1
A CRITICAL APPRAISAL OF THE CONSULTATIVE
ENVIRONMENTAL REVIEW:
DERBY TIDAL POWER PROJECT
DOCTORS CREEK, KIMBERLEY
Report to:
Derby Residents Action Group
P.O. Box 76
Derby, W.A., 6728
Joint report by:
V & C Semeniuk Research Group
21 Glenmere Rd.,
Warwick, W.A., 6024
EnviroEng Consulting P/L
27 Bardwell St.,
Thornlie, W.A., 6108
Due to the nature of this type of project, and the environmental importance of
the terrain into which it was proposed to be emplaced, this project should have
been subject to an Environmental Review and Management Programme
(ERMP) and not merely a Consultative Environmental Review (CER). The
electrical power transmission line aspect alone should have been the subject of a
CER. This aspect is important in that the wrong status accorded the project may
be the reason for the dearth of significant information provided within the CER
by the Proponent.
December 1997
2
A CRITICAL APPRAISAL OF THE CONSULTATIVE
ENVIRONMENTAL REVIEW:
DERBY TIDAL POWER PROJECT
DOCTORS CREEK, KIMBERLEY
TABLE OF CONTENTS
Summary
1.0 Introduction
2.0 International significance of Doctors Creek
2.1 Macrotidal setting in a global context
2.2 Erosional patterns in a global context
2.3 Tide-dominated deltaic estuarine setting
2.4 The fractal laboratory of Doctors Creek
3.0 Global importance of Doctors Creek mangroves
4.0 Geoheritage significance of Doctors Creek
5.0 Assessment of anticipated environmental impacts
6.0 Critique of CER: an environmental perspective
7.0 Critique of CER: an engineering perspective
8.0 Economic considerations
9.0 References
3
A CRITICAL APPRAISAL OF THE CONSULTATIVE
ENVIRONMENTAL REVIEW:
DERBY TIDAL POWER PROJECT
DOCTORS CREEK, KIMBERLEY
SUMMARY
1. There are five major problems with installing a hydro power station in the
Doctors Creek embayment; one of these concerns environmental aspects, and
four concern engineering aspects of the project:
•
the Doctors Creek area is one of International significance as a
macrotidal, mangrove-vegetated tidal flat
•
the ongoing, inexorable erosion will undermine and threaten
major civil structures
•
the La Rance tidal power installation is founded on rock
(Considine 1977), not on mud as in Doctors Creek, and so is
incomparable structurally and economically with the proposed
project
•
the La Rance installation, while technically a success, has been
assessed as uneconomic (Say 1973)
•
the substrates underlying the proposed infrastructures will
probably cause differential settling and failure of the barrages.
These points will be amplified below.
2. The terrain into which the power station is proposed to be emplaced by Derby
Hydro Power P/L is significant at several levels ranging from International to
National to State-wide. Execution of this project at any scale therefore
constitutes a major environmental impact and questions the wisdom of
continuing with the proposal.
3. The International and heritage significance of Doctors Creek should militate
against any development in this area on a priori principles alone. The
4
International and heritage significance of Doctors Creek is related to its setting
as a macrotidal tropical semi-arid mangrove coast, its erosional patterns, its tidedominated deltaic estuarine setting, and the fractal laboratory therein.
4. The mangroves of Doctors Creek in particular, and of King Sound in general
are globally significant, not because of endemic or restricted species, but
because the King Sound area was the first location where coastal erosion was
described in detail to provide insight into tidal flat processes and mangrove
responses. It stands as a global class-room for mangrove ecology in relationship
to macrotidal coastal erosion. Even though most mangroves in Doctors Creek
are not rare or unusual species, the occurrence of mangrove assemblages along
the eroding banks and headwaters here assume global importance because this
embayment represents the extreme end of a spectrum of erosional forms.
5. The aspects of the Doctors Creek system that have geoheritage significance
are: the occurrence of the Christine Point Clay at the mouth of Doctors Creek;
the relationship of the linear dunes to tidal flats; and the interactions of
hinterland freshwater to tidal flat hypersaline water.
6. The mangrove species Bruguiera parviflora in this occurring in this area is at
its most southern limit, and given the differences in mangrove biogeography on
the east and west coasts of Australia, this is of National significance.
7. The emplacement of a tidal hydropower operation within the embayment of
Doctors Creek, as proposed by the Derby Hydro Power P/L thus will have the
following impacts:
A. destruction of an Internationally significant mangrove and
coastal system;
B. destruction of Nationally to State-wide significant geoheritage
sites; and.
C. destruction of the tidal flat to hinterland groundwater interrelationships.
5
8. A critical review of the investigative reports and proposal from an
environmental perspective shows that there is :
A.
B.
C.
D.
E.
F.
G.
lack of assessment of Regional Significance
lack of contour maps
lack of modelling of mangrove response
lack of modelling of hydrodynamics
no model of groundwater dynamics
an under-estimation of erosion effects
an over-simplified estimation of biomass/productivity
A number of these deficiencies, in fact, are fatal flaws to the proposal.
9. A critical review of the investigative reports and proposal from an
engineering perspective shows the following:
A. The shortened service life experienced at La Rance coupled with the
problems caused by severe corrosion of all marine structures and equipment
along the northwest coast of Western Australia, suggests that the projected
equipment service life in this proposal is optimistic.
B. The tidal power station at La Rance should not be used in comparison with
any proposed structure in the Kimberley because it is located in a
predominantly rocky environment (Considine 1977), while that proposed in
King Sound is within an eroding estuarine deltaic system of mud and sand
with a high sediment load within the water column.
C. The aspect that “The double basin scheme has reduced power output at neap
tides (2-3 days per fortnight at 12 MW) and supplementary generation is
required”, makes the whole project ineffective both in terms of a reliable
power supply and of the claimed benefits of scrapping the Derby and Fitzroy
Crossing power stations. This factor alone should be considered a valid
basis for rejecting the proposal.
D. The notion that “Experience would also be gained on understanding and
managing the impacts of this type of project on mangroves and the marine
environment.” suggests little is known about potential impacts, which should
be offset by modelling of impacts such as the effects:
6
•
•
•
on the tidal resonance within King Sound;
of altered sedimentation/scouring patterns of the estuary or the
planned basins;
on the groundwater hydrology which will affect both upwelling of
fresh water within the estuary and the fresh/salt water interface
upgradient of the proposed project area.
E. .A basic calculation of static foundation pressure under the central prism of
the barrages suggests a pressure of about 160 kiloPascals (kPa), which
exceeds that allowable for soft clays and silts (limited to about 75 kPa) and
even for firm clays (75 to 150 kPa). The barrages may therefore sink into the
substrate with some consolidation below the barrages and plastic upwelling
of mud either side of the barrage, or if the consolidation is not uniform it
could potentially induce barrage failure. The heterogeneous nature of the
distribution of sand and mud will potentially create foundation problems as
well as ‘piping’ erosion from underflow or seepage. This is amplified by
DeF. Quinn’s (1961):
“The character of the bottom may well be the determining factor in the
type of breakwater selected, as it usually difficult, if not impossible,
and expensive to prepare a solid foundation on soft material for the
support of a wall-type gravity structure.” (Italics added for this
report).
F. The CER indicates that geotechnical surveys have yet to be undertaken,
suggesting that the proposed barrage foundation system (and hence its
construction) has yet to be determined. In the absence of such information it
is impossible to assess environmental impacts from the construction phase
since direct deposition of material, or dredging, or pile driving, or use of
cofferdams, all have vastly different implications environmentally.
