INTERNATIONAL HYDROLOGICAL PROGRAMME
Southern Africa FRIEND
Flow Regimes from International Experimental and Network Data
IHP-V Project 1.1
IHP-V 1 Technical Documents in Hydrology 1 No. 15
UNESCO, Paris, 1997
This report is dedicated to the memory of Dirk Plathe of the
Department of Water Affairs of Namibia, killed during the first meeting of the representatives of Southern African FRIEND
Published by UNESCO in cooperation with the Southern African FRIEND Steering Committee This report should be referenced as UNESCO (1997) Southern African FRIEND, Technical Documents in Hydrology No. 15, UNESCO, Paris.
Individual chapters should be referenced as ‘Chapter author(s)’ (1997), ‘Chapter Heading’, in Southern African FRIEND, Technical Documents in Hydrology No. 15, UNESCO, Paris.
Contributions by other researchers within Chapter 4 should be referenced as ‘Contributor(s)’
(1997) ‘Contribution Heading’, in Bullock A., Andrews A.J. and Mngodo R. (Eds.) Chapter 4
‘Regional surface water and drought assessment’, in Southern African FRIEND, Technical Documents in Hydrology No. 15, UNESCO, Paris.
NOTE:
The designations employed and thepresentation ofmaterial throughout thepublication do not imply the expression of any opinion whatsoever on the part of UNESCO concerning the legal status of any country territov, city or of its authorities, or concerning the delimitation of its frontiers or boundaries.
Foreword
During the inception of FRIEND in Europe during the mid- 1980s it was the strong desire of the MP Intergovernmental Council that the international collaboration encapsulated by the programme should be extended to other regions of the world. It is therefore with great pleasure that I write this foreword to Southern African FRIEND, the first regional report to be produced outside of Europe. UNESCO is greatly encouraged by the advances in FRIEND in Africa through this Southern African Programme, the Western and Central (AOC) Programme and the recently launched Nile Basin initiative. The theme of FRIEND is the application of methods of hydrological analysis using regional data sets, and an impressive component in this report is the assembled regional data sets. Africa is viewed as a continent which is poorly represented by data. The assembly of over 700 flow records and associated thematic data from 11 countries will do much to suggest otherwise, not least the fact that regional hydrology can be significantly advanced using a core of reasonable quality information. The construction of such an international database gives much credit to the participating countries for their willingness to freely exchange hydrological data.
A key direction of the Fourth Phase of IHP has been water for sustainable development - water is increasingly a scarce resource in the region, and one which is fundamental to development in the next century, particularly in the agricultural, domestic and energy sectors. A special dimension in this FRIEND project is the close integration that has occurred between operational institutions and research groups, offering improved opportunities for translating research products into operational and applied solutions. The databases will no doubt provide an invaluable foundation to many future projects; regional flood frequency analysis provides methods for improved dam safety and structure design; methods for regional water resource assessments enable the quantificatian of the volume and variability of the available resource in rivers; drought assessment will contribute to minimising the impact of
drought occurrence; and rainfall-runoff modelling provides for improved operational design and impact assessment.
This integration between research and applications has been advanced by the strong emphasis on capacity building, with dissemination of software products and 500 man-days of training. Advantages of scientific analyses across international boundaries abound in this report; with so many international river systems, national boundaries are perhaps less relevant to hydrology in this region of the world than elsewhere. Equally, there are relatively few active hydrological researchers and there are obvious benefits in pooling the expertise of the region. Yet international cooperation is not always the simplest of concepts to achieve, and substantial credit is due to the programme Coordination Centre at the University of Dar-es-Salaam, and the programme Steering Committee for their accomplishments. As the programme developed in its early days, it was very pleasing to witness the smooth assimilation of the South African hydrological community into the programme.
The future for FRIEND in Southern Africa looks very promising; the investment in database activities can only serve to ease future research; the programme is well- integrated into the SADC framework of water management objectives, and these links and interactions can only strengthen with the newly-formed SADC Water Sector and the direction of the Protocol on Shared Watercourses; there are opportunities for forging close links with the WMO Operational Hydrology Programme, not least the Hydrological Cycle Observation System (HYCOS). Africa is a priority in forthcoming UNESCO programmes, and FRIEND represents an excellent foundation. It is my understanding that the opportunities for participation in FRIEND remain open for fruitful scientific collaboration which enhances capacity; I end this foreword by repeating my earlier call for the global hydrological com,munity to support our FRIENDS in Africa, to assist them to build on their excellent achievements.
Andras +Y+%i-Nagy Internaiional Hydrological Programme
UNESCO
Introduction
The availability of water is determined by precipitation, which in the southern African region varies between on average 25 and 1 500 mm per year, but rains are seasonal in nature, extremely variable and very uncertain. Rainfall is unevenly distributed in time and evaporation losses are high with the result that there are no areas where a consumer can rely on 100% assurance of availability ofwater. In many areas in the SADC Region adequate water supply has reached a crisis or will reach it soon despite the persistent and innovative efforts of water resource experts. Reports indicating more frequent occurrences of El Nino droughts and climatic change emphasize the need for thorough hydrological assessments.
All important river basins are shared in the southern African region, and, for most countries, these provide the only resources of which the utilization can still be expanded. To ensure a sustainable, equitable and efficient development, a basin-wide approach is a primary prerequisite, and all SADC countries are in support of governing international principles as laid down in the Helsinki Rules (1966) and the Convention of Law of Non-Navigational Uses df International Water Courses (1997). Most countries have therefore already acceded to the SADC Protocol on Shard River Basins, which will be the basis for the establishment of regional river basin authorities. These institutions will develop, monitor and coordinate water use, as well as resolve conflicting interests.
Effective cooperation starts with exchange of information and ideas, and the FRIEND Project has been one of the catalysts in respect of giving scientists and engineers in the region opportunities to establish both professional and personal contacts with colleagues from other countries. This was experienced in particular by Namibia, because the FRIEND Project, which had its inception meeting in Harare in January 199 1, was the,first opportunity to take part as an independent country in regional hydrological activities.
FRIEND is one of the projects strengthening existing technical and institutional capacity of national and regional water institutions.
The first phase of the FRIEND project carried dut a fruitful exercise. Technical resources were developed at leading scientific institutions at Dar-es-Salaam and Grahamstown and shared throughout the region, with the active support of the Institute of Hydrology in Wallingford. A regional database was developed, integrating hydrological information from all 11 countries involved. This could then be used to assess regionalization of flow characteristics, with special emphasis on drought conditions, GIS applications, rainfall/runoff modeling and flood frequency analysis.
The institutional framework for water management in SADC is constantly evolving, with the creation of the Water Sector and the establishment of the Water Resources Technical Committee. FRIEND has actively sought cooperation, and has emerged as an organization stimulating regional hydrological data exchange as well as research and training activities.
A great distance has been covered, mainly in the collection and analysis of hydrological information. The next phase of the FRIEND Project should be able to build on this achievement to enlarge the scope into the planning field.
The inclusion of water resources development and utilization aspects will be of great assistance to the sustainable development of regional water resources. The continuation of the FRIEND Project will therefore answer both scientific and socio-economic questions.
