UNIVERSITY OF NAIROBI

A CASE STUDY OF FLOOD CONTROL IN NAROK TOWN

By: KAGGWA MICHAEL OPIMO

F16/1359/2011

A project submitted as a partial fulfilment for the requirement of

the award for the degree of

BACHELOR OF SCIENCE IN CIVIL ENGINEERING

2016

PROJECT SUPERVISOR: DR. S.O. DULO

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Abstract The phenomena of flooding have been experienced in various towns and cities in Kenya.

Flooding has had an extensive negative impact on a socio-economic and environmental scale.

This project is a case study of flooding in Narok town which lies in the Ewaso Ng’iro South

River Basin. The aim of the project was to identify the causes of flooding in Narok town, the

impact of flooding, the relation between rainfall and streamflow and the measures taken to

alleviate the negative impacts of flooding within Narok town and the catchment area of the

two streams flowing through the town. The methodology adopted to gather data and

information for the project was research on previous studies, review from secondary sources

and site visits. The findings included a relation being established between rainfall and

streamflow data, a categorised outline of the courses and impacts of flooding in Narok town

and its environs and identification of the flood mitigation measures that have been

implemented in order to curb flooding within Narok town and its surroundings. Owing to the

fact that the flooding is experienced within the town, it is clear that not enough has been done

in terms of flood mitigation.

IWRM and IFM principles and guidelines are globally accepted as a benchmark for proper

watershed and riparian management. Thus, this document concludes by offering solutions

using IWRM practices and IFM principles as a standard. The solutions are broadly classified

under four categories. These are, structural measures, flood forecasting and basin monitoring,

community participation and education and an integrated approach to flood management.

Commented [SD1]: This is supposed to be a summary of

the report from aim, methodology and with key figures and findings.

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Acknowledgment This study would not have been a success without the assistance and guidance of my lecturer

and supervisor Dr. S.O Dulo. Also, I would like to thank Eng. Kasabuli who was helpful in

providing raw data and maps of Ewaso Ng’iro South River Basin. Finally, I am grateful for

the support I received from my family during the undertaking of this project and to my

classmates’ assistance during data analysis.

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Table of Contents Abstract ................................................................................................................................ 1

Acknowledgment .................................................................................................................. 2

Table of Contents .................................................................................................................. 3

Abbreviations ........................................................................................................................ 5

List of figures ........................................................................................................................ 6

List of Tables ........................................................................................................................ 6

1. Introduction ................................................................................................................... 7

1.1 General Introduction .................................................................................................... 7

1.2 Scope ........................................................................................................................... 7

1.3 Objectives .................................................................................................................... 8

1.3.1 Specific Objectives ................................................................................................ 8

2. Literature Review and Theoretical Analysis ...................................................................... 9

2.1 Rainfall ........................................................................................................................ 9

2.1.1 Measurement of rainfall......................................................................................... 9

2.2 Streamflow and Stream gauging ................................................................................ 10

2.2.1 Methods of stream gauging.................................................................................. 10

2.2.2 Hydrograph ......................................................................................................... 10

2.3 Urban Drainage ......................................................................................................... 11

2.3.1 Urban Flooding ................................................................................................... 12

2.3.2 Flood Routing ..................................................................................................... 12

2.4 WRMA and IWRM ................................................................................................... 14

2.4.1 Integrated Water Resources Management ............................................................ 14

2.4.2 Water Resources Management Authority ............................................................. 14

2.5 Integrated Flood Management .................................................................................... 16

2.5.1 Principles of IFM ................................................................................................ 16

2.5.2 IFM Strategy and Implementation ....................................................................... 18

2.5.3 Challenges of Flood Management........................................................................ 19

3. Narok catchment area ...................................................................................................... 21

3.1 Methodology ............................................................................................................. 21

3.2 Drainage area ............................................................................................................. 21

3.3 Rainfall in Narok area ................................................................................................ 23

3.4 Streamflow in Narok area .......................................................................................... 25

3.5 Geology of Narok area ............................................................................................... 26

3.6 Causes of flooding in Narok town .............................................................................. 26

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3.6.1 Poor land practices .............................................................................................. 26

3.6.2 Geographic location of Narok .............................................................................. 26

3.6.3 Climate change .................................................................................................... 26

3.6.4 Encroachment on water channels ......................................................................... 26

3.7 Impact of flooding in Narok town .............................................................................. 27

3.7.1 Economic impacts ............................................................................................... 27

3.7.2 Social impacts ..................................................................................................... 27

3.7.3 Environmental impacts ........................................................................................ 28

3.8 Flood mitigation strategies in Narok town .................................................................. 29

4. Analysis and Discussion .................................................................................................. 30

4.1 Rainfall analysis of Narok area .................................................................................. 30

4.1.1 Annual rainfall analysis ....................................................................................... 30

4.1.2 Statistical Rainfall Estimation .............................................................................. 32

4.2 Flood Duration........................................................................................................... 34

4.2.1 Flood duration analysis ........................................................................................ 34

4.3 Rainfall and Runoff correlation .................................................................................. 36

4.3.1 Rainfall and runoff correlation in 2013 flood season ............................................ 36

4.3.2 Estimation of peak discharge ............................................................................... 38

4.4 ENSDA’s analysis of Narok ...................................................................................... 38

4.4.1 Isampurmpur sub-catchment area ........................................................................ 39

4.4.2 Kakiya sub-catchment area .................................................................................. 39

4.5 Settlement patterns in Narok town ............................................................................. 40

4.6 Discussion ................................................................................................................. 40

5. Recommendations and Conclusion .................................................................................. 41

5.1 Flood Management .................................................................................................... 41

5.1.1 Flood Mitigation Strategies ................................................................................. 41

5.2 Conclusion ................................................................................................................. 43

References .......................................................................................................................... 44

6. Appendices ..................................................................................................................... 45

A.1 Formulas ................................................................................................................... 45

Gumbel’s method ......................................................................................................... 45

Weibull’s method ......................................................................................................... 45

Rational Method .......................................................................................................... 45

A.2 Tables ....................................................................................................................... 46

A.3 Illustrations ............................................................................................................... 48

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Abbreviations APFM Associated Programme on Flood Management

ASAL Arid and Semi-Arid Land

CMS Catchment Management Strategies

EIA Environmental Impact Assessment

ENSDA Ewaso Ng’iro South Basin Development Authority

GWP Global Water Partnership

ICRC Indigenous Concerns Resource Centre

IFM Integrated Flooding Management

IWRM Integrated Water Resources Management

KMS Kenya Meteorological Services

KNBS Kenya National Bureau of Statistics

KRCS Kenya Red Cross Society

MCSF Maa Civil Society Forum

MDGs Millennium Development Goals

MoWI Ministry of Water and Irrigation

NDOC Kenya National Disaster Operation Centre

NEMA National Environmental Management Agency

NGO Non-Governmental Organisations

NWMP National Water Master Plan

NWRMS National Water Resources Management Strategy

SCMPs Sub-Catchment Management Plans

SDGs Sustainable Development Goals

SoK Survey of Kenya

SUDS Sustainable Urban Drainage Systems

WMO World Meteorological Organisation

WRMA Water Resources Management Authority

WRUAs Water Resource Users Associations

UN United Nations

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List of figures Figure 1: A basic standard recording rain gauge; tipping bucket rain gauge (Raghunath,

2006) .................................................................................................................................... 9

Figure 2:Components of a basic hydrograph, Raghunath 2006 ........................................... 11

Figure 3An illustration of flood routing ............................................................................... 13

Figure 4 Risk Management, WMO 2009 .............................................................................. 17

Figure 5: Integrated Flood Management Model, APFM 2004 ............................................. 18

Figure 6 Ewaso Ng’iro South catchment area, (SoK 2003) .................................................. 21

Figure 7 Narok catchment area land use, ENSDA 2013 ...................................................... 22

Figure 8 Average monthly rainfall in Narok area from 1990 to 2015 .................................. 24

Figure 9: Erosion on a farmland in the upper catchment,, ENSDA 2015 ............................ 28

Figure 10: 5-yr moving mean curve for Narok .................................................................... 31

Figure 11: Rainfall frequency curve for the Narok area ...................................................... 33

Figure 12: Log-log graph for partial duration curve for River Enkare Narok ...................... 35

Figure 13: Semi-log graph of the partial duration curve for River Enkare Narok ................ 35

Figure 14: Rainfall - runoff correlation in the Ewaso Ng'iro South river basin .................... 37

Figure 15: : Debris and sediment deposition within Narok town after flooding, ENSDA 2015

........................................................................................................................................... 48

Figure 16: Farmland on the Olopita area after deforestation, ENSDA 2015 ....................... 49

Figure 17: Encroachment on riparian land and dumping of garbage on waterways in Narok

town, ENSDA 2015 ............................................................................................................. 49

Figure 18: Undersized culvert in Narok town for storm drainage, ENSDA 2015 ................. 50

Figure 19: A vehicle partially submerged and temporary structures washed away due to

flooding in Narok town. ....................................................................................................... 50

Figure 20: Satellite image of Ewaso Ng’iro South River basin in 2009. ............................... 51

Figure 21: Satellite image of Ewaso Ng'iro South River Basin in 2014 ................................ 51

List of Tables Table 1: Rainfall distribution in Narok area from 1990 - 2015 (KMD) ................................ 23

Table 2: Mean annual, minimum and maximum monthly rainfall for Narok area from 1990 -

2015 .................................................................................................................................... 24

Table 3: Streamflow of River Enkare Narok from 1990 – 2014 ............................................ 25

Table 4: Peak yearly discharges of River Enkare Narok ...................................................... 25

Table 5: Monthly mean rainfall in Narok from 1990 - 2015 ................................................. 30

Table 6: Probability of total annual rainfall occurrence in Narok ....................................... 32

Table 7: Peak discharges for River Enkare Narok ............................................................... 34

Table 8: Daily rainfall and mean daily discharge in Narok area from March to May 2013 . 36

Table 9: Estimated runoff volume for Isampurmpur sub-catchment area, (ENSDA 2015) .... 39

Table 10: Estimated runoff volume for Kakiya sub-catchment area (ENSDA, 2015) ............ 39

Table 11: Maximum monthly discharges of River Enkare Narok ......................................... 46

Table 12: Minimum monthly discharges of Enkare Narok ................................................... 47

Table 13: Gumbel's probability data ................................................................................... 48

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Chapter 1

1. Introduction

1.1 General Introduction Narok town is situated in Narok County at the southern end of the Rift Valley within the Kenyan

borders. The town is situated at the confluence of two rivers; Isampurmpur and Kakiya. The two

streams are located within the Ewaso Ng’iro South River Basin, which covers a total area of

approximately 46.4 kilometres squared. The average annual rainfall of the catchment area is 750 mm. A

significant portion of the population within the catchment area resides in the rural areas where the chief

economic activities are animal husbandry and crop farming (subsistence and commercial).

