.855 4.790 2.873 2.506 5.479 30.235 15.411 105.664 30.235 1.900
1973 8.239 5.514 2.824 29.534 7.444 8.044 4.344 4.051 5.840 52.810 63.836 3.438 195.918 63.836 2.824
1974 1.610 1.105 3.034 60.660 30.051 12.761 37.018 17.893 5.986 6.507 9.778 5.639 192.042 60.660 1.105
1975 2.918 1.989 2.260 13.056 10.678 5.377 3.942 3.438 4.404 4.862 6.851 5.221 64.998 13.056 1.989
ANNUAL FLOW OF RGS. 3DA02 UPPER ATHI RIVER (cumec)
Table 9.0A
PP
EN
DIX
B: S
TR
EA
M F
LO
W
1976 2.125 1.663 1.667 10.425 4.257 3.057 2.545 1.749 2.047 1.493 3.395 3.514 37.937 10.425 1.493
1977 6.572 4.237 1.677 62.667 136.550 29.286 15.253 10.237 5.707 3.998 51.892 36.489 364.564 136.550 1.677
1978 32.494 10.023 76.419 111.227 105.677 25.263 16.641 10.635 7.068 7.973 20.362 20.683 444.466 111.227 7.068
1979 7.594 56.631 16.483 47.910 66.905 51.317 23.610 13.463 8.232 6.364 12.983 6.590 318.082 66.905 6.364
1980 3.761 8.122 3.443 8.804 81.061 31.768 15.061 9.793 6.412 4.690 35.104 16.537 224.555 81.061 3.443
1981 7.956 5.068 9.945 136.187 138.860 41.209 21.659 14.056 10.321 8.713 8.998 8.600 411.571 138.860 5.068
1982 5.213 2.794 2.062 11.065 36.584 28.406 10.683 7.683 6.979 32.100 30.504 46.267 220.340 46.267 2.062
1983 14.364 14.033 6.247 13.410 29.121 14.486 12.190 8.839 7.020 7.557 10.500 26.640 164.407 29.121 6.247
1984 43.104 5.823 3.632 3.655 5.496 2.647 1.737 2.662 1.635 14.054 18.097 25.504 128.046 43.104 1.635
1985 3.877 46.411 3.253 26.684 26.187 16.756 9.616 7.629 5.792 3.846 7.079 10.354 167.482 46.411 3.253
1986 3.619 1.589 4.330 28.072 109.558 20.041 10.706 6.012 4.796 4.271 10.267 35.103 238.365 109.558 1.589
1987 5.058 3.099 2.224 7.892 20.955 25.030 8.285 6.354 3.833 2.550 6.860 4.231 96.370 25.030 2.224
1988 3.301 1.575 7.602 128.838 103.279 33.616 17.257 12.314 11.111 6.782 13.220 12.631 351.526 128.838 1.575
1989 22.218 16.930 13.117 43.775 85.057 37.177 21.742 14.787 10.765 9.632 27.013 22.536 324.750 85.057 9.632
1990 75.308 13.918 25.927 145.132 63.371 42.746 20.783 13.501 10.266 9.463 22.040 19.990 462.445 145.132 9.463
1991 8.528 5.374 3.608 6.677 26.351 23.852 12.785 8.246 6.052 4.957 8.817 8.012 123.260 26.351 3.608
1992 3.288 2.034 1.816 31.711 46.443 13.001 10.537 7.437 5.567 5.373 11.570 13.669 152.446 46.443 1.816
1993 56.688 54.038 10.874 6.696 6.397 7.546 6.228 4.984 3.603 2.638 6.842 25.810 192.343 56.688 2.638
1994 6.286 2.190 5.568 64.122 23.607 25.299 12.244 26.656 25.444 23.382 7.858 22.253 244.910 64.122 2.190