G. The CER gives no indication of:
• the proposed foundation system or construction technique to build the
barrages;
• the storm surge capability of these structures;
• how any barrage failures would be rectified;
• the type of fill to be used from Point Torment;
• specifically where that fill will come from on Point Torment;
• the impacts of removing that fill from Point Torment;
• the mode of transport and deposition of that fill.
7
This suggests that the CER has been assembled either in haste or on a limited
budget - both of which are likely to result in optimistic construction cost
estimates. High risk projects of this nature need to be fully studied and
analysed prior to consolidating any proposals.
H. For the construction of the barrages, the CER fails to indicate:
•
•
•
the amount of rock to be removed from Point Torment;
the suitability of that rock to endure 120 years of marine assault;
the impacts of removing that rock from Point Torment.
There is in fact little or no rock at Point Torment, apart from the ferruginised
sandstone outcrop at Black Rocks on the eastern shore of King Sound.
Black Rock on the eastern shore, and Point Torment itself for that matter, are
significant in their own right, and should not be indiscriminately quarried for
rock.
I. Although the CER gives a safety margin on height for the levees, there is no
indication as to their capability to resist lateral thrust from the stored water.
J. The CER states: “... and there is also an option ... to develop a new gas fired
power station at an industrial estate further out of town”. A 48 Megawatt
gas-fired power station would prove cheaper than the proposed hydroelectric
station to construct initially, and in view of the potentially high maintenance
costs of the hydro station may actually provide cheaper power over its
lifetime; a comparative life cycle costing study would resolve this.
K. The CER indicates that: “In the event that decommissioning is proposed, a
decommissioning plan will be developed which will address the removal of
plant and equipment”. This is unacceptable as the timing of such planning
would be too late and the proposal does not address the civil structures. For a
complex project of this nature being shoe-horned into a sensitive
environment, a full decommissioning plan should be developed from the
onset to cater for abandonment of the project at any stage.
8
10. The stratigraphic heterogeneity in this area suggests that under conditions of
permanent to more prevailing saturation as can be expected in the proposed
flooded basins, the basin walls will probably will begin to slump and the
heterogeneous nature of the distribution of sand and mud will potentially create
foundation problems.
11. Despite all the positive commentary in the CER in relationship to the French
installation at La Rance, no data are supplied with respect to the economic
viability of the power to be generated at the proposed Doctors Creek site. A
project of this nature requires a complete life cycle costing study which
identifies all costs including:
A. initial design and site investigations;
B. construction and its problems, such as failure of the substrate, local
material found to be inappropriate for the filling of barrages or levees,
oil spills from dredges or service barges, etc.;
C. operation and maintenance, including major component servicing or
replacement such as sluice gates, turbines, raceway maintenance;
D. contingencies for force majeur such as barrage collapse or
displacement, power transmission line destruction by cyclone, etc.;
E. final decommissioning of the plant at the end of its service life, or if
the project should be abandoned at any stage, and commitment to
undertake all the restorative work necessary to return the environment
to a safe and acceptable condition.
The most critical aspect of the power station at La Rance is a reference by Say
(1973):
“The only large tidal scheme in operation is that on the River Rance in
Northern France and this, although technically successful, is hardly
economic.”
If this is still the case, then the economic benefits of the proposed Derby Hydro
Power scheme are seriously cast in doubt.
9
12. Emplacing barrages and levees within this macrotidal setting with the
substrates of mud involved is an expensive and logistically difficult and risky
task. There is no documented experience of excavating and emplacing such
structures on heterogeneous mud and sand substrates in settings with large tides.
Often, the full difficulties of working in muddy tidal environments only begin to
emerge once the project is underway. In effect, the Derby project will a first
attempt globally to attempt such a feat.
13. Finally, the economic benefits of this project cannot be ascertained until the
proponent fully explores the costs involved.
10
1.0 Introduction
Derby Hydro Power Pty Ltd propose to construct a tidally driven hydro-electric
scheme within the Doctors Creek embayment, north of Derby, King Sound
(Halpern Glick Maunsell 1997). In support of this proposal, the Derby Hydro
Power Pty Ltd prepared a Consultative Environmental Review (CER) dealing
with the description, operation, impacts of the proposed project on the natural
environment, and the proposed monitoring and environmental management
programmes.
The Derby Residents Action Group invited the V & C Semeniuk Research
Group (VCSRG) to provide commentary on the Consultative Environmental
Review document, and evaluate the environmental responsibility of the project,
and in turn, VCSRG invited EnviroEng P/L. to participate.
There is a threefold thrust to this dissertation:
• the International to State-wide significance of the area
• the engineering problems associated with this project
• critical assessment of the CER document
The most critical factor in this appraisal of the proposed project is the
International significance of the terrain in question. If the terrain was not
significant, then the problems with the project would be infrastructural and
operational, and some of these could be circumvented with expensive
engineering solutions. However, as will be shown later, the terrain into which
the hydropower project is proposed is significant at several levels ranging
from International to National to State-wide. Execution of this project at any
scale therefore constitutes a major environmental impact and questions the
wisdom of continuing with the proposal.
The main sections of this critical appraisal are seven-fold:
•
•
•
•
•
•
•
Section 2: International significance of Doctors Creek
Section 3: importance of the mangroves globally
Section 4: geoheritage significance of the Doctors Creek system
Section 5: assessment of anticipated environmental impacts
Section 6: critique of CER: an environmental perspective
Section 7: critique of CER: an engineering perspective
Section 8: economic considerations
11
2.0 International significance
of the Doctors Creek system
The International and heritage significance of Doctors Creek inlet should
mititate against any development in this area on a priori principles alone. The
International and heritage significance of Doctors Creek is related to:
•
•
•
•
its setting as a macrotidal tropical semi-arid mangrove coast,
its erosional patterns,
its tide-dominated deltaic estuarine setting, and
the fractal laboratory therein.
As will be demonstrated below, the Doctors Creek basin represents a once-off
globally unique and important system.
2.1 Macrotidal setting in a global context
Tides are classified as microtidal if their range is < 2m, mesotidal if their range
is 2-4 m, and macrotidal if their range is > 4 m. In this context, the tides of
King Sound are macrotidal. All macrotidal systems are significant sites for
world heritage (even if they are not recognised as such in their country of
residence) because they provide unusual coastal settings and models for
ecosystems, geology, and a field laboratory for the study of coastal dynamics
and stabilisation. Most of the mangrove ecosystems described in the literature
occur in microtidal and mesotidal settings, and so those mangroves in
macrotidal settings assume global significance because they occur in an
environment where the habitat range, groundwater and tidal processes are
amplified by the tidal regime.
Microtidal regimes are numerous across the globe (for instance, the well
documented systems along the North Sea coast, and the mangrove-vegetated
coast of Florida), hence they have provided an abundance of sedimentary and
ecological/palaeoecologic models for use in earth-science history in the
stratigraphic record. Macrotidal systems are not so abundant, and so any
macrotidal system, if it is a sedimentary system provides important Holocene
analogs for the stratigraphic record (Allen 1970; Thompson 1968). In this
context, it is important to note that each of the macrotidal systems located
around the globe, such as King Sound, Mont St Michel, the Bay of Fundy, and
Broome, provide a different pattern of sedimentation useful to the interpretation
of the ancient stratigraphic record (Ginsburg 1975).