Most sub-Saharan towns prone to flash floods lack a proper way to control floodwaters during seasons

experiencing high rainfall. Poor planning and insufficient infrastructure for flood control make the

situation even worse. Flood control is usually a measure taken by larger cities and towns but, even so,

not all solutions are as quite as effective. Kenya is a country that has previously faced the brunt of the

flooding. Flooding has had a deleterious effect on the country's economy, the environment and people's

livelihood. Most places that have been hit by flooding could not cope with the control of the floodwaters

and nature took its course. Narok is a town in Kenya that has faced such a calamity, which resulted in

losses in life and property. Since 1992, Narok town has existed with the scourge of flooding. Enkare

Narok is the river flowing through the town and its banks burst after heavy downpour in April 2015; this

was not the first time torrential rainfall has resulted into flooding. In response, Narok town was set to

undergo various changes not limited to building check dams and flood pans to mitigate and control the

effects of flooding. The constructions are set in preparation to beat in the incoming El-Niño rainfall that

was earlier predicted to hit between the months of October to December of 2015 and well into the

month of January in 2016. Flooding is an impediment to individual, local, national and regional

development. Owing to the severity of the most recent flood in Narok, the solutions offered to avert

flooding effects provide a proper case study, which can be adopted if they stand the test of the predicted

floods.

1.2 Scope This study aims at identifying the causes of flooding in Narok town, the patterns and cycles in relation to

hydrological cycle of Narok town during both the flooding seasons and the dry season with the aid of

statistical data obtained from MoWI. The data covers the year 1990 up to 2014. Principles, concepts and

strategies of IFM and IWRM are adopted and integrated into the study to determine appropriate

solutions to the scourge of flooding in Narok town. n

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1.3 Objectives The general purpose of this document is to outline various strategies that can be used to curb flooding

and to mitigate the impacts of flooding in Narok town in line with the principles of IWRM and IFM.

1.3.1 Specific Objectives

The specific purposes of this document are:

To analyse rainfall and flow data in the Ewaso Ng'iro South River basin.

To use statistical methods in rainfall and flow estimation for Ewaso Ng'iro South river basin and

River Enkare Narok respectively.

To analyse the relationship between rainfall and discharge in the Ewaso Ng'iro South River

basin.

To outline and discuss the causes of flooding in Narok town.

To outline the social, economic and environmental impacts of flooding in Narok town.

To identify the various methods of flood mitigation previously used in Narok town.

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Chapter 2

2. Literature Review and Theoretical Analysis

2.1 Rainfall

Precipitation is the main input process in the hydrological cycle. It replenishes the surface

water bodies, renews the soil moisture and recharges aquifers. Precipitation may be

intercepted, infiltrated, evaporated or be surface runoff. Various factors not limited to amount

of rainfall, vegetation cover, soil moisture conditions and topography affect the disposition of

precipitation. Water resources assessments and hydrologic modelling is dependent on the

form and amount of precipitation. Rainfall and snowmelt are the main sources of stormwater

depending on the climatological conditions of the place under consideration. Observations of

the properties of rainfall intensity, duration and frequency provide records that aid in the

prediction of rainfall patterns. A detailed analysis of rainfall over extended periods of time

(20-30 years) is imperative for the planning and design of urban runoff conveyance systems.

2.1.1 Measurement of rainfall

The amount of rainfall in a region is mainly measured in three ways, namely:

i.) Rain-gauges

ii.) Ground-based radar

iii.) Satellite imagery

Rain-gauges

These are simple instruments used in measuring the amount of rainfall in an area. They are

arranged in a network over a catchment area to record the amount of rainfall falling over a

given period of time. There are two types of rain-gauges, namely:

Standard non-recording rain-gauge

Recording rain-gauge

Figure 1: A basic standard recording rain gauge; tipping bucket rain gauge (Raghunath, 2006)

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2.2 Streamflow and Stream gauging

Stream gauging refers to the measurement of discharge of a stream in a catchment area. It

gives a satisfactory measure of runoff in the catchments area. Gauging stations are placed at

points in a stream section for measurements to be made. (Raghunath, 2006). Streamflow is

generated by precipitation during storm events and by groundwater entering surface channels.

During dry periods, streamflow is sustained by groundwater discharges. Where groundwater

reservoirs are below stream channels, as in arid regions, streams cease to flow during

protracted precipitation periods (Gary Lewis et al). A basin’s physical, vegetative and

climatic features determine the quality and quantity of streamflow generated. Streamflow

studies and analysis is a prerequisite to flood management.

Precipitation contributes to streamflow in four ways, namely:

Overland surface runoff

Interflow

Base flow from ground water, and

Channel precipitation

2.2.1 Methods of stream gauging

There are various methods used in determining runoff at a particular catchment. The common

methods in use are listed below.

Weirs

Venturiflumes

Sluiceways and spillways

Area-velocity methods

2.2.2 Hydrograph

A hydrograph is used to represent streamflow at a particular location. It is a graphical

representation of the properties of streamflow with respect to time. Below is a typical

hydrograph showing its components.

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Figure 2:Components of a basic hydrograph, Raghunath 2006

2.3 Urban Drainage

There are two types of water, which require drainage; wastewater and stormwater.

Stormwater is water in a developed or built up area resulting from precipitation; usually

rainfall (Davies et al, 2004). Urban drainage systems are designed to handle such water thus

minimising the problems caused to the environment and human life. A build up in the

wastewater results in pollution and this can result to major health risks and/or detrimental

effects to the environment. Urban drainage replaces a natural system in the natural

hydrological cycle thus it is prudent to have a deeper understanding of flooding; it’s causes

and impacts. Such drawbacks have to be mitigated or controlled to bypass the negative

effects on the environment and human life.

According to the hydrological cycle, when rainwater falls on the ground, some of it is lost to

the atmosphere through evaporation, transpiration, some infiltrates and becomes groundwater

while another portion is surface runoff. Depending on the nature of surface the rain falls, the

relative proportions of the losses may vary. Developed urban areas have artificial surfaces

which results in an increase in surface runoff and reduction in infiltration. Surface runoff

travels at a higher rate in these artificial surfaces in comparison to the natural surfaces. This

results in a greater peak flow since flow arrives and diminishes faster. Such a scenario

heightens the chances of abrupt flooding. Urbanisation has a drastic effect on the

hydrological cycles and meteorological characteristics of a watershed. Vegetation clearance

results in an increase in sedimentation in streams and a decrease in evapotranspiration and

interception. Infrastructure in residential, commercial and industrial area results in increased

imperviousness thus reducing time of runoff concentration. This causes an increase in peak

discharges and reduces time distribution of flow. Runoff volume and damages caused by

flooding surge higher. Construction of storm drains and channel improvements decrease

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infiltration and the groundwater table is lowered thus storm flow increases while during dry

periods, base flow decreases. The design and construction of urban stormwater drainage

collection and conveyance systems is with the purpose of reducing surface runoff in urban

areas and to control flooding in a way that transportation and movement of people is not

greatly hampered while aiding the natural cycle of water.

2.3.1 Urban Flooding

A flood is an unusual high stage of a river due to runoff from rainfall and/or melting of snow

in quantities too great to be confined in the normal water surface elevations of the river or

stream, as the result of unusual meteorological combination (Raghunath, 2006). Urban

flooding occurs over a relatively short period of time. The main causes include; flash floods,

river floods, coastal floods and sewer line failure. The types of floods include:

Flash floods

Regional floods

Estuarine floods

Coastal floods

Flash floods usually occur as a result of accelerated runoff or dam failure. They occur under a

short period of time. River floods occur over an extend period which culminates to the river

bursting its banks. Coastal floods occur along the coastline as a result of tsunamis, wave

activity or tropical cyclones.

Causes of urban flooding

Urban flooding can be pegged to:

Decrease of infiltration and increase of surface runoff due to structures.

Inadequate design of drainage systems.

Poor maintenance of existing drainage systems.

Poor urban planning practices

Urbanisation results into construction of structures. Structures in residential and industrial

zones interfere with the natural hydrological cycle of water since existing natural water ways

are changed. Urbanization ought to go hand in hand with proper planning and design of

drainage systems that are effective regardless of the climatic conditions, case in point heavy

rainfall and flooding.

2.3.2 Flood Routing

This is a procedure to estimate downstream hydrograph from upstream hydrograph (Dawei

Han). A basic routed hydrograph illustrates this below. The translation is the time lag and the

graph is attenuated.

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Figure 3An illustration of flood routing

From a flow routing system, the conservation of mass method is used to obtain the water

balance of a system.

