W O R K I N G P A P E R
HYDROBIOLOGICAL ASSESSMENT OF THE ZAMBEZI RWER SYSTEM: A REVIEW
September 1988
W
P-88-089l n l e r n a i ~ o n a l l n s l ~ i u l e for A p p l ~ r d Sysiems Analysis
HYDROBIOLOGICAL ASSESSMENT OF THE ZAMBEZI RIVER SYSTEM: A REVIEW
September 1988 W P-88-089
Working Papers are interim reports on work of the International Institute for Applied Systems Analysis and have received only limited review. Views or opinions expressed herein d o not necessarily represent those of t h e Institute or of its National Member Organizations.
INTERNATIONAL INSTITUTE F O R APPLIED SYSTEMS ANALYSIS A-2361 Laxenburg, Austria
One of the Lmporhnt P r o j e c t s within the Environment Program i s t h a t entitled: De-
*on apport *stems jbr Mancrgfnq Lurge Intemartiorrcrl Rivers. Funded by t h e Ford Foundation, UNEP, and CNRS France, t h e P r o j e c t includes t w o case stu- d i e s focused on the Danube and the Zambezi r i v e r basins.
The a u t h o r of t h i s r e p o r t , Dr. G. Pinay, joined IIASA in F e b r u a r y 1987 a f t e r completing h i s PhD at the C e n t r e dSEmlogie d e s Ressources Renouvelables in Toulouse. Dr. Pinny was assigned t h e task of reviewing t h e published l i t e r a t u r e on water management issues in the Zambezi r i v e r basin, and r e l a t e d ecological ques- tions.
A t the outset, I thought that a literature review on the Zambezi r i v e r basin would b e a r a t h e r slim r e p o r t . I am t h e r e f o r e greatly impressed with t h i s Working P a p e r , which includes a l a r g e number of r e f e r e n c e s but more importantly, syn- thesizes t h e various studies and provides t h e scientific basis f o r investigating a v e r y complex set of management issues. Dr. Pinay's review will b e a basic r e f e r - e n c e f o r f u r t h e r water management studies in t h e Zambezi r i v e r basin.
R.E. Munn
Leader, Environment Program
-
iii-
I would like to thank the IIASA library which i s really part of the research team and without them this work would not have been possible. My thanks to R.E. Munn who kindly reviewed the paper, and to Y. Taher who typed it and helped me improve the language.
Chapter I: The Zambezi River System
The Zambezi r i v e r system les between 24-38'E and 12-20's. and i s t h e larg- est of t h e African r i v e r systems flowing into t h e Indian Ocean [(Balek 1977; Davies 1986). Figure
11.
I t consists of t h r e e sections (Balon and Coche 1974): ljrlpper from i t s sourcesto
t h e Victoria Palls, Middle from t h e Victoria Palls to t h e Cahora Bassa rapids, and Lower from Cahora Bassato
t h e Indian Ocean. These t h r e e s t r e t c h e s s e e mto
have been independent until t h e Pliocene era (Balon 1978) fol- lowing which. due to tectonic movements, they merged to form t h e actual r i v e r sys- t e m (Table 1 ) .There i s much evidence to support such a picture of evolution particularly in relation with pre-impoundment fish distributions in t h e r i v e r (Jackson 1986). The length of t h e r i v e r itself is controversial. For instance, Welcomme (1977) claims i t is 2574 km, Balon and Coche (1974) 2494 km, Balek (1977) 2600 km, and Beadle (1932) 3000 km. I t flows eastwards from its sources in t h e Central African Plateau at 1 4 0 0 m altitude
to
t h e Indian Ocean (Figure 2). The surface of the Zambezi drainage basin varies greatly from 1193500 km2 (Balon and Coche, 1974) to 1 5 7 0 000 kmz (Balek 1977). In addition, one can divide t h e e n t i r e Zambezi drainage basin into subcatchments a r r e s p o n d i n gto
t h e drainage basins of t h e main tribu- taries of t h e Zambezi r i v e r m b l e 2).The Zambeei drainage basin is situated south of t h e equator between 12' and 20°S. The cool dry season is between May end September. The headwaters situated north of the basin belong
to
the tropical summer rainfall zone (climate m e I1 in W a l t e r eta.
1973). As one moves south, t h e tropicalsummer
becomes progressively more arid dueto
a prolongation of the dry season (Pigure 3). Thus, t h e upper and t h e middle Zambezi are definedas
warm temperate regions with dry winter, t h e warmest month being up to 22' C (Schulze and McGee, 1978) a s quoted by Davies (1979). while t h e Okavango basin and t h e southern part of t h e middleF m
1. The Zambezi drainage basin.%ble 1. Main f e a t u r e s of t h e t h r e e s t r e t c h e s of t h e Zambezi r i v e r
ZAMBEZI STRETCH LENGTH DRAINAGE SURFACE MEAN ANNUAL FLOW
km km 2 m3 s - I
Source
UPPER Victoria Falls
M l DDLE Cahora Bassa
rapids 853
LOWER Indian Ocean
Table 2. Main subcatchments of t h e Zambezi r i v e r system.
I
1
Chobe)
958001
43500/
154200basin km
I I I
Qvrum
Fdls V i *
A k W 1100 1 2 4 ) Q)O
a00
an
34) an
0
Sanyati
147500
1
239001
115000I I
Annual flow km 3
0 zwl 250d km length
Kafue
4.2
1
3.41
10.3UPPER
Figare 2. Longitudinal p r o f i l e of t h e Zarnbezi River.
Zambezi belong to t h e a r i d s t e p p e zone with a mean annual t e m p e r a t u r e of more t h a n 18°C. Finally, t h e lower Zambezi moves from t h e a r i d climatic zone in t h e w e s t to a n equatorial climate with d r y winters in t h e e a s t .
Huangwa
13.0
MIDDLE
1.4
I N.D.
L W E R
Hunyani S h i r e
Figure 9. Map showing precipitation r e p a r t i t i o n on t h e Zambezi d r a i n a g e basin adapted from Vieira (1961) and Bolton (1983).
2. Pain Water Retention Systems
S e v e r a l kinds of water s t o r a g e systems such as n a t u r a l lakes, man-made lakes, and swamps e x i s t along t h e Zambezi r i v e r and i t s t r i b u t a r i e s .
2.1. Natural lakes
The only l a r g e n a t u r a l l a k e on t h e Zambezi watershed is Lake Malawi. I t i s t h e t h i r d l a r g e s t l a k e in Africa with a maximum length of 580 km and a width of between 16 and 80 km, a n d a s u r f a c e of about 30000 km2. I t s volume capacity i s almost 8000 km3. The hydrological balance of t h e l a k e i s dominated by permanent rainfall which r e a c h e s 2270 mm p e r annum in t h e l a k e area. The l a k e i s s u b j e c t to a b r u p t annual and seasonal changes in i t s water level as a r e s u l t of variations in rainfall.
The S h i r e r i v e r in t h e s o u t h e r n p a r t of t h e l a k e constitutes i t s o u t l e t ; this r i v e r f l o w s through a small lake, t h e Malombe, b e f o r e i t joins t h e Zambezi in i t s lower r e a c h .
2.2. Ban-Ymdc hkam
Two man-made l a k e s , t h e K a r i b a a n d C a h o r a Bassa, are on t h e Zambezi r i v e r regulating almost 570 km of t h e length of t h e r i v e r . These impoundments r e p r e s e n t 65 p e r c e n t of t h e middle Zambezi. Some o t h e r man-made l a k e s l i e on t h e Zambezi t r i b u t a r i e s , mainly in Zambia o n t h e Kafue r i v e r a n d in Zimbabwe. The c h a r a c - teristic f e a t u r e s of t h e l a r g e r l a k e s are given in C h a p t e r 111, while t h e main f e a t u r e s of t h e most i m p o r t a n t o n e s are given in Table 3 (Marshall a n d F a l c o n e r 1973a-b; Mitchell a n d Marshall 1974; Jackson a n d Davies 1976) a n d t h e i r locations in F i g u r e s 1 a n d 4.