12
In order to assess the global significance of Doctors Creek, a comparison is
made of the macrotidal locations around the world with maximum tidal ranges
in excess of 10 m. These are ranked below in decreasing order of their tidal
range, and it is obvious that the King Sound system, of which Doctors Creek is
a part, is ranked within the first nine such sites globally. These macrotidal areas
are described briefly in terms of their important characteristics of climate
setting, geomorphic setting, occurrence of mangroves, and tidal ranges:
Table 1: The ten largest macrotidal systems globally listed in decreasing
order of maximum tidal range
Location
Climate
Geomorphic
Max. tidal Mangrove
setting
range ( m)
Bay of Fundy Temperate
funnel-shaped 15.0
none
(Nova Scotia)
ria embayment
Mont St
Temperate
complex of
15.0
none
Michel
funnel-shaped
(France)
estuaries
Severn
Temperate
funnel-shaped 14.6
none
Estuary
estuary of the
(U.K.)
Severn
Puerto
Temperate
funnel-shaped 13.2
none
Gallegos
estuary of the
(Argentina)
Gallegos
St Helier
Temperate
channel setting 12.3
none
(France)
(Coast of
Brittany)
Bhavnagar
Tropical
funnel-shaped 12.2
1 species
(India)
semi-arid
estuary of the
Sabarmati and
the Mahi
Yampi Sound Tropical
ria coast
10.9
12 species
(Australia)
subhumid
King Sound
Tropical
funnel-shaped 10.5
11 species
(Australia)
semi-arid
delta-estuary of
the Fitzroy
Broome
Tropical
carbonate mud 10.5
12 species
(Australia)
semi-arid
tidal
embayment
(Australian data from Anonymous 1996; other data from: Admiralty Chart;
Allen 1970; Knight & Dalrymple 1975; Lasonneur 1975)
13
Those macrotidal areas, listed in Table 1, that lack mangroves occur in high
latitudes, and have samphires in the upper tidal zone. There are also numerous
other macrotidal estuaries, deltas and tidal flat systems with tidal ranges in
excess of 5 m (but generally less than 8 m) that do not support mangroves (an
example being the Colorado River Delta; Thompson 1968) - these are not dealt
with further here. Note that the last four systems in the Table 1, i.e., Bhavnagar,
Yampi Sound, King Sound, and Broome, are the only macrotidal systems that
have mangroves. A comparison of these mangrove-vegetated tidal flats is
presented Table 2 below, and a comparison of the mangrove systems of the
King Sound, Broome and Yampi Sound area is presented in Table 3.
Table 2: Global comparison of macrotidal mangrove coasts
Site
Large-scale
Tidal flat description No of
geomorphic
mangroves
setting
Bhavnagar
funnel-shaped depositional system;
1 species
(India)
estuary of the
broad salt flats; narrow
Sabarmati and shrubby mangroves
the Mahi
fringing the shore
Yampi Sound rocky
rocky ria shore system 12 species
(Australia)
archipelago/
ria coast
King Sound
funnel-shaped eroding coast; broad
11 species
(Australia)
delta-estuary of salt flats; various
the Fitzroy
mangrove formations
related to coastal
dynamics
Broome
carbonate mud depositional to
12 species
(Australia)
tidal
erosional coast; broad
embayment
mangrove formations;
saltmarsh inhabiting
the high-tidal flats
14
Table 3: Comparison of the mangrove coasts in NW Australia
Site
Large-scale No of
Mangrove species
geomorphic mangroves
setting
Yampi Sound rocky
12 species Aegiceras corniculatum
Aegialitis annulata
archipelago/
Avicennia marina
ria coast
Bruguiera exaristata
Camptostemon schultzii
Ceriops tagal
Excoecaria agallocha
Lumnitzera racemosa
Osbornia octodonta
Rhizophora stylosa
Sonneratia alba
Xylocarpus mekongensis
King Sound
funnel11 species Aegiceras corniculatum
Aegialitis annulata
shaped deltaAvicennia marina
estuary of the
Bruguiera exaristata
Fitzroy
Bruguiera parviflora
Camptostemon schultzii
Ceriops tagal
Excoecaria agallocha
Osbornia octodonta
Rhizophora stylosa
Xylocarpus mekongensis
Broome
carbonate
12 species Aegiceras corniculatum
Aegialitis annulata
mud tidal
Avicennia marina
embayment
Bruguiera exaristata
Camptostemon schultzii
Ceriops tagal
Excoecaria agallocha
Lumnitzera racemosa
Osbornia octodonta
Rhizophora stylosa
Sonneratia alba
Xylocarpus mekongensis
Data from Semeniuk et al 1978, and Semeniuk 1985, 1993
15
Tables 2 and 3 above show that Yampi Sound, King Sound and Broome are the
most species-rich mangrove systems for the large macrotidal settings, and that
they are broadly comparable in terms of species-richness - thus, they stand as
globally significant sites. Yampi Sound, being a rocky ria system, in contrast to
the other two mangrove systems, however, is quite depauperate in mangrove
habitats, and the high diversity of mangroves there reflects the species-richness
of the region, rather than the species-richness of the location. However, while
all three areas have the same broad tidal range, they are quite distinct from each
other, as will be outlined in the following discussion.
In the first instance, each occurs in a different coastal sector, which means that
the geomorphic settings, sedimentary regimes, and habitat arrays are
incomparable. In terms of mangrove regions (Semeniuk 1993), Yampi Sound
occurs in the Kimberly Coast sector, King Sound is in the King Sound sector,
and Broome is located in the Canning Coast sector.
King Sound represents a coastal type of broad salt flats, incised by ramifying
and meandering tidal creeks. The whole of the system is largely in an erosional
state, and mangroves colonise habitats formed by the coastal erosional processes
(Semeniuk 1980a). Broome, on the other hand, is located in a tidal embayment
system, lacking riverine input, and hence it is carbonate-dominated (Semeniuk
1993). Saltmarsh in the upper tidal zone precludes the development of
ramifying and meandering tidal creek systems such as developed in King
Sound. Yampi Sound, being a rock ria coast system (cf. Semeniuk 1985) lacks
the broad development of tidal flats, and as mentioned above, the species there
reflect the species-richness of the region - there are no broad tidal flats where
the species occurrences are well developed. In this context, therefore, King
Sound and Broome are the systems more directly comparable in that they have
the same degree of species richness and appropriate well-developed mangrove
habitats where the species can find full expression in abundance and extent to
develop mangrove-vegetated tidal flats.
However, while King Sound and Broome appear to have similar maximum tidal
ranges, as determined by the height difference between the highest astronomical
tide (HAT) and the lowest astronomical tide (LAT), a comparison of the
prevailing mean high tidal spring range (MHWS-MLWS) and mean neap tidal
range (MHWN-MLWN) shows that King Sound overall has a higher prevailing
tidal range.
16
Table 4: Comparison between King Sound and Broome tidal ranges
Site
Range
Range
Range
HAT-LAT
MHSW-MLWS
MHWN-MLWN
King Sound
10.5
9.4
4.8
Broome
10.5
8.2
2.1
Thus, King Sound and Broome, with 11 and 12 species of mangrove,
respectively, are the most species rich macrotidal mangrove-vegetated tidal
flat systems in the world; both have a tidal range in excess of 10 m, but, the
substrate type, the geomorphic setting, and the system of tidal creeks for these
two areas are wholly incomparable, and the prevailing tidal range also is
incomparable. In this context, it is obvious that the King Sound area in its
own right is globally significant.