𝐼 − 𝑂 = 𝑑𝑆

𝑑𝑡

Where, I represent the upstream flow, O is the downstream flow and S is the storage for a

given time t. However, the above equation gives an instantaneous value. For practical results

the mean values from inflow and outflow are used. This gives:

𝐼1 + 𝐼2

2−

𝑂1 + 𝑂2

2=

𝑆2 − 𝑆1

𝛥𝑡

The downstream outflow is estimated by getting a storage function which relates the input

and output

𝑆 = 𝑓(𝐼, 𝑂)

𝑆 = 𝐾 (𝑋𝐼 + (1 − 𝑋)𝑂)

K is the storage time constant for a reach while X is the weighting factor, which ranges from

0 to 0.5 (usually taken 0.2). Substituting storage, S, from the storage equation to the water

balance equation and simplifying gives the Muskingum’s equation below

𝑂2 = 𝐶0𝐼2 + 𝐶1𝐼1 + 𝐶2𝑂1

Where;

𝐶0 = 0.5∆𝑡 − 𝐾𝑋

𝐷

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𝐶1 = 𝐾𝑋 + 0.5∆𝑡

𝐷

𝐶2 = 𝐾 − 𝐾𝑋 − 0.5∆𝑡

𝐷

𝐷 = 𝐾 − 𝐾𝑋 + 0.5∆𝑡

And,

C0 + C1 + C2 = 1

2.4 WRMA and IWRM

2.4.1 Integrated Water Resources Management

Integrated Water Resources Management (IWRM) refers to a process which promotes the co-

ordinated development and management of water, land and related resources, in order to

maximize the resultant economic and social welfare in an equitable manner without

compromising the sustainability of vital ecosystems (GWP, 2007).

Proper governance of water resources is pertinent to the achievement of MDGs. The ‘IWRM

target’, first hatched in Johannesburg in 2002 during the World Summit for Sustainable

Development states, “To develop integrated water resources management and water

efficiency plans by 2005 with support to developing countries.”

To implement IWRM, three pillars have to be addressed (Jan Hassing et al, 2009). These

three pillars are; an enabling environment, an institutional framework and management

instruments. An enabling environment requires the setup of strategies, policies and legislation

for sustainable management and development of water resources. Secondly, an institutional

framework implements the strategies, policies and legislation at hand. Lastly, management

instruments are required by the institutions to get the work done (Jan Hassing et al, 2009).

IWRM principles

The IWRM principles also referred to as the Dublin principles were formulated in January

1992 in Dublin during the International Conference on Water and the Environment. These

principles are:

Freshwater is a finite and susceptible resource, indispensable to sustain life,

development and the environment.

Water development and management should be based on a participatory approach

involving users, planners and policy makers at all levels.

Women play a central part in the provision, management and safeguarding of water

Water has an economic value in all its competing uses and should be recognised as an

economic good.

2.4.2 Water Resources Management Authority

In Kenya the umbrella body in charge of management of water resources is the Water

Resources Management Authority (WRMA). It was established in 2003 and became

functional in 2005 after the enactment of the Water Act of 2002. It was a move by the

Government to bring about reform in the Water sector. In order to implement IWRM,

15

WRMA has adopted strategies which include among others, managing an effective water

resources monitoring system for informed decision making and planning, ensuring access to

information at all levels and linking water resources to a growing economy in attaining vision

2030 through NWMP 2030.

In line with the IWRM target, the Kenyan government set up Water Efficiency Plans through

the MoWI (draft 2007) to meet the directive from the UN Secretary General in 2006. Such a

plan is effective in playing a coordinative role in management of water resources within the

country generally. Kenya is currently classified at a water scarce category of 647m3 per

capita against the global benchmark of 1000m3 (WRMA, 2015).

According to the WRMA report of 2015, the specific tasks of the WRMA include:

Protection of riparian land, water sources, water recharge areas and water bodies.

Infrastructure development for water harvesting and storage.

Real Time Water resources assessment and monitoring.

Water allocation, water use control.

Capacity building and institutional development of WRUAs.

Awareness creation and providing information to public.

Implementation of livelihood projects for income generation as a way of encouraging

communities living in our important catchment areas and ecosystems to preserve,

conserve and protect the water sources.

Mandates of WRMA

The Water Act 2002 outlines the following functions of WRMA:

To develop principles, guidelines and procedures for the allocation of water resources.

To monitor, and from time to time reassess, the national water resources management

strategy.

To receive and determine applications for permits for water use.

To monitor and enforce conditions attached to permits for water use.

To regulate and protect water resources quality from adverse impacts.

To manage and protect water catchments.

In accordance with guidelines in the national water resources management strategy, to

determine charges to be imposed for the use of water from any water resource.

To gather and maintain information on water resources and from time to time publish

forecasts, projections and information on water resources.

To liaise with other bodies for the better regulation and management of water

resources.

To advise the Cabinet Secretary concerning any matter in connection with water

resources

Challenges faced by WRMA

A number of challenges have hampered WRMA efforts for sustainable management of water

resources. According to a WRMA report of March 2015, these challenges include but not

limited to:

Inadequate data on water resources.

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Water scarcity and variability.

Enforcement of Water laws.

Climate change impacts.

Pollution of water resources.

Catchment degradation.

Temporal and spatial distribution of the resources.

Competing demands.

Water resources data and information generation.

Interference by some county governments on shared water resources.

Resolution of mandate conflict between NEMA and WRMA has taken too long to

resolve.

Low level of monitoring, evaluation and collection of water resource data, resulting in

poor data management.

High incidences of illegal abstractions and at times, over-abstraction of water

resources.

Poor visibility and low awareness of water resources management sub-sector

mandate, activities and outcomes.

Inadequate staff capacity to carry out technical functions.

High number of newly formed WRUAs without adequate funding to develop and

implement the Sub Catchment Management Plans, SCMPs.

2.5 Integrated Flood Management

Integrated Flood Management (IFM) refers to the integration of land and water management

in a river basin using a combination of measures that focus on coping with floods within a

framework of IWRM and adopting risk managements principles while recognizing that

floods have beneficial impacts that can never be fully controlled (WMO, 2009).

Incorporation of various systems such as socio-economic activities, institutional framework,

government policy, land-use practices, hydro-morphological processes, cultural concern etc.

constitute to the entire IFM process. Land management authorities and water management

authorities coordinate on an institutional capacity to implement the IFM strategies. The

hydrological cycle is considered in its entirety rather than comparing flood and drought

patterns during the planning phase for water resources development. IFM aims to reduce

injury and loss of life, environmental preservation, ensure sustainable development and to

maximise net benefits acquired from flooding. IFM requires clear and objective policies with

a multi-disciplinary approach to enforce it.

2.5.1 Principles of IFM

The World Meteorological Organisation (WMO) through the Associated Programme on

Flood Management (APFM, 2011) outlines various principles to be assimilated when

applying the IFM plan to action, these are:

Manage the hydrological cycle as a whole

Flood and drought management practices should be amalgamated. The effective use of flood

waters must be put into consideration. Moreover, the interaction between the groundwater

17

and surface water must come into play. Solutions considered must have multi-beneficial

aspects.

Integrate land and water management

To achieve consistency in the planning phase, water management and land resource

management should be coalesced. Water quantity, water quality and land degradation are

synthesised in planning. The effect of land-use practices must come into play.

Manage risk and uncertainty

Risk reduction involves three main measures; reduction of hazards, reduction of exposure and

reduction of vulnerability. Risk Management entails mitigation and preparedness, response,

recovery and rehabilitation and residual risks (WMO, 2009). This is diagrammatically

illustrated below in Figure 4.

Figure 4 Risk Management, WMO 2009

Adopt a best mix of strategies

Practice proves that one single strategy does not solve all the effects of flooding. Different

strategies have to be incorporated. However, the strategies adopted should complement one

another, otherwise the entire process becomes redundant.

Ensure a participatory approach

Impacts of flooding cross socio-economic boundaries. All stakeholders i.e. the public,

concerned institutions, policy makers, NGOs, parastatals etc. should all come into the fray.

Co-ordination and co-operation is vital to progressive participation amongst the stakeholders.

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Adopt integrated hazard management approaches

Disaster management plans should consult and involve various stakeholders on a multi-

disciplinary level. Uniformity in disaster management is paramount to aid effectiveness and

efficiency. Early warning systems and forecasts are also vital in risk assessment and disaster

management.

In the context of the IWRM approach, the IFM plan can be summarised diagrammatically as

shown below in Figure 5.

Figure 5: Integrated Flood Management Model, APFM 2004

2.5.2 IFM Strategy and Implementation

A strategy to be adopted should traverse most aspects of life if not all. It should encompass

national, economic, social, cultural and development policies (APFM, 2011). APFM outlines

the following factors to consider when implementing the IFM strategy:

A river basin is dynamic over time and space. There are a series of interactions

between water, soil/sediment and pollutants/nutrients.

Population growth and economic activities exert pressure on the natural system.

Increased economic activities in floodplains increase vulnerability to flooding.

High level of investment in floodplains and the lack of alternative land in many

countries mean that abandoning flood-prone areas cannot be a viable option for flood

damage reduction.

Changes in land use across the basin affect runoff and the probability of a flood of a

given magnitude.

Changes in the intensity and duration of precipitation patterns as a result of climate

change could increase flash floods and seasonal floods.

19

The likelihood that existing flood protection measures could fail and how such

situations should be managed need to be considered.

Riverine aquatic ecosystems provide many benefits such as: clean drinking water,

food, flood mitigation and recreational opportunities.

A trade-off between competing interests in a river basin is required to determine the

magnitude and variability of the flow regime needed within a basin to maximise the

benefits to society and maintain a healthy riverine ecosystem.

For the successful implementation of IFM plan, APFM suggests the following inputs in the

implementation process:

Clear and objective policies supported with legislation and regulation

IFM strategies ought to be adopted into policy making processes, planning and, resource

allocation and management. Policies backed by complementary laws and regulations

Institutional structure through appropriate linkage

Water management is a long-term strategy. Attaining and disbursing of knowledge on IFM

should be a continuous process. National interest, society’s well-being and regional

prosperity should find a mid-point whereby water resources are used while ensuring

sustainability is achieved.

Community based institutions

Community based institutions in a flood prone area play a pivotal role in flood management.

Society has to be educated on the on the requirements of IFM. Information is disseminated

through such channels when IFM strategies are being implemented.

Information management and exchange

Communication is a necessity when it comes to ensuring co-ordination and co-operation

between the stakeholders in a flood prone region. This improves flood preparedness and

response. Society, policy makers, experts from multidisciplinary sources and NGOs must

merge their efforts through exchange of information and data in order to address the need of

flood management.

Appropriate economic instruments

Socio-economic policies of a given government affect how far a government is willing to

fund for flood mitigation measures and flood management practices. An economic loss

accrued from the impact of flooding is shared between the government and the society. Thus

a balance should be achieved on the government’s involvement and the society’s contribution

towards economic stability with an aim to reduce losses and increase the beneficial aspects of

living in a flood prone region.