Piet SvH, Heyns Director: Resource~Management Department of Water Affairs Ministv ofAgriculture. Water and Rural Development Republic of Namibia
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PREFACE
The FRIEND (Flow Regimes from International Experimental and Network Data) research programme is a contribution to Project H-5-5 of the Fourth International Hydrological Programme of UNESCO, the aim of which is
“Application of methods of analysis using regional data sets”. The FRIEND research programme has been active in Northern and Western Europe since the mid- 1980s and has resulted so far in the publication of two European FRIEND Reports and two International FRIEND Conferences.
European FRIEND is founded on the active collaboration between 17 countries.
The success of the European initiative in FRIEND encouraged the subsequent evolution of the Alpine and Mediterranean (AMHY) FRIEND group, who have been active since 1991. In response to the desire of the International Council of the UNESCO IHP to extend the FRIEND concept beyond Europe, two active FRIEND groups evolved in the early 1990s in Africa; the Southern African FRIEND programme and FRIEND AOC (Afrique Orientale et Centrale). During 1996, new FRIEND groups were established in South-East Asia, the Nile Basin and the Hindu Kush/Himalayan region. Embryonic discussions have been held regarding future FRIEND initiatives in the Middle East and South America. A Third General FRIEND report was published in 1997.
The FRIEND research programme is essentially a coordinated collection of individual research projects with the common goal of applying methods of analysis using regional data sets. This phase of the Southern African FRIEND programme has been supported by four projects:
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‘Regional analysis of floods and low flows in Tanzania’, implemented by the University of Dar-es-Salaam on behalf of the Ministry of Energy, Water and Minerals, funded by the Irish Ministry of Foreign Affairs
‘Southern African FRIEND: the application of rainfall- runoff models in the SADC region’ implemented by the Institute for Water Research at Rhodes University, South Africa, funded by the South Africa Water Research Commission
‘Southern African Low Flows’ implemented by the Institute of Hydrology, funded by the Overseas Development Administration, UK
‘Estimation of runoff and evaporation in Southern Africa’, implemented by the Institute of Hydrology, funded by the Department For International Development, UK ‘HYDATA dissemination’, implemented by the Institute of Hydrology, funded by the Department For International Development, UK.
The FRIEND project has been supported by the active participation of the National Hydrological Services of eleven SADC countries FRIEND contacts within each country are set out below. Representatives from each country have composed the Programme Steering Committee (as tabulated), along with representatives of UNESCO, SADC Environment and Land Management Sector, the Programme Coordination Centre at the University of Dar- es-Salaam, Rhodes University and the Institute of Hydrology. Principal researchers in the Southern African FRIEND programme (see below) have been responsible for the coordination and implementation of FRIEND activities, and other hydrologists have contributed shorter term inputs.
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ACKNOWLEDGEMENTS
The contributors to the report, and the FRIEND Steering Committee, convey their appreciation to over 40 organisations including UNESCO, national IHP Committees, National Hydrological Services, Meteorological Services, Research Institutes, Universities, funding agencies, regional institutions and United Nations organisations for their assistance with Southern African FRIEND:
British Geological Survey (Hydrogeology Group), UK Climatic Research Unit, University of East Anglia, UK
Department of Civil Engineering, University of Dar-es-Salaam, Tanzania Department of Meteorology, Malawi
Department of Meteorology, Swaziland
Department of Meteorological Services, Ministry of Transport and Energy, Zimbabwe Department of Water Affairs, Botswana
Department of Water Affairs, Lesotho Department of Water Affairs, Namibia Department of Water Affairs, Zambia
Department of Water Affairs and Forestry, South Africa
Department of Water Resources, Ministry of Lands and Water Resources, Zimbabwe Department For International Development, UK
Dirrecao National de Aguas, Mozambique Directorate of Water Affairs, Angola
Global Runoff Information Database, UNEP, Nairobi, Kenya Huntings Technical Services, UK
Hydrological Branch, Ministry of Irrigation and Water Development, Malawi Institute of Hydrology, UK
Institute for Water Research, Rhodes University, South Africa International Association of Hydrological Sciences
International Institute for Applied Systems Analysis, USA Meteorological Department, Botswana
Meteorological Department, Zambia Meteorological Division, Lesotho Ministry of Foreign Affairs, Ireland
Mott MacDonald Consultants, Cambridge, UK Natural Environment Research Council, UK
National Oceanographic and Atmospheric Administration Environmental Protection Agency, USA Royal Geographical Society, UK
Southern African Development Community Environment and Land Management Sector Southern African Development Community Regional Inventory of Agricultural Base Southern African Development Community Water Sector
Southern African FRIEND Coordination Centre, University of Dar-es-Salaam, Tanzania UNESCO Division of Water Sciences, Paris, France
UNESCO Regional Offtce for Africa, Kenya
United Nations Environment Programme Global Resource Information Database United Nations Food and Agriculture Organisation
United States Geological Survey
Water Research Commission, South Africa
Water Resources Branch, Ministry of Natural Resources, Environment and Energy, Swaziland Water Resources Department, Ministry of Water, Tanzania
World Wide Fund for Nature International
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STEERING COMMITTEE MEMBERS
During Southern African FRIEND, an initial launching meeting was held in Hat-are Zimbabwe (l), followed by three programme Steering Committee meetings, held in Dar- es-Salaam, Tanzania in 1994 (2), Grahamstown, South Africa in 1996 (3), and Hat-are, Zimbabwe in 1997 (4).
National representatives to these meetings were:
Angola - Mr. F. Netoc), Mr. P. Mendesc4)
Botswana - Mr. I. Muzila”), Mr. K. Kalaote(‘%2,3*4) Lesotho - Mrs. M. Nteso”,?), Mr. M. Masopha”), Mr: S.
Makhoalibec3), Mr. S. Tauc3)
Malawi - Mr. 0. Shela(‘), Mr. A. Chirwao), Mr. D. Naketoc), Mr T Kaluwa(4) . .
Mozambique - Mr. P. Napica”), Mr. I. Chutumia(‘), Mr. C.
Cuamba(3s4’ Mr H Banzec3) . .
Namibia - Mr. D. Plathe”), Ms. A. Eggers(‘,3,4), Mr, G. van Langenhove”), Ms. B. de Bruine(3)
South Africa - Mr. S. van Biljoen(3), Mr. E. Nelc4) Swaziland - Mr. M. Lukhele”), Mr. S. Dlamini”), Mr. R.
Thabedeu), Mr K Msibi(3”) . .
Tanzania - Mr. M. Msuya(‘z’x3), Mr. S. Ferajic’), Mr. J.M.
Mihayoc4)
Zambia - Mr. M. Mulipukwa”), Mr. C. Chileshe(‘,‘*3*4) Zimbabwe - Mr. B. Chatukuta(‘), Mr. G. Mawere(‘.3.4), Mr.
R. Chikwanhac2)
Other representatives and observers at Steering Committee meetings were:
Univ. of Dar Es Salaam (Coordination Centre)
Dr. R. Kachroo(‘,?,4), Dr. J.I. Matondo’l), Mr. I.
Mwakalingac2), Mr. F. Mta10(‘*~*~), Mr. R. Mngodoc2), Mr. S.
Ml&an&(2.3.4)
UNESCO - Dr. H. Zebidi(Q), Dr. A. Szollbsi-Nagy(3), Dr.
E. Naahc4’
SADC Water Sector - Mr. 0. Shela@), Mr. L. Thamae’3*4) Rhodes University - Prof. D. Hughes(2,3*4), Mr. V.
Smakhtin(3)
Institute of Hydrology - Dr. A. Bullock(‘~?*3~4), Dr. A.
