Hydrogeological Verification of Magnetic Resonance Soundings Maun Area, Botswana

Hydrogeological verification of Magnetic Resonance Soundings Maun Area, Botswana.

Namu Mangisi February 2004

Hydrogeological Verification of Magnetic Resonance Soundings œ Maun Area, Botswana

Namu Mangisi

Thesis submitted to the International Institute for Geo-information Science and Earth Observation in partial fulfilment of the requirements for the degree of Master of Science in Water Resources and En- vironmental Management specialising in Groundwater Resources Evaluation and Management.

Thesis Assessment Board

Prof. Dr. A. M. J. Meijerink (Chairman, ITC WRS Department) Drs. J. W. Foppen (IHE) Dr. M. W. Lubczynski (Supervisor, ITC) Dr. J. Roy (ITC)

INTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATION ENSCHEDE, THE NETHERLANDS

Disclaimer

This document describes work undertaken as part of a programme of study at the International Institute for Geo-information Science and Earth Observation. All views and opinions expressed therein remain the sole responsibility of the author, and do not necessarily represent those of the institute. Data used in the thesis will not be used for publishing without written permission of the thesis supervisor

For the memory of my late sister, Lebani Ndanda, grandmother Baka Nxoli (Mxangi) and my late brother Lifalo (mu ndi pe masimba)

And

To my mother, Nchidzi, my sister Rebecca, my brother Tsipani and niece Tonto Nomphumelelo ABSTRACT

The study aims at the hydrogeological verification of Magnetic Resonance Soundings (MRS) using data from the Maun area that is located in the far distal end of the Okavango Delta of Botswana. The Magnetic Resonance Sounding (MRS) technique known also as SNMR (surface Nuclear Mag- netic Resonance) or PMR (Proton Magnetic Resonance) for groundwater exploration is relatively a new application of NMR (Nuclear Magnetic Resonance). It is the only non-invasive geophysical technique with an inherent selectivity to hydrogen and therefore to groundwater (Roy and Lubczynski, 2002). The MRS sounding (i.e. NMR response as a function of excitation moment Q) provides the following:

1. From the signal amplitude, the quantity of free water 9MRS as a function of depth. This pro-

vides a good estimate of effective porosity :e of the saturated water-bearing layer below the groundwater table, the groundwater table (GWT), storage parameters, thickness of the saturated water bearing layers (aquifer geometry) and the quantity of free water in the vadoze and its depth.

2. Characterization of the host media, pore-size through the NMR signal decay time (Td) usually

measured as T2* as a function of depth. This parameter supply reliable estimates of flow pa-

rameters like permeability (ki), hydraulic conductivity (K) and transmissivity (T) wherever hydrogeologcal conditions are known and /or appropriate calibration have been made (Roy and Lubczynski, 2000). A comprehensive assessment/evaluation of both MRS soundings and hydrogeological was made (i.e. checking whether or not MRS supplied reliable information) complimentary with the ground truth data (hydrogeological) that is currently available or that was collected during the fieldwork. MRS inversion results gave free water content results in the range 1 œ 40% and decay time in the range 57 œ 400ms. The water table depths obtained from the borehole data in the range 2 œ 20 m.b.g.l agree with the interpreted depths of MRS soundings of 0 œ14 m.b.g.l. MRS transmissivities were in the range 0.072 - 42.10 m2/d for a = 4 and b = 2 and in the range 753 œ 24793 m2/d for a = 1 and b = 2. The parameters a and b are used in equations 5.2 and 5.3 respectively that were used to determine MRS transmissivities. The pumping test transmissivities were in the range 0.97 œ 45.7 m2/d for pumping boreholes and 4 œ 53 m2/d for recovery test. The observation boreholes gave transmissivity values in the range 2.55 œ 636 m2/d. The specific yield determined from pumping test was 0.12 and the yields ranged from 2 œ35 m3/hr. The values show a large difference between MRS transmissivities and pumping test transmissivities hence no correlation was found. The hydraulic conductivity determined from laboratory tests was 0.81 m/d for fine sand unit of the aquifer unit of BH 10117. MRS gave conductivity values in the range 0.0025 œ 3.40 m/d. In this report, MRS as a contributor to groundwater investigation/quantification has been able to provide reliable/effective hydrogeological information of the Maun area; hence the report presents results and conclusions drawn from the assessment/evaluation of the MRS soundings. However, the conclusion does hold true for the transimissivities that showed large discrepancies. Therefore care should be made in drawing such a conclusion, as the results are not yet fully assessed since the available control boreholes were screened only in the deepest intersected layers in a series of water bearing layers separated by clay-rich aquitard / or that the screens were wrongly placed. ACKNOWLEDGEMENTS

First I would like to thank and am very grateful to the Netherlands Government for granting me this scholarship under the Netherlands Fellowships Programme that made it possible for me to walk this far distance. Also special thanks to the Ministry of Minerals, Energy and Water Affairs, especially my Directors, Mr. G. Gabaake and Mr. O. Katai and J. Ntshambiwa (Principal Training Officer) for giv- ing me this lengthy period in order to pursue my studies. Special thanks goes to my Supervisors, Dr. M. Lubczynski and Dr. J. Roy for guiding me through this difficult period with their constructive comments and criticisms they provided during the preparation of this report. To the Programme Director, Ir. Arno Van Lieshout, I say thank you for the brotherly love and care, the Head of WRES, Prof. A. Meijerink and other staff members who were readily available when I needed help. Drs. J. B. de Smeth, a special thank you. I also extend my profound gratitude to my fellow classmates, especially Rafael Cortez, Berihun and Marcelo for always making me belief in friendship and myself. And thanks to the ITC nurse and my Doctor, Dr. Sophie Tonmanian and nurse Maya Ranselaar for making me feel at home anytime I needed help. The entire staff of ITC, God be with you always. To Hope Okuga, a special friend. Last but not least to Boitshwarelo Moeletsi and daughter Kegomoditswe, God bless you. BA KA MENGWE, who gave me the wisdom to leave harmoniously with others.

TABLE OF CONTENTS 1. Introduction...... 1 1.1. Research Problem...... 2 1.2. Objectives...... 3 1.3. Research Questions ...... 3 1.4. Hypothesis...... 4 1.5. Research Methodology...... 4 1.5.1. Inception Study...... 4 1.5.2. Fieldwork ...... 4 1.5.3. Post-Fieldwork ...... 5 1.6. Previous Work...... 7 1.7. Data Available...... 7 2. Project Setting ...... 9 2.1. Location...... 9 2.2. Population and Socio-economics ...... 9 2.3. Physiography/Geomorpholgy...... 12 2.4. Climate ...... 13 2.5. Hydrology...... 14 3. Geology and Hydrogeology ...... 18 3.1. Geology and Stratigraphy...... 18 3.1.1. Damara Supergroup...... 19 3.1.2. The Karoo Supergroup...... 19 3.1.3. The Kalahari Beds...... 20 3.2. Regional Structure...... 20 3.3. Hydrogeology...... 20 3.3.1. Spatial Hydrostratigraphy ...... 20 3.3.2. Spatial Aquifer Parameterisation ...... 22 3.4. Hydrochemistry...... 22 4. Magnetic Resonance Technique (MRS) ...... 24 4.1. Historical overview ...... 24 4.2. The MRS Principle...... 25 4.3. MRS Data Acquisition and Inversion ...... 27 4.3.1. Data Acquisition...... 27 4.3.2. Capabilities and Limitations ...... 27 4.3.3. Data inversion ...... 28

4.3.4. Subsurface Free Water Content (MRS)...... 30

4.3.5. Decay Time Constant Td ...... 30 4.4. Hydrogeological Interpretation with MRS...... 31 4.4.1. Aquifer Geometry...... 31 4.4.2. Groundwater Table...... 31 4.4.3. Storage Parameters...... 32 4.4.4. Flow Parameters (Hydraulic Conductivity, Permeability and Transmissivity...... 32 4.4.5. Unsaturated Zone Parameter ...... 33 4.4.6. Well Siting...... 33 4.4.7. Yield Estimator...... 34 5. Magnetic Resonance Soundings (Maun) œ Data Analysis and Interpretion...... 35 5.1. Data Acquisition...... 35 5.2. Data Inversion ...... 36

5.2.1. Estimates of Permeability ki, Hydraulic Conductivity K and Transmissivity T ...... 37 5.3. Constraints and Limitations of MRS Data Acquisition ...... 38 5.3.1. Effect of Electrical Conductivity of the Subsurface Material...... 38 5.3.2. Effect of Magnetic Inhomogenity due to Ferrous Minerals...... 39 5.3.3. Signal to Noise Ratio, (S/N)...... 39 6. Other Geophysical Methods...... 40 6.1. TDEM...... 40 6.2. Borehole Geophysical Logging...... 40 7. Hydrogeological Methods...... 43 7.1. Laboratory Analysis ...... 43 7.1.1. Sieve Analysis ...... 43 7.1.2. Hydraulic Conductivity, K ...... 44 7.1.3. Porosity...... 46 7.1.4. Specific Retention / Field Capacity...... 47 7.2. Pumping Test...... 47 7.2.1. The Principle of Pump Test...... 47 7.2.1.1. Aquifer Hydraulic Parameters...... 47 7.2.1.2. Neuman Method (Unconfined) ...... 48 7.2.1.3. Hantush Method (leaky, without aquitard storage)...... 49 7.2.1.4. Theis and Jacob Recovery Test (Confined) ...... 49 7.2.2. Constant Rate Test and Recovery Test Results...... 50 8. Hydrogeological Verification of MRS Soundings ...... 52 8.1. Site Specific Hydrogeological Verification of MRS Soundings ...... 53 8.1.1. BH 8262 ...... 53 8.1.2. BH 8114 ...... 54 8.1.3. BH 8348 ...... 55 8.1.4. BH 8351 ...... 56 8.1.5. BH 8815 ...... 57 8.1.6. BH 9590 ...... 58 8.1.7. BH 9599 ...... 59 8.1.8. BH 9600 ...... 60 8.1.9. BH 9604 ...... 61 8.1.10. BH 9608 ...... 62 8.1.11. BH 9683 ...... 63 8.1.12. BH 10117 ...... 64 8.1.13. BH 10118 ...... 65 8.2. Data Integrations of Hydrogeological and MRS Data ...... 66 8.2.1. Transmissivities...... 66 8.2.2. Free Water content and Yield ...... 67 8.2.3. Borehole yield and Decay Time...... 67 9. Discussion...... 68 10. Conclusions and Recommendations ...... 69 10.1. Conclusions ...... 69 10.2. Recommendations ...... 69 11. References ...... 71

List of Figures Figure 1-1: Research Time-Activity Chart...... 5 Figure 1-2: Flow chart showing summary research programme...... 6 Figure 2-1:Location of the Project Area œ Upper Thamalakane Exploration Area...... 10 Figure 2-2:MRS Borehole Sites Location Map in the Upper Thamalakane Exploration Area ...... 11 Figure 2-3:The Okavango Delta in Botswana, with selected digitised rivers projected on a Landsat TM mosaic image (from McCarthy et al., 2002)...... 12 Figure 2-4:Maun Annual Rainfall Chart (mm) ...... 13 Figure 2-5:Mean Monthly Rainfalls for Maun (1925-2002)...... 14 Figure 2-6:Drainage Network of the Study Area ...... 15 Figure 2-7:Mohembo Total Annual Flows at Station (7112)...... 16 Figure 2-8: Ten year combined flow graph for Mohembo for the period 1991 to 2001...... 16 Figure 2-9:Mean Annual Flows at Boro Junction...... 17 Figure 3-1:Subsurface Geology (from Masedi, 2002) ...... 18 Figure 3-2 :SW œ NE Hydrogeological Cross-section from Borehole Information - MRS Area ...... 21 Figure 3-3:TDS vs. EC Plot ...... 23 Figure 3-4:Durov Plot ...... 23 Figure 4-1: NumisPlus Magnetic Resonance System (Iris Intruments 2002) ...... 25 Figure 4-2: Basics of proton magnetic resonance sounding (Iris instruments 1998)...... 26 Figure 4-3: Example of MRS Inversion results for BH9599...... 29 Figure 4-4:The Groundwater Storage Concept, after Lubczynski and Roy (2003)...... 33 Figure 6-1:Natural gamma plot with Interpreted log and 2 observed borehole logs ...... 41 Figure 7-1 :Determining Hydraulic Conductivity with a Permeameter...... 45 Figure 7-2: Plot of volume (cm3) versus time ...... 46 Figure 8-1: Comparison of MRS Inversion results with observed hydrogeological information for borehole BH 8262...... 53 Figure 8-2: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH 8114 ...... 54 Figure 8-3: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH 8348 ...... 55 Figure 8-4: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH 8351 ...... 56 Figure 8-5: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH 8815 ...... 57 Figure 8-6: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH 9590 ...... 58 Figure 8-7: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH 9599 ...... 59 Figure 8-8: Comparison of MRS Inversion results with borehole data BH9600...... 60 Figure 8-9: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH9604 ...... 61 Figure 8-10: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH 9608 ...... 62 Figure 8-11: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH 9683 ...... 63 Figure 8-12: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH 10117 ...... 64 Figure 8-13: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH10118 ...... 65 Figure 8-14: MRS Transmissimivities versus Pumping Test Transmissivities ...... 66 Figure 8-15: Borehole yield versus free water content ...... 67 Figure 8-16: Yield versus decay time ...... 67

List of Tables Table 1-1:Available Data, Information and Source ...... 8 Table 3-1:Stratigraphy of Study Area (after WRC, 1997 originally from Carney et al, 1994) ...... 19 Table 3-2:Summary Borehole Data œ MRS Area ...... 21 Table 3-3:Chemical Analysis of Results in the MRS area...... 22 Table 3-4:Groundwater Classification Based on TDS...... 23 Table 4-1:Petrophysical Information from NMR Decay Rate (After Schirov et al, 1991 and Allen et al, 1997 in Roy 2001)...... 31 Table 5-1:MRS Production Figures (Source Roy, 2001)...... 35 Table 5-2: TDEM Production Figures (from Roy, 2001 as supplied by WRC) ...... 36 Table 5-3:Summaries of MRS Inversion Results...... 37 Table 5-4:MRS Determined Transmissivities...... 38 Table 5-5:Magnetic Susceptibility Measurements...... 39 Table 6-1:Conductivity of Various Aqueous Solutions at 250C ...... 40 Table 7-1:Sieve Analysis Results...... 44 Table 7-2:Constant head method measurements of volume versus time ...... 45 Table 7-3: SUMMARY CONSTANT RATE TEST RESULTS FOR MRS TESTED SITES ...... 51 Table 8-1: MRS Determined Transmissivities versus Pumping test Transmissivities ...... 66

Appendices Appendix 1a Rainfall records œ Maun Area Appendix 1b River Discharges and Flows œ Mohembo 7112 Appendix 2 Summary of borehole yields Appendix 3a MRS graphic plots Appendix 3b Calculations from MRS Transmissivities Appendix 4 Natural gamma plots Appendix 5 Drilling Results and Sieve analysis plots Appendix 6 Pumping Test Data

List of Acronyms

B0 Earth magnetic field

BM Excitation Field

Cp Empirical pre-factors. CRT Constant rate test D Aquifer thickness ∂h/∂L Hydraulic gradient

E0 Signal amplitude EOH End of hole 1H+ Hydrogen Nuclei

9MRS Free water content ƒ Larmor frequency ki Permeability L/T Length/time

M0 Magnetic moment Mbgl Meters below ground level MGDP Maun Groundwater Development Project MRS Magnetic Resonance Sounding NMR Nucleus Magnetic Resonance

:e Effective porosity Q Excitation moment Q Discharge T Transmissivity

Td Signal decay time TDEM Time Domain Electromagnetic TDS Total dissolved solids TEM Transient Electromagnetic

T1 Longitudinal relaxation time

T2 Transverse relaxation time

T2* Free induction decay time

TMRS MRS transmissivity WRC Water Resources Consultants WT Water Table Rec Recovery S Storativity

Ss Elastic storage

Sy Specific yield SMEC Snowy Mountain Engineering Corporation SOIWDP Southern Okavango Integrated Water Development Project SWL Static water level ¢ Gyromagnetic ratio Q Time interval

0 Lamor angular frequency HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS - MAUN AREA, BOTSWANA

1. Introduction

The study aimed at the hydrogeological verification of a series of Magnetic Resonance Soundings (MRS) in the Maun area using borehole data (lithologic logs, geophysical logs, grain size analysis i.e. laboratory test or sieve tests, hydraulic parameters obtained from the pumping test and the water quality analysis results). Botswana, a semi arid country relies more on groundwater than surface water. In total, about 70% of water supply is groundwater. Whatever potable resource found it needs to be exploited. Masedi et al., (2000) have identified several factors that hamper the use of groundwater for water supply as low replenishment rates, water quality and location of major resources in relation to consumers and over development. The Botswana government has however put in place a national policy to delineate all known aquifers and assess their groundwater potential in terms of quality, quantity and replenishment (BNMWP, 1991). The Maun groundwater Development project (MGDP Phase1) was initiated in 1997 following the Southern Okavango Integrated Water Development Project (SOIWDP) to alleviate the water shortage. The Department of Water Affairs contracted the project to Water Resources Consultants, Botswana (WRC). MGDP Phase 2 was started in 2001 as follow up project to MGLP Phase 1, which tested the MRS technique within the framework of that project. Roy (2001), states that the test was triggered by limitations encountered with classical groundwater investigation techniques in the hydrogeological environment of the distal Okavango Delta and by an interest in the MRS technique as a contributor to the tasks of groundwater resources evaluation. Fresh water aquifers of the Kalahari sediments in the Maun area occur adjacent to rivers in the unconsolidated sands (shallow unconfined aquifers) and interlayered between clays (semi-confined i.e. leaky confining layers of clays, sandy silts and clays). The aquifer is bounded below and on the edges by saline groundwater and is the most important source of fresh water in the area. Information therefore on aquifer geometry and lithology (top and bottom of aquifer including thickness and extent of hydrostratigraphic units that define the aquifer dimensions was acquired from different sources which included the following geophysical methods, the Transient Electro-Magnetic (TEM), Induced Polari- zation (IP), Resistivity and Nuclear Magnetic Resonance (MRS). Water Resources Consultants adopted these methods with special emphasis on improving borehole yields; define the lateral and depth extent of fresh water aquifer, and to define relative variations in water quality and the presence of clayey units within the sand aquifers. TEM Soundings in conjunction with airborne EM conductance/resistance data were appropriate to define the lateral and depth extent of fresh water aquifers. However, evaluation of the hydrogeological data by Water Resources Consultants, (1997) suggested that boreholes tapping clean sand or coarser sand provided higher yields in comparison to those that have clay within sand in the total assemblage. The two assemblages exhibited similar formation resistivity whilst the yields differed. The TEM method did not differentiate the two lithologies, which often were attributed to the combined effect of porosity, and formation water resistivity that could result in exhibiting similar formation resistivity.

1 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS - MAUN AREA, BOTSWANA

To resolve this problem, IP/Resistivity method were also tested but the results obtained were not satisfactory possibly due to low resistivity environment and insignificant resistivity contrast. The Magnetic Resonance Sounding technique was then implemented in 2001 in collaboration with ITC, The Netherlands. The technique is non invasive (does not require the use of boreholes and pumping tests). In the Maun case the MRS soundings were made at 13 sites near and along the Thamalakane River, seven of which were carried out near existing boreholes and a further six on recommended MGDP 2 drilling sites. The sites are now drilled. An overview of the method is provided in Chapter 4. The MRS sounding inversion results and interpretations for each borehole are provided in Chapter 5 and Chapter 6 presents other geophysical methods. Hydrogeoleogical methods are discussed in Chapter 7 and Chapter 8 presents a comprehensive verification of MRS soundings using hydrogeological borehole data. The study further looks at the possibility of the applicability of the method to other parts of the country with similar environments e.g. along the Molopo River valley in the south of the country. It is also very important to mention that knowledge on data capturing using MRS technique was acquired by desk study. 12 MRS soundings were acquired near Enschede as part of this project, allow- ing hands on experience with field MRS data acquisition. The report therefore presents results and conclusions drawn from the assessment/evaluation of the study.

1.1. Research Problem The Maun area of the Upper Thamalakane (MRS locations, Figure 2.2) lies within a saline water environment. The area is located at the far edge (far distal end) of the Okavango Delta. Several river channels exist within the area and previous studies e.g. MGDP Phase 1 have shown the source of recharge to be from the river channels that are fed by the Okavango River. AEM has further located pa- leo channels active in the fresh water recharge. Two main aquifers exist, the shallow Kalahari Bed and the Bedrock aquifers. The fresh water shallow unconfined and semi-confined Kalahari Bed aquifer comprised of fine to medium grained sand and leaky confining layers of clays, sandy silts and clays are the most important source of fresh water in the study area. Given that the fresh water zones have clearly been identified (follow river channels and areas of seasonal floods) the challenge now was to locate the fresh extractable water. Several techniques that provide information on resistivity of an aquifer have been applied extensively. Roy (2001) points out that the resistivity of an aquifer is a function of many of its characteristics like geometry of the pores, porosity, water quality, water saturation and mineralogy and that in the Maun case the particular minerals susceptible to alter the aquifers resistivity are the clay minerals. Application of the TDEM did not manage to differentiate two lithologies (clean sand or coarser sand and clay within sand), which often are attributed to the combined effect of porosity and formation resistivity that can result in exhibiting similar resistivity. IP/Resistivity method did not give satisfactory results as well, possibly due to low resistivity environment and insignificant resistivity contrast. The magnetic resonance technique provides non- invasively information on groundwater from surface. It allows for identification of subsurface free water content as the signal is specific to water, hence quantification of effective porosity, storage parameters and characterization of host media in terms of flow properties through its estimate of pore size, (Lubczynski and Roy, 2003) and (Roy and Lubczynski, 2003). Joint use of MRS with TDEM yield a more complete estimate of the hydrogeological situation of the area, i.e. MRS supplying related information to positive identification of water, storage and flow properties while TDEM supply-

2 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS - MAUN AREA, BOTSWANA

ing information related to salinity. The method is efficient and costs are reduced because information normally derived from boreholes with MRS is derived directly without drilling. Other tests done in Botswana over deeper aquifers are reported to have been more demanding as compared to the MRS test in the Maun. The MRS test around Maun corresponds to a more favourable case since the water table is much shallower, the near surface water is fresh and the aquifer has in some locations a much higher effective porosity than for the unfractured Ntane sandstone e.g. the observed water content for the other porous layers of the tested sites is in the range 5-40% (Roy, 2001). Previous attempts to verify the reliability and effectiveness of the MRS test results in the study area were not adequate or effective enough because additional information was needed such as more hydraulic test, systematic geophysical logs, more borehole information drilled on MRS sites, water quality information. Most of the information was more qualitative than quantitative. Information acquired from MGDP Phase 2 has improved standard hydrogeological data availability that was needed to carry out the exercise. However a joint use of MRS with TDEM yield a more complete estimation of the hydro geological situation than in the case of them taken separately (Roy, 2001).

1.2. Objectives The main objective of the study was to verify and/or evaluate the effectiveness and reliability of a series of Magnetic Resonance Soundings (MRS) as a contributor to groundwater investigation/quantification in the Maun area with available hydrogeological data. The aim being to check whether information provided by MRS match (i.e. check whether or not MRS is supplying reliable information) with the ground truth data (hydrogeological) that is currently available or that was collected during the fieldwork. The specific objectives were: ñ To make a comprehensive evaluation of available hydrogeological data such as well boring data (lithological logs), grain size analysis, hydraulic test results, geophysical logs and hydrochemical data and the water level dynamics in the shallow unconfined aquifers due to flood- waters. ñ To acquire knowledge on the MRS technique, by desk study (hands-on experience from a separate project. ñ To assess if the MRS soundings provided reliable information on aquifer boundaries (aquifer geometry), groundwater table, effective porosity, estimates of storage and flow parameters

(K, ki, & T) in the context of regional groundwater resource estimation of the Maun area. ñ To evaluate the overall usefulness, reliability and applicability of the MRS soundings in the Maun, area and eventually the applicability of the technique in the other areas of the country with similar geology like along the Molopo River in the south of the country and the Limpopo River in the east.

1.3. Research Questions ñ Does MRS inversion of the Maun data providing free water content (%) with depth over the investigated volume of the aquifer supply accurate information on effective porosity and storage parameters? ñ Does the decay time provide reliable information of pore size of the water bearing layers,

which is used to estimate hydraulic conductivity K, transmissivity T and permeability ki of a sequence of assemblages in the area?

3 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS - MAUN AREA, BOTSWANA

ñ Can the MRS provide accurate data on aquifer boundaries (aquifer geometry i.e. aquifer/aquitard vertical boundaries), groundwater table/unsaturated zone depth in the context of regional groundwater resource estimation within the Maun area? ñ Are the MRS sounding results correlated with borehole data and pumping test data suffi- ciently to assess the regional groundwater resources of the study area from the defined corre- lations in a generic way? ñ What are the constraints and limitations of the method in the Maun area?

1.4. Hypothesis The non-invasive MRS is a suitable and reliable technique in the evaluation of groundwater resource in the shallow unconfined and semi-confined aquifers of the Maun area because of its ability to provide reliable hydrogeological information like aquifer geometry, groundwater table depths, storage parameters and estimates of flow parameters (hydraulic conductivity K, permeability ki and transmissivity T). Similar environments are known to exist elsewhere in the country (like along the Molopo River valley in the south and the Limpopo valley in the east) hence the method can be of use also there benefiting in terms of cost, speed and ability to provide the readily confirmed hydrogeological data.

1.5. Research Methodology In order to achieve the study objectives, a three-stage programme was adopted: the inception stage (pre-fieldwork), fieldwork and post field work stage (data analysis and final reporting). The study was projected and completed within a period of six (6) months. Inception study was allocated three weeks starting from 21st August to 10th September 2003. Fieldwork took approximately 4 weeks and was completed in mid October 2003. Data analysis and final reporting were completed in February 2004 being spread over a period of 4 months. (Figure 1-1) shows the research activity chart. A summary of methodology is presented in (Figure 1-2).

1.5.1. Inception Study The inception stage included office desk study to collect and collate all existing information relevant to the study (review of all available data), to create a database and digitize the base maps. Appropriate materials /tools for field work were identified and included Global Positioning instruments, electric dippers, conductivity meters, previous hydro geological and geological reports, maps etc. Aerial photographs and satellite images for the study area were also acquired. The air photos provided a stereo- scopic coverage of the study area.

1.5.2. Fieldwork The second stage/phase of the study focused on data collection that entailed the compilation of all relevant hydrogeological, MRS soundings and hydrological data pertinent to the study area. The data was collected from the following institutions: Government Departments of Water Affairs, Meteorological Services, Geological Survey, the University of Botswana Harry Oppenheimier Okavango Research Center and Water Resources Consultants, Botswana (WRC) involved in MGDP Phase 2 who provided most of the data. The hydrogeological data that was collected and/or compiled: included borehole data (lithology, depth, water levels (swl), estimated borehole yields, sieve analysis, geophysical logs), TDEM data, hydrochemical data and pumping test data, meteorological data which

4 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS - MAUN AREA, BOTSWANA

included rainfall, air temperature, relative humidity, wind speed, sunshine hours, pan evaporation and river gauging data. A field reconnaissance trip to the research area was also made and this provided an overall insight of the study area. Field ground truthing for all parameters provisionally identified during the inception, e.g. general hydrogeology of the area, were examined and verified. Information derived from the interpretation of air photos and satellite images were verified. Global positioning was done in some selected sites like some boreholes. Water levels where accessible were checked using electric dippers. The MRS sounding data was available at ITC (Dr. J. Roy). No further MRS data acquisition was done during the research period. The data capturing using MRS technique and MRS data inversion was done in the Netherlands under the supervision of Dr. J. Roy. There were however two MRS sites, which were not drilled during the fieldwork period. The drilling of the two sites was arranged at the time of fieldwork and all the hydrogeological data pertaining to the two boreholes were received in December 2003. Soil samples were collected for permeability and sieve analysis.

1.5.3. Post-Fieldwork Data analysis involved the interpretation of all relevant hydrogeological data, collected to verify the MRS soundings. An overview of the MSR principle and data processing is given in Chapter 4. MRS inversion results are given in Chapter 5. The ground truthing hydrogeological verifications of the MRS soundings are presented in Chapter 8. Finally all the research findings are documented in this report therein.