Figure 4. Locations of man-made lakes mound H a r a r e , Zimbabwe.
C e r t a i n c h a r a c t e r i s t i c s of man-made l a k e s are t r p i c a l f o r most of them, a n d , t h e r e f o r e , are distinguishable f r o m n a t u r a l l a k e systems. The development of t h e s h o r e l i n e is slightly h i g h e r t h a n t h a t f o r n a t u r a l l a k e s ; if t h e r i v e r i s confined
Table 3. Hydrological f e a t u r e s of t h e main r e s e r v o i r s of t h e Zambezi drainage basin.
I
Lake s u r f a c e Drainage basinI
(kmZ) (km2)Kariba Cahora Bassa Ithezithezi Kafue Gorge McIlwaine Mazoe Mwenie
between high banks, t h e new l a k e will b e long and narrow; if t h e r e are t r i b u t a r i e s , water will b e held back giving t h e new l a k e a d e n d r i t e form. In comparison, t h e e x t e n t of shoreline modification in a r e s e r v o i r is g r e a t e r t h a n in a n a t u r a l l a k e because t h e annual drawdown exposes a l a r g e r area t o t h e e f f e c t s of s h o r e p r o c e s s e s . Whereas normally n a t u r a l l a k e s are d e e p e s t n e a r t h e c e n t r e , man-made l a k e s are almost always d e e p e s t just upstream from t h e dam. They are t h e n r e f e r r e d to as "half-lakes" (Ellis 1941). The incoming water does not mix immedi- ately with t h e water in t h e r e s e r v o i r due to differences in t e m p e r a t u r e and con- t e n t of dissolved or suspended solids. I t l e a d s to density c u r r e n t s and hypolimnetic withdrawals (Baxter 1977). The retention time in man-made l a k e s is v e r y s h o r t compared to t h a t of n a t u r a l lakes. F o r instance, t h e r e t e n t i o n time of water in t h e Kariba w a s measured at f o u r y e a r s , while i t i s about one y e a r for t h e Cahora Bassa.
According to Wetzel (1975) a swamp i s a more or l e s s permanently water- logged system with p e r s i s t e n t standing water in t h e vegetation. In Africa h e r b a - ceous swamps may b e defined as f l a t areas t h a t are flooded to a shallow d e p t h densely c o v e r e d with h e r b a c e o u s vegetation whose shoots r i s e above t h e water level to more t h a n one metre. The swamps are bottom-rooted or floating (Howard- Williams and Gaudet 1979). T h e r e are s e v e r a l r e a s o n s why swamps should b e t a k e n into consideration f o r t h e i r hydrological and biological processes. Among them water retention, water loss by evapotranspiration, t h e sedimentation p r o c e s s , f i s h e r y r e s o u r c e s , and grazing p a s t u r e s may b e mentioned. The p r e s e n t c h a p t e r p r e s e n t s some f e a t u r e s of t h e main swamps in t h e Zambezi d r a i n a g e basin, a n d t h e
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2.3.1. Barotse swamps
The B a r o t s e floodplain l i e s on t h e u p p e r c o u r s e of t h e Zambezi r i v e r in t h e C e n t r a l African p l a t e a u in w e s t e r n Zambia. I t i s a 240 km long a n d 40 km wide floodplain t h r o u g h which t h e Zambezi r i v e r meanders. The a n n u a l r a i n f a l l i s a b o u t 1 0 5 0 mm of which 9 0 p e r c e n t o c c u r s between November a n d March. Flooding of t h e u p p e r Zambezi normally commences in November, b u t may v a r y depending on t h e intensity of t h e e a r l y r a i n s in t h e h e a d w a t e r catchments. Usually t h e flood p e a k s are in April in t h e B a r o t s e floodplain, a n d r e c e d e slowly o v e r a p e r i o d of six months between May a n d O c t o b e r (FAO-UN 1969; Burgis a n d Symoens 1987).
2.3.2. Okavango delta
The Okavango d e l t a system i s r a t h e r complex b e c a u s e of i t s hydrological f e a t u r e s leading to g e n e r a l flow p a t t e r n s as well as sedimentation p r o c e s s e s t h a t c h a n g e t h e d e l t a ' s t o p o g r a p h y . S u r p r i s i n g l y t h e Okavango d e l t a h a s a r e g u l a r conical s h a p e with a s l o p e of a b o u t 1 in 3 6 0 0 . Thus, r e l a t i v e l y small i r r e g u l a r i t i e s p r o v i d e t h e p a t t e r n of channels. r i d g e s , swamps a n d pools. Estimates of t h e area of t h e Okavango swamp v a r y between 1 0 000 a n d 1 8 0 0 0 km2, b u t t h e estimation of Wilson a n d Dincer (1976) from s a t e l l i t e imagery i s 1 0 0 0 0 km2. The water b a l a n c e of d e l t a i c swamps d i f f e r s f r o m usual r i v e r basins or l a k e s , mainly by varying swamp areas a n d flow d i s t r i b u t i o n . Thus, hydrological f e a t u r e s v a r y l a r g e l y as functions of water i n p u t ( p r e c i p i t a t i o n o n t h e d r a i n a g e basin) a n d o u t p u t (evapo- t r a n s p i r a t i o n , runoff).
The Okavango c a t c h m e n t c o n s i s t s mainly of two r i v e r systems, t h e Cubango with a catchment area of 1 1 5 0 0 0 km2 with a n a v e r a g e a n n u a l r a i n f a l l of 9 8 3 mm, a n d t h e Cuito with a d r a i n a g e basin of 6 5 0 0 0 km2 a n d a n a v e r a g e annual rainfall of 8 7 6 mm [(Wilson a n d Dincer 1976) F i g u r e 63. The t w o r i v e r s t h e n m e r g e to form t h e Okavango r i v e r b e f o r e e n t e r i n g t h e Okavango d e l t a .
Usually, t h i s input of water is completely r e t a i n e d in t h e Okavango d e l t a w h e r e e v a p o t r a n s p i r a t i o n i s t h e main p r o c e s s (about 2 8 3 0 mm/year/m 2 ). E x c e s s water flows t h r o u g h t h e Boteti Channel to Makgadikgadi P a n s system. During high r a i n f a l l y e a r s t h e Okavango swamps system c a n d r a i n t h e e x c e s s water t h r o u g h Selinda spillway to t h e Chobe r i v e r , a n d t h e n o n to t h e Zambezi r i v e r (Figure 6).
The Selinda spillway i s t h e only link between t h e Okavango d r a i n a g e basin a n d t h e Zambezi, which means t h a t t h e Okavango d r a i n a g e basin i s r e l a t e d t o t h e Zambezi r i v e r only during t h e heavy r a i n f a l l season. Wilson a n d Dincer (1976) h a v e given a
Figure 6. Drainage basin of t h e Okavango d e l t a and i t s connection with t h e Zam- bezi r i v e r system.
t e n t a t i v e water b a l a n c e f o r t h e Okavango d e l t a (Table 5).
TPrble 5. Water b a l a n c e f o r t h e Okavango d e l t a (Wilson a n d Dincer 1976).
P r o c e s s e s
I
Annual inputI
Annual o u t p u tE v a p o t r a n s p i r a t i o n Outflow (Boteti r i v e r ) Groundwater outflow Inflow of Okavango r i v e r P r e c i p i t a t i o n
Total
To complicate t h e hydrology, t h e function of t h e Chobe r i v e r is to r e v e r s e t h e flow when t h e u p p e r Zambezi i s flooded (Davies 1986). Although t h e Okavango d r a i n a g e basin (almost 2 0 0 0 0 0 km2) is a p a r t of t h e Zambezi d r a i n a g e basin, i t h a s n o t t h e e x p e c t e d e f f e c t s o n t h e Zambezi r i v e r itself (runoff) d u e to t h e b u f f e r e f f e c t of t h e Okavango d e l t a a n d t h e u n s t a b l e connection between them.