1995 6.883 3.206 24.484 28.287 40.269 25.041 19.142 11.671 8.657 5.608 12.539 19.990 205.778 40.269 3.206
1996 8.191 4.331 4.878 4.878 3.803 2.749 6.397 2.945 1.056 1.665 1.759 2.869 45.520 8.191 1.056
0.0
100.0
200.0
300.0
400.0
500.0
600.0
700.0
800.0
900.0
1957 1962 1967 1972 1977 1982 1987 1992 1997
AN
NU
AL
FLO
W m
m
YEARS
Fig FLOW HYDROGRAPH OF RGS 3DA2
Series1
YEAR JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ANNUAL MAX MIN
1957 1.07 1.18 2.44 3.86 25.28 10.64 3.77 2.16 1.43 1.00 1.64 3.05 57.53 25.28 1.00
1958 1.20 2.47 3.69 3.31 34.08 11.46 5.92 3.94 2.20 1.47 1.22 0.96 71.93 34.08 0.96
1959 0.69 0.51 0.53 1.29 5.35 3.82 1.41 0.95 0.74 0.65 2.38 1.24 19.55 5.35 0.51
1960 0.66 0.50 0.88 4.93 5.30 2.19 1.29 0.84 0.67 0.64 1.96 1.02 20.88 5.30 0.50
1961 0.56 0.53 0.51 0.93 3.01 1.36 1.15 0.96 1.16 4.52 38.49 27.08 80.27 38.49 0.51
1962 20.68 4.84 2.15 3.41 21.98 6.70 3.85 2.40 1.77 1.71 1.72 2.85 74.07 21.98 1.71
1963 2.88 2.57 1.91 14.15 41.34 10.58 4.96 2.58 1.66 1.34 2.59 19.52 106.08 41.34 1.34
1964 6.85 2.23 4.00 17.04 21.78 7.24 3.23 2.91 2.06 1.91 1.99 2.81 74.04 21.78 1.91
1965 2.86 1.52 0.96 2.12 4.83 3.47 1.73 1.15 0.74 0.76 4.68 3.77 28.60 4.83 0.74
1966 1.66 1.33 2.72 17.90 24.89 4.32 2.33 1.61 1.28 0.83 3.38 1.28 63.52 24.89 0.83
1967 0.63 0.42 0.37 2.00 28.51 11.77 4.05 2.58 2.31 2.67 8.64 6.73 70.67 28.51 0.37
1968 2.27 1.37 6.74 11.42 17.36 8.75 4.13 2.46 1.47 1.39 13.42 29.28 100.06 29.28 1.37
1969 3.60 2.51 2.30 1.60 6.10 3.33 1.67 1.21 0.84 1.81 0.77 0.61 26.34 6.10 0.61
1970 0.59 0.45 0.52 15.71 16.74 7.26 3.18 1.95 1.26 0.82 1.08 0.73 50.29 16.74 0.45
1971 0.16 0.72 0.48 4.85 15.35 5.27 3.28 2.27 2.23 1.33 1.02 2.02 38.98 15.35 0.16
1972 1.12 0.75 0.72 0.58 2.69 1.20 0.59 1.17 0.98 2.89 18.33 5.97 36.98 18.33 0.58
1973 2.18 1.19 0.68 0.89 1.75 2.00 1.05 0.84 0.63 0.59 0.78 0.79 13.37 2.18 0.59
1974 2.36 1.71 0.66 1.82 5.27 2.52 11.44 3.86 1.74 1.26 1.96 1.24 35.84 11.44 0.66
ANNUAL FLOW OF RGS. 3CB05 NDARUGU RIVER
Table
1975 0.76 0.42 0.42 1.15 5.58 2.82 1.16 3.47 1.14 1.18 2.77 2.79 23.67 5.58 0.42
1976 1.00 0.49 0.44 4.00 3.41 2.69 1.20 0.59 0.36 0.39 0.44 1.48 16.51 4.00 0.36
1977 0.45 0.27 0.53 22.22 48.95 7.75 3.29 2.25 1.34 1.06 10.84 8.68 107.64 48.95 0.27
1978 4.13 2.93 3.85 52.54 25.86 4.41 1.11 0.63 0.76 1.80 7.16 6.65 111.81 52.54 0.63
1979 0.76 3.61 2.93 12.18 23.32 11.14 5.85 1.64 1.66 0.66 2.35 0.70 66.79 23.32 0.66