Activity August 2003 Sept. 2003 Oct. 2003 Nov.2003 Dec. 2003 Jan.2004 Feb. 2004 Inception Fieldwork Existing data Pumping test Post fieldwork Data processing Mid Presentation Thesis

Figure 1-1: Research Time-Activity Chart

5 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS - MAUN AREA, BOTSWANA

Satellite images and Archive Data aerial photographs Review of available data Digitizing base maps

Interpretation Geology, structural Data acquisition map (Collection)

Geophysics Hydrogeology MRS data (ITC), TDEM Borehole logs, grain size, (WRC), borehole geo- test pumping, chemistry, physical data water levels

Data interpretation Data processing and interpretation: Test pumping analysis, making lithologic MRS data inversion, geophysical logs graphs, extracting geometry data and chemical data,

Correlate and check results

Aquifer hydraulic parameters (Transmissivity, hydraulic conductivity, storage, specific yield) Geometry (Thickness, areal extent, depth, lithology) Salinity, yield estimates

Summary and conclusions

Figure 1-2: Flow chart showing summary research programme

6 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS - MAUN AREA, BOTSWANA

1.6. Previous W ork The Maun water supply works date to as far back as 1960 with the installation and commissioning of borehole BH2134 (WRC, 2001). It is noted that the area experienced significant population growth over the past few decades. A hydrological assessment shows that the area has experienced some major changes in water availability, the 1970‘s being generally a decade of above average outflow from the delta, the 1980‘s a decrease in outflow and the 1990‘s having some of the lowest outflows from the delta. This situation indicates the inflow to area has been altered over time, see chapter 2. In 1984 because of water shortage the Department of Water Affairs, Botswana commissioned Bureau De Recherches Geologiques et Minieres (BRGM) to explore new sources of supply to Maun. Thirty- two boreholes were installed in the Thamalakane river and the lower part of the Shashe river valley. The six production boreholes installed in the Shashe River served as a major source of supply for Maun in the 1980‘s to 1990‘s. DWA further installed some more boreholes in the Shashe valley between 1987 and 1988. In 1993 Snowy Mountains Engineering Corporation (SMEC) carried out the Southern Okavango Inte- grated Water Development (SOIWDP) study for the government. The SOIWDP project proposed a large-scale surface water scheme for surface water utilization. The project was subsequently reviewed by the International Union for Conservation of Nature (IUCN) for the government. The ICUN recommended the best solution to the long term Maun supply was the conjunctive use of surface water and groundwater. Following this project the MGDP Phase 1 was implemented and completed during 1995 to 1997. In 2001 MGDP Phase 2 was implemented as a follow up project to MGDP Phase 1 Project. As an additional requirement for the project a test of an MRS method was implemented to evaluate its appro- priateness as an investigation tool complementary to the array of the methods used. The tests were conducted with the aim of verifying the capacity of MRS method to provide reliable estimates on free water content (storage property) and pore size (flow property). An integrated use with TDEM provided a more reliable and complete estimate of the hydrogeological regime. A qualitative assessment of the MRS test was done (Roy 2001), but did not allow for verification of the soundings since more information such as pumping test results, grain size analysis and geophysical logging of some boreholes were still to be made. This is done in this thesis

1.7. Data Available Data available for the research and source is presented in Table 1-1 below.

7 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS - MAUN AREA, BOTSWANA

Table 1-1:Available Data, Information and Source

Data Source Details MRS data ITC (Dr. Roy) MRS data inversion completed for 13 sites Lithologic logs, summary drilling borehole construction details, WRS, est. Drilling WRC yields, TDS, Grain size analysis WRC Grain size analysis results All MRS tested boreholes, Pumping test data WRC Pumping and observation Geophysical Log- MRS boreholes WRC ging Distance of Pump- MRS boreholes only ing boreholes from WRC Observation points Total Monthly Rainfall (mm) for: Maun airport;- period October, 1921-oct, 2003; Shakawe;- Oct, 1922-Oct, 2003; Including Meteorological associated localities Hydrologic/Climatic services, Mean Monthly temp: Maun:- 0ct, 1962-2003: Shakawe:- 1960-2003; Mean Montlhly W indspeed: Maun:- 1960-2003, Shakawe:- 1960-2003 Gaborone Mean Monthly Humidity: Maun:- 1960-2003, Shakawe:- 1960-2003 Sunshine Hours:- Maun:- 1960-2003, Shakawe:- 1960-2003 Monthly Evaporation: Maun 1960-2003, Shakawe, shakawe:- 1960-2003 Various Consultants reports: Maun Groundwater Development Projects Reports sources Publications and Journals: MRS related subject by various authors MSc Thesis ITC Library Various Borehole well-level Dynamic water level data for the project boreholes area WRC monitoring

8 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS - MAUN AREA, BOTSWANA

2. Project Setting

2.1. Location The study area, approximately 12 500km2 is located in northwestern Botswana in the Ngamiland Dis- trict. The area stretches from Toteng village in the southwest to Mababe village in the Northeast and constitutes four MGDP-2 groundwater investigation areas, Figure 2-1. The major area of interest is however, an area where the MRS soundings are located, Figure 2-2. The soundings lie in an area near and parallel to the southeast border of Upper Thamalakane Exploration Area (271km2); Upper Thamalakane river, which extends for about 23km from the Boro river junction to the confluence of the Gomoti and Thamalakane rivers. One site (Bh8815-12-13) is situated in the Lower Thamalakane. The area encompasses the distal end of the Okavango Delta and is within the Delta distributary‘s system. The sub-urban Maun lies 900km to the north of the capital city of Botswana, Gaborone. The area can be accessed from Francistown via a 500km stretch of metalled road and from Ghanzi by 200km of tarred road. The Maun area is 380km to the southeast of Shakawe. Other connections from the associated localities are either gravel/sand or muddy dirty roads.

2.2. Population and Socio-economics The area of study falls under the jurisdiction of the Northwest District Council and covers the Ngami- land, Chobe and the Okavango districts. The district headquarters is located in the sub-urban Maun also the traditional capital of the Batawana tribe. Maun is the principal population centre in the entire District and the commercial centre for the Northwest Botswana. The actual population of Maun and associated localities as recorded in the 2001 population census is 49 882 persons. Maun has developed progressively over the years because of its location in the far distal end of the Delta and proximity to the Moremi Reserve and Chobe National Park. A strong tourism trade encour- aged by the provision of campsites within the parks and privately run safari camps has provided important economic benefits for Maun and nationally. Other services include local craft industries, commercial and administrative services and research institutes. The Tawana Land board, District Commissioner, many central government offices including health services like hospitals and several clinics are located in Maun. The Maun airport provides primary link to the Okavango Delta and tour- ist centres. The sub-urban Maun has both a traditional settlement pattern and some modern residential style. Tra- ditional type residential housing areas along both sides of the Thamalakane River characterize settle- ments predominantly. A large section of the population is also involved in subsistence agriculture and pastoralism. Because of rapid development and increasing population and therefore increase in water demand which are prevalent in the Maun, it is critical to provide rapid, cheap reliable means of locat- ing fresh groundwater sources for the entire region hence verification of the MRS soundings within the area of study was done.

9 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Figure 2-1:Location of the Project Area œ Upper Thamalakane Exploration Area

10 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

SW-NE cross-section

Figure 2-2:MRS Borehole Sites Location Map in the Upper Thamalakane Exploration Area

11 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

2.3. Physiography/Geomorpholgy A detailed study of the topography of the Maun/Okavango area is given in Ellery and McCarthy (1999), McCarthy and et al (1993b), Water Resources Consultants (1997), Masedi (2002) etc. At a regional scale, relief is very low the altitude ranging from 925 m.a.m.s.l at Makalamabedi area in the east of the study area to about 1020 m.a.s.l at Mohembo in the west, a rise of some 95 m over approximately 300km. By any standards, this is generally a flat terrain. Local relief is intricate, the topography gently undulating with relief up to 2m over short distances. The Okavango Delta, Figure 2-3 is the most prominent topographical feature in the area and topographically provides insight into the local tectonic and sedimentary history. The delta is an alluvial fan and one of the world‘s largest inland river deltas. The fan is of uniform gradient with no evidence of regional tilting, Gumbricht et al (1985). Masedi (2002) shows that the area is dissected by numerous lineaments and fault controlled river channels. Masedi (2002) after Thomas and Shaw (1989) also shows the area has been affected by two parallel faults, one at the lower extremity of the delta passing through Maun (the Thamalakane fault) and the other along northern edge of the delta along the line of Selinda Spillway (the Gomare fault). The Kunyere fault lies just northwest and parallel to the Thamalakane fault. It is apparent from Figure 2-3 that the Thamalakane fault defines the southeastern limit of the delta. Gumbricht et al (1985) reports that the sedimentation in the delta appears to be causing crustal sag- ging of the central delta, which has tilted and detached a sliver of the ridge along the Thamalakane fault. The Selida Spillway occupies a marked local depression, which is a graben between the Gomare fault and the extension of the Lenyanti fault. Silcretes, calcretes, siltstones and silicified sandstones are reported to occur alone the Thamalakane and Boteti River. Further McCarthy et al (1993b) report that the area is characterized by longitudinal dune system with a strike of 105 degrees that is less developed in the Kunyere-Thamalakane interfault zone.

Gomare fault

Gomare fault Thamalakane fault

Kunyere fault

Figure 2-3:The Okavango Delta in Botswana, with selected digitised rivers projected on a Landsat TM mosaic image (from McCarthy et al., 2002).

12 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

The Okavango River originates in the highlands of Angola and enters Botswana at Mohembo in the northwest. At that point the river enters a fault-controlled zone (northwest to southeast trending faults) and then splits after crossing one fault line, (the Gomare fault) into several waterways and channels that form a fan like pattern, the Okavango delta. Thomas and Shaw (1989) as reported in Masedi (2002), describe the pattern as an open hand like structure with each finger representing a channel, Selinda, Thaoge, Manachira, Jao and Mboroga. Masedi (2002) divided the area into three geomorphological regions, the Panhandle, the Upper fan (permanent swamps) and the lower fan (seasonal). The panhandle is the main Okavango River, which empties into the delta from the northwest. The Upper fan is the area immediately east of the Gomare fault and include one the large piece of land immediately east, which has become slightly elevated forming the chiefs island. The lower fan comprises the far distal end of the delta, the study area. This is an area of seasonal swamps where channels are clearly visible and well defined. Where channels are poorly defined, the incoming flood is spread laterally into neighbouring floodplains and hollows of melapo (Masedi, 2002). A detailed study of the geomorphology of the project area was made by WRC (1995) during the inception period and Masedi (2002) as a chapter in his MSc thesis.

2.4. Climate The climate of Maun is hot semi-arid. Though records of various climatic elements were collected for the area e.g. rainfall data, minimum and maximum temperature, sunshine hours, wind speed, etc only rainfall data for the Maun area is discussed because of sufficient length and consistency. Rainfall records for the period October 1921-2003, appendix 1 recorded at Maun airport show that rainfall is highly variable and individual precipitations events typically occur as high intensity storms. Figure 2-4 illustrates annual rainfall that shows variability over the years. The highest rainfall oc- curred in 1973/74 and the lowest in 1994/95. Figure 2-5 illustrates mean monthly rainfall and shows the rainfall pattern is characterized by a wet season that stretches from November to March.

1400

1200

1000

) m 800

m (

l l

a f

n 600 i

a R

400

200

0 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 Year

Figure 2-4:Maun Annual Rainfall Chart (mm)

13 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

120

100

) m m (

l l 60 a f n i

a R

0 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Month

Figure 2-5:Mean Monthly Rainfalls for Maun (1925-2002)

2.5. Hydrology Hydrological data was compiled from information obtained from the Department of Water Affairs (DWA) and Water Resources Consultants (WRC) in Botswana. The data comprises river flows and water level data measured at Mohembo River Gauging Station (No. 7112) and the Boro Junction Sta- tion. The Mohembo station data is important because it represents the majority of inflows to the Okavango Delta and the records obtained cover a period October 1974 to June 2003. Further the Okavango River feeds all the small tributaries within the area and as well cover the study area situated in the lower far distal end of the Delta. The Boro Junction records cover the period from October 1969 to June 2003. It is important to the study area because it is where the Boro River joins the Thamalakane River and the fact that it is situated at the confluence of the Boro river and the fact that is within the study area. The hydrologic characteristics of rivers in the study area are of importance to the understanding and assessment of the hydrogeological environment and nature of aquifers. It has been established though that there are 19 river gauges in total located within the Okavango Delta catchment. Data for the other stations was not considered per say because in assessing all the records the only stations chosen were found to cover quite a significant period of time and also the fact that there had few missing data. The records for the stations are presented in appendix 1b. The Okavango River enters Botswana at Mohembo and flows southeast to Seronga before disintegrat- ing into a series of complex and poorly developed channels and shallow basins that form the Okavango Delta, (Masedi, 2002). The flow of the waters is very slow because of extremely low gradi- ents (about 1:3300) across the Delta often causing the waters to reach the far distal end of the Delta after four to five months. After Seronga, the Okavango main channel divides or dissects into three river channels: the Thaoge channel which runs in the western side of the delta; the Nqoga River drain- ing the north and northeast parts of the Delta and the Jao which drains the central delta area. These three rivers as they flow southwards, further disperses into a series of anatomising channels and include such channels as the Gomoti, the Mboroga and Santantadibe Rivers. The Gomoti and Santan- tadibe flow southwards and when they reach the Thamalakane fault, they bend abruptly following the Fault zone and form the Thamalakane River. The Thamalakane River is the main watercourse in the

14 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

area of study and flows in a southwesterly direction and currently the Boro River is its main tributary. The Magogelo and the Khwai rivers flow to the northeast into the Mababe Depression. The Jao River passes west of Chiefs Island and then disintegrates to form a tributary, the Boro River that flows towards the town of Maun and other tributaries join the Gomoti River. The Boro River is thought to be perennial and in mid winter it rises and overtops the Kunyere fault causing annual flooding in the lower reaches of the delta and these floods drain into the Xasamare and the Lower Thamalakane but also backup northeast of the Thamalakane-Boro junction into the Upper Thamalakne River (WRC, 2002). In the northwest of Buffalo fence the Boro River divides into several channels, some of which form the Shashe and the Chuchube rivers. Records on the Shashe show the river channel has not received any measured water flows since 1989 (Masedi, 2002). When the Thamalakane passes Maun it breaks down into the Boteti River and flows sporadically to the southeast into Lake Xau and the Makgadikgadi Pans. The Nhabe River flows towards Lake Ngami. The lake has no natural outlet and is also fed by the Kunyere River, which receives delta flow from Marophe, Xudum and Matsibe Rivers. Less and less water has been flowing through the western side of the Okavango marshes during the 20th century, so that 180km2 of Lake Ngami-famous is usually dry and almost unrecognisable as a lake (WRC, 2001). Figure 2-6 shows the drainage pattern in the study area.

Figure 2-6:Drainage Network of the Study Area

15 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Figure 2-7 is the total annual flows over the years for the Mohembo River for the period 1974 to 2002. The graph shows high total annual flows for the years 1975/76, 1978/79 and 1984. This significant increase in flows particularly for these years can be explained by the fact that there was also a corresponding increase in rainfall, which was greater than normal for those years. In general the annual flows show a decline with the years. This is further envisaged in the ten year combined flow graph for Mohembo for the period 1991 to 2001, Figure 2-8. The graph shows that peak flows can occur more than once and that there is a general shift of flow pattern to the right.

12000 ) r y

/ 10000 M

C 8000 M (

w 6000 o l F

l 4000 a u

n 2000 n A 0 0 8 6 4 2 0 8 6 4 2 0 8 6 4 0 9 9 9 9 9 8 8 8 8 8 7 7 7 0 9 9 9 9 9 9 9 9 9 9 9 9 9 2 1 1 1 1 1 1 1 1 1 1 1 1 1 Start of year

Figure 2-7:Mohembo Total Annual Flows at Station (7112)

750 700 1990/91

) 650 1991/92 1 - 600 1992/93 s 3 550 1993/94 m

( 500

1994/95

e 450 t 1995/96 a 400 r 1996/97

e 350 1997/98 g r 300 1998/99 a 250 h 1999/00 c 200

s 2000/01 i 150 D 100 50 0 l t t r r y y v c p g n n u c c a a a a o e e u u a J O O - J J M M N S A D M M ------1 - - 1 1 0 0 1 1 0 9 0 0

3 1 1 3 3 3 3 3 2 3 3 3 Time (months)

Figure 2-8: Ten year combined flow graph for Mohembo for the period 1991 to 2001

16 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

25.00

20.00 ) r h / 15.00 3 m (

w 10.00 o l F 5.00

0.00 8 6 4 2 0 8 5 3 1 9 7 5 3 1 9 9 9 9 9 9 8 8 8 8 7 7 7 7 7 6 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Years

Figure 2-9:Mean Annual Flows at Boro Junction

A graph of mean annual flow for the Boro Junction data for the period 1969 to 2000 is presented as Figure 2-9. A very distinct feature in this graph is the very large annual flows in the 1970s and there- after a subsequent general decline in flows. This general trend is also visible in the Mohembo data, Figure 2-8.

17 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

3. Geology and Hydrogeology

3.1. Geology and Stratigraphy The geological framework of the study area presented in this report is based on the work carried out by Water Resources Consultants (WRC) in their final report of the Maun Groundwater Development Project, Phase 1 of October 1997 and work carried out by Masedi (2002). Proterozoic rocks of Damara Supergroup underlie the area. The Karoo Supergroup rocks of Carboniferous to Jurassic in age overly these rocks. The bedrock geology is completely obscured by Kalahari cover except in the Kgwebe Hills outcrop area. These bedrock geology however, particularly the post Karoo Dyke swarm and the aerial extent of the Stormberg Lava Group were interpreted from aeromagnetic data by WRC consultants. The stratigraphy of the study area is presented in the Table 1-1 and the geological map in Figure 3-1.

Study area

Figure 3-1:Subsurface Geology (from Masedi, 2002)

18 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Table 3-1:Stratigraphy of Study Area (after W RC, 1997 originally from Carney et al, 1994)

Age Supergroup Group Formation Lithologies Cretaceous to Kalahari Undivided Fine to medium sands, silts, clays cal- Recent Beds crete, silcrete, thin basal gravels to conglomerates locally developed Carboniferous Karoo Stormberg Undivided Flood basalts, massive to vesicular to Lebung Bodibeng Homogeneous fine to medium sandstone Jurassic Sandstone Ecca Marakwena Conglomerates and sandstones intercalated with silty mudstones. Tale Silty mudstones with thin bands of minor carbonate Proterozoic Damara Ghanzi Ngami Fine grained meta-arkoses, shales and minor carbonate - Kgwebe Interbedded sandstones and volcanics, porphyry, tuff and diabase

3.1.1. Damara Supergroup The Proterozoic rocks of the Damara Supergroup are the oldest rocks in the study area and comprise of metavolcanic Kgwebe Formation and Metasedimentary Ghanzi Group. The Kgwebe formation consist of porphyry, felsites, diabase and tuffaceous sandstones and are the only outcropping rocks in the area. The Ghanzi Group rocks, folded into large isoclinal folds which trend in a northeast direction consists of sandstones, siltstones shales, quartzites and minor carbonates. These rocks occur to the west of the Kwebe Hills and along the shores of Lake Ngami.

3.1.2. The Karoo Supergroup The Karoo Supergroup, Carboniferous to Jurassic in age overlies unconformably the basement rocks, which consist of three groups; the Ecca, the Lebung and Stormberg Lava Groups. The Ecca Group, the basal rocks of the Karoo are divided into two formations; the Tale Formation, which is comprised of fine-grained meta-arkoses, shales and minor sandstone, and the Marakwena Formation consisting of conglomerates and sandstones intercalated with silty mudstones. The Lebung Group is represented by the Bodibeng sandstone correlated with the Ntane sandstone of the Lebung Group in eastern Botswana, Smith (1984) in WRC‘S Phase 1 final report of 1997 and is mainly a ho- mogenous fine to medium sandstone. The rocks are reported exposed on the southeastern shores of Lake Ngami. The upper group which caps the sequence is the Stormberg Group rocks, undivided and mainly Flood basalts, massive to vesicular. According to WRC‘s Phase 1 Final report these rocks are not exposed but are indicated in the Geological Map of Botswana (1:1,000 000 scale; Mortimer, 1984) as occurring in the interfault zone between the Kunyere and Thamalakane Faults, between the villages of Ko- mana and Toteng and to the northeast of the study area.

19 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

3.1.3. The Kalahari Beds. These are mainly riverine or fluviatile sediments of cretaceous to recent. The sediments are mainly unconsolidated sands, which range from very fine to medium grained (occasionally coarse grain), clays, silts, calcretes, silcretes, mudstones, siltstones and sandstones. The occurrence of these sediments has been proven from the drilling and the geophysical logging results carried out in the area. The investigated aquifers are comprised of the Kalahari.

3.2. Regional Structure The regional structural framework of the area is based on the interpretation on satellite images, the Geological Map of Botswana (1:1000000) and review of work carried out by WRC (1997) and Masedi (2002) as mentioned in section 3.1 above. The obvious structure that can be seen from the satellite images is the Okavango Delta pattern, Figure 2-3. The Thamalakane fault and the Kunyere faults are also clearly visible from the satellite images, Fig- ure 2.3. According to WRC (1997) Final Report these two faults are defined by topographic expres- sion and aeromagnetic pattern and are characterised by surface scarps with downthrow to the northwest. The area adjacent and immediately northwest of Thamalakane fault represent the MRS tested area. This area lies within the Okavango Graben, which is bounded by the northwest to southeast trending Thamalakane and the Gomare Fault zones. The extensive northwest to southeast trending dolerite swarm in Figure 3-1 can clearly be picked out from the satellite images. The Kunyere fault, which occurs to northwest of the Upper Thamalakane, is also clearly visible from the satellite images. River valleys like the Thamalakane River, which clearly follow the Thamalakane fault zones to the southwest and then turn abruptly southeast to its confluence with the Boteti River along another lineament, indicate that these features are structurally controlled. The Boteti River flows south eastwards and also appears to be structurally controlled. Figure 6.3 in Masedi (2002) shows the faults in the study area.

3.3. Hydrogeology The fresh water shallow unconfined and semi-confined Kalahari bed aquifer comprised of fine to medium grained sand and leaky confining layers of clays, sandy silts and clays is the most important source of fresh water in the area. These fresh water zones have clearly been identified (follows river channels and areas of seasonal floods), (Masedi (2002) and the challenge is now to locate the fresh extractable water. The shallow aquifer in the Maun area is interpreted as single unit extending from surface to a depth of approximately 18 meters (WRC, 2002). Linn and Masie (2000) report the thickness of the freshwater zone (<1500 mg/l TDS) to vary from 25 to 120 m.b.g.l and that the transition from fresh to brackish and saline conditions both laterally (5 to 20m) and vertically (<5m) is abrupt. Little is known about the bedrock aquifer because of its water quality. An exploration borehole drilled to 245 m.b.g.l between the Kunyere and Thamalakane Faults that yielded over 100 m3/hr, had TDS range 17 850 to 26 560 mg/l. This borehole was terminated in the Bodibeng Sandstone. Groundwater flow is radially away from the delta and laterally away from the rivers (Linn and Masie, 2000)

3.3.1. Spatial Hydrostratigraphy Figure 1-1 illustrate the hydrogeological cross-section based on the drilling information and is marked in Figure 2-2. Due to the closeness of some boreholes, a few of the boreholes in MRS area are represented in the cross-section. Of note is that there is great variation in lithology both laterally and verti-

20 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

cally as can clearly be observed from boreholes BH9598 and BH9599, Figure 6.1 in Chapter 6. The boreholes are 11.25m from each other. The yields also vary greatly, BH9599 pump tested at 12m3/hr and BH9598 tested at 2m3/hr. A summary of borehole yields is given appendix 2 and Table 1-1.

Table 3-2:Summary Borehole Data œ MRS Area

Transmissivity Specific Drilled Yield BH Screen SW L EC (m2/d) Capacity Site ID Depth (m3/hr) No Details (mbgl) (s/cm) 24hrs (m) PT CRT Rec. (m3/hr/m) 30-36 8262 BH8262-5-1 73 51-54 12.29 12 660 58 53 - 61-64 8114 BH8114-14-12 29.5 19-28 6.05 7.5 160 2.46 12 0.78 8348 PMP8348-13-3B 81 43-69 12.50 22 1300 10 27 0.87 8351 BH8351-2-10 74 43-69 11.60 35 650 31.82 32.73 51-60 8815 BH8815-12-13 71 13.46 5 - 2.16 12.1 0.36 63-66 9590 BH9503-3-11 67 59.50-62.42 12.53 1.8 640 4 4 0.089 25.40-37 25 9599 MRS-7-5 59 12.70 12 1160 27 0.99 48.30-57 9600 BH9475-10-7 35 18.00-29.60 2.67 3 169 0.97 6 0.15 24-38.50 9604 TH3-8-6 63 9.87 5 260 4 14.4 0.36 44.40-59 9608 TT16-4-2 57 25.78-51.88 12.37 2 380 21-38.52 9683 TT3-1-9B 65 47-50.92 15.81 20 660 2.56 29.2 1.11 57-59.13 7-10 10117 TT2-9-8A 77 20.35 2 0.18 22-52 10118 WBH8348-6-4A 60 - - dry - - - - PT = Pumping test rate

SW 8114 9603 9598 9607 8262 NE

10 ?

? ? ? 20 Saturated section

30 Saturated section ? Saturated section Saturated section 40

? ? 50 Saturated section Saturated section 60 Saturated section

70 ? ? ? ? 80 Mudstone Clay Silcrete Static water level 90 Sand Sandy Clay Silt/siltstone 100 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Distance (km) Figure 3-2 :SW œ NE Hydrogeological Cross-section from Borehole Information - MRS Area

21 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

3.3.2. Spatial Aquifer Parameterisation Spatial aquifer parameterisation refers to the hydraulic properties like transmissivity and storage. As reported earlier the fresh shallow water aquifer of the Kalahari is the most important in terms of water supply to the area and is restricted to the river channels. The aquifers are basically unconfined to semi-confined and are comprised of fine to medium grained sand and leaky confining layers of clays, sandy silts and clays. In the previous studies, WRC (2002) reports hydraulic conductivity values ranging 16 œ 35 m/d that decrease across the flood plain to 5 œ 10 m/d. Masedi (2002) obtained a specific yield value of 0.12 and WRC (2002) adopted a Sy value of 0.14 in their model. This is consistent with the determined pumping test value from the Neuman method of 0.11 œ 0.13, refer to Chapter 7. Table 3.2 above gives a summary of some hydraulic parameters of the study area.

3.4. Hydrochemistry Hydrochemical analysis results of the project boreholes and analysis results of some boreholes within the area are presented in Table 3-3. The hydrochemical data particularly EC was evaluated against availed geophysical methods like MRS, TDEM and hydrogeological data in order to develop a better understanding of hydrochemistry of the aquifers. A subsurface with high electrical conductivity affects the alternating magnetic field hence the MRS signal of an area investigated is also affected.

Table 3-3:Chemical Analysis of Results in the MRS area

BH Alk HCO3 NO3 Date K Na Ca Mg SO4 Cl F Fe Mn EC pH TDS TH No. (Calc) 9683 25/5/02 13 129 16 2 46 18 272 331.6 0.59 0.22 0.14 0.06 660 8 422 47 9593 29/5/02 6.4 14 8.5 1.9 8.5 1.7 60 73.2 <0.1 0.1 8.2 0.38 130 6.6 84 29 9599 3/6/02 13 185 71 3 322 25 255 310 0.14 0.23 2.4 0.1 1160 7.5 742 189 9606 7/6/02 14 84 3 5.8 39 19 149 181.7 0.29 0.27 52 0.34 400 7.5 256 31 9688 26/7/02 19 69 45 9.5 8.9 3.6 300 365.8 2.9 0.23 0.26 0.2 610 7.6 390 152 9608 27/702 12 53 25 1.7 29 4.6 158 0 0.1 0.4 35 0.21 380 8.3 243 69 9602 1/8/02 8.1 236 3 0.53 81 16 445 0 <0.1 0.92 0.21 <0.05 1010 8.2 646 10 9604 1/8/02 6.3 49 7.40 0.68 31 3.2 102 124.4 0.10 0.13 7.7 0.08 260 7.3 166 21 9590 7/8/02 14 63 62 10 24 15 300 365.8 <0.1 0.23 0.64 0.31 640 7.5 410 195 9595 8/8/02 15 631 5.6 0.75 164 622 329 0 <0.1 0.50 0.13 <0.05 2950 8.6 1888 17 9600 15/9/02 9.4 18 7.4 2.40 25 3.7 48 58.5 <0.1 <0.1 0.87 <0.05 169 6.4 108 28 9882 3/3/03 5.5 10 17 4.30 0.2 2.1 74 90.2 <0.1 0.10 1.7 - 180 6.4 113 60 9884 10/3/03 7.3 8.1 22 3.90 0.2 1.1 93 113.4 <0.1 <0.1 1.2 - 200 6.7 128 73 WHO Maxi- 25 6.5- mum 500 10 1.5 0.3 0.1 1000 0 8.5 Guideline All units are in mg/l except for EC, which is in WS/cm and pH dimensionless

The water quality of the boreholes varies from fresh (TDS = 0-1000mg/l) to brackish (TDS =1000- 10000mg/l), refer to groundwater classification based on TDS below, Table 3-4. This is highly ex- pected considering the fact that these boreholes tap a fresh shallow aquifer within a saline environment, hence moderate values are observed.

22 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Table 3-4:Groundwater Classification Based on TDS

Class TDS (mg/l) Fresh water 0-1000 Brackish water 1000-10000 Saline water 10000-100000 Brine water >100000

A plot of TDS versus EC using data from Table 3-3, Figure 3-3 shows the two parameters are correlated and related by the following; TDS = 0.64EC œ 0.32 (3.1) 2000

1600

TDS = 0.64*EC - 0.32

1200 ) l / g m (

S D T 800

400

0 1000 2000 3000 EC (mS/cm) Figure 3-3:TDS vs. EC Plot The expanded Durov plot (refer to Table 1-1), Figure 3-4shows predominantly two water types; type 1 is predominantly sodium bicarbonate and type 2 is of mixed cation, Na-Mg HCO3 or Ca-Mg-HCO3 water type. There are some exceptions like BH9599 and BH9595 that are of Na-SO4-Cl type possibly representing the ingress of poorer quality water laterally and also possibly an intrusion from the deeper waters. This is possibly due to high evapotranspiration rate (98%) across the Delta reported by Gieske (1996) and also abstraction.

