Artificial aquifer recharge system

FACULTY OF ENGINEERING
DEPARTMENT OF MINING AND WATER RESOURCES
ENGINEERING
WATER RESOURCES ENGINEERING PROGRAMME
FINAL YEAR PROJECT REPORT
DESIGN AND SIMULATION OF AN AQUIFER RECHARGE
SYSTEM FOR RUBONGI SUB COUNTY, TORORO DISTRICT
BY
OYUKI GODFREY
BU/UP/2014/626
Email: oyukigodfrey99@gmail.com; +256 777105373/0759759677
SUPERVISORS
MAIN SUPERVISOR: Mr. MUYINGO EMMANUEL
CO-SUPERVISOR: Mr. OKETCHO YORONIMO

OYUKI GODFREY, BU/UP/2014/626, FINAL REPORT I
ABSTRACT
The water supply for Rubongi sub county in Tororo district is highly reliant on groundwater.
This project is aimed at coming with a technique that will be used in artificial groundwater
recharge of the existing aquifer in the area. With an increasing population having a recent
growth factor of 2.73%, groundwater demand is on the rise. For me to solve this problem I first
of all needed to determine the groundwater supply and availability in the sub county and also
other surface water sources including surface runoff from precipitation. This was done using
the aquifer potential map of the sub county on a GIS platform, establishing the water demand
of the area through population projection, hydrological analysis and water systems engineering
and finally getting the specifications of the recharge system. The water balance for the area
was obtained and this indicated the water supply would cater for the needs of the area.
It was observed that the area has high evaporation rates therefore the amount of recharge of the
rainfall (108.88 MCM/year) and runoff (27.47MCM/year) was minimal but all the same due to
the fissure characteristics in the area and the direction of flow recharge does occur. With the
design of the structure, open trapezoidal channels were used due to their design and
maintenance ease and these trapezoidal basins therefore serve a horizontal recharge purpose.
The main aim of recharging the aquifer is because as the population increases the water demand
also increases also leading to increased demand. As demand increases most people turn to
groundwater for sustenance which may lead to over abstraction. To prevent this, we have to
recharge what is currently there and ensure continuous supply of water.
The simulation of the system was then done using MODFLOW, a groundwater modelling and
simulation software that yielded the results for recharge rate based on the aquifer characteristics
and recharge parameters of the study area in majorly six main steps leading to the performance
of a steady-state flow simulation i.e. Create a new model, Assign model data, Perform the flow
simulation, check simulation results, calculate sub regional water budget, Produce output

OYUKI GODFREY, BU/UP/2014/626, FINAL REPORT II
ACKNOWLEDGEMENTS
I would like to extend my sincere thanks to the almighty GOD who has gifted me with life and
has enabled me to reach this academic height as he has been the provider of all the necessary
requirements.
Great thanks to my beloved friend, Mudondo Lubba for her moral support and I promise her
that I have to succeed in this presentation. Not forgetting my sisters, Barbra, Mercy, Joy and
Fridah for their prayers and courage given to me in the course of this project.
Special thanks to all my brothers, Peter, Emma and Derick for all their moral support, financial
support and togetherness in all ways of life towards the success of this proposal.
Let me convey my heartfelt appreciation to my supervisors, Mr. Oketcho Yoronimo and Mr.
Muyingo Emmanuel for their advice as well their guidance during the preparation of this paper.
Special appreciation to the management of central materials laboratory in Kampala, for their
guidance on the soil and rock details of the study area. Not forgetting the ministry of water and
environment that provided the relevant data that led to the completion of this project, Geostatic
Surveys and engineering consultants Tororo, for providing the various survey instruments for
use in the fields, Ministry of Geology and Mineral development, for providing relevant data on
the geology and soils of the study area, and so any other organizations that aided this research
project to this level.
Great appreciation goes to my all-time friend that always sacrificed his time and discussed with
me the achievement of most of my objectives and the entire project, Mr. Tebugulwa Dan. I
really appreciate your effort in making this project a success
I can’t forget my great friends especially class mates and roommates for the guidance and
brotherhood assistance towards achieving this work.

OYUKI GODFREY, BU/UP/2014/626, FINAL REPORT III
DECLARATION
I OYUKI GODFREY, declare that all the material portrayed in this project proposal report is
original and has never been submitted in for award of any Degree, certificate, or diploma to
any university or institution of higher learning.
Signature Date
………………………….. …………………………

OYUKI GODFREY, BU/UP/2014/626, FINAL REPORT IV
APPROVAL
This is to certify that the project proposal has been carried out under my supervision and this
report is ready for submission to the Board of examiners and senate of Busitema University
with my approval.
MAIN SUPERVISOR:
MR. MUYINGO EMMANUEL
SIGNATURE: ……………………………………
DATE: …………/…………………/………………
CO-SUPERVISOR:
MR. OKETCHO YORONIMO
SIGNATURE: ……………………………………
DATE: …………/…………………/……………….

OYUKI GODFREY, BU/UP/2014/626, FINAL REPORT V
TABLE OF CONTENTS
ABSTRACT................................................................................................................................i
ACKNOWLEDGEMENTS.......................................................................................................ii
DECLARATION..................................................................................................................... iii
APPROVAL .............................................................................................................................iv
LIST OF FIGURES ..................................................................................................................ix
LIST OF TABLES.....................................................................................................................x
LIST OF ACRONYMS/ABBREVIATIONS...........................................................................xi
1 CHAPTER ONE: INTRODUCTION................................................................................1
1.1 Background of the study .............................................................................................1
1.2 Problem statement.......................................................................................................3
1.3 Purpose of the study....................................................................................................3
1.4 Justification .................................................................................................................3
1.5 Objectives....................................................................................................................3
1.5.1 Main objective of the study.......................................................................................3
1.5.2 Specific Objectives ...................................................................................................4
1.6 Scope of the Project.....................................................................................................4
2 CHAPTER TWO: LITERATURE REVIEW....................................................................5
2.1 GROUND WATER.....................................................................................................5
2.1.1 Factors that affect ground water recharge in an area ................................................5
2.1.1.1 Lithology................................................................................................................6
2.1.1.2 Land use/cover.......................................................................................................6
2.1.1.3 Lineaments.............................................................................................................6
2.1.1.4 Drainage.................................................................................................................7
2.1.1.5 Rain fall..................................................................................................................7
2.1.1.6 Soil.........................................................................................................................7

OYUKI GODFREY, BU/UP/2014/626, FINAL REPORT VI
2.1.1.7 Slope ......................................................................................................................8
2.1.2 Identification the basic factors determining the existence and quantity and recharge
of ground water in an area .................................................................................................9
2.1.3 Hydrological cycle....................................................................................................9
2.1.4 Groundwater Occurrence........................................................................................10
2.1.5 Groundwater Recharge ......................................................................................12
2.1.6 Artificial Recharge..................................................................................................15
2.1.7 Artificial aquifer recharge practices in Uganda......................................................18
2.1.8 Groundwater Movement and Flow .........................................................................18
2.1.9 Porosity ...................................................................................................................19
3 CHAPTER THREE: METHODOLOGY ........................................................................20
4.0 Methods and activities required to achieve the objectives........................................20
4.1 To identify appropriate potential aquifer recharge sites for the study area...............20
4.1.1 Software employed ............................................................................................21
4.1.2 Methods to be employed for the study;..............................................................21
4.1.3 Thematic layers include;....................................................................................21
4.2 Requirement for specific objective 2 ........................................................................22
4.2.1 Water balance.....................................................................................................22
4.2.2 Runoff estimation for the study area..................................................................24
4.3 To design the artificial aquifer recharge system .......................................................25
4.3.1 The conveyance system .....................................................................................25
4.3.2 The recharge basin .............................................................................................26
4.3.3 Determination of the channel freeboard ............................................................27
4.3.4 Estimating the reservoir capacity.......................................................................27
4.3.5 Average Shear Stress on Channel Boundary (the Tractive Force): ...................27
4 CHAPTER FOUR: PRESENTATION AND DISCUSSIONS OF RESULTS...............28

OYUKI GODFREY, BU/UP/2014/626, FINAL REPORT VII
4.1 Analysis of hydro-geological data.............................................................................28
4.1.1 Hydrological analysis of the rainfall data ..........................................................28
4.1.2 Soil Infiltration potential....................................................................................30
4.1.3 Drainage map.....................................................................................................31
4.1.4 Land use map .....................................................................................................31
4.1.5 Slope map...........................................................................................................32
4.1.6 Soil map .............................................................................................................33
4.1.7 Geological map ..................................................................................................33
4.1.8 Weighted overlay analysis.................................................................................34
4.2 To estimate the water balance and runoff potential of the study area ...........................37
4.2.1 Water balance.....................................................................................................37
4.2.2 Runoff Estimation..............................................................................................39
4.3 To design a groundwater recharge system for the aquifer in the study area.............39
4.3.1 Design of conveyance System from the water collection point.........................39
4.3.2 Design of the Recharge Basins ..........................................................................41
4.3.3 Estimating the reservoir capacity.......................................................................44
4.3.4 Trapezoidal channel Freeboard:.........................................................................45
4.3.5 Average Shear Stress on Channel Boundary (the Tractive Force): ...................45
4.4 SIMULATION OF THE SYSTEM ..........................................................................46
4.4.1 Groundwater flow parameters using simulated using MODFLOW.......................46
4.5 Discussion .................................................................................................................53
5 CHAPTER FIVE .............................................................................................................54
5.0 CHALLENGES FACED, CONCLUSION AND RECOMMENDATIONS ...........54
5.2 Conclusion.................................................................................................................54
5.3 Recommendation.......................................................................................................54
6 REFERENCES .....................................................................................................................56

OYUKI GODFREY, BU/UP/2014/626, FINAL REPORT VIII
Appendix 2: Average monthly minimum temperatures for Tororo district............................59
Appendix 3: Boreholes in Rubongi sub county of Tororo district...........................................60
Appendix 4: Monthly Rainfall Totals......................................................................................62
Appendix 5: Top view of borehole ..........................................................................................65
Appendix 6: Material arrangement in the recharge shaft.........................................................66
Appendix 7: Watershed map for Rubongi Sub County ...........................................................67
Appendix 8: Aquifer yield map of Rubongi Sub County based on Borehole yield ................68
Appendix 9: Porosity map of Rubongi sub county..................................................................69

OYUKI GODFREY, BU/UP/2014/626, FINAL REPORT IX
LIST OF FIGURES
Figure 1: The hydrological cycle ...............................................................................................9
Figure 2: confined and unconfined aquifers ............................................................................11
Figure 3:Natural groundwater recharge/discharge to a stream (Sophocleous, 2004)..............13
Figure 4:Lysimeter (after Adeleke et al., 2015).......................................................................14
Figure 5: Artificial recharge using a percolation tank (Huntington and Williams, 2012).......16
Figure 6: Injection well with cone of recharge (Huntington and Williams, 2012)..................17
Figure 7: Flow chart leading to the derivation of aquifer recharge sites .................................21
Figure 8: Graph of average annual rainfall of Tororo district against years............................29
Figure 9: Minimum and maximum temperatures of Tororo different .....................................29
Figure 10: Evaporation rate of Rubongi sub county................................................................30
Figure 11: The infiltration potential of different soil types in Rubongi Sub county ...............30
Figure 12: Drainage density map of Rubongi Sub county.......................................................31
Figure 13: Land use map of Rubongi sub county....................................................................32
Figure 14: Slope map of Rubongi Sub county.........................................................................32
Figure 15: soil map for Rubongi Sub county...........................................................................33
Figure 16: Geology map of Rubongi Sub county....................................................................34
Figure 17: Aquifer recharge site map of Rubongi Sub County ...............................................36
Figure 18: Longitudinal Section of the recharge basin............................................................43
Figure 19: Cross Section of the recharge basin .......................................................................44
Figure 20: Complete 2-D recharge system View.....................................................................46

