Introduction
It is easy to think of Africa as a continent of desert in the north
and tropical forest elsewhere, but in fact arid conditions dominate
much of southern Africa too. The subcontinent is a land of contrasts,
from the tropical north to the temperate south, from the mesic east
to the hyperarid west, and from the relatively wealthy South Africa
to the desperately poor Lesotho. Issues of water resources thus span
the whole gamut from individual families' supply to supply for
vast industrial complexes, from drought to flood, and from water quality
to the conservation of aquatic ecosystems. And all of these issues
need to be seen in the context of poverty and overpopulation.
This paper attempts to highlight, for southern Africa, some of the
more pressing issues of management of both water as a resource and
the ecosystems from which it is drawn. It looks first at the physical
and climatic features of the land, then at water supply and demand,
issues related to water quality, and the conservation of aquatic ecosystems.
I will concentrate mostly on the situation in South Africa and Namibia,
because I am most familiar with those countries and because more statistical
information is available about them than about most other southern
African states. Finally I attempt to indicate some other general management
issues, and conclude with a short discussion of South Africa's
new Water Act.
For convenience, southern Africa is taken (fairly arbitrarily) as
the continent south of 10oS. It includes the political entities
of South Africa, Lesotho, Swaziland, Namibia, Botswana, Mozambique,
Zimbabwe, and Malawi, as well as most of Zambia and Angola, and forms
a geographically recognizable unit.
Physical Features of Southern Africa
The physical features of any land mass determine the forms of river
channels and lake basins, while the natural water chemistry of aquatic
ecosystems is determined by the chemical nature of the rocks in contact
with the water. Being part of the ancient African plate, the land
is generally old and heavily weathered. Geomorphologically it consists
of an elevated, relatively flat, central plateau tilted downwards
to the west and descending precipitously to the sea in the south and
east. Except at the continental margins the land is relatively flat
and unbroken. Because of this fact, and because southern Africa has
largely escaped major periods of glaciation since the Permian, deeply
dissected valleys and large lake basins are uncommon. Exceptions are
in the far north-east, which is in the process of being split by the
tectonic movements that are forming the African Rift Valley, and on
the coastal escarpments. Details of the geomorphology of southern
Africa may be found in Moon and Dardis (1988).
Geologically, the central plateau consists of the Karoo sedimentary
basin of Tertiary age, surrounded to the south mostly by the much
older, heavily weathered sedimentary rocks of the Cape Supergroup,
and to the north and west by mineral-rich igneous rocks of various
ages (Martin, 1965; Tankard et al, 1982). These rocks include
some of the oldest exposed on earth, in the highlands of Swaziland,
as well as the relatively young tertiary basalts of the Drakensberg
Mountains. The distinct lithologies result in the mineral composition
of surface waters varying noticeably in different parts of southern
Africa (Day, 1993; Day and King, 1995).
Climatic Features
Southern Africa is characterized by strong latitudinal and longitudinal
climatic gradients (e.g., Tyson, 1986) that, in turn, impose gradients
on the structure of natural floral communities and therefore also
on the agricultural potential and the human populations of the area
(e.g., Davies and Day, 1998). The major latitudinal gradient is in
temperature and the major longitudinal gradient is in rainfall. The
overall result is that the climate varies from tropical in the north
to subtropical or even temperate in the south, and from mesic in the
east to hyperarid in the west.
Rainfall is remarkably seasonal in the more mesic areas, becoming
more unseasonal, more unpredictable, and more episodic in the arid
regions to the south and west. On the one hand, this climatic feature
means that virtually the entire region is without any significant
quantity of rain at least for several months of each year, so water
has to be stored for use in the dry months. The situation is particularly
crucial for growing crops in the Mediterranean-climate region of the
western Cape, where summer drought coincides with the hottest time
of year. On the other hand, where interannual variability in rainfall
is large, sufficient water has to be stored to ensure supply in the
dry years. Southern Africa is particularly prone to this problem.
The coefficient of variation of mean annual runoff in the rivers of
South Africa is 117 percent, in comparison with values of 38 percent
for the continental United States, 22 percent for Europe, and 53 percent
for the state of Victoria in Australia, for instance (van Biljon and
Visser, undated). Furthermore, on average less than 10 percent of
rainfall appears as stream flow in South Africa and Namibia, in comparison
with values of about 25 percent for the United States, and between
50 and 75 percent for Canada, Sweden, and Italy (Alexander, 1985).