Figure 3-4:Durov Plot

23 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

4. Magnetic Resonance Technique (MRS)

The inversion of Magnetic Resonance data E0(Q) and T2*(Q) provides the depth, thickness (b), water content (9MRS) and relaxation time for each of the water saturated layer (Legchenko et al, 2002). The application of MRS and its capability for hydrogeological aquifer parameterization has been discussed widely and presented by many authors to date like Roy and Lubczynski (2000), Yaramanci (2002), Legchenko et al (2002), Lubczynski and Roy (2003) etc. In hydro geological context however, it is clear that some MRS inversion parameters are directly useful and these are free water content (9MRS), water bearing layer depth and thickness. The other parameter used, the decay rate or relaxation time

(Td) is an indirect indicator of information such as pore size, hydraulic conductivity and yield. In an MRS investigation, the reliability of the subsurface water detection is dependent on the signal amplitude and this has been shown to be largely influenced by the following: the magnitude and inclination of the geomagnetic field (which varies according to the geographical coordinates of the test site); the electrical conductivity of the subsurface (screen effect); size and shape of the antenna; the decay time of the signal (which depends on the water type containing rocks) (Legchenko et al, 1997). A summary of the MRS capabilities is herewith presented in this report and is based on past-presented publications on MRS. In order to understand the capabilities for aquifer parameterization of the MRS derived information a summary review of the MRS principle is presented below together with the historical background.

4.1. Historical overview The Magnetic Resonance Sounding (MRS) technique known also as SNMR (surface Nuclear Mag- netic Resonance) or PMR (Proton Magnetic Resonance) for groundwater exploration is relatively a new application of NMR (Nuclear Magnetic Resonance). It is the only non-invasive geophysical technique with an inherent selectivity to hydrogen and therefore to groundwater (Roy and Lubczynski, 2003). The technique is site dependent; hence the geomagnetic field and electrical conductivity of the subsurface influence its performance. Legchenko et al, (2002) state that where the resistivity is larger than 50Ym, groundwater can be detected down to 150m in areas with high geomagnetic field and only to about 100 m.b.g.l in areas with low geomagnetic field. The first idea in the use of NMR to investi- gate groundwater came from Varian in 1962 as reported in Legchenko et al (1997). The concept was then developed in the 1970‘s by a Russian team under Semenov who built the first MRS equipment, the HYDROSCOPE. The technique has been used in Russia and routinely tested in many different countries and environments as reported by Schirov et al., (1991), Goldman et al., (1997a), Gev et al., (1996), in Legchenko and Valla (1998). The MRS has since developed and improved, the first commercial instrument NUMIS becoming available by 1996 (Iris Instruments, 2001). Since the commer- cialising of the Numis Instrument, there has been a lot of interest to learn more about the method. Fur- ther tests have been done using the set of equipment in many countries; e.g. France by Legchenko et al., (1995), Germany by Yaramanci et al., (2002), Saudi Arabia by Legchengo et al (2002), etc.

24 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

In Botswana‘s Maun area a qualitative assessment of the MRS test was done by Roy (2001) of ITC but did not allow for verification of the soundings since more information such as pumping tests and geophysical logging of some boreholes were still to be made. Prior to that, Kgotlhang did an evaluation of the method as a groundwater investigation tool using MRS data from Botswana in 2000 as an Msc thesis topic. Roy and Lubzcynski (2000b) further presented a verification of the MRS extractable groundwater water content using pumping test data from the Southern African Karoo Sandstone layer. Of recent Lubzcynski and Roy (2004) presented yet another publication on MRS as a new method for water assessment using data from Delft, the Netherlands and Serowe, Botswana. The latest version available is the NUMISPlus (Iris Instruments, 2002) and is graphically represented as Figure 4-1. The instrument comprises: (1) two identical DC/DC converters used to program a variable amount of electric energy to produce the loop excitation current in a form of required pulse moment (0); (2) the main MRS unit used both for the AC loop excitation and signal acquisition; (3) a reel of copper cable used to lay out the loop; (4) the tuning box, (5) a high capacity rechargeable battery used to power the system and (6) a normal PC laptop for overall system control, data recording and processing.

2 1

6 5

Figure 4-1: NumisPlus Magnetic Resonance System (Iris Intruments 2002)

4.2. The MRS Principle The Nuclear Magnetic resonance (NMR) is a property of specific nuclei including hydrogen, which produce a magnetic field when they are excited by an alternating field (electric current), produced by the loop in the presence of static magnetic field (earth magnetic field). Most hydrogen atoms located in the ground are coming from water molecules. The most important water selectivity advantage of MRS refers to water environment where possible water contamination with hydrogenated compounds (e.g. Gasoline) is negligible as compared to overall quantity of investigated hydrogen nuclei 1H+ (Lubczynski and Roy, 2004), hence the direct detection of water can thus be envisioned with such a method. The basics of the 1H+ magnetic resonance sounding are graphically presented as Figure 4-2. In the MRS technique three magnetic fields are considered:

1. The earth‘s magnetic field (B0) used as the static field, the amplitude of which determines the precession frequency of the 1H+, the Larmor frequency ( The hydrogen nucleus is made of a single proton and hydrogen nuclei (1H+) occur as one of the major constituent of the water molecule The nucleus has a weak nuclear magnetic dipole moment aligned with the ambient magnetic field at steady state. It has also a weak spin angular momentum. If the magnetic momentum is misaligned by a mo-

25 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

mentary external excitation, it will precess around the static local magnetic field at the Larmor frequency. The basic concept is therefore, an alternating (AC) magnetic field at Larmor frequency (resonance) and oriented perpendicular to the static magnetic energizes the volume to be investigated (which can be relatively large up to 106 m3, Lubczynski, 1997) thereby providing an excitation field

BM. The excitation is used to displace the average nuclear magnetic moment (M0) from the direction of the static magnetic field. Each isotope with a spin has a specific gyromagnetic ratio Z. The 1H+ Larmor precession frequency (in Hz) is directly proportional to the site-specific earth‘s magnetic field

B0 (in nT) and is determined by the relation;

ƒ = B0Z/2[ (4.1)

0 = B0Z (4.2) Where Z is the gyromagnetic ratio of protons [Z = 0.268 rad/s.nT]

0 is the Larmor angular frequency in radians/sec

ƒ = 0.04258B0 (4.3) The earth‘s magnetic field is determined by carrying a normal magnetic survey with a magnetometer and then the readings are averaged. This average is then used to determine the Larmor frequency using equation (4.3) above. 2. The excitation field, produced by an electric current into a loop laid on the surface of the ground at a frequency equal to the Larmor frequency ( The measurements are made using a loop (size L usually 50-150m) of circular, rectangular or eight-shape layout. The shape and the dimension of the loop are very significant to the signal measured. The actual procedure is that an alternating current of known intensity I is then passed through the loop for a limited time (Q) (controlled time interval in ms) at Larmor frequency generating a magnetic field so that an excitation quantity (pulse moment in A.ms) of Q = IQ is achieved. As this is achieved a quantity of 1H+ nuclei are precessing in phase hence producing a weak magnetic field, which induces an alternating voltage in the MRS loop system. E0, the initial signal amplitude is given by a relation:

E0 = ∫V 2[ƒBM(r) M0 9(r) sin (0.5ZBM(r) Q) dv (4.4) where: 1 + M0 is the magnetic moment of H 9(r) is the water content Q is the pulse moment (I*Q)

BM is the component of the excitation field perpendicular to the static field (site-specific earth magnetic field)

Figure 4-2: Basics of proton magnetic resonance sounding (Iris instruments 1998)

26 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

3. The relaxation field produced by the protons excited by the previous field. The amplitude of relaxation field measured at the surface after the excitation current is turned off, is directly linked to the number of 1H+ which have been excited and thus to the water content. The decay of relaxation field produced by the 1H+ (magnetic resonance response) is given by:

* E = E0 exp (-t/T2 ) cos (2[ƒt + _) (4.5)

T2* is the free induction decay time constant _ is the phase shift between the excitation current and relaxation voltage measured in the loop

In reality three decay rates or relaxation time are considered in NMR: T1, the spin-lattice or longitunal * relaxation time, T2, the spin-spin or transverse relaxation time and T2 , the free induction decay rate which is similar to T2 to which effects of magnetic field inhomogeniety have been added (Lieblich et * al 1994, Kenyon, 1997). At present mainly T2 is evaluated although recently with longer acquisition time, T1 can also be estimated (Lubczynski and Roy, 2003). T2 is not yet available in the commercial * market, but in the absence of magnetic effects, the MRS measured T2 ≈ T2

4.3. MRS Data Acquisition and Inversion

4.3.1. Data Acquisition The layout is as shown in Figure 4.1 above and the procedure followed is outlined below. A few readings of the geomagnetic field strength of the area are measured and an average is then calculated to determine the Lamor frequency. This determined figure is then put in the data acquisition system and a mini-sounding conducted for calibration purposes. The fine tuning adjustments are made in accordance with the response from the mini sounding. A full sounding then follows. A stacking number (number of iterations the system will take to average-out a good stable signal value) depends on the noise level that is recorded before the start of each pulse when there is transmission. Repeat measurements are made when corrupted values or anomalous values are obtained. Of note should be the monitoring of the geomagnetic strength during the survey, which usually varies with time.

4.3.2. Capabilities and Limitations The success of an MRS investigation depends on the amplitude of the signal and noise and these are greatly influenced in different ways by several factors herewith presented below: Type of water containing rock œ A study was made by Legchenko et al, (1997) where two sites where compared, one located in Colorado, USA and composed of fractured sandstone and the other in France which is comprised of water-saturated karst limestone. The results obtained yielded both high measured signal and decay time for the limestone layer in France an indication that the type of rock has some influence on the MRS measurements. Depth and amount of subsurface water of an aquifer œ The MRS principle is based on the fact that a signal obtained is specific to water of the subsurface of the aquifer investigated. The higher the signal amplitude, the larger the quantity of free water content. Observations made from different environments e.g. in Palla Road and the Netherlands, Lubzcynski and Roy, (2003) show that below 50-60m the hydrostratigraphic information becomes less reliable and often unreadable. It is therefore clear the

27 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

signal strength is much stronger in shallower aquifer environments and that this is attributed to the uncertainty of data interpretation, which increases with depth. The magnitude and inclination of the geomagnetic field, which varies according to the geographical coordinates of the test site œ If an area investigated, has a strong earth‘s magnetic field, groundwater (even in small quantities) can easily be detected. Generally the geomagnetic field is much larger in areas closer to the poles (about 70 000 nT near the Antarctica) and smaller towards the equator and given the same hydrogeological environments the performance of the MRS depends on the geographical location. It varies between 22 000 nT and 40 000 nT in South America and Africa and in Bot- swana where the study is located, the average magnetic field is about 29 000 nT. The electrical conductivity of the subsurface œ A subsurface with high electrical conductivity affects the alternating magnetic field hence the MRS signal of an area investigated is also affected.

4.3.3. Data inversion The MRS data inversion is provided by the commercial available NumisPlus software tools (Iris In- struments, 2001). A procedure normally followed is that a forward 1D model with hypothetical layers parallel to the ground surface is numerically evaluated for the number of layers set equal to the number of Q values, predefined at logarithmic spacing, from shallow to maximum depths specified by the user. Then a least square with a smoothing operator (regulation factor used as a smoothness con- straint) is finally used. The regulation factor applied is used to determine the water content that best fit each layer using a single decay rate also evaluated from the above. The MRS inversion has widely been described in many publications like in Legchenko and Shushakov (1998), Roy and Lubczynski (2003). Three data inversions are usually considered in NMR data interpretations, and depend on the knowledge of available hydrogeological data. The inversions are; the MCI (Measurement Constrained In- version) carried out to get an idea about the complexity of the subsurface, the LCI (layer Constrained Inversion) to optimize a provisionally schematized aquifer/aquitard distribution. This can be conducted with MRS data from locations with no lithological data. The Layer and Depth Constrained In- version (LDCI) is the most accurate and usually is done for MRS data in areas with available hydrological data. The various physical hydrogeological parameters measured after an excitation pulse has been transmitted into the loop are:

Amplitude of the NMR signal E0 as a function of pulse moment Q, which provides the water content, designated as aMRS as a function of depth; * Decay time constant T2 as function of pulse moment Q provides the pore size as a function of depth The phase shift _ between signal and current as a function of pulse moment Q is dependent on the rock layer resistivity as well as other factors and currently is used only at the quality control of MRS data acquisition step.

The results are typical summarized in a sounding graph showing the E0 vs Q relationship. An example of the MRS inversion results for borehole BH9599 is presented as Figure 4-3. In the example the free water content goes to about 10% at depths around 12-13 m.b.g.l that agrees very well with the water rest levels of the two wells. The loop size is 114m.

28 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Numis MRS Inversion Results

BH 959 9 D ate: 2 5-1 0-0 1

Site : MR S-7-5 Square loop , L= 114m Procesiin g wind ow = 200 ms Smoo thing = 500 Average S/N = 5.7 7 Filter band width = 10H z

Measured Signal Average Signal Modelled Signal Average Noise 200 120

160 100 ) V n

( 80

) 120 0 V E

n ( e

60 0 g a E

80 r e

v 40 A 40 20 0 0 100 1000 10000 100 1000 10000 Excitation moment Q (A-ms) Excitation moment Q (A-ms)

TDEM (ohm-m) Free water content (%) Decay time (ms) Litholog 0 10 20 10 100 1000 1 10 100

0 Light brown very fine clayey sand 10 Brown fine sand

20 Grey clay Brwon fine sand fine to medium at 32-33m 30 Green clay Brown very fine sand Light green sandy clay 40 Brown fine clayey sand Green siltstone ) Brown fine clayey sand

m 50 (

h Green fine clayey sand t

p 60 e D 70 SWL = 13.54m Yield = 12m3/hr 80 EC = 1400mS/cm Screen = 25.40-37m 37-40m 90 EOH = 59m Saturated Zone 100 Static water level Pumping BH 110 2 TC R T = 30m /d 2 TR ec = 25m /d Observation BH9598 (r = 11.25m) 2 TC R T = 38.2m /d 2 TR ec = 38.7m /d S = 0.00095 Sy = 0.11

Figure 4-3: Example of MRS Inversion results for BH9599.

29 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

A borehole graphic log is also included for comparison between borehole data and MRS Inversion results.

4.3.4. Subsurface Free W ater Content (MRS)

The amplitude of NMR E0 as a function of pulse moment Q provides the free water content aMRS as a function of depth. The measured free water content represents the subsurface free water content (af) portion of groundwater defined as the water in interconnected pores located below the water table in unconfined aquifers or located in a confined aquifers (Fetter, 2001). Within a given aquifer, the measured MRS water content in a saturated zone, water in unconnected pores and the dead pores not considered is equal to the effective porosity, :e (aMRS = :e). Effective porosity :e is the volume of void spaces through which water or other fluids can travel in a rock or sediment divided by the total volume of the rock or sediment (Fetter, 2001). In an unconfined aquifer, the dominant gravitational type of storage is evaluated by the specific yield Sy normally considered to be equal to their storage coefficient since S = Sy + SsD (4.6) and other term is usually small. D is the thickness of the saturated zone. Storativity of unconfined aquifers ranges from 0.01 to 0.30. Specific yield as defined by Driscoll (1995) is the ratio of the volume of water that a given mass of saturated rock or soil will yield by gravity to the volume of the body itself. It is expressed as a percentage. Specific yield is given by porosity : minus specific retention Sr, ie Sy = : - Sr (4.7). If the measured MRS water content aMRS is now applied, the parameter Sy can be obtained by subtracting the specific retention Sr, which is the ratio of the volume of water the rock or sediment will retain against the pull of gravity to the total volume, hence Sy = aMRS - Sr (Lubczynski and Roy, 2003). The specific yield Sy from the MRS is ac- tually less because the MRS instrumentation is characterized with a dead time of 30ms. Bound water is not included in the MRS water content quantification. Another parameter easily obtained is the product of aMRS and the corresponding depth, which gives the hydrostatic column Hw. The specific storage Ss can be obtained by applying the formula Ss = bw*g (c + aMRS d) (4.8) where bw is the density of water, g is acceleration of gravity, c is compressibility of aquifer skeleton, d is compressibility of water and aMRS is the MRS determined porosity. It is the elastic storage coefficient defined as the amount of water per unit volume of saturated formation that is stored or expelled from storage owing to compressibility of the mineral skeleton and the pore water per unit change in head (Fetter, 2001). In a confined aquifer, water released from storage is obtained primarily by compression of the aquifer and expansion of the water when the head (pressure) is reduced during pumping. The storativity comprises an elastic component called elastic storativity not detected by the MRS and a gravitational component that applies only when the piezometric surface falls below the bottom of the confining layer, hence unconfined conditions are created (Lubczynski and Roy, 2003). This storage component is therefore the one detectable by MRS and has been termed the specific drainage Sd (Lubczynski and

Roy, 2003), hence the following relation, Sd = aMRS œ Sr (4.9). The storativity of a confined aquifer Sc can be obtained by applying the formula Sc = Se + Sd (4.10) where Se is the elastic storativity of the confined aquifer.

4.3.5. Decay Time Constant Td The decay time constant as a function of pulse moment Q provides the pore size (flow properties of the medium) as a function of depth and can also help to differentiate free water from bound water

(Lubzcynski and Roy, 2003). The relaxation time (Td) is measured in NMR as T1, the longitudinal * relaxation time, T2, the transverse relaxation time and T2 , the free induction decay rate and is similar to T2 but includes the effect of the non uniformity of the static magnetic field. The relaxation time Td

30 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

is the time required by the excited precessing hydrogen nuclei to make a series of hits against the solid walls of the rock pores to loose energy and phase coherence (Lubczynski and Roy, 2003). Kenyon (1997) defines the pore size as the relation between pore volume and pore area and therefore the shorter the decay time constant the smaller the pore size of the media. Studies on correlating MRS decay rates and borehole lithology have been done by Shirov et al (1991) in Roy (2001) using data from the former Soviet Union, Table 4-1 below shows such a relation.

Table 4-1:Petrophysical Information from NMR Decay Rate (After Schirov et al, 1991 and Allen et al, 1997 in Roy 2001)

Signal decay rate Petrophysical information MRS detectability

T2 < 3 ms Clay bound water No

T2 < 30 ms Sandy clays No or marginally

30 < T2 < 60 ms Clay sands, very fine sands Yes

60 < T2 < 120 ms Fine sands Yes

120 < T2 < 180 ms Medium sands Yes

180 < T2 < 300 ms Coarse and gravely sands Yes

300 < T2 < 600 ms Gravel deposits Yes

600 < T2 < 1500 ms Surface water bodies Yes

A detailed interpretation of the relaxation time Td is presented in Roy and Lubczyski (2000a), Leg- chenko et al (2002), Lubczynski and Roy (2003). The phase shift _ between signal and current as a function of pulse moment Q is dependent the rock layer resistivity as well as other factors and currently is used only at the quality control of MRS data acquisition step.

4.4. Hydrogeological Interpretation with MRS

4.4.1. Aquifer Geometry Aquifer geometry refers to the top and bottom including thickness and lateral extent of the hydrostratigraphic units that defines the aquifer dimensions or the volume of aquifer unit being investigated.

The concept is based on the fact that MRS provides free water content aMRS and an estimate of permeability with depth, hence information on aquifer geometry (unconfined groundwater table and layer boundaries can easily be derived and detected. To determine the top and the bottom of aquifer layers a combined analysis of parameters, free water content aMRS and the relaxation time Td with depth are applied. Observations made from different environments e.g. in Palla Road and the Netherlands (Lubczynski and Roy, 2003) show that below 50- 60m the hydrostratigraphic information becomes less reliable and often unreadable. This is attributed to the uncertainty of data interpretation, which increases with depth, abundance of water in the top shallow aquifers, which masks the underlying layers and the current 1D inversion model, which does not take into account the heterogeneity of the different layers.

4.4.2. Groundwater Table Groundwater table is the undulating surface at which pore pressures is equal to atmospheric pressure. Lubczynski and Roy (2003) states that there is no universal and unique recipe to mark the position of groundwater table using a combination of aMRS and the relaxation time and currently the derived in-

31 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

formation depends on field hydrogeological data available. However conflicting ideas still do exist in regard fractured rocks. In Israel for instance, the benefit of using MRS in groundwater table determi- nation as presented by Gev et al (1996) where MRS results were different from early piezometric measurements but became consistent with the piezometric measurements levels after one day stabili- zation period. Lubczynski and Roy (2003) had a different experience in hard rock that indicated some different results where it was difficult to identify the groundwater table. The current study, which is in an unconfined and semi-confined condition show a better correlation as will be observed in Chapter 8.

4.4.3. Storage Parameters The storage refers to storativity in confined aquifers and specific yield in unconfined aquifers, refer to section 4.3.4 where the concept is discussed in detail. In confined aquifers the storativity S is calculated as S = DSs, where D is the estimated layer thickness, which can also be estimated by MRS. In unconfined aquifers specific yield Sy can be estimated from Sy = MRS - Sr where Sr (specific retention or field capacity) can be estimated from hydrogeological means or laboratory tests such as determina- tion of porosity if say bound water and water in dead pores is neglected.

4.4.4. Flow Parameters (Hydraulic Conductivity, Permeability and Transmissivity Hydraulic conductivity K is a proportionality describing the rate at which water can move through a permeable medium (Fetter (2001). In MRS developments empirical relation between decay rate Td and hydraulic conductivity is given by the following:

a b K = C aMRS Td (4.6)

This provides the hydraulic conductivity K (Kgotlhang, 2001), Legchenko et al (2002), Lubczynski (2003) depending on the factor C, the formation-specific proportionality factor that is estimated according to the rock type and deposition environment and easily obtainable from pumping test. No proper guide has yet been established for an appropriate use of the parameters a and b of the equation in the NMR. Seevers (1966) assumes a = 1 and b = 2 and obtained good results in secondary porosity of diorites, gneiss and karstic porosity of limestones (Legkhenko, 2002), Lubczynski and Roy, 2003). Kenyon et al (1989), assumes a = 4 and b = 2 and had acceptable results in a dual porosity sandstone. 4 4 Yaramanci et al (1999) used the formula K= 1.1Td which was later generalized to K= Td (Yaramanci et al, 2002). This formula however tends to overestimate the K value of aquifer. Lubczynski and Roy * (2003) however agrees with Legkhenko et al (2002) who assumes a = 1 and 4 and b = 2 and Td = T2 and T1 depending on the rock types. The transmissivity T, is defined as a rate at which water of a prevailing density and viscosity is transmitted through a unit width of an aquifer or confining bed under a unit gradient and it is a function of properties of liquid, the porous media and thickness of the porous media (Fetter, 2001). It is the product of the hydraulic conductivity K and thickness D of the aquifer. In NMR the hydraulic conductivity K can be estimated using the formula above and thickness of the layers can be obtained by using the MRS free water component in combination with the relaxation time hence the formula T = KD can be applied to compute and estimate the transmisissvity T. However reliability of the data depends on the calibration with pumping test results prior to computing the MRS transimissivity.

32 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

4.4.5. Unsaturated Zone Parameter The unsaturated zone in a soil is the interval where chemical processes are at their most active. Its extent is determined partly by the content of the soil water, but it cannot extend beyond the water table, below which voids are completely filled with water. The Oxford Dictionary of Natural History. Allavy, M. Ed.; pg.662. Copyright Oxford University press 1985.] This zone consists of gravitational water and capillary water including firmly bound water and loosely bound water, Figure 4-4 below after Lubzcynski and Roy (2003). MRS is able to detect water in an unsaturated zone but this is being deterred by instrument limitations in measurements of water decay times shorter than 30ms, the instrument dead time and of cause the heavy machinery currently used.

Specific retention capacity (Sr) Specific Yield (Sy)

Bound Water (Hb) Free Water Content (af)

V Z

a r o r d e

e n

t Capillary Gravitational W ater o t e a s a

w W ater

d d n n u

u Bound o o S b b

a W ater y Z t y l l u e Unconnected and Flowing W ater o r s m

n a o r e t i o

Dead e F d L end W ater

Non-flowing water porosity Effective porosity (ne)

Total porosity (n)

Figure 4-4:The Groundwater Storage Concept, after Lubczynski and Roy (2003)

4.4.6. W ell Siting Given that there are other geophysical profiling techniques more efficient in well siting like EM, TDEM etc, the challenge now is to locate the fresh extractable water. The inversion of the MRS sounding provides two parameters; free water content and signal decay time constant which below the water table is approximately equivalent to the effective porosity, while the decay rate provides information on pore sizes. In hydrogeological context, layers with higher water content and larger decay time represent coarse (high transmissivity) sediments and form potential targets for borehole development. The reliability of such information depends on the correlation between MRS results and available hydrogeological data. Such relations have been observed in Botswana‘s Ntane sandstone aquifer (Kgotlhang (2000). The method is rapid and costs are reduced (more than 50% in costs saved (Kgotlhang, 2000) because information often derived from boreholes of extractable water is derived directly without drilling. However a joint use of MRS with TDEM yield a more complete estimation of the hydro geological situation than in the case of them taken separately (Roy, 2001).

33 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

4.4.7. Yield Estimator.

Based on the NMR determined free water content 9MRS and using available yield information from pumping tests previously executed in boreholes located at the MRS sites an empirical borehole‘s yield estimator can be determined using the formula:

* B Yestm = A*9MRS*D*(T2 ) (Roy, 2001) (4.7)

Where Yest is the Yield Estimator

9MRS is the MRS determined free water content or effective porosity D is the Layer‘s thickness * T2 is the decay time A, B are constants determined empirically using the data from the already drilled tested sites and the accuracy of these parameters depend on the adequate availability of hydraulic test data.

34 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

5. Magnetic Resonance Soundings (Maun) œ Data Analysis and Interpretion

This chapter basically explains all the procedures used in obtaining the MRS data from the Maun area, which totalled thirteen (13) soundings, (see Figure 2.2, Chapter 2). Section 5.1 provides procedures followed in the data acquisition explained in detail in Roy (2001) and 5.2 deal with data inversion and the inversion results obtained. It should be clear however that the data acquired and used in this chapter and for the entire report was field generated by Dr. J. Roy of ITC and the author of this thesis was not in anyway involved in the acquisition of the data. Section 5.3 deals with interpretation of the MRS inversion results. Some variations in the MRS signal, section 5.4 are also discussed in this report although the signal to noise ratio S/N was not much of problem, i.e. the S/N according to the data set was in general good. It is also important to mention that the author of this thesis acquired knowledge of MRS data acquisition in the Netherlands using the latest version of the Numis equipment, the Numisplus instrument under the supervision of Dr. J. Roy of ITC.

5.1. Data Acquisition As explained above the data acquisition procedure was explained in detail in Roy (2001). The investigations conducted included three components: magnetic survey, TDEM survey and an MRS sounding. The data was acquired during the late night / early morning times since a problem of high noise levels was observed during the day although the loop layout, the magnetometric survey and the TDEM surveys were carried during the day. Table 5-1, below gives a summary of the production soundings with MRS technique, Roy (2001).

Table 5-1:MRS Production Figures (Source Roy, 2001)

Date Sites 2001-10-20 TT3-3-9B (aborted due to noise) 2001-10-21 TT3-1-9B 2001-10-22 BH8351-2-10 2001-10-23 BH9503-3-11, TT16-4-2, BH8262-5-1 2001-10-24 WBH8348-6-4A, MRS-7-5 (Aborted-noise) 2001-10-25 MRS-7-5 2001-10-26 TH3-8-6, TT2-9-8A (aborted œ noise) 2001-10-27 TT2-9-8A, BH9475-10-7 2001-10-29 BH81114-11-12, BH8815-12-13 (aborted œ noise) 2001-10-30 BH8815-12-13, PMP8348-13-3B

35 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

The magnetic data was done by measuring 35 stations spread at regular interval along 3 lines from the MRS measuring station. The station readings were then transferred into the static field notebook where the variations were examined and an average value for each site was made out of the undisturbed readings. That average was used to calculate the local Lamor frequency further used in the first MRS ”mini-survey‘ for each of the sites. Since the main MRS survey was done at another time (during the night) three to four magnetic readings were taken (repeated) before the start of the survey to check for any diurnal change in the interval between the magnetic and MRS surveys. It should be em- phasized however, that the above magnetometric survey is done to determine the Lamor frequency and also to check any significant magnetic gradient at the scale of MRS survey. The survey is only necessary if no prior detailed magneometric survey is available for the area but if there was an earlier survey then two to three readings are necessary to check for diurnal shift. For the MRS component, data for eleven sites was acquired with a square loop of 114m*114m. In site BH9475-10-7 square sided eight loop of dimension, L = 37.5m was used and at site BH8114-11-12 square eight loop of dimension, L = 57m was applied. The TDEM sounding was executed and processed by WRC personnel, Roy (2001). In five of the sites two TDEM soundings were executed; one using the standard WRC 40m*40m TX loop while the other used the L = 114m loop used for the MRS work. Table 5-2 presents a summary TDEM production figures after Roy (2001) and original supplied by WRC.

Table 5-2: TDEM Production Figures (from Roy, 2001 as supplied by W RC)

Date Site Surveyed with TDEM Three TDEM: two with 40*40m at 500m on each sides of TT3, one with 114m 2001-10-21 at TT-3 2001-10-22 One TDEM at BH8351 site with 114*114m loop 2001-10-23 One TDEM at BH9503 with 40*40m loop 2001-10-24 Two TDEM with 40*40m loop: one ~ 230m SW OF bh8348 and one at BH8348 2001-10-25 Two TDEM at MRS-7: one with 40*40m loop and another with 114*114m loop 2001-10-26 One TDEM with 40*40m loop at MRS-8 2001-10-27 One TDEM with 40*40m loop at BH9475 2001-10-30 Three TDEM: one 40*40m at two (40*40m and 114*114) at BH8815 *At some sites, existing TDEM was used. The TDEM data was used in the computation of the matrix files which is one of the input files incorporated into the inversion software in addition to the MRS data files (the observed MRS response).

5.2. Data Inversion The MRS data is made of 3 types of data; a mini sounding data set carried out to adjust the system accordingly, the main sounding data set and repeat sections attempting to improve the data quality or reliability of portions of the main sounding. The data set that was received for inversion was already edited and ready for use. The matrix files were provided as already computed and the data inversion was done using the Nu- misPlus software with Samovar Program of Automatic Inversion of the Surface Nuclear Resonance

36 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Sounding, version 4.04 developed by Anatoly Legchenko, BRGM, France (2001). Graphic plots are given in appendix 3a, whereas the Table 5-3 below gives a digital summary of the inversion results from a continuous model.