Mention also should be made of Cambridge Gulf area in northern Western
Australia, a system that is nearest to King Sound in tidal flat features. These
two areas have an equivalent estuarine-gulf setting, broad tidal flats, broad salt
flats, ramifying and meandering tidal creeks, a comparable climate, and a
variety of mangrove species. The Cambridge Gulf system is different from the
King Sound area because of the following: the tidal flats are nestled in a rocky
range setting; the maximum tidal range is 7.7 m; and there are only 7 species of
mangrove
From a global perspective, only Bhavnagar, located in the Gulf of Cambay (or
Khambhat) in India, also could be viewed superficially as approaching the King
Sound situation. However, again, there are significant differences that indicate
that the Gulf of Cambay cannot be viewed as a direct equivalent to King Sound.
Bhavnagar is located in the driest part of the Indian subcontinent, approximately
22o N (the latitude equivalent to Onslow on the Western Australian coast).
These three locations (King Sound, Bhavnagar, and Onslow) are compared in
Table 4 below.
Table 4: Global perspective of latitudinal setting and the number of
mangroves at King Sound, Onslow, and Bhavnagar:
Location
No of mangrove species
o
King Sound 17-18 S
11 species
o
Onslow 22 S
5 species
o
Bhavnagar 22 N
1 species (+ rare Rhizophoraceae)
Interestingly, the Indian Government has recognised the importance of the
mangroves in the Gulf of Cambay (De Roy & Thadani 1992) by taking
17
appropriate administrative action in spite of the fact that, generally, mangrove
formations of Indian region are heavily exploited for firewood.
Many of the other macrotidal systems outside Australia, for instance Mont St
Michel, and the Bay of Fundy, also are anthropogenically modified, and in this
context, the Doctors Creek system becomes important because it is pristine, and
constitutes a macrotidal-flat wilderness, unique globally as being a terrigenous
and erosional system with the largest tide for tropical mangrove setting.
Within King Sound, the Doctors Creek system is part of the Fitzroy River
estuary, a deltaic estuarine environment with a tide-dominated delta. The
Doctors Creek basin represents the accumulation of deltaic sediments within a
setting where deltaic sedimentation is interacting with an embayed and crenulate
coast.
It is obvious, therefore, that the Doctors Creek system represents a unique
and globally important system. It is located in a setting that has these
features:
it is a semi-arid macrotidal coast that is species rich
in terms of mangroves.
Other systems that are also macrotidal to this extent either lack mangroves (Bay
of Fundy, St Helier, St Mont Michel, Puerto Galegos, etc.), or are depauperate
in mangroves (Bhavnagar). This underpins the global significance of Doctors
Creek.
2.2 Erosional patterns in a global context
The King Sound area is a net erosional situation (Semeniuk 1980b). There is
minor local deposition and accretion (Semeniuk 1982), but the overwhelming
and major megascale process is coastal erosion. This is an important feature to
note from two points of view:
1. that of considering the area as a global classroom, and
laboratory, and
field
2. that related to engineering problems stemming from its location in an
erosional environment (see Sections 6.0 & 7.0).
Aerial photographs spanning 28 years suggest that erosion has been a long-term
process (Jennings 1975; Semeniuk 1980b). Stratigraphic evidence leads to a
18
similar conclusion.
erosion:
Several other features reinforce the conclusions about
• nodules under the tidal flats;
• the imprint of (supratidal) vegetation roots on the substrate;
• dieback of terrestrial vegetation.
Firstly, nodules of Mg-calcite, aragonite, dolomite, calcite (or their mixtures)
are imbedded in Holocene and Pleistocene formations and are related to
unconformities or hypersaline groundwater fields. Nodules precipitated from
hypersaline groundwater within Holocene formations can indicate the extent
erosion has proceeded. Such nodules, originally formed under Holocene salt
flats, are being exhumed along seacliffs and form gravel lags on low-tidal flats.
Secondly, extensive areas of salt flat in the shallow sub-surface (1-3 m) are
riddled with fine rootlet structures. These structures are unlike the coarse root
structures forming under mangrove cover. The modern analogue for fine
rootlets can be found under supratidal grassy plains. Such grasses have long
since retreated from this area of the now salt flat, but a record of supratidal
conditions is present as rootlet structures.
Thirdly, aerial photography shows that supratidal grassy plains (and samphire
flats) were more extensive in past decades. The vegetation died back as erosion
lowered supratidal surfaces to tidal levels. The dieback continues today around
residual grassy or samphire hummocks and locally along the edge of the
terrestrial shrub of the hinterland. Here, as sheet erosion proceeds, the shrub is
eliminated and replaced by samphires and salt flat.
The first two overprints (nodules and rootlets) in many localities are now out of
their environment and show that (as coastal erosion proceeded) the geomorphic
surface passed from supratidal with fresh groundwater, to salt flat with
hypersaline groundwater, to the seacliff with oceanic groundwater. The
displaced diagenetic features indicate loss of at least several kilometres of coast
in the Holocene.
19
The erosional patterns described in King Sound assume global significance
because this area presents a model of coastal erosion wherein sheet, tidal creek
and cliff erosion singularly, or in combination act to develop coastal landforms
(Semeniuk, 1980a,b). The King Sound area was the first location globally
where coastal erosion was described in detail to provide insight into tidal flat
processes. As such, it stands as a global class-room. In this context, the
Doctors Creek embayment represents one end of a spectrum of erosional forms
in the system; it represents Erosional Stage No 6 in a system that has at least 6
Stages (Semeniuk 1980b).
All of the patterns described above also point to a long term and relentless
retreat of the coastal zone, and defy the projected 120-year life expectancy of
the proposed project (to be dealt with in Section 7.0).
2.3 Tide-dominated deltaic estuarine setting
The importance of King Sound and Doctors Creek in terms of global tidedominated deltaic estuarine settings relates to the tide-dominated nature of its
depositional landforms. Delta systems are classified on their form as generated
by fluvial vs wave vs tidal processes. Thus, if fluvial processes dominate, then
deltas tend to be fluvial-dominated in form (i.e., birdsfoot delta form, or
digitate); those in wave agitated settings become wave-dominated deltas (Niger
Delta, or the Nile Delta).
The importance of a macrotidal range in the
development of deltas and estuarine-deltaic systems is that they become tidedominated, rather than wave-dominated (Niger Delta, or the Nile Delta) or
fluvial-dominated. In this context, the King Sound system represents a hightidal estuarine delta, and stands as a global example. In contrast, other deltas
of the high-tidal type generally have a much lower tidal range (the welldocumented Malaysian high-tide delta, for example, has a tidal range of 4 m
(Coleman et al 1970).
2.4 The fractal laboratory of Doctors Creek
One of the most important aspects of the King Sound area is the natural fractal
laboratory that is embedded in the system. In this area, there is a gradational
development of tidal creek systems (Semeniuk 1980b). Creeks begin their
history in the crevices of mudcracks and with time they deepen, widen and
extend their headwaters to landward, progressively evolving to become large
and deep meandering systems. Thus the gradation from small rut to large
channel reflects stages of creek development. The array of mud cracks coupled
with the tidal flat slope generates the meandering channel which becomes
entrenched and remains through all stages of creek growth. Within 10-20 years
the ruts develop into small channels: these are flooded only during spring tides
20
and undergo sheet erosion typical of salt flats except that channelled ebbing
waters are more erosive. Creeks continue to deepen and widen slowly until the
floor reaches a level where sediment remains moist and water-logged. A new
process then operates; water-logged banks repeatedly slump, and there is a more
rapid widening and deepening of the channels; creek cross-sections then change
from a shallow V-shape to a deeper, U-shape.