2.5.3 Challenges of Flood Management

According to APFM, challenges on flood management can be classified in four broad

categories:

Population increase and economic development

Increasing human settlements in flood prone areas increase the flood risk magnitude owing to

the constructions that follow which limit the path water follows in its natural cycle. The more

a settlement expands and develops the higher the economic impact in relation to losses when

flooding occurs. Thus, vulnerability to flooding increases and more pressure is exerted on the

natural water system. Abandoning a flood prone region is never a popular option despite the

20

risk involved since settlements are usually socio-economically dependent on the region.

Furthermore, population increase may result in the change of land use affecting runoff.

Climate variability

Global warming has resulted in altered weather patterns on the globe; case in point El Niño.

Changes in duration, intensity and amount of precipitation affect the magnitude of the impact

of a flash flood.

Securing livelihoods

Certain economic activities that are vital to the survival of a population are difficult to discard

due to they are a source of livelihood to the population in a flood prone region despite such

activities having detrimental effects on the natural waterways and conveyance systems. Such

activities include mining, farming etc. The entire ecosystem is not usually adequately taken

into account in land use planning (APFM, 2011).

Decision and policy making

Due to the involvement of various stakeholders, there is bound to emerge conflicting

interests. Lack of proper co-ordination and co-operation between stakeholders in the IFM

plan hampers with flood management strategies. Usually, stakeholders make decisions

unilaterally and with their interests taking greater priority. Such situations result in slow

policy making processes yet floods lack such stalling abilities.

21

Chapter 3

3. Narok catchment area

3.1 Methodology

The methodology adopted for data and information collection was through site visits and

document review from secondary sources. Research on previous studies on Narok town were

helpful in gathering data concerning Narok town and the catchment basin of River Enkare

Narok.

3.2 Drainage area

A catchment is the land area over which rain falls while a water shed is the land area that

contributes surface runoff at a particular location of interest (Gary Lewis et al, pp 153).

Flooding in Narok town is as a result of excessive runoff from two sub-catchments. These are

the rivers Isampurmpur and Kakiya whose sub-catchments cover an area of 15.24km2 and

30.74km2 respectively. Both collectively cover an area of approximately 46.38 km2 of which

roughly 11.07 km2 is urbanized while 35.31 km2 is the rural area. Both streams flow only

during the rainy seasons. The entire sub-catchment area for both streams has a dendritic

stream pattern. Both rivers drain into Enkare Narok river. Below is a figure showing the sub-

catchment areas of the two rivers.

Figure 6 Ewaso Ng’iro South catchment area, (SoK 2003)

22

The Kakiya sub-catchment has areas of 23.24 km2 and 7.10 km2 under rural and urban

respectively while the Isampurmpur sub-catchment has areas of 12.07 km2 and 3.17 km2

under rural and urban respectively. The average slope of the catchment is 0.033. The flow

length is estimated at 10, 000 m. The soil is generally clay loam soil in the rural areas which

cover an area of 45.4 km2 and the urban area has an imperviousness of over 70% and an area

of 1.1km2.

The land use characteristics are diagrammatically represented below. For both sub-catchment

areas, the prevalent land use activity is generally crop farming. The main cash crops being

maize and wheat.

Figure 7 Narok catchment area land use, ENSDA 2013

23

3.3 Rainfall in Narok area

Narok town receives a bimodal rainfall pattern. Rainfall is maximum during the months of

March to May and November to January. The table below shows the rainfall measurements

according to the Kenya Meteorological Department throughout each year from 1990 to 2015.

It also provides the mean monthly rainfall for each year.

Table 1: Rainfall distribution in Narok area from 1990 - 2015 (KMD)

Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Mean

1990 35.9 122.9 154.9 160.9 84.9 14.2 2.5 19.8 20.3 61.8 24.8 26.9 60.81

1991 55.2 9.5 77.9 131.2 121.8 50.5 9.1 8.3 5.3 43 43.5 62 51.44

1992 11.2 84.3 31.9 138.1 35.8 18.2 27.5 4.2 13.8 38 11.1 55.2 39.10

1993 258.2 94.3 32.4 21.6 151.5 90.5 0.8 34.4 0.6 24.3 35.9 48.3 66.06

1994 58.4 117.6 109.6 113.4 144.6 13.8 11.7 46 0 21.5 134.4 23 66.16

1995 43.7 57.9 0 47.3 160.2 33.5 7 24.2 61 19.3 39 34.3 43.95

1996 77.9 131.8 138.7 86.3 37.7 114.1 89.2 35.8 22.1 12 47.5 45.4 69.87

1997 32.1 6.3 47.8 370.5 151.5 25.5 10.2 34.5 10.6 37.2 256.5 123.7 92.20

1998 204.5 185.7 14.22 130.5 192.3 61.2 3.3 31.5 40.7 10.5 27.6 7.3 75.77

1999 37.5 5.2 289.2 65.3 23.5 3.9 2.9 23.5 8.3 51.4 54.4 124.1 57.43

2000 10.2 18 58 73.8 18.7 2.4 4.6 11.4 15.1 9.3 143.9 107.8 39.43

2001 232.9 80 56.1 136.7 26.2 22.6 50 25.1 22 14.8 38.2 35.8 61.70

2002 166.1 59.2 94.5 108.6 172.7 2.9 9.6 10.1 8.3 51.5 186.7 172.2 86.86

2003 144.2 73 49.5 136.4 284 10.3 2.6 79.3 8.9 19.9 22.1 15.4 70.46

2004 32.3 68.8 103.2 204.9 134.6 3.2 0 0 44 8.3 28.1 74.3 58.47

2005 26.3 32.5 130.3 78.3 106.4 30.5 20.4 13.7 7.6 15.4 18.8 16.6 41.40

2006 101.3 34.3 150.1 210.8 59.1 1.6 5.1 32.7 21.7 1 242.2 154.8 84.55

2007 75.5 162.4 62.6 89.9 37.3 83.4 8.8 24.4 69.4 7.5 30.3 39.2 57.55

2008 8.1 101 194 96.2 7.8 1.4 9.2 20.8 32.7 57.2 86.3 5.6 51.69

2009 52.1 23.3 20.7 106.3 101.9 35.5 3.7 3.6 15.7 33.1 57.4 123.8 48.09

2010 142.3 103.4 86.8 75.9 113.9 8.5 5.1 36.2 61.6 49.2 59.6 38.1 65.05

2011 49.2 45.5 88.1 25 54.8 33.1 2.8 47.9 86.2 146.8 142.4 146.1 72.32

2012 0 39.5 64.4 208.5 185.5 8.5 22 53.8 2.8 16.2 56.9 162.4 68.37

2013 73.3 83.2 102.3 348.7 66.3 2.7 11.7 14.9 58.8 0 15.9 - 70.70

2014 49.9 107.7 144.6 11.8 20.6 37.1 27.9 17.1 51.4 47.3 55.6 119.6 57.55

2015 70.7 50.7 17.8 176.4 167.8 49.2 26 13.2 7.2 54.4 213.1 - 76.95

Below is a bar chart showing the mean monthly rainfall in Narok from 1990 to 2015. The bar

chart is generated from mean monthly rainfall in the years of concern in addition to the

maximum and minimum rainfall for each year.

24

Figure 8 Average monthly rainfall in Narok area from 1990 to 2015

The minimum and maximum monthly rainfall are as shown in the table below including the

mean annual rainfall for each year including the months in which they occur.

Table 2: Mean annual, minimum and maximum monthly rainfall for Narok area from 1990 - 2015

Year Mean annual

rainfall (mm)

Min. monthly

rainfall (mm)

Month Max. monthly

rainfall (mm)

Month

1990 60.81 2.5 July 160.9 April

1991 51.44 5.3 September 131.2 April

1992 39.10 4.2 August 138.1 April

1993 66.06 0.6 September 258.2 January

1994 66.16 0 September 144.6 May

1995 43.95 0 March 160.2 May

1996 69.87 12 October 138.7 March

1997 92.20 6.3 February 370.5 April

1998 75.77 3.3 July 204.5 January

1999 57.43 2.9 July 289.2 March

2000 39.43 2.4 June 143.9 November

2001 61.70 14.8 October 232.9 January

2002 86.86 2.9 June 186.7 November

2003 70.46 2.6 July 284.0 May

2004 58.47 0 July/August 204.9 April

2005 41.40 7.6 September 130.3 Mar

2006 84.55 1 October 242.2 November

2007 57.55 7.5 October 162.4 February

2008 51.69 1.4 June 194.0 March

2009 48.09 3.6 August 123.8 December

2010 65.05 5.1 July 142.3 January

2011 72.32 2.8 July 146.8 October

2012 68.37 0 January 208.5 April

2013 70.70 0 October 348.7 April

2014 57.55 11.8 April 144.6 March

2015 76.95 7.2 October 213.1 November

0

20

40

60

80

100

120

140

Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec

Ran

fall

(mm

)

`

Mean monthly rainfall in Narok area from 1990 to 2015

25

3.4 Streamflow in Narok area

The River, Enkare Narok, is served by two tributaries namely; Kakiya and Isampurmpur.

Both tributaries lack river gauge stations. However, Enkare Narok does have river gauge

stations for the purpose of flow measurements. Below is a graph showing streamflow

readings from the river gauge stations from 1990 to 2014. The table provides the river gauge

stations measurements in cumecs on the streamflow of River Enkare Narok.