Table 5-3:Summaries of MRS Inversion Results

Range of free Range of Decay Site ID W ater bearing layer Depth (m) water content rate, T * (ms) (%) 2 Vadose 0 - 13.5 0 - 2 54 - 69 BH8262-5-1 Saturated 13.5 - 49.5 6 -18 86 - 120 Vadose 0 - 1 - - BH8114-11-12 Saturated 1 1 - 20.2 8 - 42 67 - 100 Saturated 2 42.9 - 90 4 - 50 101 - 133 PMP8348-13-3B Saturated 0 œ 71.2 1 - 15 150 - 605 Vadose zone 0 - 5 < 1 BH8351-2-10 Saturated 5 œ 52.5 7 - 25 150 - 400 Vadose 0 œ 8.4 - - BH8815-12-13 Saturated 8.4 œ 71.2 2 - 11 111 - 370 Vadose 0 -5 < 1 58 - 216 BH9503-3-11 Saturated 5 œ 71.2 1 - 13 126 - 547 Vadose 0 œ 8.4 - - MRS-7-5 Saturated 8.4 œ 71.1 2 - 10 57 - 320

BH9475-10-7 Saturated 0 - 60 5 - 37 164 - 305

TH3-8-6 Saturated 0 œ 38.7 2 - 16 140 - 260 Vadose 0 œ 11.4 - - TT16-4-2 Saturated 1 11.4 œ 28.6 2 -7 84 -154 Saturated 2 38.7 œ 96.6 3 - 6 63 - 74 Vadose 0 œ 6.2 <1 80 - 231 TT3-1-9B Saturated 6.2 œ 71.2 2 œ 27 130 - 392 Saturated 1 0 - 4 4 - 14 61 - 74 TT2-9-8A Saturated 2 15.5 œ 52.2 2 œ 7 140 - 139 Vadose 0 - 3 0.5 - 2 77 -140 WBH8348-6-4A Saturated 1 5.1 œ 13.5 1 - 5 111 - 295 Saturated 2 18.6 œ 94.6 3 - 5 122 - 347

5.2.1. Estimates of Permeability ki, Hydraulic Conductivity K and Transmissivity T Permeability or intrinsic permeability as defined in Chapter 4, Section 4.4.4 is a measure of the relative ease with which a porous medium can transmit a liquid under a potential gradient (Keys and MacCary, 1985). In NMR logging, Kenyon, (1997) hydraulic conductivity estimation is based on the form, a b K = Cpa MRS T 1(2) (5.1) where aMRS is the porosity estimated by NMR

T1 or T2 is the relaxation time

37 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Cp is an empirical pre-factor. In this study a = 4; and b = 2 that gives a better results for sandstone as reported by Kenyon, (1989) in

Legchenko, (2002) and T2* provided by the MRS instrument are used. Transmissivity as mentioned in earlier chapters is the product of the hydraulic conductivity K and thickness D. In MRS transmissivity is estimated as T2* 2

TMRS1 = Cp1 ∫D 9MRS (T2*) ¡ D (5.2) And T2* 4 2

TMRS2 = Cp2 ∫D 9MRS (T2*) ¡ D (5.3) Where T2* T2* Cp1 and Cp2 are empirical pre-factors. N ƒTi-bh i=1 Cp = N (5.4) ƒ Fi i=1 Where

Ti-bh transmissivity given by pumping test in borehole i a b

Fi = ∫b w (T2*) ¡ D (5.5) The pre-factor used in this study was determined using pumping test transmissivities from 10 boreholes in the MRS tested area using equation 5.4 and the calculations are given in appendix 3b. Table 5-4 presents the calculated transmissivities.

Table 5-4:MRS Determined Transmissivities

H T * D H4 (T *)2 H4 (T *)2D T T T T MRS Site MRS 2 2 2 K [m/s] PT PT MRS MRS % [s] [m] [s2] [s2m] [m2/s] [m2/d] [m2/s] [m2/d] BH 8262-5-1 13.42 0.11 36 3.92E-06 0.000141 1.98E-06 0.000613 53 7.12E-05 6.15 BH 8114-11-12 29.73 0.10 33 7.81E-05 0.002578 3.94E-05 0.000139 12 1.30E-03 112 PMP8348-13-3B 7.4 0.25 71.2 1.87E-06 0.000133 9.44E-07 0.000313 27 6.72E-05 5.81 BH 8351-2-10 12.87 0.25 47.5 1.71E-05 0.000814 8.64E-06 0.000379 32.73 4.10E-04 35.5 BH 8815-12-13 6.33 0.19 62.8 5.80E-07 3.64E-05 2.92E-07 0.000142 12.74 1.83E-05 1.58 BH 9503-3-11 6.35 0.28 66.2 1.27E-06 8.44E-05 6.42E-07 4.63E-05 4 4.25E-05 3.67 MRS- 7-5 6.56 0.19 62.7 6.68E-07 4.19E-05 3.37E-07 0.000289 25 2.11E-05 1.82 TH3-8-6 8.2 0.26 38.7 3.40E-06 0.000131 1.71E-06 6.94E-05 6 6.63E-05 5.72 TT16-4-2 4.57 0.10 37.9 4.36E-08 1.65E-06 2.20E-08 0.000167 14.4 8.33E-07 0.072 TT3-1-9B 12.02 0.27 65 1.52E-05 0.000989 7.67E-06 0.000338 29.2 4.98E-04 43.10

CP = 0.503814

5.3. Constraints and Limitations of MRS Data Acquisition

5.3.1. Effect of Electrical Conductivity of the Subsurface Material The effect of electrical conductivity was not that prevalent in the tested area although the inversion results are deemed good only to depths of up to about 50-60 m.b.g.l and below that the hydrostratigraphic information becomes less reliable and often unreadable, Lubzcynski and Roy (2003)

38 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

5.3.2. Effect of Magnetic Inhomogenity due to Ferrous Minerals The measurement of the magnetic susceptibility on the Maun sample was also made using Magnetic susceptibility meter and the results are presented below in Table 5-5. According to values, this gave no problem to data acquisition.

Table 5-5:Magnetic Susceptibility Measurements

Sample Description Depth (m) Magnetic Susceptibility [SI units TT2-9-8A 37 0.044 X 10-3 TT2-9-8A 33,34 0.026 X 10-3 WBH8348-6-4A 47 0.043 X 10-3

5.3.3. Signal to Noise Ratio, (S/N) The MRS signal to noise ratio are dependent on both natural and artificial factors, but the influence of these factors affect the MRS results differently hence remedial conditions should be as according to the location if any. In the Maun case data was acquired during the late night / early morning times since a problem of high noise levels was observed during the day. The signal as observed from the data collected in the nights was good, refer to individual plots appendix 3a.

39 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

6. Other Geophysical Methods

6.1. TDEM As already discussed in the previous chapter, the time domain electromagnetic (TDEM) data was used in the computation of the matrix files which is one of the input files incorporated into the inversion software in addition to the MRS data files. TDEM yields information on the electrical conductivity of subsurface (resistivity of the subsurface layers and their thickness) and further this data provides information on the salinity of the subsurface. It is already known that the electric conductivity greatly attenuates the MRS signal, hence information from TDEM is very important when dealing with MRS data. TDEM plots presented together with MRS graphics clearly show that beyond 80 m.b.g.l in the Maun area, brackish conditions start creeping in and saline conditions prevail at deeper depths. Table 6-1presents the conductivity and resistivities of various aqueous solutions and this will help in regard the subsurface condition that is detrimental to the limitations and constraints of the method as clearly indicated in Chapter 5.3. The TDEM values for 13 boreholes in the study area can be found in the matrix files.

Table 6-1:Conductivity of Various Aqueous Solutions at 250C

Component Conductivity Resistivity Pure water 0.05 WS/cm 200 000 Y-m Power plant boiler water 0.05 œ 1 WS/cm 10 000 œ 200 000 Y-m Distilled water 0.5 WS/cm 20 000 Y-m Deionized water 0.1 œ 10 WS/cm 1000 œ 100 000 Y-m Demineralized water 1 œ 80 WS/cm 125 œ 10 000 Y-m Mountain water 10 WS/cm 1000 Y-m Drinking water 0.5 œ1 mS/cm 10 œ 20 Y-m Wastewater 0.9 œ 9 mS/cm 1 œ 10 Y-m KCL solution (0.01M) 1.4 mS/cm 7 Y-m Potable water maximum 1.5 mS/cm 7 Y-m Brackish water 1 œ 80 mS/cm 0.1 - 10 Y-m Industrial process water 7 œ 140 mS/cm 0.07 œ 1.4 Y-m Ocean water 53 mS/cm 0.19 Y-m 10% NaOH 355 mS/cm 0.028 Y-m

10% H2S04 432 mS/cm 0.023 Y-m

31% HNO3 865 mS/cm 0.011 Y-m (After Eijkelkamp Conductivity Cell Guide, 1997)

6.2. Borehole Geophysical Logging Borehole geophysical logging in groundwater resources assessment is usually carried out to identify and differentiate lithological units, sand thickness and water quality variation with depth. It provides

40 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

more information for better hydrogeological conceptualisation in terms of aquifer geometry and therefore provides more complementary information in the verification of the Magnetic Resonance sounding results, which is the current study. The section provides the results of borehole natural gamma logging work conducted in the MRS tested boreholes. Water Resources Consultants (WRC) provided borehole-logging data. The logging data was acquired using a GEOTRONTM R400 logging unit for Natural Gamma (N) in counts per second (cps) units measured at 0.10m intervals and this was the only data available although the use of other parameters like Resistivity (RES) in Ohm-meters in the lateral (3“ and 30“) configuration and Spontaneous-Potential (SP) in millivolts (mV) would have provided a more complete picture of the subsurface. Figure 6-1 shows one of the geophysical logging plots together with the interpreted litho logs. Other natural gamma plots are given in appendix 4.

Geophysical Log BH9598/9599 (Site: MRS-7-5)

Borehole Log BH9599 Borehole Log BH9598 Natural gamma (cps) Interpreted Litholog (Bh 9598) 0 10 20 30 40 50

0 0 Sand with clay Light brown fine Tan sandy clay clayey sand Sand Sand with c;ay 10 10 Brown very fine sand Sand

Sand with clay Brown fine Brown silty sand sand 20 Brown clayey sand 20 Sand Brown sandy clay Grey clay Clay Brown fine to very fine sand Brown very Sand 30 fine sand 30

Sand with clay Green clay Brown silty sand

) Brown very fine

m Sand

( clayey sand

h Light green sandy Tan clayey sand t 40 40

p clay Tan sandy clay

e Brown fine to very

D fine clayey sand Brown silty/clyey sand Light green siltstone Sand with clay Brown very fine sand 50 Brown very fine 50 sand Green fine to very fine sand Light green very Sand fine sand Green silcrete Sand with clay 60 60 Green silty sand Clay Green silty mudstone Sand with clay Sand 70 Green fine sand 70 Sand with clay

80 80

SWL = 13.54m SWL = 13.50m Yield = 12m3/hr Yield = 2m3/hr EC = 1400mS/cm EC = 11620mS/cm EOH = 59m Screen = 25-34, 37-40m Screen = 25.4-37, 48.30-57m EOH = 75m

Water bearing layer

Figure 6-1:Natural gamma plot with Interpreted log and 2 observed borehole logs

41 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Natural Gamma Logs are used in borehole lithological interpretations and in lithostratigraphic correla- tions. The logs are effective in delineating sands, silts and clay horizons, Figure 6.1 above. The tool comprises of a Sodium-Iodide (NaI) crystal, which counts natural gamma radiation originating from Potassium-40 Isotope, Uranium and Thorium occurring in shales and clays. In principle a probe that encloses a NaI crystal is lowered in a borehole and measurements are taken whilst moving the probe in an up ward direction inside the hole. The measured gamma counts per second (cps) units are then plotted against the borehole depth. An analysis of the plot is then made and interpreted lithological log made. In natural gamma logging the volume sampled is about 0.5m3 of the rock surrounding the detector at each measurement (i.e. 10 to 30cm radius depending on the rock density), http://borehole.gsc.nrcan.ca/gamma_e.html (2003). Interpretation of the logs was based on literature review work, lecture notes handout and some personal discussions with lecturers. As already mentioned above the interpretation of natural gamma logs yielded information on depth to different lithologic boundaries. In particular three units were clearly distinguished, the clean sands horizons, the interbedded sand, clays/silt and the silcretes. The clean sand was interpreted as having lower gamma counts e.g <10 cps, interbedded sand, clay/silt with moderate gamma counts clays, silcretes to have higher gamma counts.

42 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

7. Hydrogeological Methods

This chapter discusses the hydrogeological data that was used for the verification of MRS soundings. Section 7.1 provides the laboratory analysis that has been conducted on the rock samples obtained from the drilling of borehole BH10117, which is one of the MRS tested sites. BH10118 was dry. Sec- tion 7.2 deals with the pumping test. The drilling of the boreholes has been presented briefly in this chapter. Drilling data provides information on aquifer geometry (top and bottom of the saturated zones), depth of the vadose zone, borehole lithologies, water strikes, water quality stratification; estimates on yield, water rest levels and to a certain extend information on the type of aquifer which is discussed in Section 7.2. Samples for sieve analysis are also obtained from the drilling. All the drilling data are very important in the comparison with the MRS data inversion results. The drilling results from 11 MRS tested boreholes were provided by Water Resources Consultants, (WRC) while the results for two other boreholes were provided by DWA. The drilling results are presented in appendix 5 and the graphic representations are given together with the geophysical logs and some with MRS Inversion plots in appendix 3a. It is however worthy mentioning that the drilling was carried out using reverse circulation mud rotary method. In this type of drilling the drilling fluid flows from the mud pit down the borehole outside the drill rods, then passes upward through the bit into the drill rods after entraining the cuttings, Driscol (1995). After flowing through the swivel and mud pump, it passes into the mud pit where the cuttings settle out. The method was used because of the collapsible nature of the clays and fine sands. Though the porosity and permeability of the formation is relatively undisturbed near the borehole as compared to other methods, proper identification of materials are problematic in that there is a problem of formation contamination. Suspended clay and silt that recirculate with the fluid are mostly fine materials picked from the formations as drilling proceeds. Further, water strikes are not easily recognizable as in the method the drilling fluid can be described as muddy water.

7.1. Laboratory Analysis Laboratory analysis is based on rock samples obtained from one of the borehole where MRS soundings were conducted and the samples represent a depth interval around 37 m.b.g.l. of the aquifer material. Furthermore some sieve analysis results were provided by WRC. Grain size of the aquifer units is reported to be of extremely uniform (coefficient of uniformity in the range of 1.9 to 2.3), Linn and Masie (2000).

7.1.1. Sieve Analysis Sieve analysis pertains to grain-size analysis and also known as particle-size analysis or granulometric analysis is the most basic sedimentological technique to characterize and interpret sediments, as is the case with the Maun aquifers that mainly comprise of fine sands, sandy clay, clay sand, silcretes and calcretes. Keys and MacCary (1985) states that the importance of grain size in analysing the hydrologic characteristics of a rock can be seen from its effect on permeability, porosity and specific yield. A fairly consistent increase in permeability has been shown with increase in grain size; hence infor-

43 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

mation obtained from the analysis results will further strengthen the argument herein stipulated in this report. The sample analysed was collected from a depth of 37 m.b.g.l. at BH10117, MRS site TT2-9-8A. Measurements carried out were by means of sieving of the sand fractions. Table 7-1 presents sieve analysis results. Total weight of sample was 540.6g

Table 7-1:Sieve Analysis Results

Sieve Size (mm) W eight (g) % >0.5 7 1.29 0.25-0.5 184.4 34.11 0.10-0.25 317.7 58.77 0.05-0.10 18.4 3.40 <0.05 8.1 1.49

From the table above the sample mainly uniform and fine grained material. A microscopic analysis of the sample was also done. The sand mainly composed of very shiny transparent, extremely rounded and smooth quartz grains, some fragments of greyish white quartzite material, and some whitish feld- spar grains. Some woody material was also noticed in the sample, suggesting contamination either due to the drilling or handling.

7.1.2. Hydraulic Conductivity, K Hydraulic Conductivity (K) with dimensions of length/time (L/T) or velocity is defined as the volume of water that will move through an aquifer in unit time under a unit hydraulic gradient through a unit area at right angles to the direction of flow. Permeability or intrinsic permeability as defined in Chap- ter 4, Section 4.4.4 is a measure of the relative ease with which a porous medium can transmit a liquid under a potential gradient, Keys and MacCary (1985). This aquifer parameter as defined above is rep- resentative of the porous medium alone. It depends on size of openings, degree of interconnection, and amount of open space. It thus depends on grain size and sorting hence coarse grained and well- sorted sediments have higher permeabilities. The relation below relates it to hydraulic conductivity as given in Darcy‘s law;

K = ki (Z/W) = ki (bg/W) (7.1) Where b is fluid density and W is fluid dynamic viscosity. K is the hydraulic conductivity 2 ki is the permeability (m or Darcy) 1 Darcy = 9.87 x 10-9 cm2 Fluid density and viscosity and density depend on temperature, salinity and pressure. This parameter was measured directly with a permeameter using the constant head method, Figure 7-1. It should however be clear that laboratory samples are extremely small compared to the aquifer as a whole. Fur- thermore, some degree of disturbance always accompanies the collection of samples and for these rea- sons it is difficult to conclude on the character of an aquifer based on these tests. Table 7-2 presents the results of the experiment.

44 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Figure 7-1 :Determining Hydraulic Conductivity with a Permeameter.

Table 7-2:Constant head method measurements of volume versus time

Time (min) Volume (cm3) 0 0 1 1.1 2 2.1 3 3.2 4 4.3 5 5.5 6 6.7 7 8.0 8 8.9 9 10.1 10 11.3 11 12.3 12 13.4 13 14.5 14 15.6 15 16.7

A plot of volume in cubic centimetres as a function of time was made to determine slope (V/t) and Figure 7-2 below shows the plot of V versus time. From Darcy‘s law

45 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Q = K A dh/dl (7.2) V/t = KA ∆h/L (7.3) K = VL/At∆h (7.4) From equation 7.4, the hydraulic conductivity was found to be 0.81 m/d for sand unit of the aquifer.

20 )

3 15 m c (

e 10 m u

l y = 1.1225x - 0.0625 o

v 5 R2 = 0.9997 0 0 5 10 15 20 time (min)

Figure 7-2: Plot of volume (cm3) versus time

7.1.3. Porosity The porosity : is the percentage of rock or soil that is void of solid material. Keys and MacCary (1985) defines porosity as the ratio of void volume of porous medium to the total volume and is generally expressed as a percentage. Usually in sediments, porosity that is split into total and effective porosity cannot be easily distinguished hence they are nearly the same and in actual fact are taken to be the same. The weight of a soil sample was saturated and then dried and the volume of the original sample was determined. The porosity was then computed using equation 7.5 below.

Porosity : = 100 (1 - (bb/bd) (7.5) Where 0 bb is bulk density of the material, which is the mass of the sample after oven drying (105 C) divided by the original sample volume (Fetter, 2001). 3 3 bd is particle density of the material. The value of the particle density used is 2.65 g/cm (2650 kg/m ) given in Fetter (2001). The results are presented below. Weight cylinder + saturated sand = 235.82g Weight of dry sand + cylinder = 205.54g Cylinder weight = 92.60g Weight of saturated sand = 143.22 Weight of dry sand = 112.94g Cylinder diameter = 5cm Cylinder height = 5cm Volume of original sample = [ r2 h = 79.52cm3 3 bb = 112.94/79.52 = 1.4203g/cm Porosity = 46.40%

46 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

7.1.4. Specific Retention / Field Capacity The specific retention was estimated using the equation 4.7, where the specific yield value of 12% was obtained from pumping test results. The value for the specific retention obtained Sr = 34.4% and has been applied to determine the MRS specific yield.

7.2. Pumping Test Pumping tests of boreholes are tests carried to acquire information on borehole hydraulic parameters (well losses and percent laminar flow) and aquifer hydraulic parameters (transmissivity and storage). The tests comprise of a calibration test, a step drawdown test, a constant rate test and a recovery test. As it was mentioned in the introductory chapter that an evaluation of all pumping test data of the MRS tested boreholes will be made, this chapter however attempt to look at all the pumping test data to determine the aquifer characteristic (transmissivity, hydraulic conductivity and storage parameters) of the Kalahari sediment aquifers of the study area. A brief overview of the pumping test theory mod- els for the analytical solutions used for the interpretation of the pumping test data is also provided in the chapter, refer to User‘s Manual for Aquifer Test by Rohrich (1992), Driscol (1995) and Fetter (2001). In the constant rate test analysis the pumping boreholes allowed for the calculation of transmissivities only while in the observation boreholes both transmissivity and storativity were determined. Specific yield values were obtained from the Neuman method in addition to the transmissivity and storativity. The recovery data was interpreted using the Thies recovery method and this provided trasnsmissivity values only. The methods used were chosen on the basis of their suitability for unconfined and semi-confined conditions within the area.

7.2.1. The Principle of Pump Test The principle of a pump test is that if water is pumped from a well and the discharge is measured along with the drawdown in the pump well and a piezometer (of known distance from the pump well) and by substituting this data into flow equations the aquifer hydraulic parameters can be determined.

7.2.1.1. Aquifer Hydraulic Parameters It has already been explained in section 7.2 introduction that aquifer hydraulic parameters as determined from the constant rate test refers to transmissivity (T), the hydraulic conductivity (K) and storage (S) which is of two types, confined storage (storativity) and unconfined storage (specific yield). This section was provided in an attempt to try and explain some terms that are often used but not well understood to some users both familiar and not familiar to them. Hydraulic Conductivity (K) with dimensions of length/time (L/T) or velocity is defined as the volume of water that will move through an aquifer in unit time under a unit hydraulic gradient through a unit area at right angles to the direction of flow. It is a function of both the porous medium and the fluid passing through it and it is a proportionality constant in Darcy‘s Law expressed in general terms as equation 7.2 above. and rearranging the equation it becomes: K = -Q / A (dh / dl) (7.6) Where; Q = Discharge in volume/time (L3/T) A = Cross sectional area (L2) dh/dl = Hydraulic gradient (L/L)

47 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

This term is used in other works as the coefficient of permeability (Fetter (2001) as was explained earlier in chapter 4, section 4.5.4. Transmissivity (T) in L2/T is defined as the product of the average hydraulic gradient (K) and the saturated thickness D or other words it is the measure of the amount of water that can be transmitted horizontally through a unit width by the full saturated thickness of the aquifer under a unit hydraulic gradient (Fetter, 2001) and it is given by the following equation: T = DK (7.7) Where; T = Transmissivity (m2/d, m2/sec) D = Saturated thickness of the aquifer (m) K = Hydraulic conductivity (m/d) Storage coefficient or storativity (dimensionless) is the volume of water that a permeable unit will absorb or expel from storage per unit surface area per unit change in head, (Fetter, 2001). In a confined aquifer the storativity (Sc) is volume of water released from storage per unit surface area of the aquifer per unit decline in the hydraulic head. It is also referred to as elastic storage (Se) as it is the product of specific storage (Ss) and the aquifer thickness (D):

Sc = D *Ss. (7.8) It should be clear that under confined conditions (overlain by confining layers) water is held in pore spaces under pressure and as it is removed it expands.

The specific storage (Ss) as has been described earlier in chapter 4, section 4.5.1 is the elastic storage coefficient defined as the amount of water per unit volume of saturated formation that is stored or expelled from storage owing to compressibility of the mineral skeleton and the pore water per unit change in head (Fetter, 2001).

Ss = bw*g (c + : d) (7.9)

In unconfined conditions (connected to the surface) specific yield (Sy) is often used for the storage component and is the volume of water an aquifer releases from storage per unit surface area per decline in water table. Water is released due to gravity rather than pressure release effects. As explained earlier the storativity for the unconfined is given by:

S = Sy + DSs (7.10) Where (D) is the thickness of the saturated zone.

However the value of Sy is usually several magnitudes greater than the value of DSs and as a result the storativity for unconfined aquifer is equal to the specific yield. The yield refers to the water abstraction rate or the discharge rate at which a borehole or a well will safely supply when pumped. It is the recommended pumping rate usually determined from the step test and used to run a constant rate test in a pumping test exercise.

7.2.1.2. Neuman Method (Unconfined) The Neuman method (1975) represents drawdown in an unconfined aquifer and it is expressed as:

S = Q / 4[ T * W ( uA, uB, d ) (7.11) Where:

W ( uA, uB, d ) is the unconfined well function 2 uA = r S / 4Tt (Type A curve for early time) 2 uB = r Sy / 4Tt (Type B curve for later time) 2 2 d = r Kv / b Kh

48 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

r = distance of observation well t = time

Kv = vertical hydraulic conductivity

Kh = horizontal hydraulic conductivity The above equation shows that a well pumping water from unconfined aquifers releases water from elastic storage as with the Thies curve for early time and a later drawdown data when the effects of gravity drainage become more significant.

7.2.1.3. Hantush Method (leaky, without aquitard storage) The flow equation for a confined aquifer with leakage takes the following form:

2 2 2

¡ ¡ ¡ ¡ ¡ h / r + 1 h / r ∂r œ HK‘/TD‘ = S h / T t (7.12) Where: K‘ is the vertical hydraulic conductivity of the leaky aquifer D‘ is the thickness of the leaky aquitard. The Hantush and Jacob (1955) solution to the above equation is given by: Ñ S = Q / 4[ T —1/ exp(-y - r 2 - L2 y)ïy (7.13) u Where: S = Q / 4 [ t W (u, r/L) (7.14) u = r2S / 4[ T (7.15) A log/log scale plot of the relationship W(u, r/L) along the y axis versus 1/u along the x axis is used as the type curve as with Thies method. The field measurements are plotted as t along the x-axis and s along the y-axis. Curve matching does the data analysis.

7.2.1.4. Theis and Jacob Recovery Test (Confined) Where observation well data is not available, it is necessary to sometimes estimate aquifer properties with only a pumping well. This is done by measuring the recovery of the water level in the well after the pump has been shut down. The drawdown is plotted on the logarithmic y-axis and time is plotted on the linear x-axis as the ratio of t/t‘ (total time since pumping began divided by the time since the pumping ceased). According to Thies (1935), the residual drawdown after pumping has ceased is: s‘ = Q/ 4[ T W(u) œ W(u‘) (7.16) Where: u = r2S / 4Tt‘ (7.17) u‘ = r2S‘ / 4Tt‘ (7.18) S and S‘ are the storativity values during pumping and recovery pumping respectively and t and t‘ are the elapsed times from the start and ending of pumping respectively. Using the approximation for the well function in Copper and Jacob method, this equation becomes: s‘ = Q / 4[ t (ln 4Tt /r2S œ ln 4Tt‘/r2S‘) (7.19) Where S and S‘ are constant and equal and T is constant, this equation reduced to: s‘ = 2.3Q / 4[ T log (t/t‘) (7.20) s‘ is then plotted on the logarithmic y-axis and time is plotted on the linear x-axis as the ratio of t/t‘ (total time since pumping began divided by the time since the pumping ceased).

49 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

7.2.2. Constant Rate Test and Recovery Test Results The constant rate test and recovery test results were analysed using Aquitest, version 2.5. The results are summarised in Table 7-3 below. The pumping test data is presented in appendix 6. The results show transmissivity values ranging from 0.97 m2/d to 45.7 m2/d for the pumping boreholes. The observation boreholes gave transmissivity values ranging form 2.55 m2/d to 674 m2/d. The storativity values ranges from 0.0000002 to 0.057. The specific yield values ranged from 0.0021 to 0.13. Recov- ery gave T values between 3.38m2/d and 40.9 m2/d.

50 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Table 7-3: SUMMARY CONSTANT RATE TEST RESULTS FOR MRS TESTED SITES

BH NO Pump CRT SW L Q Q Pumping BH Observation BH Intake Duration (m) (m3/hr) (m3/d) T (m2/d) CRT Rec Obs Dist (m) (Hrs) CRT Recovery T T BH (m) S Sy (m2/d) (m2/d) 8262 29.45 72 12.29 12 288 58 53 N/A 8114 19.41 72 6.05 7.5 155 2.46 12 N/A 10 N 636 N 8348 45.6 420 12.50 22 527 27 8347 40 0.0035 0.005 40.9 14.2H 567 H 8351 42.65 72 11.60 35 840 31.82 32.73 8350 35.5 34 H 0.00018 36.92 2.16 N 8815 48.5 48 13.46 5 120 12.1 N/A N/A 2.36 H 5.81 N 0.000013 9590 24 12.53 1.8 43 4 4 9503 9.2 0.13 16.6 5.81 H 0.0013 27 N. 38.2 N 0.00095 9599 45.6 72 12.7 12 288 25 9598 11.25 0.11 38.7 31 H. 38.2 H 0.00067 0.000000 3.6 N 9601 11.20 3 0.008 3.38 0.97 N 2.55 H 9600 24 2.67 2.5 60 6 0.0063 1.94 H 12.8 N 0.000012 9475 12.4 0.12 5.34 6.42 H 0.00052 0.000000 4 N 40.8 N 9604 24 9.87 5.1 122 14.4 9603 11.6 2 0.0021 36 6.43 40.8 H 0.0017 9608 24 12.37 2 48 9607 9.7 2.56 N 427 N 0.00001 9683 52.80 72 17.58 20 480 29.2 9682 11.25 0.11 2.56 H 479 H 0.054 N = Neuman method H = Hantush method Screened intervals (refer to appendix 5 BH 10118 was dry.