In brief, much of southern Africa suffers from a serious water deficit
most of the time and is periodically hit by severe droughts. Some
seem to be linked to ENSO (El Nino-Southern Oscillation) events and
others to some other, roughly 11-year, climatic cycle (e.g., Tyson,
1986). (Floods, when they occur, can also be devastating, but that
is not the issue here.)
Water Supply and Demand
Provision of adequate water for human needs presupposes that sufficient
water as well as financial and other resources are available to develop
the necessary infrastructure. In many parts of southern Africa, neither
the water nor the infrastructure conditions apply.
As a result of the variations in geology, geomorphology, and climate
described above, southern Africa exhibits major geographical differences
in the availability of natural surface waters, but one of the more
striking features of the region as a whole is the paucity of natural
surface waters of any size.
Following is a brief analysis of the types of aquatic ecosystems to
be found in the region. Further details can be found in Davies and
Day (1998).
Natural Aquatic Ecosystems
- Rivers are the dominant form of aquatic ecosystem
throughout the region. Those draining the south and east coasts are
perennial, but towards the south many tributaries and smaller rivers
are, at best, seasonal. Namibia's only two perennial rivers are
those that form the northern and southern borders, and both are allogenic,
draining much better-watered catchments far inland. The largest rivers
in the region are the Kunene and Orange in the west and the Zambezi
and Limpopo in the east.
- Evaporation exceeds rainfall throughout most of the region
so true lakes, defined as having permanent waters deep enough
that rooted plants cannot grow, are very scarce. Indeed, south of
20oS there are no real lakes at all. The two largest lakes
are Lake Banguela in Zambia and Lake Malawi in Malawi.
- Coastal lakes, most of which are relict estuaries,
are common along the south and east coasts. The largest clusters of
such lakes occur on the wide coastal plain between Inhambane in Mozambique
and St. Lucia in South Africa, and the Wilderness and Agulhas Lakes
on the south coast of South Africa.
- As is the case throughout the world, wetlands take
numerous forms. They vary from reedbeds in river courses to mangrove
swamps and salt lakes. Two of the largest and best known of the permanent
systems are the Okavango Swamps in Botswana and the Kafue floodplain
in Zambia. The drier and more seasonal parts of the region support
temporary waters of various kinds, from the huge salt pan systems
of Etosha in Namibia and Makgadikgadi in Botswana to tiny potholes
in granite inselbergs in the Namib Desert of Namibia.
Larger wetlands of this type are crucial for local human populations,
in that they provide natural resources such as fish, grazing for domestic
stock, reeds, medicines, and wood. In general, however, they are not
used as bulk suppliers of water, usually because they occur in well-watered
areas where irrigation is not required. Some water may be abstracted
for domestic supply.
Constructed Aquatic Ecosystems
Even the cursory analysis above of the surface water resources of
southern Africa is enough to indicate that much of the region is short
of water and that rivers represent the major (often the only) surface
sources. Virtually the whole area is subject to seasonality of discharge
to such an extent that water flowing in rivers in the wet season has
to be stored for use in the dry months. In the more arid regions,
and where population pressures are particularly heavy, far more than
a single year's supply has to be stored in order ensure supply
during droughts that might last for several years.
Large dams are found throughout the region. Those forming the largest
reservoirs are the Kariba and Cahora Bassa dams on the Zambezi River,
and the Gariep and Vanderkloof dams on the Orange River. While those
on the Orange are largely used for water storage, those on the Zambezi
are mostly used for the generation of hydroelectric power. Added to
other problems, Cahora Bassa and many of the dams in Angola have been
affected by the civil wars of the last several decades. In the case
of Cahora Bassa, the water has been maintained at a constant level
for 20 years or more, with virtually no electricity generated, while
many of the dams in Angola have been physically damaged (Day, 1997).
As well as large dams constructed by or on behalf of the state, the
subcontinent is littered with tens of thousands of small farm dams.
We are only now becoming aware of the impact that these dams have
on regional hydrology, or the extent to which they increase the biodiversity
of aquatic organisms, particularly of arid areas (Davies and Day,
in press).
Other Sources of Water
Ground water: As is so often the case in arid lands, the westernmost
parts of southern Africa rely heavily on ground water, even though
it may be "fossil" water (and thus not recharging at the
rate at which it is used) and although its quality is sometimes not
ideal. Good-quality ground water is particularly abundant in the dolomitic
areas of the Witwatersrand of South Africa and the Karstveld of the
Grootfontein area of Namibia. Water of sometimes poorer quality underlies
much of the Orange River basin in South Africa; indeed, the population
of most of the Orange River basin, which covers about a third of the
surface area of the entire country of South Africa, relies largely
or entirely on ground water.