Table 3: Streamflow of River Enkare Narok from 1990 – 2014

Year Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Total

1990 16.26 6.33 25.70 88.72 147.70 67.92 39.01 - - 14.28 18.31 12.52 436.74

1991 7.26 6.25 6.25 13.71 13.00 21.97 15.03 22.31 15.45 9.87 7.84 6.82 145.75

1992 3.78 4.06 3.44 5.83 10.25 9.36 20.61 25.89 34.26 25.96 10.14 6.40 160.00

1993 10.77 18.01 6.85 4.48 7.03 12.44 10.40 10.33 9.47 5.26 4.67 4.29 104.00

1994 3.17 3.61 4.27 5.95 11.78 17.02 - 18.74 14.22 5.33 10.01 8.50 102.59

1995 3.96 4.21 4.74 4.84 12.26 6.30 7.83 6.06 5.56 8.96 8.88 4.57 78.17

1996 4.14 4.38 4.71 7.87 4.94 8.35 11.86 - - - - - 46.25

1997 - - 2.82 15.94 14.03 6.75 11.73 12.23 8.23 5.75 7.33 - 84.81

1998 76.77 43.46 18.30 18.58 35.30 25.83 19.72 13.84 20.17 10.64 5.67 288.29

1999 4.15 8.34 10.22 10.24 10.63 7.71 7.99 13.40 16.45 - - - 89.13

2000 6.20 8.93 8.96 9.68 9.64 9.06 10.57 12.42 11.24 11.45 12.66 10.72 121.52

2001 26.43 - - - 8.16 15.79 20.64 25.75 15.61 17.47 - - 129.85

2002 12.19 7.68 7.88 10.18 45.00 9.62 7.73 13.70 11.05 8.22 11.52 12.56 157.33

2003 26.95 7.55 5.03 8.13 - - - - 35.83 - 8.10 - 91.60

2004 5.03 4.13 5.01 12.53 23.42 - - - - - - - 50.12

2005 3.96 - - - - - - 36.23 37.90 11.92 8.50 4.77 103.28

2006 5.01 3.01 6.22 17.28 17.77 5.49 6.63 15.61 12.66 6.33 10.78 32.45 139.26

2007 49.25 32.49 13.07 22.04 17.58 36.25 22.68 49.41 42.75 10.10 7.74 5.90 309.27

2008 4.42 5.00 4.95 12.41 6.70 6.29 9.13 24.11 20.53 14.50 18.86 8.10 135.00

2009 5.23 4.72 4.20 5.87 8.81 6.95 5.21 5.60 6.39 6.53 6.20 - 65.70

2010 - - - - - - - - 27.75 27.72 17.49 6.98 79.94

2011 11.09 6.85 0.19 4.62 11.44 15.72 15.72 26.01 35.54 10.07 24.85 28.78 190.89

2012 6.77 4.15 5.75 18.94 54.13 15.43 18.43 17.97 21.55 10.33 11.01 5.64 190.09

2013 10.80 - 4.28 49.80 33.32 12.66 11.69 23.11 - 9.80 9.92 - 165.39

2014 8.76 - 5.57 - - - - - - - - - 14.33

Table 4 Peak yearly discharges of River Enkare Narok

050

100

150200250300

350400450500

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

Stre

amfl

ow

(cu

mec

s)

Year

Annual discharge of River Enkare Narok

26

3.5 Geology of Narok area

Narok is geologically situated within the southern flunk of the Rift Valley within Kenyan

borders where formation stability depends predominantly on occasional tectonic plate

movements. The basaltic formation during the late Miocene to the early Pleistocene period

characterise mild to severe occurrences of active tectonic movements resulting in Southern

and Northern Grabens throws. In the Narok area, the bulk of volcanic activity took place at

two widely separated periods, the Miocene period and the Pleistocene period, and erosion of

the first Naitiami fault scarp is estimated to have proceeded during a long interval in the

Pliocene. The local geology of Narok and its environs consists of overburden comprising of

top clayey soil and alluvial deposits these are underlain by conglomerates, trachytes,

phonolites old land surface and basement system at depth in that order of geologic

succession.

3.6 Causes of flooding in Narok town

The cause of flooding in Narok town cannot be pegged to one sole reason. Various factors

come into play making Narok town susceptible to flooding. These factors are:

Poor land use practices

Geographic location of Narok

Climate change

Encroachment on water channels

Inefficient flood mitigation strategies

3.6.1 Poor land practices

Indiscriminate clearance of vegetation to provide room for farming has left the top soil bare

and exposed to the common forms of erosion. This is especially common in the Olopita area

where trees have been felled to create space for farming. Inappropriate agricultural practices

such as lack of terraces, lack of wind breakers on farmlands and not practising contour

farming has left the top soil exposed and runoff is left unchecked.

3.6.2 Geographic location of Narok

Narok town is located at the confluence of the two tributaries of River Enkare Narok as

shown in figure 4. Due to this, the town is exposed to runoff emanating from all the two

streams converging on the town. This results into greater surface runoff coming from two

sources.

3.6.3 Climate change

Global warming has resulted in shifts in the weather and climatic patterns. There are more

periods of prolonged droughts followed by intensive flash floods. After heavy torrential

rainfall upstream during the El Niño season, Narok town had to face the brunt of flash

flooding.

3.6.4 Encroachment on water channels

Various buildings both commercial and residential are constructed close to water ways

especially along the Kakiya and Isampurmpur streams. This restricts the movement of water

since there is lesser space for water to make its way downstream. The water channels are also

polluted with debris and garbage resulting into clogging and blockages which further reduces

the efficiency of water conveyance by the waterways and water channels.

27

3.7 Impact of flooding in Narok town

The impact of flooding in Narok town and its environs can be classified under three broad

spectra, these are:

Economic impacts

Social impacts

Environmental impacts

3.7.1 Economic impacts

Damage to physical infrastructure

Destruction of roads disrupted the movement of people and services.

Loss of livelihoods

Disruption of transportation and communication links caused by flooding in Narok town

hampered the day to day businesses of local residents. ENSDA places the estimates in terms

of income loss at Ksh. 122,594,000 in the latest flooding incident in April 2015. The spill

over effect was felt even by businesses not affected by flooding directly.

Tourism

Due to main roads being rendered impassable. Tourists opting to pass through Narok town

and head to Maasai Mara and other tourist destinations were stranded. Losses in revenue and

income for the tourism sector.

Agriculture

Crop damage, soil erosion and water logging due to flooding has resulted into reduced

productivity in farms. This is a precursor to food insecurity.

3.7.2 Social impacts

Loss of life and property

During every flooding incident there has been fatalities in term of loss of life and damages to

property. The Rapid Impact Assessment Report of 2015 places the cost of loss and

destruction of property at an estimated Ksh. 205,325,000 after the April floods in Narok town

in 2015.

Health

Pollution caused by flooding in Narok town was due to water sources being contaminated,

blockage of sewers and open drains. Pests such as flies bred in the decomposing debris and

refuse. Sediments from upstream of the catchment was deposited in the CBD area and once

the water dried up, the remaining dust posed serious respiratory disease occurrence to

residents and business people within the vicinity

Education

Inaccessibility to schools and closure of certain institutions due to flooding led to lower

attendance rates for school going children.

Displacement of people

Residents leaving in the flood hit areas of the town had to relocate in order to save their lives.

Owing to the destruction of livelihoods, some investors and SMEs had to relocate to areas

less likely to be affected by flooding.

28

3.7.3 Environmental impacts

Water and soil pollution

Soil pollution from oil residues from garages and shops and industrial chemicals was

experienced during flooding in Narok town. Water was contaminated and rendered unworthy

for human and livestock consumption after mixing with wastewater. Dust formed as a result

of dried up sediments from the upstream that deposited in the town. This increased the air

pollution.

Land Degradation

In the upper and middle catchment areas where 90% of the land use practice is crop farming,

erosion was experienced. Gully erosion caused environmental hazards and destroyed farm

lands. Sheet erosion caused the washing away of the top fertile soil leaving the land bare and

less productive. Below is a picture showing the effects of erosion in the upper catchment in

Olopito area. Years of poor farming practices has culminated into an environmental

nightmare and a maker to future food insecurity issues.

Figure 9: Erosion on a farmland in the upper catchment,, ENSDA 2015

29

3.8 Flood mitigation strategies in Narok town

Past interventions focused on the CBD area and these included lining of existing drainage

channels and construction of culverts which have not been able to mitigate the problems of

floods in the town. Check dams constructed in prior to the El Niño season were destroyed

after flooding.

ENSDA was formed to manage the catchment area that results into flooding in Narok town. It

has conducted research on the catchment area in line with the causes and impact of flooding,

outlined measures to curb flooding and conducted an analysis on the catchment

characteristics.

30

Chapter 4

4. Analysis and Discussion

In line with the objectives outlined in chapter 1 and with the data results obtained, this

chapter focuses on the analysis of rainfall, discharge, the correlation of rainfall and discharge,

and the progression of settlement patterns within Narok town and the catchment area at large

over a given period.

The data collected, especially on streamflow from the river gauging station in River Enkare

Narok had missing records for certain months. In addition, the rainfall data of the catchment

area lacked full records for a few months.

4.1 Rainfall analysis of Narok area

4.1.1 Annual rainfall analysis

Narok town and its environs receive an average annual rainfall of about 750mm. The peak

rainfall generally occurs between the months of March to May and November to January.

From table 1, the mean annual rainfall from 1990 to 2015 is obtained using the formula:

�̅� = ∑ 𝑥

𝑛

For the catchment area, the mean annual rainfall is:

�̅� = 19460.8

26= 748.5 𝑚𝑚

Below is the average monthly rainfall in Narok’s catchment area. It is obtained by summing

up a single month’s rainfall measurement from 1990 – 2015 and dividing by the number of

years (26).

Table 5 Monthly mean rainfall in Narok from 1990 - 2015

Month Mean monthly

rainfall (mm)

Jan 78.80

Feb 73.00

Mar 89.21

Apr 128.97

May 102.36

Jun 29.16

Jul 14.37

Aug 25.63

Sep 26.77

Oct 32.72

Nov 79.70

Dec 73.41

Commented [M.K.2]:

31

The graph below shows the 5 year moving mean curve developed from the rainfall data

obtained. It aids in developing a long-term trend of the rainfall in the catchment area

throughout the observed period. The years, 1997, 2002 and 2006 mark the highest mean

annual rainfall while 1992, 2000 and 2005 mark the lowest mean annual rainfall recorded in

the catchment area.

