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A particular water regime will favour certain species.
It will therefore affect the composition of the community
developing from seeds and eggs in the soil.
Continuous flooding and drying creates habitats that are
similar over large areas for long periods. When water
levels fluctuate, habitats change in conjunction with
the water levels. The variety of habitats then created
within the wetland encourages diversity amongst the biota.
Rapid flooding and drying induced by pumping water into
or out of a wetland is often stressful for plant establishment
and growth. Allowing water levels to fluctuate naturally
favours the biological diversity of a wetland.
(Taken from: Brock, M.A., Casanova, M.T., Berridge, S.M.,
(2000). Does your wetland flood and dry? Water regime
and wetland plants. LWRRDC, UNE, DLWC and EA.)
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| A wetland is an ecosystem
affected by water. There is great diversity in wetland systems
due to differences in their location, origin, water regime,
water chemistry and vegetation, soil and sediment characteristics.
Wetlands are one of the most biologically diverse and
productive ecosystems on earth. They occur on almost all
continents (except Antarctica), in all climatic zones,
on the coast, inland, and can be formed naturally or man-made.
They provide food, fibre and medicines, a buffer from
storms and floods, and act as water filters. They provide
windows into the past, habitat for a wide range of plants
and animals, a place of beauty and tranquillity. Wetlands
are also one of the most threatened natural systems in
the world.
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 Work
has commenced to understand the environmental implications
associated with the eventual Lake drawdown process.
Although many storages are drawn down to very low
levels every year to supply irrigation demands,
none have been drawn down for the purpose of preparing
the area for one of the biggest wetland rehabilitation
projects attempted in Australia, or the world.
The research and learning opportunities presented
by the rehabilitation project are enormous. Although
there have been numerous wetland rehabilitation
projects undertaken throughout Australia and the
world, the majority have been introducing water
back into areas previously denied natural flooding
events. The Mokoan Wetland rehabilitation project
is unique in that it is about reviving a literally
"drowned" environment.
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 Lake
Mokoan was designed and constructed by the former State
Rivers and Water Supply Commission and commissioned in 1971.
The primary purpose of the project was to harvest and store
water to assist Lake Eildon supply irrigation for the Goulburn
and Murray irrigation systems.
As dams are often the most significant and direct modifiers
of natural river flows, the decommissioning of Lake Mokoan,
is a key step towards returning a more natural water regime
to the Broken System.
Water regime is the term used to describe the pattern
of water presence and absence in a wetland. Wetlands include
standing water such as ponds, puddles and dams, as well
as flowing water - creeks, streams and rivers.
There were in excess of 300 separate assets built to operate
and manage Lake Mokoan as a storage facility. These assets
have been identified and assessed to determine whether
they should be retained, removed or rendered inoperable.
The assessment process involves identifying risks of implementing
any one option, compared with the current situation. Risks
to the community, environment, and the future management
of the land in question on a wide range of issues e.g.
safety, flooding, public liability will be considered.
| Major infrastructure
components that are under investigation are outlined
in the following table. |
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Inlet Works
-------------> |
- Inlet
Channel |
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- Broken
River Diversion Works |
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- Blind
and Kennedy's Creek Crossing |
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- Holland
Creek Diversion Works |
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- Channel
Drainage Works |
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- Bridges |
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- Measuring
(Drop) Structures |
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Dam Structure
----------> |
- Embankment |
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Outlet
Works ------------> |
-
Intake Tower |
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- Outlet
Culvert |
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- Outlet
Channel |
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- Channel
Drainage Works |
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-
Bridges |
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- Measuring
(Drop) Structures |
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A Draft Asset Decommissioning Package is under preparation
by Goulburn-Murray Water and consultants GHD. Refinement
of options now involves two steps:
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Further hydraulic studies
to understand drainage patterns and requirements along
each of the inlet and outlet channel alignments and
catchment areas. |
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Consultation - this
process will require consultants to visit each of
the landowners adjacent to the inlet and outlet channels
and the embankment to identify any issues which need
to be taken into account in order to formalise a final
draft Asset Decommissioning Package. This process
will also include discussions with council and other
road, rail, communications, power and emergency service
agencies. |
The Draft Asset Decommissioning package will provide
recommendation on the future of each of G-MW's assets, including:
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Recommendations
for the embankment opening and the outlet structures, |
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Preliminary
plans for embankment opening, concrete removal and
the removal and protection of other structures, |
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Identification
of any significant safety issues and actions to address, |
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Identification
of any socio-economic implications, |
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An estimation
for the above works and an implementation program
for the timing of the above works. |
The draft Asset Decommissioning Package will also be reviewed
and enhanced by input from the Lake Mokoan Future Land Use
Steering Committee before its release for broader community
review and comment.
The actual works associated with the decommissioning
of assets will not commence until after harvesting of
water ceases in 2008/09
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