51 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

8. Hydrogeological Verification of MRS Soundings

This is the main chapter of the thesis where a comparison of hydrogeological data i.e. borehole lithologs, TDEM plots, geophysical plots, water table depth, saturated thickness etc and information obtained from the inversion of MRS soundings like free water content and the decay time are directly correlated to see if the two data sets compliment each other. Section 8.1 clearly attempts to correlate the two data sets on borehole-by-borehole bases and section 8.2 discusses the integration of hydrogeological and MRS data. It is however, worthy reviewing a few of some of the issues already discussed in detail from the above chapters as this will help the reader get a better visualisation/conceptualisation of the descriptions herewith given in the sections below. The fresh water shallow unconfined and semi-confined Kalahari bed aquifer comprised of fine to medium grained sand and leaky confining layers of clays, sandy silts and clays is the most important source of fresh water in the area. These fresh water zones have clearly been identified (follows river channels and areas of seasonal floods), refer to Masedi (2002) and that the challenge is now to locate the fresh extractable water. The MRS sounding (i.e. NMR response as a function of excitation moment Q) is from the signal amplitude, the quantity of free water 9MRS as a function of depth able to provide a good estimate of effective porosity :e of the saturated water-bearing layer below the groundwater table, the groundwater table (GWT), storage parameters, thickness of the saturated water bearing layers (aquifer geometry) and the quantity of water in the vadoze zone and its depth. Lubczynski and Roy (2003) further states that there is no universal and unique recipe to mark the position of groundwater table using a combination of aMRS and the relaxation time and currently the derived information depends on field hydrogeological data available. However, the groundwater table is often determined in unconfined aquifers (see Figure 8-1).

Characterization of the host media, pore-size through the NMR signal decay time (Td) usually measured as T2* as a function of depth as this parameter can supply reliable estimates of flow parameters like permeability (ki), hydraulic conductivity (K) and transmissivity (T) wherever hydrogeological conditions are known and /or appropriate calibration have been made, Roy and Lubczynski (2000a). MRS investigation refers to large investigated volumes, usually in a range of several thousand m3 (up to ~106 m3) of subsurface media according to the loop and excitation value used (Lubczynski and Roy, 2003b). In natural gamma logging the volume sampled is about 0.5m3 of the rock surrounding the detector at each measurement (i.e. 10 to 30cm radius depending on the rock density). Such other factors as the drilling method should be taken into consideration when defining the saturated zones, the groundwater table depths and the unsaturated zone depth, (personal communication with WRC personnel). The sieve analysis results provided and presented by WRC of the main sand units are presented as obtained from their MGDP review report.

52 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

8.1. Site Specific Hydrogeological Verification of MRS Soundings The hydrogeological verification of the MRS sounding was done on borehole-by-borehole basis.

8.1.1. BH 8262

BH8262 Date: 23-10-01 Site: BH8262-5-1 Square Loop = 114m Processing window =100ms Smoothing = 500 Average S/N = 9 Filter bandwith = 10 Hz

Free water content Decay time TDEM (ohm-m) Natural gamma (cps) Litholog (%) (ms) 0 10 20 30 40 10 100 1000 0.1 1 10 100 0 80 160 0 0 Dark grey clay 10 10 Tan fine sand

Tan fine sand interlayered 20 20 with green clay White fine sand 30 30 White fine to medium sand

40 40 Tan fine to medium sand interlayered with green clay

) 50 50 Fine to medium sand m (

h t

p Green sandy clay

e 60 60 D Olive green fine to medium 70 70 sand interlayered with siltstone

Screens 80 80 SWL = 12.29m Yield = 12m3/hr 90 90 EC = 660 mg/l Screen = 30-36m 51-54m 100 100 61-64m TDS = 422mg/l EOH = 73m 110 110 Saturated zone

2 TC RT = 53m /d 2 TR ec = 53m /d

Figure 8-1: Comparison of MRS Inversion results with observed hydrogeological information for borehole BH 8262. Borehole Bh 8262 was collared in the Kalahari sediments. The unsaturated zone is estimated to about 12mbgl and comprises dark grey clay to 10 m.b.g.l. From 10 to 15 m.b.g.l., drilling intersected fine sand followed by fine sand interlayered with green clay from 15 to 22 m.b.g.l. and then white fine sand to 27 m.b.g.l. Fine to medium sand is intersected up to 57 m.b.g.l (fine to medium sand interlayered with clay occurring at 39 to 44 m.b.g.l) and then green sandy clay to 61 m.b.g.l. The hole terminates in fine to medium sand interlayered with silcrete at 73 m.b.g.l, (EOH œ end of hole). The static water level is at 12.29 m.b.g.l and the yield as obtained from the pumping test record is 12 m3/hr. The saturated zone is estimated from about 12 m.b.g.l to end of the hole. From MRS inversion results, Figure 8-1 the groundwater table is estimated at 13.5 m.b.g.l and the saturated zone occurs from that depth to about 50 m.b.g.l. The water content ranges from 6 to 18% with a decay time of roughly 86 to 120 ms, the highly permeable zone at about 18 to 30 m.b.g.l. In any standards the two data sets are in

53 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

agreement with each other. The TDEM shows fresh water conditions to about 70 m.b.g.l. Further the natural gamma log correlate well with the litholog.

8.1.2. BH 8114

B H 8114 Coordinates: x = 763255 Dat e:29-10-01 y = 7796006 Sit e: BH 8114-11-12 Sq uare eigh t lo op, L=57m Proces sing windo w = 200m s Sm oot hing = 5 00 Average S/N = 6 Filter bandwi dth = 10 Hz

Free water content (%) Decay time (ms) TDEM (ohm-m) Litholog 0 10 20 30 40 50 60 10 100 1000 1 10 100

0 0 Black clay

10 10 White fine sand

20 20 Coarse sand with green clay Silty sand Fine sand 30 30 interbedded with silcrete

Screens ) 40 40 m

( SWL = 6.05m 3

h Yield = 7.5m /hr t

p EC = 140mS/cm e 50 Screen = 19-28m

D 50 EOH = 29.5m

60 Saturated zone 60 2 TC R T = 2.46m /d T = 12m2/d 70 R ec 70

80 80

90 90

Figure 8-2: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH 8114 This borehole, Figure 8-2 was drilled through black clayey soil to 1 m.b.g.l. and then penetrated white fine sand, clean and well rounded to 22 m.b.g.l. Drilling then proceeded into very coarse sand mixed with green clay to 23 m.b.g.l, followed by silty sand from 23 to 26 m.b.g.l. The borehole was terminated in very fine sand interbedded with silcrete at 29.5 m.b.g.l. The static water level was measured at 6.05 m.b.g.l and the yield obtained from pumping test was 7.5 m3/hr. The water-bearing layer is estimated from about 6.05 m.b.g.l to 29.5 m.b.g.l. From MRS the % free water content starts from 1 m.b.g.l to 20 m.b.g.l. and ranges from about 8 to 42%. This shallow water-bearing zone has a decay time ranging from 67 to 100 ms. From 20.2 m.b.g.l to about 51 m.b.g.l. MRS indicates a dry layer and below that depth another layer with % free water content of up to 50% at 90 m depth and decay time ranging from 101-129 ms. Although MRS shows some free water below the depth of about 50 m.b.g.l., drilling was terminated at a shallower depth hence it was not possible to make a correlation beyond 30 m.b.g.l. However consistent with the fact that reliability of the data diminishes with depth, Lubczynski and Roy (2003) this information is henceforth questionable. Transmissivity values of 2.46 m2/d and 12 m2/d were obtained for the constant rate test and the recovery test. At this borehole site

54 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

however it was not possible to correlate groundwater table although the other factors were well in agreement. TDEM shows fresh water conditions to about 53 m.b.g.l.

8.1.3. BH 8348

BH8348 Coordinates: x = 768811.08 Date:30-10-01 Site:PMP8348-13-3B y = 7802494.58 Square Loop, L=114m Processing window = 200ms Smoothing = 500 Average S/N = 9 Filter bandwitdh = 10Hz

Free water content (%) Decay time (ms) TDEM (ohm-m) Natural gamma Litholog (cps) 0 10 20 10 100 1000 1 10 100 0 40 80 120 0 0 White well sorted sand 10 10 Brown sandy clay interlayered with green friable silcrete Tan / white fine 20 20 to medium sand Cemented sand and coarse quartz 30 30 Fine to medium sand Mixed sample:silcrete,coarse 40 40 quartz and sand Green fine to medium ) 50 50 slightly silty sand m ( Green soft clay/ clatstone h t

p interlayered with sand e 60 60 D 70 70 Green predominantly fine to medium sand with claystone 80 80

90 90 SWL = 12.50m Yield = 22m3/hr 100 Screens = 47-76m 100 EOH = 81mE EC= 1300m S/cm 110 110 Saturated zone Pumping BH 2 TCR T = 41.8m /d 2 Screens TRec = 27m /d Observation BH 8347 (r = 40m) 2 TCR T = 39.7m /d 2 TRec = 40.9m /d S = 0.0035

Sy = 0.005

Figure 8-3: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH 8348 This borehole, Figure 8-3 went through 7 m of white well-sorted sand and then brown sandy clay interlayered with friable silcrete from 7-16 m.b.g.l. Fine to medium sand with fine to medium quartz was intersected from 16-39 m.b.g.l, mixed silcrete, coarse quartz and sand at 39-40 m.b.g.l., fine to medium slightly silty sand from 40-51 m.b.g.l and then clay with silty sand at 51-61 m.b.g.l. The hole was terminated in green fine to medium sand interlayered with clay at 81 m.b.g.l. The rest water level was measured at 12.50 m.b.g.l. and the yield as obtained from pumping test is 22 m3/hr. The saturated zone roughly extends from 12.50 m.b.g.l. to 81 m.b.g.l. From MRS free water content starts at 2% around 1m below the surface and reaches 15% at 5 m.b.g.l., then drops gradually to 3% until 28.6 m.b.g.l. The free water content rises to slightly 8% again to 52.5 m.b.g.l; hence it is appropriate to estimate the saturated zone to be from 2 m.b.g.l. to 52.5 m.b.g.l. A decay time >300 ms is observed in

55 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

the shallow 2-3 m.b.g.l that then drops sharply to about 200-250 ms to a depth of 71 m.b.g.l. This high decay time can possibly explain the high yield of up to 22 m3/hr not seen in the water content graph. The water table cannot be explained from MRS since the two values are not in the same range. The high transmissivity values in the range of 40 m2/d can further explain the high decay time, though the same is not seen in the water content graph. Though the specific yield value from pumping test is ex- pected to be smaller than the free water content, the very fine sediments observed from the litholog can explain the fact that it is much smaller. TDEM shows fresh water conditions to 90 m.b.g.l.

8.1.4. BH 8351

BH 8351 Coordinates: x = 764529 Date: 22-10-01 y = 7798933 Site: BH8351-2-10 Square Loop, L = 114m Processing window = 200ms Smoothing = 500 Average S/N = 15 Filter bandwidth = 10Hz

Free water content (%) Decay time (ms) TDEM (ohm-m) Natural gamma (cps) Litholog 0 10 20 30 10 100 1000 0.1 1 10 100 0 40 80 0 0 Brown sandy clay White medium sand 10 10 Tan fine sand interlayered with clay 20 White fine to medium 20 sand Tan sandy clay 30 30 White medium sand Tan fine to medium sand interlayered with clayey sand 40 40 Light green clayey

) fine to medium sand Tan fine to medium sand m 50

( 50 Tan clay

h Green to white siltstone t Fine to medium sand p 60 60

e interbedded

D with green siltstone to 70 70 cemented sand Green Silcrete 80 80 SWL = 11.60m 3 90 Yield = 35m /hr 90 EC = 650mS/cm Screen = 42.9-69.0m 100 100 EOH = 74m 110 110 Saturated zone Pumping BH 2 TC RT = 31.82m /d T = 32.73m2/d Screens R ec Observation borehole BH8350 (r = 35.5m) 2 TC RT = 34m /d 2 TR ec = 36.92m /d

Figure 8-4: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH 8351 This borehole alike the other boreholes in the area tap the shallow unconfined and semi-confined Ka- lahari beds aquifer. As seen from Figure 8-4 above, the hole intersects sandy clays, white medium grained sands, tan sands interlayered with clays, green clayey sands, siltstones and terminates in green dense silcrete at 74 m.b.g.l. The static water level is 11.60 m.b.g.l and the yield is given as 35 m3/hr. The water-bearing layer is estimated to begin at about 11.60 m.b.g.l and extends to the top of the dense silcretes. Leaky beds of sandy clay and clays, siltstones occur at 25-28 m.b.g.l and 51-55 m.b.g.l respectively. From MRS % free water of 8% is seen at about 5 m.b.g.l, which increases to 25% at around 11.40 m.b.g.l (the rest water level depth) and then drops to about 13% until 9% as from 15 m.b.g.l to 52 m.b.g.l. A high decay time of 500 ms, which drops to around 400 ms and then 300 ms is

56 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

observed as from 4 m.b.g.l. to 15.5 m.b.g.l. This corresponds very well with the % free water content of about 25% at that depth. The decay time then drops to about 200 ms and then 150 ms from 15.5 m.b.g.l to 52.5 m.b.g.l., which as well can be considered to be corresponding well with the rest of the data. The saturated zone as observed from drilling agrees well with this MRS data, which shows water to occur to a depth of up to 52 m.b.g.l. A high decay time corresponds to big pores hence high yields and therefore the 35 m3/hr measured from the borehole can easily be explained from the above data. The transmissivity values of range 31-36 m2/d obtained from pumping test further strengthen the argument. The TDEM shows fresh conditions to about 80 m.b.g.l. and then brackish conditions beyond that depth. A good correlation is clearly visible between the natural gamma log and borehole lithology.

8.1.5. BH 8815

BH 8815 Date: 29-10-01

Site: BH8815-12-13 Square loop, L = 114m Processing window = 200ms Smoothing = 500 Average S/N = 5.33 Filter bandwidth = 10 Hz

Free water content (%) Decay time (ms) TDEM (ohm-m) Litholog 0 10 20 10 100 1000 1 10 100 0 0 Brown calyey sand White fine sand to medium sand 10 10 White medium sand with coarse sand White fine sand with minor 20 20 clay and calcrete

30 30 Tan sandy clay and clay 40 40 Green clay and fine sand

) 50 50 Fine sand with silcrete m ( Clay with fine sand h t 60 Clay with silcrete p

e 60 Clay with fine sand D 70 Green clay 70 80 SWL = 13.46m 80 Yield = 5m3/hr Screen = 51-60m 90 90 63-66m EOH = 71m 100 100 Saturated zone 110 Pumping BH 110 2 TCR T = 2.16m /d 2 TRec = 12m /d Screens

Figure 8-5: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH 8815 Borehole BH 8815 was drilled through brown clayey sand, white fine to medium and coarse sands, sand with minor clay and calcrete, clay with sand, clay with silcrete and terminates in green clay,

57 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Figure 8-5 above. The rest water level was recorded at 13.46 m.b.g.l and the pumping test yield was 5 m3/hr. The water-bearing horizon is approximated from 13.46 m.b.g.l. to 22 m.b.g.l.and then from 47 m.b.g.l. to 66 m.b.g.l. TDEM shows fresh water conditions to depths of up to 80 m.b.g.l and then brackish conditions after that depth. MRS shows the following; a free water content of 2% at 8.4 m.b.g.l. to 11.4 m.b.g.l. (the water table well comparable) that increases gradually to 11% at 21 m.b.g.l. and then decreases to 3% at 71 m.b.g.l. A high decay of 370 ms at 8.4 m.b.g.l. to 11.4 m.b.g.l is observed which drops to 290 ms at around 15 m.b.g.l. Then it decreases to about 110-150 ms from 15 m.b.g.l. to 61 m.b.g.l. The borehole‘s moderate yield as compared with other boreholes within the area show the parameters obtained to be in good comparison. The static water level agrees very well but the other parameters though in agreement per say are still questionable because of resistivity < 10 Y-m. TDEM shows fresh water conditions to 80 m.b.g.l.

8.1.6. BH 9590

BH 9590 Coordinates: x = 963364 D ate: 23 -10 -01 y = 7798418 Site: BH 950 3-3-11 Square loop , L = 114m Smoo thing = 500 Processing windo w = 200m s Ave rag e S/N = 11 Filter band width = 10H z

Free water content Decay time (ms) TDEM (ohm-m) Natural Gamma Litholog (%) (cps) 0 10 20 10 100 1000 1 10 100 0 20 40 0 0 Fine grained sand 10 10 Fine to coarse sand 20 Brown fine silty sand 20 Green fine clayey sand 30 30 Fine clayey sand 40 40 Fine to medium sand

) 50 50 Silcrete

m F ine sand (

Green clay h t 60 Fine to medium sand p

e 60 Grey silcrete D 70 70 SWL = 12.53m 80 80 Yield = 2.5 m3/hr EC = 640mS/cm 90 Screen = 59.50-62.42m 90 EOH = 67m Saturated zone 100 100 Pumping BH 2 110 TC R T = 4m /d 110 2 TR ec = 4m /d Observation BH9503 (r = 9.2m) 2 Screens TC R T = 5.81m /d 2 TR ec = 16.6m /d S = 0.0013

Sy = 0.13

Figure 8-6: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH 9590 This borehole, Figure 8-6 was drilled through various lithologies comprising fine to medium grained sand, fine sand, clay, silty sand as well as silcretes and terminates at 67 m.b.g.l. The saturated layer is identified as from 12.53 m.b.g.l extending through to 67 m.b.g.l separated by intervening clayey/silty layers and relatively thin at depths of about 55 m.b.g.l to 58 m.b.g.l. The water rest layer was measured at 13.53 m.b.g.l and the yield as from pumping test was 2.5 m3/hr. The unsaturated zone is identified from 0 to 13.53 m.b.g.l. MRS shows relatively low free water content of 1% at 5 m.b.g.l., which

58 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

increases moderately to 13% at around 15.5 m.b.g.l and then drops again to 1% at 71 m.b.g.l. A decay time of 400 ms as from 4 m.b.g.l increasing to about 500ms at 11.4 m.b.g.l. is observed but this drops to around 200 ms after that depth. The relatively low yield of about 2 m3/hr measured from pumping test compares well with the free water content observed. Further a specific yield of 0.13 has been determined and this agrees well with the other data. However, the high decay time do not correspond well with above information, the transmissivity values ranging from 4 m2/d to 16 m2/d. The TDEM shows fresh water conditions to about 80 m.b.g.l. Relatively both the information from MRS and borehole hydrogeological data, correspond very well. Natural gamma log correlate well with lithology.

8.1.7. BH 9599

BH 9599 Date : 25-10-01 Coordinates: x = 767553 Site: M RS-7-5 y = 7801460 Squ are lo op, L= 114 m Procesiing w indow = 2 00ms Sm oothing = 500 Avera ge S/N = 5 .77 Filter ba ndwidth = 10 Hz

Free water content Decay time (ms) TDEM (ohm-m) Natural gamma Litholog (%) (cps) 0 10 20 10 100 1000 1 10 100 0 20 40 0 0 Light brown very fine clayey sand 10 10

Brown fine sand 20 20 Grey clay Brw on fine sand 30 30 fine to medium at 32-33m Green clay Brow n very fine sand 40 40 Light green sandy clay Brown fine clayey sand Green siltstone ) 50 Brown fine clayey sand m 50 (

h t Green fine clayey sand p 60 e 60 D

70 70 SWL = 13.54m Yield = 12m3/hr 80 80 EC = 1160mS/cm Screen = 25.40-37m 48.3 - 57m 90 90 EOH = 59m Saturated Zone 100 100 Static water level Pumping BH 110 2 110 TC RT = 30m /d 2 TR e c = 25m /d Observation BH9598 (r = 11.25m) Screens 2 TC RT = 38.2m /d 2 TR e c = 38.7m /d S = 0.00095

Sy = 0.11

Figure 8-7: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH 9599 Borehole BH 9599, Figure 8-7 was drilled through fine to medium grained sand, fine sand, silty sand, sandy clay, siltstone, mudstone and silcretes. The borehole was terminated at 59 m.b.g.l and the static water level measured is 13.54 m.b.g.l. The borehole was pump tested at a rate of 12 m3/hr. The satu-

59 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

rated layer extends from about 13.54 m.b.g.l to 59 m.b.g.l with clay aquitards observed at 22 m.b.g.l to 25 m.b.g.l. MRS shows % free water content of 4% at 8.4 m.b.g.l that increases slightly with depth to about 9% at 11.4 m.b.g.l to 38.7 m.b.g.l. This then drops to 5% after that depth until 2% at 71.2 m.b.g.l. A high decay time (455 ms) is seen at about 6.2 m.b.g.l to 8.4 m.b.g.l. This drops to 250 ms until 11.4 m.b.g.l. Between 11 m.b.g.l and 15.5 m.b.g.l there is an abrupt drop of decay time to about 57 ms that then rise again to 219 ms, 300 ms and then 200 ms again at 38.7 m.g.b.l. The decay time stays about 120 ms after that depth. The decay time is explained by the relatively high transmissivity values ranging 25 m2/d to 38 m2/d. A specific yield value of 0.11 has been determined which corresponds to the 9% free water content from MRS. Alike most of the boreholes the data compare well. However an observation well BH 9598 drilled 11.25 m away and yield estimated at 2 m3/hr seem more in agreement with observed MRS response. The low yield observed from this borehole as compared to BH 9599 shows how the intervening clays probably can influence aquifer characteristics at so close range.

8.1.8. BH 9600

BH 9600 Coordinates: x = 764101 y = 778016 Date: 27-10-01 Average S/N = 6.8 Square Loop, L = 37.8m Site: BH 9475-10-7 Smoothing = 500 Processing Window = 200ms Filter bandwidth = 10Hz

Free water content (%) Decay time (ms) TDEM (ohm-m) Litholog 0 10 20 30 40 100 1000 1 10 100 0 0 Green sandy clay Brown fine sand

Light green fine clay sand,fine at 5-7m 10 10 Brown medium to coarse sand

20 20 Brown fine to medium sand ) m ( Brown fine to medium h t 30 very clayey sand

p 30 e

D Green very fine sand

SWL = 2.67m 40 40 Yield = 3 m3/hr Screen = 18-29.6m EOH = 35m

Saturated zone

50 50 Pumping BH 2 TC R T = 0.97m /d 2 TR ec = 6m /d Observation BH9475 (r = 12.4m) T = 12.8m2/d 60 60 C R T 2 TR ec = 5.34m /d S = 0.12 Screens y

Figure 8-8: Comparison of MRS Inversion results with borehole data BH9600

60 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

This hole, Figure 8-8 was drilled to a total depth of 35 m.b.g.l. Drilling intersected various lithologies of fine to medium grained sand, fine sands, clay, silty sand, sandy clay, clayey sand and fine coarse grained sand. The estimated yield after drilling was 3 m3/hr and rest water level recorded was 2.67 m.b.g.l. Sieve analysis results for this borehole indicates that uniformity coefficient (ratio of sieve size on which 40% of material is retained to the 90% of material retained) ranges from 1.4 to 1.7. From MRS the % free water content ranges from 5 to 37% and the decay time range is 164ms to 305ms. The saturated zone is interpreted to extend from 0 to 60 m.b.g.l and that the information is reliable to about 17 m.b.g.l. The sounding was of high resolution at shallow depth considering the square loop size of 37.8 m. TDEM show fresh conditions up to 60 m depths, consistent with the reported TDS information of the fresh water zone in Linn and Masie (2000).

8.1.9. BH 9604

BH 9604 Coordinates: x = 766500 Date: 26-10-01 Site: TH3-8-6 y = 7800525 Square loop, L=114m Processing window = 200ms Smoothing = 500 Average S/N = 9 Filterbandwidth = 10Hz

Litholog Free water content Decay time (ms) TDEM (ohm-m) (%) 0 10 20 10 100 1000 1 10 100

0 0 Grey silty sand White medium to coarse sand 10 10

Brown clay 20 20 Clay with fine to medium sand Fine to coarse sand 30 30 Green sandy clay with coarse sand 40 40 Tan sandy clay Brow n clay Tan fine to coarse sandstone ) 50 50

m White calcrete (

h Tan fine to coarse sand t

p Green sandy clay

e 60 60 Green mudstone D 70 SWL = 9.87m 70 Yield = 5.4 m3/hr EC = 260mS/cm 80 80 Screen = 24-38.50m 44.50-59m EOH = 63m 90 90 Saturated zone Pumping BH 100 100 2 TC R T = 10.4m /d 2 TR ec = 14.4m /d 110 110 Observation BH9603 (r = 11.6m) 2 TC R T = 40.8m /d 2 TR ec = 36m /d Screens S = 0.0017

Sy = 0.0021

Figure 8-9: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH9604 This borehole was drilled to a total depth of 63 m.b.g.l. Drilling of the borehole intersected grey silt, white medium sand, clay, sandy clay, clayey sands, calcrete and mudstone. The static water level was recorded at 9.87 m.b.g.l and the yield from pumping test rate was 5.4 m3/hr. The water bearing layers are from 9.87 m.b.g.l to 20 m.b.g.l, 23 m.b.g.l. to 42 m.b.g.l and 45 m.b.g.l to 59 m.b.g.l. Transmissiv-

61 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

ity values obtained from pumping test range from 10.4 m2/d to 40 m2/d. Sieve analysis carried out on the main sand unit show that the uniformity coefficient (ratio of sieve size on which 40% is retained to 90% material retained) is between 2.2 and 3.8. From MRS, Figure 8-9 the saturated zone extends from 0 to 38 m.b.g.l and the free water content ranges between 2-16%. The decay time ranges from 140ms to 260 ms indicating uniform grain size and moderate permeability. All the data sets from both the borehole data and MRS agree with each other. The TDEM shows fresh water conditions to about 80 m.b.g.l and below that brackish condition.

8.1.10. BH 9608

Coordinates: x = 771292 BH 9608 Date: 23-10-01 y = 7805667 Site: TT16-4-2 Square loop, L = 114m Processing window = 200ms Smoothing = 500 Average S/N = 3.5 Filter bandwidth = 10 Hz

Free water content (%) Decay time (ms) TDEM (ohm-m) Litholog 0 10 20 10 100 1000 0.1 1 10 100

0 0 Grey clay Tan clay sand Brown fine sand 10 10

20 20 White fine to medium sand, coarse at 30-36m 30 30

White clayey sand White fine to coarse sand 40 40 Green sandy clay Green fine too medium sand

) 50 50 White fine to medium m

( clayey sand

h Tan clayey sand t p

e 60 60

D SWL = 12.37m 70 70 Yield = 2 m3/hr EC = 370mS/cm Screen = 25.78-51.88m 80 80 EOH = 57m Saturated zone 90 90 Pumping BH 2 TC R T = 2.2 m /d 2 100 100 TR ec = 6.3 m /d Observation BH9607 (r = 9.7m) 110 110 2 TC R T = 3.7 m /d 2 TR ec = 6.3 m /d S = 0.001 Screens

Figure 8-10: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH 9608 This borehole, Figure 8-10 was drilled to total depth of 57 m.b.g.l. The hole was drilled through various lithologies comprising medium grained sand, fine to very fine sand, clay, silty sand, sandy clay and clayey sand. The static water level was measured at 12.37 m.b.g.l and the yield from pumping test was 2 m3/hr. The saturated zone extends from 12.37 m.b.g.l to 57 m.b.g.l. Sieve analysis carried on

62 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

the main sand units indicates that the uniformity coefficient (ratio of 40 % of material retained to the 90% of material retained) is 1.7 to 1.9 (a fairly uniform grain size). From MRS the unsaturated zone extends from 0 to 11.4 m.b.g.l. There are two saturated zones; one extending from 11.4 m.b.g.l to 28.6 m.b.g.l and free water content ranging 2-7% and a decay time of 84 ms to 154 ms. The second zone extends form about 38.7 m.b.g.l to 96.6 m.b.g.l and free water content of 3-6%. The decay time ranges from 63 ms to 74 ms. This borehole indicates very low yields and of interest is the transmissivity values of 2.2 m2/d to 6.3 m2/d. The MRS agrees very well with borehole data. The EC was measured as 370 WS/cm and this agrees well with the TDEM that shows fresh water conditions to about 90 m.b.g.l and brackish conditions beyond that depth.

8.1.11. BH 9683

BH 9683 Coordinates: x = 766500 Date : 21-10-01 y = 7800525 Site: TT3-1-9B Sq uare loop, L = 1 14m Processing windo w = 250m s Smooth in g = 5 00 Avea rge S/N = 13 Filterb and w idth = 10 H z

Free water content (%) Decay time (ms) TDEM (ohm-m) Litholog 0 10 20 30 10 100 1000 1 10 100

0 0 Brown very fine sand

Brown fine to very 10 10 fine clayey sand

20 20 Tan sandy clay Brown fine to very 30 30 clayey sand

40 40 Light green clay

Light green ) 50 50 fine sand m ( Green siltstone/ h t mudstone at 56-57m p Light green fine sand e 60 60

D Green sandy clay Brown very fine sand with minor silcrete 70 70 SWL = 15.81m Yield = 20m3/hr 80 80 EC = 660mS/cm Screen = 25.78-51.88m EOH = 57m 90 90 Saturated zone Pumping BH 100 2 100 TC R T = 2.56 m /d

TR ec = 29.2 m2/d 110 110 Observation BH9682 (r = 11.25m) 2 TC R T = 427 m /d Screens S = 0.00001 Sy = 0.11

Figure 8-11: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH 9683 This borehole was drilled through fine to medium grained sand, fine sand, fine to very fine sand, fine to coarse grained sand, clay, silty sand, sandy clay, clayey sand, mudstone, siltstone and silcrete. The hole was drilled to 65 m.b.g.l and the static water level is 15.81 m.b.g.l. The pumping rate yield from

63 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

constant rate test was 20 m3/hr and the saturated zone extends from 15.81 m.b.g.l to about 40 m.b.g.l. The transmissivity values of this borehole range from 2.56 m2/d to 29.2 m2/d for constant rate test. Of interest is an adjacent observation borehole BH 9682 11.25 m away with a high transmissivity value of 427 m2/d and specific yields value of 0.11. MRS, Figure 8-11 shows the vadose zone to extend to 6.2 m.b.g.l. The saturation zone extends from 6.2 to 71.2 m.b.g.l and free water content of 2-27%. The decay time range is from 130-392 ms indica- tive of moderate to high permeable sediments. The high decay time of 392 ms can be explained by the high yield of 20.m3/hr and the high transmissivity values from the adjacent borehole. It is however clear from the two data sets that there is good correlation between the two. The EC measured was 660 WS/cm and corresponds well with the TDEM that shows fresh water conditions to about 80 m.b.g.l.