11 X 109m3 5 x 1 0 ) ~ ~
1 6 x 1 0 m 1 6 x 109m3
2.3.3. Kafue armmps
The Kafue r i v e r i s t h e l a r g e s t t r i b u t a r y of t h e Zambezi r i v e r . Almost 1 5 0 0 km in length i t d r a i n s a n area of about 155000 km2. T h r e e main swamps make up t h e d r a i n a g e basin (Figure 7).
Lukanga swamp
This occupies a shallow depression extending to about 2 6 0 0 km2, but 2 1 0 0 km2 only i s permanent swamp. The a v e r a g e water capacity i s estimated at 7.38.10 m3 (Burgis and Symoens 1987). I t r e c e i v e s water from s e v e r a l catchment streams as well as from t h e Lukanga r i v e r , a t r i b u t a r y of t h e Kafue, which d r a i n s a n area of 1 4 2 4 5 km2. During high water level periods, i t a l s o r e c e i v e s water from t h e Kafue r i v e r itself.
Busanga swamp
This comprises a b o u t 1 0 0 0 km2 along t h e Lufupa r i v e r , a t r i b u t a r y of t h e Kafue r i v e r . Although i t i s not well known ecologically n o r i s i t exploited because i t i s in t h e tsetse fly zone, t h i s swamp i s similar to t h e Lukanga swamp f r o m t h e physiographical point of view (Burgis and Symoens 1987).
K-e
flatsA t Itezhitezhi t h e Kafue r i v e r b r e a k s through a r a n g e of l o w hills b e f o r e i t flows eastward across t h e Kafue f l a t s . H e r e i t meanders f o r 410 km t r a v e r s i n g a distance of 250 km across t h e floodplain at a n a v e r a g e g r a d i e n t of only 2.7cm/km (White 1973; Dudley 1974). During i t s c o u r s e through t h e f l a t s , t h e r i v e r falls only 15 m in 410 km (Rees 197th). After flowing through t h e floodplain, t h e r i v e r plunges down 670 m as i t flows through t h e 30 km Kafue Gorge to t h e Zambezi r i v e r .
I t i s typical f o r t h e waters of t h e Kafue r i v e r to start to r i s e in l a t e November or e a r l y December s h o r t l y a f t e r t h e start of t h e r a i n y season. The highest water levels are in April/May, a b o u t o n e month a f t e r t h e termination of t h e local rainfalls (Dudley 1979), when a b o u t 5 6 5 0 km2 may b e inundated; t h e water recedes slowly until November. The n a t u r a l hydrological c y c l e of t h e Kafue f l a t s v a r i e s tremendously. T h r e e - q u a r t e r s of t h e floodplain c a n change from a n aquatic to a t e r r e s t r i a l environment within one season. A t t h e e a s t e r n end of t h e Kafue f l a t s , a shallow area of a b o u t 1 2 1 5 km2 i s flooded more or less permanently (Burgis a n d Symoens 1987). The major input of water to t h e system i s f r o m t h e headwater
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Figure 7. Location of swamps on the Kafue river system (Burgis and Symoens, 1987).
areas of t h e Kafue r i v e r above Itezhitezhi (controlled by a dam since 1978), d i r e c t rainfall, and seasonal runoff from t h e surrounding h i g h e r grounds. Water i s lost by d i s c h a r g e through t h e Kafue Gorge (regulated by a dam since 1972) and by eva- potranspiration.
A tentative water balance in t h e Kafue r i v e r system i s given by Burgis and Symoens (1977) (Figure 8). Thus, i t h a s been estimated t h a t from t h e e n t i r e runoff of t h e Kafue drainage basin, which i s about 1 2 . 1 6 . 1 0 ~ m ~ . 7 3 p e r c e n t ( o r 8.88.109m3) r e a c h e s t h e Kafue Rail Bridge (downstream Kafue flats). The remain- ing 27 p e r c e n t ( o r 3.28.109m3) i s believed to be lost through evapotranspiration jointly from t h e Kafue floodplains and t h e Lukanga and Busanga swamps.
Figure 8. Water balance d t h e Kafue r i v e r system (Burgis and Symoens, 1987).
A review of t h e examples cited above, mainly of t h e Okavango d e l t a and t h e Kafue f l a t s f o r which more d a t a are available, shows t h e importance of swamps in t h e water balance of a n e n t i r e drainage basin, especially in those t r o p i c a l regions where t h e evapotranspiration p r o c e s s is intensified.
3. Flow Regime of the Zambezi
The g e n e r a l f e a t u r e of hydrological cycles in t h e t r o p i c s i s v e r y similar to those in more moderate regions, although s e v e r a l factors affecting water move- ment from t h e atmosphere through and o v e r t h e e a r t h ' s s u r f a c e into t h e r i v e r s are of p a r t i c u l a r importance, and t h e resulting effects deviate f r o m t h a t experienced outside t h e t r o p i c s . For instance, t h e specific function of interception, different time a n d space distribution of rainfall, t h e pronounced influence of swamps, and soil problems are e x a c e r b a t e d in t h e s e regions (Balek 1977). global water balance f o r t h e e n t i r e Zambezi r i v e r i s estimated and evaluated for t h e d i f f e r e n t subcatch- ment basins corresponding to t h e t h r e e s t r e t c h e s identified above (Table 6).
%ble 6. Water balance of t h e Zambezi d r a i n a g e basin (Balon and Coche 1974;
UNEP 1986a; Davies 1986).
A s shown above, water retention systems like swamps and man-made lakes play a c r u c i a l role in t h e global water balance of t h e Zambezi r i v e r system, a l s o in t h e dynamics of t h e flow itself. F o r t h e s a k e of presentation and because i t c o r r e s p o n d s t o r e a l i t y from t h e hydrological point of view, t h e Zambezi r i v e r will b e examined in t h r e e sections which more or l e s s coincide with t h e t h r e e n a t u r a l s t r e t c h e s .
Zambezi s t r e t c h e s Upper Middle Lower
3.1. The Upper Stretch
The u p p e r s t r e t c h c o r r e s p o n d s to t h e section between t h e s o u r c e of t h e Zam- bezi in a marshy bog n e a r t h e Kalene hills about 1 5 0 0 m a b o v e sea-level and t h e Victoria Falls n e a r t h e town of Livingstone. The 1 6 5 0 wide Victoria Falls with a mean annual d i s c h a r g e of 1 2 3 7 m3/s form a 98 m high b a r r i e r between t h e u p p e r a n d t h e middle Zambezi. The u p p e r s t r e t c h i s t h e most n a t u r a l to t h e Zambezi r i v e r owing to t h e a b s e n c e of impoundments. Rainfall in t h e d r a i n a g e basin r a n g e from 1 4 0 0 mm/year in t h e headwater zone to 700 mm southward. Temperatures r e a c h 20-22°C with a r a n g e of 6-8" C. The rainy season i s between November and April, and t h e d r y season from May to July. The double flood peak r e c o r d e d during
Drainage basin (km2>
320 000 1 118 000 1 400 000
Precipitation (km3>
360 830 1 3 1 7
Evapotrans iration (km
?
)245 688 1 0 0 0
Runoff (km3>
49.2 74.8 106.4
t h e rainy season upstream from t h e Barotse is balanced by t h e d r y season. The resulting single flood peak due t o t h e buffer e f f e c t of t h e Barotse swamps i s then f u r t h e r equalized by t h e Chobe swamps (Balon and Coche 1974).
Figure 9. Average flow regime (1925-1966) a t Livingstone, and flow regime during a d r y (1949-1950) and a w e t (1957-1958) period (Balon and Coche, 1974).