OYUKI GODFREY, BU/UP/2014/626, FINAL REPORT X
LIST OF TABLES
Table 1:multi-influencing factors that affect groundwater recharge and existence...................5
Table 2: different types of soils and there relative porosity.......................................................7
Table 3:Soil infiltration rates .....................................................................................................8
Table 4: Project data sources ...................................................................................................20
Table 5:analysis of the water demand of the area was accessed as follows ............................22
Table 6:Determination of the actual water supply for the study area......................................22
Table 7: variation of groundwater abstraction with time.........................................................23
Table 8: runoff estimation for the catchment...........................................................................24
Table 9: Pairwise comparison of the different recharge factors ..............................................35
Table 10: Water Demand of Rubongi Sub County..................................................................37
Table 11: Supply yield total of the different sources in Rubongi Sub county.........................37
Table 12: Water Demand projection for Rubongi Sub County ...............................................38
Table 13: Average Monthly Runoff Estimates for Rubongi Sub County................................39
Table 14: Average Monthly Runoff Volume...........................................................................41
Table 15: Volumetric budget for the entire model written by MODFLOW............................52

OYUKI GODFREY, BU/UP/2014/626, FINAL REPORT XI
LIST OF ACRONYMS/ABBREVIATIONS
ASTER – Advanced space borne Transmission Emission and Radiometer data
DEM – Digital Elevation Model
DGSM – Directorate of Geological Survey and Mines
DWD – Directorate of Water Development
DWRM – Directorate of Water Resources Management
ETM – Enhanced Thematic Mapper
GIS – Geographical Information System
MWE – Ministry of Water and Environment
NARO – National Agricultural Research Organization
NASA – National Aeronautics and Space Administration
NFA – National Forestry Authority
NRSA – National Remote Sensing Agency
RS – Remote Sensing
UNMA – Uganda National Meteorological Authority
USGS – United States Geological Survey
UTM – Universal Transverse Mercator
WGS – World Geodetic System
WIOA – Weighted Index Overlay Analysis

OYUKI GODFREY, BU/UP/2014/626, FINAL REPORT 1
1 CHAPTER ONE: INTRODUCTION
This chapter briefly gives the general information relevant to the research while clearly
showing the problem of interest for the intended design. It as well shows how this study will
help reduce the problem through the fulfilment of a number of objectives listed therein.
1.1 Background of the study
Water is the most essential natural resource on the planet earth. It is categorized into saline
water-which is ocean water and fresh water which is a finite resource essential for life
development and the environment. According to the UN annual report 2010, saline water
(oceans) cover about 97% of the earth’s waters and fresh water is only a small proportion of
the total water (3%) and mainly stored in ice and glacier form. Fresh water sources are mainly
groundwater and surface water sources. According to the UN annual report, 2010, ice caps
and glaciers contribute 68% of the fresh water, groundwater 30.1%, surface water 0.3% and
others 0.9%.
According to Banks, D., Robins, N., (2002). Groundwater is a form of water held under the
ground in the saturated zone that fills all the pore space of soils and geologic formations. Its
formed by rainwater or snow melt water that seeps down through the soil and into the
underlying rocks (aquifers). It’s the major resource of water supplies as provides more than
half of humanity’s freshwater for everyday uses such as cooking, hygiene as well as 30% of
irrigated agriculture and industrial development.(Pilla, Torrese and Bersan, 2010) .
As of 2010, the world’s aggregated groundwater abstraction was estimated at approximately
1000km3
per year, approximately 67% of which is used for irrigation, 22% for domestic
purpose and 11% for industrial purposes.(Unesco and United, 2009). The rate has at least
tripled over the past 50years and continues to increase by 1-2% per year. The estimates suggest
that the abstraction of groundwater accounts for approximately 26% of the total global water
withdrawal and equals approximately 8% of the mean global groundwater
recharge.(UNESCO, 2012).
Groundwater is crucial for the livelihoods and food security of 1.2 to 1.5billion rural
households in poorer regions of Africa and Asia, but also for domestic supplies of a large part
of the population elsewhere in the world. The global volume of stored groundwater is poorly
known, estimated range 15.3 to 60million km3
including 8 to 10 million of freshwater, while
the remainder is the brackish and saline groundwater is predominantly at great depth(Global
and Usage, 2016). Significantly groundwater storage depletion is taking place in many areas
of intensive groundwater withdrawal.

Groundwater is the most important source of portable water in Uganda, especially in rural areas
and provides 80% or more of the total water supply.(Victoria, 2000). According to MWE,
(Nsubuga, 2014), water sources in Uganda are estimated at 66km3
/year corresponding to about
2800m3
/person/year. The spatial and temporal distribution of water resources is uneven, which
possess a big problem to their management. There is increasing pressure on water resources
due to rapid population growth, increased urbanization uncontrolled environmental
degradation and pollution.
Groundwater recharge assessments have recently have been carried out in Apac in Northern
Uganda, Mbarara in western Uganda, Wobulenzi in central Uganda, Nkoknjero in eastern
Uganda and Hoima in mid-western Uganda. Results obtained using the various methods on
groundwater recharge reveal a range between 90mm and 220mm per annum and accounts for
7% and 20% of the average annual precipitation in Uganda. (Abaho et al., 2009)
Groundwater potential in various areas of the country is exhibited by presence of deep
boreholes, shallow wells and springs. The drilling depth in most areas of the country determines
availability of groundwater in any given area. Tororo district has an average drilling depth of
56.6m, which is lower than that for most of the districts in Uganda.(Development and Basin,
2000).
One of the main country’s grand challenges is to implement an aquifer storage and recovery
scheme, which requires understanding of the flow regime and quantification of the natural
rainfall recharge.(Republic, 2011)
Artificial recharging an aquifer may be achieved by either surface spreading, injection in wells,
or altering the natural conditions of stream channels to increase infiltration. Except for recharge
using injection wells directly into an aquifer, artificially recharged water must first move
through the unsaturated zone. For the most part, the unsaturated zone provides the underground
storage space for recharge, although the amount of storage is dependent on the water retention
characteristics and the natural recharge occurring at the site.(Aiken and Kuniansky, 2002)
The terrain of most parts of Rubongi Sub County, is steep, characterized by a hilly topography,
which inadequate time for natural recharge fastens runoff and gives to occur. There should be
continued efforts in sub county for development of ground water resources to meet the
increasing demands of water supply, especially in the last few decades. In certain high demand
areas, ground water development has already reached a critical stage, resulting in acute scarcity
of the resource.

Artificial Recharge of Ground Water should provide detailed guidelines on investigative
techniques for selection of sites, planning and design of artificial recharge structures,
monitoring and economic evaluation of artificial recharge schemes to increase the
sustainability of groundwater resources.
1.2 Problem statement
Water scarcity has been a very big problem of concern for quite a while. Due to growing
population, livestock, agriculture and industrial water demands, surface water sources have
become inadequate and this has led to increased exploration and abstraction of water from
groundwater aquifers to sustain the demands. Since the rate of natural groundwater recharge
has become lower than the rate of groundwater abstraction, there has been an observed
reduction in the groundwater table and drying up of many boreholes. The steep terrain nature
of the larges parts of Rubongi sub county coupled with hilly terrains fasten runoff and provides
inadequate time for natural recharge to occur, which has also been another contributing factor
to borehole drying in this area.
1.3 Purpose of the study
The purpose of this study is to design an appropriate artificial aquifer recharge system that
utilizes surface runoff to as the major source of water for this recharge practice. The study
aimed at understanding the drainage, slope, runoff, geological, geomorphological, land use and
topographical factors of the study area that affect the rate of recharge.
1.4 Justification
The completion of this research has led to better generation of knowledge for siting artificial
recharge points for groundwater aquifers, understanding the different factors that affect
groundwater recharge and providing a better design parameters and considerations for artificial
recharge. This will in turn lead to a rise in groundwater table, an in increase the quantity of
water in groundwater aquifers during rainy season and improve the sustainability of these
aquifers during both rainy and dry season for very many years hence eliminating borehole
drying problems. Artificial groundwater recharge systems provide a better handling
mechanism for surface runoff, increasing the infiltration and groundwater recharge rates and
also improving the soil condition for both micro-organisms and agriculture.
1.5 Objectives
1.5.1 Main objective of the study
To design and simulate a groundwater recharge system for Rubongi sub county.

1.5.2 Specific Objectives
1. To identify appropriate potential aquifer recharge sites for the study area.
2. To assess the water balance and runoff potential of Rubongi Sub county.
3. To design a groundwater recharge system for the aquifer in the study area
4. To simulate the aquifer recharge potential
1.6 Scope of the Project
This project is limited to the designing an appropriate artificial recharge technique for
groundwater using surface runoff from the available precipitation in Rubongi sub county.
Specifically, it involves analysis of topographical, geologic, geomorphologic, drainage and
hydrological data using ArcGIS 10.1 software and employing conveniently chosen variables,
analyzing the relationship between the maps developed from satellite imagery, in effort to come
up with the most suitable sites for groundwater recharge and design of the artificial
groundwater recharge system for Rubongi sub county.

2 CHAPTER TWO: LITERATURE REVIEW
This chapter discusses the opinions, findings from different authors, publications, magazines,
websites, journals and all possible sources as a basis of foundation for this research study. It is
divided into definition of terms, relationship between ground water, remote sensing (RS) and
geographical information system (GIS), the basic factors that determines the existence, quantity
and recharge of ground water in an area.
2.1 GROUND WATER
Groundwater is a form of water held under the ground in the saturated zone that fills all the
pore space of soils and geologic formations. It is formed by rainwater or snowmelt water that
seeps down through the soil and into the underlying rocks (Sophocleous, 2004). It is the major
resource of water supply for about half of the nations. It plays a key role in Nature by providing
more than half of humanity’s freshwater for everyday uses such as drinking, cooking, and
hygiene, as well as thirty percent of irrigated agriculture and industrial developments. (Zuppi,
G.M., 2007)
Groundwater potential zones can be said to be water bearing formations of the earth’s crust
that act as conduits for transmission and as reservoirs for storing water. Its identification and
location is based on indirect analysis of some observable terrain features such as geologic,
geomorphic, landforms and their hydrologic characteristics.
Groundwater recharge refers to the entry of water from the unsaturated zone into the saturated
zone below the water table surface, together with the associated flow away from the water table
within the saturated zone (Hsin-Fu Yeh, 2008). Recharge occurs when water flows past the
groundwater level and infiltrates into the saturated zone. It directly affects the existence of
ground water in an area.
2.1.1 Factors that affect ground water recharge in an area
The factors influencing groundwater recharge as well as existence, and their relative
importance, are compiled from previous literature. Duplicate factors were combined and only
representative factors were extracted. This study uses lithology, land use/cover, lineaments,
drainage, soil, rainfall and slope as the seven significant factors affecting groundwater
recharge potential.
Table 1:multi-influencing factors that affect groundwater recharge and existence
Factor Basis of categorization
Lithology Rock type, weathering character, joints,
fractures

Land cover/land use Type, a real extent, associated vegetation
cover
Lineaments Lineament – density value
Drainage Drainage – density value
Slope Slope gradient
Soil Porosity, type and mineral composition
Rainfall Depth
2.1.1.1 Lithology
Shaban et al. (2006) pointed out that the type of rock exposed to the surface significantly affects
groundwater recharge. Lithology affects the groundwater recharge by controlling the
percolation of water flow. Although some investigations have ignored this factor by regarding
the lineaments and drainage characters as a function of primary and secondary porosity, this
study will include lithology to reduce uncertainty in determining lineaments and drainage.
2.1.1.2 Land use/cover
Land use/cover is an important factor in groundwater recharge and thus existence. It includes
the type of soil deposits, the distribution of residential areas, and vegetation cover. Shaban et
al. (2006) concluded that vegetation cover benefits groundwater recharge in the following
ways.
 Biological decomposition of the roots helps loosen the rock and soil, so that water can
percolate to the surface of the earth easily.
 Vegetation prevents direct evaporation of water from soil.
 The roots of a plant can absorb water, thus preventing water loss.
2.1.1.3 Lineaments
The analysis of lineaments has been applied extensively to explain geological status since
geological images were first utilized in the 1930s. Lineaments are generally referred to in the
analysis of remote sensing of fractures or structures. Lineament photos from satellites and
aerial photos have similar characteristics but the results of the explanation in on-site may be
different. Lineaments are currently not fully defined.
This study will use lineament – length density (𝐿 𝑑,𝐿−1
) (Greenbaum 1985), which represents
the total length of lineaments in a unit area, as:
𝐿 𝑑 =
∑ 𝐿 𝑖
𝑖=𝑛
𝑖=1
𝐴
…………………………………………………………….Equation 1

