The Kedron Brook

The Kedron Brook is a natural water body which flows from the D'Aguilar Range through the northern suburbs of Brisbane, before emptying into the Schulz Canal at Nudgee Beach. Descending over 220 metres throughout its 29km length, the Kedron Brook is an essential component of the local environment, sustaining a diverse and critical ecosystem. Additionally, it holds a unique status to local traditional landowners, who have been actively involved in its conservation for thousands of years. Over the past 20 years, growth in population and urbanisation paired with the escalating effects of anthropogenic climate change have induced a manifold of geographic challenges to the land cover of the Kedron Brook.

The primary focus of this investigation is to evaluate the anthropogenic and biophysical impacts of urban development on the Kedron Brook. In particular, a focus will be drawn on the increased vulnerability of the site to erosion, and how the consequences of urbanization will entail future anthropogenic and biophysical effects. Quantitative data will be collected through samples assessing water quality, while qualitative data will be collected in the form of visual assessments made on local ecosystem populations, water erosion, and pollution. As majority of the quantitative data yielded ideal results, this report will focus on the qualitative data to identify how the lack of riparian vegetation (as a consequence of urban encroachment) resulted in increased erosion. It is important to note that the primary data will be collected in ideal conditions in specific locations, although recent flooding may have impacted the results (Figure 1).

Secondary data was incorporated into this investigation for the purpose of evaluating long-term impacts. Notable instances of this include the use of ArcGIS WayBack imagery, statistics from landcare organizations and federal databases, and diagrams.

The most important change observed in Figure 3 was the removal of the Riparian vegetation to make way for hard surface development. . This coincides with the created land use map, which suggests urban encroachment has resulted in Site A consisting primarily of LR Low and MR Medium density residential land use (Figure 3). The various infrastructure expansions observed impact the local ecosystem in various ways, such as motorways increasing air pollution, residential expansion displacing wildlife populations, and chemicals being released into the environment via urban runoff.

Land change in Site B consists of a major airport expansion initiated in 2015. This development is displayed in both the swipe map below (Figure 5) and in the Site B land use map (Figure 4). This expansion resulted in both mangrove area clearance and the Schultz canal having to be manually diverted.

The Kedron – Gordon Park area population has undergone an accelerated period of growth since 2007 (Figure 6). Figure 5 also indicates an increase in semi-detached housing and apartments to accommodate for this population growth. This replacement of low-density housing with high-density housing indicates urban consolidation, which further contributes to erosion and urban runoff.

The principal consequence of these land transformations was the mass clearing of riparian vegetation along the banks of the Kedron Brook. The Riparian zone plays a critical role in the local ecosystem, preserving waterway health through biophysical processes such as infiltration, soil profile stability, and providing shade (Figure 7).

There was extensive damage to the Riparian zone at Site 1, primarily due to flooding and heavy urban development. However, thanks to directed conservation efforts through zoning, the mangrove areas at Nudgee Beach were largely intact. 

Impervious, developed surfaces such as bike paths drastically increase the rate of flow during rainfall and flooding, therefore increasing the severity of urban runoff. This is due to the lack of natural vegetation to slow and filter this flow. Furthermore, the construction of these bike paths has greatly impeded the riparian zone, reducing its length from 14.2m to 9.3m (Figure 8).

The loss of Riparian Vegetation entails a plethora of anthropogenic and biophysical effects. Through the introduction of hard surfaces, disrupting the natural process of infiltration, and the destruction of water bank soil profiles, the site's vulnerability to flooding will increase exponentially as the Riparian zone is cleared further.

As flooding becomes more severe as a result, nearby residential areas will be placed under threat. Furthermore, it will become progressively more difficult for ecosystems to recover from the effects of erosion and pollution, causing issues within the local and wider food chain.

Whilst erosion is a natural, biophysical process that occurs both with or without anthropogenic land change, the rate and extent of erosion observed at both sites was extensively affected by increasing urbanization.

As the local area is developed under both commercial and residential zoning, the natural riparian zone which preserves the local soil profile is threatened, subsequently resulting in large amounts of water-borne sedimentation, or turbidity.

Variables such as low rates of dissolved oxygen, high levels of algae and water turbidity all contribute towards harsh conditions for local flora and fauna. This correlation provides an indication of overall poor ecosystem health, all as a direct consequence of urbanization and erosion.

Increasing water turbidity at the Nudgee Beach site is particularly alarming, as the site is a major estuary and critical fish breeding ground. Mangroves and seagrass provide the ideal conditions for fish nesting, and thus water quality at the Nudgee Beach site is essential for sustainment of the ecosystem.

In 2018, Queensland fisheries returned over $300 million dollars in production value (Figure 14). Furthermore, trends indicate that previous flooding such as the 2011 floods contribute strongly to past downturns in fisheries production value.

Should pollution render the Nudgee Beach estuary unsuitable for nesting, it would become difficult for local fish species to replenish themselves, thus leading to a reduction in species population.

A lapse in supply would present devastating impacts on both local and wider economy. Employment and food security would be put under considerable risk.

In order to produce a feasible and sustainable solution, three key priorities have been selected to mitigate the effects of urban encroachment along the Kedron Brook:

1. Containing Erosion
2. Preventing further Riparian loss
3. Managing urban runoff

Highly coordinated Landcare transformation plans have been undertaken on other regional waterways to address similar issues, most notably at Oxley Creek. The Oxley Creek plan targets specific variables that contribute to poor waterway health, erosion, and vulnerability to flooding.

Considering the success observed at Oxley Creek by a coordinated transformation plan, it is therefore recommended that a similar plan be orchestrated for the Kedron Brook.

The Oxley Creek plan identifies key priority areas to direct land care efforts. Landcare methods consist of a diverse mix of riparian zone regeneration, stormwater treatment, and waterway stabilization (Figure 15).

Displayed below is the aspects of the Oxley Creek transformation deemed viable to replicate at the Kedron Brook:

Targeted maintenance and restoration of bank vegetation is critical in combating erosion. Through manual replanting of riparian vegetation and the replacement of lost soil, the natural and sustainable process of infiltration is restored, thus mitigating urban runoff. Additionally, through restoring the local soil profile, the bank vegetation becomes more resilient towards future flooding.

Waterway stabilization efforts were undertaken at both Site A and Nudgee Beach, such as the construction of rock seawalls to prevent erosion (Image 6). By preventing water flow stagnation, artificial riffles at Site A contributed by increasing rates of dissolved oxygen. Considering the existing success of these measures, it is recommended that further seawalls and riffles are constructed along the brook in order to further mitigate the effects of erosion.

Stormwater was a major source of runoff pollution observed at both Site A and B. By treating and filtering this runoff, the toxic nutrient load released into the waterway via stormwater can be mitigated.

The shallow ponding area of a Biorentation Basin facilitates a natural process for reducing water turbidity. Additionally, the vegetation and underdrain system reduces excess pollutants such as nitrates through nutrient cycling.

These reductions in water pollution will assist Site A in recovering waterborne dissolved oxygen. Site B will benefit greatly from these reduced toxicity and sedimentation levels, with fish nesting grounds returning to ideal conditions.

The effects of erosion and urbanization were observed as playing a key role in land transformations along the Kedron Brook. These changes were then observed to have increasingly damaging anthropogenic and biophysical effects. Despite this, there is an opportunity for restoration and innovation in the face of compounding ecological challenges, and for a more sustainable future for the brook.