1980 0.67 1.01 0.77 1.28 12.66 7.12 1.50 1.00 0.59 0.86 5.02 3.97 36.45 12.66 0.59
1981 1.97 0.85 1.55 10.82 19.93 6.01 2.96 1.67 0.81 1.23 1.43 1.71 50.95 19.93 0.81
1982 1.03 0.63 0.41 1.66 11.10 7.29 2.05 0.93 0.84 2.45 1.20 1.66 31.25 11.10 0.41
1983 2.36 1.71 0.66 1.82 16.21 1.47 1.20 1.66 1.79 1.20 1.14 2.35 33.58 16.21 0.66
1984 1.31 0.50 0.54 0.69 0.21 0.32 0.02 0.03 0.31 2.38 0.41 1.66 8.39 2.38 0.02
1985 1.03 1.18 2.42 4.96 2.58 1.66 1.34 0.48 0.62 2.86 1.45 2.22 22.80 4.96 0.48
1986 0.67 0.61 3.01 1.36 1.15 0.96 2.29 1.60 1.31 1.11 1.75 2.74 18.56 3.01 0.61
1987 1.56 1.05 0.67 1.22 2.47 4.39 2.28 2.44 0.91 1.00 2.56 2.19 22.73 4.39 0.67
1988 0.76 0.48 0.63 3.07 6.32 4.80 2.98 2.58 1.91 1.21 2.13 2.38 29.26 6.32 0.48
1989 3.10 3.13 2.44 3.42 6.27 5.14 3.19 2.22 1.67 1.45 3.14 5.02 40.19 6.27 1.45
1990 5.17 2.68 3.67 6.00 5.74 5.05 2.64 1.93 1.48 1.45 3.14 2.57 41.53 6.00 1.45
1991 1.72 1.13 1.00 1.39 4.25 4.84 2.56 1.80 1.29 1.27 2.08 1.32 24.65 4.84 1.00
1992 0.90 1.15 0.98 2.01 4.15 2.91 2.15 1.80 1.74 2.25 1.89 2.99 24.93 4.15 0.90
1993 4.74 5.82 2.21 2.15 2.11 1.53 1.93 1.89 1.48 1.50 1.34 2.07 28.77 5.82 1.34
0.0
20.0
40.0
60.0
80.0
100.0
120.0
1955 1960 1965 1970 1975 1980 1985 1990 1995
AN
UA
LL F
LOW
mm
Years
Fig FLOW HYDROGRAPH FOR RGS 3CB05 NDARUGU RIVER
Series1
YEAR JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ANNUAL MAX MIN
1957 3.84 2.87 16.40 19.41 20.69 27.06 16.52 10.35 7.80 9.06 6.21 14.69 154.89 27.06 2.87
1958 3.72 7.08 11.99 8.29 15.26 25.23 21.73 15.92 9.59 3.80 5.95 6.53 135.08 25.23 3.72
1959 3.22 2.55 14.03 8.82 15.04 6.77 15.26 10.79 9.14 5.36 17.45 5.01 113.44 17.45 2.55
1960 2.42 2.31 7.54 13.68 13.42 6.63 5.01 2.74 3.40 3.72 16.62 10.60 88.08 16.62 2.31
1961 2.40 8.19 21.26 12.01 11.70 2.69 3.83 9.60 9.65 14.90 30.04 27.81 154.08 30.04 2.40
1962 58.42 21.39 13.17 25.26 61.10 37.10 13.81 16.40 20.28 14.46 12.98 23.23 317.60 61.10 12.98
1965 3.94 6.81 14.13 39.36 36.75 15.79 26.55 25.44 23.38 7.86 9.65 7.31 216.97 39.36 3.94
1966 4.86 4.61 6.70 40.93 53.72 12.97 8.05 6.09 5.41 3.80 8.75 4.00 159.88 53.72 3.80
1967 2.44 2.72 1.88 8.58 137.35 28.65 15.19 10.85 8.38 8.71 13.48 23.38 261.61 137.35 1.88
1968 6.57 6.88 29.50 62.93 56.78 27.88 16.31 11.75 7.65 6.73 46.88 65.66 345.53 65.66 6.57
1969 14.06 11.69 10.09 6.92 20.56 9.33 6.55 6.08 4.20 3.48 4.44 3.38 100.79 20.56 3.38
1970 3.84 2.87 4.55 27.54 33.23 20.90 11.33 7.99 5.59 4.68 5.46 3.25 131.24 33.23 2.87