Gustard(‘,‘,3’, Mr. A. Andrews(‘.314) SANCIAHS - Mr. H. Maaren”) IAHS - Dr. J. Roddac3) UNEP - Ms I. Vanderbeckt3) FAO - Mr. J.-M. Fauresc3)
UNDP/WMO Drought Monitoring Centre - Mr. L.
Unganai(4)
European Union -’ Mr. P.. Devillez(4)
West and Central Africa FRIEND - Mr. B. Chuzeville(r), Dr. E. Servatc4)
Zimbabwean observers at the 1997 Harare Meeting were Mr. D.S. Durham, Dr. J. Sakupwanya, Mr. E. Madamombe, Mr. W. Luxemburg and Mr. J. Merka
PROGRAMME COORDINATOR
The current programme coordinator is Dr. S. Mkhandi, FRIEND Coordination Centre, Dept. of Civil Engineering, University of Dar-es-Salaam, PO Box 35 13 1, Tanzania, (Tel./Fax. 255-5 l-43029,water@udsm.ac.tz)
RESEARCH CONTRIBUTORS
The principal researchers in Southern African FRJEND have been:
Mr. A.J. Audrews, Institute of Hydrology, Wallingford, UK, aja@ua.nwl.ac.ul
Dr. A. Bullock, Institute of Hydrology, Wallingford, UK, anb@ua.nwl.ac.uk
Prof. D. Hughes, Rhodes University, South Africa, denis@iwr.ru.ac.za
Dr. R. Kachroo, University of Dar -es-Salaam, Tanzania, water@udsm.ac.tz
Dr. S. Mkhandi, University of Dar-es-Salaam, Tanzania, water@udsm.ac.tz
Dr. R. Mngodo, University of Dar-es-Salaam, Tanzania, water@udsm.ac.tz
Mr. I. Mwakalinga (Hydrological Service of Tanzania) was River Flow Database Manager at the Programme Coordination Centre.
A. Chirwa (Hydrological Branch, Malawi), Mr. J.
Matondo (then University of Dar-es-zsalaam) and D.
Mazvimavi (University of Zimbabwe) contributed to
“Analysis of flow regimes in Malawi, Tanzania and Zimbabwe - a feasibility study for Africa FRIEND”.
Contributions to the river flow database project have been made by staff of the National Hydrological Services of the eleven participating countries.
Other contributions have been made by; Ms. A. Hatutale, Department of Water Affairs, Namibia
and to the Spatial Database Project by Mr. K. Wencel, Mr.
P. de Henaut, Mr. S. Neale, Ms. S. Hills, Mr. H. Noor and Mrs. J. Dixon of the Institute of Hydrology.
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HYDROLOGICAL SERVICES
Eleven national hydrological services have actively participated in FRIEND:
Angola - Department of Water Affairs, Ministry of Energy and Water, PO Box 143, Luanda.
FRIEND Contact: Mr. F. Neto Tel: 244 2390385
Fax: 244 233403712397979
Botswana - Department of Water Affairs, Private Bag 0029, Gaborone
FRIEND Contact: Mr. K. Kalaote Tel: 267 3607100
Fax: 267 303058
Lesotho - Department of Water Affairs, PO Box 772, Maseru- 100
FRIEND Contact: Mrs. M. Nteso Tel: 266 310437
Fax: 266 317516
Malawi - Hydrological Branch, Ministry of Irrigation and Water Development, Private Bag 390, Lilongwe 3 FRIEND Contact: Mr. A. Chirwa
Tel: 265 780344 Fax: 265 784678
Mozambique - Direccao National de Aguas, Av. 25 de Setembro, C.P. 1611, Maputo
FRIEND Contact: Mr. C. Cuamba Tel: 258 1420469
Fax: 258 1421403
Namibia - Department of Water Affairs, Private Bag 13193, Windhoek
FRIEND Contact: Ms. A. Eggers Tel: 264 61263141
Fax: 264 61 2637741263222
South Africa - Department of Water Affairs and Forestry, Private Bag X3 13, Pretoria
FRIEND Contact: Mr. S. Van Biljoen Tel: 27 12 3388784
Fax: 27 12 3261488
Swaziland - Water Resources Branch, Box 57, Mbabane
FRIEND Contact: Mr. K. Msibi Tel: 268 4232 1
Fax: 268 42015
Tanzania - Ministry of Water, Energy and Minerals, PO Box 35066, Dar-es-Salaam
FRIEND Contact: Mr. M. Msuya Tel: 255 051 43452
Fax: 255 05143278
Zambia - Department of Water Affairs, PO BOX 30530, Lusaka
FRIEND Contact: Mr. C. Chileshe Tel: 260 1 25 1525/248304/242827 Fax: 260 1 2431361252589
Zimbabwe - Hydrological Branch, Ministryof Lands and Water Development, Box Cy 726, Causeway, Harare,
FRIEND Contact: Mr. G. Mawere Tel: 263 4 707861/793551 Fax: 262 4 722752
ABBREVIATIONS AND SYMBOLS
No rationalisation of abbreviations and symbols has been attempted between different chapters in the report since it would have been counter to common usage and potentially would have caused more confusion than it avoided. Because of the widely different ways in which terms with common letters are used, there is little danger of misunderstanding.
Full descriptions of the Pitman and VT1 mode] parameters are presented in Tables 5.1 and 5.3 respectively. That information is not replicated in the following list.
