Kedron Brook Physical Environment

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.

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.

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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.

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. 

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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.

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. Refer also to History of urban development.