1971 2.87 2.16 1.43 6.86 51.38 13.36 9.07 7.04 4.80 3.70 3.65 7.25 113.58 51.38 1.43
1972 3.72 3.84 2.36 1.97 4.28 4.05 3.25 2.21 1.98 3.68 19.99 9.04 60.38 19.99 1.97
1973 6.55 3.61 1.92 6.45 4.92 4.58 2.98 2.53 2.37 1.92 2.60 1.95 42.38 6.55 1.92
1974 1.14 0.97 1.38 14.66 9.20 6.82 21.64 11.00 8.43 4.27 6.15 3.85 89.49 21.64 0.97
1975 28.76 19.27 17.18 94.22 96.15 62.12 42.38 32.48 44.64 52.60 3.72 3.42 496.95 96.15 3.42
1976 1.81 1.56 1.57 4.14 3.61 2.65 2.39 1.92 2.30 2.06 2.33 2.40 28.74 4.14 1.56
1977 2.33 2.10 2.24 51.42 62.93 20.99 12.99 9.74 6.01 5.17 35.28 19.83 231.03 62.93 2.10
1979 3.76 7.38 12.16 36.37 48.58 39.72 19.51 12.47 7.97 6.25 11.00 5.98 211.14 48.58 3.76
1980 3.37 5.31 3.13 6.66 46.61 21.96 10.03 6.72 4.45 3.35 21.27 9.98 142.84 46.61 3.13
1981 4.95 3.30 4.98 49.08 53.93 29.03 15.45 10.60 7.15 6.33 6.32 6.07 197.18 53.93 3.30
1982 3.27 2.00 1.35 6.98 20.08 15.82 6.86 0.48 3.94 8.92 24.46 59.50 153.66 59.50 0.48
1983 10.09 9.55 5.18 13.79 18.31 10.98 8.84 6.15 4.22 4.91 4.78 11.35 108.15 18.31 4.22
1984 4.44 1.65 1.85 2.42 1.75 1.22 1.29 1.11 1.71 1.54 2.36 2.81 24.14 4.44 1.11
ANNUAL FLOW OF RGS. 3BA32 NAIROBI RIVERTable
0.0
100.0
200.0
300.0
400.0
500.0
600.0
1955 1960 1965 1970 1975 1980 1985 1990
AN
NU
AL
FLO
W m
m
YEARS
Series1
YEAR JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ANNUAL MAX MIN
1961 0.223 0.269 0.145 0.231 2.219 0.596 0.384 0.327 0.421 2.392 59.966 5.450 72.622 59.966 0.145
1962 4.185 1.109 0.509 1.297 7.555 1.371 0.810 0.494 0.340 0.318 0.360 0.316 18.664 7.555 0.316
1963 0.533 0.389 0.346 5.802 13.477 1.448 0.588 0.365 0.294 0.155 0.203 0.987 24.587 13.477 0.155
1964 0.939 0.490 1.030 5.234 3.849 1.342 0.680 0.651 0.272 0.255 0.441 0.575 15.757 5.234 0.255
1965 0.604 0.431 0.297 0.273 1.517 1.048 0.484 0.384 0.251 0.259 2.078 1.031 8.654 2.078 0.251
1966 0.441 0.294 0.390 0.497 0.868 0.945 0.688 0.392 0.339 0.198 0.457 0.218 5.727 0.945 0.198
1967 0.117 0.071 0.087 0.422 3.560 1.808 0.636 0.476 0.397 0.419 1.421 1.403 10.815 3.560 0.071
1968 0.483 0.353 0.878 2.682 2.894 1.636 0.830 0.434 0.275 0.226 2.602 3.378 16.671 3.378 0.226
1969 0.636 0.512 0.370 0.293 1.513 0.809 0.448 0.305 0.194 0.153 0.216 0.122 5.571 1.513 0.122
1970 0.190 0.204 0.138 2.202 4.348 1.409 0.653 0.539 0.397 0.269 0.293 0.170 10.812 4.348 0.138
1971 0.139 0.129 0.166 0.258 1.065 1.106 0.799 0.528 0.345 0.190 0.181 0.284 5.191 1.106 0.129
