|
Tell Tale Signs
Interview Transcript
Associate Professor
of Zoology Bryan Robert Davies
Co-founder of First World Research Unit University Capetown
"The major impacts
of the Cahora Bassa Dam involve a complete reversal of the
flooding and dry season cycle and this has meant that in less
than a quarter of a century the entire geomorphology of the
valley has radically altered. The floodplain no longer receives
annual inundation, the lower area the Marromeo Reserve the
mangrove and the coastal dunes do not receive sediments or
any freshwater inputs of any magnitude the impacts on the
sefala bank fisheries have been enormous the collapse of the
prawn industry the collapse of the riverine fisheries, but
I think most importantly its changed the way in which the
people who lived in the valley for so many millennia - the
way in which they use it - they used to practice what I would
call floodplain recession agriculture whereby when the flood
came down during the wet season which is November through
April."
"In the Zambezi
predams the population which used to amount to about one and
a quarter million people practised what we call flood plain
recession agriculture whereby they migrated off the flood
plain during the wet season in summer November through April,
and then post the flood as it receded they would come back
onto the floodplain and plant their crops which they harvested
one two or three depending on how good the winter was - so
that's been an annual migration over the millennia."
"Post Cahora
Bassa there's been no release of floodwaters which some would
say is a good thing others would say is a very bad thing,
I think it's a very bad thing because it has changed the pattern
of utilization of the valley. Now we've got a situation where
they river, no longer flooding, no longer with high sediment
loads actually cuts down a new channel or a series of new
channels and the people in the area have been forced for their
water, for their fisheries and for their agriculture to migrate
onto the old floodplain, now that means that should a large
flood not be held by the large dams on the Zambezi they are
in grave danger and we have seen more than sufficient evidence
of that in the last two to three years, - the people have
now moved onto the floodplain into the path of the floods
and when the dams can't hold them they flow away - last year
we saw something in the order of 120 people killed by the
flooding which was released by Cahora Bassa and in the order
of several hundred thousand refugees and food aid having to
be poured in - many of those people are still in the refugee
camps as I speak."
"These dams there
are two involved here - the major ones on the Zambezi are
Kariba upstream of Cahora Bassa by about 500 km - what has
happened since Kariba closed in 1958, it took six years to
fill, once it had reached full supply a drought started to
bite in the central Zambezi and it started to fall in level,
in 1975 some 20 odd years later, Cahora Bassa closed, now
Cahora Bassa when it filled reversed the flood cycle."
"There are two
dams involved, Cahora Bassa in Mozambique and Kariba in Zimbabwe
- both dams have stopped the annual drought flood regime -
this has changed people's habitation and utilization patterns
of the flood plain - they move onto the flood plain in order
to be next to the fisheries which have now shrunk and in order
to plant their crops - when a dam cannot hold a large flood
and in the case of Kariba and Cahora Bassa there has been
no real flooding for - maybe twice in the last 25 years, people
habitually live in the path of the old flood regime, now along
comes a climate change, change in the weather patterns, whatever
the reason and a large flood hit Kariba, Kariba had to discharge,
Cahora Bassa did not respond for nearly two weeks - then when
it did respond it had to discharge an overlay flood and one
that had already come from Malawi downstream, so we got a
small flood a one in ten year flood suddenly becoming much
larger and that rapidly inundated the floodplain and the people's
livelihoods and properties - hence we've got drowning and
hence we've got a major refugee crisis."
"Now on top of
that you've got the ecological problem that for 25 years water
and nutrients absorbed into silts are not being allowed into
the delta - the delta is being eroded by sea-landward action,
erosion, its not driving, the food isn't sufficient to drive
prawn industry, fisheries of the river and also sea fisheries.
So all of these are knock on effects and people who are hungry
and poor and believe you me you're talking about an extremely
poor community in terms of wealth - with poor communications
living in very primitive conditions they're loosing out, their
fight in the centre, everything they do is wrong in terms
of the fact that the change in the hydrological cycle is affecting
their lives, they have to be next to the protein and water
but if the dam doesn't hold the flood they're in trouble.
"Utterly predictable,
in 1974-5 I was working with a group of Portugese scientists
and our reports at the end of that project just timed with
the closure of Cahora Bassa in in 1975 predicted that if engineers
did not allow flooding to take place that a major ecological
change would take place in the valley coupled with a geomorphological
change - if you don't have an erosive river and a floodplain
system if you don't allow it to continue to flood then you
will get major changes - for example all of the sediments
that historically were transported from the upper Zambezi
catchment down through the river into the coastal floodplains
and into the inshore coastal zone are now locked up behind
two major dams and their not locked up behind the wall they're
locked up at the upper end of the reservoir, now Kariba reservoir
is nearly 300 km long, Cahora Bassa is 270 so unless we can
find some way of taking that sediment that's now forming deltas
at the upper end of the reservoir and dumping it below the
dam wall the river becomes highly erosive even though it may
be at a lower flow it has no sediment in it and that's what
we call silt hunger and so -to give you an example - if you've
got a river flowing at 1000cubic metres of water per second
which is plus or minus the discharge of one gate of Cahora
Bassa dam - there's one thousand tonnes of water moving over
sediments per second and that picks up sediments and takes
or transports them further down; as it does so it chops into
the valley and so the river cuts down, we believe this river
has cut down probably several metres, in other words its shrunk
- the old channels now, if they're going to flood, you need
a heck of a lot more water - if they're not going to flood
the people have to move next to the channels and so again
it’s a knock on effect people have to move next to their
resource and this system has not been managed correctly in
terms of either flow or sediment.
