Phone: 0417641440. Web: LRAM.COM.AU E: [email protected]
PO Box 79 Kalbar Qld 4309. 1569 TAROME ROAD, MOORANG VIA KALBAR, QUEENSLAND
4309
Review of the Agricultural Impact
of a
proposed solar farm.
Various Lots
D’Aguilar Highway
Harlin
Prepared by
Bill Thompson
Wednesday, January 17, 2018
M 0417641440
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Summary
The project is located partially on lands that are designated as ALC A and B lands. This
designation is based on the Brisbane Valley soils report soil unit boundaries of 1999. The
report amongst other findings concluded that there were no lands at the project site suited
for cropping of field crops. The work did however conclude that the soils would be able to
support annual irrigated horticulture but provided no data on whether irrigation itself was
feasible in this area.
The soil mapping is in error in a number of key matters impinging on this project. There is in
fact an extensive area of cracking clay soils along the northern edge of the project site that
is suited for dryland cropping and on this basis alone those areas are ALC A. At this stage
there is no intent to locate panels on these flood prone lands.
The other significant error is that the lower and mid slopes of the area to the south of the
alluvial plain includes land as ALC B which comprise stony, shallow, dispersive texture
contrast soils which are in fact ALC C – suited to pasture use only.
It is proposed that this area will be in the panel array as well as extensive areas to the south
comprising hilly terrain. The panel array area has significant existing erosion due to grazing
pressure and excessive clearing. This report recommends that ground cover be increased in
these area by reducing or eliminating grazing pressure and pasture improvement. The
report also recommends that the feasibility of detention basins within the panel area and on
the alluvial plain be established in order to minimize the export of sediment from the
project site.
Buffering requirements for a project of this type are likely to be minimal. The property
boundary to the location of the possible panel array ranges from 250m to over 1.2 km.
1 The Project
The project covers 17 rural lots bordering the D’Aguilar Highway with a total area of 2055
ha. The project would involve 1500 ha of solar infrastructure located approximately in the
mid to upper slopes.
This report reviews current land use and the associated soils and landscapes and examines
the likely consequences for agricultural land use within the subject land as well as on the
general area.
2 Current Land Use
The subject land forms part of 3 separate grazing properties. Grazing of nominally improved
pastures along with associated management infrastructure such as yards, sheds and
dwellings is the only substantive current land use.
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With the exception of small parts of the creek line along the north western boundary and
small areas of mostly regrowth scattered along the ridge crests, the whole of these
properties have been extensively cleared.
There is little significant evidence of sustainable improved pastures in these cleared lands.
The one exception is along the northern creek line where better quality soils occur.
One feature of the land use is the absence of reliable stock water supplies in other than the
northern lower slopes where the creek line and smaller stockwater dams are located.
2 Soils and Cropping potential
Figure 2.1 attached to this report contains soil and Agricultural Land Class (ALC) boundaries
overlaying satellite imagery.
That figure is based on 1:50,000 scale soils and land suitability mapping1 along with field
inspection of the subject land completed 11th December 2017.
2.1 Soil Survey and Land Suitability and the Agricultural Overlay
The soil survey report maps and describes soil groups as well as Hills and Mountains
landforms. That report at Section 6.3 and Table 38 (commencing on page 79), sets out an
Agricultural Land Classification (ALC) for the area.
The soil map unit boundaries appear to be the basis for the Agricultural Overlay (OM1) for
the planning scheme which shows parts of the mid and lower slopes as either ALC A or ALC
B. The land suitability section of the soils report and the land suitability maps associated
with that report shows that none of the subject area is mapped as suitable for dryland
cropping but that parts of it which corresponds to the OM1 overlay are suited for irrigated
small crops such as melons pumpkins etc. The soil survey report qualifies the irrigation
suitability assessment because there was no assessment of whether irrigation water is
available or not.
2.2 Soils
The 5 major soils mapped by QDNR comprise three differing land forms and soil groups. The
results of our field inspection and these groups are summarized in Table 2.1 and form the
basis of Figure 2.1. A photo montage of the landscape erosion is given in Table 2.2.
1 B.P.Harms and S.M. Pointon (1999) Land Resources Assessment of the Brisbane Valley, Queensland. QDNR
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Figure 2.1 ALC
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Table 2.1 Soils and Land Suitability based on QDNR report and field observations.
Alluvial Plains – some within 1:100 flood line
Cooeeimbardi
and Basel
Grey and dark cracking and non
cracking clays, some areas prone to
excessive wetness.