ACC/ISGWR - (UN) Administrative Committee on Coordination/Inter-Secretariat Group for Water Resources ACRU - Agricultural Catchment Research Unit rainfall- runoff model
ADS - ARC Digitising System (within ARC-INFO Geographical Information Software)
AE - Actual Evaporation (in mm) AM - Annual Maximum (flood series)
AMHY - Alpine and Mediterranean region of FRIEND AML - ARC Macro Language (within ARC-INFO Geographical Information Software)
AOC - West and Central Africa (Afrique Orientale et Centrale) region of FRIEND
AP - Annual Rainfall (in mm) AR - Annual Runoff (in mm)
ARC - Agricultural Research Council (South Africa) ARC - One component of ARC-INFO Geographical Information Software
ARC/INFO - a Geographical Information Software package b - PDM model parameter determining the spatial variability of maximum soil capacity
BFI - Base Flow Index
BL - Block Length within the BFI calculation algorithm c - parameter in a decaying infiltration rate function CAD - Computer Assisted Design
CAT-CHAR - ORACLE table of catchment characteristics CC - coefficient of variation of at site Lcv’s
CD-ROM - Compact Disk-Read Only Memory CE - Coefficient of efficiency
CIOC - Central Indian Ocean Coast primary river basin Ck - coefficient of kurtosis
CLICOM - WMO climate archiving software CO2 - carbon dioxide
CRU - Climate Research Unit, University of east Anglia (UK)
Cs - coefficient of skewness
CSIR - Council for Scientific and Industrial Research (South Africa)
CV - Coefficient of Variation
CV(AR) - Coefficient of Variation of Annual Runoff D - discordancy measure
DBMS - Database Management System DEM - Digital Elevation Model
DG - Directorate General DHI - Danish Hydraulics Institute DNA - Direccao National de Aguas DOS - Disk Operating System
DTED - Digital Terrain Elevation Data DWA - Department of Water Affairs (Namibia)
DWAF - Department of Water Affairs and Forestry, South Africa
E0 - Penman Potential Evaporation (in mm)
ECMWF - European Centre for Medium-range Weather Forecasts
ENS0 - El Nino Southern Oscillation EPA - US Environment Protection Agency EROS - Earth Resources Observation Satellite
ESRI - Environmental Systems Research Institute Incorporated
EVl - Form of the Gumbel distribution EXP - exponential distribution
f c code - FRIEND catchment code -- f h zone - FRIEND hydrometric zone -- f.s.e. - factorial standard error
FAO - United Nations Food and Agriculture Organisation FID - FRIEND IDentification
FLOWPATH - routine within ARC-INFO for constructing flowpaths with the DEM
FORTRAN - a computer programming language
FREND - Flow Regimes from Experimental and Network Data (a predecessor of FRIEND)
FRIEND - Flow Regimes from International Experimental and Network Data
GCM - Global Climate Model GED - Global Environmental Data GEV - General Extreme Value distribution GIS - Geographic Information System GPA - General Pareto distribution
GRID - UNEP Global Resource Information Database H - Heterogeneity measure statistics
HEP - Hydro-electric Power HRU - Hydrological Research Unit
HYCOS - WMO HYdrological Cycle Observation System Programme
HYDATA - Institute of Hydrology (UK) software for archiving, processing and analysing hydrological data HYFFAP - Institute of Hydrology (UK) software for flood frequency analysis
HYLUC - Institute of Hydrology (UK) software for land- use change studies
HYMAS - Rhodes University Institute for Water Research Hydrological Modelling Application System
HYRROM - Institute of Hydrology (UK) rainfall-runoff modelling software
IAHS - International Association of Hydrological Sciences
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IGBP - International Geosphere Biosphere Programme IDD - International Direct Dialling
IFR - Instream Flow Requirement IH - Institute of Hydrology
IHP - International Hydrological Programme of UNESCO IHP IV Fourth Phase of the IHP
IMTR - Institute for Meteorological Training and Research (Nairobi, Kenya)
INFO - Database component of ARC/INFO ITCZ - Intertropical Convergence Zone
IUCN - International Union for the Conservation of Nature IWR - Institute for Water Research at Rhodes University, JICA - Japanese Internation Cooperation Agency Grahamstown, South Africa
k - parameter in a decaying infiltration rate function k - parameter in a non-linear storage discharge equation km - kilometre
1 - litre
LDF - Lateral Distribution Factor
LHWP - Lesotho Highlands Water Project LLG - Log-logistic distribution
Ln - log-normal
LN3 - 3 parameter log-normal distribution m - metre
MAF - Mean Annual Flood
MAP - Mean Annual Rainfall (in mm)
MAPE - Mean Annual Potential Evaporation (in mm) MAPEER - Mean Annual PEER (in mm)
MAR - Mean Annual Runoff (in mm) MCM - Million Cubic Metres MF - Mean Flow (in m3 s-l)
MIKE SHE - Version of the Systeme Hydrologique Europeen rainfall-runoff model
Ml - Megalitre
ML - Maximum Likelihood parameter estimation method MOM - Method of Moments parameter estimation method MS WINDOWS - Microsoft Windows (a commercial Operating System)
MWEM - Ministry of Water, Energy and Minerals (Tanzania)
n - number in a sample
n - parameter in a non-linear storage discharge equation n c code - National catchment code --
n h zone - National hydrometric zone
NAM - a lumped conceptual rainfall-runoff model NAMROM - a Namibian rainfall-runoff model NDVI - Normalised Difference Vegetation Index NERC - Natural Environment Research Council NIOC - North Indian Ocean Coast primary basin NOAA - US National Oceanographic and Atmospheric Administration
NR - normal distribution
OBS - observed river flow series
OKACOM - Okavango River Basin Commission
ONC - Operational Navigational Charts
ORACLE - a commercial relational database management system
p - annual exceedance percentile P - Parent distribution
P3 - Pearson Type 3 distribution pe - probability of exceedance PC - Personal Computer
PDM - Probability Distributed Model PE - Potential evaporation
PEER - Potential Evaporation Excess Rainfall PWM - Probability Weighted Moments parameter estimation method
Q - Discharge
QinS, - Instantaneous discharge Q~rvmx - Maximum mean discharge q - daily mean flow
Q(P) - Discharge associated with an exceedance percentile on the flow duration curve
r - AEIMAPE
r, - first order serial autocorrelation coefficient rmse root mean square error
R - correlation coefficient R’ - Coefficient of Determination
RDBMS - Relational Database Management System RDF - Rainfall Distribution Factor
REGION - routine within ARC-INFO for associating polygons
RIARB - Regional Inventory of Agricultural Resource Base s - second
S - Storage term
S - Soil moisture content within the PDM model S - covariance matrix
s.e. - standard error
SHE - Systtme Hydrologique Europeen rainfall-runoff model
Smax - PDM model parameter defining the constant maximum amount of water that may be held in the soil ST - Moisture storage parameter
So - st. dev. of observed flow series S, - st. dev. of simulated flow series St. dev. - standard deviation
S 1085 - definition of catchment slope (between the 10 and 85 percentiles of mainstream length, in an upstream direction)
SADC - Southern African Development Community SADCC - Southern African Development Coordination Conference (a predecessor of SADC)
SANCIAHS - South African National Committee for IAHS SCS - US Soil Conservation Service
SIM - simulated
SIOC - Southern Indian Ocean Coast SMD - Soil Moisture Deficit
SMEC - Snowy Mountain Engineering Corporation
VIII .
SO1 - Southern Oscillation Index SPILLC - spillway capacity SPILLW - spillway width
SVAT - Soil-Vegetation-Atmosphere-Transfer Model T - return period
TCEV - two component extreme value distribution TIME - cumulative time since the start of a rainfall event u - vector within the discordancy measure
UDSM - University of Dar-es-Salaam, Tanzania UNDP - United Nations Development Programme UNEP - United Nations Environment Programme UNEP-GRID - United Nations Environment Programme Global Resource Information Database
UNESCO - United Nations Educational, Scientific and Cultural Organisation
USDMA - United States Defence Mapping Agency USGS - United States Geological Survey
UTM - Universal Transverse Mercator UK - United Kingdom
VDF - Vertical Distribution Factor VT1 - Variable Time Interval W - watts
WAKS - form of the Wakeby distribution WATBAL - a rainfall-runoff model WB - Weather Bureau (South Africa) WMO - World Meteorological Organisation
WR90 - Water Resources 1990 study of South Africa WRC - Water Research Commission, South Africa WWF - World Wide Fund for Nature International WY - Water Year (October to September)
CONTENTS
Foreword i
Introduction ii
PREFACE
ACKNOWLEDGEMENTS Steering Committe Members Hydroloigcal Services Abbreviations and Symbols Executive Summary
1. INTRODUCTION
1.1 Introduction
1.2 FRIEND and the UNESCO IHP
1.3 Key hydrological features and institutions of Southern Africa 1.4 Setting priorities for research
1.5 From research to design 1.6 Structure of the report References
2. SOUTHERN AFRICA RIVER FLOW DATABASE
2.1 Introduction
2.2 Identification and selection of flow series 2.2.1 Master register of gauging stations 2.2.2 Selection of appropriate flow series 2.3 Database construction
2.3.1 A new regional unifying gauging station numbering scheme 2.3.2 A common flow archiving software system
2.3.3 Establishment of data transfer agreements 2.3.4 Assembly of the database
2.4 Data validation
2.4.1 Validation of flow data
2.4.2 Data categorisation for research purposes 2.5 Data distribution
2.6 Content of the river flow archive
2.6.1 Record lengths and catchment areas 2.6.2 Geographic extent of the archive
2.6.3 Distribution of flow records within research categories
2.7 Summary of accomplishments of the FRIEND river flow database project 2.8 Recommendations
Reference
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1 1 4 5 8 12 13
15
15 15 15 15 16 16 17 18 18 18 18 18 19 19 19 20 20 21 21 22
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3. SOUTHERN AFRICA FRIEND SPATIAL DATABASE 23
3.1 Introduction
3.2 An introduction to the concepts of geographic information systems 3.3 Source information for the FRIEND spatial database
3.3.1 Topographic and thematic maps 3.3.2 Digital data sets
3.4 Southern Africa FRIEND spatial coverages
3.4.1 An integrated coverage of river basin, gauged catchment and national boundaries 3.4.2 Elevation and slope
3.4.3 River network 3.4.4 Rainfall
3.4.5 Potential evaporation 3.4.6 Vegetation and land use 3.4.7 Soils
3.4.8 Wetlands
3.4.9 Geology and hydrogeology
3.4.10 Morphometric catchment information 3.5 Database sampling and retrieval methods 3.6 Accomplishments of the Spatial Database Project
3.7 Recommendations for the future application and development of the spatial database References
23 23 24 24 25 25 25 28 29 29 30 30 30 33 33 36 36 37 38 39 4.