"Now the sediment
issue is one of the major issues that scientists around the
world are failing to address - eg we had a conference here
at the University of Capetown in March this year it was called
Environmental Flow Management - and not one single paper addressed
the issues of how one can resupply the sediment to the river
that has been trapped by the reservoirs. Until we can resolve
that issue all floodplain rivers around the world are going
to show similar rapid degradation, shifts in human habitation
and utilization patterns and hence the myth that dams prevent
floods will ultimately be exposed."
"One of my concerns
as an ecologist who's worked on large dams and rivers for
nearly 30 years is that there is a myth perpetuated by engineers,
civil engineers who build these structures, and that is that
building a dam stops floods which is good for people. Well
yes dams stop floods but they can't ever stop all floods -
when they fail to stop a really severe flood then the people
who've had their livelihoods changed and their living patterns
changed in the valley below dams where floods have been prevented
let's say for 20 years, suddenly find a one in 21 year flood
coming down that cannot be contained by the dam. So, whereas
before we had people who were aufait with flooding and moved
off and on and off and on on an annual basis we now have fixed
populations who've lost their flood memory and who are now
suddenly in great danger of a major flood. We saw this catastrophically
in China in 1970's in the disaster known as the BangChow disaster
- but effectively a one in 2000 year monsoon flood event arrived
in the catchment in central China and that flood was so severe
it took out two large dams and 60 smaller dams in a few hours
- the resulting catastrophe killed nearly a quarter of a million
people almost in the same day. And subsequent to that another
third of a million people also died. The floods were so vast
that rescue missions could not get into the area and I worry
that with climate change, unpredictable climates changes in
weather patterns the dams that have been sold to politicians
and the public as flood control agents will infact become
flood initiation agents - in so far as people have put themselves
in the path of what cannot be controlled."
"One of the problems
with building such large structures is that although one can
possibly plan for 10 or 20 or 25 years, it is very difficult
to get politicians and engineers to plan for a lot longer
- 50-100 - what's going to happen in 100 years. I know that
not one of my colleagues in the environmental area is arguing
about whether or not climate change is taking place - it is
there is no doubt - what we're arguing about is the rate,
the intensity and the noise the variability before it settles
down into new patterns. So what I forsee and what many of
my climatological colleagues see is an increasing variability
of drought the degree to which drought will occur - the severity
is the word I want and the severity of floods. If we go into
a phase where flooding and drought become far more severe
then the original planning and design of such large structures
begins to look like Noddy in Toyland - how can somebody as
we gave the example of the Bang Chow disaster how can you
possibly budget for a one in a hundred and fifty year flood
- you can't - how can you also predict what will happen to
concrete in 50 years - Cahora Bassa is what, 25 years old?
What's its structure going to be like in 50 years, 75 years,
even more so, what's its structure going to be like in relation
to climate and to the population which is now lulled into
a false sense of security that no floods can come - so it's
a conundrum - its something that cannot be answered and unless
some serious rethinking of management and operational criteria
comes into the melting pot I see a very dangerous situation
developing not just on the Zambezi but on large floodplain
rivers worldwide."
"One of the least
understood aspects of large dams is the way in which they
appear to be capable of creating earthquakes - they call this
phenomenon reservoir induced siesmicity - and there are at
least 2-3dozen examples of where large dams have done exactly
that - imagine a river valley - and build a large dam in it
- Kariba is the second largest human constructed lake in the
world - its over 5 thousand 700 square kilometres in surface
area and it has a mass when its full of 182 thousand million
tonnes. Cahora Bassa has a mass when its full of 64 thousand
million tonnes. This mass of water now pressing on substrates
and faultlines acts both as a pressure and a lubricant - what's
happened? Kariba has already had a 5.8 rictor scale earthquake
event in the 60's and Cahora Bassa is believed to have had
something similar. One of these days one of these large dams
is going to trigger a really large one and if one has not
constructed a dam to withstand high seismic shocks then we
have an all fall down scenario which is the worst case. Now
I don't want to be a doom and gloomer, but that worries me
and there are a large number of dams worldwide which are showing
signs of seismic activity - so how do you budget for that
in your calculations - aging concrete, human patterns of utilization
change because you've stopped the floods, earthquake risk
activity - it makes for a very tricky soup to eat."
