A Case Study of Horongo, Mali, West Africa
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QUANTIFYING AVAILABLE WATER AT THE VILLAGE LEVEL: A CASE STUDY OF HORONGO, MALI, WEST AFRICA By Cara W. Shonsey A REPORT Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE CIVIL ENGINEERING MICHIGAN TECHNOLOGICAL UNIVERSITY Copyright © 2009 Cara W. Shonsey This report, “Quantifying Available Water at the Village Level: A Case Study Horongo, Mali, West Africa,” is hereby approved in partial fulfillment of the requirements for the degree of Masters of Science in the field of Civil Engineering. Civil and Environmental Engineering Department: Signatures: Report Advisor __________________________________________________________________________ Typewritten Name _____John S. Gierke_____________________________ Department Chair _____________________ ____________________________________________________ Typewritten Name ___William M. Bulleit___________________________ Date _________________________________________________________________________ ii Table of Contents 1 Executive Summary ....................................................................................................................................... 1 2 Introduction ..................................................................................................................................................... 2 2.1 Project motivation ................................................................................................................................ 4 2.2 Objectives ................................................................................................................................................ 5 3 Project site: Horongo, Mali (N 13o02’, W 9o36’) ................................................................................ 6 3.1 The Horongo watershed .................................................................................................................... 7 3.2 Water access outside the Horongo Watershed ........................................................................ 9 3.3 Water access in the Horongo Watershed ................................................................................. 10 4 Methods ............................................................................................................................................................ 13 4.1 The water balance .............................................................................................................................. 14 4.2 Evapotranspiration ............................................................................................................................ 16 4.3 Hydraulic conductivity ..................................................................................................................... 20 4.4 Water use interviews ........................................................................................................................ 21 4.5 The groundwater flow model ........................................................................................................ 23 5 Resu lts ............................................................................................................................................................ 26 5.1 Net precipitation ................................................................................................................................. 26 5.2 Hydraulic conductivity ..................................................................................................................... 28 5.3 Village water use ................................................................................................................................. 29 5.4 Calibration of the groundwater flow model ............................................................................ 35 6 Available water ............................................................................................................................................ 39 7 Future work .................................................................................................................................................... 43 8 Conclusions ..................................................................................................................................................... 43 Append ic es ............................................................................................................................................................... 49 A. Cultural attributes of Horongo ...................................................................................................... 49 B. Observed well construction ........................................................................................................... 51 C. Examples of well reinforcement .................................................................................................. 52 D. Water leaving the watershed as vegetables ............................................................................ 54 E. Annual numerical estimates of net precipitation and evapotranspiration from the water balance ................................................................................................................................................. 55 F. Digital Files on attached CD ........................................................................................................... 56 G. Recovery curves from AQTESOLVE ............................................................................................ 57 i H. Observed, seasonal groundwater levels in hand‐dug wells .............................................. 62 I. Image publication permission ....................................................................................................... 63 J. Human subject research approval: Michiagan Technological University ................... 64 List of Figures Figure 2.1, Increased global water stress (UNEP/GRID‐Arendal 2009) .................... 2 Figure 3.1 Map of Mali, West Africa (adapted from Map Library 2009) ................................. 6 Figure 3.2 The Horongo watershed (ASTER DEM image. Source LPDAAC 2008) ................................................................................................................................. 7 Figure 3.3 Distribution of well reinforcement in Horongo ....................................... 11 Figure 4.1 Data input and expected outcomes for the groundwater flow model .............................................................................................................................. 13 Figure 4.2 The hydrologic cycle ................................................................................... 15 Figure 4.3 Conceptual model of the Horongo watershed (the image was exported from GMS 6.5) ................................................................................................ 24 Figure 5.1 Annual evapotranspiration and net precipitation estimated from the water balance and the corresponding annual, cumulative precipitation records from Kita ........................................................................................................... 26 Figure 5.2 Monthly water balance estimated from the Thornthwaite‐Mather and Hamon method ........................................................................................................ 27 Figure 5.3 Hydraulic conductivity for the aquifer under the village of Horongo at varying saturated depths .......................................................................... 28 Figure 5.4 Daily domestic water use for the village of Horongo .............................. 30 Figure 5.5 Seasonal water extraction from each well in Horongo ............................ 33 Figure 5.6 Simulated subsurface water levels for the calibrated model at the end of rainy season (the image was exported from GMS 6.5) ................................... 36 Figure 5.7 Contours of water table drop (m) around the time of the February observations or after 120 days of no recharge (the image was exported from GMS 6.5) ................................................................................................ 37 Figure 5.8 Contours of water table drop (m) around the time of the May observations or after 230 days of no recharge (the image was exported from GMS 6.5) .......................................................................................................................... 38 Figure 6.1 Simulated GWT draw downs at the end (230 days) of the dry seasons if the entire area under the village was evenly pumped (the image was exported from GMS 6.5) ........................................................................................ 40 Figure 6.2 Estimated GWT drawdowns at the end of hot season from two pumps, assuming equal extraction. (the image was exported from GMS 6.5) ......... 41 Figure 6.3 Simulated GWT draw downs for the maximum production of four pumps (80‐100 m3/day) at the end of the dry seasons (230 days) (the image was exported from GMS 6.5) ............................................................................. 42 ii List of Tables Table 4.1 Range of root zone depth and soil field capacity for the Thornthwaite‐Mather and Hamon water balance model ........................................... 17 Table 4.2 Parameter combinations run in the MODFLOW‐2000, steady‐state, rainy‐season model ....................................................................................................... 25 Table 5.1 Daily water use for the village