Moderately suited to
dryland cropping as
well as irrigated
cropping. Location
close to major stream
increases possibility
of some irrigation
These areas
would be ALC A
and are mapped
as such in Figure
2.1
There are major areas of Spencer soils
on these plains mapped incorrectly in
the QDNR mapping. The area of
alluvial plains is greater than that
which is indicated in the QDNR
mapping.
Lower and footslopes, convex slopes of 1 to 5% derived from Neara volcanic – described by QDNR as mid and high terraces.
Spencer These are texture contrast sodosol
with bleached sandy surface soils.
Rock outcrops occur in 15% of the
area where soils may be less than 60
cm deep.
Unsuited to cropping.
Stone soil depth and
soil water
storage/availability
are the main
limitations.
These areas
would be ALC C1
– suitable to
sustain improved
pastures. They
are mapped in
the Overlay as
ALC B … some
areas as A.
As shown in Figure 2.1, approximately
155 ha of severe and moderate gully
erosion occur in these areas out of a
total area of around 500 ha. The QDNR
mapping did not map erosion
separately but did report that erosion
in these landscape is significant.
Middle and Upper Slopes of Neara Volcanics and Sandstone areas. slopes 3 to >15%
Various soils,
including
Linville,
Moore,
Dunwich
These area shallow often stony rock
outcrops areas with both dispersive
texture contrast (Moore) and non
dispersive (Linville) soils
Unsuited to cropping These area ALC
C2 lands – suited
only to native
pastures. Some
areas would be
ALC D.
In Figure 1 these areas are included
with the mountain and hill units as ALC
C2. Erosion is extensive in these area
as well including minor areas of slope
instability
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Table 2.2 Landscape photos
Unstable gully head erosion in middle and upper slopes
Unstable erosion on Spencer soils in lower and mid slopes
Unstable stream banks on alluvial flats – eastern end of site
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2.3 ALC, State Interests and Agricultural Land Overlay Code
The project site along with most of catchment in which the subject land lies does not fall
within the state defined IAA.
The 2017 SPP and the council Agricultural Land Overlay Code have broadly similar
requirements and are dealt with as one in this report.
Both the state interest and the overlay code centers around whether the site lies within an
Important Agricultural Area (IAA) and/or contains ALC A or B lands. In essence lands within
these categories ought to be protected from fragmentation and from the development of
land uses which would be in conflict with agricultural uses.
The land in this valley does not fall within a state defined IAA.
The agricultural overlay map includes some of subject land as ALC A and B, however
this is only relevant if irrigation is available (see Section 2.1 above), otherwise only
the alluvial plain areas are ALC A or B. All other areas south of the alluvial plain
(shown as ALC A) in Figure 2.1 are in fact pastoral quality land.
Given that the solar farm land uses will be located mostly in the middle and upper
slopes and not in the lower elevation lower slopes and alluvial plain, nonagricultural
uses will be restricted to lands which are not ALC A or B.
Other matters canvassed in the Overlay code deal with fragmentation. The proposal does
not involve any lot re-configuration nor does it fragment the actual location of the ALC A
lands.
Whilst the issue of land degradation is not dealt with in the State Interests or Overlay Code,
the issue of improved natural resource outcomes by minimizing land degradation will be an
important component of this project.
3 Land Degradation
The extent of currently unstable gully and rill erosion is shown in Figure 2.1. Almost all of
this erosion is on the Spencer soils which have sodic subsoils and once groundcover and
surface soils have been disturbed, these soils rapidly erode.
Apart from the erosion prone nature of these soils, overgrazing which has minimized surface
soil cover along with the extensive clearing and concentration of livestock around water
points are the primary causes of this unstable erosion.
Reducing the grazing pressure to increase ground cover along with some judicious pasture
improvement and exclusion of livestock from the worst affected areas would be needed to
stabilize these areas.
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4 Agriculture Impact
4.1 Impact on Cropping Area
The project does not involve the construction of solar panels on most of the area identified
as ALC A. This area is largely within the 1:100 m flood line on the alluvial plain. All runoff
from the proposed solar farm area must pass through this ALC A area and if the area is
maintained under improved pasture and conservatively grazed, this will act as a filter and
runoff detention area for the solar panel part of the catchment.
4.2 Impact on Grazing Land Use
It is common for solar farms to use a combination of grazing and physical slashing of
vegetation to control excess grass and woody weed growth. Grazing is often the preferred
method where it can be carried out without adversely affecting the solar farm itself. Key
matters that need to be focussed on are:
• Grazing land management that maintains ground cover to minimise erosion.
