Yarra Yarra Catchment
Management Group
PO Box 14, Kalannie WA 6468
Ph (08) 9666 2140
Fax (08) 9666 2130
Email: yycmg_kalannie@westnet.com.au
Offset planting for proposed drainage in the Mongers area, Yarra Yarra
catchment (Clearing Permit CPS 1969/1)
Dr Ian Fordyce
Project Officer, Yarra Yarra Catchment Management Group
Kalannie
(08) 9666 2140,
yycmg_kalannie@westnet.com.au
20 June 2008
The vegetation and offsets described in this proposal are confined to the section
of the proposed drain south of Taylor Rd. An offset plan for the section north of
Taylor Rd has already been submitted (5/5/08) and approved in your letter dated
17/5/08.
Pre-drain Vegetation
The existing vegetation subject to this permit is low shrubland/herbland
dominated by the chenopod genera Maireana (bluebush), Atriplex (saltbush), or
Sclerolaena (bindii). A large remnant of York gum woodland immediately south
of Taylor Rd (defined in the Decision Report as Plan 1961/1b) is severely
degraded. Almost all of the canopy trees along the route of the proposed drain
are completely or near-completely defoliated (and probably dead), the
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understorey is a relatively simple community of salt-tolerant colonists, and there
are salt efflorescences on the ground.
In general, there are few trees or shrubs along the proposed drain-line.
However, by analogy with apparently similar landscapes in the rangelands, and
from the species make-up of volunteer vegetation, uncleared paddock trees and
remnants, we infer that the pre-European vegetation was probably a York gum
woodland, with patches of myrtaceous (mostly Melaleuca spp. and Thryptomene
spp.) and wattle (Acacia spp.) shrubland.
The drainage lines, at that time, were probably no more than chains of ill-defined
water-gaining sites. The chenopod-dominated vegetation, which now
characterises valley floors throughout the region, is a post-clearing phenomenon.
It is a response to the rise of saline water-tables over the last few decades. In
some cases, the spread of such vegetation over previously productive farmland
can be attributed to particular events (e.g. the 1999 floods).
If drainage is successful and the local watertable is lowered even a few tens of
centimetres across the valley floor, then it is unlikely that salt- and waterloggingtolerant communities, such as samphire, will survive. Our plan is to resurrect the
pre-European vegetation – or something that resembles it.
Design
The excavation we envisage is a double-leveed deep drain, with shallow drains
on either side (outside the spoil banks) to carry surface water (Fig. 1).
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Fig.1. Cross section of proposed drain, showing the separation of groundwater
and surface water.
A system of buried pipes and flow-on areas will ensure that groundwater and
surface water can be kept separate until the final discharge. There are a number
of advantages with this design.

Peak flows after storms are reduced, which means that there is less
erosion and decreased maintenance requirements.

Road crossings, which are an expensive component of drain construction,
do not need to be so elaborate.

Groundwater is likely to be hypersaline and might also become acidic and
moderately toxic. If a requirement develops for pre-disposal treatment,
then it would be easier to deal with a discrete and steady flow.

Surface water, which is relatively fresh, can be redirected as required to
revegetation plantings on the valley floor.
Other distinguishing features of our design are that the spoil-heaps will be
draped-over with topsoil and will be closely revegetated with grass and shrubs.
The entire drain complex (deep drain and shallow drains) will become the core of
a 100 m-wide revegetation corridor (Fig. 2). This is expected to provide
biodiversity benefits to the landscape by creating new habitat and linkages
between existing remnants. From a distance, the earthworks themselves will be
barely visible. In ecological terms, however, the complex will function as a
rehabilitated waterway.
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Fig. 2 Idealised cross section of a rehabilitated waterway.
All affected landholders have signed a memorandum of understanding, which
grants the Yarra Yarra Catchment Management Group an easement over a 100
m-wide strip (centred on the drain) for the express purpose of revegetation. The
total revegetated area between Simpson Rd (north) and Taylor Rd (south) will be
approximately 49 ha.
Revegetation
Many of the plantings will be broombush (Melaleuca atroviridis of the M. uncinata
complex in non-saline situations; the slower-growing but more salt-tolerant M.
hamata in places currently supporting samphire); tubestock of both species will
be grown from locally collected seed. Seedling densities are taken from
Greening Australia recommendations

Twin rows, 2 m apart, then 4 m gap.

Seedlings at 1 m intervals along planting line

Effective stocking density = 3400 stems/ha (i.e. approx. 2200 stems/100 m
drainlength)
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Some areas, unsuitable for broombush plantations, will be dedicated to
biodiversity plantings; various species – small-medium trees and shrubs, planted
5-8 m apart, not in obvious rows (purely for aesthetic reasons); dense thickets
planted at random locations to provide cover for woodland fauna; understorey
initially of mixed chenopods (mostly Atriplex spp. and Maireana spp.), later (as
soil becomes less saline and less sodic) replaced by various woody shrubs,
planted only 1-3 m apart; all plantings from tubestock, direct seeding of
groundstorey species after several years; all from local seed-collections.
Species will be selected from the following list, according to local soil type, seed
availability and the make-up of existing remnants. Final species choice will be
influenced by experience of other local groups, e.g. Buntine-Marchagee Land for
Wildlife Group, Morawa Farm Improvement Group, and also by landholder
preference.
1.
Colluvial flat (red-brown earth)
Eucalyptus loxophleba ssp. supralaevis
E. loxophleba ssp. lissophloia
(York gum)
(oil mallee)
E. myriadena
E. brachycorys
E. spathulata
Casuarina obesa
(swamp sheoak)
Melaleuca eleuterostachya
M. lateriflora
M. uncinata complex
(broombush)
M. adnata
Acacia obtecta
A. microbotrya
(manna gum)
A. jennerae
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A. brumalis
A. eremaea
A. hemiteles
(tan wattle)
Hakea preissii
(needlebush)
Maireana brevifolia
2.
(small-leaf bluebush)
Colluvial flat (clay)
Eucalyptus loxophleba ssp. supralaevis
E. loxophleba ssp. lissophloia
Casuarina obesa
(York gum)
(oil mallee)
(swamp sheoak)
Melaleuca adnata
M. eleuterostachya
M. lateriflora
M. acuminata
M. uncinata complex
(broombush)
Callistemon phoeniceus
Acacia hemiteles
(tan wattle)
Hakea preissii
(needlebush)
Maireana brevifolia
3.
(bottlebrush)
(small-leaf bluebush)
Alluvial flat (sand over clay)
Eucalyptus loxophleba ssp. supralaevis
E. salicola
E. sargentii
(York gum)
(salt gum)
(Salt River gum)
Melaleuca halmaturorum
M. uncinata complex
(broombush)
M. eleuterostachya
M. lateriflora
M. acuminata
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M. thyoides
Acacia eremaea
A. hemiteles
(tan wattle)
Pittosporum angustifolium
Maireana brevifolia
(weeping pittosporum)
(small-leaf bluebush)
Timing
Timing and ground-preparation will be informed by 6-monthly monitoring of soil
condition, particularly salinity and sodicity. Experience nearby suggests that
newly drained soil needs at least two good winters to flush enough salt out to
support trees and shrubs. Sodic soils and soils that remain incompletely drained
might require special treatment, e.g. deep-ripping and gypsum application for
sodic soils, mounding for poorly drained sections. In the meantime, samphire
and other salt-tolerant plants will be encouraged to recolonise cleared areas near
the drain itself, to provide at least some plant cover.
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