Next, a c h a r a c t e r i s t i c flood peak i s observed at Livingstone. Figure 9 gives t h e a v e r a g e monthly runoff at t h e Livingstone pump station calculated from t h e d a t a obtained between 1925 and 1966. The flow starts to i n c r e a s e in December t o r e a c h a peak in April (3500 m3/s), t h e n i t d e c r e a s e s to about 350 m3/s in October.
However, because of t h e e r r a t i c rainfall p a t t e r n of t h e region, t h e Zambezi flow v a r i e s g r e a t l y from y e a r to y e a r . Table 7 gives t h e frequency p e r month of t h e minimum or maximum discharge.
Thus, Balon (Balon and Coche 1974) h a s estimated t h a t i t normally t a k e s approximately t h r e e to f o u r weeks f o r t h e b a s e flood peak to move from Balovale, upstream to Barotse swamps, to Kariba. The annual runoff from t h e u p p e r Zambezi
Tcrble 7. Frequency of minimum and maximum d i s c h a r g e between 1 9 2 5 and 1 9 6 6 (Balon a n d Coche 1974).
Minimum d i s c h a r g e Maximum d i s c h a r g e
Months Frequency Months Frequency
S e p t e m b e r 9 F e b r u a r y 2
O c t o b e r 26 March 11
November 20 April 23
December 1 Hay 6
J u n e 1
c a t c h m e n t d u r i n g t h e p e r i o d 1924-1979 (Figure 1 0 ) shows a r i s e d u r i n g t h e l a t e 1 9 4 0 s a n d e a r l y 1950s. According to DuToit (1982), only 30 p e r c e n t of t h e i n c r e a s e could b e explained by a n i n c r e a s e of r a i n f a l l o v e r t h e catchment a r e a . Various explanations f o r t h e i n c r e a s e in r i v e r flow h a v e been s u g g e s t e d , s u c h as c h a n g e s in r a i n f a l l p a t t e r n s (spatial a n d s e a s o n a l distribution of mean water d e p t h s as well as intensities) a n d c h a n g e s in t h e watershed r e s p o n s e (Puzo 1978).
To s u p p o r t t h i s idea, DuToit (1982) o b s e r v e d t h a t t h e v a r i a t i o n s of t h e mean annual d i s c h a r g e became m o r e pronounced in t h e y e a r s 1950-1980, suggesting t h a t t h e s u r f a c e runoff i n c r e a s e d at t h e e x p e n s e of t h e underground water t a b l e r e c h a r g e a n d i n c r e a s i n g t h e d i f f e r e n c e s in runoff between w e t a n d d r y y e a r s . Undoubtedly, f u t u r e man-made d r a i n a g e of t h e B a r o t s e a n d Chobe swamps would promote t h i s e f f e c t .
O t h e r h y p o t h e s e s c o n c e r n c h a n g e s in t h e f e a t u r e s of t h e catchment r a t h e r t h a n c h a n g e s in t h e r a i n f a l l (Puzo 1978). Variations in t h e a n n u a l flow from high to low flow y e a r s h a v e become m o r e pronounced, which might s u g g e s t t h a t when r a i n d o e s o c c u r , i t flows off t h e land r a p i d l y d u e to s u p e r f i c i a l c h a n g e s r a t h e r t h a n p e r c o l a t i o n , maintaining a s u p p o r t i n g flow t h r o u g h a following d r i e r y e a r (DuToit 1982). Possible d r a i n a g e of B a r o t s e a n d Chode swamps should h e i g h t e n t h i s e f f e c t . In a n y c a s e , t h e problem r e m a i n s unsolved. S i n c e 1980-1981, t h e u p p e r Zambezi c a t c h m e n t h a s e x p e r i e n c e d a n u n p r e c e d e n t e d d r o u g h t causing o t h e r problems f o r t h e management of t h e K a r i b a R e s e r v o i r .
Figure 10. Annual r u n o f f s of t h e u p p e r Zambezi oatchment d u r i n g the p e r i o d 1924-1979 (five y e a r s running means, DuToit, 1983).
3.2. The Middle Stretch
The n a t u r a l r i v e r s i t u a t i o n of t h e middle as well as t h e lower s t r e t c h e s h a s changed d r a s t i c a l l y by c r e a t i n g l a k e s K a r i b a a n d C a h o r a Bassa, both within t h e flooded area a n d downstream from t h e dams. B e f o r e t h e impoundments, t h i s r i v e r was defined as a "sand-bank" r i v e r , like t h e Huangwa a n d t h e Limpopo r i v e r s , by Jackson (1961). Due to t h e c r e a t i o n of t h e two man-made l a k e s , t h i s p a r t of t h e r i v e r should now b e c o n s i d e r e d as a " r e s e r v o i r r i v e r " , such as t h e Kafue o r t h e S h i r e r i v e r s . In i t s n a t u r a l s t a g e , t h e middle Zambezi h a s h a d two high flood p e r i o d s e v e r y y e a r (Figure 11): t h e "Gumbura" as called by t h e local p e o p l e comes usually in F e b r u a r y . with l e s s t u r b u l e n t flood w a t e r s , c a r r y i n g local runoff. The second high flood, known as the"Murorwe" used to come in April, b u t s i n c e t h e K a r i b a w a s c o n s t r u c t e d , i t n o l o n g e r inundates t h e floodplain below t h e wall.
One c a n n o t i c e t h a t t h e Kafue c a t c h m e n t runoff joining t h e Zambezi down- stream a n d t h e K a r i b a i s f l a t t e n e d d u e to a n a c c e n t u a t i o n of t h e n a t u r a l " r e s e r v o i r r i v e r " of t h e Kafue r i v e r by i t s impoundments (Itezhitezhi, Kafue G o r g e dams).
F i g u r e 12 r e p r e s e n t s t h e s i t u a t i o n in r e c e n t y e a r s f o r t h e monthly inflows a n d spil- l a g e s f o r L a k e Kariba. This g r a p h r e v e a l s t h e f a c t t h a t f o r t h e p e r i o d c o n s i d e r e d , t h e K a r i b a scheme d o e s n o t s e e m to h a v e r e g u l a t e d t h e Zambezi flow on a monthly s c a l e , although t h e inflow i s somewhat g r e a t e r t h a n t h e outflow d u r i n g t h e f i r s t p a r t of e v e r y r a i n y s e a s o n , a n d t h e outflow is somewhat g r e a t e r t h a n t h e inflow d u r i n g t h e d r y s e a s o n . On t h e o t h e r hand, t h e K a r i b a s c h e m e h a s r e g u l a t e d well
months
Figure 11. Mean monthly flows upstream from Kariba f o r t h e period 1924-1979 (DuToit, 1982).
t h e s h a r p flood peaks of 1963, 1969 and 1970. For instance, t h e flood peak at Vic- t o r i a Falls in 1969 was estimated at 8100 m3/s, while t h e spilling through t w o floodgates amounted no more t h a n 3000 m3/s.
3.3.
The h e r StretchBefore t h e Kariba impoundment w a s built, t h e Zambezi showed a r e g u l a r annual cycle, usually r e a c h i n g i t s peak in F e b r u a r y or March at 5000-20000 m3/sec and falling to 200-800 m3/sec in October-November. Now 90 p e r c e n t of t h e flow into t h e Cahora Bassa r e s e r v o i r is regulated. The Kariba dam has r e s u l t e d in an i n c r e a s e in d r y season flows and a delay in t h e timing of floods
Figure 12. Monthly inflow and outflow f o r Kariba from October 1976 to September 1979 (DuToit, 1982).
during t h e w e t season (Bernacsek and Lopes 1984). The flood magnitude h a s been d e c r e a s e d by a n a v e r a g e of 24 p e r c e n t during eight y e a r s in t h e 19'70-80 period.