Where ∑ 𝐿𝑖
𝑖=𝑛
𝑖=1 denotes the total length of lineaments (L), n denotes the number of lineaments
and A denotes the unit area (L2
). A high lineament – length density infers high secondary
porosity, thus indicating a zone with high ground water recharge potential as well as existence.
2.1.1.4 Drainage
The structural analysis of a drainage network helps assesses the characteristics of the
groundwater recharge zone. The quality of a drainage network depends on lithology, which
provides an important index of the percolation rate. This study will use drainage – length
density (𝐷 𝑑, 𝐿−1
), as defined by Greenbaum (1985), indicates the total drainage – length in a
unit area, and is determined by:
𝐷 𝑑 =
∑ 𝑆 𝑖
𝑖=𝑛
𝑖=1
𝐴
…………………………………………………..Equation 2
Where ∑ 𝑆𝑖
𝑖=𝑛
𝑖=1 denotes the total length of drainage (L) and A denotes the unit area (L2
). The
drainage – length density is significantly correlated with the groundwater recharge; a zone with
a high drainage – length density has a high level of groundwater recharge.
2.1.1.5 Rain fall
Rainfall is the main source of groundwater recharge in tropic and sub-tropic regions. Long
duration and low intensity rain fall allows more water to infiltrate into the soil and percolate to
the deeper layers of the aquifer because less run off is generated as compared to short duration
and high intensity rainfall that allow enough time for runoff collection and flow most especially
if the slope is steep.
2.1.1.6 Soil
Different soil types have different properties that affect ground water recharge such as porosity
which is a measure by the ratio of the contained voids in a solid mass to its total volume. It is
given by;
𝜃 =
𝑉𝑣
𝑉
………………………………………………………………Equation 3
Where θ is the porosity, 𝑉𝑉 is the volume of voids and V is the total volume.
Table 2: different types of soils and there relative porosity
Soil type Porosity, n
Peat soil 60 – 80%
Clay 45- 60%

Silt 40-50%
Sand 30-40%
Gravel 25-35%
Sand stone 10-20%
Shale 0-10%
Lime Stone 0-10%
Lime stone dissolved 10-50%
Hard rock 0-5%
Source: Ontario
2.1.1.7 Slope
The slope gradient directly influences the infiltration of rainfall. Larger slopes produce a
smaller recharge because water runs rapidly off the surface of a steep slope during rainfall, not
having sufficient time to infiltrate the surface and recharge the saturated zone.
Table 3:Soil infiltration rates
Soil texture type 0 – 4.9% 5 – 7.9% 8 – 11.9% 12 – 15.9% 16 and above
Coarse sand 1.25 1 0.75 0.5 0.31
Medium sand 1.06 0.85 0.64 0.42 0.27
Fine sand 0.94 0.75 0.56 0.38 0.24
Loamy sand 0.88 0.70 0.53 0.35 0.22
Sandy loam 0.75 0.6 0.45 0.30 0.19
Fine sandy loam 0.63 0.50 0.38 0.25 0.16
Very fine sandy
loam
0.59 0.47 0.35 0.24 0.15
Loam 0.54 0.43 0.33 0.22 0.14
Silt loam 0.50 0.40 0.30 0.20 0.13
Silt 0.44 0.35 0.26 0.18 0.11
Sandy clay 0.31 0.25 0.19 0.12 0.08
Clay loam 0.25 0.20 0.15 0.10 0.06
Silty clay 0.19 0.15 0.11 0.08 0.05
Clay 0.13 0.10 0.08 0.05 0.03
Source: USDA, (Agriculture and water use)

2.1.2 Identification the basic factors determining the existence and quantity and recharge
of ground water in an area
The factors that determine the existence and recharge of ground water in an area are categorized
into three;
 Hydrological factors
 Geographical factors
 Geomorphological factors
Hydrological factors
The Hydrological factors that determine the existence, recharge and quantity of ground water
in an area include; drainage – networks configuration, rainfall (intensity and duration), sub-
surface flow, infiltration rate, evaporation and evapotranspiration.
Geographical factors
The Geographical factors include; vegetation cover/ land use, slope/topography and soil. Field
surveys was conducted to ascertain the existence of geographical features such as vegetation
cover, land use, topography as well as existence of hills in the study area. GPS coordinates was
also obtained to locate the study area.
Geomorphological factors
Geomorphological factors include; slope steepness, lineaments and lithology. The geology of
the study area based on the available data of the existing boreholes which was be obtained from
DWRM as well as lithology and lineament datasets which was obtained from DGSM.
The data is interpolated in an ArcGIS environment to obtain the nature of rocks underlying
Rubongi Sub county and their contribution to ground water obtained basing on their
characteristics such as porosity, transimitivity and their ability to hold and transmit water.
2.1.3 Hydrological cycle
Figure 1: The hydrological cycle
Hydrologic Cycle (Source: Water Cycle Lesson Plans)

Groundwater is water that exists in the pore spaces and fractures in rocks and sediments beneath
the Earth’s surface. It originates as rainfall or snow, and then moves through the soil and rock
into the groundwater system, where it eventually makes its way back to the surface streams,
lakes, or oceans. Groundwater constitutes one portion of the earth ‘s water circulatory system
known as the hydrologic circle. Figure below illustrates some of the many processes involved
in this cycle. Water bearing formations of the earth ‘s crust act as conduits for transmission and
as reservoirs for storage of water. Water enters these formations from the ground surface or
from bodies of surface water, after which it travels slowly for varying distances until it returns
to the surface by action of natural flow, plants or humans. Principal sources of natural recharge
include precipitation, streamflow, lakes and reservoirs. Other contributions, known as artificial
recharge, occur from excess irrigation, seepage from canals, and water purposely applied to
augment groundwater supplies.(Taylor and Geography, 2013)
Typically, most water from precipitation that infiltrates do not become recharge, but is instead
stored in the soil and is eventually returned to the atmosphere by evaporation and plant
transpiration. The percentage of precipitation that becomes diffuse recharge is highly variable
and depends upon many factors, such as depths to the water table, properties of surface soils,
aquifer properties and many other factors.(Bouwer, 2006)
2.1.4 Groundwater Occurrence
Aquifers are underground storage reservoirs usually of large extent. The aquifers are either
confined or unconfined. Confined aquifer occurs where underground water is sandwiched
between two impermeable layers or strata. An unconfined aquifer has a water table serving as
the upper surface zone of saturation. Other forms of aquifers are aquiclude and aquifuge which
may contain water but are incapable of transmitting significant amount e.g. clay. The aquifer
characteristics include: - hydraulic conductivity, recharge, and water level elevation and aquifer
boundaries.

Figure 2: confined and unconfined aquifers
Once groundwater is pumped from the water-table aquifer at rates sufficient to lower water
levels the problem of water depletion starts and sometime it completely exploits the aquifer.
Studies carried out in arid and semi-arid areas in Africa continent (Foster et al., 2009) show
that by the year 2050 the rainfall in Sub-Saharan Africa could drop by 10% which will cause a
major water shortage. This 10% decrement in precipitation would reduce drainage by 17% and
the regions which are receiving 500 to 600 mm/year rainfall will experience a reduction by
50% to 30%in the surface drainage. The possibility of the similar types of impact in other parts
of the world is high therefore, it becomes imperative to implement effective water resource
management plan in critical areas.(Taylor and Geography, 2013).
Groundwater recharge or deep drainage or deep percolation is a hydrologic process where
water moves downward from surface water to groundwater. The process of ground-water
replenishment results in the interstices present in the soil getting filled up with water. Recharge
occurs both naturally through the water cycle and through artificial groundwater recharge or
artificial storage and recharge (ASR), where rainwater and/or collected water is routed to the
subsurface. Groundwater is recharged naturally by rain and to a smaller extent by surface water
that is from rivers and lakes.
The factors that influence the amount and type of recharge include:
 precipitation
 topography
 vegetation and evapotranspiration
 soil and subsoil types

 flow mechanisms in the unsaturated
zone
 bedrock geology
 available groundwater storage
 presence of influent rivers
 Presence of karst features.
In Uganda groundwater is mainly recharged using rainwater and water infiltrated from the
rivers or lakes. Recharge may be impeded somewhat by human activities which include
development, irrigation. Groundwater recharge is an important process for sustainable
groundwater management, since the volume-rate abstracted from an aquifer in the long term
should be less than or equal to the volume-rate that is recharged as shown by the formula below;
𝑃 = 𝐴𝐸 + 𝑄 + 𝑈 + ∆𝑆𝑔 + ∆𝑆𝑚 …………………………………………..Equation 4
Where
P = Precipitation,
AE = Actual Evaporation,
Q = runoff,
U = net unmeasured outflows,
∆𝑆𝑔 = change in groundwater
storage,
∆𝑆𝑚 = change in moisture content.
2.1.5 Groundwater Recharge
2.1.5.1 Natural Recharge
Natural groundwater recharge is the process of replenishing of groundwater, mainly by
precipitation. Replenishment rates vary with precipitation patterns, surface runoff and stream
flow. Other factors like the soil permeability, topography and type of vegetation; and land-use
also cause variations (Baalousha, 2016). Soil conservation measures are necessary, to increase
natural groundwater recharge rates. In urban settings, where natural ground has been altered
preventing groundwater percolation, other measures are taken to aid in this process.
Rainwater falling directly on the land surface above aquifers replenishes groundwater quickly,
while in other areas surface water in streams, rivers and lakes recharge the aquifer when their
water levels are higher than the water table on a pervious layer. Certain quantities pass into the
ground along river banks at times of high flow and generally sustain the flow by returning
water to the rivers as the flow recedes. The long term renewal of groundwater, however, is
brought about by the rainfall infiltration over a catchment area.