8.1.12. BH 10117

BH 10 117 D ate: 27-10 -01

Site: T T2-9-8A Squ are loop , L = 11 4m Processing wind ow = 2 00m s Smo othin g = 500 Average S/N = 3 .55 Filter ba ndw idth = 1 0 H z

Free water content (%) Decay time (ms) TDEM (ohm-m) Litholog 0 10 20 10 100 1000 0.1 1 10

Black soil 0 0 Yellowish clay very fine sand Calcrete 10 10 Yellowish clay, vrey fine sand 20 20

30 30 Clay

40 40 Sand, very fine

Light greenish clay ) 50 50

m Greenish fine sand (

h t p 60 60 Greenish silcrete e D Greenish very 70 70 fine sand

80 80 SWL = 20.35m 90 90 Yield = 2m3/hr Water Strike = 19m 100 Screen = 22 - 52m 100 EOH = 77m

110 110 Saturated Zone Screens

Figure 8-12: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH 10117

64 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

The borehole, Figure 8-12 was drilled through clays, fine sands, calcrete and silcretes and was terminated at 77 m.b.g.l. The static water level recorded was 20.35 m.b.g.l and yield as recorded from the pumping test was 2m3/hr. The waters strike was estimated at about 19 m.b.g.l. The borehole has three saturated zones at 20.35 m.b.g.l to 25 m.b.g.l, 34-43 m.b.g.l and at 50 m.b.g.l to 55 m.b.g.l. MRS shows a saturated zone from 0-4 m.b.g.l with free water content ranging 4-14% and decay time of range 61-74 ms. A second saturated zone from 15.5-52.2 m.b.g.l with free water content of range 2- 7% and decay time of 140-139 ms. The two data sets are consistent with each other. TDEM shows fresh water conditions to about 80 m.b.g.l and then brackish conditions beyond that depth.

8.1.13. BH 10118

BH 10118 Date: 24-10-01 Site: WBH8348-6-4A Square loop, L= 114m Processing window = 200ms Smoothing = 500 Average S/N = 4.3 Filter bandwidth = 10Hz

Free water content (%) Decay time (%) TDEM (ohm-m) Litholog 0 10 20 10 100 1000 1 10 100 C layey soil 0 Greenish clay w ith fine sand Wet green clay 10

20 Clay with fine sand 30

) 50

m Greenish clay (

w ith very fine sand h t

p 60 e D 70 The borehole is dry 80

100

110

Figure 8-13: Comparison of MRS Inversion results with observed hydrogeological data for borehole BH10118 This borehole was drilled through clayey soil, fine sand, dump clay at about 5-6 m.b.g.l and was terminated in greenish clay with fine sand at 60 m.b.g.l. The borehole was dry. MRS, Figure 8-13 shows a saturated zone from 5.1-13.5 m.b.g.l and free water content of 1-5%. The second zone extends from

65 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

18.6 to 94.6 m.b.g.l that of course is unreliable data as reliability of MRS diminishes with depth. The high decay times are not in any way consistent with the rest of data.

8.2. Data Integrations of Hydrogeological and MRS Data

8.2.1. Transmissivities The MRS estimated transmissivities and pumping test transmissivities are given in Table 8-1 below and Figure 8-14 gives correlation between the two data sets. The MRS transmissivities used in this case were determined using equation (5.2) mentioned in Chapter 5. From Table 8-1and Figure 8-14 it is clear that there was poor correlation between MRS transmissivities and pumping test transmissivities. It should be noted however, that the available control boreholes were screened only in the deepest intersected layer in a series of water bearing layers separated by clay-rich aquitard.

Table 8-1: MRS Determined Transmissivities versus Pumping test Transmissivities

2 2 2 MRS Site TMRS [m /s] TMRS TMRS [m /s] TMRS TPT TPT [m /s] a=4; b=2 [m2/d] a=1; b=2 [m2/d] [m2/d] BH 8262-5-1 7.12E-05 6.15 0.029 2544 53 0.000613 BH 8114-11-12 1.30E-03 112 0.049 4270 12 0.000139 PMP8348-13-3B 6.72E-05 5.81 0.17 1433 27 0.000313 BH 8351-2-10 4.10E-04 35.5 0.19 1663 32.73 0.000379 BH 8815-12-13 1.83E-05 1.58 0.072 6246 12.1 0.000142 BH 9503-3-11 4.25E-05 3.67 0.17 14346 4 4.63.E-05 MRS- 7-5 2.11E-05 1.82 0.075 6463 25 0.000289 TH3-8-6 6.63E-05 5.72 0.11 9588 6 6.94E-05 TT16-4-2 8.33E-07 0.072 0.009 753 14.4 0.000167 TT3-1-9B 4.98E-04 43.10 0.29 24793 29.2 0.000338

PT = Pumping test 0.0016

0.0012 ] s / 2 m [

0.0008 S R M T

0.0004

0 0.0002 0.0004 0.0006 0.0008 TPumping Test [m2/s] Figure 8-14: MRS Transmissivities versus Pumping Test Transmissivities

66 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

8.2.2. Free W ater content and Yield

0.35

t 0.3 y = 0.0048x + 0.0658 n e

t 2

n 0.25 R = 0.2758 o c

0.2 r e t

a 0.15 w

e 0.1 e r

F 0.05 0 0 10 20 30 40 Yield [m3/hr]

Figure 8-15: Borehole yield versus free water content Figure 8-15 above shows borehole yields versus free water content. The plot shows poor correlation between the two parameters possibly because of the inappropriate screening of the water bearing layers.

8.2.3. Borehole yield and Decay Time

0.3 0.25 ] s [ 0.2 e m i t

0.15

y y = 0.0025x + 0.1699 a

c 0.1 2

e R = 0.1272 D 0.05 0 0 10 20 30 40 Yield [m3/hr]

Figure 8-16: Yield versus decay time Figure 8-16 shows a poor correlation between borehole yields and decay time and this possibly can be explained by the same effect as above.

67 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

9. Discussion

The MRS based screens intervals were provided by Roy (2001). However, only four boreholes (BH‘s 8815, 9590, 9599 and 9683 were screened as per the MRS recommendation. As a result, this has greatly influenced the outcome of study as will be seen from the discussion below. The drilling results show borehole depths in the range 29.5 m.b.g.l to 77 m.b.g.l. Yields were in the range 2 m3/hr to 35 m3/hr. The aquifers are unconfined and semi-confined. However, according to observations made from the borehole construction details, the screening of the boreholes was not effective, as the screens were not placed at the most productive horizons. The porosity value obtained from laboratory measurements was 46.40%. From the microscopic analysis, the sample is mainly of uniform and fine-grained material comprised of shiny transparent, smooth quartz grains, suggesting a long history. Based on the specific capacities, the boreholes were grouped into two groups; boreholes BH‘s 8815, 9590, 9600, 9604 and BH 10117 having a specific capacity of < 0.5 m3/hr/m. BH‘s 8114, 8348, 9599 and 9683 have a specific capacity of > 0.5 m3/hr/m. A correlation between the MRS transmissivities and pumping test transmissivities did not yield good results. A Forchheimer correction was applied to improve the pumping test transmissivities using true borehole aquifer thickness but still no improvement was achieved in the relation between the two transmissivities. The calculations using the Forchheimer factor are given in appendix 3b. It should be clear that the discrepancies were possibly due to the available control boreholes that were screened only in the deepest intersected layers in a series of water bearing layers separated by clay rich aquitards / or the fact that the screens were simply wrongly placed. Both the two methods are of large scale; hence a comparison of results should be in agreement. Furthermore, the fact that the results obtained from MRS were determined using methods (equations) applied in the laboratory petrophysical experiments also contributed to the large differences observed from the results of the two methods. Pumping test in anyway usually provides more accurate results than most methods. The other factor that possibly contributed to the above effect, was the drilling method implored that did not allow for the proper identification of the water strikes or the possible identification of the rock samples because of contamination from the drilling fluid and the recirculating mud. As is evidenced from the above observations made, a more effective and appropriate method and final borehole construction is recommended to reliably and fully verify the MRS method using appropriate hydrogeological data, see section 10.2 for the recommended methods.

68 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

10. Conclusions and Recommendations

10.1. Conclusions

The inversion of Magnetic Resonance data E0(Q) and T(Q) provided reliable information on the depth, thickness D, water content 9MRS for each of the water saturated layer for the Maun area. The information is however reliable to depths of about 60/70 m.b.g.l and below that reliability of the information from MRS soundings obtained becomes less because of the surrounding saline environment. The petrophysical information from NMR decay rate obtained from the MRS inversion results of the Maun area data (Table 5-3) are in agreement with Table 4-1; Petrophysical Information from NMR Decay Rate (After Schirov et al, 1991 and Allen et al, 1997 adapted from Roy 2001). The hydraulic conductivity determined from the laboratory for BH 10117 was 0.81 m/d. The hydraulic conductivity from MRS was in the range 0.002 œ 3.40 m/d. The transmissivities obtained from pumping test were in the range 0.97 œ 45.7 m2/d for pumping boreholes and 4 œ 53 m2/d for recovery test. The observation boreholes gave transmissivity values in the range 2.55 œ 636 m2/d. The MRS transmissivities ranged from 0.072 œ 43.10 m2/d for a = 4 and b = 2 and in the range 753 œ 24793 m2/d for a = 1 and b = 2. There was no correlation between MRS transimissivities and pumping test transmissivities as can be seen from Table 8-1 and Figure 8-14. The TDEM has been able to give accurate information of the fresh water zone, with depth ranging from 0 to about 80 m.b.g.l consistent to that given by Linn and Masie (2000). The sieve analysis results have shown that the grain size of sand unit of aquifer for BH 10117 is of uniform size comprising mainly of fine sand. The water table depths obtained from the borehole data in the range 2 œ 20 m.b.g.l. agree with the interpreted depths of MRS soundings. The information is however debatable given that research has shown there is no universal and unique recipe to mark the position of groundwater table using a combination of aMRS and the relaxation time and that the information only holds true depending on field hydrogeological data available (Lubczynski and Roy, 2003). However, the groundwater table was often determined in unconfined aquifers as observed in some of figures, e.g. Figure 8-1. The results are however, not yet fully assessed since the available control boreholes were screened only in the deepest intersected layer in a series of water bearing layers separated by clay-rich aquitard or that the screens were not placed as per MRS recommendations.

10.2. Recommendations As evidenced from the above findings based in the Maun area data, the method is considered to be of an advantage to the country as it can be used to confirm drilling sites identified by other geophysical methods. To fully assess the MRS results, it is recommended that large diameter boreholes (i.e. 15“ diameter drilling that is then narrowed to 12“ diameter drilling to termination depth of about 60 m.b.g.l be drilled next the exploration boreholes and 8“ final casing installed. The annulus should then be filled

69 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

with proper gravel pack sized material to about 1 m.b.g.l and the rest of the hole then grouted to the top. The screens should be placed at the correct identified clean sand horizons for the maximum exploitation of the aquifer sand units. Furthermore the shallow aquifer identified from MRS should be fully exploited. The other possibility is to recommend for horizontal well technology, i.e. infiltration galleries and collector wells that would allow for maximum exploitation or tap groundwater resources in shallow and/or thin high permeability water bearing layers identified form MRS. The country relies more on groundwater and since it is of semi arid conditions the method will be an advantage considering the limiting factors in which the method can be used. For example during rainy seasons the method cannot be used, hence it can be applied in waste conditions. Moreover, crystalline rocks cover large parts of the country and drilling in these areas has been expensive, hence costs of drilling dry boreholes can be reduced. It is therefore recommended that further MRS tests be conducted in such areas.

70 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

11. References

BNWMP, 1991. Botswana National Water Master Plan Study, Vol. 5, Hydrogeology, Final Report, Ministry of Minerals, Energy and Water Affairs, Gaborone, Botswana.

Carney, J.N., Aldiss, D.T. and Lock, N.P., 1994. The Geology of Botswana, Bulletin 37, Geological Survey Department. Ministry of Minerals, Energy and Water Affairs, Gaborone, Botswana.

Driscoll, F.G., 1995. Groundwater and Wells. Johnson Filtration System, ST Paul, Minnesota.

Eijkelkamp Agrisearch Equipment, 1997. Manual Handleinding , Eijkelkamp EC 18.34. Giesbeek, The Netherlands.

Fetter, C.W., 2001. Applied Hydrologeology, Macmillan Publishing Company

Forchheimer, P., 1930. Hydarulik. Berlin-Leipzig.

Gieske, A., 1996. Modelling of outflow from the Jao/Boro flow system œ Okavango Delta, Botswana. Journal of Hydrology, 193, 214 œ 239.

Goldman, M., Rahinovich, M., Gilad, I.G. and Schirov, M., 1994. Application of the integrated NMR- TDEM method in Groundwater explorations in Israel. Journal of Applied Geophysics, 31 (1994) 27- 52.

Gumbricht, T., McCarthy, T.S. and Merry, C.L., 1985. The topography of the Okavango Delta, Bot- swana, and its tectonic and sedimentological implications. South African Journal of Geology, 104 (3), p. 243-264.

Iris Intruments, 1998. Iris-Instruments.com.

Iris Intruments, 2001. Iris-Instruments.com.

Iris Intruments, 2002. Iris-Instruments.com.

Kenyon, W.E., Howard, J.J., Sezgininer, A., Straley, C., Matteson., Horkowitz, K., 1989. Pore-size distribution and NMR in microsporous cherty sandstones. Spwla 13TH annual Logging Symposium, Paper LL.

Kenyon, W.P., 1997. Petrophysical applications of NMR logging. Log Anal., pp21-43, March-April.

71 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Keys, S. W and MacCary, L. M., 1985. Applications of Borehole Geophysics To Water-Resources Investigations. Techniques of Water-Resources Investigations of the United States Geological Survey, USGS.

Kgotlhang, L., 2000. Evaluation of the magnetic resonance sounding technique as a tool for groundwater exploration. Case study-Botswana. MSc thesis, ITC. The Netherlands.

Legchenko, A.V., Shushakov, O.A., 1998. Inversion of surface NMR data. Geophysics 63, 75-84.

Legkgenko, A.V. and Valla, P., 1998. Processing of proton magnetic resonance signals using non- linear fitting. Journal of Applied Geophysics, 39, 77-83.

Legchenko, A., Beause, A., Guillen A, Valla P. and Bernard, J., 1997. Natural Variations in the Mag- netic Resonance Signal Used in PMR Groundwater Prospecting From the Surface. European Journal of Environment and Enginnering Geophysics, 2, 173-190.

Legchenko, A., Baltassat, J.M. and Bernard, J., 2002. Nuclear magnetic resonance as a geophysical tool for hydrogeologists. Journal of Applied Geophysics 50 (2002) 21-46.

Legchenko, A.V., Shushakov, O.A., Perrin, J. and Portslan, A.A., 1995. Noninvasive NMR study of subsurface aquifers in France. Abstracts of the International Exposition and SEG 65th Annual Meet- ing, October 9-12, 1995, Houston, USA, p.365-367.

Lieblich, D.A., Legchenko, A., Haeni, F.P. and Portselan, A., 1994. Surface Nuclear Magnetic Reso- nance Experiments to Detect Subsurface Water at Haddam Meadows, Conneticut. Symposium on the Application of geophysics to engineering and Environmental Problems.

Lubczynski, M. and Roy, J., 2003. Hydrogeological interpretation and potential of new magnetic resonance sounding (MRS) method. Journal of Hydrology. 283, p 19 œ40.

Lubczynski, M.W. and Roy, J., 2004. Magnetic resonance sounding (MRS)-New Method for Groundwater Assessment. Groundwater Journal, 42/2.

McCarthy, J.M, Gumbricht, T. R, McCarthy, T. S. and Frost P. E., 2002. Fluctuations of Inundated Area in the Okavango Delta Captured from Satellite Images and Space Shuttle Photography for the Period 1962-2000

Masedi, V. G., 2002, Modelling Recharge from River Infiltration, Thamalakane River, Botswana. MSc. Thesis, ITC, The Netherlands.

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McCarthy, T.S., Green, R.W. and Franey, N.J., 1993b. The influence of-tectonics on water dispersal in the north-eastern regions of the Okavango swamps, Botswana. Journal of African Earth Sciences, 17, pg 23 œ 32.

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74 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Appendeces

75 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Appendix 1a: Rainfall Records œMaun area Year Month Annual OCT NOV DEC JAN FEB MAR Apr May Jun Jul Aug Sept

1921/22

1922/23

1923/24

1924/25 166.5 244.1 158.8 48.3 62.3 1.5 0.0 0.0 13.7 1925/26 1.3 9.6 83.1 62.6 27.7 78.6 14.0 9.2 0.0 0.0 0.0 0.0 286.1 1926/27 16.8 38.8 102.1 38.4 41.5 10.7 17.8 0.0 0.0 0.5 0.5 0.0 267.1 1927/28 67.3 3.3 39.3 161.6 39.5 0.0 0.0 0.0 0.0 0.0 0.0 0.6 311.6 1928/29 4.3 71.9 87.2 113.0 53.8 14.2 0.0 0.0 0.0 0.0 0.0 1.3 345.7 1929/30 0.8 22.8 108.4 47.5 66.3 9.5 90.9 0.0 0.0 0.0 0.0 0.0 346.2 1930/31 1.8 12.7 106.7 88.8 103.0 84.1 35.8 0.0 0.0 0.0 0.0 0.0 432.9 1931/32 11.4 46.5 41.8 25.4 174.2 273.8 14.0 0.0 0.0 0.0 0.0 0.0 587.1 1932/33 2.9 13.7 51.4 89.7 20.0 15.3 0.0 0.0 0.0 0.0 0.0 0.0 193.0 1933/34 0.0 115.6 56.7 122.7 110.5 44.9 47.7 2.6 0.0 0.0 0.0 0.0 500.7 1934/35 3.3 56.9 49.4 73.8 56.6 16.0 13.2 0.0 0.0 0.0 0.0 0.0 269.2 1935/36 4.3 57.3 63.6 106.9 47.5 269.9 28.9 33.6 0.0 0.0 0.0 0.0 612.0 1936/37 2.8 14.8 84.4 60.0 169.4 39.1 9.5 0.0 0.0 0.0 0.0 0.0 380.0 1937/38 0.3 16.8 44.1 138.8 46.0 19.6 48.3 0.0 0.0 0.0 0.0 0.0 313.9 1938/39 33.0 115.4 100.2 62.4 215.5 43.1 0.5 0.0 1.0 0.0 0.0 10.4 581.5 1939/40 22.1 36.2 101.2 69.2 56.5 153.1 90.9 0.0 0.0 0.0 0.0 4.3 533.5 1940/41 10.9 14.5 44.0 151.1 59.9 0.0 10.2 0.0 0.0 0.0 0.0 0.0 290.6 1941/42 40.6 36.0 56.9 31.5 71.6 120.7 9.8 13.7 0.0 0.0 0.0 0.0 380.8 1942/43 30.9 0.8 96.8 93.4 11.2 57.8 82.4 18.3 0.0 0.0 0.0 0.0 391.6 1943/44 5.0 23.9 72.3 145.8 318.7 15.8 6.9 0.0 3.3 0.0 0.0 0.0 591.7 1944/45 15.9 38.1 38.4 17.9 43.0 161.8 1.0 2.0 0.0 0.0 0.0 0.0 318.1 1945/46 15.1 48.2 81.4 395.9 95.3 0.0 0.0 3.8 0.0 0.0 0.0 0.0 639.7 1946/47 10.3 21.9 16.3 83.5 32.0 125.4 0.0 0.0 0.0 0.0 0.0 0.0 289.4 1947/48 1.0 92.0 102.0 110.9 174.6 172.1 67.9 0.0 0.0 0.0 0.0 0.3 720.8 1948/49 23.1 61.6 19.6 82.1 7.7 128.2 1.3 0.0 10.4 0.0 0.0 0.0 334.0 1949/50 5.1 61.6 132.9 106.9 118.7 40.4 38.3 28.2 0.0 0.0 0.0 0.0 532.1 1950/51 0.0 10.1 129.8 100.9 72.5 51.4 36.8 22.6 0.0 0.0 0.3 0.0 424.4 1951/52 61.0 70.4 88.6 91.5 108.4 10.3 0.3 10.2 0.3 0.0 0.0 0.0 441.0 1952/53 32.7 169.6 77.9 92.8 157.1 77.4 21.3 0.8 0.0 0.0 0.0 0.0 629.6 1953/54 4.8 77.1 136.8 142.1 96.7 86.9 16.1 0.0 0.0 0.0 0.0 0.0 560.5 1954/55 9.3 11.9 223.1 183.1 245.7 167.9 20.2 2.3 0.0 0.0 0.0 0.0 863.5 1955/56 32.2 48.1 82.3 54.0 129.1 53.3 25.6 2.8 0.0 0.0 0.0 11.6 439.0 1956/57 4.4 42.4 64.0 72.3 104.8 92.2 14.8 0.0 1.5 0.0 0.0 2.1 398.5 1957/58 29.4 27.5 95.9 230.9 124.9 88.6 3.1 0.0 0.0 0.0 0.0 1.1 601.4 1958/59 54.3 36.1 101.8 133.1 71.0 66.0 12.5 5.3 1.8 0.7 0.0 0.1 482.7 1959/60 2.1 18.3 80.2 30.5 73.4 21.0 71.0 16.2 3.3 0.0 0.0 0.0 316.0 1960/61 2.7 54.2 49.3 111.8 133.2 145.3 12.2 24.4 0.0 5.4 0.0 0.0 538.5 1961/62 3.8 30.0 35.2 155.1 35.5 8.3 41.2 0.0 0.0 0.0 3.9 0.0 313.0 1962/63 4.4 79.9 113.6 208.7 58.0 66.6 12.8 4.8 0.3 0.0 0.0 0.0 549.1 1963/64 29.8 98.9 208.7 79.2 70.1 17.6 0.0 0.0 0.0 0.0 0.0 0.3 504.6 1964/65 16.0 50.0 50.3 33.4 54.0 6.4 58.0 0.0 0.0 0.0 0.0 2.5 270.6 1965/66 8.8 35.6 52.5 106.6 160.0 123.6 59.7 0.2 17.1 0.0 0.0 29.2 593.3 1966/67 0.0 2.7 108.3 137.4 186.1 20.8 120.4 0.0 0.0 0.0 0.0 0.0 575.7 1967/68 8.8 111.9 64.1 109.9 104.2 81.8 65.5 33.8 0.0 0.0 0.0 0.0 580.0 1968/69 2.1 70.2 59.8 50.2 246.7 36.9 15.4 0.1 0.0 0.0 9.6 21.0 512.0 1969/70 12.6 67.6 13.1 123.1 21.2 9.2 1.4 0.0 0.0 0.0 0.0 10.9 259.1 1970/71 0.0 60.0 160.1 108.4 12.1 33.4 44.6 0.0 0.0 0.0 0.0 1.6 420.2 1971/72 9.7 66.8 94.4 260.3 69.7 192.9 19.8 0.0 0.0 0.0 0.0 0.0 713.6 1972/73 10.5 2.0 47.2 80.8 67.5 21.9 14.8 0.0 0.0 0.0 0.0 0.0 244.7 1973/74 100.8 43.9 270.1 341.9 365.7 17.9 50.1 0.0 0.0 0.0 0.0 11.1 1201.5 1974/75 6.5 116.2 30.9 168.5 60.8 191.4 71.3 3.5 0.0 0.0 0.0 0.0 649.1 1975/76 1.2 10.5 71.2 112.6 68.1 108.3 3.7 2.7 0.0 0.0 0.0 12.0 390.3 1976/77 25.3 74.2 37.5 114.8 126.0 126.5 19.2 4.0 0.0 0.0 1.2 31.9 560.6 1977/78 3.1 77.1 226.7 91.9 226.2 37.4 12.1 14.4 12.0 0.0 0.0 0.2 701.1 1978/79 11.2 17.5 73.2 124.8 30.2 25.8 7.3 0.0 0.0 0.0 0.1 0.0 290.1 1979/80 27.0 20.1 36.5 91.0 290.5 42.5 1.2 0.0 0.0 0.0 0.0 1.9 510.7 1980/81 3.0 74.0 27.7 126.3 160.6 92.9 5.2 6.1 0.0 0.0 0.0 0.0 495.8 1981/82 8.2 74.7 61.1 30.8 17.0 11.3 14.9 0.0 0.0 0.0 0.0 0.0 218.0 1982/83 101.1 84.2 34.6 98.6 11.4 25.1 19.5 15.8 1.0 0.0 0.0 0.0 391.3 1983/84 20.0 53.5 153.4 20.0 17.9 81.8 8.3 0.9 0.0 0.0 0.3 0.5 356.6 1984/85 20.2 92.5 12.6 76.8 41.8 55.1 2.4 0.0 0.0 0.0 0.0 0.0 301.4 1985/86 21.6 7.8 135.2 53.8 70.0 34.6 52.4 10.7 0.0 0.0 0.0 19.2 405.3 1986/87 49.6 49.3 57.1 32.2 60.3 27.3 0.0 0.0 0.0 0.0 0.0 3.9 279.7 1987/88 8.5 6.1 92.3 38.2 106.7 80.4 19.2 0.0 0.0 0.0 0.0 7.6 359.0

76 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

1988/89 17.0 14.6 69.5 215.5 180.2 44.3 96.3 0.0 0.0 0.0 0.0 0.0 637.4 1989/90 0.0 7.2 40.1 84.1 110.1 33.3 17.3 0.0 0.0 0.0 0.0 0.0 292.1 1990/91 17.4 5.5 41.5 177.6 133.9 122.7 0.0 0.0 0.0 0.0 0.0 5.8 504.4 1991/92 28.5 13.3 78.4 50.1 7.4 87.3 5.0 0.0 0.0 0.0 0.0 1.4 271.4 1992/93 6.7 40.7 55.1 66.5 122.0 15.4 47.4 0.0 0.0 0.7 0.0 8.2 362.7 1993/94 14.3 23.9 154.8 275.0 50.0 6.2 0.0 0.0 0.0 0.0 0.0 0.0 524.2 1994/95 0.0 44.0 15.2 27.0 14.4 48.3 0.0 2.0 0.0 0.0 0.0 21.6 172.5 1995/96 11.2 16.6 54.1 139.3 260.6 9.0 0.4 2.9 0.0 0.0 0.0 0.5 494.6 1996/97 3.5 104.7 46.1 153.8 19.2 64.8 1.8 5.1 0.0 0.0 0.0 12.6 411.6 1997/98 26.6 24.8 67.8 150.2 18.6 28.4 32.6 0.0 0.0 0.0 0.0 0.0 349.0 1998/99 1.7 50.5 109.0 110.2 56.5 41.2 3.8 10.2 0.0 0.0 0.0 0.0 383.1 1999/00 7.9 14.2 63.5 255.0 183.5 31.2 21.7 2.3 2.6 0.0 0.0 0.0 581.9 2000/01 5.7 43.7 45.0 34.0 103.8 47.7 87.8 3.5 0.0 0.0 0.0 0.0 371.2 2001/02 0.0 126.2 29.3 58.6 36.0 15.3 6.0

77 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Appendix 1b: River Discharges and Flows œ Mohembo 7112 Average of Flow (m3/sec) MONTH YEAR Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total 1974 172.5 172.5 1975 252.3 436.5 724.8 747.3 535.5 355.8 259.2 203.6 181.7 142.8 142.7 173.5 354.7 1976 196.4 368.0 540.7 739.1 771.1 521.0 355.8 320.0 484.7 1977 475.4 578.1 357.7 253.4 140.5 126.9 171.2 297.0 1978 256.9 319.5 380.2 563.6 604.6 398.4 270.2 206.2 175.5 148.6 144.3 181.2 309.7 1979 224.1 332.1 654.9 773.0 513.4 348.8 243.0 209.9 185.2 156.3 231.3 355.9 1980 259.1 358.2 556.1 471.4 377.7 181.2 179.3 126.6 109.7 103.5 292.8 1981 150.7 224.2 346.8 539.4 445.8 278.6 221.7 193.2 163.2 121.1 116.5 125.7 253.7 1982 129.4 188.6 352.6 416.2 351.6 222.4 189.8 146.5 131.9 265.3 1983 260.7 283.6 353.0 263.0 193.4 153.4 134.1 118.5 103.0 118.0 198.4 1984 344.5 547.2 542.3 581.8 523.5 400.4 290.5 234.8 198.7 158.5 181.9 234.9 352.6 1985 316.3 352.6 340.5 449.9 501.7 346.9 270.1 213.9 178.7 144.8 144.4 144.7 283.2 1986 138.8 250.1 434.2 665.3 488.6 300.0 242.9 185.9 162.8 148.1 175.3 222.8 284.4 1987 244.6 301.2 366.1 421.2 309.8 226.1 165.1 165.2 142.8 128.5 114.9 148.0 227.2 1988 176.2 299.1 408.5 442.0 494.8 351.7 223.0 192.8 172.6 146.3 138.8 210.7 271.2 1989 377.9 552.5 454.2 401.1 474.2 378.6 272.1 213.4 182.3 145.4 120.9 103.5 304.7 1990 148.0 277.5 395.1 422.6 466.1 276.5 207.5 165.2 147.4 126.3 121.5 174.4 246.5 1991 276.4 371.0 333.7 368.6 307.6 207.9 170.6 144.7 127.9 111.4 138.4 197.6 228.2 1992 315.5 474.9 585.8 609.0 393.9 242.3 194.8 174.0 150.5 118.3 121.1 136.9 292.2 1993 152.1 220.8 233.9 336.3 311.1 242.5 181.4 143.8 124.1 111.6 109.8 145.9 192.3 1994 286.8 332.7 311.9 299.9 239.4 170.0 146.9 124.4 112.0 93.8 93.6 125.4 193.6 1995 146.4 167.1 266.0 401.1 359.0 213.5 165.0 142.2 121.6 103.0 105.8 122.5 192.8 1996 164.6 192.8 255.3 340.1 238.8 151.2 130.3 115.0 102.4 85.7 83.2 107.7 163.7 1997 154.1 213.8 301.6 378.1 320.3 210.5 147.1 119.2 112.8 93.1 94.8 99.2 186.5 1998 163.7 287.9 389.5 463.0 356.3 207.9 152.5 135.5 119.4 96.2 96.8 129.2 216.4 1999 196.7 280.7 416.0 599.6 488.8 278.8 206.6 162.1 132.8 115.5 106.7 146.8 260.6 2000 327.3 322.7 306.1 356.5 397.8 281.0 205.9 157.3 135.4 110.3 96.6 97.8 232.8 2001 127.3 219.0 420.1 566.0 581.7 361.5 260.1 189.1 155.5 319.9 total 219.8 314.7 406.9 488.2 429.6 290.3 214.6 170.9 146.8 122.3 123.3 153.9 263.5