The e r r a t i c water management of Cahora Bassa h a s completely a l t e r e d t h e normal water flow downstream to t h e floodplain and t h e delta. A s shown in Figure 13, max- imum d i s c h a r g e s almost always t a k e p l a c e out of season. Most y e a r s tend to h a v e t w o flood r e l e a s e s , and in some cases even t h r e e as in 1981 (Figure 13).
Since t h e c l o s u r e of t h e Cahora Bassa dam in December 1974, a period of t w o y e a r s (1979 and 1980) may b e considered as "normal" from t h e hydrological and operational perspectives, although even during t h i s period t h e Zambezi hydrologi- cal c y c l e w a s tremendously disturbed (Figure 14) with a r e t e n t i o n of flood peak in t h e r e s e r v o i r between F e b r u a r y and May, c r e a t i n g t w o a r t i f i c i a l flood p e a k s o u t of season.
8. m 16 m
>
ramI L .m
i
,,.,:
lorn1
b m I P
P w e 13. Water flow through Cahora Bassa reservoir. (A) total monthly inflow and outflow volume; (B) difference in monthly inflows (Bernacsek and Lopes, 1984).
I I I I I I I I I I I I ~
O N O J F M A M J J A S nm
Figure 14. Water flow Ulrough Cahora Bassa reservoir in 1980. Shaded a r e a represents buffering e f f e c t of the lake during floods.
3.4. Conclusions
As shown a b o v e , now t h e Zambezi i s f a r from from t h e d e s c r i p t i o n of J a c k s o n ' s in 1 9 6 1 as having sand-bank c h a r a c t e r i s t i c s : ' k a v e v e r y d e e p b e d s with well- defined s t e p b a n k s c u t i n t h e alluvial e a r t h , t h r o u g h which t h e r i v e r s meander at l o w level, o f t e n l i t t l e more t h a n a connection between a s e r i e s of pools f r i n g e d with r o c k s a n d sand b a n k s with l i t t l e a q u a t i c vegetation, and s t i l l less marginal vegeta- tion o n t h e banks, while t h e flood i s violent but of comparatively s h o r t d u r a t i o n , with t h e floodplains inundated f o r a r e l a t i v e l y s h o r t s p a c e of time." (Jackson 1961) The impoundment of t h e middle a n d lower Zambezi a n d i t s main t r i b u t a r i e s (Kafue a n d S h i r e ) h a s t r a n s f o r m e d t h i s r i v e r to a " r e s e r v o i r system" d e p e n d e n t on a n t h r o p o g e n i c management. The i n t e r n a t i o n a l s t a t u s of t h e Zambezi r i v e r escalates t h e problems r e l a t e d to i t s management. As underlined by Bernacsek and Lopes (1984) f o r instance, d e s p i t e t h e f a c t t h a t a b o u t 9 0 p e r c e n t of t h e inflow i n t o C a h o r a Bassa r e s e r v o i r is r e g u l a t e d , major problems in flood p r e d i c t i o n a n d management remain. T h e following c h a p t e r i s devoted to t h e s e i n t e r n a t i o n a l c h a r a c t e r i s t i c s of t h e Zambezi r i v e r basin.
Chapter II: The Zambezi Drainage Basin
1. Political Boundaries
The Zambezi d r a i n a g e basin i s s h a r e d by eight c o u n t r i e s of t h e s o u t h e r n Afri- c a n region. They are Angola, Botswana, Malawi, Mozambique, Namibia, Tanzania, Zambia and Zimbabwe (Figure 15). According to t h e i r geographical locations, they s h a r e t h e catchment with a l a r g e r a n g e of s u r f a c e contributions. Table 8 surnrnar- izes t h e contributions of t h e eight countries to t h e Zambezi d r a i n a g e basin.
Table 8. S h a r e of t h e Zambezi d r a i n a g e basin by t h e e i g h t countries.
% watershed Countries
Angola Botswana Malawi Mozambique Namibia Tanzania Zambia Zimbabwe
Total s u r f a c e
I
S u r f a c e in t h ekm2
1
watershedThe concept of t h e d r a i n a g e basin means t h a t all land drained to a r i v e r o r i t s t r i b u t a r i e s belongs t o t h e catchment of t h i s r i v e r . One must a l s o consider t h a t some c o u n t r i e s d o not have d i r e c t c o n t a c t with t h e Zambezi r i v e r itself, but t h a t p a r t of t h e t e r r i t o r y i s drained by a t r i b u t a r y of t h e Zambezi. This i s t h e case in Malawi and Tanzania t h a t are d r a i n e d towards Lake Malawi and t h e S h i r e (Figure 15). These boundary d i f f e r e n c e s among c o u n t r i e s entail d i f f e r e n t i n t e r e s t s in t h e Zambezi r i v e r . Complicating t h e political situation in e a c h country as well as f o r international negotiations, many ministries s h a r e water administration and manage- ment in e a c h nation. Table 9 gives t h e number of ministries concerned with water management in e a c h country.
I I km2
f'l
Z A M B E Z I D R A I N A G E BASIN P O L I T I C A L BOUNDARIES-
Figure 15. Political boundaries of t h e Zambezi drainage basin.
TabLe 9. Number of ministries sharing water administration in t h e Zambezi coun- t r i e s .
Countries Angola Botswana Malawi Mozambique Namibia Tanzania Zambia Zimbabwe
Number of ministries ND
6 5 6 ND
8 7
8
2. Economic Situation
2.1. Population
Within i t s area of a b o u t 1400000 km 2 , t h e Zambezi d r a i n a g e basin h a s more t h a n 20 million inhabitants. Table 10 gives t h e population distribution within t h e catchment f o r e a c h c o u n t r y .
Among them Malawi, Mozambique, Zambia a n d Zimbabwe a c c o u n t f o r 94.70 p e r c e n t of t h e population in t h e basin, while t h e o t h e r s s h a r e 5.3 p e r c e n t although t h e d r a i n a g e area t h e y c o v e r i s a q u a r t e r of t h e t o t a l Zambezi catchment. The g e n e r a l p a t t e r n i s towards a n i n c r e a s e of population in e a c h c o u n t r y s i n c e 1965, a n d a d e c r e a s e in p e r c e n t a g e of population economically a c t i v e in a g r i c u l t u r e (Figure 16). Nonetheless, more t h a n 70 p e r c e n t of t h e population is involved in a g r i c u l t u r e in a l l t h e r i p a r i a n c o u n t r i e s , e x c e p t Botswana (66 p e r c e n t ) and Nami- bia (38.3 p e r c e n t ) .
TabLe 10. Population distribution of t h e Zambezi d r a i n a g e basin.
Botswana
1
1149000/
8 1 0 0 ) 0.701
0.04I
p o i E i o nMalawi
1
7178000(
71780001
1001
32.70Mozambique
1
143420001
2566708(
17.89(
11.69Angola I
1
8900000,
303740,
3.411
1.38Basin population
I I
Namibia
1
15960001
400101
2.50 1 0.18Z
of t o t a l1
X of basinpopulation , population
Tanzania
1
233340001
8154201
3.491
3.71Zambia
1
68980001
4482396(
70.21
20.42v a s t r e g i o n generally with sandy soil. Predominant c r o p s are sorghum and bulrush Zimbabwe
millet. ( c ) E a s t e r n Cuando-Cubango i s a r e g i o n of p o o r soil a n d s p a r s e population.
S u b s i s t e n c e farming and food collecting are dominant with pastoralism in t h e d r y
Total , 72496000 , 21954753
1
30.3!
1009099000
s o u t h e a s t e r n area.
65603791 72.1 29.88
p p
Figure 16. Evolution of population in t h e Zambezi r i p a r i a n c o u n t r i e s (.-.) and p e r c e n t a g e of population economically a c t i v e in a g r i c u l t u r e (.---.) (FAO, 1986).
