|
Location
Landform
Geology
Soils
Climate
The physical environment affects all aspects
of creeks and the associated biota. Geology and landform determine the
soils present. Climate influences the flora and fauna and how they
behave in an area.
The landform is particularly important in
determining the types of streams that develop in an area. The geology
will influence the chemistry and erodability of the surrounding soils.
Flow patterns reflect the seasonal fluctuations in climate. All factors
combine to produce the local ecological patterns and processes. In an
urban catchment like Kedron Brook, these patterns are overlaid by the
impacts and constraints of human land use.
Back to top
Location
Kedron Brook lies to the north of the
Brisbane CBD. It rises in the D’Aguilar Ranges east of Brisbane where
there are two main tributaries, Kedron Brook and Cedar Creek. The
uppermost sections of Kedron Brook are ephemeral gullies draining the
southern slopes of the Samford State Forest section of Brisbane Forest
Park.
Cedar Creek drains the northern slopes of Mt
Nebo including Bellbird Grove and Camp Mountain Reserve. It joins
Kedron Brook at Ferny Grove to the west of the Keperra Golf Course.
From here, the stream meanders with an almost permanent flow through
the well-established urban areas of Arana Hills, Mitchelton, Everton
Park and Grange. Low hills on either side of Kedron Brook confine the
meanders on the coastal plain.
Sandy Creek joins Kedron Brook at Grinstead
Park (Alderley). This tributary drains bushland in the Enoggera
Military Camp then flows through urban and industrial land before
entering Kedron Brook. Although Kedron Brook has been channelised
through the Lutwyche, Wooloowin and Toombul reaches, extensive areas of
open parkland or bush are associated with the floodway. Downstream from
Toombul the channel is under a tidal influence. The original channel
has been modified and re-routed to the north to drain the site of the
current Brisbane Airport. Kedron Brook enters Moreton Bay on the
southern boundary of the Boondall wetlands.
Back to top
Landform
Landforms are a consequence of erosion and
deposition. Landforms within Kedron Brook catchment have also been
influenced by sea-level changes and geological history of the area.
Kedron Brook flows from the foothills of the
D’Aguilar Range through undulating hills of the upper and middle
reaches of the stream. Here the flood plain is broad and the stream
meanders through scattered hills in the landscape.
As the stream flows towards Moreton Bay, it
passes through hills of several geological types. The lowermost
sections of the stream pass though low-lying tidal areas that have been
re-engineered for the development of the Brisbane Airport. Prior to the
original airport development, the tidal areas were a complex of
low-lying swamplands and mangrove flats.
Back to top
Geology
Geologically the Kedron Brook catchment
contains several of the formations occurring in the Brisbane area. This
diversity of geological types is reflected in the diversity of
landforms occurring in the area.
The oldest rocks in the catchment are
metasediments called the Nerangleigh-Fernvale formations, which is
widespread in the Brisbane area. These 240 million year old rocks were
deposited as sediments that have been crumpled and folded, then
uplifted. They were once part of a major mountain range that has been
lowered by erosion over millions of years.
A period of volcanic activity over 200
million years ago led to larva flows that form the Brisbane Tuff. These
rocks are best seen at the Kangaroo Point Cliffs and can also be seen
at the Windsor Quarry (Lutwyche Road). Brisbane Tuff forms the hills
around Lutwyche and Kedron.
As streams matured following the volcanic
activity, swamps formed. Swamp vegetation, mud and clay deposited in
swamps were compacted to form coal. Coal deposits in the Kalinga area
were worked early in Brisbane’s history; they supplied coal to the
local area. The deposits were too small for long-term production.
Basalt lava outcrops occur in the Clayfield
and the Nudgee areas. These soils erode to red clays and were exploited
for agriculture early in Brisbane’s settlement.
Terraces in the vicinity of Nudgee are
remnants of a higher sea level that existed about 60,000 years before
present. At this time of higher sea-level sediments from the eroding
mountain ranges were deposited on the floodplain. These now form the
substrate between rocky hills in the middle and lower reaches of Kedron
Brook.
The original mouth of Kedron Brook was a
former channel of the Brisbane River that has migrated south over
time.
Back to top
Soils
The soil in an area reflects the geology and
climate of the location. In the Kedron Brook catchment, soils on hilly
areas are generally stony, clay and often nutrient poor.
Soils that have developed on the alluvial
terraces tend to be sandier, and even more gravely. These were more
fertile and exploited for early agricultural activities. Finer clay
soils are associated with more recent sediment deposits in the lower
catchment.
Urban soils differ in
many ways from the soils under natural vegetation.
Back to top
Climate
Brisbane has a subtropical climate with hot
wet summers and a mild dry winter. The temperature lies within levels
suited to biological growth during the whole year, thus a diversity of
flora and fauna have developed in the region.
Most of Brisbane’s rain falls in the summer
months and early autumn. Rainfall patterns affect streamflow. During
summer and autumn, Kedron Brook experiences periodic floods in response
to intense rainfall in the catchment.
During the dry winters, the level of flow in
Kedron Brook drops. A steady flow is maintained in the mid and lower
catchment due to discharge from the surrounding water table. Low
humidity at the end of winter can greatly increase the water loss
through evaporation, particularly from areas of standing water.
Variable rains in winter lead to conditions of moisture stress for
plants during the period August-December.
Summer rainfall conditions, high
temperatures and high amounts of solar radiation provide conditions for
rapid growth for many plant species.
The climate in urban areas is often
3-4ºC warmer than surrounding rural or natural areas. Urban Climate
Back to top
|