1972 0.177 0.160 0.083 0.101 0.536 0.533 0.384 0.244 0.147 1.024 1.809 0.573 5.771 1.809 0.083
1973 0.738 0.407 0.255 0.483 0.861 0.530 0.379 0.213 0.205 0.178 0.253 0.141 4.643 0.861 0.141
1974 0.098 0.065 0.106 0.353 1.021 0.749 1.208 1.345 0.825 0.417 0.457 0.395 7.038 1.345 0.065
1975 0.256 0.141 0.149 0.185 0.589 0.283 0.232 0.226 0.211 0.316 0.356 0.327 3.269 0.589 0.141
1976 0.211 0.151 0.093 0.197 0.323 0.383 0.313 0.232 0.211 0.145 0.107 0.122 2.488 0.383 0.093
1977 0.079 0.101 0.124 3.082 5.409 1.218 0.590 0.403 0.266 0.198 2.167 1.624 15.260 5.409 0.079
1978 0.876 0.596 1.337 4.327 4.058 0.946 0.535 0.401 0.311 0.260 0.573 0.474 14.695 4.327 0.260
1979 0.496 0.559 0.821 4.252 3.924 4.321 1.079 0.512 0.356 0.300 0.327 0.185 17.130 4.321 0.185
1980 0.124 0.118 0.106 0.272 3.074 1.581 0.548 0.357 0.242 0.179 0.639 0.569 7.808 3.074 0.106
1981 0.358 0.193 0.232 2.815 4.088 1.317 0.587 0.388 0.294 0.315 0.249 0.349 11.186 4.088 0.193
1982 0.203 0.133 0.085 0.494 4.677 1.778 0.482 0.252 0.265 0.996 3.109 2.618 15.092 4.677 0.085
1983 0.264 0.454 0.300 0.582 2.507 0.909 0.687 0.542 0.359 0.295 0.303 0.278 7.479 2.507 0.264
1984 0.234 0.158 0.088 0.075 0.105 0.066 0.061 0.049 0.039 0.159 0.264 0.256 1.554 0.264 0.039
1985 0.224 0.173 0.167 1.278 4.322 1.198 0.512 0.352 0.281 0.196 0.256 0.237 9.196 4.322 0.167
1986 0.139 0.081 0.100 0.503 2.427 1.796 0.653 0.332 0.243 0.181 0.295 0.319 7.068 2.427 0.081
1987 0.225 0.162 0.096 0.276 0.701 1.918 0.655 0.320 0.181 0.104 0.192 0.098 4.928 1.918 0.096
1988 0.105 0.041 0.099 3.137 3.443 1.455 0.692 0.398 0.318 0.226 0.459 0.498 10.871 3.443 0.041
1989 0.950 2.194 1.152 0.976 3.221 1.477 0.716 0.433 0.376 0.226 2.456 1.806 15.982 3.221 0.226
1990 2.009 0.610 0.755 3.113 3.423 1.703 0.609 0.307 0.236 0.189 0.409 0.386 13.749 3.423 0.189
1991 0.258 0.148 0.135 0.152 0.353 2.070 0.683 0.400 0.262 0.183 0.201 0.128 4.973 2.070 0.128
1992 0.100 0.047 0.135 0.778 2.056 1.166 0.764 0.493 0.313 0.278 0.409 1.042 7.581 2.056 0.047
1993 1.364 1.246 0.715 0.380 0.489 0.567 0.490 0.340 0.141 0.049 0.094 0.178 6.052 1.364 0.049
1994 0.102 0.009 0.028 0.647 3.117 1.454 0.905 0.384 0.568 0.597 3.940 1.610 13.359 3.940 0.009
Table
ANNUAL FLOW FOR RGS STATION 3BD08
0.000
10.000
20.000
30.000
40.000
50.000
60.000
70.000
80.000
1960 1965 1970 1975 1980 1985 1990 1995
AN
UA
LL F
LOW
mm
YEARS
Fig FLOW HYDROGRAPH FOR RGS 3BD08
Series1