2.2. Land-Use
For e a c h country s h a r i n g t h e Zambezi r i v e r basin, t h e s t a t i s t i c s shown below were t a k e n from t h e FA0 Production Yearbook (1977-1987) concerning t h e whole c o u n t r y , and not just t h e p a r t belonging to t h e Zambezi catchment. Nevertheless, t h e s e d a t a provide a quite a p p r o p r i a t e idea of t h e situation on t h e d r a i n a g e basin, at l e a s t f o r Malawi, Mozambique, Zambia and Zimbabwe. Concerning t h e o t h e r countries* it shows at l e a s t b e main f e a t u r e s and tendency.
2.2.1. Angola
Since 1965, s t a t i s t i c s show a n i n c r e a s e in a r a b l e land mainly between 1970 and 1975 which is certainly due t o increased d e f o r e s t a t i o n during t h e s a m e period.
However, permanent c r o p area h a s not increased. The p a r t of Angola belonging to t h e Zambezi d r a i n a g e basin c o v e r s t h r e e regions: (a) East Central Moxico, with r i v e r basins subject to flooding, and villages located on low elevations. Hoe cul- tivation of subsistence c r o p s i s done during t h e rainy season. The region close to t h e Zambezi r i v e r i s a more favoured area f o r c r o p farming with relatively impor- t a n t stock raising, e x c e p t in t h e tsetse-infested zones. (b) S o u t h e r n Moxico is a
Table U . Land-use in Angola. S t a t i s t i c s in km2.
Land-Use
!
1965!
1970/
1975!
1980!
1985Arable Permanent c r o p Permanent p a s t u r e F o r e s t I r r i g a t i o n
2.2.2. Botswana
A s shown above, Botswana's area belonging to t h e Zambezi d r a i n a g e basin is mainly r e p r e s e n t e d by t h e Okavango region.
In Botswana, t h e r e is a major study called "Southern Okavango Integrated Water Development Study" u n d e r p r e p a r a t i o n . I t seems t h a t s o m e 150 krn2 would b e suitable for large-scale i r r i g a t i o n f o r a g r i c u l t u r a l development (UNEP 1986b).
The Okavango d e l t a i s a l s o s u b j e c t to large-scale c a t t l e raising, mainly in t h e s o u t h e r n p a r t of t h e delta. Development of t h i s region i s d u e p a r t l y to t h e e r a d i - cation of t h e tsetse fly which h a s allowed settlement by people.
Table 12. Land-use in Botswana. S t a t i s t i c s in km2.
Land-Use A r a b l e P e r m a n e n t c r o p P e r m a n e n t p a s t u r e F o r e s t I r r i g a t i o n
2.2.3. Malawi
Almost 1 0 0 p e r c e n t of Malawi t e r r i t o r y belongs to t h e Zambezi d r a i n a g e basin.
Table 23. Land-use in Malawi. S t a t i s t i c s in km2
Land-Use A r a b l e P e r m a n e n t c r o p P e r m a n e n t p a s t u r e F o r e s t I r r i g a t i o n
Tea a n d t o b a c c o are t w o main c r o p s t h a t c o v e r 2 1 0 a n d 9 0 0 km2, r e s p e c t i v e l y . Coffee now s u r v i v e s l a r g e l y as a small-holder c a s h c r o p in t h e n o r t h . Commercial s u g a r p r o d u c t i o n i s impossible without i r r i g a t i o n . More a n d m o r e land i s becoming permanently c u l t i v a t e d a n d u s e of a r t i f i c i a l f e r t i l i z e r i s i n c r e a s i n g , although n o f e r t i l i z e r is used to grow c a s s a v a , millet, maize, sorghum, c o t t o n a n d r i c e , e x c e p t when c o t t o n a n d r i c e are grown in o r g a n i z e d land s c h e m e s w h e r e f e r t i l i z e r u s e i s e n c o u r a g e d .
2.2.4. Mozambique
With a b o u t 2 0 p e r c e n t of i t s t e r r i t o r y , t h e area belonging t o t h e Zambezi d r a i n a g e basin h a s g r e a t a g r i c u l t u r a l potential. Thus, almost 2 5 0 0 km2 were iden- tified as potential a r a b l e land mainly on t h e Zambezi flood plains.
Table 14. Land-use in Mozambique. S t a t i s t i c s in km2.
Land-Use Arable P e r m a n e n t c r o p P e r m a n e n t p a s t u r e F o r e s t I r r i g a t i o n
T e t e highlands r e g i o n i s predominantly humid a n d t e m p e r a t e with mainly fer- r a l l i t i c soils on which maize and p o t a t o e s are cultivated. Close t o t h e Zambezi r i v e r , soils are predominantly brown soils with sorghum, millet, maize a n d c o t t o n production. The main t y p e s of farming in t h e r e g i o n s belonging t o t h e Zambezi watershed are semi-subsistence farming a n d s u b s i s t e n c e farming with livestock.
2.2.5. Namibia
The area of Namibia belonging t o t h e Zambezi d r a i n a g e basin i s c a l l e d t h e Caprivi s t r i p , a r e g i o n v e r y s p a r s e l y populated. S t a t i s t i c s f o r t h e whole c o u n t r y given in Table 15 c a n n o t b e t a k e n as r e p r e s e n t a t i v e of t h e Caprivi s t r i p land use.
Table 25. Land-use in Namibia. S t a t i s t i c s in km2.
Land-Use A r a b l e P e r m a n e n t c r o p P e r m a n e n t p a s t u r e
F o r e s t
1
ND1
3 5 0 0 01
3 2 0 0 01
2 9 0 0 0 2 6 0 0 0I r r i g a t i o n ND 6 0 7 0 8 0 8 0
2.2.6. Tanzania
A l m o s t t h r e e p e r c e n t of Tanzania t e r r i t o r y which i s d r a i n e d to L a k e Malawi i s s t i l l at i t s e a r l y s t a g e of a g r i c u l t u r a l development. A s shown in T a b l e 1 6 , i t i s not t h e case f o r t h e main p a r t of t h e t e r r i t o r y . In t h i s small a r e a , i r r i g a t i o n p r a c t i c e s are n o t well d e v e l o p e d . E x c e p t f o r t o b a c c o , n o s u b s t a n t i a l c a s h c r o p i s grown, b u t normal s u b s i s t e n c e c r o p s are p r o d u c e d .
Table 16. Land-use in Tanzania. S t a t i s t i c s in km2.
Land-Use A r a b l e P e r m a n e n t c r o p P e r m a n e n t p a s t u r e F o r e s t I r r i g a t i o n
2.2.7. Zambia
In Zambia, t h e t o t a l area of a r a b l e land i s e s t i m a t e d at a b o u t 1 0 million h e c - t a r e s . A t p r e s e n t , t h e d e v e l o p m e n t of t h i s r e s o u r c e b a s e h a s high p r i o r i t y in t h e n a t i o n a l d e v e l o p m e n t planning.
Although t h e a m o u n t s v a r y c o n s i d e r a b l y f r o m y e a r t o y e a r , maize, g r o u n d n u t s a n d c o t t o n are most i m p o r t a n t sectors of involvement. T h e t w o main t y p e s of t i m b e r are p i n e a n d e u c a l y p t u s f o r u s e in t h e mining a n d c o n s t r u c t i o n i n d u s t r i e s . Commercial c u l t i v a t i o n i s mainly a l o n g t h e Kafue r i v e r s y s t e m a n d t h e s o u t h e r n a g r i c u l t u r a l b e l t .
Table 17. Land-use in Zambia. S t a t i s t i c s in km2.
