Epupa Dam and Reservoir Options - A Review of the Aquatic Ecological Aspects of the Draft Feasibility Report
SUMMARY OF COMMENTS
The main concerns can be summarised as follows:
Flow regulation
The regulation of flow in the Cunene River, downstream of the
Epupa and Baynes dam sites, is recommended in the absence of an
instream flow requirements (IFR) study. A minimum flow of 20m³/s
has been recommended during the construction phase, but no supporting
evidence for this flow is provided. Flows will vary daily during
operation of the hydroelectric power station, but the effects
of this variation are not investigated in the report.
Riverine Biota
The Cunene River has not previously been described in terms of
its aquatic ecology. However, the report does not provide detail
on the invertebrate communities which inhabit the river, and how
these communities will be affected by either dam option. Few assumptions
can be made in the absence of such data, and predictions of effects
of impoundment are thus tentative.
Loss of Habitat and Biodiversity
Epupa reservoir will completely eliminate the spray-zone habitat
of the Falls Area, and reduce riffle areas. This will lead to
the loss of biodiversity, which cannot completely be mitigated.
The River Mouth
The likelihood of saltwater intrusion into the river mouth of
the Cunene River cannot be ignored without sufficient evidence.
Thus it cannot be assumed that the recommended minimum flow of
20m³/s during the construction phase will be sufficient to prevent
this.
Water Quality
An increase in phosphorus concentrations in both impoundments
could lead to blue-green algal blooms. Any mixing of inflowing
water with the epilimnion, where light and temperature conditions
allow primary production, will allow this phenomenon to occur.
The report assumes no mixing, but this is a tentative assumption.
In conclusion, the report is inadequate for the assessment of
the dam options, and no conclusions can be drawn as to whether
either dam option should go forward.
A first general comment must be made about the lack of completion
of this study. Although this was not the aim of this particular
review, it is of great concern that the requirement for a comprehensive
public consultation process and the development of a social mitigation
program was not included in this report. This is a significant
component of the study, and in its absence the report is of little
value, to all interested and affected parties. In Section 1.4
of both Executive Summary reports, it is indeed written: "The
omission of this element renders this an incomplete EA.."
The report is thus unacceptable in terms of the Integrated Environmental
Management methodology, which was adopted in South Africa as the
accepted environmental impact assessment technique.
Furthermore, the two studies, Epupa and Baynes, are virtually
identical in terms of the aquatic ecological effects of impoundment
at the two sites. The production of two reports was thus a repetition
of results, that could have been less-confusingly presented as
one, concise report.
Flow regulation
The regulation of flow in the Cunene River, downstream of the
Epupa and Baynes dam sites, is recommended in the absence of an
instream flow requirements (IFR) study. A minimum flow of 20m³/s
has been recommended during the construction phase, but no supporting
evidence for this flow is provided. Flows will vary daily during
operation of the hydroelectric power station, but the effects
of this variation are not investigated in the report.
It is of great concern that regulation of flow in the Cunene River
downstream of the Epupa and Baynes dams is recommended in the
absence of a complete instream flow requirements (IFR) study.
Such a study examines a river system in terms of its biota, water
chemistry and discharge, and determines the flow requirements
of the system in order to maintain its ecological functioning.
The results of an IFR study provide a total quantity of flow that
it required annually, as a percentage of mean annual runoff (MAR),
and divides this total into blocks of flow throughout the year,
according to seasonal requirements of the system. For example,
this method determines the frequency and magnitude of required
floods, as well as low flow periods.
It is unacceptable that any flow recommendations can be made in
the absence of such a study.
For example, both studies claim in their executive summaries that
"Maintenance of a minimum flow of approximately 20m³/s (during
the construction phase) is deemed sufficient to create a functioning
aquatic habitat in the river." The report fails to provide
supporting information for this assumption. In addition, the construction
phase of either dam option is more than five years, within which
damage can be done to the river due to the alteration of the flow
regime.
Furthermore, it is stated that "The environmental consequences
of the inevitable daily variation of water levels is more difficult
to assess." This concerns in particular the fish and benthic
life forms. The report then proposes that such concerns will be
addressed only during the construction phase, at which time the
mitigation programme will be launched. Subsequent monitoring activities
will further gather information on whether the proposed compensation
flows are indeed sufficient. This is an unacceptable approach,
where flows are determined retrospectively. The case of the Lesotho
Highlands Water Project should be remembered here, where a retrospective
IFR study produced results that showed that there was insufficient
water in the Lesotho Highlands catchments to provide the instream
flow requirements of the rivers, and to provide water to South
Africa.