78 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Total flow - MCM/month Days: 31 31 30 31 30 31 31 30 31 30 31 year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total 1974 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 461.9 461.9 1975 675.9 1056.1 1941.3 1937.1 1434.2 922.3 694.2 545.3 471.0 382.5 369.8 464.8 10894.4 1976 526.0 922.0 1448.1 1915.8 2065.3 1350.5 953.1 857.1 0.0 0.0 0.0 0.0 10037.9 1977 0.0 0.0 0.0 1232.3 1548.3 927.1 678.8 0.0 0.0 376.3 328.9 458.5 5550.1 1978 688.1 773.0 1018.3 1460.9 1619.4 1032.7 723.6 552.3 455.0 398.1 374.1 485.2 9580.7 1979 600.2 803.5 1754.2 2003.6 1375.0 904.1 650.9 562.2 480.0 0.0 405.1 619.5 10158.3 1980 694.0 897.5 1489.4 1221.9 1011.7 0.0 485.2 480.2 0.0 339.1 284.3 277.3 7180.6 1981 403.6 542.4 928.9 1398.2 1194.1 722.1 593.9 517.5 423.0 324.2 301.9 336.7 7686.7 1982 346.5 456.2 944.5 1078.9 941.7 576.4 508.2 392.5 341.8 0.0 0.0 0.0 5586.6 1983 0.0 630.6 759.6 915.1 704.3 501.3 410.8 359.1 307.1 275.9 305.8 0.0 5169.7 1984 922.7 1371.1 1452.6 1508.1 1402.0 1037.9 778.0 628.9 515.0 424.4 471.5 629.1 11141.5 1985 847.2 853.0 912.0 1166.2 1343.6 899.2 723.5 573.0 463.2 387.8 374.3 387.5 8930.5 1986 371.8 605.2 1162.9 1724.4 1308.7 777.6 650.7 497.9 422.0 396.7 454.4 596.8 8968.9 1987 655.1 728.7 980.4 1091.7 829.7 586.2 442.2 442.4 370.2 344.3 297.8 396.5 7165.2 1988 471.9 749.5 1094.0 1145.6 1325.2 911.6 597.3 516.3 447.4 391.7 359.7 564.3 8574.5 1989 1012.1 1336.7 1216.5 1039.6 1270.0 981.4 728.8 571.6 472.6 389.4 313.3 277.3 9609.2 1990 396.3 671.3 1058.3 1095.3 1248.4 716.6 555.8 442.6 382.1 338.3 315.0 467.0 7687.0 1991 740.2 897.6 893.8 955.3 823.8 538.9 457.0 387.5 331.6 298.5 358.7 529.4 7212.3 1992 845.1 1189.9 1568.9 1578.6 1055.0 628.0 521.7 466.1 390.0 316.8 314.0 366.6 9240.6 1993 407.4 534.3 626.4 871.7 833.2 628.4 485.9 385.1 321.7 298.9 284.6 390.7 6068.3 1994 768.3 804.8 835.3 777.3 641.1 440.5 393.5 333.2 290.4 251.1 242.7 335.9 6114.2 1995 392.0 404.3 712.4 1039.7 961.4 553.5 442.0 380.8 315.2 275.8 274.3 328.0 6079.3 1996 440.8 483.1 683.7 881.5 639.5 392.0 349.1 308.0 265.3 229.5 215.7 288.5 5176.8 1997 412.7 517.2 807.9 980.1 858.0 545.5 393.9 319.3 292.4 249.3 245.7 265.8 5887.9 1998 438.3 696.5 1043.2 1200.1 954.3 538.9 408.6 363.0 309.5 257.6 250.8 346.0 6806.9 1999 526.9 679.0 1114.3 1554.2 1309.1 722.7 553.3 434.2 344.3 309.4 276.5 393.1 8217.1 2000 876.7 808.7 819.9 924.1 1065.4 728.3 551.3 421.3 350.8 295.6 250.4 262.0 7354.5

79 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Mean Monthly Discharge Rate (m3/sec) at Boro

Junction

MONTH ANNUAL YEAR OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP MEAN 1969/70 11.02 9.87 3.60 1.34 9.24 0.00 0.00 3.77 10.78 15.30 13.28 8.97 7.26 1970/71 5.24 1.98 0.66 0.40 0.40 0.45 0.44 0.90 5.09 10.12 12.00 9.18 3.90 1971/72 4.59 2.14 0.80 0.28 1.65 1.92 2.58 3.06 3.18 4.80 7.63 7.94 3.38 1972/73 5.23 2.16 0.29 0.04 0.00 0.00 0.00 0.00 0.12 2.60 4.63 3.55 1.55 1973/74 1.36 0.60 0.33 1.21 2.60 11.25 15.83 12.87 11.56 13.29 17.13 16.44 8.71 1974/75 13.52 11.55 8.54 5.92 5.11 4.90 5.76 7.97 20.74 28.56 25.75 21.91 13.35 1975/76 16.64 11.08 6.37 3.22 2.33 2.52 3.45 4.40 16.60 28.52 26.49 22.28 11.99 1976/77 19.25 13.27 7.01 2.83 2.68 5.19 10.11 14.74 15.17 21.57 25.96 24.04 13.49 1977/78 19.16 11.40 5.61 8.47 19.38 25.14 21.86 19.74 20.01 25.65 28.46 28.13 19.42 1978/79 24.46 15.07 6.89 3.13 2.13 1.82 1.43 5.30 29.49 30.62 27.00 19.98 13.94 1979/80 11.59 6.68 3.42 2.05 1.93 2.13 2.67 6.45 19.61 26.65 24.30 18.38 10.49 1980/81 9.73 3.44 1.38 0.61 1.17 3.01 2.69 2.22 12.96 27.08 24.27 20.08 9.05 1981/82 11.17 5.64 2.88 1.18 0.35 0.07 0.00 0.01 5.74 17.65 18.71 12.49 6.32 1982/83 5.30 1.30 0.51 0.25 0.00 0.00 0.00 0.01 1.38 6.14 6.88 4.38 2.18 1983/84 2.18 0.64 0.20 0.07 0.02 0.00 0.00 1.22 8.16 26.52 26.71 17.73 6.95 1984/85 12.25 8.25 4.53 1.25 0.50 0.21 0.00 0.00 0.17 4.20 11.30 9.68 4.36 1985/86 5.54 1.36 0.51 0.29 0.33 0.09 0.00 0.00 1.05 13.43 11.85 9.27 3.64 1986/87 6.85 4.25 1.37 0.72 5.65 1.09 31.97 6.97 6.00 2.72 6.76 1987/88 0.99 2.97 0.00 0.00 0.00 0.00 0.00 0.00 0.06 2.46 7.76 8.30 1.88 1988/89 5.65 2.24 0.85 1.87 1.85 5.65 8.88 14.06 16.88 16.72 16.82 14.01 8.79 1989/90 11.85 8.93 4.30 1.88 1.41 1.25 0.71 0.46 0.48 6.04 11.24 9.92 4.87 1990/91 5.48 1.69 0.76 0.40 0.93 1.05 1.53 1.74 3.14 4.75 7.14 6.86 2.95 1991/92 3.97 2.32 1.14 0.91 0.34 0.01 0.00 0.63 5.11 9.09 8.93 6.24 3.22 1992/93 2.86 1.28 0.49 0.21 0.21 0.14 0.16 0.17 0.22 0.41 1.00 1.27 0.70 1993/94 0.76 0.42 0.30 0.47 0.74 0.44 0.25 0.28 0.41 0.65 1.22 1.28 0.60 1994/95 0.90 0.47 0.28 0.05 0.00 0.00 0.00 0.00 0.00 0.75 2.08 1.61 0.51 1995/96 0.40 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.03 1996/97 0.06 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.22 0.96 0.70 0.16

80 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

1997/98 0.19 0.10 0.09 0.03 0.00 0.00 0.00 0.00 0.00 1.63 2.23 0.75 0.42 1998/99 0.15 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.00 2.27 2.32 1.09 0.49 1999/00 0.39 0.09 0.01 0.00 0.08 0.13 0.15 0.42 0.80 1.35 1.47 2.09 0.58 2000/01 1.59 0.94 0.51 0.28 0.09 0.00 3.59 4.65 4.24 1.77 2001/02 1.90 1.09 1.06 0.56 0.39 0.14 0.02

81 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Appendix 2: Summary of borehole yields

BH No. Drilled Depth (m) Yield (m3/hr) 8262 73 12 8114 29.5 7.5 8348 81 22 8351 74 35 8815 71 5 9590 67 1.8 9599 59 2 9600 35 3 9604 63 5 9608 57 2 9683 65 20 10117 77 2 10118 60 dry

82 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Appendix 3a: MRS Inversion Plots

Numis MRS Inversion Results

BH8262 Date: 23-10-01 Site: BH8262-5-1 Square Loop = 114m Processing window =100ms Smoothing = 500 Average S/N = 9 Filter bandwith = 10 Hz

Measured Signal Average Signal Modelled Signal Average Noise 400 160

300 120 ) V n ( )

0 V E n

(

200 e 80 0 g E a r e v 100 A 40

0 0

100 1000 10000 100 1000 10000 100000 Excitation moment Q (A-ms) Excitation moment Q (A-ms)

Free water content (%) Decay time (ms) TDEM (ohm-m) Llitholog 0 10 20 30 40 10 100 1000 0.1 1 10 100 0 Clay 10 Fine Sand 20 Fine Sand with clay

30 Fine Sand

40 Fine Sand with silt

) 50 Fine to medium m (

Sand h t p

e 60 D Fine to medium 70 Sand with silt Clay 80 SWL = 12.24m Yield = 12m3/hr 90 TDS = 660 mg/l Screen = 30-36m 51-54m 100 61-64m EOH = 73m 110

83 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Numis MRS Inversion Results BH 8114 Date:29-10-01 Site: BH8114-11-12 Square eight loop, L=57m Processing window = 200ms Smoothing = 500 Average S/N = 6 Filter bandwidth = 10 Hz

Measured Signal Average Signal Modelled Signal Average Noise 300 100 250

) 80 V n

200 (

) 0

V 60 E n

(

150 e 0 g E a 40 100 r e v 50 A 20

0 0 100 1000 10000 100 1000 10000 Q (A-ms) Q (A-ms)

Free water content (%) Decay time (ms) TDEM (ohm-m) 0 1020 30 40 50 60 10 100 1000 1 10 100 Litholog

0 Clay

10 Fine sand

20 Coarse sand with clay Silty sand Fine sand 30 interbedded with silcrete

) SWL = 6.05m

m 40

( 3

Yield = 7.5m /hr h t TDS = 140mg/l p Screen = 19-28m e

D 50 EOH = 29.5m

84 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Numis MRS Inversion Results

BH8348 Date:30-10-01 Site:PMP8348-13-3B Square Loop, L=114m Processing window = 200ms Smoothing = 500 Average S/N = 9 Filter bandwitdh = 10Hz

Measured signal Average signal Modelled signal Average Noise 160 300

) 120 V n (

200 0 ) E

V e 80 n g ( a

r 0 e E v 100 A 40

0 0 100 1000 10000 100 1000 10000 Excitation moment Q (A-ms) Excitation moment Q (A-ms)

Free water content (%) Decay time (ms) TDEM (ohm-m) Litholog 0 10 20 10 100 1000 1 10 100 0 White sand

10 Brown sandy clay with friable silcrete 20 Fine to medium sand 30

Mixed silcrete, coarse quartz 40 and sand Fine to medium

) 50 silty sand m (

h Caly with silty sand t p

e 60 D

70 Fine to medium sand with clay 80

90 SWL = 12m Yield = 22m3/hr TDS = 800mg/l 100 Screen = 47-76m EOH = 81m 110

85 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Numis MRS Inversion Results

BH 8351 Date: 22-10-01 Site: BH8351-2-10 Square Loop, L = 114m Processing window = 200ms Smoothing = 500 Average S/N = 15 Filter bandwidth = 10Hz )

V 250

400 n (

E 200

300 l a )

n 150 V g n i (

200 0 S

100 E e g

100 a 50 r e v 0 A

100 1000 10000 100 1000 10000 Excitation moment Q (A-ms) Excitation moment Q (A-ms)

Free water content (%) Decay time (ms) TDEM (ohm-m) 0 10 20 30 10 100 1000 0.1 1 10 100

0 Sandy clay 10 White meidium grained sand 20 Fine sand w ith clay 30 Fine to medium sand 40 with caly ) m

( 50 Clay

h t

p 60 Fine to medium sand with siltstone e D 70 Green dense silcrete

80 SWL = 11.60m Yield = 35m3/hr 90 TDS = 500mg/l Screen = 43-69m 100 EOH = 74m 110

86 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Numis MRS Inversion Results

BH 8815 Da te : 29 -1 0-01

Site: BH 88 15 -1 2-13 S qua re loo p, L = 1 14m Processin g w ind ow = 20 0m s S mo oth in g = 5 00 A verag e S /N = 5.3 3 Filte r ban dw idth = 10 H z

Average Signal Measured Signal Average Noise Modelled Signal

120 250 100

200 ) V n

( 80

0 E ) 150 V e 60 n g (

a 0 r E e

100 v 40 A 50 20 0 0 100 1000 10000 100 1000 10000 Excitation moment Q (A-ms) Excitation moment Q(A-ms)

Free water content (%) Decay time (ms) TDEM (ohm-m) Litholog 0 10 20 10 100 1000 1 10 100 0 Brow n calyey sand White fine sand to medium sand 10 White medium sand w ith coarse sand White fine sand with minor 20 clay and calcrete

30 Tan sandy clay and clay 40 Green clay and fine sand

) 50 Fine sand with silcrete m (

Clay with fine sand h t

p Clay with silcrete

e 60 Clay with fine sand D Green clay 70

80 SWL = 13.46m Yield = 5m3/hr TDS = 90 Screen = 51-60m 63-66m 100 EOH = 71m

110

87 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Numis MRS Inversion Results

BH 9590 Da te: 23-10 -0 1

Site: BH 950 3-3-11 Squ are lo op, L = 1 14m Processing w in do w = 2 00 ms Sm oot hing = 500 Ave ra ge S/N = 11 Filte r ban dw idth = 10H z

Measured Signal Average Signal Modelled Signal Average Noise 300 160

) 120 V n (

200 ) 0 V E n

( e

80 g 0 a E r e

100 v

A 40

0 0

100 1000 10000 100 1000 10000 Excitation moment Q (A-ms) Excitation moment Q (A-ms)

Free water content (%) Decay time (ms) TDEM (ohm-m) Litholog 0 4 8 12 16 20 10 100 1000 1 10 100 0 0 Fine grained sand 10 10 Fine to coarse sand Brown fine silty sand 20 20 Green fine clayey sand 30 30 Fine clayey sand 40 40 Fine to medium sand

) 50 50 Silcrete m (

Fine sand

h Green clay t p 60 60 Fine to medium sand e Grey silcrete D 70 70

SWL = 12.53m 80 80 Yield = 2.5 m3/hr EC = 530mS/cm 90 90 Screen = 59.50-62.42m EOH = 67m 100 100

110 110

88 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Numis MRS Inversion Results

BH 9600 Date: 27-10-01 Average S/N = 6.8 Square Loop, L = 37.8m Site: BH 9475-10-7 Smoothing = 500 Processing Window = 200ms Filter bandwidth = 10Hz

200 120

160 ) V

n 80 (

) 0 V E n ( e

120 0 g a E r e

v 40 80 A

40 0

100 1000 10000 100 1000 10000 Excitation moment Q (A-ms) Excitation moment Q (A-ms)

Free water content (%) Decay time (ms) TDEM (ohm-m) Litholog 0 10 20 30 40 100 1000 1 10 100

0 0 Green sandy clay Brow n fine sand

Light green fine clay sand,fine at 5-7m 10 10 Brow n medium to coarse sand

20 20 Brow n fine to medium sand ) m ( Brow n fine to medium h t 30 very clayey sand

p 30 e

D Green very fine sand

SWL = 2.67m 40 40 Yield = 3 m3/hr Screen = 18-29.6m EOH = 35m

Saturated zone 50 50 Pumping BH 2 TC RT = 0.97m /d 2 TR ec = 6m /d Observation BH9475 (r = 12.4m) T = 12.8m2/d 60 60 C RT 2 TR ec = 5.34m /d

Sy = 0.12

89 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Numis MRS Inversion Results

BH 9599 D ate: 2 5-1 0-01

Site: M RS-7-5 Square loop , L= 114m Procesiing window = 200m s Smoot hin g = 500 Average S/N = 5.77 Filter bandw idth = 10H z

Measured Signal Average Signal Modelled Signal Average Noise 200 120

160 100 ) V n

( 80

) 120 0 V E

n ( e

60 g 0 a E 80 r e

v 40 A 40 20 0 0 100 1000 10000 100 1000 10000 Excitation moment Q (A-ms) Excitation moment Q (A-ms)

TDEM (ohm-m) Free water content (%) Decay time (ms) Litholog 0 10 20 10 100 1000 1 10 100

0 Light brown very fine calyey sand 10 Brown fine sand

20 Grey clay Brwon fine sand fine to medium at 32-33m 30 Green clay Brown very fine sand Light green sandy clay 40 Brown fine clayey sand Green siltstone Brown fine clayey sand ) 50 m ( Green fine clayey sand h t

p 60 e D

70 SWL = 13.54m Yield = 12m3/hr 80 EC = 1400mS/cm Screen = 25.40-37m 90 37-40m EOH = 59m 100 Saturated Zone Static water level 110

90 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Numis MRS Inversion Results BH 9604 Date: 26-10-01 Site: TH3-8-6 Square loop, L=114m Processing window = 200ms Smoothing = 500 Average S/N = 9 Filterbandwidth = 10Hz

Measured Signal Average Signal Modelled Signal Average Noise 240 160 200 ) 120 V n (

160 0 ) E v n e ( 80 120 g 0 a E r e 80 v A 40 40 0 0

100 1000 10000 100 1000 10000 Excitation moment Q (A-ms) Excitation moment Q (A-ms)

TDEM (ohm-m) Free water content (%) Decay time (ms) Litholog 0 10 20 10 100 1000 1 10 100

0 Grey silty sand White medium to coarse sand 10

Brown clay 20 Clay with fine to medium sand Fine to coarse sand 30 Green sandy clay with coarse sand 40 Tan sandy clay Brown clay Tan fine to coarse sandstone ) 50

m White calcrete (

h Tan fine to coarse sand t

p Green sandy clay

e 60 Green mudstone D 70 SWL = 9.87m Yield = 5.4 m3/hr 80 EC = 1300mS/cm Screen = 24-38.50m 44.50-59m 90 EOH = 63m

100

110

91 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Numis MRS Inversion Results

BH 9608 Date: 23-10-01 Site: TT16-4-2 Square loop, L = 114m Processing window = 200ms Smoothing = 500 Average S/N = 3.5 Filter bandwidth = 10 Hz

Measured Signal Average Signal Modelled Signal Average Noise 200 50

40 160 ) V n (

) 0 30 v 120 E

n ( e

g 0 a E 80 r 20 e v A 40 10

0 0 100 1000 10000 100 1000 10000 Excitation moment Q (A-ms) Excitation moment (A-ms)

Free water content (%) Decay time (ms) TDEM (ohm-m) 0 10 20 10 100 1000 0.1 1 10 100 Litholog

0 0 Grey clay Tan clay sand Brown fine sand 10 10

20 20 White fine to medium sand, coarse at 30-36m 30 30

White clayey sand White fine to coarse sand 40 40 Green sandy clay Green fine too medium sand

) 50 50 White fine to medium m

( clayey sand

h Tan clayey sand t p

e 60 60 D 70 70 SWL = 12.37m Yield = 2 m3/hr EC = 370mS/cm 80 80 Screen = 25.78-51.88m EOH = 57m 90 90

100 100

110 110

92 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Numis MRS Inversion Results

BH 9683 Date: 21-10-01 Site: TT3-1-9B Square loop, L= 114m Processing window = 250ms Smoothing = 500 Avearge S/N = 13 Filterband width = 10 Hz

Measured Signal Average Signal Modelled Signal Average noise 300 400 ) V n

( 200

300 0 E )

V e n g (

a 0 r e E

v 100

200 A

0 100 100 1000 10000 100 1000 10000 Excitation moment Q (A-ms) Excitation moment Q (A-ms) Free water content (%) Decay time (ms) TDEM (ohm-m) 0 10 20 3010 100 1000 1 10 100 Litholog

0 0 Brow n very fine sand Brown fine to very 10 10 fine clayey sand

20 20 Tan sandy clay

Brown fine to very 30 30 clayey sand

40 40 Light green clay

Light green ) 50 50 fine sand m (

Green siltstone/ h

t mudstone at 56-57m

p Light green fine sand

e 60 60 Green sandy clay D Brown very fine sand 70 70 with minor silcrete

80 80 SWL = 15.81m Yield = 20m3/hr EC = 370mS/cm 90 90 Screen = 25.78-51.88m EOH = 57m 100 100

110 110

93 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Numis MRS Inversion Results

B H 1 011 7 D ate: 27-10-01

Site: TT2-9-8A Squa re lo op, L = 114 m P ro ce ssing wind ow = 2 00m s Smo othing = 5 00 Average S/N = 3.55 Filter ba ndw id th = 10 Hz

Measured Signal Average Signal Modelled Signal Average Noise 120 60 50

100 ) V n (

40 ) 0

V 80 E

n ( e

30 g 0 a E 60 r

e 20 v A 40 10

20 0 100 1000 10000 100 1000 10000 Excitation moment Q (A-ms) Excitation moment (A-ms)

Free water content (%) Decay time (ms) TDEM (ohm-m) Litholog 0 10 20 10 100 1000 0.1 1 10 Black soil Yellowish clay 0 very fine sand Calcrete Yellowish clay, 10 vrey fine sand

20 Clay 30 Sand, very fine 40 Light greenish clay Greenish fine sand ) 50 m ( Greenish silcrete h t p 60 e

D Greenish very fine sand 70

80 SWL = 20.35m Yield = 2m3/hr 90 Water Strike = 19m Screen = 22 - 52m EOH = 77m 100 Saturated Zone 110

94 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Numis MRS Inversion Results BH 10118 Date: 24-10-01 Site: WBH8348-6-4A Square loop, L= 114m Processing window = 200ms Smoothing = 500 Average S/N = 4.3 Filter bandwidth = 10Hz

Measured Signal Average Signal Modelled Signal Average Noise 160 60 )

120 V n

( 40

) 0 V E

n ( e 80 g 0 a E r

e 20 v

40 A

0 0

100 1000 10000 100 1000 10000 Excitation moment Q (A-ms) Excitation moment Q (A-ms)

Free water content (%) Decay time (%) TDEM (ohm-m) 1 10 100 Litholog 0 10 20 10 100 1000 Clayey soil 0 0 Greenish clay with fine sand Wet green clay 10 10

20 20 Clay with fine sand 30 30

40 40

) 50 50

m Greenish clay ( with very fine sand h t p 60 60 e D 70 70

80 80

90 90

100 100

110 110

95 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Appendix 3b: Calculations for MRS Transmissivities

4 2 2 4 2* 2 2 2 2 2 2 BH No. QMRS % D [m] T2* [s] Q (T2*) [s ] Fi = Q (T2*) D [s /m] TPT[m /d] TPT[m /s] K [m/s] TMRS [m /s] TMRS [m /d] K*D [m /s] KD [m2/d] 8262 13.42 36 0.11 3.92E-06 0.000141 53 0.000613 1.98E-06 0.02945172 2544.62835 7.12E-05 6.15 8114 29.73 33 0.1 7.81E-05 0.002578 12 0.000139 3.94E-05 0.04942869 4270.63862 1.30E-03 112 8348 7.4 71.2 0.25 1.87E-06 0.000133 27 0.000313 9.44E-07 0.16590595 14334.2741 6.72E-05 5.81 8351 12.87 47.5 0.25 1.71E-05 0.000814 32.73 0.000379 8.64E-06 0.19249631 16631.6811 4.10E-04 35.5 8815 6.33 62.8 0.19 5.80E-07 3.64E-05 12.24 0.000142 2.92E-07 0.07230041 6246.75581 1.83E-05 1.58 9590 6.35 66.2 0.28 1.27E-06 8.44E-05 4 4.63E-05 6.42E-07 0.16604202 14346.0306 4.25E-05 3.67 9599 6.56 62.7 0.19 6.69E-07 4.19E-05 25 0.000289 3.37E-07 0.07480813 6463.42265 2.11E-05 1.82 9604 8.42 38.7 0.26 3.40E-06 0.000131 6 6.94E-05 1.71E-06 0.11097879 9588.56742 6.63E-05 5.72 9608 4.57 37.9 0.1 4.36E-08 1.65E-06 14.4 0.000167 2.20E-08 0.00872621 753.944512 8.33E-07 0.072 9683 12.02 65 0.27 1.52E-05 0.000989 29.2 0.000338 7.67E-06 0.28695618 24793.0141 4.98E-04 43.10

4 2 2 Cp Q (T2*) Cp Q(T2*) *D

0.004952 0.002495 Cp = 0.503814

96 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Determining TMRS with the application of Forchheimier correction and using real aquifer thicknesses from boreholes 2 TRPT[m /d 4 2 2 4 2* 2 2 2 2 2 2 2 BH No. Q (T2*) [s ] Fi = Q (T2*) D [s /m] D [m] TPT[m /d] ] TRPT[m /s] K [m/s] TMRS [m /s] TMRS [m /d] L [m] D/L [m] f KD [m /s] KD [m /d] 8262 3.92E-06 1.41E-04 36 53 30.74 0.000356 2.74E-06 9.86E-05 8.52E+00 9 4 0.58 9.86E-05 8.52E+00 8114 7.81E-05 1.05E-03 13.45 12 10.44 0.000121 5.45E-05 7.34E-04 6.34E+01 9 1.4944 0.87 7.34E-04 6.34E+01 8348 1.87E-06 1.22E-04 65 27 16.47 0.000191 1.31E-06 8.51E-05 7.35E+00 19 3.4211 0.61 8.51E-05 7.35E+00 8351 1.71E-05 6.86E-04 40 32.73 28.4751 0.00033 1.20E-05 4.79E-04 4.14E+01 26.1 1.5326 0.87 4.79E-04 4.14E+01 8815 5.80E-07 3.64E-05 62.8 12.24 12.24 0.000142 4.05E-07 2.54E-05 2.20E+00 ? 2.54E-05 2.20E+00 9590 1.27E-06 2.93E-05 23 4 1.64 1.9E-05 8.90E-07 2.05E-05 1.77E+00 2.92 7.8767 0.41 2.05E-05 1.77E+00 9599 6.69E-07 3.01E-05 45 25 19.5 0.000226 4.67E-07 2.10E-05 1.81E+00 20.3 2.2167 0.78 2.10E-05 1.81E+00 9604 3.40E-06 1.12E-04 33 6 5.22 6.04E-05 2.37E-06 7.83E-05 6.76E+00 28.6 1.153 0.87 7.83E-05 6.76E+00 9608 4.36E-08 1.61E-06 37 14.4 12.528 0.000145 3.05E-08 1.13E-06 9.74E-02 26.1 1.4176 0.87 1.13E-06 9.74E-02 9683 1.52E-05 4.87E-04 32 29.2 25.404 0.000294 1.06E-05 3.40E-04 2.94E+01 26.1 1.2261 0.87 3.40E-04 2.94E+01 Cp Cp Q4(T2*)2 Q(T2*)2*D 2.70E-03 0.001883 6.98E-01

97 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Appendix 4: Geophysical Plots

Geophysical Log BH8351 (Site: BH8351-2-10)

Natural gamma (cps) Borehole Log BH 8351 Notes 0 40 80 0 0 SWL = 11.60m Brown sandy clay Yield = 35m3/hr TDS = 416mg/l Screen = 42.9-69.0m White medium sand EOH = 74m 10 10

T an fine sand interlayered with clay 20 20 White fine to medium sand

T an sandy clay 30 30 White medium sand Tan fine to medium sand interlayered with clayey sand ) m ( Light green clayey

h 40 t 40 fine to medium sand p e D Tan fine to medium sand 50 50 Tan clay Green to white siltstone

60 60 Fine to mediumsand interbedded with green siltstone to cemented sand

70 70 Green Silcrete

80 80

98 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Geophysical Log BH9600 (Site: BH9475-10-7)