Land-Use A r a b l e P e r m a n e n t c r o p P e r m a n e n t p a s t u r e F o r e s t I r r i g a t i o n
2.2.8. Zimbabwe
Due to i t s dominance in t h e economy, t h e government h a s d e c l a r e d t h e development of a g r i c u l t u r e as t h e h i g h e s t p r i o r i t y in t h e c u r r e n t f i v e y e a r s national development plan (UNEP 1986b). One p r i n c i p a l means of i n c r e a s i n g a g r i - c u l t u r a l p r o d u c t i o n i s to i n c r e a s e t h e t o t a l area of c u l t i v a t e d land mainly in t h e Zambezi d r a i n a g e basin.
Table 28. Land-use in Zimbabwe. S t a t i s t i c s in km2.
Land-Use Arable P e r m a n e n t c r o p P e r m a n e n t p a s t u r e F o r e s t I r r i g a t i o n
The area lying in t h e Zambezi d r a i n a g e basin i s divided i n t o t h r e e g e o g r a p h i - c a l regions: ( a ) t h e high veld, t h e h i g h e s t e x t e n s i v e s u r f a c e which l i e s l a r g e l y between 1 2 0 0 a n d 1 5 0 0 m e t r e s , f o r m s t h e w a t e r s h e d between t h e Zambezi r i v e r a n d t h e n o r t h . (b) In t h e w e s t e r n p a r t of t h e Zambezi basin t h e middle veld f o r m s a v e r y e x t e n s i v e p l a t e a u . ( c ) The Zambezi low veld i s m o r e limited a n d i s mostly cut- off from t h e rest of t h e c o u n t r y by s t e e p e s c a r p m e n t s a n d r u g g e d t e r r a i n . The main c r o p s are maize a n d Virginia t o b a c c o . F o r e s t s are i m p o r t a n t , e s p e c i a l l y in t h e n o r t h w e s t e r n q u a r t e r with e x t e n s i v e r e s e r v e s of indigenous hardwoods c o v e r i n g some 9 5 0 0 km2, a n d in t h e e a s t e r n highlands t h e r e are a b o u t 6 5 0 km2 of pines.
3. Water Quality
A w a t e r quality s u r v e y of t h e Zambezi r i v e r system i s n o t y e t v e r y developed (UNEP 1986b), mainly d u e to t h e s h o r t a g e of manpower a n d equipment. Yet, hydro-chemistry of t h e middle a n d lower Zambezi i s r e l a t i v e l y well documented. A s u r v e y h a s b e e n made principally of t h e main t r i b u t a r i e s of t h e Zambezi r i v e r , a n d
t h e main impounded zones. Thus, Coche (1968), and Balon and Coche (1974) have detailed t h e physic-chemistry of Lake Kariba, while McLachlan (1970a), King and Lee (1974) and Bowmaker (1976) have focused on t r i b u t a r i e s e n t e r i n g Lake Kariba.
Hall et aL. (1976; 1977) h a v e described t h e physico-chemical s t a t u s of t h e lower Zambezi p r i o r to and during t h e c l o s u r e of t h e Cahora Bassa dam and i t s main t r i - butaries. Hydro-chemical and hydrobiological s u r v e y s h a v e been done a l s o on t h e Kafue f l a t s (Carey 1971; S a l t e r 1979; 1985). S o m e information i s available on smaller impoundments like t h e McIlwaine l a k e on t h e Hunyani r i v e r (Marshall and Falconer 1973a, b).
N o major pollution problems have been r e p o r t e d on t h e Zambezi drainage sys- t e m (UNEP 1986b), e x c e p t at some specific s i t e s such as t h e c o p p e r b e l t in Zambia, Lusaka and H a r a r e areas, and some o t h e r major towns from which domestic and industrial effluents could o c c u r . The regulation of t h e middle and lower Zambezi and t h e i r transformation into a " r e s e r v o i r r i v e r " might a g g r a v a t e t h e water qual- ity problems, like eutrophication due to f e r t i l i z e r leaching. Although soil fertili- zation i s not developed, as shown in Table 19, t h e situation may change if l a r g e s c a l e i r r i g a t i o n development o c c u r , and a l s o because development of a g r i c u l t u r a l programmes i s one of t h e main goals of t h e r i p a r i a n countries. Another problem t h a t could a r i s e soon i s sedimentation in man-made l a k e s due to soil erosion in deforested areas ( s e e Section 3). P r e s e n t l y , t h e water quality of t h e middle and lower Zambezi depends mainly on p r o c e s s e s t h a t o c c u r in t h e impoundments. Water quality d a t a will b e given in C h a p t e r 3 o n impoundments.
TrrbLe 19. Fertilization rates in c o u n t r i e s s h a r i n g t h e Zambezi d r a i n a g e basin (FA0 F e r t i l i z e r Yearbooks 1981,1986).
Botswana 0.9 0.7 0.4 0.4
1
0.27 0.31 0.17 0.131970 1976 1980 1984
Angola 2.1
Malawi 3.8 8.3 3.5 5.5
1
0.27 0.31 0.17 0.131970 1976 1980 1984 0.3
Mozambique 1.7 2.2 1.5 2.412.18 2.18 1.35 0.61
Namibia ND ND ND ND
I
ND ND ND NDTanzania 1.7 2.6 2.8 3.0
1
0.31 0.96 0.39 0.44Zambia 4.1 7.9 7.5 8.510.83 1.57 1.27 1.40
Zimbabwe 23.1 24.2 27.8 30.3 15.85 7.55 6.37 7.24
Another problem r e l a t e d
to
t h e development of a g r i c u l t u r e is t h e use of pesti- cides, especially DDT to e r a d i c a t e tsetse f l i e s which are a sine qua none condition b e f o r e settlement c a n begin in t h e s e infested areas. DDT i s a l s o used for t h e e r a d - ication of Anopheles flies, c a u s e of malaria. The u s e of p e s t i c i d e s i s d a n g e r o u s because of c o n c e n t r a t i o n in t h e food chain. Endosulfane and o t h e r "soft" pesti- cides have been t e s t e d as s u b s t i t u t e s f o r DDT.4. Energy Planning
The S o u t h e r n African Development Coordination Conference (SADCC) w a s esta- blished in April 1980 by a d e c l a r a t i o n of t h e governments of t h e nine independent states of s o u t h e r n Africa, namely Angola, Botswana, Lesotho, Malawi, Mozambique, Swaziland, Tanzania, Zambia and Zimbabwe. The o b j e c t i v e s of t h e regional e n e r g y policy h a v e been summarized by Bhagavan (1985) as follows:
-
"to r e s t r i c t t h e u s e of petroleum p r o d u c t s solely t o applications where a l t e r n a t i v e r e s o u r c e s c a n n o t b e envisaged-
t o develop regional e l e c t r i f i c a t i o n a n d extend i tto
t h e t r a n s p o r t and a g r i - c u l t u r a l s e c t o r s , to exploit t h e v a s t h y d r o e l e c t r i c r e s o u r c e s of t h e r e g i o n in o r d e r to a c h i e v e t h i s , a n d a l s o t o make u s e of small h y d r o e l e c t r i c power plants t h r o u g h o u t t h e r u r a l areas- to
promote t h e interconnection of t h e national g r i d system t o e n s u r e t h a t production and distribution c a p a c i t y i s utilized m o r e efficiently among t h e v a r i o u s states in t h e r e g i o n-
to develop p r o s p e c t i n g a n d exploitation of fossil f u e l deposits, such as o i l , n a t u r a l g a s and c o a l-
to develop new technologies f o r t h e utilization of s o l a r e n e r g y , biomass a n d o t h e r renewable e n e r g y s o u r c e s a n d t o make them available t o t h e r u r a l areas-
to promote r e s e a r c h a n d development in renewable e n e r g y technologies at t h e regional level-
to promote r e g i o n a l programmes of r e f o r e s t a t i o n and e f f i c i e n t exploitation a n d utilization of wood."This review of objectives o f f e r s a c l e a r idea of what is at s t a k e on t h e Zam- bezi d r a i n a g e basin since t h e signing of t h e declaration by seven of t h e eight r i p a r i a n c o u n t r i e s of t h e Zambezi r i v e r , and i t is assumed by both SADCC and t h e South West African People's Organisation (SWAPO) t h a t a n independent Namibia would join SADCC.