REGIONAL SURFACE WATER RESOURCES AND DROUGHT
ASSESSMENT
4.1 Introduction
4.2 Spatial variability of mean annual runoff and monthly regimes 4.2.1 Introduction to mean annual runoff
4.2.2 Mean annual runoff from gauged catchments
4.2.3 Integration of national estimates of mean annual runoff 4.2.4 Regional water balance estimates of MAR
4.2.5 A grid-scale modelling approach
4.2.6 Soil moisture deficit and evaporation accounting models
4.2.7 An assessment of the validity of SVAT models for Global Climate Modelling 4.2.8 Mean annual runoff accumulation and international rivers
4.2.9 Monthly river flow regimes 4.3 Temporal variability of annual runoff
4.3.1 Coefficient of variation of annual runoff 4.3.2 Variability within historic records 4.4 Base flow contributions to river flow
4.4.1 Base flow estimation procedures
4.4.2 An evaluation of the ‘smoothed minima’ Base Flow Index 4.4.3 Regional variability of base flow
4.5 Flow duration characteristics
4.5.1 Derivation concepts and key features 4.5.2 Pooled and ‘type’ flow duration curves 4.5.3 Spatial variability of flow duration curves 4.5.4 Towards flow duration curve estimation 4.6 Regional drought assessment
4.6.1 Assessing the severity of current hydrological droughts 4.6.2 Drought vulnerability assessment
4.6.3 Hydrological drought relationships with the ENS0 4.7 Conclusions and discussion
References
40
40 40 42 43 46 47 54 57 58 61 63 65 65 67 68 69 70 72 75 75 79 79 80 81 81 84 84 88 92
xii
5. RAINFALL-RUNOFF MODELLING
5. I Introduction
5.1.1 Aims and objectives 5.1.2 Research programme 5.2 HYMAS and the models used
5.2.1 HYMAS - history of development and general philosophy 5.2.2 HYMAS - a brief description
5.2.3 The models in HYMAS 5.2.4 The Pitman model 5.2.5 The VT1 model
5.2.6 Other supporting models 5.3 Data availability and catchments used
5.3.1 Streamflow data 5.3.2 Rainfall
5.3.3 Evaporation
5.3.4 Other time series data
5.35 Spatial data (catchment descriptions)
5.3.6 General comments on information availability and resolution 5.3.7 Catchments used for model testing
5.4 Summary and discussion of results 5.4.1 Introduction
5.4.2 Pitman model 5.4.3 VT1 mode1
5.4.4 Model simulations of land-use change impacts 5.4.5 Other models (used in this project)
5.4.6 Other models (not used in this project) 5.5 Conclusions and recommendations
5.5.1 Recommendations for training
5.5.2 Recommendations for the future application of models within the region References and Bibliography
6.
REGIONAL FLOOD FREQUENCY ANALYSIS FOR SOUTHERN AFRICA
6.1 Introduction
6.1.1 Background
6.1.2 The framework of the study 6.2 Data analysis
6.2.1 Available data for the study 6.2.2 Extension of flood data 6.2.3 Data screening
6.2.4 Flood statistics of Southern Africa 6.3 Regionalization of Southern Africa
6.3.1 Introduction
6.3.2 Procedure applied to regionalize Southern Africa 6.3.3 Results of regionalization
6.4 Choosing statistical distributions of flood flows 6.4.1 Introduction
6.4.2 Use of L-moments ratio diagram
6.4.3 Results of identifying the underlying distribution
6.5 Predictive ability tests to select suitable frequency procedure for the analysis of flood flows 6.5.1 Introduction
6.5.2 Methodology to select the most robust flood estimation procedure 6.5.3 Analysis of results from predictive ability tests
94
94 94 94 96 96 96 100 101 105 110 112 112 112 112 113 113 113 113 114 114 114 117 120 121 123 124 125 127 127
130
130 130 130 130 130 130 131 132 133 133 132 134 138 138 138 139 141 141 141 141
XIII
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7.