Figure 10: 5-yr moving mean curve for Narok

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

19

90

19

91

19

92

19

93

19

94

19

95

19

96

19

97

19

98

19

99

20

00

20

01

2002

20

03

20

04

20

05

20

06

20

07

20

08

20

09

20

10

20

11

20

12

20

13

20

14

20

15

Rai

nfa

ll (

mm

)

Year

Moving mean Curve for Narok

32

4.1.2 Statistical Rainfall Estimation

The annual rainfall readings are sorted from the highest in a descending fashion. This gives

the table 6 below which also includes the probability of the corresponding rainfall amount to

occur.

Table 6: Probability of total annual rainfall occurrence in Narok

Year

Rainfall

(mm) Rank P(%)

1997 1106.4 1 3.703704

2002 1042.4 2 7.407407

2006 1014.7 3 11.11111

1998 909.3 4 14.81481

2011 867.9 5 18.51852

2015 846.5 6 22.22222

2003 845.6 7 25.92593

1996 838.5 8 29.62963

2012 820.5 9 33.33333

1994 794.0 10 37.03704

1993 792.8 11 40.74074

2010 780.6 12 44.44444

2013 777.8 13 48.14815

2001 740.4 14 51.85185

1990 729.8 15 55.55556

2004 701.7 16 59.25926

2007 690.7 17 62.96296

2014 690.6 18 66.66667

1999 689.2 19 70.37037

2008 620.3 20 74.07407

1991 617.3 21 77.77778

2009 577.1 22 81.48148

1995 527.4 23 85.18519

2005 496.8 24 88.88889

2000 473.2 25 92.59259

1992 469.3 26 96.2963

The above table is used to develop a semi-log graph of annual rainfall against frequency to

obtain a rainfall frequency curve which can be used to determine the probability of

occurrence for a particular rainfall measurement and the recurrence intervals.

33

Figure 11: Rainfall frequency curve for the Narok area

From the rainfall frequency curve, it can be estimated that, the annual rainfall for a 6-yr

recurrence interval is 700mm while that for a 10-yr recurrence interval is 1000mm and that of

a 50-yr recurrence interval is 1140mm.

On the other hand, the frequency of attaining the mean amount of annual rainfall (748.5mm)

is 38% which translates to a probability of occurrence of 0.38.

110100

0

200

400

600

800

1000

1200

1400

1 10 100

Recurrence interval T-yr

An

nu

al R

ain

fall

(mm

)

Frequency (%)

Rainfall frequency curve

Median748.5 mm

Mean

34

4.2 Flood Duration

4.2.1 Flood duration analysis

Using the peak discharges data, a flood duration curve is developed. Using the largest one

discharge values arranged in order irrespective of time, the following data is obtained. The

table produced can develop the partial duration curve on a log-log graph or semi-log graph.

The graphs are plotted with frequency in years against flood magnitude.

Table 7: Peak discharges for River Enkare Narok

Month -

yr.

Q

(cumecs) Rank

Probable frequency in

100 years

May-90 147.696 1 4.000

Jan-98 76.772 2 8.000

May-12 54.131 3 12.000

Apr-13 49.803 4 16.000

Aug-07 49.411 5 20.000

May-02 45.001 6 24.000

Sep-05 37.905 7 28.000

Sep-03 35.833 8 32.000

Sep-11 35.542 9 36.000

Sep-92 34.264 10 40.000

Dec-06 32.447 11 44.000

Sep-10 27.750 12 48.000

Jan-01 26.432 13 52.000

Aug-08 24.110 14 56.000

May-04 23.416 15 60.000

Aug-91 22.307 16 64.000

Aug-94 18.743 17 68.000

Feb-93 18.014 18 72.000

Sep-99 16.452 19 76.000

Apr-97 15.938 20 80.000

Nov-00 12.655 21 84.000

May-95 12.264 22 88.000

Jul-96 11.860 23 92.000

May-09 8.810 24 96.000

Jan-14 8.765 25 100.000

Upon extrapolation, the 100-year recurrence flood can be obtained. Also the probability of

receiving a discharge amount per given flooding occurrence. As per the graphs, the 100-year

recurrence discharge amount is 88 cumecs on the semi-log graph and 84 cumecs on the log-

log graph. It is observed the variation between the 2 values though notable but it’s not quite

significant.

35

Figure 12: Log-log graph for partial duration curve for River Enkare Narok

Figure 13: Semi-log graph of the partial duration curve for River Enkare Narok

10.000

100.000

1000.000

1.000 10.000 100.000

Flo

od

mag

nit

ud

e (c

um

ecs)

Frequency in Years (%)

Partial duration curve for River Enkare Narok

0.000

100.000

200.000

300.000

400.000

500.000

600.000

700.000

800.000

900.000

1000.000

1.000 10.000 100.000

Flo

od

mag

nit

ud

e (c

um

ecs)

Frequency in Years (%)

Partial duration curve for River Enkare Narok

36

4.3 Rainfall and Runoff correlation

For the rainfall – runoff correlation, certain periods in the calendar were picked to analyse the

relationship between rainfall and runoff in the Ewaso Ng’iro South river basin analysis.

4.3.1 Rainfall and runoff correlation in 2013 flood season

In the year 2013, peak rainfall and discharge occurred in the months between March and

April as shown in the table below

Table 8: : Daily rainfall and mean daily discharge in Narok area from March to May 2013

Mar April May

Date

Rainfall

(mm)

Discharge

(cumecs) Date

Rainfall

(mm)

Discharge

(cumecs) Date

Rainfall

(mm)

Discharge

(cumecs)

01/03/2013 0.0 4.149 01/04/2013 0.0 11.463 01/05/2013 5.0 105.206

02/03/2013 0.0 4.149 02/04/2013 0.0 13.637 02/05/2013 0.0 98.714

03/03/2013 0.0 3.998 03/04/2013 0.0 13.145 03/05/2013 37.0 53.259

04/03/2013 0.0 3.998 04/04/2013 7.8 14.669 04/05/2013 0.0 47.648

05/03/2013 0.0 3.925 05/04/2013 6.6 34.278 05/05/2013 0.0 87.220

06/03/2013 0.0 3.851 06/04/2013 40.5 15.991 06/05/2013 4.6 91.387

07/03/2013 0.0 3.851 07/04/2013 60.5 61.708 07/05/2013 0.0 46.198

08/03/2013 0.0 3.707 08/04/2013 19.2 34.094 08/05/2013 0.0 33.811

09/03/2013 0.0 4.149 09/04/2013 12.0 34.380 09/05/2013 10.6 34.218

10/03/2013 13.5 4.305 10/04/2013 0.0 35.480 10/05/2013 9.1 36.448

11/03/2013 0.5 4.461 11/04/2013 0.0 43.472 11/05/2013 0.0 36.753

12/03/2013 0.0 4.382 12/04/2013 57.1 143.524 12/05/2013 0.0 38.291

13/03/2013 0.0 4.303 13/04/2013 16.8 167.901 13/05/2013 0.0 31.598

14/03/2013 0.0 4.074 14/04/2013 6.4 79.795 14/05/2013 0.0 28.463

15/03/2013 0.0 4.074 15/04/2013 0.0 66.386 15/05/2013 0.0 24.903

16/03/2013 0.0 3.925 16/04/2013 27.6 49.137 16/05/2013 0.0 21.957

17/03/2013 0.0 3.851 17/04/2013 0.0 43.132 17/05/2013 0.0 20.654

18/03/2013 7.6 4.074 18/04/2013 23.2 44.162 18/05/2013 0.0 19.019

19/03/2013 2.1 4.149 19/04/2013 7.9 37.409 19/05/2013 0.0 17.650

20/03/2013 0.0 4.149 20/04/2013 0.0 37.472 20/05/2013 0.0 16.167

21/03/2013 0.0 4.149 21/04/2013 0.0 82.568 21/05/2013 0.0 15.457

22/03/2013 0.0 4.149 22/04/2013 21.9 92.952 22/05/2013 0.0 14.595

23/03/2013 0.0 4.226 23/04/2013 1.7 48.759 23/05/2013 0.0 13.767

24/03/2013 0.0 4.149 24/04/2013 0.0 41.481 24/05/2013 0.0 13.282

25/03/2013 0.0 4.074 25/04/2013 0.0 36.160 25/05/2013 0.0 12.966

26/03/2013 0.0 6.356 26/04/2013 0.0 29.153 26/05/2013 0.0 12.503

27/03/2013 14.8 5.131 27/04/2013 0.0 35.620 27/05/2013 0.0 11.900

28/03/2013 2.7 4.957 28/04/2013 39.5 71.522 28/05/2013 0.0 9.941

29/03/2013 0.0 4.957 29/04/2013 0.0 35.113 29/05/2013 0.0 9.284

30/03/2013 27.5 7.714 30/04/2013 0.0 30/05/2013 0.0 9.678

31/03/2013 33.6 31/05/2013 0.0 9.284

37

From table 8, a graph showing the relationship between rainfall and discharge is as shown

below

Figure 14: Rainfall - runoff correlation in the Ewaso Ng'iro South river basin

From the above table and graph, it can be concluded that rainfall and discharge have a

directly proportional relation. The peak discharge during the 3-month period goes hand in

hand with the amount of rainfall in the watershed. The discharge peaks soon after consecutive

occurrences of high rainfall spaced by at least a week. The rate of infiltration having reduced

due to the ground conditions after previous heavy downpour results into larger amounts of

surface runoff. Initially the soil is dry but after rainfall intensity increases, soil saturation

increases and infiltration reduces at a steady rate.

Within the 3-month period, the sample covariance and correlation coefficient for the two sets

of data are;

Sample covariance = 167.76

Correlation coefficient = 0.4322

These results indicate a close linear relationship.

A comparison between the maximum monthly discharge to the rainfall data in the catchment

area shows that there is a correlation between the amount of rainfall and discharge within the

Ewaso Ng’iro South river basin. The probability of flood occurrence can be shown from data

during the flooding periods in Narok town. Using table 11 it can be seen that the flooding

0

20

40

60

80

100

120

140

160

180

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

Dis

char

ge (

cum

ecs)

Rai

nfa

ll (m

m)

Date

Rainfall/Discharge relation for Narok area

Rainfall Discharge

38

periods in 1990, 1997, 1998, 2012 and 2013 illustrates the influence of rainfall on the

discharge. High rainfall between the months of March to May in 1990 resulted into high

discharges during the aforementioned months. The severity of flooding increases with the

high rainfall experienced in consecutive days.