Figure 3:Natural groundwater recharge/discharge to a stream (Sophocleous, 2004)
Part A in Figure above represents a Gaining Stream ‘, where the water table is at a level higher
than the water level in the stream, thus recharging the stream, while part B represents a Losing
Stream ‘, where the water table is at a level lower than the water level in the stream, thus
recharging the aquifer. This same principle is applicable for other sources such as lakes.
Natural groundwater recharge for the aquifer underneath the study area is to the West,
occurring on the slopes of the rift zone where the volcanic rocks are incised by numerous
streams related to fault lines and weathered zones of the previous lands surfaces. Infiltration of
wastewater, excess rainfall and water mains leakage also form part of the natural recharge
system (Somaratne, 2015). Part of the infiltration however, is intercepted by perched aquifers
and discharge locally to streams.
2.1.5.2 Groundwater Recharge Estimation
Although the estimation of amounts of groundwater recharged involves complex computations,
the various methods used are highlighted below(Adeleke et al., 2015)
Direct measurements
 Lysimeter(s)
This is a device consisting of an in situ weighable soil column of a 1𝑚2
or greater cross-
sectional area. The flux by rainfall into the column, the outflow by seepage in the 1 − 2𝑚 depth
and the weight are continuously measured. A water budget is then reconstructed and the
missing term, evaporation, calculated. Recharge is directly measured if it can be assumed that
the lower end of the Lysimeter is below the zero flux plane. The working principles of a
Lysimeter are illustrated using Figure below:

Figure 4:Lysimeter (after Adeleke et al., 2015)
 Soil moisture budget by neutron probes
This method relies on the fact that water molecules will scatter neutrons. The amount of
scattering is proportional to the amount of water present, which essentially determines the
vertical distribution of the soil ‘s moisture content.
2.1.5.3 Water balance methods (Including hydrograph methods)
 River channel water balance
This is used where recharge is confined to seepage from a river channel. If flow is measured
between two points along the river, the difference will at least convey some information on the
seepage thus giving an upper bound for recharge.
 Water table rise method
This is the clearest indicator of recharge if all abstractions remain unchanged and atmospheric
pressure effects are neglected. Knowing the storage coefficient of the aquifer, the spatially
interpolated water table rise can be converted into water volume.
 River base flow method
This is based on the assumption that low flow conditions in the river represent pure
groundwater outflow. In the long run, this outflow balances the inflow or recharge.
 Rainfall-recharge relationships
Recharge can be expressed as a percentage of rainfall although verification with other methods
is necessary. The method is upgraded by starting the linear relationship only after some
threshold value for minimum rainfall required to observe recharge is established.
2.1.5.4 Darcyan methods
These methods estimate the flux using the hydraulic gradient and the hydraulic conductivity.
An accurate determination of these two quantities is representative of the scale on which the
flux is to be determined. The advantage of this method is that all quantities involved on the

right-hand side of Darcy ‘s equation are measurable. The downside however, is that hydraulic
conductivity of a soil is poorly known due to heterogeneity and varies with saturation.
2.1.5.5 Tracer methods
Environmental tracers can be used in both unsaturated and saturated zones. Tracer methods
tend to a more averaged behavior over time than hydraulic variables owing to the fact that
pressure travels faster in the aquifer than solute. The tracer distribution pattern may thus not
correspond to momentary piezometric head distributions and recharge.
2.1.6 Artificial Recharge
General
Artificial recharge refers to the process of augmenting the natural movement of surface water
into underground formations either by spreading of water or by changing the natural conditions.
It serves for subsurface storage of water, although expensive. The main purposes of this process
are to deal with adverse conditions such as continued lowering of groundwater levels and
reducing significant land subsidence due to over abstraction (Al-qubatee, 2009). Artificial
recharge methods for groundwater storage improvement provide a socially-sustainable solution
to combat water demand variability due to climate change and over-pumping of groundwater
(Bhattacharya, 2010). This method of aquifer recharge has been practiced successfully in
different parts of the world such as the development of percolation tanks in India to enhance
groundwater resources.
Large amounts of water are necessary for this process. Outlined below are the possible water
sources:
 Collection of storm-water/ floodwater runoff in reservoirs
 Use of treated wastewater
 Directing of piped water or by use of channels from a source further away from the
recharge zone.
The many achievements that this has include the capability of floodwater disposal, water
quality improvement by removal of suspended solids during ground infiltration, supplementing
the quantity of groundwater available, balancing of salt water intrusion and storage of water to
reduce pumping and piping costs. Bhattacharya noted that both in-situ wastewater disposal and
urban mains leakages usually result in large volumes of accidental groundwater recharge, and
reason that it should be feasible to achieve similar outcomes on a planned basis.
Artificial Recharge Methods
A. Water Spreading

These methods are most effective in areas where subsurface strata do not restrict the downward
passage of water. The main objective when using water spreading techniques is to lengthen the
time and the area over which the water is being recharged. It can be classified into two;
 Basin Method
This involves releasing water into basins separated by levees running on contours. The designs
of the basins are adapted to the slope of the land, and are periodically maintained to improve
infiltration rates. The method is especially suitable in low rainfall areas.
 Furrow Method
Here, water is diverted from a main channel into a series of parallel furrows. These furrows are
generally shallow and flat-bottomed to increase the surface area coming in contact with water.
The furrows are constructed where the permeable layer is available at shallow depths. Filtration
materials are used to backfill the furrows.
B. Pit method
This method involves filling up of pits, 1-2m wide and 3m deep, with water, preferably that
with low silt levels. It is applicable where the impermeable layer is encountered in large depths,
and is used for recharging shallow aquifers. Using abandoned excavations on permeable
ground is suitable, for economical purposes. The pits are backfilled using layers of coarse
sands, gravels and boulders as shown in Figure below using a percolation tank.
Figure 5: Artificial recharge using a percolation tank (Huntington and Williams, 2012)
C. Flooding method

Water is led using canals to spread evenly over a large flat area. It moves at low speeds and is left
to form a thin sheet of water over the land. The method is most suitable for areas with vegetation
cover.
Recharge through wells
This method involves injecting water into a recharge well, which can be an injection well,
inverted well, diffusion well or a disposal well. It is used to recharge deep confined aquifers
and is applicable where there is limited land space to have surface methods of recharge e.g. in
urban areas. Filter media are used to pass water through, to prevent choking of the wells. The
flow in such wells is the reverse of a pumping well although the construction is usually the
same. The cone of depression in the pumping well becomes the cone of recharge in the recharge
well with an inverted shape as demonstrated using Figure below:
Figure 6: Injection well with cone of recharge (Huntington and Williams, 2012)
Several considerations have to be made for successful groundwater recharging. Field
conditions have to be analyzed to determine appropriate storage, movement and proposed use
of the recharge water. An analysis of the geology of the area for recharge to determine its
suitability and the determination of the availability of adequate quantities of water for recharge
has to be done. The rates of recharge have to be sustained at adequate levels; and the chemical
compatibility and temperatures of the recharge water to the existing groundwater have to be
considered. For sub-surface storage, controlled transport to the recharge areas and subsequent
storage is required to allow for infiltration to take place (Al-qubatee, 2009)
Artificial aquifer recharge is especially important in urban areas, where the natural ground
has been altered making it impervious by being constructed or paved over, preventing water
percolation into the aquifers. The changes increase the quantities of storm water runoff,

which can be dealt with greatly. Reduced risks of urban floods and loads on storm sewers are
additional benefits. Generally, RWH combined with injection methods are highly beneficial
in the compensation of the relatively large non- infiltration areas and the high groundwater
extraction in the urban areas.
The RWH technologies available for direct or subsequent groundwater recharge include:
 Rooftop RWH; for buildings
 Surface runoff RWH; for roads
 Open Ground Water Recharge RWH; for open spaces
 Closed Ground Water Recharge RWH; for forests
2.1.7 Artificial aquifer recharge practices in Uganda
Artificial aquifer recharge, though not widely adopted on a large scale in Uganda, is being
practiced with minimum understanding in different parts of the country through the following
activities:
 Dug Terraces, which is prepared by digging a ditch and throwing the soil uphill to form
a barrier ridge which retains water and soil. This is used to improve retention and for
the control of soil erosion. This is done by very many farmers all over the country.
 Sand Dams, which are made by building a wall across a riverbed thus trapping water.
There are minimal water losses due to low evaporation, and the lateral and vertical
recharges are high. This method has a great potential of creating shallow artificial
aquifers. This is mainly practiced in the North eastern parts of Uganda (karamoja
region)
 Other methods being used involve the use of dug tanks, micro-catchments, grass strips
developed by leaving strips of uncultivated land and trash lines. Most of these methods
only offer subsurface recharge and do not provide for the deep aquifers.
2.1.8 Groundwater Movement and Flow
Groundwater in its natural state is invariably moving. The movement is governed by
established hydraulic principles. Factors influencing the water movement are geology,
hydraulic head, hydraulic gradient, velocity, soil, aquifer properties and topography. Darcy ‘s
principle which is valid for laminar flow at low velocities is used to express the flow through
the porous media. It states that the quantity of water discharge per unit area is proportional to
the head loss and inversely proportional to the length of path. (David and Larry, 2005)
𝑄 = 𝐾𝐴
𝑑ℎ
𝑑𝑙
……………………………………………………………………Equation 5
The velocity of flow is given by:

𝑉 =
𝑄
𝐴
= 𝐾
𝑑ℎ
𝑑𝑙
………………………………………………………………...Equation 6
Where:
𝑑ℎ
𝑑𝑙
= 𝑡ℎ𝑒 ℎ𝑦𝑑𝑟𝑎𝑢𝑙𝑖𝑐 𝑔𝑟𝑎𝑑𝑖𝑒𝑛𝑡
𝐾 = 𝑝𝑒𝑟𝑚𝑒𝑎𝑏𝑖𝑙𝑖𝑡𝑦 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 (m/s)
𝑄 = 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑑𝑖𝑠𝑐ℎ𝑎𝑟𝑔𝑒𝑑(m3
/s)
𝐴 = 𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝑎𝑟𝑒𝑎 (𝑚2
)
𝐿 = 𝐿𝑒𝑛𝑔𝑡ℎ (𝑚)
𝑉 = 𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 (m/s)
2.1.9 Porosity
Those portions of a rock or soil not occupied by solid mineral matter can be occupied by
groundwater. (Braja, 2008) These spaces are known as voids, interstices, pores or pore spaces.
The porosity of a rock or soil is a measure of the contained interstices or voids expressed as the
ratio of the volume of interstices to the total volume. If n is the porosity, then
𝑛 =
𝑉𝑣
𝑉
=
𝑉𝑡−𝑉𝑠
𝑉𝑡
…………………………………………………………….Equation 7
𝑉𝑣 = 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑣𝑜𝑖𝑑𝑠
𝑣 = 𝑡𝑜𝑡𝑎𝑙 𝑣𝑜𝑙𝑢𝑚𝑒
𝑉𝑡 = 𝑡𝑜𝑡𝑎𝑙 𝑣𝑜𝑙𝑢𝑚𝑒
𝑉𝑠 = 𝑣𝑝𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑠𝑜𝑙𝑖𝑑𝑠

3 CHAPTER THREE: METHODOLOGY
This chapter addresses the procedures and methods used in obtaining the relevant data required
for design of an aquifer recharge system using surface runoff in Rubongi sub county, Tororo
district.
4.0 Methods and activities required to achieve the objectives
4.1 To identify appropriate potential aquifer recharge sites for the study area
The following datasets were used.
Table 4: Project data sources
Data Source Function
SRTM digital elevation
model (DEM)
http://srtm.csi.cgiar.org/. To generate a slope map
Geological data Directorate of Geological
Survey and Mines (DGSM)
To generate the geology map
Soil data FAO/NARO To generate the soil map
Borehole data DWRM, field data To generate the aquifer yield
map
Land use data NARO, field data record To generate the land use map
Landsat +ETM2013 Google earth To verify the accuracy of the
thematic map layers
Lithological data DGSM To generate the lithology
map
The thematic map layers were then overlayed on ArcGIS 10.1 platform and using the weighting
overlay analysis, Analytic Hierarchy process (AHP) and Multi Criteria Evaluation (MCE), the
aquifer recharge sites were then obtained as shown in the figure below.