6.6 Derivation of regional frequency curves 6.7 Prediction of mean annual flood
6.7.1 Introduction
6.7.2 Derivation of regression models 6.7.3 Results of regression analysis 6.8 Summary, conclusions and recommendations
6.8.1 Summary and conclusions 6.8.2 Recommendations References
CONCLUSIONS AND RECOMMENDATIONS FOR FURTHER RESEARCH
7.1 Project coordination and administration 151
7.2 Southern African FRIEND river flow database 151
7.3 Southern African FRIEND spatial database 152
7.4 Regional surface water resources and drought assessment 154
7.5 Rainfall-runoff modelling 156
7.6 Regional flood frequency 158
7.7 Capacity building and training 158
7.8 Summary 159
Annex 1: Administration of hydrometeorologicql services within the nations participating in Southern Africa FRIEND
FIGURES AND TABLES
FIGURES
Figure 1.1 Geographical scope of the Southern African FRIEND programme Figure 1.2 Global status of FRIEND in 1997
Figure 1.3 Organisation of Southern Africa FRIEND Programme
Figure 1.4 (a) Frequency distribution of catchment areas of all gauging stations in Southern Africa Figure 1.4 (b) Frequency distribution of catchment areas of all hydrometric zones in Southern Africa Figure 1.4 (c)Frequency distribution of catchment areas of all 6.8 million lkm’ grid squares Figure 1.4 (d) Cumulative frequency of catchment areas of gauging stations, hydrometric zones and Figure 1.5
Figure 2.1 Figure 2.2 Figure 2.3 Figure 2.4 Figure 3.1 Figure 3.2 Figure 3.3 Figure 3.4
1 km? grid squares in Southern Africa
Design Scenario Cube - a conceptualisation of the variety of approaches to estimate flow regimes
Location of FRIEND gauging stations
Frequency distribution of period of record amongst Southern African FRIEND gauging stations
Frequency distribution of record length amongst Southern African FRIEND gauging stations
Distribution of gauging stations in Southern African river basins Spatial extent of FRIEND gauged catchments
Implementation of the FRIEND and national numbering schemes across national boundaries
Implementation of the FRIEND numbering scheme in nested catchments
Comparison of GIS-derived catchment areas and catchment areas published by the National Hydrological Services for individual gauged catchments
144 146 146 147 147 147 147 149 149
151
161
8 10 16 19 19 20 26 27 27 28 xiv
___-.--..--- ._ -
Figure 3.5 Figure 3.6 Figure 3.7 Figure 3.8 Figure 3.9 Figure 3.10 Figure 3.11 Figure 3.12
Figure 4.1 Figure 4.2 Figure 4.3 Figure 4.4 Figure 4.5 Figure 4.6 Figure 4.7 Figure 4.8 Figure 4.9 Figure 4.10 Figure 4.11 Figure 4.12 Figure 4.13 Figure 4.14 Figure 4.15 Figure 4.16 Figure 4.17 Figure 4.18 Figure 4.19 Figure 4.20 Figure 4.2 1 Figure 4.22
Figure 4.23 Figure 4.24 Figure 4.25 Figure 4.26 Figure 4.27 Figure 4.28 Figure 4.29 Figure 4.30 Figure 4.3 1
Delineation of the Save and Runde Basins of Zimbabwe
using
the DEMdegraded
to 1 Okm2 resolution
0.5”xO.5” gridded coverage of mean annual rainfall for Southern Africa
Comparison of observed raingauge data in Namibia, Zimbabwe and Malawi against 0.5”xO.5” grid coverage estimates
0.54tO.5” gridded coverage of mean annual evaporation for Southern Africa 0.5”xO.5” gridded coverage of percentage forest in the Southern African region FAO 0.5”xO.5” grid of wetland density in Africa
FRIEND 0.25”xO.25” gridded wetland coverage
Geographic distribution of the ‘Regional lithology’ attribute within the Southern African geologylhydrogeology coverage
Spatial variability of mean annual runoff amongst FRIEND gauged catchments
MAR in Southern Africa composed of different national estimates for hydrometric zones Regional relationship between mean annual runoff and mean annual rainfall
Catchment-based annual rainfall and runoff relationships, demonstrating apparent linear and non-linear responses
Regional relationship between annual runoff and annual rainfall
Regional relationship between mean annual potential evaporation and mean annual rainfall Calculation of Potential Evaporation Excess Rainfall (PEER)
Relationship between Mean Annual PEER (MAPEER) and MAP Regional relationship between mean annual runoff and MAPEER Regional relationship between annual runoff and annual PEER
Demonstration of local variability of MAR amongst catchments with similar rainfall and evaporation in Malawi
Relationship between AE (termed Losses, or P-Q) and MAP Relationship between r (AEMAPE) and MAP
Upper bound on actual evaporation (defined by MAPMAPE)
Relationship between catchment departures below the upper bound on actual evaporation and MAP
Forest cover impacts on departures below the upper bound on actual evaporation and MAP Sensitivity in estimates of MAR to errors in estimating MAP-AE
Grid-based simulation of mean annual runoff using the modified PDM model
Results of the sensitivity analysis for a grid cell in western Angola and in south-eastern South Africa
Comparison of grid-based simulated MAR and observed MAR
Comparison of gridded average annual rainfall compared to recorded raingauge rainfall in three SADC countries
Comparison of modelled predictions to observed lake levels:
a) Assuming a constant forest cover of 64%,
b) Assuming a constant 64% forest cover until 1967 followed by a 13% decrease of forest during the period 1967 to 1990.
Land surface scheme of the Unified Global Climate Model of the UK Meteorological Office Categoristion of different runoff generating zones in an international river basin context for Zimbabwe
Identification of shared watercourses in Zimbabwe based in intersections of the DEM-derived river network and national boundary polygons
Monthly flow and rainfall regimes in Southern Africa within 4” x 4” grid cells Histogram of calculated Coefficient of Variation of Annual Runoff (CV(AR))
Relationships between the coefficient of variation of MAR and CV of annual runoff for Southern African catchments compared with different regions of the world
Grid-based,simulation of the CV of annual runoff using the modified PDM model Historic departures from median annual (a) rainfall and (b) runoff
Relationship between above- and below-normal rainfall and above- and below-normal runoff
29 31 30 31 32 32 34 34 45 45 48 48 49 49 50 50 50 51 51 52 52 52 53 53 54 66 56 57 57
58 49 62 64 66 65 65 67 68 68 -
xv
Figure 4.32 Figure 4.33 Figure 4.34 Figure 4.35 Figure 4.36
Figure 4.37 Figure 4.38 Figure 4.39 Figure 4.40 Figure 4.4 1 Figure 4.42 Figure 4.43 Figure 4.44 Figure 4.45 Figure 4.46 Figure 4.47 Figure 4.48 Figure 4.49 Figure 4.50 Figure 4.5 1 Figure 4.52
Figure 5.1 Figure 5.2 Figure 5.3 Figure 5.4 Figure 5.5 Figure 5.6 Figure 5.7 Figure 5.8 Figure 5.9 Figure 5.10 Figure 5.11 Figure 5.12 Figure 5.13 Figure 5.14 Figure 5.15 Figure 5.16 Figure 5.17 Figure 5.18
Categorisation of individual water years into above- and below-normal classes within the nine principal river basins
Standard deviation of annual BFI values at FRIEND gauging stations
Relationship between Base Flow Index and catchment area within selected basins Spatial variability of BFI amongst gauged catchments
A three-stage explanation of the spatial variability of BFI based on (a) potential recharge (as determined by mean annual rainfall), (b) regional lithology and
(c) different aquifer properties for the same lithology
Comparison of a natural and artificially influenced flow duration curve for the Sabie river, South Africa
Comparison of flow duration curves derived by different methods -
the period-of-record method and the mean (and median) annual curve method
Hydrographs and flow duration curves for three gauged catchments of equivalent area which display different flow regimes
Variability of standardised period-of-record flow duration curves amongst 29 1 gauged flow records from across Southern Africa
Spatial distribution of the percentile associated with zero flow Histogram of the percentile associated with mean flow
Pooled flow duration curves for perennial rivers in Southern Africa Regional relationship between BFI and Q70
A generalised procedure for the estimation of flow duration curves at ungauged sites Current flows (January, February 1995) in the context of historic mean and extreme flows within the Zambezi and Kafue Basins of Zambia
Spatial variability of hydrological drought severity across Southern Africa on 1st April, 1987 Groundwater drought vulnerability map for Malawi
Representative Southern African (a) rainfall series 1901-1996 (after Hulme (ed) 1996) and (b) runoff series (1942 to 1990)
Relationship between departures from normal within the single Southern African annual river flow series (Octwy-Sepwy+l) and the mean of SO1 (Aprwy-Mar,+l), where wy is the water year Relationship between July to September SO1 and subsequent water year annual runoff
Relationship between July to September SO1 and subsequent water year annual runoff within the Central Indian Ocean Basin
HYMAS main menu options Utility options in HYMAS
Setup options
Spatial catchment data options Time series data options Model setup and run options
Results and observed data analysis options in HYMAS
Flow diagram representation of the version of the Pitman model within HYMAS Illustration of the effect of the new Rainfall Distribution Factor (RDF) parameter Illustration of the effect of different VPOW parameters on the decay of vegetation cover over time
Flow diagram representing the VT1 model structure
Illustration of the patching algorithm for a Swaziland catchment with a single source station Catchment E 19, Zimbabwe - observed and simulated time series of monthly runoff volumes Upper Black Mbuluzi catchment (SwaziIand) - observed and simulated time series of monthly runoff volumes
Time series of simulation results for the Pungoe river (Mozambique)
Catchment 45 11 (Botswana, Tati River): observed and Pitman simulated flow duration curves Monthly flow volume duration curves for Etemba
Daily rain and flow (observed and simulated) time series for the Sabie River, Mpumulanga, South Africa (X3H006)
69 71 71 74
75 76 77 78 79 74 79 80 80 82 83 84 85 86 87 87 87 96 97 97 97 98 98 99 102 101 104 107 111 115 115 115 116 116 118
xvi
-___
-.