Typically 50% ground cover is a conservative minimum objective and this is best
obtained by the use of improved pastures and a paddock management system that
allows for livestock to be rotated through paddocks. Because of the extensive
erosion on the site, no grazing should occur until full ground cover is established and
the pastures have seeded. This may take up to 2 years.
• If and when grazing is re-introduced, the areas mapped as gully erosion in Figure 2.1
should be fenced off and livestock excluded. There will be some regeneration of
woody weeds over time. It is unlikely that these areas will ever be sustainably
grazed in the future for other than excess ground layer fuel control.
• Improved stockwater systems.
5 Erosion and Stormwater Management
For this project site, erosion and stormwater management plans will be the critical
elements. Whilst the impact of the solar panels on stormwater has not formed part of this
assessment, there are four major aspects of stormwater management that should be
addressed:
1. Whether grazing in some form continues on the site and on the panel area. The high
rates of existing erosion and associated runoff are a product of intense grazing and
clearing. If grazing intensity is reduced, runoff intensity and amount will decline as
ground cover is improved.
2. Offsetting the above effect will be increased runoff from the panel field – due solely
to the increased hardening of the catchment. Strategies to mitigate or off set this
will need to be incorporated. Strategically located small detention basins and
diversion bank structures may need to be incorporated in the stormwater design.
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3. The main alluvial plain with a partially unstable riparian zone will be mainly outside
the panel field. However, larger detention basin approaches that slow down the
passage or water and sediment from the panel field through this area will also be
worth considering.
4. The actively eroding areas shown in figure 2.1, will need to be stabilised and
strategically revegetated.
5 Buffering and Revegetation Requirements
5.1 Buffering
Buffering to adjoin land uses is normal for these types of developments and is particularly
important in closer settled or in intensive agriculture areas. Terrain aspects also plays a
major role in the importance and design of buffers.
For this project site, the following features are important considerations in assessing the
need and type of buffers.
1. The site has a northerly aspect facing towards the highway.
2. The panel field will range from be over 250 m from the highway and will be up
aspect of the highway. This should be a sufficient distance buffer. It is unlikely that a
feasible design of a visual screen buffer of sufficient height at this offset from the
highway could be put in place.
3. The southern aspect is up aspect from the panel array and high hills essentially
provides for the buffer requirements in the southern aspects.
4. In the eastern and western end, a series of low hills also provides a buffer with the
proposed panel field over 250 m from the property boundary.
5.2 Revegetation and pasture improvement requirement
Table 5.1 contains a list of species likely to be best adapted to both buffer and pasture
improvement/soil conservation requirements.
Table 5.1 Revegetation List
Species
(Common Name)
Use Comment Restrictions
Common black Ti
Tree
Sally Wattle
Mountain She
Oak
Gum Top Box
Gully head
stabilisation... plant at
200 /ha
Plant as advanced
seedling tube stock into
20 cm deep rip lines
holes with gypsum added
Do not use
lime.
Lightly fertilise
and plant after
October rains,
water in.
Local provenance
blue gum on flats,
iron bark on
slopes for upper
Landscape Screening
where needed to up
400/ha
These will grow to 20
plus meters, however for
screening purposes they
should be coppiced at 5 -
10 m high
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Species
(Common Name)
Use Comment Restrictions
story and river
she oak
Local provenance
bottle brush,
wattles for mid
story
These will have life times
of 5 to 10 years,
coppicing of upper storey
species will provide infill
effects after senescence
of these species.
Improved
Pastures on
alluvial plain
Use Katambora Rhodes
over sown with
Setarias. Other species
such as Kikuyu and
Creeping blue are slow
to establish and will
not compete with
these pastures.
These will provide
permanent ground cover
and be excellent
sediment traps.
Only lightly
fertilise
otherwise these
pastures will
become rank
and generate
high fuel loads.
Improved
pastures on
slopes
Use Callide Rhodes and
Creeping blue grass in
combination with
Wynn’s Cassia (pasture
legume).
Fertiliser is the key to
maintenance of these
pastures. A compound
fertiliser such as MAP or
DAP should be used and
seed planted into a burnt
native pasture in late
Spring early summer.
Most improved
pasture species
can be used.
Leucaena which
is extensively
grown in the
Somerset area
should not be
used. It is a
browse legume
that can grow
to over 10 m
height unless
heavily grazed.
