Digital Atlas of the World Water Balance, Version 1.0, May 1997
Education Folder

Center for Research in Water Resources
University of Texas at Austin

Table of Contents


The purpose of these exercises is to provide instruction in the use of the Arcview and Arc/Info geographic information systems in their application to hydrology and water resources problems in Africa. All the data files required for them are available via anonymous ftp from in directory /pub/crwr/gishydro/africa. Some of the exercises were adapted from a GIS in Water Resources course taught each Spring semester by David R. Maidment in the Dept of Civil Engineering, University of Texas at Austin. Others were developed specifically for a GIS in Water Resources short course taught by Dr Maidment at the Direction Generale de l'Hydraulique in Rabat, Morocco, in November 1996. The translations of the exercises were prepared by Christine Dartiguenave (into French) and Francisco Olivera (into Spanish). Each exercise normally takes 3-4 hours to be completed. If you don't have access to the Arcview software needed to do the exercises, you can still read through them and understand the nature of the analysis from the instructions and pictures presented there.

The first Exercise uses climatological data from Morocco to introduce the reader to spatial data presented in Arcview. Map projections are described in the second Exercise in which latitude-longitude coordinates on a curve earth surface are transformed into (x,y) coordinates on a flat map. The soil water balance of a region of Morocco near Marrakesh is used in Exercise 3 to show how monthly precipitation, temperature and net radiation data are transformed into monthly soil water content, evaporation and soil water surplus values using Arcview Avenue programs prepared by Seann Reed. A map-based surface water simulation model of the Niger Basin in West Africa is presented in Exercise 4 which routes the soil water surplus produced by the model in Exercise 3 through the Niger River, using the computation of the discharge at the Koulikoro gaging station as an example. The watershed flow routing methodology for this exercise was developed by Francisco Olivera. Groundwater flow simulation in Avenue is presented in Exercise 5 using a simple 5x5 grid of cells representing a uniform porous medium between two rivers subject to a uniform infiltration. This groundwater model has been connected to the surface water flow simulation in Exercise 4 by Zichuan Ye . In Exercise 6, the Arcview Spatial Analyst is used to delineate the watersheds and stream network of the Souss Basin in Morocco and the surface flow simulation routine in Exercise 4 is prepared for this basin.

Directory of Exercises

Table of Contents

Table des Matières


Application to the Niger Basin

The exercises are intended for self-learning in the application of GIS using Arcview to hydrologic issues in West Africa, in particular, in Morocco and in the Niger River basin of West Africa, which are used as case study regions for the database and model development.Monthly soil water surplus is calculated using a Thornthwaite soil water balance model, although the evaporation computation has been modified to include a spatial database of net radiation obtained from the Earth Radiation Balance Experiment. These water surpluses are transferred onto subwatersheds of the Niger Basin

and routed through its river system using the Muskingum method. The flow from the subwatershed to the river moves partly through the subsurface system and partly through the surface system, each delayed in time by a differing amount. The graphics attached depict the simulated and observed flow for the Niger river at Koulikoro, one of the principal gaging stations on the Niger river above its Inner Delta. The results are obtained by clipping out a portion of the main basin model to form a Koulikoro submodel, including just those watersheds whose drainage passes through the gage at Koulikoro.

Then the model parameters are optimized so that the discharge record there is fitted as well as possible. The simulations carried out are for a 90 month period from July 1983 to December 1990. In the attached flow chart, the horizontal axis is the time in months from July 1983, the vertical axis is the Niger River discharge in cubic meters per second, the green lines are the calculated flows and the red lines are the measured flows at Koulikoro. The observed flow data were obtained from the Global Runoff Data Center in Koblenz, Germany.

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These materials may be used for study, research, and education, but please credit the authors and the Center for Research in Water Resources, The University of Texas at Austin. All commercial rights reserved. Copyright 1997 Center for Research in Water Resources.