Figure 5.19 Figure 5.20 Figure 5.2 1 Figure 5.22
Figure 6.1 Figure 6.2 Figure 6.3 Figure 6.4 Figure 6.5 Figure 6.6 Figure 6.7 Figure 6.8 Figure 6.9 Figure 6.10 Figure 6.11 Figure 6.12 Figure 6.13
TABLES
Table 1.1 Table 1.2 Table 1.3 Table 1.4 Table 2.1 Table 2.2 Table 2.3 Table 2.4 Table 2.5 Table 2.6 Table 3.1 Table 3.2 Table 3.3 Table 3.4 Table 3.5 Table 3.6 Table 3.7 Table 4.1 Table 4.2
Daily rain and flow (observed and simulated) time series for the Tati River, Botswana (45 11) Daily rain and flow (observed and simulated) time series for the Mosetse River,
Botswana (5211)
Erin (Zimbabwe) total catchment, monthly flow duration curves for observed and simulated (Pitman - using fixed grassland and varying forest parameter values)
Time series of observed and simulated (Pitman - using grass and modified parameter values) monthly flows for Mokobulaan (South Africa, afforested in 197 1)
Delineated hydrological homogeneous regions of Botswana Delineated hydrological homogeneous regions of Malawi Delineated hydrological homogeneous regions of Namibia Delineated hydrological homogeneous regions of Zimbabwe Delineated hydrological homogeneous regions of Tanzania Delineated hydrological homogeneous regions of South Africa
The comparison of L-moment relationships between the theoretical distributions and the observed data from 11 countries in Southern Africa
Frequency curves for six countries in Southern Africa (Angola, Botswana, Lesotho, Mozambique, Swaziland, Zambia)
Frequency curves for four regions in Malawi Frequency curves for four regions in Namibia Frequency curves for six regions in Zimbabwe Frequency curves for 12 regions in Tanzania Frequency curves for 13 regions in South Africa
Institutions responsible for coordination of research themes Projected Scarcity Index of Annual Renewable Freshwater
The contribution of flow regime measures, river/water management objectives and water management measures to different development, economic and environmental sectors Summary of procedural components and inputs for different hydrological design requirements Primary basins in the Southern Africa region used in the FRIEND numbering scheme Summary of HYDATA usage and attendance at HYDATA training within Southern Africa Distribution of Southern African FRIEND gauging stations by catchment area
Number of gauging stations and station years of data contributed by participating countries in Southern African FRIEND
Distribution of gauging stations within countries and primary river basins Distribution of station years of data within countries and primary basins
Topographic map coverages for countries participating in Southern African FRIEND Summary of attribute information of the integrated national, river basin and catchment boundary coverage
Illustration of the implementation of the ‘thematic’ nesting structure National geology and hydrogeology maps available to the Southern African FRIEND programme
Regional lithology classification
Summary of mapped and estimated hydrogeological attributes
Summary of existing information on morphometric indices of FRIEND catchments Summary of flow regime measures for Water resources and drought assessment Applications of mean annual runoff in water resources assessment and planning, with examples from Southern Africa
118 119 121 121 135 135 136 136 137 137 140 145 145 145 145 145 146
6 8 9 11 17 18 19 20 21 21 24 26 28’
35 35 36 36 41 43
xvii
Table 4.3 Table 4.4.
Table 4.5 Table 4.6 Table 4.7 Table 4.8 Table 4.9 Table 4.10 Table 4.11 Table 4.12 Table 4.13 Table 5.1 Table 5.2 Table 5.3 Table 5.4 Table 5.5 Table 5.6
Table 6.1 Table 6.2 Table 6.3 Table 6.4 Table 6.5 Table 6.6 Table 6.7 Table 6.8 Table 6.9 Table 6.10 Table 6.11 Table 6.12 Table 6.13 Table 6.14 Table 6.15
Summary of recent national water resource assessment studies involving regionalisation of MAR
Performance evaluation of empirical relationships for estimating the ratio of actual to potential evaporation
Comparison of the predicted annual water balance of the Kafue Basin, Zambia for four simulations of a Global Climate Model, compared with observed mean annual runoff Categorisation of different runoff generating zones in an international river basin context Three estimates of BFI using different hydrograph separation methods for catchments in South Africa
Sensitivity of Base Flow Index to selected block length
Sensitivity of the Base Flow Index to varying rainfall seasonality Characteristic BFI values for 9 Regional’Lithology Groupings Flow duration statistics for type curves
Ranking of Zambezi and Kafue February 1995 monthly mean flow within the historic series of February monthly mean flows
Provincial analysis of the state of major dams in Zimbabwe as at 6th March, 1995 Pitman model parameters
Effects of increasing model parameters on the properties of the simulated runoff time series Parameters of the VT1 model
Summary of Pitman model results based on monthly streamflows Summary of VT1 model results based on daily flows
Approximate summary of the parameter changes used for the two models to reproduce the landuse effects represented by the example catchments
Summarized information on available flood data for the study
Number of sites identified as discordant. serially correlated and cross-correlated Unbiased flood statistics for all stations used in the analysis for the 11 countries in Southern Africa
Description of delineated homogenous regions of Botswana Description of delineated homogenous regions of Malawi Description of delineated homogenous regions of Namibia Description of delineated homogenous regions of Zimbabwe Description of delineated homogenous regions of Tanzania Description of delineated homogenous regions of South Africa
Results of the homogeneity test for the proposed regions according to Hosking and graphical plot procedures
Underlying distribution identified for the delineated region/countries in Southern Africa using the L-moment ratio diagram
Robust flood estimation procedures selected for the delineated homogeneous regions in Southern Africa
Regional parameter estimates for the procedures selected for flood frequency analysis for the regions in Southern Africa
Catchment characteristics considered in the development of a model to predict MAF Derived regression models to predict mean annual floods from catchment characteristics in Southern Africa
46 54 60 63 70 72 72 73 80 83 83 103 105 106 117 119 122 131 132 133 135 135 136 136 137 137 138 139 142 144 147 148
. . . xvlu
Executive Summary
1. Background
This report contains the results of the first Phase of the Southern African FRIEND (Flow Regimes from International Experimental and Network Data) programme.
The content will be of interest to four broad user groups of knowledge and information relating to water in Southern Africa;
0 water resource planners and policy makers, concerned with managing water at the scales of river basins, countries and the Southern African region
0 operational hydrologists concerned with databases and methods of data analysis and simulation
0 hydrological researchers concerned with the spatial and temporal variability of river flow regimes
0 international agencies concerned with water, and agencies funding water-related activities in Southern Africa.