4.3.2 Estimation of peak discharge

Due to inconsistency in discharge data obtained for river discharge in form of missing data

for the streams (Kakiya and Isampurmpur) draining into River Enkare Narok, it would be

erroneous to use the discharge data for analysis to achieve the set objectives. The peak

discharge data can be used in the design of structural components used in flood control such

as canals, dykes, check dams, swales, culverts etc. By use of the rational method, the peak

discharge can be determined based on the basin characteristics.

The urban area in the entire catchment covers an area of 11.07 km2 while the rural area

covers an area of 35.31 km2. The streams concentration time is 5400 seconds

Rural area

Runoff in rural areas is less pronounced as in urban areas, thus two thirds of the total runoff is

a good measure of the estimated discharge. Using the rational method, the runoff in the rural

area of the catchment area can be estimated at;

Q = 153.74 cumecs

Thus volume of discharge from the rural area is

V = 830,226.375 m3

Urban area

Due to increased perviousness in urban areas and minimal water conservation measures, the

discharge was multiplied by a factor of 1.0

Q = 94.94 cumecs

Thus the volume of discharge from the urban area is

V = 512,679.375 m3

The estimated total volume of discharge for the entire catchment area is 1,342,905 m3.

4.4 ENSDA’s analysis of Narok

A previous analysis carried out by ENSDA in 2015 used empirical formulae to estimate the

peak discharge in both sub-catchments.

The rational method was used to determine the estimated discharge.

𝑄 = 𝐶𝑖𝐴

360

The time of concentration was calculated using the following equation.

𝑇𝑐 = 𝐿0.77

𝑆0.385

39

Taking the flow length (L) as 10,000 m and the slope (S) as 0.033, the time of concentration

was estimated to be 1.5 hours. By interpolating the rainfall frequency atlas values, i was

estimated to be 47.5

In the estimation of peak discharge, a factor of 0.75 was applied to the discharge from rural

areas owing to the fact that conservation measures were already being put into place.

Thus, the discharge from the catchment areas was calculated as follows;

Urban discharge,

𝑄 = 𝐶𝑖𝐴

360

Rural discharge,

𝑄 = 0.75𝐶𝑖𝐴

360

The summation of the two gave the total estimated discharge in the entire catchment area.

The estimated runoff volume was calculated by multiplying the total estimated discharge by

the storm duration (ts) in seconds using the formula:

𝑉𝑝 = 𝑄𝑡𝑠

4.4.1 Isampurmpur sub-catchment area

The results obtained using empirical analysis by use of the rational formula were as follows.

Table 9: Estimated runoff volume for Isampurmpur sub-catchment area, (ENSDA 2015)

L (m) S Tc Mod Tc C i (mm/hr) A (ha) Q (m3/s) ts (sec) Vp (m3)

URBAN 10000 0.033 89.4133 90 0.65 47.5 317 27.18715 5400 146810.6

RURAL 10000 0.033 89.4133 90 0.5 47.5 810 40.07813 5400 216421.9

The total estimated runoff volume from Isampurmpur sub-catchment was 363,241.87 m3

which was rounded-off to 360,000 m3

4.4.2 Kakiya sub-catchment area

The results for Kakiya sub-catchment were as follows.

Table 10: Estimated runoff volume for Kakiya sub-catchment area (ENSDA, 2015)

L (m) S Tc (min) Mod Tc C i (mm/hr) A (ha) Q (m3/s) t s (sec) Vp (m3)

URBAN 10000 0.033 89.41 90 0.65 47.5 958 82.16181 5400 443673.8

RURAL 10000 0.033 89.41 90 0.5 47.5 2156 106.6771 5400 576056.3

The total estimated runoff volume from the Kakiya sub-catchment was 1,109,322 m3

40

The design for urban runoff conveyance systems and check dams was done on the basis of

the total estimated streamflow of the two sub-catchment areas.

4.5 Settlement patterns in Narok town

Narok town was first located at the confluence of River Isampurmpur and Kakiya. Over the

years there was a marked population increase, improvement of livelihoods and emergence of

economic activities. New constructions of commercial and residential buildings developed

along the two streams from the confluence heading upstream with disregard to the impact

they have on the natural waterways. A comparison of aerial maps along a chronological

timeline starting from the past to present shows the progression of various settlements and

construction along the two streams. Furthermore, the aerial maps indicate the changes in land

use practices and the extent of land clearance that has been experienced in the sub-catchment

area.

4.6 Discussion

The Ewaso Ng’iro South River basin receives a mean annual rainfall of 750mm. The

calculated peak discharge for River Kakiya and Isampurmpur was estimated to be 1.3 million

meters cubed. The results were consistent with a previous assessment done by ENSDA in

2015.

Poor land practices, encroachment of waterways, the geographic location of Narok town and

climate change have contributed to the severity of flooding in Narok town. Poor land use

practices identified included deforestation and poor farming practices which were lack of

terraces on farms in the upper catchment area. With such practices there’s an increase in

surface runoff and soil erosion. The geographic location of Narok town at the confluence of

two streams further increases the severity of flooding in Narok town during the rainy seasons.

Global warming has also resulted in far greater rainstorms and as observed from rainfall data

during the El-Niño season.

However, the stream gauge and rainfall data was not consistent. There lacked complete

records of certain days, months and years. The data however is sufficient enough to portray

the general characteristics of the catchment area. These were the notable discrepancies. In

addition, the time of the storms and regular data taken in short intervals was unavailable.

41

Chapter 5

5. Recommendations and Conclusion

5.1 Flood Management

In line with water resources management practices outlined through the IWRM and IFM

concepts and principles, flood management should encompass all sectors affected both

directly and indirectly. Flood mitigation strategies go beyond structural solutions of flood

control. The causes of flooding ought to be addressed and either curtailed or have their

influence reduced. Flash floods occur over a short period of time yet their impacts are

colossal in magnitude; it’s economic footprint is significant. An integrated approach to the

management of drainage basins is imperative in coming up with solutions to the seasonal

flooding within Narok town.

5.1.1 Flood Mitigation Strategies

Various flood mitigation strategies can be adopted which when used to complement each

other, favourable results are achieved. Below are flood mitigation strategies that can be

adopted to alleviate the effects of flooding in Narok town.

Structural measures

To complement the use of check dams and flood pans, expansion of cross-sections of Kakiya

and Isampurmpur downstream will help increase the capacity of the two streams. Thus during

peak discharges, surface runoff would not develop in the lower catchment which is in Narok

town.

The improvement of the current stormwater conduits in the town. Such rectifications should

be on the basis of design of conveyance systems that can better handle excessive runoff from

the two streams during the flood seasons. In that they are designed to handle peak flows.

In addition, other proper structural measures that can be employed in Narok town include:

confining the flow between high banks by constructing levees,

dykes, or flood walls.

channel improvement of streams in the upper catchment area by cutting, straightening

or deepening and following river training works.

diversion of a portion of the flood through bypasses or flood ways within the town, or

rather to divert flood waters away from the town.

providing a temporary storage of the peak floods by constructing upstream reservoirs

and detention basins.

flood proofing of specific properties by constructing a ring levee or flood wall

around the property.

As much as there’s provision of drainage measures, it is imperative to also consider their

maintenance to ensure that the laid structures serve their purpose throughout their lifetime.

42

Flood forecasting and basin monitoring

Monitoring of the Ewaso Ng’iro drainage basin can be achieved by sufficient streamflow

analysis through setting up gauging stations on the Kakiya and Isampurmpur streams. This

will allow for proper assessment of the streamflow. Rainfall and streamflow data are

important in flood forecasting. Effective warning systems should be put in place at vulnerable

areas to facilitate evacuation in affected areas in the catchment area.

Community participation and education

Community involvement in flood mitigation strategies is imperative. Involvement entails

education and awareness programs. Practices such as indiscriminate destruction of trees, poor

farming practices and construction close to streams and waterways should be pointed out and

discouraged. Proper soil management is essential in the catchment area in order to alleviate

the negative impact of flooding. Outreach programmes be put in place that designed to

educate society concerning the dangers of living in a flood plain and how to respond to

emergency situations arising as a result of flooding.

The public should be made aware of the negative effects of extensive land clearing,

deforestation and poor farming practices.

Integrated approach to Flood Management

Flood management requires an integrated approach since several factors come into play and

the impacts of flooding cover social, economic and environmental aspects. Flood

management involves but not limited to setting up of basin management systems and

formulation of basin action plans. Management starts at the regional level and trickles down

to sub-catchments.

Proper planning for flood mitigation strategies, consistent financing and co-ordination are

vital to the success of basin management systems. Under a water management framework,

structures are set up to assess water resources within the catchment area, set up

communication and information systems to bolster public awareness, resolve conflicts in

allocation of water, establish regulations to control encroachment of existing waterways and

riparian land, establish self-regulation, research and develop, undertake development works

ensure accountability and to develop organisational capacity.

43

5.2 Conclusion

The specific objectives mentioned in the first chapter were achieved although the results were

not totally conclusive owing to the occurrences of missing data for stream and rainfall

records. An analysis of the rainfall and streamflow data, farming practices, improper

construction practices and flood mitigation measures are all factors that contribute to flooding

in Narok town. As illustrated in appendix 3, the images give a preview of the farming

practices in Narok town and the structural measures taken to alleviate the destructive effect of

flooding. There was insufficient information obtained to suggest that global warming has

contributed to the severity of flooding in Narok town. Streamflow data in Ewaso Ng’iro

South river basin relates to the flooding experienced in Narok town which is located and the

confluence of the River Kakiya and River Isampurmpur. The impacts of flooding in Narok

town are as mentioned in chapter 3 and are broadly categorised under economic, social and

environmental impacts. Under these broad categories are sub-categorised to address the

impacts of flooding under the main categories. Appendix 3 gives images showing the effects

of flooding within Narok town with an emphasis on the negative impacts.