Inter-basin transfers of water: Southern African engineers
are proud of their ability to move large amounts of water from one
catchment basin to another. Early schemes included the transfer of
water from the Orange River southwards to the salinizing waters of
the Fish River in the Eastern Cape, and from the Tugela to the Vaal,
both in South Africa. A much more ambitious scheme, the Eastern National
Water Carrier, is underway in Namibia to transfer water about 800
kilometers from the Okavango River on the northern border to the capital
city of Windhoek. In a further massive project, South Africa will
buy water from the upper reaches of the Orange River in Lesotho and
transfer it through the Drakensberg Mountains to the Vaal River in
order to provide water for Gauteng, the industrial heartland of the
country. (The sale of this water is likely to double the gross national
product of Lesotho.)
Schemes are frequently touted for the sale of water to wealthier South
Africa from the Zambezi in Zimbabwe, or even from the Congo River
in the Congo ( formerly Zaire), but as yet these notions appear to
have no substance.
Water Demand
AIDS notwithstanding, the greatest social and environmental problem
in southern Africa (indeed, in Africa as a whole) is the continued
rapid expansion of the human population. Accurate figures are not
easy to come by but the official 1996 population census in South Africa
supposedly showed a total human population of 37 million (figured
by many experts to be two to four million too few) and that of Namibia
was considered in 1994 to be about two million (Population Planning
Unit, 1994). The annual growth rate of the human population of South
Africa may be as much as 2.3 percent (Davies and Day, 1998), and of
Namibia, three percent (Population Planning Unit, 1994). Even if exact
values are not known, it is likely that the growth rate throughout
the region under discussion is well over two percent per year, which
will result in a doubling of the population in less than 25 years.
This puts enormous pressure on all natural resources, and, of course,
in the more arid areas water is the most limiting of all resources.
The complexity of the situation cannot be appreciated without reference
to poverty. Although a small proportion of the population lives in
relative wealth in towns and cities, and an even smaller proportion
lives on commercially viable farms, the vast majority of the people
of southern Africa lives on or below the breadline. At the same time,
few of the states themselves are financially able to improve the conditions
of their citizens. Thus huge numbers of people live uncomfortable
lives. The "poverty spiral" of poor nutrition, education,
and housing leads to ignorance and disease, an inability to compete
successfully in the workforce, and high rates of population increase.
Poor people are seldom concerned about their natural environments,
except as sources of food or materials, and so poverty leads to pollution,
waste, land erosion, and rapid degradation of natural resources. "Developments"
are usually unplanned and often environmentally devastating. Ultimately,
unless the spiral of overpopulation and poverty can be halted, any
attempts to plan for sustainable development are doomed to failure.
As in any other part of the world, in southern African cities water
is required mostly for domestic consumption and industrial use. About
10 percent of the total consumption of water in South Africa can be
attributed to domestic use, and about 20 percent in Namibia. Mines
and power stations use less than 10 percent. In each country, more
than two thirds of all water is used for irrigation, mostly on large
commercial (as opposed to subsistence) farms: dryland farming is not
viable over almost the whole western half of southern Africa.
Many millions of people throughout the subcontinent have no access
to clean water or to sanitation. In these communities it is usually
the women whose lives are taken up in walking to water points, waiting
for pumps to work, and carrying on their heads enough water to support
their families for the next day. If they are wealthy enough, they
will buy water at exorbitant prices in order to avoid this backbreaking
chore. Provision of a simple standpipe can change the lives of whole
communities of women previously tied to the provision of water. Surprisingly,
and much to their annoyance, Namibian authorities report that taps
of standpipes are often left running, usually to allow cattle free
access to water (cows represent wealth throughout Africa). This situation
leads not only to waste of a precious resource but also to the provision
of suitable habitats for breeding mosquitoes, as well as improved
grazing, which encourages the settlement of people and subsequent
overgrazing in years of low carrying capacity (Day, 1997). In South
Africa, where millions of people still have no access to clean water,
the government Department of Water Affairs is providing standpipes
at a rate sufficient to provide water to thousands of people every
week.
Few suitable sites remain for the construction of large new dams in
South Africa, but a few are in the planning or construction phase.