Figure 7: Flow chart leading to the derivation of aquifer recharge sites
4.1.1 Software employed
 ArcGIS 10.1 for derivation of thematic layers and Weighted Index Overlay Analysis
 IDRISI 32 for calculation of weights
 Micro soft office packages, (word and excel)
4.1.2 Methods to be employed for the study;
The methods used to achieve this objective included;
 Digital image processing
 Thematic map integration
 Geo-referencing
 Spatial analysis
 Weighted Index Overlay Analysis
 Analytic Hierarchy process (AHP)
 Multi Criteria Evaluation (MCE)
4.1.3 Thematic layers include;
The thematic maps of the identified factors that the possible sites for artificial recharge in the
study area are used to generate the final recharge sites map. These include the following;

 Digital elevation model (DEM)
 Geological map
 Soil map
 Land use/cover map
 Slope map
 Drainage map
4.2 Requirement for specific objective 2
To examine the water balance and runoff potential of Rubongi sub county
4.2.1 Water balance
The water balance of Rubongi sub county was determined based on the difference between the
water demand and supply within the sub county. The value was then projected up to 2032 in tabula
forms as indicated below
4.2.1.1 water demand
Table 5:analysis of the water demand of the area was accessed as follows
Name Year Number Demand
(l/day)
Days in a
year
Demand
(l/year)
Demand
(m3
/year)
Population
Livestock units
Irrigation
Municipal
Environmental flow
Ecological flow
Basic human need
Evaporation rate
Total
Table 6:Determination of the actual water supply for the study area
Type of source m3
/day m3
/day
Surface water
Rivers and streams
Groundwater
Total
Difference between demand and supply, indicates the sustainability of the current water supply in
comparison with the needs of the residents.
4.2.1.2 Determination of projections for both livestock and humans
The year-by-year population projections for the study area was then be computed by applying the basic
equation;

𝑃𝑛 = 𝑃0(1 + 𝐾𝐺𝑅) 𝑁
………………………………………...Equation 8
Where,
𝑃𝑛 = the projected population after nth year from initial year
𝑃𝑜 = the population in the initial year of the period concerned
𝑘 = population growth constant due to limited facilities
𝐺𝑅 = the average growth rate between the 2 periods
𝑁 = number of years between 𝑷 𝒐 and 𝑷 𝒏
4.2.1.3 Determination of growth rates (𝑮𝑹)
Using the equation below the average annual growth rate within the last censual period (in this case
from 2011 to 2014): is determined.
𝑮𝑹 = (
𝑷 𝟐𝟎𝟏𝟒
𝑷 𝟐𝟎𝟎𝟐
)
𝟏
𝒏
− 𝟏 …………………………………...............Equation 9
𝑮𝑹 = annual growth rate (multiply by 100 to get percentage growth rate)
𝑷 𝟐𝟎𝟏𝟒 = Is the population by the last census
𝑷 𝟐𝟎𝟎𝟐 = Is base year population
𝒏 = number of years between the two census
Population projection will be made for the next few years to determine how groundwater
abstraction will vary with time as shown below.
Table 7: variation of groundwater abstraction with time
Name 2002
Number
2002
Demand
2012
Number
2012
Demand
2018
Number
2018
Demand
2022
Number
2022
Demand
Population
Livestock units
Irrigation
Municipal
Environmental
flow
Evaporation
rate
TOTAL

4.2.2 Runoff estimation for the study area
4.2.2.1 Materials and equipment
 GPS for determining the catchment area
 Rainfall data for Tororo district from Uganda Meteorological Authority
 Arc SWAT 9.0 for watershed delineation in ArcGIS 10.1
4.2.2.2 Determination of the direct runoff
This was determined using the Curve Number Method (by using the Soil Conservation
Services(SCS) of united states)
𝑄 =
(𝑃−0.2𝑆)2
(𝑃+0.8𝑆)
… … … … … … … … … … … … … … … … … … … … … … …Equation 10
𝑄 = 𝐷𝑖𝑟𝑒𝑐𝑡 𝑅𝑢𝑛𝑜𝑓𝑓(𝑚𝑚)
𝑃 = 𝑃𝑟𝑒𝑐𝑖𝑝𝑖𝑡𝑎𝑡𝑖𝑜𝑛(𝑚𝑚)
𝑆 = 𝑝𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑟𝑒𝑡𝑒𝑛𝑡𝑖𝑜𝑛 𝑎𝑓𝑡𝑒𝑟 𝑟𝑢𝑛𝑜𝑓𝑓 𝑏𝑒𝑔𝑖𝑛𝑠(𝑚𝑚)
𝑆 = (
1000
𝐶𝑁
) − 10
𝐶𝑁 = 𝐶𝑢𝑟𝑣𝑒 𝑁𝑢𝑚𝑏𝑒𝑟 𝑡ℎ𝑎𝑡 𝑟𝑎𝑛𝑔𝑒𝑠 𝑓𝑟𝑜𝑚 0 𝑡𝑜 100, 𝑎𝑛𝑑 𝑑𝑒𝑝𝑒𝑛𝑑𝑠 𝑜𝑛 𝑡ℎ𝑒
ℎ𝑦𝑑𝑟𝑜𝑙𝑜𝑔𝑖𝑐𝑎𝑙 𝑠𝑜𝑖𝑙 𝑔𝑟𝑜𝑢𝑝
4.2.2.3 Application of the rational method to determine the runoff
I.e.
𝑄 = 0.00278𝐶𝐼𝐴 ……………………………………………………………………Equation 11
Where;
Q = Estimated runoff (m3
/s)
C = Runoff coefficient
I = Rainfall intensity (mm/hr.)
A = Catchment area (ha)
The runoff data was represented in a format shown below;
Table 8: runoff estimation for the catchment
Year JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
Average
rainfall(mm/month)
Rainfall intensity
(mm/hr.), l
Rainfall intensity
(m/s), l

Run-off coefficient
©
Catchment
area(ha), (A)
Catchment area
(m2
), A
Q = CIA
The highest runoff value for a specific month of the year will be used as the design value for the
aquifer recharge structure.
4.3 To design the artificial aquifer recharge system
Functional requirements for the structure include;
4.3.1 The conveyance system
Open Channels are selected as conveyance system because they are easy to design and the
maintenance cost is minimum. The channel is trapezoidal in shape, lined with concrete since the
soils in the study area are stable. This conveyance system is to allow the flow of water from the
collection point to the recharge basin. To get the size of the conveyance system, the following
computations are made;
The hydraulic radius for the conveyance system will be determined from the manning’s equation
below
𝑉 =
1
𝑛
× 𝑅
2
3 × 𝑆
1
2 ……………………………………………………………… Equation 12
Where;
V = average velocity (from the runoff coefficient table above)
R = hydraulic radius
S = slope (will be got from the survey reports of the study area)
𝑛 = manning’s roughness coefficient (value for concrete will be used)
4.3.1.1 Area of the conveyance system
From, 𝑄 = 𝐴𝑉………………………………………………..Equation 13
𝑄 = 𝑑𝑖𝑠𝑐ℎ𝑎𝑟𝑔𝑒(𝑔𝑜𝑡 𝑓𝑟𝑜𝑚 𝑡𝑎𝑏𝑙𝑒 𝑎𝑏𝑜𝑣𝑒)
𝑉 = 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑜𝑓 𝑟𝑢𝑛𝑜𝑓𝑓
𝐴 = 𝐴𝑟𝑒𝑎 𝑜𝑓 𝑐𝑜𝑛𝑣𝑒𝑦𝑎𝑛𝑐𝑒 𝑠𝑦𝑠𝑡𝑒𝑚
Making A, a subject,
𝐴 =
𝑄
𝑉

4.3.1.2 Determination of wetted perimeter of the conveyance system
𝑅 =
𝐴
𝑃
……………………………………………………Equation 14
Where P is the wetted perimeter
𝑃 =
𝐴
𝑅
4.3.1.3 Determination of the length and width of the conveyance system
𝑃 = 𝑏 + 2𝑑(𝑧2
+ 1)
1
2 …………………………………...Equation 15
Where;
𝑝 is the wetted perimeter
𝑏 is the length of conveyance system.
𝑑 is the width of the conveyance system.
𝑧 is the slope design value for the structure.
4.3.2 The recharge basin
The bottom of the recharge basin will be filled with sand and gravel to protect it from any clogging
and scouring of the surface level.
The recharge basin will be a trapezoidal section and the following will be the design considerations
based on
Top width of the section
𝑇 = 𝑏 + 2𝑚𝑦 …………………………………………………………...Equation 16
Where;
𝑇 𝑖𝑠 𝑡ℎ𝑒 𝑡𝑜𝑝 𝑤𝑖𝑑𝑡ℎ
𝑏 𝑖𝑠 𝑡ℎ𝑒 𝑏𝑎𝑠𝑒 𝑤𝑖𝑑𝑡ℎ
𝑚 𝑖𝑠 𝑡ℎ𝑒 𝑠𝑙𝑜𝑝𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑡𝑟𝑎𝑝𝑒𝑧𝑜𝑖𝑑𝑎𝑙 𝑠𝑒𝑐𝑡𝑖𝑜𝑛
Wetted perimeter of the trapezoidal section
𝑃 = 𝑏 + 2𝑦√(1 + 𝑧2) ………………………………………………Equation 17
Where;
𝑃 𝑖𝑠 𝑡ℎ𝑒 𝑤𝑒𝑡𝑡𝑒𝑑 𝑝𝑒𝑟𝑖𝑚𝑒𝑡𝑒𝑟
𝑦 𝑖𝑠 𝑡ℎ𝑒 𝑡𝑜𝑡𝑎𝑙 𝑑𝑒𝑝𝑡ℎ 𝑜𝑓 𝑡ℎ𝑒 𝑐ℎ𝑎𝑛𝑛𝑒𝑙 𝑎𝑓𝑡𝑒𝑟 𝑡ℎ𝑒 𝑓𝑟𝑒𝑒 𝑏𝑜𝑎𝑟𝑑
𝑧 𝑖𝑠 𝑡ℎ𝑒 𝑠𝑙𝑜𝑝𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑐ℎ𝑎𝑛𝑛𝑒𝑙
Area of the trapezoidal open channel

𝐴 = 𝑏𝑦 + 2𝑦2
………………………………………………………...Equation 18
Where;
𝐴 𝑖𝑠 𝑡ℎ𝑒 𝑎𝑟𝑒𝑎 𝑜𝑓 𝑡ℎ𝑒 𝑡𝑟𝑎𝑝𝑒𝑧𝑜𝑖𝑑𝑎𝑙 𝑠𝑒𝑐𝑡𝑖𝑜𝑛
4.3.3 Determination of the channel freeboard
𝐹 = 0.55√ 𝑐𝑦 ………………………………………………………..Equation 19
𝐹 𝑖𝑠 𝑡ℎ𝑒 𝑓𝑟𝑒𝑒𝑏𝑜𝑎𝑟𝑑 𝑖𝑛 𝑚𝑒𝑡𝑒𝑟𝑠
𝑦 𝑖𝑠 𝑡ℎ𝑒 𝑑𝑒𝑠𝑖𝑔𝑛 𝑑𝑒𝑝𝑡ℎ 𝑖𝑛 𝑚𝑒𝑡𝑒𝑟𝑠
𝑐 𝑖𝑠 𝑡ℎ𝑒 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 𝑡ℎ𝑎𝑡 𝑣𝑎𝑟𝑖𝑒𝑠 𝑤𝑖𝑡ℎ 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑡 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑑𝑒𝑠𝑖𝑔𝑛
Where;
4.3.4 Estimating the reservoir capacity.
To provide a larger surface and a more stable embankment of the pond in relation to the large
volume of water it is intended to hold, a slope of 2:1 has been adopted as per the national standard
by Ministry of Water and Environment.
The Volume of the pond is estimated on the basis of the prismoidal formula
V =
(𝐴+4𝐵+𝐶)
6
𝑋 𝐷
Where;
V is the volume of excavation required for the pond in cubic meters
A is the area of the excavation at the ground surface in square meters
B is the area of the excavation at the mid depth point (1/2 D) in square meters
C is the area of excavation at the bottom of the pond in square meters
D is the depth of the pond in meters.
4.3.5 Average Shear Stress on Channel Boundary (the Tractive Force):
𝜏0 = 𝛾𝑅𝑆
𝜏0 = specific weight of water
𝑆 =hydraulic slope for uniform flow; this is substituted with 𝑆𝑓for non-uniform flow conditions.

4 CHAPTER FOUR: PRESENTATION AND DISCUSSIONS OF
RESULTS
This chapter discusses, how the earlier obtained hydrological and geological data as well as the
thematic layers developed were critically studied and analyzed to assess their impact on ground
water in Rubongi Sub County and the results are presented in form of maps, tables and graphs.
4.1 Analysis of hydro-geological data
Various trips were made to DWD and UNMA where the hydrological data (mean annual rain fall
data, mean temperature, humidity) as well data about the existing boreholes was obtained. This
data was analyzed using MS Excel 2016.
4.1.1 Hydrological analysis of the rainfall data
The data was obtained in form of daily rainfall records, it was analyzed in excel to obtain the mean
monthly and mean annual rain fall. (Appendix 2)
Rainfall in Uganda varies significantly across the country and throughout the year, with most parts of
the country having two distinct rainy seasons. The long rains fall from March to Jun, and the short‖
rains fall from October to November. National average annual rainfall is approximately 855 mm per
year. The western semi-humid part of the country receives more than 1,800 mm annually, while the
northern and eastern arid/semi-arid regions, receive a mere 200 to 400 mm annually. However, data
obtained from the Uganda National Metrological Authority about Tororo district rainfall indicates the
district can have up to a yearly average of 2,217.34mm/year.
The results of the meteorological information are presented in tables in appendices and in graphs as
shown below.