Water management should be placed in the higher echelons of the development agenda to

protect the population against the adverse effects of flooding. Watershed development

answers two fundamental issues; flood and drought. IWRM principles demand a holistic

approach to water management. With proper institutional set-up, supporting legislation and

communal participation, the negative effects of flooding can be controlled and/or eliminated

altogether. Water management ensures the proper use and administration of water as an

irreplaceable resource for the survival and well-being of life on earth.

44

References Authority, W. R. M., 2015. Strengthening Regulations for Sustainable Water Resources

Management in Kenya, Nairobi: Water Resources Management Authority.

Butler, D. & Davies, J. W., 2004. In: Urban Drainage. 2nd ed. New York: Spon Press.

ENSDA, 2015. NAROK TOWN INTEGRATED FLOODS, s.l.: EWASO NG’IRO SOUTH

RIVER BASIN DEVELOPMENT AUTHORITY, .

Han, D., 2010. In: Concise Hydrology. Bristol: s.n.

International Network for Basin Organisations, G. W. P., 2009. In: A Handbook for

Integrated Water Resources Management in Basins. s.l.:GWP; INBO.

McCuen, R. H., 1998. In: M. Horton, ed. Hydrologic Analysis and Design. 2nd ed. Upper

Saddle River(New Jersey): Prentice Hall.

NDOC, UNDP/MOSSP, KRCS, NDMA, G.O.K -COUNTY DEPARTMENTAL

REPRESENTATIVES, 2013. INITIAL RAPID ASSESSMENT REPORT FOR FLOODING IN

NAROK, s.l.: s.n.

Raghunath, H. M., 2006. In: Hydrology: Principles, Analysis and Design. 2nd ed. New Delhi:

New Age International Publishers.

Tamoo, D. & ole Koissaba, B. R., 2009. The State of Our Environment, s.l.: Indigenous

Concerns Resource Center.

Warren Viessman, J. & Gary, L. L., n.d. In: Introduction to Hydrology. 4th ed. s.l.:s.n.

WRMA, 2009. Integrated Water Resources Management and Water Efficiency Plan for

Kenya, s.l.: s.n.

45

Chapter 6

6. Appendices

A.1 Formulas

Gumbel’s method

Reduced variate,

𝑦 = (𝑥 − �̅�) + 0.45𝜎

0.7797𝜎

Recurrence interval,

𝑇 = 1

(1 − 𝑒−𝑒−𝑦)

Probability,

𝑃 =

1

𝑇 × 100%

Standard deviation

𝜎 = √(𝑥 − �̅�)2

𝑛 − 1

Coefficient of variation

𝐶𝑣 = 𝜎

�̅�

Coefficient of skew

𝐶𝑠 = ∑(𝑥 − �̅�)3

(𝑛 − 1)𝜎3

Coefficient of flood

𝐶𝑓 =

�̅�

(𝐴0.8/2.14)

Weibull’s method

Recurrence interval 𝑇 = 𝑚

𝑛 + 1

Probability 𝑃 =

1

𝑇 × 100%

Rational Method

𝑄 = 𝐶𝑖𝐴

360

Q = Discharge

C = Runoff coefficient

A = Area of the catchment

46

A.2 Tables

Table 11: Maximum monthly discharges of River Enkare Narok

Year Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec MAX

1990 87.98 39.37 121.91 182.71 195.21 98.64 43.97 16.35 29.23 15.06 195.21

1991 8.65 6.65 6.65 68.30 23.80 39.26 18.48 42.30 30.95 13.95 9.14 8.90 68.30

1992 4.15 10.47 3.85 9.16 25.38 20.44 37.97 69.91 97.29 44.48 16.53 7.95 97.29

1993 112.56 49.43 12.50 5.13 11.31 23.05 21.72 15.45 18.42 6.05 5.67 5.67 112.56

1994 4.30 4.79 6.85 14.76 36.15 77.43 39.22 36.15 10.75 18.81 15.11 77.43

1995 6.65 5.86 6.05 9.41 30.46 7.95 10.47 9.16 13.44 17.65 13.44 8.66 30.46

1996 5.13 6.44 22.16 24.43 7.95 16.90 25.38 25.38

1997 3.43 74.55 30.46 11.03 36.15 36.15 13.44 5.86 25.38 74.55

1998 211.54 193.72 23.05 42.46 116.29 36.15 36.15 36.15 36.15 15.11 7.95 211.54

1999 4.15 9.16 15.11 16.90 13.44 9.16 10.47 36.15 49.43 49.43

2000 6.85 9.16 9.93 11.03 9.93 9.67 14.43 16.90 13.12 15.81 20.86 23.05 23.05

2001 49.43 11.31 36.15 45.86 49.43 20.44 30.46 49.43

2002 27.85 8.66 11.60 25.38 95.06 12.20 9.16 20.86 18.42 8.66 27.34 34.96 95.06

2003 116.29 9.41 5.31 32.10 79.38 18.81 116.29

2004 9.16 5.86 16.90 27.85 95.06 95.06

2005 6.65 118.82 106.52 16.16 11.60 5.67 118.82

2006 48.71 4.00 30.46 44.48 36.15 8.19 9.67 25.38 23.05 9.67 51.66 117.55 117.55

2007 168.81 95.06 25.38 65.45 30.46 61.18 41.15 146.02 131.98 20.86 9.16 6.24 168.81

2008 5.67 5.86 7.73 16.53 10.47 6.85 25.38 42.46 42.46 22.60 28.36 13.44 42.46

2009 6.65 5.49 5.13 16.90 21.72 15.11 6.24 6.85 7.28 9.67 10.47 21.72

2010 106.52 84.41 33.23 10.20 106.52

2011 16.90 10.20 0.19 10.47 14.09 22.60 28.36 57.09 151.90 25.38 70.82 211.54 211.54

2012 10.47 4.62 7.28 65.45 185.17 30.46 49.43 53.17 40.50 13.76 23.05 11.90 185.17

2013 20.86 6.85 191.99 160.98 20.03 18.03 176.87 13.44 16.90 191.99

2014 15.11 7.50 15.11

47

Table 12: : Minimum monthly discharges of Enkare Narok

Year Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec

1990 3.69 3.29 3.55 35.44 96.89 46.26 32.49 12.09 12.37 1.52

1991 6.06 5.86 5.86 7.95 8.90 13.64 10.98 14.93 1.14 8.65 6.86 6.25

1992 3.17 3.43 3.17 3.43 6.44 4.15 14.09 15.11 13.12 15.81 6.65 4.96

1993 4.46 9.67 4.96 4.00 4.62 5.31 8.19 5.49 6.05 4.30 3.71 3.85

1994 1.76 2.80 3.57 3.43 5.49 9.16 7.95 6.85 3.85 3.71 5.86

1995 3.43 3.43 3.85 3.57 6.44 4.96 5.86 4.79 4.00 5.67 5.67 2.80

1996 3.43 3.43 3.57 3.04 3.71 3.43 3.43

1997 2.80 4.96 6.85 4.15 7.73 7.95 4.96 5.67 3.57

1998 13.44 20.86 10.47 7.95 4.79 16.53 13.44 7.95 11.90 6.85 4.15

1999 4.15 7.50 7.73 7.95 7.95 7.07 7.50 10.47 6.85

2000 5.31 8.91 8.66 8.66 9.16 8.91 9.41 10.47 9.93 9.93 9.41 7.95

2001 7.95 5.86 7.73 12.50 13.44 11.31 11.31

2002 7.50 6.85 6.65 6.24 12.20 7.50 6.85 7.28 7.73 7.95 7.28 5.67

2003 9.41 6.85 4.96 5.13 25.38 5.86

2004 4.15 3.43 4.15 5.86 7.95

2005 3.43 13.12 16.90 8.91 5.49 3.85

2006 3.71 2.80 3.71 3.85 8.19 4.62 4.96 8.19 9.16 4.62 4.46 15.11

2007 20.86 13.44 7.95 7.07 11.90 19.62 15.81 25.38 20.86 1.85 5.49 5.86

2008 2.45 4.79 3.85 6.85 5.86 5.67 5.67 16.90 11.03 10.47 10.47 3.71

2009 4.62 4.15 3.85 4.15 5.13 5.67 4.79 4.79 5.67 4.96 5.86

2010 16.90 13.44 9.16 4.15

2011 4.15 0.19 0.19 0.19 9.67 10.47 11.60 11.90 13.12 7.28 13.44 10.47

2012 4.79 3.43 4.15 0.83 19.21 10.47 11.31 11.90 13.12 7.95 7.28 3.43

2013 5.86 3.71 10.47 9.16 7.95 9.16 11.03 7.95 6.44

2014 5.86 4.62

48

Table 13: Gumbel's probability data

Reduced Variate

(y)

Recurrence Interval

(T)

Probability of exceedance

(P)

-1.53 1.01 0.99 (=1.0)

-0.475 1.25 0.80

0 1.58 0.63

0.37 2.00 0.50

0.58 2.33 0.43

1.50 5 0.20

2.25 10 0.10

2.97 20 0.05

3.90 50 0.02

4.60 100 0.01

5.30 200 0.005

5.70 300 0.0033

6.00 403 0.0025

6.24 500 0.002

6.92 1000 0.001

7.62 2000 0.0005

8.54 5000 0.0002

9.92 10000 0.0001

A.3 Illustrations

Figure 15: : Debris and sediment deposition within Narok town after flooding, ENSDA 2015

49

Figure 16: Farmland on the Olopita area after deforestation, ENSDA 2015

Figure 17: Encroachment on riparian land and dumping of garbage on waterways in Narok town, ENSDA 2015

50

Figure 18: Undersized culvert in Narok town for storm drainage, ENSDA 2015

Figure 19: A vehicle partially submerged and temporary structures washed away due to flooding in Narok town.

51

Figure 20: Satellite image of Ewaso Ng’iro South River basin in 2009.

Notice the lightly coloured portions of the image in the upper catchment area. Land has been

cleared for agricultural practices. Land that is covered by trees appears as a dark green colour

in a satellite image.

Figure 21: Satellite image of Ewaso Ng'iro South River Basin in 2014