The major development is the Lesotho Highlands Water Project which,
when complete, will deliver 2.2 billion cubic meters of water per
year from the upper reaches of the Orange River in Lesotho into a
tributary of the Vaal River, for consumption in Gauteng.
Reconciling Supply and Demand
Given that the amounts of rain and ground water are roughly constant,
and that the human population of the region continues to grow explosively,
there clearly must be some point at which demand will outstrip supply.
The carrying capacity of the land itself is also affected, in that
the more water exploited by the human population, the less is available
for natural ecosystems .
Carrying capacity is difficult to estimate. Still, a comparison with
Australia is instructive. Australia has a surface areas four times
that of South Africa and Namibia combined, and a population of less
than 20 million people. As noted, Namibia has a population of about
two million, and South Africa a population of about 40 million. W.D.
Williams of the University of Adelaide has suggested in a personal
communication that the human population of Australia is already exceeding
the carrying capacity, but that evidence for this assumption is likely
to become clear only several decades from now (when it will probably
be too late to remedy the effects on the land or on aquatic ecosystems).
If that is true for Australia, how much more true is it likely to
be for southern Africa, where the population density is more than
eight times that of Australia? How the carrying capacity is estimated,
and how the size of the human population can be reconciled to it,
are moot points.
Water demand management (control of consumption rather than supply)
is being instituted in both South Africa and Namibia. The topic is
a large and complex one and cannot be covered here. Some details of
the South African campaign are addressed in Davies and Day (1998),
and Namibian issues in Day (1997).
Water Quality
Water quality is defined here as the combined physical attributes
and chemical constituents of water that contribute to its usefulness
for a particular purpose. Wherever water supplies are scarce, as they
are throughout most of the southern African region, there is a danger
that even minimal human interference will affect water quality.
In various parts of southern Africa, water quality is impaired by
industrial or mine effluents, sewage or sewage return flows, runoff
of nutrients and pesticides from farmlands, and salinization as a
result of inappropriate spray irrigation. Land clearance is generally
not a major issue here. Although many cities, particularly in the
south, still retain adequate stormwater systems and sewage plants,
urbanization, particularly in the form of informal ("squatter")
settlements, is rapidly becoming a major issue because of its unplanned
nature and the lack of infrastructure to deal with its effluents.
In both South Africa and Namibia, present water quality legislation
is based on effluent standards. In South Africa, in addition to a
General Effluent Standard there is a Special Effluent Standard, designed
to protect mountain streams that can support trout (Water Act 54 of
1956). The irony is that trout are vicious invasive alien fish that
have probably been responsible for the extinction of more than one
species of indigenous local fish, and yet they are the only living
organisms (other than humans) mentioned in the 1956 Water Act.
Effects on Aquatic Ecosystems
With the great social contrasts in southern Africa, it is not surprising
that some of the effects of development on its aquatic ecosystems
should be typically "first world" and others typically "third
world." In the "first world" parts of the region, mostly
in South Africa and Namibia, these effects are largely loss of water
as a result of river regulation, as well as organic pollution and
cultural eutrophication. Urban rivers are heavily "engineered,"
usually by canalization. Urban or periurban wetlands are often eutrophic,
and encroachment by marginal reedbeds is common. Some rivers in the
north-central parts of South Africa are heavily polluted by mine effluents.
In the rural, "third world" parts of the region, environmental
damage is generally quite different, and results from the overexploitation
of living resources. The far north of Namibia, for instance, is a
well-watered area that supports nearly three quarters of the entire
Namibian population on much less than 10 percent of the land area.
Although cash wages are significant in some areas, most of the people
survive only because of the natural resources of the rivers and swamps
of the region. The increasing human population has resulted in a scarcity
of many of these resources and consequently in new methods of exploitation.
As an example fish, which used to be caught in woven baskets, are
now caught in mosquito netting. Catches are getting smaller, and most
of the fish are being caught before reaching breeding age. Trees are
felled for building materials, for fuel, for carving, and to provide
more grazing for cattle. Little notice is taken of the fact that it
is illegal to remove living trees or shrubs from within 100 meters
of a water course (Day, 1997), and it has been estimated that more
than 70 percent of riparian forest may have already been removed from
the Namibian section of the floodplain of the Okavango River. Reeds
and other plants are also removed for weaving, food, and medicine.
These activities, together with overgrazing, have detrimental effects
on the hydrology and water quality of the river.