Southern African FRIEND is a contribution to the Fourth International Hydrological Programme of UNESCO, targeting the application of regional hydrological data sets for the sustainable utilisation of water resources. The geographical focus of the Southern African programme is the eleven mainland states of the Southern African Development Community (SADC); Angola, Botswana, Lesotho, Malawi, Mozambique, Namibia, South Africa, Swaziland, Tanzania, Zambia and Zimbabwe. This programme is one of four current FRIEND initiatives worldwide - the others being in Northern Europe, Alpine and Mediterranean regions (AMHY) and West and Central Africa (AOC). Other FRIEND initiatives are emerging in the Nile Basin, South East Asia and the Hindu Kush/
Himalayan region.
2. Summary of Phase One of Southern African FRIEND ,
FRIEND contributes an international framework for the implementation of hydrological research relating to river flow regimes across Southern Africa. The baseline of data, analytical techniques and technology summarised in this report can contribute commonality and advances to broad SADC policy goals, river basin interests and national
concerns. Chapter 1 of this Report stresses the contribution of research to river/water management objectives, and ultimately to the sustainable management of water in different development, economic and environmental sectors. Southern African FRIEND is the first example of implementing a hydrological research programme across Southern Africa, and substantial advances have been made in six areas, each defined as objectives by senior hydrologists amongst the participating countries;
Southern African FRIEND river flow database The principal objective of the River Flow Database Project, coordinated by the Institute of Hydrology (UK) and the University of Dar-es-Salaam (Tanzania), has been to underpin the analytical research projects by the establishment of a common international database of river flows. This objective placed emphasis on the collation of historic daily flows (as demanded by low flow analyses and daily rainfall-runoff models) and instantaneous peak discharges (as demanded by regional flood frequency analyses). It was not an objective to establish an operational flow database. In association with National Hydrological Services, a Master Register of Southern African gauging stations was created, compiling me&data for over 10,500 stations. The Master Register provided a foundation for the selection of appropriate flow series with criteria applied to meet the demands of the research projects. Selection of daily flow series identified 676 gauged flow records for inclusion on the FRIEND database, each categorised according to their suitability for different research analyses, comprising a total of 15,190 data years with a modal length of 27 years.
Most records commence during the 1960s and end in the early 1990s. A new unifying station numbering scheme enables rapid identification of all FRIEND stations in a country or river basin, or combinations thereof. For the purposes of the FRIEND project, establishment of a common hydrological software platform, HYDATA, facilitated the exchange of data between different countries.
Each country willingly contributed flow data for analysis within the confines of FRIEND as determined by Data exchange agreements. Flow records from each country were transferred.to a river flow database coordination facility at the Coordination Centre at the University of Dar-es-Salaam.
Collation of the validated data series on a single database facilitated the objective of the Project of data distribution to research projects.
xix
Southern African FRIEND spatial database
The direction of the Spatial Database Project, coordinated by the Institute of Hydrology (UK), was determined by the demand for region-wide, standardised coverages on a common geographical reference system of those thematic factors considered significant in determining flow regimes and extremes. An underpinning principle was to benefit from existing public-domain Geographical Information System (GIS) coverages and to create new coverages where necessary.
A new integrated coverage of river basin (over 500 national hydrometric sub-divisions), gauged catchment (over 1,000, including all FRIEND stations) and national boundaries (11 countries) has been created. Each of the 2886 polygons carries five labels; (i) a nation code, indicating territorial ownership; a river basin hydrometric zone code being both (ii) the national reference code and (iii) the FRIEND unifying code; and a gauging station code being both (iv) the national code of the downstream gauging station (frequently a different country from (i)) and (v) the equivalent unique FRIEND code. River basins and gauged catchments are both structured using the ARC-INFO REGION module - selection of a single polygon automatically leads to retrieval of that polygon and all polygons upstream. A 1-km? resolution Digital Elevation Model (DEM) was made available by the United States Geological Survey. Using the hydrological modelling tools within ARC-INFO, flow direction from each cell has been derived, permitting the accumulation of grid cells in a downstream direction. An existing digitised river network for Southern Africa was provided by UNEP (Nairobi) and a 1:250,000-derived network for South Africa by the Department of Water Affairs and Forestry. Both networks comprise independent arcs without an interrelating directional structure. A simulated river network has been generated utilising the flow direction routine and the DEM within ARC-INFO.
Precipitation data was available in two forms: point values from raingauges (93 1 daily series, and 3046 monthly series from eight countries with an additional variety of long-term and standard period (1960- 1990) statistics), as supplied principally by national Meteorological Services; and a 0.5”
grid-based time series (1961-1990) of monthly rainfall.
Potential evaporation was also available in two forms: point values (66 monthly time series of Class A evaporation pan losses) and gridded coverages of mean monthly and annual statistics of Penman Potential Evaporation within a0.5”grid, generated from component micro-meteorological variables from UNEP. FAO made available a polygon coverage of wetland boundaries which identifies the major wetland systems, such as the Okavango and Zambezi floodplains but omits the many headwater dambo wetlands. Thus, the extent of wetland is underrepresented by at least 50%. A
new wetland density grid, based on 15 x 15 minute grid squares, was created by sampling mapped wetlands on 1:250,000 maps (1:50,000 maps in Zimbabwe, Malawi and Lesotho, 1:500,000 for South Africa and Angola). Different national maps categorise wetlands in different ways, and the national systems were preserved by adopting a 16-class wetland definition system. Coverages of vegetation cover were made available from the US Environment Protection Agency CD-ROM and UNEP, specifically the Olson vegetation (30 ecosystem types). Remotely-sensed NDVI (Normalised Difference Vegetation Index) data for 1986 and 1987, made available by NOAA, was used to construct a new grid of percentage forest cover. Two existing soils GIS databases were made available: a polygon coverage of the FAO Soil Map of the World, with full regional coverage and the SADCC Soil Map, integrating national soil maps for nine countries (Namibia and South Africa were non- members of SADCC at the time of production). Both databases use the FAO coding scheme, which contains information on soil associations, texture and depth. A new regional geologylhydrogeology coverage was created by digitising, integrating and standardising ten national maps (except South Africa). The 74 18 polygons are labelled with five items; (i) the national lithology, (ii) a new regional integration of national lithology, (iii) 8-class UNESCO aquifer type (e.g. predominantly intergranular), (iv) aquifer productivity (high, medium, low or local) and (v) aquifer yield. Separate GIS coverages of geology and hydrogeology for South Africa were made available by Department of Water Affairs and Forestry, but remain to be integrated into the regional coverage.
Regional surface water resources and drought assessment
The Regional Surface Water Resources and Drought Assessment Project, coordinated by the Institute of Hydrology (UK) and the University of Dar Es Salaam (Tanzania), represents the first region-wide investigation of water resources and droughts for Southern Africa and has been directed towards five key issues; the spatial variability of mean annual runoff and regimes, temporal variability of annual runoff, base flow contributions to river flow, flow duration characteristics and estimation and regional drought assessment. The objective has been to advance methods to characterise the spatial and temporal variability of flow regimes and to provide guidance on their estimation for hydrological design purposes. The project has investigated relationships between 676 daily river flow series and associated thematic data.
Data presentation techniques using the GIS have been developed to display and retrieve gauging station measurements of MAR and past national estimates of MAR for hydrometric zones. Despite the Southern African region representing gross differences in climatic inputs, a hierarchy -
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