For those tidal creeks that are meandering and ramifying, the small scale
patterns reflect the large scale patterns, and the small scale patterns are
embedded in and control the development of the larger scale forms. The small
scale creek systems, and all intervening creek sizes, could be viewed as
miniatures of the larger scale. Thus, there appears to be an underlying fractal
pattern to the tidal creek system.
This aspect of the fractal nature of the tidal creek erosion contrasts with other
tidal systems in the region (e.g., Yampi Sound, and Broome), because of the
climatic, sedimentologic, and vegetational setting of the King Sound tidal flats.
This fractal property is a powerful and Internationally significant feature of
the natural history of the area, which will provide important insights into the
processes shaping tidal flat forms. Currently, this subject matter is being
explored as a research topic (Semeniuk & Woodroffe in prep).
3.0 Global importance
of the Doctors Creek mangroves
The mangroves of Doctors Creek in particular, and of King Sound in general
are of global significance, as will be discussed below. In general, to assess the
global significance of mangroves in a given area, it is necessary to determine
the species richness of the region, and the variability of coastal style (habitat
setting) where mangroves are located. In order to assess the global significance
of mangrove formations specifically in Doctors Creek, the discussion that
follows centres on two inter-related aspects: the species pool, and the erosiongenerated habitats.
21
The mangroves of northwestern Australia belong to the Eastern Group (=Old
World) of mangroves, centred on the Indian-Pacific Ocean area (Tomlinson
1986), and within this region, they more specifically belong to the IndoMalesian Group that encompasses Pakistan, India, Burma, Malaysia, Indonesia,
Celebes, northern Australia and Papua-New Guinea (Chapman 1977). This
Indo-Malesian group is the most species-rich region of mangroves world-wide
(Chapman 1976). Within this grouping, however, northern Australia is part of
the Northern Australian-Papuan sub-group, being less species-rich than some of
the other sub-groups but having some species features unique to that region
(Chapman 1977). In terms of endemism and restricted species, from a global
perspective, Doctors Creek does not support any unusual, endemic, or restricted
mangrove species. In fact, all mangrove species here are common and
widespread elsewhere, and so in this sense, the species of mangroves here are
not globally significant. However, Doctors Creek does provide two aspects of
significance. The first is that the mangrove species Bruguiera parviflora
occurring here is at its most southern limit, and given the differences in
mangrove biogeography on the east and west coasts of Australia, this is of
National significance. The second is that the mangroves are related to habitats
generated by erosional processes.
The erosional patterns in King Sound, mentioned earlier, as they relate to
mangroves, is another matter. The relationship of erosion to mangrove patterns
assume greater global significance when it becomes apparent that this area
presents a model of coastal erosion wherein sheet, tidal creek and cliff erosion
singularly, or in concert act to develop mangrove habitats (Semeniuk, 1980a,b).
While globally most mangrove areas are viewed to be sites where mangrove
habitation is linked to coastal accretion, the King Sound area was the first
location where coastal erosion was described in detail to provide insight into
tidal flat processes and mangrove responses. As such it stands as a global classroom for mangrove ecology in relationship to macrotidal coastal erosion.
In this context, even though the bulk of the mangroves in Doctors Creek are not
rare or unusual species, the occurrence of mangrove assemblages along the
eroding banks and headwaters here assume global importance because this
embayment represents the extreme end of a spectrum of erosional forms. Thus,
Doctors Creek represents Stage 6 of a intergradational series of tidal creek
forms, noted by Semeniuk (1980b) as Stages 1-6. Erosion of tidal creek
systems has nearly gone to completion in the Doctors Creek area, and the
mangrove assemblages established there have formed in habitats in a Stage 6
erosional setting.
22
4.0 Geoheritage significance
of the Doctors Creek system
Geoheritage is a concept which encompasses the diversity of minerals, rocks
and fossils, and the features that indicate their origin through time, and it
includes landforms and other geomorphologic features that illustrate the effects
of present, and past exposure to climate and earth forces (Joyce 1995; Eberhard
1997).
There are three aspects of the Doctors Creek system that have geoheritage
significance. These are:
• stratigraphic type location of the Christine Point Clay
• relationship of the linear dunes to tidal flats
• interaction of hinterland freshwater with tidal flat hypersaline water
The Doctors Creek embayment, towards the mouth of Doctors Creek, is the
stratigraphic type section of the location of the Christine Point Clay (Semeniuk
1980c). This formation, in its stratigraphic context of King Sound, is the most
southerly occurrence of the sedimentary unit known as the “Big Swamp”
complex described by Woodroffe et al (1985). The “Big Swamp” phase of
northern Australia records an early Holocene history of rapid sedimentation,
with large extensive mangrove forests, and humid climate, unlike anything seen
today in the region. Embedded in this stratigraphic unit at Christine Point,
therefore, is the history of this part of Australia in terms of sedimentation
style, sedimentation rates, mangrove ecology, and climate.
Fairbridge (1961) described Quaternary red sand dunes descending beneath the
Holocene tidal flat deposits of the Doctors Creek embayment, and thus alerted
scientists to the occurrence of this important climatic and stratigraphic
relationship. This relationship occurs mostly and is best developed along the
western edge of the Doctors Creek embayment. Later, Jennings & Coventry
(1973) and Jennings (1975) explored the relationship of these red dunes to the
overlying tidal flat deposits, writing a paper on the history of the Holocene
transgression into the red sand dune terrain. As such the work became an
international classic in coastal stratigraphy. In this context, in the light of the
works of Fairbridge (1961), Jennings & Coventry (1973) and Jennings (1975),
this area has become known internationally, and is of International
geoheritage significance.
23
In the future, this site will continue to be a site of stratigraphic and climatic
research, as the basic work carried out by those authors is re-explored, refined,
and amplified. It is therefore imperative that the terrain remains accessible as a
site of Quaternary research.
The third matter relates to the interaction of hinterland freshwater with tidal flat
hypersaline water. The configuration of the red sand dunes descending
stratigraphically below the tidal flat sediments provides a conduit for freshwater
seepage that discharges under the tidal flats. This seepage was detected by
Jennings (1975) and by Semeniuk (1980a). Jennings (1975) documented “dune
ghosts” outlined by strings of vegetation on the vegetation-free hypersaline tidal
flat, where groundwater of lower salinity, resided in the buried dune fingers
under the tidal flat. Semeniuk (1980a) documented groundwater hypersalinity
diluted by this seepage within buried fingers of dune sand under the tidal flat.
These occurrences of sub-tidalflat seepage assume geoheritage significance.
5.0 Assessment of anticipated environmental impacts
In the discussions of impacts that follow, the argument concentrates on impacts
on the Internationally significant mangroves and the coastal zone, and the
geoheritage significance of the area. While note is made here that the
Consultative Environmental Review (Halpern Glick Maunsell 1997) did not
deal with avifauna and fish, these aspects of the environment are also outside
the scope of this critical appraisal of environmental impacts.
In their Consultative Environmental Review, Halpern Glick Maunsell (1997)
outline the scope of the Derby Hydro Power project in terms of infrastructure,
alterations to the environment, operational procedures, and impacts. As
mentioned in the Introduction of this report, these descriptions, discussions, and
impact assessments presented in the Consultative Environmental Review would
be valid if the proposed project was not located in an environmentally
significant area. The site selected by Derby Hydro Power Pty Ltd unfortunately
does not exist elsewhere along the Australian coast.