Biodiversity and Biological Integrity
Because the area is so large and the number of trained biologists
so small, there is still a great deal to learn about the biodiversity
and the biological integrity of the aquatic ecosystems of the region.
Namibia is in the middle of a biodiversity inventory, and South Africa
is in the process of developing a biomonitoring program to assess
and keep tabs on a series of reference sites throughout the country.
One of the difficulties is finding suitable "pristine" sites
(if such things still exist). A very successful tool has been developed
using macro-invertebrates for the rapid bioassessment of water quality
in rivers (e.g., Dallas et al, in press).
Alien Organisms
Although alien organisms have, on occasion, had devastating effects
on southern African ecosystems (e.g., the explosive blooms of Kariba
weed, Salvinia molesta, in Lake Kariba in the 1970s), none
has been as impressive as the effects of either water hyacinth or
Nile perch in Lake Victoria.
The alien aquatic plants Salvinia molesta, Pistia stratiotes, Eichhornia
crassipes, Azolla filiculoides, and Myriophyllum aquaticum
are all found in southern Africa, and all have the potential to bloom
explosively and destructively. All are declared alien weeds in South
Africa and in many of the other states in the region too. Some successes
have been achieved in the biological control of Salvinia molesta
and Eichhornia crassipes.
The most destructive alien animals by far have been fish, particularly
trout, bass, and carp. Trout and bass, in particular, have been implicated
in the extinction from various river systems of indigenous fish, including
the slow-growing yellowfish of the western Cape. Ironically, Cape
Nature Conservation, the Western Cape conservation agency, began life
as an organization devoted to the distribution of trout in local streams.
It was only in the 1980s that trout were declared undesirable in mountain
streams, and stocking programs are still carried out by private groups.
Although aquaculturists would like to culture a variety of edible
crustaceans (which might well escape into local streams and wetlands),
it seems that so far such introductions have been avoided.
Some General Management Issues
Below I list and comment briefly on some management issues that are
particularly pertinent to, but not necessarily confined to, southern
Africa.
"Sustainable" management plans vs. social and financial
constraints: Sustainable management of water and living resources
is not possible without a relatively constant human population living
within the carrying capacity of the land, good legislation and suitable
policies notwithstanding.
Laws vs. "community" issues: Traditional behavior
patterns often conflict with western laws or policies. It is inconceivable
to many local people, for instance, that large mammals, which represent
a valuable source of protein, are conserved in protected natural areas
when the humans themselves may be going hungry.
International water resources: Several national borders in
southern Africa are demarcated by rivers. Furthermore, water is a
valuable and scarce commodity. Thus countries can cooperate in buying
and selling water, but the potential exists for conflict in the use
of water from border rivers and where rivers arise in one country
and flow to the sea in another (e.g., the rivers of southern Mozambique
arise in South Africa).
Exploitation of water resources vs. conservation of aquatic ecosystems:
The issue of the further exploitation of water in rivers is particularly
important in the drier countries, such as South Africa and Namibia.
In both countries, but particularly in South Africa, tools are being
developed for estimating the instream flow requirements of rivers.
This approach is expanded in South Africa's new Water Act (see
below).
Toward a New Ethic: South Africa's New Water Act
The new political dispensation in South Africa has provided an opportunity
to rewrite many pieces of legislation, not least of which is the new
Water Act and other legislation related to water supply and pollution
control. The entire Act is a complex piece of legislation, many aspects
of which need not concern us here. Two are of major significance for
the management of water and aquatic ecosystems, however.
The first is the intention to remove the concept of "private"
water. At present, owners of riparian lands have "riparian rights,"
which entitle them to use some or all of the water in the river. Thus
farms with riparian rights are particularly valuable. In future, all
water will be kept in trust by the state for the use as appropriate.
The second is that the water in rivers (and other wetlands, and even
in aquifers), belongs to the river itself. The first call on this
water will be a small "reserve" of drinking water (about
25 liters per person per day). After that, an "ecological"
or "environmental" reserve will be set aside to protect
the integrity of each ecosystem. Only when that value has been decided
upon may further water in the system be exploited, by river regulation
or in any other way. Details of the ways in which the reserves can
be calculated are presently being examined.
The setting aside of a reserve is an exciting and innovative approach
to the management of water resources, particularly given that South
Africa is so short of water. It seems highly unlikely, however, that
many water supply managers have understood what the consequences of
this legislation will be. Aquatic scientists here and elsewhere will
be following the process of implementation of the scheme with great
interest.
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