Natural Gamma (cps) Interpreted Litholog Borehole Log BH9600 0 10 20

0 Green sandy clay

C lay with sand Brown fine sand

Light green fine clayey sand Sand

Clay with sand

10 Sand

Brown medium to coarse sand Clay with sand

Sand Clay with sand ) ) m m ( (

h h t t 20 p Brown fine to medium p Sand e sand e D D

Clay with sand

Brown fine medium very clayey sand 30 Sand Green very fine clayey sand

SWL = 2.67m Yield= 3m3/hr 40 EOH = 35m

99 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Geophysical Log BH8262 (Site: BH8262-5-1)

Natural gamma (cps) Borehole Log BH8262 Notes 0 40 80 120 160 SWL = 12.29m 0 0 Yield = 12m3/hr TDS = 660 mg/l Dark grey clay Screen = 30-36m 51-54m 61-64m 10 10 TDS = 422mg/l EOH = 73m Tan fine sand

Tan fine sand interlayered 20 20 with green clay

White fine sand

30 30 White fine to medium sand ) ) m m ( (

h h t 40 t 40 p Tan fine to medium sand p e e interlayered with green clay D D

50 50 Fine to medium sand

60 60 Green sandy clay

Olive green fine to medium sand interlayered w ith siltstone 70 70

80 80

100 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Geophysical Log BH8348 (Site: PMP8348-13-3B)

Natural gamma (cps) 0 40 80 120 Borehole litholog BH8348 Notes

0 0 White w ell sorted sand SWL = 12.50m Yield = 22m3/hr Screens = 47-76m Brown sandy clay interlayered EOH = 81m 10 10 with green friable silcrete TDS = 832mg/l

Tan / white fine 20 20 to medium sand

C emented sand and coarse quartz

30 30

Fine to medium sand

40 40 Mixed sample: silcrete, coarse quartz and sand

Green fine to medium slightly silty sand 50 50

Green soft clay/ clatstone interlayered with sand 60 60

Green predominantly fine to 70 70 medium sand w ith claystone

80 80

101 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Geophysical Log BH9590/9503 (BH9503-3-11)

Borehole Log Natural Gamma (cps) Resistivity (ohmm) Interpreted litholog 0 20 40 0 100 0 0 Sand with clay

Fi ne grained s and

Sand 10 10 Sand with clay Sand F ine to coarse sand

Brow n fine silty sand Sand with clay 20 20

Green fine clayey sand

Clay with sand 30 30 ) m (

h Clay t Green fine clayey sand p e D 40 40 Clay with sand Alternate green fine clayey sand

50 Tan Silcrete 50 Silcrete Green fine sand Sand with clay Green clay Green silt Clay with silcrete Fine to medium sand 60 60 Sand with clay C lay Grey silcrete

70 70 SWL = 12.53m Resistitvity 16" Yield = 2.5 m3/hr EC = 530 mS/cm Resistivity 64" Screen = 59.5-62.42m EOH = 67m

102 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Geophysical Log BH9598/9599 (Site: MRS-7-5)

Borehole Log BH9599 Borehole Log BH9598 Natural gamma (cps) Interpreted Litholog 0 10 20 30 40 50

0 0 Sand with clay Light brown fine Tan sandy clay clayey sand Sand Sand with c;ay 10 10 Brown very fine sand Sand

Sand with clay Brown fine Brown silty sand sand 20 Brown clayey sand 20 Sand Brown sandy clay Grey clay C lay Brow n fine to very fine sand Brown very Sand 30 fine sand 30

Sand with clay Green clay Brown silty sand ) Brown very fine m Sand

( clayey sand

h Light green sandy Tan clayey sand t 40 40 p clay Tan sandy clay e Brown fine to very

D fine clayey sand Brow n silty/clyey sand Light green siltstone Sand with clay Brown very fine sand Brown very fine 50 sand 50 Green fine to very fine sand Light green very Sand fine sand Green silcrete Sand with clay 60 60 Green silty sand Clay Green silty mudstone Sand with clay Sand 70 Green fine sand 70 Sand with clay

80 80

SWL = 13.54m SWL = 13.50m Yield = 12m3/hr Yield = 2m3/hr EC = 1400mS/cm EC = 11620mS/cm EOH = 59m Screen = 25-34, 37-40m Screen = 25.4-37, 48.30-57m EOH = 75m

Water bearing layer

103 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Geophysical Log BH9603 / BH9604 (Site: TH3-8-6)

Natural gamma (cps) Interpreted litholog Borehole Log BH9604 Borehole BH9603 0 10 20 30

0 Sand and clay 0 Silty sand Grey clayey sand Clayey sand White clayey sand Sand

White fine to coarse sand 10 10 Sand and clay White medium to coarse White clayey/silty sand grained sand Sand Brow n clayey silty/sand Clay 20 Grey sandyclay 20 Brow n clay Grey clay with fine to White fine to medium sand coarse sand Sand White fine to coarse sand 30 Clay 30 White fine to Green sandy clay with medium sand coarse white sand Sand ) White fine to m (

coarse sand

H T an sandy clay 40 T 40 Tan silty sand Sand and clay P

E Brown sandy clay Brown clay D T an clayey/silty sand Tan sandstone Sand 50 50 Tan fine to coarse White calcrete sand Sand and clay Tan fine to coarse sand Green mudstone Green sandy clay 60 Sand 60 White fine to Clay Green mudstone medium sand Sand White fine to coarse sand Clay 70 70 Whit silty sand/mudstone Sand and clay Whit silty sand Green silcrete 80 80 SWL = 9.87m SWL = 14.60m Yield = 2m3/hr Yield = 5.4m3/hr EC = 4000 mS/cm EC = 1300 mS/cm Screen = 18-29.6m Screen = 25.40-39.60m 45.28-59.48m EOH = 63m 65.16-68.00m EOH = 77m

104 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Geophysical Log BH9607/BH9608 (Site: TT16-4-2)

Borehole Log BH9608 Borehole BH9607 Natural Gamma (cps) Interpreted Litholog 0 10 20

Ggrey clay 0 Grey clay 0 Sand Tan clay sand Tan silty sand

Brow n fine to very fine sand Sand with clay Brown fine to very 10 fine sand Brow n clayey sand10 SWL = 12.55m

Brow n fine to very fine sand Sand 20 20

Fine to medium sand Brow n fine sand coarse at 30-36m Sand with clay ) m ( h t 30 30 p e D Sand Brow n fine to very fine sand White slightly clayey sand White fine to coarse sand Brow n very fine Sand with clay 40 Green sandy clay sand 40 Sand

Light green fine to medium sand coarse at 46-50m Brow n clayey sand Sand with clay

White fine to medium sand 50 Brow n fine to very 50 C oarse at base Sand fine sand

Tan clayey sand Brow n clayey sand Sand with clay 60 Brow n fine sand 60

SWL = 12.37m SWL = 12.55m Yield = 2m3/hr Yield < 1m3/hr EC = 370mS/cm EC = 400mS/cm Screens = 25.78-51.88m Screen = 21-33m EOH = 57m 50-56m EOH = 62m

105 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Geophysical Log BH9682/9683 (Site: TT3-1-9B)

Borehole BH9683 Borehole Log BH9682 Natural gamma (cps) Interpreted Log 0 10 20 30 40 0 0 Brow n very Brown fine sand fine sand Sand Grey clayey sand Ggrey clay Clay Brown fine to very 10 Brow n fine to very fine sand 10 Sand fine clayey sand Brown fine to medium sand Sand and clay Brown fine sand Sand Tan sandy clay Brown clayey sand Sand and clay 20 Brown sandy clay 20 Sand

Brwon fine to very Sand and clay fine sand Brow n fine to very 30 clayey sand 30 Sand ) m ( h t

p Green fine sand e and clay D Sand and caly 40 Green sandy clay 40 Green clayey sand Light green clay Green sandy clay

Light green Green clayey sand 50 fine sand 50 Green snady clay Green siltstone/ Green siltstone Clay/siltstone mudstone at 56-57m Light green Green very fine Sand and clay fine sand sand and clay 60 Green sandy clay 60 Clay Brown very fine sand Green fine to with minor silcrete very fine sand Clay with sand/silcrete

Green silcrete Clay Green clay Green very fine 70 sand 70 SWL= 15.81m SWL = 9.78m yield = 20m3/hr Yield = 1m3/hr EC = 910mS/cm EC = 450mS/cm Screen = 21-38m Screen = 22.66-39.66m 48-50.92m 48.16-50.99m 57-59.93m 56.62-59.44m EOH = 65m EOH = 71m

106 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Appendix 5: Summary Hydrogeological Borehole Data for the MRS Area

BH No SITE ID Location EOH RWL Yield TDS Completion Details Geophysical Logging Geology Easting Northing (m) (m) (m/hr) (mg/l) Cased Screen Logged Paramaters Depth Lithology/ depth (m) metrage measured (m) Formation (m) (m) (m) 8262 BH8262-5-1 7760098.29 7809426. 73 12.24 12 660 73 30-36 73 Natural 0-12 Red brown clay 48 51-54 Gamma (N) 12-18 Fine Sand, tan 61-64 18-22 Fine sand with green clay 22-38 Fine to medium sand 38-43 Fine sand with silt 43-62 Fine to medium sand granite 62-69 Fine to medium sand interbedded with siltstone and sandstone 69-73 Fine sand and green sandy clay 8348 PMP834813- 768811.08 7802494. 81 12.50 22 800 81 47-76 81 Natural 0-7 White well sorted white sand 3B 58 Gamma 7-16 Brown sandy clay interlayered with friable silcrete 16-39 Fine to medium sand with fine to medium quartz 39-40 Mixed silcrete, coarse quartz and sand 40-51 Fine to medium slightly silty sand 51-61 Clay with slightly silty sand 61-81 Green fine to medium sand interlayered with clay

107 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

8351 BH8351-2-10 764529 7798933 74 11.60 35 500 74 43-69 74 Natural 0-4 Brown Sandy clay Gamma (N) 4-12 White medium-grained sand 12-20 Tan fine sand interlayered with clay 20-25 Fine to medium sand 25-28 Tan sandy clay 31-35 Fine to medium sand interlayered with 35-44 clay 44-51 Light green clayey fine to medium 51-53 sand 53-55 Tan fine to medium sand 55-69 Tan clay Green to white siltstone 69-74 Fine to medium sand wth thick siltstone beds Green dense silcrete 8114 BH8114-11-12 763255 7796006 29.5 6.05 7.5 140 29.5 19-28 N/A N/A 0-1 Black clayey soil 1-22 Fine sand, 1-7 and 8-22 white, 7-8 22-23 brown 23-26 Coarse sand mixed with clay 26-29.5 Silty sand Very fine sand interbedded with silcrete 8815 BH8815-12-13 71 13.46 5.10 51-60 N/A N/A 0-1 Brown clayey sand 63-66 1-12 White fine to medium sand 12-15 White medium to coarse sand 15-22 White fine sand with minor clay and calcrete 22-35 Tan sandy clay and clay sand 35-39 Tan clay 39-47 Tan green clay with minor green clay 47-51 Green clay with fine sand 51-56 Tan fine sand with tan silcrete 56-59 Green clay interlayered with fine sand 59-63 Green clay with green silcrete 63-66 Green clay interlayered with tan fine 66-71 sand Green clay

108 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

9590 BH9503-3-11 963364 7798418 67 12.53 2.5 410 62.42 59.5-62.42 67 Natural 0-10 Brown fine grained sand Gamma (N) 10-12 Brown fine to medium sand Resistivity 12-15 Brown fine to coarse grained sand (RES) 15-18 Brown fine grained sand Self- 18-20 Brown fine grained silty sand Potential 20-23 Tan fine grained clayey sand (SP) 23-30 Brown fine grained sand 30-32 Green fine grained clayey sand 32-35 Green sandy clay 35-37 Green fine grained clayey sand 37-39 Grey fine grained sand 39-40 Green sandy clay 40-45 Green fine grained sand 45-47 Green sandy clay 47-49 Green fine to medium grained sand 49-50 Green fine grained sand 50-52 Tan silcrete 52-54 Green fine grained sand 54-55 Green clay 55-56 Green silt 56-57 Green clay 57-60 Brown fine to medium grained sand 60-67 Grey silcrete

109 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

9599 MRS-7-5 767553 7801460 59 12.70 12 742 58.5 25.4-37 N/A N/A 0-1 Light brown very fine clayey sand 48.3-57 1-13 Brown very fine grained sand 13-22 Brown fine grained sand 22-25 Grey clay 25-34 Brown fine grained sand; fine to medium at 32-33m 34-35 Green clay 35-38 Brown very fine grained sand 38-41 Light green sandy clay 41-42 Brown very fine grained clayey sand 42-44 Brown fine grained sand 44-45 Brown fine grained clayey sand 45-47 Light green siltstone 47-48 Brown very fine grained sand 48-50 Brown fine grained clayey sand 50-53 Brown fine grained sand 53-54 Light green fine grained clayey sand 54-57 Light green very fine grained clayey 57-59 sand Green very fine grained sand 9600 BH9475-10-7 764101 778016 35 2.67 3 260 31.60 18-29.6 35 Natural 0-2 Green sandy clay Gamma (N) 2-3 Brown fine grained sand 3-10 Light green fine grained clay sand, fine at 5-7m 10-15 Brown medium to coarse grained sand 15-28 Brown fine to medium sand, medium to coarse at 22-23m 28-30 Brown fine to medium very clayey 30-35 sand Green very fine grained clayey sand

110 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

9604 TH3-8-6 766500 7800525 63 9.87 5.4 1320 61 24-38.50 63 Natural 0-1 Dark grey silt 44.40-59 Gamma (N) 1-2 White Silty sand 2-3 White slightly clayey sand 3-8 White medium to coarse grained sand 8-20 White fine to coarse grained sand 20-23 Brown clay 23-25 Grey clay with fine to medium 25-30 grained sand 30-32 Whit fine to coarse grained sand 32-34 Green sandy clay with white coarse sand 34-35 Green clay interlayered with white 35-43 fine to coarse sand 43-45 Green clay with white sand 45-47 Tan sandy clay 47-50 Brown clay 50-54 Tan fine to coarse grained sand 54-55 Tan sandstone 55-56 White calcrete 56-57 Tan fine to coarse grained sand 57-58 Tan clay with minor fine to coarse 58-60 sand 60-63 Tan fine to coarse grained sand Tan fine to coarse grained sand Green sandy clay Green mudstone

111 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

9608 TT6-4-2 771292 7805667 57 12.37 2 243 54.88 25.78-51.88 N/A N/A 0-1 Grey clay 1-4 Tan clay sand 4-12 Brown fine grained sand 12-15 Brown fine to very fine grained sand 15-30 White fine to medium grained sand 30-36 White fine to coarse grained sand 36-37 White fine to medium grained sand 37-38 White slightly clayey sand 38-39 White fine to coarse grained sand 39-42 Green sandy clay 42-46 Light green fine to medium grained 46-50 sand 50-51 Light green fine to coarse grained sand 51-52 White fine to medium grained slightly clayey sand 52-55 White fine to coarse grained slightly 55-57 clayey sand Tan clayey sand Tan clayey sand 9683 TT3-1-9B 766500 7800525 65 15.81 20 422 62.38 21-38.40 N/a N/a 0-5 Brown very fine grained sand 47.45-50.35 5-17 Brown fine to very fine grained clayey 57.40-59.3 17-20 sand 20-35 Tan sandy clay 35-38 Brown fine to very fine grained clayey 38-39 sand 39-48 Brown fine grained sand 48-52 Brown fine grained clayey sand 52-58 Light green clay 57-60 Light green fine grained clayey sand 60-61 Green siltstone, mudstone at 56-57m 61-62 Light green fine grained sand 62-64 Green sandy clay Brown very fine grained sand 64-65 Brown fine grained sand with minor green silcrete Brown fine to very fine grained sand

112 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

10117 TT2-9-8A 77 4.5 77 7-10 N/A N/a 0-1 Black soil 22-23 1-6 Yellowish clay, very fine sand 6-10 Calcrete 10-24 Yellowish clay, very sand 24-34 Clay 34-43 Sand, very fine 43-50 Clay, light greenish clay 50-55 Greenish very fine sand 55-63 Greenish silcrete 63-77 Greenish very fine sand 10118 WBH8348-6- 60 DRY DRY N/A N/A N/A N/A N/A 0-1 Clayey soil 4A 1-5 Greenish clay with fine sand 5-6 Wet light green clay 6-47 Clay with fine sand 47-60 Greenish clay with very fine sand

113 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Appendix 6: Pumping Test Data Time BH8262 BH9683 9590 9599 9600 9604 9608 (min) dd Rd dd R dd Rd dd Rd dd Rd dd Rd dd Rd d 0.25 2.72 0.04 19.57 2.75 11 1 15.83 0.83 12.85 0.2 10.49 0.5 5.22 0.65 18.84 3.68 9.24 1.3 14.92 1.88 11.92 0.7 9.86 1 9.64 1.2 17.66 5.18 7.58 2.09 14.47 2.79 11.41 1.39 8.96 2 17.04 2.65 16.16 6.25 6.85 3.8 12.77 4.28 11.22 2.53 7.74 3 19.94 4.13 13.85 6.68 6.24 3.3 11.03 5.62 9.17 3.25 6.65 4 0 21.99 5.4 12.02 6.65 6.04 6.3 9.54 6.44 7.71 4.02 5.9 5 0.01 22.79 6.62 10.37 6.95 5.63 7 8.67 7.34 5.67 4.67 4.95 6 0.01 23.24 7.68 8.99 7.44 5.53 7.6 7.85 7.96 4.83 5.44 4.4 7 0 23.73 8.73 7.7 7.67 5.35 8.09 7.1 8.44 4.33 5.72 3.86 8 0.03 24.11 9.74 6.6 7.87 5.27 8.85 6.4 8.88 3.76 6.07 3.6 9 0.03 24.34 10.5 5.93 7.99 5.18 9.6 5.8 9.17 3.62 6.29 3.37 10 0.04 24.53 11.25 5.24 8.14 5.1 10.2 5.43 9.37 3.41 6.63 3.05 11 0.04 24.76 11.88 4.14 8.23 8.82 10.68 5.43 9.55 9.55 6.85 2.54 12 0.05 24.86 12.55 2.8 8.37 5 10.84 4.95 9.65 2.98 7.06 2.16 15 0.07 25.07 14.2 1.8 8.64 4.93 11.54 4 9.91 2.72 7.25 1.78 18 0.09 16.24 1.8 8.82 9.33 11.54 3.73 10.21 2.72 7.25 1.78 20 0.1 25.44 16.24 1.08 9.04 4.07 12.2 2.89 10.21 2.27 8.18 1.59 25 0.11 25.63 19.86 0.84 9.17 3.63 12.67 2.58 10.45 2.12 8.63 1.42 30 0.12 25.84 20 0.7 9.33 3.4 12.96 2.28 10.57 2 8.82 1.24 40 0.12 26.11 20.3 0.38 3.32 13.3 2.08 10.87 1.89 9.05 1.07 50 0.14 26.25 20.42 0.01 9.7 3.22 13.5 1.74 11.07 1.8 9.2 0.9 60 0.14 26.40 20.57 9.8 3.05 13.7 1.55 11.31 1.71 9.3 0.72 75 0.16 26.62 20.72 9.95 2.84 13.95 1.42 11.49 1.61 9.42 0.67 90 0.17 26.75 20.4 10.08 2.83 14.02 1.34 11.62 1.6 9.5 0.58 105 0.18 26.90 20.37 10.15 2.6 14.17 1.3 11.74 1.42 9.56 0.5 120 0.2 26.97 20.4 10.26 2.5 14.23 1.09 11.83 1.31 9.59 0.39 150 0.21 27.20 20.35 10.42 2.45 14.46 1 12.01 1.19 9.8 0.35 180 0.24 27.33 20.33 10.53 5.24 14.6 0.95 12.17 1.17 10.05 0.27 240 0.25 27.54 20.26 10.75 2.35 14.81 0.9 12.74 0.93 10.09 0.21 300 0.26 27.81 20.1 10.89 2.15 14.97 0.8 12.82 0.88 10.2 0.15 360 0.27 28.01 19.95 10.95 2.04 15.09 0.7 13.01 0.81 10.24 0.14 420 0.29 28.04 19.7 11.01 1.95 15.21 0.6 13.11 0.81 10.42 0.11 480 0.29 28.14 19.75 11.08 1.85 15.29 0.57 13.14 0.77 10.44 0.08 540 0.3 28.15 19.62 11.11 1.76 15.4 0.56 13.19 0.71 10.46 0.07 600 0.3 28.16 19.53 11.21 1.62 15.43 0.55 13.41 0.67 10.48 0.07 660 0.3 28.16 19.35 11.21 1.49 15.5 0.43 13.51 0.63 10.49 0.06 720 0.32 28.12 19.32 11.25 1.42 15.56 0.4 13.54 0.59 10.51 0.05 780 0.33 28.12 19.4 11.29 1.38 15.65 0.37 13.56 0.51 10.51 0.03 840 0.33 28.16 19.45 11.35 1.34 15.7 0.33 13.66 0.47 10.52 0.02 900 0.33 28.21 19.56 11.37 1.29 15.79 0.3 13.69 0.42 10.55 0.03 960 0.33 28.31 19.75 11.43 1.19 15.83 0.27 13.72 0.41 10.57 0.02 1020 0.34 28.37 20 11.54 1.17 15.86 0.26 13.81 0.39 10.62 0.02 1080 0.34 28.38 20.15 11.67 1.13 15.89 0.25 13.85 0.37 10.66 0.02 1140 0.34 28.40 20.27 -8.22 1.09 15.93 0.23 13.92 0.33 10.67 0.02 1200 0.35 28.48 20.27 12.07 1.05 16 0.2 13.99 0.31 10.75 0.02 1260 0.36 28.52 20.3 12.13 1 16.03 0.18 14.02 0.27 10.77 0.01 1320 0.36 28.52 20.33 12.13 0.97 16.05 0.15 14.05 0.23 10.78 0.01

114 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

1380 0.37 28.60 20.35 12.14 0.95 16.06 0.1 14.09 0.21 10.75 0.01 1440 0.37 28.79 20.37 12.15 0.94 16.07 0.05 0.18 10.75 0.01 1500 0.37 28.90 20.38 12.2 0.94 0.08 0.16 10.75 0.01 1560 0.38 28.96 20.45 12.28 0.93 0.07 0.13 10.8 0.01 1620 0.38 29.00 20.5 12.3 0.91 0.06 0.11 10.85 0 1680 0.39 29.04 20.64 12.33 0.05 0.08 10.9 1740 0.39 29.07 20.79 12.3 10.9 1800 29.09 20.65 12.25 10.9 1860 29.09 20.55 12.2 10.9 1920 29.11 20.6 12.2 1980 29.13 20.55 12.2 2040 29.13 20.4 12.23 2100 29.15 20.4 12.22 2160 29.15 20.39 12.22 2220 29.18 20.38 12.35 2280 29.19 20.36 12.35 2340 29.19 20.3 12.36 2400 29.19 20.24 12.48 2520 29.19 20.22 12.48 2580 29.20 20.25 12.51 2640 29.20 20.26 12.57 2700 29.21 20.27 12.58 2760 29.21 19.91 12.58 2820 29.21 12.6 2880 29.22 12.61 2940 29.31 12.65 3000 29.27 12.65 3060 29.42 12.58 3120 29.47 12.55 3180 29.47 12.65 3240 29.48 12.67 3320 29.48 12.7 3480 29.48 12.68 3600 29.48 12.69 3720 29.48 12.69 3840 29.48 12.68 3960 29.48 12.69 4080 29.49 12.68 4200 29.50 12.69 4320 29.50 12.72 4460 29.51 12.73 4580 29.52 12.75 4600 29.52 12.76 4720 29.52 12.78 4840 29.56 12.79 4960 29.68 12.79 5080 29.79 12.83 5200 29.86 12.75 5320 30.01 12.74 5440 30.01 12.84 Dd = draw down (m) Rd = Residual draw down (m)

115 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

Appendix 6: Pumping Test Data (cont.)

Time BH 8348 BH 8815 BH 8114 BH 9608 (min) dd Rd dd R dd Rd dd Rd d 0.25 3.71 0.2 10.49 0.5 4.52 22.45 5.09 2.55 0.7 9.86 1 7.97 18.69 3.03 6.77 1.87 1.39 8.96 2 11.40 15.64 8.70 8.78 0.98 2.53 7.74 3 13.50 12.98 10.62 0.55 3.25 6.65 4 14.93 11.62 11.14 9.17 0.34 4.02 5.9 5 15.63 10.99 12.44 9.36 0.23 4.67 4.95 6 16.21 10.45 13.57 9.46 0.17 5.44 4.4 7 16.66 9.99 14.60 9.53 0.14 5.72 3.86 8 17.02 9.77 15.59 9.55 0.12 6.07 3.6 9 17.24 9.59 16.16 9.58 0.12 6.29 3.37 10 17.41 9.21 16.82 9.58 0.11 6.63 3.05 11 17.63 9.06 16.82 9.58 6.85 2.54 12 17.82 8.82 17.99 9.60 0.10 7.06 2.16 15 18.23 8.51 19.23 7.25 1.78 18 19.23 9.59 0.10 7.25 1.78 20 18.06 7.96 20.63 9.60 0.10 8.18 1.59 25 18.24 7.59 22.44 8.63 1.42 30 18.50 7.13 22.45 9.58 0.09 8.82 1.24 40 18.91 6.71 22.67 9.56 0.09 9.05 1.07 50 19.85 6.37 23.06 9.56 0.09 9.2 0.9 60 21.06 6.07 23.13 9.55 0.09 9.3 0.72 75 9.42 0.67 90 21.83 5.42 23.15 9.56 0.08 9.5 0.58 105 9.56 0.5 120 22.36 4.94 23.39 9.54 0.07 9.59 0.39 150 22.70 4.68 23.28 9.56 0.07 9.8 0.35 180 22.98 4.32 23.11 9.57 0.07 10.05 0.27 240 23.49 3.98 232.4 9.57 0.06 3 10.09 0.21 300 23.72 3.72 24.50 9.56 0.06 10.2 0.15 360 23.92 3.47 24.48 9.56 0.06 10.24 0.14 420 24.05 3.24 24.60 9.56 0.05 10.42 0.11 480 24.07 3.09 24.84 9.55 0.05 10.44 0.08 540 24.10 2.89 25.16 9.57 0.05 10.46 0.07 600 24.18 2.81 25.06 9.59 0.05 10.48 0.07 660 24.23 2.74 25.41 9.58 0.04 10.49 0.06 720 24.33 2.67 25.34 9.59 0.04 10.51 0.05 780 24.37 2.53 27.11 9.58 0.04 10.51 0.03 840 24.47 2.39 26.36 9.60 0.04 10.52 0.02 900 24.52 2.25 26.41 9.62 0.04 10.55 0.03 960 24.53 2.12 26.55 9.61 0.04 10.57 0.02 1020 24.64 2.10 26.69 9.61 0.04 10.62 0.02 1080 24.69 2.07 26.80 9.62 0.04 10.66 0.02 1140 24.73 2.02 26.91 9.66 0.04 10.67 0.02 1200 24.79 1.94 27.06 9.66 0.04 10.75 0.02 1260 24.96 1.90 27.15 9.66 0.04 10.77 0.01

116 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

1320 25.01 1.84 27.37 9.67 0.05 10.78 0.01 1380 25.12 1.79 27.40 9.66 10.75 0.01 1440 25.28 1.74 26.82 9.66 10.75 0.01 1500 26.75 9.66 10.75 0.01 1560 25.45 26.69 9.66 10.8 0.01 1620 26.50 9.66 10.85 0 1680 25.64 26.72 9.67 10.9 1740 26.42 9.68 10.9 1800 25.60 26.52 9.64 10.9 1860 26.55 9.63 10.9 1920 25.49 26.49 9.63 1980 26.66 9.63 2040 25.41 26.98 9.64 2100 27.21 9.64 2160 25.45 27.52 9.64 2220 27.74 9.64 2280 25.46 27.89 9.64 2340 28.09 9.64 2400 25.45 28.24 9.64 2520 28.33 9.64 2580 25.50 28.39 9.65 2640 28.51 9.65 2700 25.52 28.64 9.70 2760 28.66 9.70 2820 25.56 28.72 9.70 2880 28.70 9.70 2940 25.91 9.70 28.60 3000 29.27 9.73 3060 26.15 29.42 9.74 3120 29.47 9.73 3180 26.19 29.47 9.73 3200 29.48 9.73 3220 26.21 29.48 9.73 3240 29.48 9.74 3260 26.21 29.48 9.74 3280 29.48 9.69 3300 25.59 29.48 9.71 3320 29.48 9.71 3340 25.92 29.49 9.73 3360 29.50 9.73 3380 25.92 29.50 9.72 3400 29.51 9.73 3420 25.98 29.52 9.72 3440 29.52 9.72 3460 25.99 29.52 9.72 3480 29.56 9.72 3500 26.01 29.68 9.73 3520 29.79 9.73 3540 26.25 29.86 9.73 3560 30.01 9.73 3580 26.39 30.01 9.73 3600 9.73

117 HYDROGEOLOGICAL VERIFICATION OF MAGNETIC RESONANCE SOUNDINGS œ MAUN AREA, BOTSWANA

3620 9.74 3640 9.73 3660 9.73 3680 9.73 3700 9.73 3720 9.74 3740 9.74 3760 9.74 3780 9.74 3800 9.74 3820 9.75 3840 9.75 3860 9.75 3880 9.75 3900 9.75 3920 9.78 3940 9.78 3960 9.78 3980 9.77 4000 9.77 4020 9.77 4040 9.77 4060 9.77 4080 9.77 4100 9.81 4120 9.81 4140 9.81 4160 9.82 4180 9.82 4200 9.81 4220 9.81 4240 9.81 4260 9.81 4280 9.81 4300 9.81 4320 9.79

118