Figure 8: Graph of average annual rainfall of Tororo district against years
Figure 9: Minimum and maximum temperatures of Tororo different
0
50
100
150
200
250
300
350
400
AVERAGEYEALYRAINFALL(mm)
YEAR
A GRAPH OF AVERAGE YEARLY RAINFALL AGAINST YEARS
AVERAGE YEARLY RAINFALL(mm)
0
5
10
15
20
25
30
35
1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016
TEMPERATURE
YEARS
MINIMUM AND MAXIMUM TEMPERATURES
MINIMUM TEMPERATURE MAXIMUM TEMPERATURE

Figure 10: Evaporation rate of Rubongi sub county
4.1.2 Soil Infiltration potential
Different soil textures have different porosities and thus different infiltration rates. Rubongi Sub
County consist three soil texture types.
From the curve below, the infiltration rate of loam soil is higher, followed by clay loam and then
clay with the lowest infiltration rate.
Figure 11: The infiltration potential of different soil types in Rubongi Sub county
Five different thematic layers were derived prior to weighted overlay analysis. These are layers of
the major factors that determine the existence and quantity of ground water in an area.
0
2
4
6
8
10
12
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2007
2008
2009
2010
2011
2012
2013
AVERAGEPERYEAR
YEARS
EVAPORATION RATES OF RUBONGI
Average per Year
0
20
40
60
80
100
120
140
1990 1995 2000 2005 2010 2015
INFILTRATIONPOTENTIAL
YEARS
INFILTRATION POTENTIAL IN DIFFERENT SOIL TYPES
LOAM CLAY LOAM CLAY

4.1.3 Drainage map
A watershed map showing all the water streams and the natural drainage canals (Drainage map)
was derived from a digital elevation model (SRTM DEM) of Rubongi sub county using ArcSWAT
Tools (version 9.0), an ArcGIS-based system; which is a series of tools built on top of the Arc
Swat database, geared to support water and soil resources applications. In deriving a drainage
density map, “density tool” of spatial analyst extension in ArcGIS was employed for deriving the
density of drainage lines. The drainage map is shown below.
Figure 12: Drainage density map of Rubongi Sub county
4.1.4 Land use map
Land use map of Rubongi Sub County was derived from USGS imagery through supervised
classification where different categories of interpretation were selected from Google Earth
Imagery of the study area, based on their relative importance towards ground water recharge siting
influence. Finally, field verification concluded the land use map with four categories which include
agriculture, wetland, forest and farm land.

Figure 13: Land use map of Rubongi sub county
4.1.5 Slope map
This was derived from SRTM Digital Elevation Model (DEM) as percentage rise. For each cell,
the Slope tool calculates the maximum rate of change in value from that cell to its neighbors.
Basically, the maximum change in elevation over the distance between the cell and its eight
neighbors identifies the steepest downhill descent from the cell.
Figure 14: Slope map of Rubongi Sub county

4.1.6 Soil map
Soil type and texture directly affect ground recharge in any area as it directly affects infiltration of
runoff whenever it rains. The soil layer of Uganda was obtained from NARO and later, the one of
Rubongi Sub County was clipped out. Rubongi Sub County has got four soil texture types; clay,
sandy clay loam, loam and sandy loams as shown in the thematic map below.
Figure 15: soil map for Rubongi Sub county
4.1.7 Geological map
Geology studies rocks, their origin and formation and mineral composition and classification. The
geology was obtained from DGSM and later the existing borehole lithology were geo referenced
for accuracy. Rubongi sub county is occupied by mainly two types of graphs as shown below

Figure 16: Geology map of Rubongi Sub county
4.1.8 Weighted overlay analysis
4.1.8.1 Analysis of Drainage density layer
Drainage density is an inverse function of permeability, and therefore it is an important parameter
in evaluating the groundwater recharge zones. Area of high drainage density indicates high
infiltration which restricts runoff and hence acts as a good groundwater recharge zone. This is
because major part of the rainwater over the area is lost as surface runoff with little infiltration for
recharging the groundwater reservoir in areas with low drainage area. On the other hand, low
drainage density areas permit low infiltration and recharge to the groundwater reservoir, hence can
be described as a poor zone for groundwater recharge.
4.1.8.2 Analysis of Slope layer
Area of high slope value will cause more runoff due to low retention time and less infiltration thus,
have poor groundwater recharge zones as compared to low slope regions where the retention time
is high and the infiltration is also high leading to low runoff. Therefore, regions with low slopes,
allow high runoff infiltration and hence more water to replenish the ground water aquifers.
4.1.8.3 Analysis of Land use layer
The forest and wetlands are ranked excellent because the runoff water is slow and high percolation
due to the presence of trees and water. The vegetation and agriculture have the good percolation

capacity of water so it has been ranked in very good category. These are present in sufficient
amount covering the study area.
4.1.8.4 Analysis of soil layer
According to the ground water recharge, the soil plays an important role in the ground water
percolation and holding capacity.
In summary, the following tables were used for the Weighted overlay analysis to come up with the
aquifer recharge areas within Rubongi sub county.
Table 9: Pairwise comparison of the different recharge factors
DRAINAGE SLOPE GEOLOGY SOILS LANDUSE
DRAINAGE 1 2 3 4 5
SLOPE ½ 1 2 3 4
GEOLOGY 1/3 1/2 1 2 3
SOILS ¼ 1/3 ½ 1 2
LANDUSE 1/5 1/4 1/3 ½ 1
TOTAL 2.28 4.08 6.83 10.50 15.00
DRAINAGE SLOPE GEOLOGY SOILS LANDUSE WEIGHT WEIGHT
DRAINAGE 0.44 0.45 0.44 0.38 0.33 0.41 41
SLOPE 0.22 0.23 0.29 0.29 0.27 0.26 26
GEOLOGY 0.15 0.11 0.15 0.19 0.20 0.17 17
SOILS 0.11 0.08 0.07 0.10 0.13 0.10 10
LANDUSE 0.09 0.06 0.05 0.05 0.07 0.06 6
1.00 0.93 1.00 1.00 1.00 1.00 100
DRAINAGE DRAINAGE SLOPE SLOPE GEOLOGY GEOLOGY SOILS SOIL LAND
USE
LAND
USE
DRAINAGE 1.00 0.41 2.00 0.52 3.00 0.51 4.00 0.40 5.00 0.30
SLOPE 0.50 0.21 1.00 0.26 2.00 0.34 3.00 0.30 4.00 0.24
GEOLOGY 0.33 0.14 0.50 0.13 1.00 0.17 2.00 0.20 3.00 0.18
SOILS 0.25 0.10 0.33 0.09 0.50 0.09 1.00 0.10 2.00 0.12
LANDUSE 0.20 0.08 0.25 0.07 0.33 0.06 0.50 0.05 1.00 0.06
TOTAL 2.28 0.94 4.08 1.06 6.83 1.16 10.50 1.05 15.00 0.90

DRAINAGE SLOPE GEOLOGY SOIL LANDUSE SUM WEIGHT SUM/WEIGT
DRAINAGE 0.41 0.52 0.51 0.4 0.3 2.14 0.41 5.22
SLOPE 0.205 0.26 0.34 0.3 0.24 1.345 0.26 5.17
GEOLOGY 0.136666667 0.13 0.17 0.2 0.18 0.81666667 0.17 4.80
SOIL 0.1025 0.0866667 0.085 0.1 0.12 0.49416667 0.1 4.94
LANDUSE 0.082 0.065 0.056666667 0.05 0.06 0.31366667 0.06 5.23
AVERAGE 5.07
0.016
These weights shown in the table 9 was used to generate the Aquifer recharge sites Map of
Rubongi sub county. The delineation of aquifer recharge sites was carried out by reclassifying into
four different aquifer recharge potential sites: low recharge sites, Moderate recharge sites, high
recharge sites and very high recharge sites as shown in the figure below.
Figure 17: Aquifer recharge site map of Rubongi Sub County

4.2 To estimate the water balance and runoff potential of the study area
From the groundwater yield potential map based on the borehole yield data, the average yield of
Rubongi sub county boreholes is 4.317m3
/hr. Therefore, the yield in m3
/year is 37,816.92 m3
/year.
4.2.1 Water balance
4.2.1.1 Demand
Table 10: Water Demand of Rubongi Sub County
Name 2002 Demand
(l/day)
number of days in a
yr.
Demand (l/year) Demand (m^3/year)
Population 28547 40 365 416786200 416786.2
Livestock 7432 68 365 184462240 184462.24
Irrigation 0 0 0 0
Ecological flow 2.2m3
/s 69379200
Basic human need 28547 25 365 260491375 260491.375
Evaporation rate 9.8mm/year 252378.42
TOTAL 70,493,318.24
4.2.1.2 Supply
Table 11: Supply yield total of the different sources in Rubongi Sub county
Name Quantity Catchment area,
𝒎 𝟐
𝐦 𝟑
/𝐲𝐞𝐚𝐫
Surface water 184.78mm/year 25,752,900 4,758,620.862
Runoff 27,470,221.6
River/streams 39,001,013
Groundwater 37,816.92
Total 71,267,672.38
4.2.1.3 Projection
Determination of the population growth rate for Rubongi sub county, Tororo district
Using the equation below the average annual growth rate within the last censual period (in this
case from 2002 to 2014): is determined.
𝐺𝑅 = (
𝑃2014
𝑃2002
)
1
𝑛
− 1
𝐺𝑅 = annual growth rate (multiply by 100 to get percentage growth rate)
𝑃2014 = Is the population by the last census

𝑃2002 = Is base year population
𝑛 = number of years between the two census
According to the national population and housing census, the population of Rubongi sub county
in 2002, was, 28,547 people and was 39,439 people in 2014. The growth rate will be,
𝐺𝑅 = (
39439
28547
)
1
12
− 1
𝐺𝑅 = 0.0273 = 2.73%
Assuming livestock population growth rate is 1%.
Therefore, water supply and demand in the next 10 years.
Determination of projections for both livestock and humans
The year-by-year population projections for the study area will then be computed by applying the
basic equation;
𝑃𝑛 = 𝑃0(1 + 𝐾𝐺𝑅) 𝑁
Where,
𝑃𝑛 = the projected population after nth year from initial year
𝑃𝑜 = the population in the initial year of the period concerned
𝑘 = population growth constant due to limited facilities ; 𝑘 = 0.92 𝑓𝑜𝑟 𝑢𝑔𝑎𝑛𝑑𝑎𝑛 𝑏𝑎𝑠𝑖𝑠
𝐺𝑅 = the average growth rate between the 2 periods
𝑁 = number of years between 𝑷 𝒐 and 𝑷 𝒏
Table 12: Water Demand projection for Rubongi Sub County
Name 2002
Number
2002
Demand
(m3
/yr.)
2012
Number
2012
Demand
(m3
/yr.)
2018
Number
2018
Demand
(m3
/yr.)
2022
Demand
(m3
/yr.)
2032
Demand
(m3
/yr.)
Population 28547 416786.2 36597.254 534319.9084 42471.11327 620078.2537 684998.123 878167.593
Livestock 7432 184462.24 8212.36 203830.7752 9629.813336 239011.967 225233.007 248882.472
Irrigation 0 0 0 0 0 0 0 0
Ecological
flow
2.2m3
/s 69379200 2.2m3
/s 69379200 2.2m3
/s 69379200 69379200 69379200
Basic
human need
25 260491.375 36597.254 333949.9428 42471.1133 387548.91 428123.827 548854.746
Evaporation 9.8mm/hr. 252378.42 9.8mm/hr. 252378.42 9.8mm/hr. 252379.42 252378.42 252378.42
Totals 70,493,318.28 70,703,679.05 70878217.55 7096933.38 71,307,483.23