However, as discussed earlier, the Doctors Creek system is a significant area. It
represents an Internationally significant system in terms of mangrove ecology,
coastal geomorphology, Quaternary geoheritage, and national site of
geoheritage for hinterland groundwater to tidal flat groundwater interactions. In
this context, the proposed project will have serious impact on the Doctors Creek
area.
Thus, the emplacement of a hydropower operation in the Doctors Creek system,
as proposed by Derby Hydro Power will result in:
24
1. by calculations of the consultants, destruction of some 1500ha of
Internationally significant mangroves;
2. destruction of an Internationally significant geomorphic system, i.e.,
the tidal flat system and tidal creeks;
3. destruction of International to State-wide significant geoheritage
sites;
4. alteration of the tidal flat to hinterland groundwater interactions.
The argument developed here is that the Doctors Creek system is essentially a
wilderness, and its importance lies in its naturalness as a tidal flat classroom of
International grade. Emplacing barrages, altering the tidal system, emplacing
retaining levees, inundating the basin artificially, and creating artificial sites for
mangrove colonisation seriously degrades the quality of this area. From this
perspective, the loss of some 1500ha of mangroves and its replacement by
recruitment eventually in other sites created by association with the altered tidal
regime and by local sedimentation is unacceptable environmentally, and Point2,
above, in the view of the International importance of the area also is
environmentally unacceptable.
Point 3, the destruction of sites of geoheritage (the type location of the Christine
Point Clay, and the relationship of the red sand dunes to the tidal flats) by the
construction of the barrage, and the inundation of the high-tidal flats,
respectively, must be viewed as environmentally unacceptable.
In regards to Point 4, as outlined in an earlier Section, there are interactions of
hinterland freshwater with tidal flat hypersaline water through red sand dunes
descending stratigraphically below the tidal flat sediments which provide a
conduit for freshwater seepage that discharges under the tidal flats.. These
occurrences of seepage beneath the tidal flat, located in the buried dune
“fingers” under the tidal flat, assume geoheritage (hydrological) significance.
Ponds of more permanent saline water located in the upper tidal zone created by
the barrage will fundamentally alter the hydrostatics and dynamics of this
system, and thus will destroy a site of geoheritage significance.
25
6.0 Critique of investigative reports and proposal:
an environmental perspective
This Section provides a critique, from an environmental perspective of the
investigative reports and the overall proposal, to highlight errors of fact and
inadequacies in the studies carried out. The issues are dealt with as follows:
1. lack of assessment of Regional Significance
2. lack of contour maps
3. lack of modelling of mangrove response
4. lack of modelling of hydrodynamics
5. no model of groundwater dynamics
6. an under-estimation of erosion effects
7. an over-simplified estimation of biomass/productivity
6.1 Lack of assessment of Regional Significance
One of the most critical problems in the CER in relationship to environmental
matters, is in the Appendix dealing with “Mangrove assemblages in Doctors
Creek, Derby, their regional significance and the potential impacts of a tidal
power station’. While the title of the Appendix foreshadows a treatment of
“Regional Significance”, in fact, this subject matter is not dealt with in the
report. As noted earlier in this critique of the CER, the mangroves and the tidal
flat system in the Doctors Creek area are highly significant, Internationally hence Regionally.
6.2 Lack of a contour map
On the second point, there is no map of topographic contours of the tidal flat in
the CER. Such a map, perhaps at a contour interval of 0.5 m or 1.0 m, would
logically form the foundation to modelling of hydrodynamics of the proposed
operation, to the modelling of the areas of inundation, and to the prediction of
possible recolonisation of tidal terrain by mangroves. The lack of such a map
casts doubt on the scientific validity of the assessments of impacts and the
predictions offered in the CER.
6.3 Lack of modelling of mangrove response
Critical to interpreting and predicting mangrove response to a very altered
hydrodynamic system is development of a model integrating occurrences of
mangroves in various hydrodynamic, inundation, tidal settings, and salinity
regimes. In order to obtain such a model, there would be need to obtain
information on contours, hydrodynamics, mangrove assemblage and mangrove
species tolerance to various environmental variants in the Doctors Creek
setting, salinity fields, and groundwater to surface water interactions. This
would be the most rigorous way to deal with predicting the mangrove responses
26
to the impacts of the proposed project; any treatment short of this is speculation.
The actual impacts that would flow on from commissioning a hydro-power
station in the Doctors Creek area are too serious to be based on the approach
taken in the CER.
6.4 Lack of modelling of hydrodynamics
The development of a model integrating tidal dynamics, contours, inundation,
tidal settings, and salinity regimes is critical to interpreting and predicting
hydrodynamic response to a very altered system. Such a model as proposed
here would be the most rigorous way to deal with predicting the hydrodynamic
patterns that would form as a result of the altered environment and the newly
imposed infrastructures. Again, any treatment short of this is speculative and
unacceptable in both scientific and engineering terms. Figure 6.2 in the CER is
deficient in this regard.
6.5 Groundwater dynamics
There is no description of tidal zone groundwater dynamics, and no treatment of
hinterland to tidal flat groundwater interactions. As a result, there really cannot
be any predictions made of the impact of a semi-permanent to more-floodedthan-normal saline water body on the natural groundwater system. In many
ways, the new system will mimic the effects on local groundwater of saline
holding ponds of solar salt lagoons operational in the Pilbara, but the difference
here is that this system will be more proximal to the hinterland freshwater body,
it will also change the prevailing tidal flat groundwater system nearby, and it is
located in a semi-arid environment.
Since there has been no study by the proponent of the tidal zone groundwater
system, there can be no valid prediction on the effects of the project on the
groundwater bodies, and the effects on ecosystems that are
sustained/maintained by this groundwater.
6.6 Under-estimation of erosion effects
The CER has under-estimated the effects of erosion in this region. As described
earlier in this report, and further amplified here, there are a number of features
that point to net erosion being the dominant feature in the evolution of the tidal
zone: stratigraphy truncated by the geomorphic surface, receding cliffs and
headwaters of tidal creeks, residual knolls of supratidal land, relicts after
grasslands under the now salt flat, the cheniers and spits making a zone of
incision in the dune terrain, and exposed roots of old trees. These are not local
scale or short term features. All the evidence from the latter Holocene points to
long term erosion. On the other hand, there may be short term deposition,
27
where eroded sediment finds a temporary repository before being overwhelmed
by the inexorable net coastal erosion.
An example of the engineering implications of this long term erosion is
afforded by the former Derby civil airstrip. Semeniuk in the mid 1970’s, after
concluding that the tidal flats in the Derby area were undergoing massive, net
erosion, alerted the appropriate government agency personnel to the effects of
this prevailing erosion on the western extremity of the Derby Airstrip. No
action was taken then, probably because a solution was not possible to arrest
this erosion. Consequently, however, the airstrip was de-commissioned circa
1992.
The implications, as outlined above, are that erosion will affect man-made
structures.
Superficially, from a consideration of the emplacement of deltaic-estuarine
sediment in the Holocene, and the ongoing contribution from the Fitzroy River,
it would appear that the tidal flats in King Sound are net accreting. The thesis
developed above, from information in Semeniuk (1980a, b,c), is that the area is
in fact in a net erosional situation.
There is an explanation for this net erosion within an area that once had
obviously accreted sediment in the Holocene. In a broader perspective,
Jennings (1975) and Semeniuk (1980b) both ascribed a regional climate change
in the latter part of the Holocene to account for the change from net deposition
to net erosion. Essentially, with a trend to semi-aridity, the sediment budget of
the Fitzroy River changed, and the King Sound system became relatively
“sediment-starved”. Semeniuk (1995), in a continental scale assessment of
climate change in the latter part of the Holocene, related the climatic shift from
humid to semi-arid in the King Sound region to the effects of earth-axis
precession.