The results of the Epupa and Baynes reports are unacceptable in
the absence of an IFR study.
Riverine Biota
The Cunene River has not previously been described in terms of
its aquatic ecology. However, the report does not provide detail
on the invertebrate communities which inhabit the river, and how
these communities will be affected by either dam option. Few assumptions
can be made in the absence of such data, and predictions of effects
of impoundment are thus tentative.
The Cunene River has not previously been described in terms of
its aquatic ecology. Thus, the riverine biota and the physical
and chemical aspects of the river are not well-known. It is alarming
that the sections of the report (such as those describing the
Local Setting) that deal with these aspects are lacking in data.
As a result, few assumptions can be made in the absence of such
data, and predictions of effects of impoundment are thus meaningless.
For example, sections in the main report on the invertebrate communities
in the river deal only with the freshwater prawn, Macrobrachium
vollenhovii. The reproduction of this prawn is described as being
"...cued by seasonality and/or natural variability in the
Cunene River, and that modifications thereof, flow and water temperature,
in particular, may have significant implications on this population."
It is very likely that the reproductive success of this species
of prawn will be adversely affected by river regulation in the
Cunene. In addition, the river must support a wide variety of
other invertebrate species, that are not mentioned in the report.
Many riverine invertebrates are dependent on flow cues for reproduction,
and on the supply of organics and nutrients from upstream, for
their survival. Therefore, it can be stated that these species
will be affected by both the Epupa and Baynes dams. The lack of
detail on these very important riverine inhabitants in the report
is of great concern.
An example of the significance of a lack of data on the invertebrate
fauna which can lead to negative and far-reaching consequences,
is that of the blackfly, of the dipteran family Simuliidae. In
South Africa, a number of cases have been documented where river
regulation has led to the proliferation of pest species within
this dipteran group (e.g. de Moor...). The females of these pest
species require a bloodmeal for reproductive success, much like
the mosquito, Anopheles spp. In most cases, local stock provide
the food source for these invertebrates, leading to stock deaths
or decreases in the general health of stock, especially cows.
The Simuliidae proliferate in conditions of high flow below dam
structures, and often outcompete other fast-flow species. This
possibility was not addressed in the report, despite the fact
that this could have devastating effects on Himba cattle herds.
Furthermore, it is likely that a warm monomictic lake, with water
levels fluctuating regularly for hydropower production, will provide
an ideal habitat for mosquitoes such as the malaria-carrier species
of Anopheles spp. These species have extremely rapid turnover
times, and proliferate in backwaters where temperatures are fairly
high. Such backwaters could form suitable pools during drawdowns.
It cannot be assumed that fish populations will keep the mosquitoes
in check through predation.
Loss of Habitat and Biodiversity
Epupa reservoir will completely eliminate the spray-zone habitat
of the Falls Area, and reduce riffle areas. This will lead to
the loss of biodiversity, which cannot completely be mitigated.
It has been stated in a World Bank report on choosing sites for
Hydroelectric Projects (Ledec et al., 1997) that "If critical
natural habitats not occurring elsewhere are lost to a hydroelectric
project, the result is an irreversible loss of biodiversity."
Such a consequence cannot be completely mitigated.
In the case of Epupa Dam, the report states that "...the
reservoir will also completely eliminate the spray-zone habitat
of the Falls Area...." Such an impact cannot be mitigated
and, especially in the absence of data on the communities supported
by this habitat, should be seen in a very serious light.
Furthermore, the report adds, "...Epupa reservoir would reduce
the cutoff pools and riffle habitats by 64%...and the loss of..(shallow
riffle habitat)...is estimated at 58%." The riffle habitats
often support the highest diversity in a river system, thus the
loss of these habitats will inevitably lead to a loss of biodiversity.
The River Mouth
The likelihood of saltwater intrusion into the river mouth of
the Cunene River cannot be ignored without sufficient evidence.
Thus it cannot be assumed that the recommended minimum flow of
20m³/s during the construction phase will be sufficient to prevent
this.