4.2.2 Runoff Estimation
Runoff estimation, Q = 0.00278CIA(ms
/s)
Table 13: Average Monthly Runoff Estimates for Rubongi Sub County
Month JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
Average rainfall
(mm)
36.89 35.23 70.75 313.31 461.35 295.52 201.1 242.39 164.44 155.36 154.02 57.24
Rainfall
intensity
(mm/hr.), I
0.05 0.04 0.10 0.44 0.66 0.41 0.27 0.33 0.23 0.21 0.21 0.08
Constant 0.00278 0.00278 0.00278 0.00278 0.00278 0.00278 0.00278 0.00278 0.00278 0.00278 0.00278 0.00278
Runoff
coefficient, C
0.48 0.48 0.48 0.48 0.48 0.48 0.48 0.48 0.48 0.48 0.48 0.48
catchment area,
A(ha)
2575.29 2575.29 2575.29 2575.29 2575.29 2575.29 2575.29 2575.29 2575.29 2575.29 2575.29 2575.29
Q = 0.00278CIA 0.17182 0.14746 0.34365 1.51205 2.26807 1.40895 0.92785 1.13403 0.79039 0.72166 0.72166 0.27496
The highest runoff is in the month of May at 2.26807m3/s. This is the value that was used to design
the conveyance system for the aquifer recharge structure.
4.3 To design a groundwater recharge system for the aquifer in the study area
4.3.1 Design of conveyance System from the water collection point
Open Channels are selected for conveyance system because they are easy to design and the
maintenance cost is minimum. The proposed channel is trapezoidal in shape, lined with concrete
since the soils is stable. This conveyance system is to allow the flow of water from the collection
point to the recharge basin/pond. To get the size of the conveyance system, the following
computations are made;
The runoff, Q is 2.26807m3/s, gotten from the 35year weather data for the study area
The average velocity is 4.57m/s, the velocity ranges for concrete channels from chow, 1959
The slope is 52%. gotten from the slope map for the study area i.e.
0+1.04
2
= 𝟎. 𝟓𝟐
Manning ‘s roughness coefficient, n is 0.011 for Concrete.
Therefore, the Hydraulic Radius, R of the conveyance system can be found using;
𝑉 =
1
𝑛
× 𝑅
2
3 × 𝑆
1
2
4.57 =
1
0.011
× 𝑅
2
3 × 0.52
1
2

𝑅 = 0.01841𝑚
From flow equation,
𝑄 = 𝐴𝑉
Making A, the subject, 𝐴 =
𝑄
𝑉
Area of the conveyance system, 𝐴 =
2.26807
4.57
= 0.4963𝑚
Wetted perimeter of the conveyance system, 𝑃 =
𝐴
𝑅
𝑃 =
0.4963
0.01841
= 26.96𝑚
However, area of the conveyance system can also be got from,
𝐴 = 𝑏𝑑 + 𝑧𝑑2
Where;
𝑏 𝑖𝑠 𝑡ℎ𝑒 𝑤𝑖𝑑𝑡ℎ 𝑜𝑓 𝑡ℎ𝑒 𝑐𝑜𝑛𝑣𝑒𝑦𝑎𝑛𝑐𝑒 𝑠𝑦𝑠𝑡𝑒𝑚
𝑑 𝑖𝑠 𝑡ℎ𝑒 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑡ℎ𝑒 𝑐𝑜𝑛𝑣𝑒𝑦𝑎𝑛𝑐𝑒 𝑠𝑦𝑠𝑡𝑒𝑚
0.4963 = 𝑏𝑑 + 0.52𝑑2
… … … … … … … … … … . .1
Also, wetted perimeter can also be got from,
𝑃 = 𝑏 + 2𝑑(𝑧2
+ 1)
1
2
26.96 = 𝑏 + 2𝑑(0.522
+ 1)
1
2
26.96 = 𝑏 + 2.254𝑑 … … … … … … … … … … … 2
From equations 1 and 2,
𝑑 = 15.53𝑚
𝑏 = 8.04𝑚
The length of the conveyance system is therefore 15.53m and the width is 8.04m

4.3.2 Design of the Recharge Basins
The design of the recharge ponds is based on the annual runoff volume expected in the catchment
area as shown in the table below.
Table 14: Average Monthly Runoff Volume
Month JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
Q =
0.00278CIA
0.17182 0.13746 0.34365 1.51205 2.26807 1.40895 0.92785 1.13403 0.79039 0.72166 0.72166 0.27492
Monthly
runoff
volume (𝑚3
)
460202.7 332543.2 920432.2 3919234 6074798.69 3651998.4 2485153.44 3037386 2048691 1932894 1870543 736345.7
Total runoff
volume (𝑚3
)
27,470,221.6
The total volume of runoff in the catchment area annually irrespective of the losses, is got from
the table above giving a total annual runoff volume of 27,470,221.6𝒎 𝟑
in the catchment area.
Based on the results of the total run off volume, I therefore chose to use the horizontal recharge
shafts which are also capable of recharging groundwater aquifers. These structures are trapezoidal
in shape and suitable for the construction in places with high surface runoff and discharge as for
the case study area. Horizontal shaft allows infiltration of large volumes of surface run-off.
The design criteria of the recharge basin
Area, 𝐴 = (𝑏 + 𝑚𝑦)𝑦
Where, b is the bottom width of the recharge basin;
𝑚 is the side slope of the basin; basin slope is 2:1
𝑦 𝑖𝑠 𝑡ℎ𝑒 𝑑𝑒𝑝𝑡ℎ 𝑜𝑓 𝑡ℎ𝑒 𝑏𝑎𝑠𝑖𝑛
For an effective basin design for the area, the design is based on the ministry of water and
environment design manual, 2013, the bottom width, b ranges between 15m – 20m and an average
depth of 10m – 12m (which includes even the filtration facilities to be installed.
Therefore, analyzing the longitudinal section of the section of the trapezoidal recharge pond.
𝐴 = (𝑏 + 𝑚𝑦)𝑦

𝐴 = (15 + 2 × 10)10
𝐴 = 350𝑚2
𝑊𝑒𝑡𝑡𝑒𝑑 𝑝𝑒𝑖𝑚𝑒𝑡𝑒𝑟, 𝑃 = 𝑏 + 2𝑦√(1 + 𝑚2
)
= 15 + (2 × 10)√(1 + 22
)
= 𝟓𝟗. 𝟕𝟐𝒎
𝐻𝑦𝑑𝑟𝑎𝑢𝑙𝑖𝑐 𝑟𝑎𝑑𝑖𝑢𝑠, 𝑅 =
𝐴
𝑃
𝑅 =
350
59.72
= 𝟓. 𝟖𝟔𝒎
Top width of the trapezoidal section,
𝑇 = 𝑏 + 2𝑚𝑦
𝑇 = 15 + 2 × 2 × 10
𝑻 = 𝟓𝟓𝒎
𝐻𝑦𝑑𝑟𝑎𝑢𝑙𝑖𝑐 𝑑𝑒𝑝𝑡ℎ, 𝐷 𝑜𝑓 𝑡ℎ𝑒 𝑡𝑟𝑎𝑝𝑒𝑧𝑜𝑖𝑑𝑎𝑙 𝑠𝑒𝑐𝑡𝑖𝑜𝑛 =
(𝑏+𝑚𝑦)𝑦
𝑏+2𝑚𝑦
𝐷 =
(15+2×10)10
15+2×2×10
= 𝟔. 𝟑𝟔𝒎

Figure 18: Longitudinal Section of the recharge basin
Therefore, analyzing the cross section of the section of the trapezoidal recharge pond.
𝐴 = (𝑏 + 𝑚𝑦)𝑦
𝐴 = (10 + 2 × 10)10
𝐴 = 300𝑚2
𝑊𝑒𝑡𝑡𝑒𝑑 𝑝𝑒𝑖𝑚𝑒𝑡𝑒𝑟, 𝑃 = 𝑏 + 2𝑦√(1 + 𝑚2
)
= 10 + (2 × 10)√(1 + 22
)
= 𝟓𝟒. 𝟕𝟐𝒎
𝐻𝑦𝑑𝑟𝑎𝑢𝑙𝑖𝑐 𝑟𝑎𝑑𝑖𝑢𝑠, 𝑅 =
𝐴
𝑃
𝑅 =
300
54.72
= 𝟓. 𝟒𝟖𝒎
Top width, T of the trapezoidal section,
𝑇 = 𝑏 + 2𝑚𝑦
𝑇 = 10 + 2 × 2 × 10

𝑻 = 𝟓𝟎𝒎
𝐻𝑦𝑑𝑟𝑎𝑢𝑙𝑖𝑐 𝑑𝑒𝑝𝑡ℎ, 𝐷 𝑜𝑓 𝑡ℎ𝑒 𝑡𝑟𝑎𝑝𝑒𝑧𝑜𝑖𝑑𝑎𝑙 𝑠𝑒𝑐𝑡𝑖𝑜𝑛 =
(𝑏+𝑚𝑦)𝑦
𝑏+2𝑚𝑦
𝐷 =
(10+2×10)10
10+2×2×10
= 𝟔𝒎
Figure 19: Cross Section of the recharge basin
4.3.3 Estimating the reservoir capacity.
The pond depth, y = 10m
To provide a larger surface and a more stable embankment of the pond in relation to the large
volume of water it is intended to hold, a slope of 2:1 has been adopted as per the national standard
by Ministry of Water and Environment.
The Volume of the pond is estimated on the basis of the prismoidal formula
V =
(𝐴+4𝐵+𝐶)
6
𝑋 𝐷
Where;
V is the volume of excavation required for the pond in cubic meters
A is the area of the excavation at the ground surface in square meters
B is the area of the excavation at the mid depth point (1/2 D) in square meters

C is the area of excavation at the bottom of the pond in square meters
D is the depth of the pond in meters.
𝐴 = 55 × 50 = 2750𝑚2
4𝐵 = 4((15 + 20) + (10 + 20)) = 4,200𝑚2
𝐶 = 10 × 15 = 150𝑚2
V =
(2,750+4,200+150)
6
𝑋 10
𝑽 = 𝟏𝟏, 𝟖𝟑𝟑. 𝟑𝒎 𝟑
With this capacity, the pond can hold most of the surface run off in the catchment area in relation
to the highest runoff volume is in the month of May which is estimated at 6,074,798.69 𝒎 𝟑
.
4.3.4 Trapezoidal channel Freeboard:
𝐹 = 0.55√𝑐𝑦
𝐹 𝑖𝑠 𝑡ℎ𝑒 𝑓𝑟𝑒𝑒𝑏𝑜𝑎𝑟𝑑 𝑖𝑛 𝑚𝑒𝑡𝑒𝑟𝑠
𝑦 𝑖𝑠 𝑡ℎ𝑒 𝑑𝑒𝑠𝑖𝑔𝑛 𝑑𝑒𝑝𝑡ℎ 𝑖𝑛 𝑚𝑒𝑡𝑒𝑟𝑠
𝑐 𝑖𝑠 𝑡ℎ𝑒 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 𝑡ℎ𝑎𝑡 𝑣𝑎𝑟𝑖𝑒𝑠 𝑎𝑡 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑡𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑑𝑒𝑠𝑖𝑔𝑛
𝑐 =1.5 (for 0.6 m3/sec) to 2.5 (≥ 85 m3/sec)
Therefore, from the design runoff discharge through the conveyance system,𝑸 = 𝟐. 𝟐𝟔𝟖𝟎𝟕𝐦 𝟑
/𝐬 ,
c = 5.67 and design depth, y = 10m
𝐹 = 0.55√5.67 × 10) = 𝟒. 𝟏𝟒𝒎
4.3.5 Average Shear Stress on Channel Boundary (the Tractive Force):
𝜏0 = 𝛾𝑅𝑆
𝜏0 = specific weight of water
𝑆 =hydraulic slope for uniform flow; this is substituted with 𝑆𝑓for non-uniform flow conditions
𝜏0 = 9.81 × 5.86 × 2 = 114.973𝑁/𝑚2