"One of the major
problems with large dam management is that there is huge political
pressure to construct them - there's also huge socioeconomic
pressure that leads to their construction - for instance the
requirement for industrial development the generation of hydropower,
electricity for the continuation of such development the growth
of economies etc, and in many instances the indigenous peoples
of a large number of river valleys have been ignored because
of political and socioeconomic pressures to develop. That
has lead to something in the order of - a guess about 80-100
million people being forcibly removed from their homes to
make way for large hydroelectric power schemes. Those people
disappear into the great urban sprawls and they are disenfranchised.
Secondly, ecosystems cannot speak for themselves, wildlife
cannot speak for itself, so it takes long haired radicals
like myself to actually learn about them and to speak on their
behalf, and they're very important. The ecosystems themselves
sustain the livelihoods of the vast masses of poor people,
so if we don’t maintain them and we don’t shout
about them then the poor are going to suffer. So we've got
this dichotomy, we've got this political and economic pressure
on one hand and developments requirements and we've got ecosystems
which sustain poor communities and those communities don’t
have a voice - neither the ecosystem nor the people themselves
and so they tend not to get heard, and so organisations like
the World Commission on Dams have been significant in terms
of getting political and socioeconomic awareness up at a higher
level and so to realise to help designers and managers and
politicians to realise that in fact they're not just taking
a decision for an entire country they're taking it and badly
affecting a group of people and how can we compromise and
one of the problems is learning how to find that middle ground
and that compromise and it's a difficult one."
"In terms of
Cahora Bassa the wildlife of the lower Zambezi has been catastrophically
altered - one of the things we found when we were working
in the 1970's is that the lower floodplain system in an area,
a wonderful area called Marromeu - a wetland ecosystem supported
huge heards of grazing ungulates, large mammals and on an
annual basis the flood would come in and drown any refractory
vegetation - refactory vegetation on the trees with hard stems,
grazers can't tackle those, browsers can so what was happening
was that the grazing population of large game and we had in
Marromeu the largest heard of waterbuffalo for example 78,000
head, that's the largest in Africa it was being maintained
by flooding - grass was encouraged to grow, trees were drowned.
One of our predictions was that if the flooding stopped, trees
would take over and that is exactly what has happened within
25 years one can fly over the area and see 18 year old, 20
year old, 22 year old trees developing into forest and that
has completely altered the large game structure. Browsers
have come in and all of the grazers have gone. So that’s
partly a function of the flooding it also could be a function
of the prolonged civil war and the action of the AK47 but
nonetheless the flooding has transformed the ecology of the
system. It has changed bird ecology it has changed the fisheries,
the invertebrate ecology in the river and so on, so it's a
knock on effect.
Question: are these
people aware of it?
"No they're not,
they are in a way - the interesting thing about this whole
business of floodplain recession agriculture, onto the floodplain
in the dry season, off during the wet season, the people have
a historical memory - over a generation that memory has been
lost so no longer do we get this contraction and expansion
of migratory peoples we get fixed populations, and they grow
their agriculture right throughout the year, they fish right
throughout the year - there's no seasonal change in the system
because the dams have stopped that change and the result is
that something in the order of half to three quarters of a
million people are now fixed in what used to be a regularly
fluctuating environment - and the real worry and I can stress
it strongly enough is that we've got nearly - huge numbers
of people who are not aware who are no longer aware that floods
are part and parcel of the natural cycle - but when a flood
does come and we had an instance in last year, in March April
where twice as much water was being discharged from Kariba
into the upper end of Cahora Bassa that was being discharged
by Cahora Bassa, if it had reached critical mass and Cahora
had been forced to discharge Kariba's input then we would
not just have 250,000 refugees and 120 dead we would have
had a lot more dead and a far larger displaced population
- much of that population is still displaced 18 months later.
Malaria is in the area, cholera is in the area starvation
is the order of the day and the aid organisations its no longer,
how do I put it, sexy footage, there's no longer babies being
born in trees, people are actually dying in refugee camps
and that’s where the tragedy is now."
"What's happening
at the moment a series of workshops is being held with politicians,
engineers and ecologists, the latest one was only at the beginning
of July this year - in that situation we are discussing how,
not just to release environmental flows to set the ecology
back on track but how to educate the population and this requires
an enormous social science input to an area where radios are
not ten a penny and where newspapers just don't get distributed,
where there's no TV - so there has to be the implementation
of an enormous social, political programme of reeducation
that floods are needed and that sooner or later they're going
to come.
Recent surveys in
the valley, when one goes into the communities, the people
know that floods have been removed - they want floods to be
restored but they don’t want big floods - so there's
now got to be quite a tradeoff - the older generation has
still got that memory but they don't move because there's
no point, its not going to come - now we're telling them that
it will come and we've got to trade off just how much of it
will come. What we can’t trade off is the big one we
can't stop and that's the real worry so we've got to get in
there now and educate, in fact we should have got in there
5, 6, 7, 8 years ago, before this simultaneous filling of
both large reservoirs took place as the weather patterns shifted
and that’s what we've seen in the year 2000 and 2001.
Before it happens again we've got to go back in there and
sort the people out."
back to Tell Tale Signs
main page...
|