It is stated in the executive summaries of both reports that "The
daily regulation of water...is of little importance to the river
mouth area." This is proposed to be due to the retardation
and buffering effects of the 210km of river between the Epupa
Dam and the river mouth, and the 180km distance between Baynes
Dam and the mouth. This statement is then contradicted in the
following sentence "The minimum flow, however, is more important,
since it prevents inflow of salt water to the fresh water habitat
of the river mouth." The recommended minimum flow of 20m³/s
is indeed part of the daily regulation of water in the river,
and in the absence of supporting evidence for this recommended
minimum flow, the claim that this quantity of water will maintain
the river mouth is unsubstantiated and unacceptable.
Water Quality
An increase in phosphorus concentrations in both impoundments
could lead to blue-green algal blooms. Any mixing of inflowing
water with the epilimnion, where light and temperature conditions
allow primary production, will allow this phenomenon to occur.
The report assumes no mixing, but this is a tentative assumption.
The quality of water in the reservoirs could have significant
implications for both the reservoirs themselves and the downstream
reaches of the river. For example, phosphorus, as stated in the
report, will be provided by the inflowing water and the decomposition
of flooded vegetation. Increased phosphorus concentrations will
lead to increased primary productivity, of, for example, blue-green
algal groups such as Microcystis and Anabaena spp. Blue-green
algae exude chemicals which may be toxic, such as geosmin (Harding,
1992). Such chemicals will affect fisheries productivity. In the
Western Cape in South Africa, for example, the presence of geosmin,
released by algae in an impoundment, has concentrated in the flesh
of trout in a downstream trout farm (Snaddon & Davies, in
press.). The chemical results in a distinctive and unacceptable
odour and taste.
The report assumes that the stratification of the reservoirs will
result in the trapping of phosphorus below the thermocline, while
primary productivity occurs in the epilimnion. This will indeed
be true if there is no mixing, and if the inflowing water is of
a lower temperature than the reservoir epilimnion. In the event
of mixing, such as the inflow of turbulent river water, an algal
bloom may occur, with serious consequences for water quality in
the reservoir, and thus the fisheries supported by the impoundment.
Although some of the specialist reports have gone into some
detail on the local setting of the Cunene River and its fauna
and flora (such as the ornithological report), there are some
areas of the report that lack the detail that is necessary for
a comprehensive assessment of the dam option and indeed, whether
any dam should be constructed. The riverine invertebrate communities
have not adequately been assessed and recorded for this river,
and the regulation of flow could have devastating effects on the
invertebrates, with some consequences for local human populations.
Furthermore, in the absence of an IFR study, it cannot be accepted
that the recommended flows and mitigation measures that have been
suggested in the report, will maintain the ecological functioning
of the Cunene River, and its estuary.
Thus, the report is inadequate for the assessment of the dam options,
and no conclusions can be drawn as to whether either dam option
should go forward.
REFERENCES
Harding, W.R. 1992. Ph.D thesis
Ledec, G., Quintero, J.D. & Mejia, M.C. 1997. Good Dams and
Bad Dams: Environmental and Social Criteria for Choosing Hydroelectric
Project Sites. Sustainable Development Dissemination Note #1.
A report produced for the World Bank. 22pp.
Snaddon, C.D. & Davies, B.R. In press. A preliminary assessment
of some of the effects of a small inter-basin water transfer scheme
in South Africa on discharge and invertebrate communities. Submitted
to River Regulation: Research and Management.
Comments by
Kate Snaddon, Freshwater Ecologist
Freshwater Research Unit, Department of Zoology
Rondebosch 7700, South Africa
Phone: 27-21-650 3638 Fax: 27-21-650 3301
e-mail: ksnaddon@botzoo.uct.ac.za
and Associate Professor Bryan Davies
Freshwater Ecologist and Senior Lecturer
Freshwater Research Unit, Department of Zoology
Rondebosch 7700, South Africa
Phone: 27-21-650 3638 Fax: 27-21-650 3301
Further Reviews:
- CDM Auditing Process Cheats the Climate, by Sid Harring
- Large Hydro Carbon Credits Banned from European Climate Exchange, by Steve Rivkin
- Outcomes of CDM Executive Board Meeting, by Jamal Gore
- A Year of Rivers, Water and Rights, by Kate Snaddon
- Brazil: Don't Shove Belo Monte Down Our Throats!, by Peter Willing
- US Companies Favoring Efficiency Over Offsets , by Steve Rothert
- California Climate Legislation and Offsets, by Hans Eggers