In brief, contrary to the intimations of the CER, erosion is a prevailing,
ubiquitous, and long term feature of this area. This has implications for the
project in terms of stability of civil structures (see later), and potential
accelerated erosion patterns resulting from execution of the project.
28
6.7 Estimation of biomass/productivity
The estimation of biomass in the CER is speculative. There are no data.
Similarly, the estimation of the productivity is extrapolated from other studies
elsewhere in Australia. To present conclusions on productivity on mangroves
in this area needs data from this area.
7.0 Critique of investigative reports and proposal:
an engineering perspective
This Section provides a critique from an engineering perspective of the
Consultative Environmental Review (CER) and the overall proposal, to
highlight errors of fact and inadequacies in the information provided. The
issues dealt with below are referenced to the Section notation and heading
numbers in the CER, i.e., bold headings refer to the corresponding section in
the CER.
CER Section 2.1 Overview - paragraphs 2 & 3
These paragraphs refer to the tidal power plant at La Rance in France as having
been in operation since 1966, with a 120 year design life and planned equipment
replacement at 40 and 80 years. Yet the CER indicates that equipment
replacement at La Rance has already begun:
1997 - 1966 = 31 years
NOT 40 years as planned (which would be 2006).
Electrical connection to the first group of generators was made in August 1966.
Final connection of the 24 turbo-alternator sets to the electrical grid occurred
in early December 1967 (Considine 1977).
Corrosion of all marine structures and equipment along the northwest coast of
Western Australia is a major operational problem, and the shortened service life
experienced at La Rance is indicative that the projected equipment service life
in this proposal is optimistic. In addition, such premature equipment failure
creates high maintenance costs and may lead to abandonment of the project
should the operator become insolvent. These matters are not adequately
addressed within the CER and the proposal should not continue until these
matters are fully investigated and an acceptable and satisfactory plan of
remedial action developed to accommodate project abandonment at any stage of
its life.
29
The tidal power station at La Rance also should not be used in comparison with
any proposed structure in the Kimberley for another very important reason. The
site at La Rance is founded on a predominantly rocky substrate (Considine
1977), while that proposed in the King Sound area is to be founded on eroding
estuarine deltaic deposits of mud and sand with a high load of suspended
sediment within the water column.
CER Section 2.1 Overview - paragraph 10
Paragraph 10 states: “The double basin scheme has reduced power output at
neap tides (2-3 days per fortnight at 12 MW) and supplementary generation is
required”.
In essence, this makes the whole project ineffective both in terms of a reliable
power supply and of the claimed benefits of scrapping the Derby and Fitzroy
Crossing power stations. This factor alone should be considered a valid basis
for rejecting the proposal. Stations such as La Rance feed into a large, strong
electrical network from which it can draw power for pumping or inject whatever
power is being generated. In the case proposed for Doctors Creek, the hydro
plant will be connected to an electrically weak network and will frequently
require bolstering by a diesel or gas-fired power plant.
The discussion above suggests that the proposed plant will not provide power at
competitive rates, and this brings the viability of the proposed project into
question. Additionally, it is not possible to establish the exact nature of load
matching or whether peak-lopping may be required, which will also need to
draw upon diesel or gas-fired plant because the CER fails to provide:
1. electrical load curves for the market serviced; and
2. power generation curves for the proposed hydro-plant;
This is a matter that should be resolved before any further consideration is given
to proceeding with the proposal.
CER Section 3.3.1 National and Western Australian Benefits - paragraph 2
The CER states: “Experience would also be gained on understanding and
managing the impacts of this type of project on mangroves and the marine
environment.” This statement suggests very little is known about potential
impacts. In brief, to undertake such a project without experience on the
environmental outcome is irresponsible. In the absence of any other data, and in
absence of consultation with authorities conversant with these matters (such as
the RijksWaterstaat in the Netherlands), the following modelling of impacts at
least should have been undertaken:
30
1. the tidal resonance within King Sound;
2. altered sedimentation/scouring patterns of the estuary or the planned
basins;
3. the groundwater hydrology which will affect both upwelling of fresh
water within the estuary and the fresh/salt water interface upgradient
of the proposed project area.
This predictive modelling should be undertaken prior to any further
consideration of the proposal.
CER Section 4.1 Alternative Sites Doctors Creek Derby paragraph 3
The stratigraphy of the sedimentary formations underlying the proposed site of
the barrage, i.e., the Doctors Creek Formation and the Christine Point Clay, is
described in Semeniuk (1980c). This work indicates that there is an extensive
thickness of mud and sand interlayered with mud on the estuary floor. A basic
calculation of static foundation pressure under the central prism of the barrages
(using a low density of 1325 kg/m3 for the fill) suggests a pressure of about 160
kiloPascals (kPa). This pressure exceeds that allowable for soft clays and silts
(limited to about 75 kPa) and even for firm clays (75 to 150 kPa) - bearing
pressures sourced from Blake (1989). The barrages may therefore sink into the
substrate with some consolidation below the barrages and plastic upwelling of
estuarine mud either side of the barrage. If the consolidation is not uniform, it
could potentially induce barrage failure. This matter is explored further in terms
of the stratigraphic heterogeneity below.
The many stratigraphic cross-sections in Semeniuk (1980c), in fact, show
sedimentary heterogeneity at the scale 1 m - 10 m, so that this aspect is not a
trivial one. Semeniuk (1980c) shows not only thick sections of plastic mud, but
that it is irregularly interposed with 3-4 m thick sections of interlayered mud
and sand, which in turn overlie sand. Under conditions of permanent to more
prevailing saturation as can be expected in the proposed flooded basins, the
sandy sections probably will slump. A corollary is that the heterogeneous
nature of the distribution of sand and mud will potentially create foundation
problems as well as ‘piping’ erosion from underflow or seepage (Blake 1989),
as is abundantly evident along the daily exposed margins of large sand shoals
exposed at low tide.
Paragraph 3 indicates that geotechnical surveys have yet to be undertaken,
which suggests that the proposed foundation system (and hence its construction)
has yet to be determined. In the absence of such information it is impossible to
31
assess environmental impacts from the construction phase since direct
deposition of material, or dredging, or pile driving, or use of cofferdams, all
have vastly different implications environmentally. This issue should be
addressed prior to any further consideration of the proposal. This is amplified
by DeF. Quinn’s (1961, p 148) comment (which is equally applicable to
barrages and breakwaters in this context):
“The character of the bottom may well be the determining factor in
the type of breakwater selected, as it usually difficult, if not
impossible, and expensive to prepare a solid foundation on soft
material for the support of a wall-type gravity structure.” (Italics
added for this report).
In conjunction with the results of Semeniuk (1980c), this clearly points to major
problems in the proposed construction of the barrage in Doctors Creek.
CER Section 5.1 Barrages paragraph 1
In this section of the CER, there is no indication of:
1. the proposed foundation system or construction technique to build the
barrages;
2. the storm surge capability of these structures;
3. how any barrage failures would be rectified;
4. the type of fill to be used from Point Torment;
5. specifically where that fill will come from on Point Torment;
6. the impacts of removing that fill from Point Torment;
7. the mode of transport and deposition of that fill.