4.1. Fuelwood
Fuelwood i s t h e primary s o u r c e of e n e r g y f o r all r u r a l households and a l a r g e p a r t of t h e urban households of t h e r i p a r i a n c o u n t r i e s of t h e Zambezi r i v e r . Table 20 gives t h e evolution of wood use as a s o u r c e of e n e r g y in t h e Zambezi r i p a r i a n countries.
Table 20. Evolution of woodstock in 103m3 used as e n e r g y s o u r c e in t h e Zambezi r i p a r i a n c o u n t r i e s (FA0 F o r e s t P r o d u c t s 1975, 1986).
Angola Botswana Malawi Mozambique Namibia Tanzania Zambia Zimbabwe
Fuelwood plays a dominant r o l e in t h e curing of t o b a c c o and tea, t h e major cash c r o p s of t h e region. F o r instance, Bhagavan (1985) r e p o r t e d t h a t in Malawi and Zimbabwe, tobacco and tea curing accounts for about 40 p e r c e n t of t h e t o t a l firewood consumption. A s a n example, Hosier (1986) gives t h e e n e r g y consumption in Zimbabwe (Figure 17) with t h e a c t u a l end-use and p r o j e c t e d requirements for t h e y e a r 2000. I t a p p e a r s t h a t even in Zimbabwe with abundant supply of coal and e l e c t r i c i t y , wood r e s o u r c e s will continue t o b e essential for most of t h e f o r e s e e - a b l e f u t u r e . This poses a major problem d u e to t h e increasing s c a r c i t y of fuelwood supplies in all t h e Zambezi r i p a r i a n countries. Due to t h i s demand for fuelwood in r u r a l and u r b a n households a s well as clearing land f o r a g r i c u l t u r e and timber
,
8o1
End-use requirements in 1982Fuelwood Coal Commercial wood L ~ q u ~ d fuel Electrlclty
Rural Industry Transport Agriculture Urban Other
Households Households
Projected end-use requirements for 2002
SECTOR
Fuelwood Coal
Commerc~al wood Liquid fuel Electr~clty
Rural Industry Transport Agriculture Urban Other
Households Households
Figure 17. Energy consumption in Zimbabwe (Hosier, 1986).
t r a d e , r a p i d d e f o r e s t a t i o n i s o c c u r r i n g on t h e Zambezi d r a i n a g e basin, c o n t r i b u t - ing t o soil e r o s i o n as well as t o c h a n g e s in runoff from s u c h d i s t u r b e d areas. Thus, Mumeka (1986) h a s shown t h a t d e f o r e s t a t i o n led t o a n i n c r e a s e in streamflow, and a c h a n g e in t h e flood h y d r o g r a p h of t h e Kafue headwaters. Elwell (1978; 1984) and Elwell a n d Stocking (1982) h a v e developed models to p r e d i c t soil l o s s e s by a r a b l e lands in Zimbabwe. Such estimations of soil l o s s are v e r y important in determining t h e impact of sediment t r a n s p o r t e d by r i v e r s o n r e s e r v o i r l i f e of man-made l a k e s in t h e Zambezi basin (Bolton 1984; Kabell 1984; P i t t a n d Thompson 1984; White and Bettess 1984).
4.2. Hydroelectric schema and other energy sources
F i r s t , dealing with oil production, Angola i s t h e only Zambezi r i p a r i a n c o u n t r y t h a t p r o d u c e s a n d e x p o r t s s u b s t a n t i a l quantity of oil. On t h e o t h e r hand, t h e r e are massive d e p o s i t s of coal in Botswana, Mozambique, Tanzania, Zambia a n d Zimbabwe.
Unfortunately. t h e d e c r e a s e in world demand f o r c o a l h i n d e r s p r i v a t e f o r e i g n investment f o r developing c o a l r e s e r v e s f o r e x p o r t (Bhagavan 1985). Concerning n a t u r a l gas, big r e s e r v e s h a v e b e e n d i s c o v e r e d only at two o f f s h o r e s i t e s in Mozambique.
Actual and potential h y d r o e l e c t r i c power are abundant. T h e r e i s more t h a n enough installed g e n e r a t i o n c a p a c i t y today t o meet t h e c u r r e n t demands of u r b a n households, i n d u s t r i e s a n d t h e s e r v i c e sector. Table 21 gives t h e n e t c a p a c i t y installed in e l e c t r i c i t y g e n e r a t i o n plants, while Table 22 shows t h e utilization of e l e c t r i c i t y a c c o r d i n g t o t h e t y p e of plant.
Table 21. Installed c a p a c i t y of e l e c t r i c i t y g e n e r a t i n g p l a n t s of t h e Zambezi r i p a r i - a n c o u n t r i e s (UN Yearbooks 1972, 1983, 1987).
Angola Botswana Malawi Mozambique Namibia Tanzania Zambia Zimbabwe
Thermal c a p a c i t y lo3 kw 1961 1970 1980 1985
60 101 200 200
ND ND ND ND
11 21 39 34 94 241 280 280
ND ND ND ND
30 94 70 180 241 184 190 191 502 487 487 906
H y d r o e l e c t r i c i t y c a p a c i t y lo3 kw 1961 1970 1980 1985 28 211 400 400
ND ND ND ND
1 28 67 126
65 114 1520 1523
ND ND ND ND
20 49 188 260 43 180 1538 1538 562 705 705 633
Table 22. Utilization of installed e l e c t r i c i t y g e n e r a t i n g c a p a c i t y a c c o r d i n g to t h e t y p e of p l a n t a n d c o u n t r y .
Botswana
I
ND ND ND NDI
ND ND ND ND1
Thermal KWH p e r KW1
H y d r o e l e c t r i c i t y Kwh p e r KWMalawi
1
3000 609 769 7711
2000 5038 6030 37751961 1970 1980 1985
Mozambique
1
1383 1711 1607 14641
1846 2353 8914 10081961 1970 1980 1985
Zambia 1672 970 526 183 6186 910 5722 6538
Angola
1
517 1228 2000 2275Namibia Tanzania
Zimbabwe
1
1147 2388 1094 1051 3925 7443 5685 53555357 2464 2750 3338
ND ND ND ND ND ND
ND 1851 2571 6224 2819 2365
Nowadays, e v e n if utilization of t h e existing e l e c t r i c i t y c a p a c i t y scheme i s below t h e potential, t h e supply of e l e c t r i c i t y comfortably e x c e e d s demand in t h e Zambezi r i p a r i a n c o u n t r i e s . Bhagavan (1985) underlined t h a t "demand h e r e means ability of t h e end-use c u s t o m e r to pay t h e a s k e d f o r p r i c e which effectively l e a v e s o u t a b o u t 70 to 90 p e r c e n t of t h e population, who at p r e s e n t d o n o t h a v e t h i s abil- ity to pay." If a t t e m p t s were made to m e e t t h i s l a r g e r n e e d , t h e p r e s e n t supply would b e c l e a r l y i n a d e q u a t e . L a r g e s t installed a n d p o t e n t i a l c a p a c i t y in h y d r o e l e c t r i c i t y of t h e Zambezi d r a i n a g e basin i s b a s e d mainly on t h e Zambezi r i v e r itself a n d o n t h e Kafue r i v e r (Table 23).
Table 23. H y d r o e l e c t r i c power p l a n t s on t h e Zambezi and t h e Kafue r i v e r s (Bolton 1983).
Power P l a n t
Victoria Falls K a r i b a
C a h o r a Bassa Kafue G o r g e
Installed c a p a c i t y
in Mw 108
P r o v i s i o n c a p a c i t y
in Mw
