DSD-INT 2016 Regional groundwater flow systems in the Kenya Rift Valley - Murunga Wakhungu

Regional Groundwater Flow Systems

in the Kenya Rift Valley

MSc. RESEARCH PROJECT

MSc. CANDIDATE: Patrick Murunga Wakhungu

Student Number: s6024882

SUPERVISORS : Dr. Robert Becht

Ir. Gabriel Parodi

Problem Definition

• Regional linkages between the surface and groundwater regimes in the RV is not known. Natural

and anthropogenic factors that influence the system are not properly understood

• Only lake Naivasha has been studied extensively due to its freshness.

• Lack of a tool provides technical basis for decisions on groundwater utilization activities in the

region for sustainable development

• The effect of geothermal cells on groundwater flow patterns is not known

University of Twente, Faculty of Geo-information and Earth Observation _Regional Groundwater Flow Systems in the Rift Valley

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Adapted from Pearson Prentice Hall Inc. (2005)

Study Area 3


No legend. Figures have an illustrative meaning only

Study Objectives

Main Objective The principle objective is to build and use a groundwater model to investigate possible groundwater flow systems in the Kenyan Rift Valley.

Specific Objectives are:

1. Develop and calibrate a 3D steady state groundwater model for the RV in Kenya

2. To describe the North and South extent of groundwater flow with respect to Lake Naivasha

3. To estimate the long term water balance of the Kenya Rift Valley lakes

4. To analyze and use existing isotope data in constraining the model to observed natural flow patterns

Research Questions are:

1. Can the observed hydrogeology of the Rift Valley be transformed to a numerical model?

2. What are the natural flow patterns of groundwater in RV that depict observed water sources & sinks?

3. What are the long term water balances and how do the fluxes in the aquifer/lake system vary in space?

4. Will isotopic hydrochemistry provide evidence of the source of water feeding RV Lakes?

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Previous Work 5


Topics 2016

Fred A. Muno (2002) • F.A Muno (2002)Used spreadsheets to model groundwater • Muno modelled four Lakes (Smaller area) • 2D Modelling • Used data sets up to 1999

IWRAP/Deltares • iMOD Numerical Modelling for L. Naivasha • Use of current hydrological data (Beyond 1999) • 3D modelling and visualization as opposed to Muno’s 2D • Multi layer aquifers

Notable Authors • Thompson and Dodson (1960) • B.H Baker (1971) • Lydia Olaka (2010) • Robert Becht(2006) • Zachary N. Kuria (2011) • Fred A. Muno (2002)

Notable Publications • Geology of the Naivasha Area • Structure and Evolution of the

Kenya Rift Valley • Sensitivity of E.A Lakes to

Climate Fluctuations • Seismotectonics of Active Faults:

The Magadi Fault System • Water Balance of the Southern

Kenya RV Lakes

Groundwater Flow 6

University of Twente, Faculty of Geo-information and Earth Observation _Water Cycle and Climate Research Topics 2016

Why Model? Modelling is a useful thinking tool which can be used to understand groundwater systems, predict

the systems response to a stress and help to design field studies that can be used in groundwater

resource development

Methodology 7

Required Data Method

Tools

Purpose

Topographical Maps Satellite Maps Precipitation Data Evaporation Data Digital Elevation Models Lake Bathymetry Data Geomorphology

Hydrological Model/Conceptual Model

ILWIS • Partly answers Research Question 3 • Preparation and visualization of sub-catchment files for

precipitation, evaporation, river networks, lake surface area

Pros: Ease of use of software, Use of different Datasets Cons: Need for many versions of ILWIS to do some tasks

Well Hydraulic Heads Stream Flow Data Lake level measurements Aquifer parameter data 3D Visualization

Numerical Model

iMOD • Answers Research Question 1 • Perform a numerical model that estimates total inflow

and outflows from every sub-basin as well as estimating Storage

Pros: Interactive User interphase, Use of variable resolution Datasets Regular and irregular grid sizes Cons: The lake package is yet to be published officially

Water Inflow Data Water Outflow Data Water Abstraction Data Aquifer Thickness Estimates Loss Estimates

Water Balance

Spreadsheets

• Answers Research Question 3 and 2 • Estimates fluxes and changes in storage • To caution against groundwater overdraft/Mining Pros: Possible to estimate volumes of water losses Cons: Does not resolve unaccounted for water appropriately

Conceptual Model

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Adapted from R. Becht (2006) Extracted from the National WMP

Boundary Conditions Hydraulic Conditions Faults

Numerical Model

Software Selection iMOD (Interactive editing the geometry of the subsurface)

Spatial extends of the input parameters do not have to be the same

Easy to improve a model whenever new data becomes available

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State Variables Lake levels

Hydraulic Heads

River Discharge

Boundary Conditions No flow boundary

Constant Head boundary

Driving Forces Precipitation/Recharge

Evapotranspiration

Abstraction

Grid Design Rows – 560

Columns – 190

Layers - 6

Model Area Area – 35206 Km2

Length – 500 Km

Width – 50- 100Km

Grid Design Coarse Grids - 1000m

Fine Grids - 500m

Model Calibration

R2 = 0.8666

1774

1775

1776

1777

1778

1779

1775,00 1776,00 1777,00 1778,00 1779,00Ca

lc. L

eve

l (m

a s

l)

Observed Level (m a s l)

CORRELATION BETWEEN CALCULATED AND OBSERVED LEVELS(JAN 1958 TO AUG

1978)

Why iMOD? 10


Topics 2016

Key features of iMOD: Spatial extends of the input parameters do not have to be the

same

Easy to improve a model whenever new data becomes available

One expandable data set covering all possible future areas of interest

Efficient numerical modelling

Fast interactive 2D- and 3D-analysis and visualization

Interactive editing the geometry of the subsurface

Consistency between regional and sub-domain models

Leaving the era of building series of individual models behind

Flow model nesting, toggling between grid resolutions and moving to new areas of interest

Expected Results 11

University of Twente, Faculty of Geo-information and Earth Observation _Water Cycle and Climate Research Topics 2016

Expected Results Time invariant groundwater regional model

Long term lake water balances

Spatial variability in groundwater fluxes

Groundwater flow map

END OF PRESENTATION ☺

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Thank You