This suggests that the CER has been assembled either in haste or on a limited
budget - both of which are likely to result in optimistic construction cost
estimates leading to an unrealistic project viability and (worse), in executing the
construction contracts, contractors will need to ‘cut corners’ to match the work
costs to the estimates. This generally leads to unsatisfactory structures which
are likely to perform poorly, suffer premature failures, or impose high
maintenance costs. High risk projects of this nature need to be fully studied and
analysed prior to consolidating any proposals.
CER Section 5.1 Barrages paragraph 3
In this section on the constructions of the barrages, there is no indication of:
1. the amount of rock to be removed from Point Torment;
2. the suitability of that rock to endure 120 years of marine assault;
3. the impacts of removing that rock from Point Torment.
32
There is, in fact, little or no rock exposed at Point Torment. There is rock at
depth in the Point Torment area, but perhaps the CER meant to refer to Black
Rocks, on the eastern shore of King Sound, a location where ferruginised
sandstone crops out. At any rate, this eastern shore, and Point Torment itself for
that matter, are significant in their own right, and should not be indiscriminately
quarried for rock.
CER Section 5.2 Levees
Although a safety margin on height is given for the levees, there is no indication
as to their capability to resist lateral thrust from the stored water.
CER Section 5.7 Neap Tide Enhancement paragraph 3
The CER states: “... and there is also an option ... to develop a new gas-fired
power station at an industrial estate further out of town”.
A 48 Megawatt gas-fired power station would prove cheaper than the proposed
hydroelectric station to construct initially, and in view of the potentially high
maintenance costs of the hydro plant, may actually provide cheaper power over
its lifetime; a comparative life cycle costing study would resolve this and needs
to be undertaken prior to any further consideration of this proposal.
CER Section 5.11 Decommissioning
For a complex project of this nature being imposed onto a sensitive
environment, a full decommissioning plan should be developed from the outset
to cater for abandonment of the project at any stage. The CER indicates that:
“In the event that decommissioning is proposed, a decommissioning plan will
be developed which will address the removal of plant and equipment”. This is
unacceptable as:
33
1. the timing of such planning would be too late - decommissioning
costs can be very high and often are not provided, thus little or no
decommissioning may occur due to lack of funds leaving derelict
plant, equipment and structures to dissipate naturally (usually
unaesthetically on the landscape);
2. the proposal does not address the civil structures (barrages, levees,
channels, etc.) for either removal or the environmental impacts of
leaving such structures in situ; for example were the proponent to
become bankrupt with only half of one barrage constructed, what
would be the impacts of leaving such a structure in situ?
8.0 Economic considerations
Despite all the positive commentary in the CER in relationship to the French
installation at La Rance, no data are supplied with respect to the economic
viability of the power to be generated at the proposed Doctors Creek site.
A project of this nature requires a complete life cycle costing study which
identifies all costs including:
1.
2.
3.
4.
5.
initial design and site investigations;
construction and its problems, such as failure of the substrate, local
material found to be inappropriate for the filling of barrages or
levees, oil spills from dredges or service barges, etc.;
operation and maintenance, including major component servicing or
replacement such as sluice gates, turbines, raceway maintenance;
contingencies for force majeur such as barrage collapse or
displacement, power transmission line destruction by cyclone, etc.;
final decommissioning of the plant at the end of its service life, or if
the project should be abandoned at any stage, and commitment to all
the restorative work necessary to return the environment to a safe
and acceptable condition.
34
There is another matter in regard to economic factors, and this is in relationship
to the power station at La Rance. Say (1973, p. 6-5) states:
“The only large tidal scheme in operation is that on the River Rance in
Northern France and this, although technically successful, is hardly
economic.”
If this is still the case, then the economic benefits of the proposed Derby Hydro
Power scheme are seriously cast in doubt.
Emplacing barrages and levees within this macrotidal setting on a deep
substrates of mud and sand is an expensive and a logistically difficult and risky
task. There is no documented experience of excavating and emplacing such
structures on such heterogeneous muddy-sandy substrates in settings with such
large tides. VCSRG experience elsewhere in Western Australia (e.g.,
environmental assessment of trenching for emplacing a pipeline though a
mangrove area; and assessment of trenching for bridge foundations, amongst
others), in settings with similar though a lesser thickness of mud, and with lower
tidal ranges, shows that engineers fail to appreciate the difficulties of working
muddy macrotidal environments. Often, the full difficulties of working in
muddy tidal environments only begin to emerge once the project is underway
and the earth-moving machinery is in place, bogged and/or floundering.
The reality in this proposed engineering exercise is that the Doctors Creek
embayment is macrotidal, with spring tides exceeding 10 m, and with an
underlying substrate deep muddy thixotropic sediment. This is an extremely
difficult, expensive and risky environment to work in, and not one that can be
designed from a desk-top. To re-emphasise an earlier point: there is no
experience documented in working in such environments elsewhere, and in
effect, the Derby project will a first attempt globally to attempt such a feat.
Note should be taken that the La Rance hydro-power station is located in a very
different geological (and geomorphicl) setting, with rock basement forming
headland spurs, and sharply defining the estuary banks, and with a rocky island
(Ilot de Chalibert) three quarters of the distance between the left and right
extremities of the dam; there also is a regular rocky seabed which forms a solid
foundation for the dam (Considine 1977). This effectively is the engineering
antithesis of Doctors Creek, a completely different situation which is vastly
simpler in engineering terms. Note also that La Rance setting is not in a net
erosional state.
35
In summary, for this Section on economic considerations:
•
the economic benefits cannot be ascertained until the proponent fully
explores the costs involved in this project
•
the La Rance model for tidal power is not considered to be economic
(Say, 1973)
•
there probably will be large costs and risks involved in the emplacement
of the barrages and the levees because of the enormous logistic
problems of working in this difficult tidal flat environment
•
the La Rance installation is situated in a rock-bordered and rock-floored
embayment, with a regular rocky seabed, and thus cannot be used as a
model for the Doctors Creek situation.
CER Section 2.1 Overview - paragraph 9
The last sentence in this section of the CER states: “Six 8 MW or four 12MW
turbine-generators would be installed in concrete structures producing up to
210 Gwh per annum”; which equates to an average output of about 24
Megawatts (continuous) over an 8766 hour year which is half the installed
generating capacity. This represents a significant under-utilisation of
equipment placing a cost penalty on the power delivered from this project. The
CER lacks a cost-benefit analysis, hence it is not clear whether this underutilisation has been factored into assessing the economic viability of the project.
The CER also does not assess how competitive the hydro-power is in
comparison to conventional power plants (Note comment by Say 1973 under
Economic Considerations).
CER Section 2.1 Overview - paragraph 11
In relationship to mentioning the Broome power plant, the CER here fails to
address two points: 1. who will maintain the Broome power plant “in the short
term as a backup”, and 2. whether the cost of maintaining this station has been
included in the operational costing for the proposed project. It is doubtful
whether on the scale of proposed hydro-power generation that the proposed
project would be capable of carrying such an extra cost burden.
36
CER Section 4.1 Alternative Sites Doctors Creek Derby paragraph 3
The mooted possibility of “ongoing siltation of basins” implies a significant
maintenance cost and may threaten the economic viability of the project. Such
an impediment should be thoroughly investigated at the outset, at least in a
theoretical sense so that subsequent site investigations can be kept to a
minimum both as a cost saving measure and to minimise environmental
disruption.
Semeniuk (1980c) shows massive erosion of the tidal flats in this region, a
process that will not cease because a tidal power station has been built. Massive
erosion means on-going large-volume sediment transport, a factor that is likely
to result in large amounts of siltation.
37
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