Recharge basin
Figure 20: Complete 2-D recharge system View
4.4 SIMULATION OF THE SYSTEM
4.4.1 Groundwater flow parameters using simulated using MODFLOW
LISTING FILE: output.dat
UNIT 3
OPENING bas.dat
FILE TYPE: BAS UNIT 1
OPENING bcf.dat
FILE TYPE: BCF UNIT 11
OPENING oc.dat
FILE TYPE: OC UNIT 22
OPENING wel.dat
FILE TYPE: WEL UNIT 12
OPENING rch.dat
FILE TYPE: RCH UNIT 18
OPENING pcg2.dat
FILE TYPE: PCG UNIT 23
OPENING budget.dat

FILE TYPE:DATA(BINARY) UNIT 50
OPENING heads.dat
OPENING ddown.dat
OPENING mt3d.flo
1 MODFLOW
U.S. GEOLOGICAL SURVEY MODULAR FINITE-DIFFERENCE GROUND-WATER FLOW
MODEL
THE FREE FORMAT OPTION HAS BEEN SELECTED
3 LAYERS 30 ROWS 30 COLUMNS
1 STRESS PERIOD(S) IN SIMULATION
MODEL TIME UNIT IS SECONDS
BAS5 -- BASIC MODEL PACKAGE, VERSION 5, 1/1/95 INPUT READ FROM UNIT 1
ARRAYS RHS AND BUFF WILL SHARE MEMORY
INITIAL HEAD WILL BE KEPT THROUGHOUT THE SIMULATION
26172 ELEMENTS IN X ARRAY ARE USED BY BAS
26172 ELEMENTS OF X ARRAY USED OUT OF 20000000
BCF5 -- BLOCK-CENTERED FLOW PACKAGE, VERSION 5, 9/1/93 INPUT READ FROM
UNIT 11
STEADY-STATE SIMULATION
CELL-BY-CELL FLOWS WILL BE SAVED ON UNIT 50
HEAD AT CELLS THAT CONVERT TO DRY= -0.10000E+31
WETTING CAPABILITY IS NOT ACTIVE
LAYER LAYER-TYPE CODE INTERBLOCK T
--------------------------------------------
1 1 0 -- HARMONIC
2 0 0 -- HARMONIC
3 0 0 -- HARMONIC
1803 ELEMENTS IN X ARRAY ARE USED BY BCF
WEL5 -- WELL PACKAGE, VERSION 5, 9/1/93 INPUT READ FROM UNIT 12
MAXIMUM OF 3 WELLS
12 ELEMENTS IN X ARRAY ARE USED BY WEL
RCH5 -- RECHARGE PACKAGE, VERSION 5, 6/1/95 INPUT READ FROM UNIT 18
OPTION 1 -- RECHARGE TO TOP LAYER
900 ELEMENTS IN X ARRAY ARE USED BY RCH
0PCG2 -- CONJUGATE GRADIENT SOLUTION PACKAGE, VERSION 2.1, 6/1/95
MAXIMUM OF 50 CALLS OF SOLUTION ROUTINE
MAXIMUM OF 30 INTERNAL ITERATIONS PER CALL TO SOLUTION ROUTINE

MATRIX PRECONDITIONING TYPE: 1
24300 ELEMENTS IN X ARRAY ARE USED BY PCG
53187 ELEMENTS OF X ARRAY USED OUT OF*******
1
BOUNDARY ARRAY FOR LAYER 1
READING ON UNIT 1 WITH FORMAT: (20I3)
AQUIFER HEAD WILL BE SET TO -999.99 AT ALL NO-FLOW NODES (IBOUND=0).
INITIAL HEAD FOR LAYER 1
READING ON UNIT 1 WITH FORMAT: (20G14.0)
OUTPUT CONTROL IS SPECIFIED EVERY TIME STEP
HEAD PRINT FORMAT CODE IS 0 DRAWDOWN PRINT FORMAT CODE IS 0
HEADS WILL BE SAVED ON UNIT 51 DRAWDOWNS WILL BE SAVED ON UNIT 52
COLUMN TO ROW ANISOTROPY
DELR
DELC
HYD. COND. ALONG ROWS FOR LAYER 1

BOTTOM FOR LAYER 1
VERT HYD COND /THICKNESS FOR LAYER 1
TRANSMIS. ALONG ROWS FOR LAYER 2
VERT HYD COND /THICKNESS FOR LAYER 2
TRANSMIS. ALONG ROWS FOR LAYER 3
0
SOLUTION BY THE
CONJUGATE-GRADIENT METHOD
-----------------
--------------------------
0 MAXIMUM NUMBER OF CALLS TO PCG
ROUTINE = 50
MAXIMUM ITERATIONS PER CALL TO
PCG = 30
MATRIX PRECONDITIONING
TYPE = 1
RELAXATION FACTOR (ONLY USED WITH PRECOND. TYPE
1) = 0.10000E+01
PARAMETER OF POLYMOMIAL PRECOND. = 2 (2) OR IS
CALCULATED: 1
HEAD CHANGE CRITERION FOR
CLOSURE = 0.10000E-02
RESIDUAL CHANGE CRITERION FOR
CLOSURE = 0.10000E-02
PCG HEAD AND RESIDUAL CHANGE PRINTOUT
INTERVAL = 1
PRINTING FROM SOLVER IS LIMITED (1) OR SUPPRESSED
(>1) = 0
DAMPING
PARAMETER = 0.10000E+01
1
STRESS PERIOD NO. 1, LENGTH = 0.9467000E+08
----------------------------------------------
NUMBER OF TIME STEPS = 1
MULTIPLIER FOR DELT = 1.000

INITIAL TIME STEP SIZE = 0.9467000E+08
3 WELLS
LAYER ROW COL STRESS RATE WELL NO.
------------------------------------------
1 15 25 -0.10000E-09 1
2 15 25 -0.10000E-09 2
3 15 25 -0.12000E-02 3
RECHARGE
0
3 CALLS TO PCG ROUTINE FOR TIME STEP 1 IN STRESS PERIOD 1
17 TOTAL ITERATIONS
0MAXIMUM HEAD CHANGE FOR EACH ITERATION (1 INDICATES THE FIRST INNER
ITERATION):
0 HEAD CHANGE LAYER, ROW, COL HEAD CHANGE LAYER, ROW, COL HEAD
CHANGE LAYER, ROW, COL HEAD CHANGE LAYER, ROW, COL
-------------------------------------------------------------------------
-----------------------------------------------
1 1.071 (1, 29, 17) 0 0.5121 (3, 11, 21) 0 -0.2808 (3, 30, 20) 0 -
0.1496 (3, 30, 13)
0 -0.6869E-01 (3, 30, 10) 0 -0.3275E-01 (3, 30,7) 0 0.1718E-01 (1, 8,
11) 0 0.1663E-01 (1, 3, 12)
0 0.7977E-02 (1, 2, 16) 0 -0.7636E-02 (3, 30, 10) 0 -0.4459E-02 (3,
28, 15) 0 0.2464E-02 (3, 2, 19)
0 -0.1400E-02 (3, 6, 24) 0 0.7897E-03 (1, 4, 15) 1 0.2283E-02 (1,
10, 19) 0 0.8238E-03 (3, 1, 21)
1 0.4333E-03 (3, 7, 17)
0
0MAXIMUM RESIDUAL FOR EACH ITERATION (1 INDICATES THE FIRST INNER
ITERATION):
0 RESIDUAL LAYER, ROW, COL RESIDUAL LAYER, ROW, COL
RESIDUAL LAYER, ROW, COL RESIDUAL LAYER, ROW, COL
-------------------------------------------------------------------------
-----------------------------------------------
1 -0.1081E-02 (3, 15, 25) 0 -0.8550E-03 (3, 15, 25) 0 -0.5770E-03 (3,
15, 25) 0 -0.3126E-03 (3, 15, 25)
0 -0.1353E-03 (3, 15, 25) 0 0.5551E-04 (3, 30, 5) 0 0.3618E-04 (3,
30, 4) 0 0.2194E-04 (3, 30,3)
0 -0.1912E-04 (3, 30, 29) 0 -0.1359E-04 (3, 30, 29) 0 -0.7166E-05 (3,
30, 29) 0 0.4588E-05 (3, 30, 2)
0 0.2866E-05 (3, 30, 2) 0 0.1474E-05 (3, 30, 2) 1 0.1723E-05 (3,
30, 29) 0 0.1753E-05 (3, 30, 29)
1 0.1435E-05 (3, 30, 29)
0
HEAD/DRAWDOWN PRINTOUT FLAG = 1 TOTAL BUDGET PRINTOUT FLAG = 1
CELL-BY-CELL FLOW TERM FLAG = 1

OUTPUT FLAGS FOR EACH LAYER:
HEAD DRAWDOWN HEAD DRAWDOWN
LAYER PRINTOUT PRINT OUT SAVE SAVE
-----------------------------------------
1 0 0 1 1
2 0 0 1 1
3 0 0 1 1
UBUDSV SAVING " CONSTANT HEAD" ON UNIT 50 AT TIME STEP 1, STRESS
PERIOD 1
UBUDSV SAVING "FLOW RIGHT FACE " ON UNIT 50 AT TIME STEP 1, STRESS
PERIOD 1
UBUDSV SAVING "FLOW FRONT FACE " ON UNIT 50 AT TIME STEP 1, STRESS
PERIOD 1
UBUDSV SAVING "FLOW LOWER FACE " ON UNIT 50 AT TIME STEP 1, STRESS
PERIOD 1
UBUDSV SAVING " WELLS" ON UNIT 50 AT TIME STEP 1, STRESS
PERIOD 1
UBUDSV SAVING " RECHARGE" ON UNIT 50 AT TIME STEP 1, STRESS
PERIOD 1
HEADS AND FLOW TERMS SAVED ON UNIT 32 FOR USE BY MT3D TRANSPORT MODEL
HEAD WILL BE SAVED ON UNIT 51 AT END OF TIME STEP 1, STRESS PERIOD 1
DRAWDOWN WILL BE SAVED ON UNIT 52 AT END OF TIME STEP 1, STRESS PERIOD
1
1
VOLUMETRIC BUDGET FOR ENTIRE MODEL AT END OF TIME STEP 1 IN STRESS
PERIOD 1
------------------------------------------------------------------------
-----
CUMULATIVE VOLUMES L**3 RATES FOR THIS TIME STEP
L**3/T
------------------ ------------------------
IN: IN:
--- ---
CONSTANT HEAD = 209698.0940 CONSTANT HEAD =
2.2150E-03
WELLS = 0.0000 WELLS =
0.0000
RECHARGE = 254472.9380 RECHARGE =
2.6880E-03
TOTAL IN = 464171.0310 TOTAL IN =
4.9030E-03
OUT: OUT:
---- ----
CONSTANT HEAD = 350574.1880 CONSTANT HEAD =
3.7031E-03

WELLS = 113604.0310 WELLS =
1.2000E-03
RECHARGE = 0.0000 RECHARGE =
0.0000
TOTAL OUT = 464178.2190 TOTAL OUT =
4.9031E-03
IN - OUT = -7.1875 IN - OUT = -
7.5437E-08
PERCENT DISCREPANCY = 0.00 PERCENT DISCREPANCY =
0.00
TIME SUMMARY AT END OF TIME STEP 1 IN STRESS PERIOD 1
SECONDS MINUTES HOURS DAYS YEARS
------------------------------------------------------
-----
TIME STEP LENGTH 9.46700E+07 1.57783E+06 26297. 1095.7 2.9999
STRESS PERIOD TIME 9.46700E+07 1.57783E+06 26297. 1095.7 2.9999
TOTAL TIME 9.46700E+07 1.57783E+06 26297. 1095.7 2.9999
1
Table 15: Volumetric budget for the entire model written by MODFLOW

Artificial aquifer recharge system

Artificial aquifer recharge system

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