Metropolitan Melbourne Investigation Discussion Paper - Victorian ...

freshwater from the river was a key reason for the
establishment of Melbourne. Over the years, the river has
been altered in many ways by the straightening of several
sections and the carving of new channels.
The catchment of the Yarra River is the largest of the
region at some 4,000 square kilometres. The upper
Yarra catchment provides the majority of Melbourne’s
drinking water. 40
Other major rivers of the region include the Maribyrnong
River, one of the few large rivers developed on the volcanic
plains north and west of Melbourne, and the Werribee
River, which forms a broad, delta-like alluvial plain edged
with spectacular cliffs and coastal salt marshes. Many
watercourses provide the basis for natural linkages of
public land across the investigation area (e.g. Merri Creek
trail, Dandenong Valley Parklands, Plenty River Parklands).
Figure 2.3
Major catchments and waterways in the
investigation area
River and stream condition
The condition of waterways is measured by the Index of
Stream Condition (ISC). 41 It integrates the condition of river
hydrology, water quality, streamside zone (vegetation),
physical form (bed and bank condition and instream
habitat) and aquatic life. The index measures the change
from natural conditions and indicates the capacity of the
waterway to support a diverse biological community.
In essence, it is a measure of change from natural or
ideal conditions for all Victorian streams at a common
point in time. This allows different types of streams to be
compared across Victoria.
River and streams in the hilly, forested areas in the
north-east of the investigation area are generally in
better condition than those further downstream in more
urbanised areas. None of the rivers and streams within
the investigation area is in excellent condition, with only
a small percentage in good condition. Most rivers and
streams are in poor condition, largely due to land use
changes such as urbanisation, vegetation removal,
drainage and fl ood control works, stock access, increased
storm water runoff and invasion by weeds. The lower
reaches of some rivers such as the Yarra and Mordialloc
Creek are so heavily modifi ed that they contain almost
no natural streamside vegetation. 17
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