As a requirement for our Planning 204 class, we were asked to prepare an Integrated Catchment Management Plan on the Pakuranga estuary and stream, sub-catchment of Tamaki estuary (the catchment study area). It is important to understand Integrated Catchment Management (ICM) as it is an approach used by planners to preserve and restore the catchment and its natural hydrological regime. ICM provides a range of techniques and approaches that is used to investigate the biophysical, social and economic forces affecting water as a vulnerable resource on a catchment basis. ICM is also significant in helping to address the need for multidisciplinary and interdisciplinary approaches to resource management. Through ICM, the relationship of effects between human activities and natural resources throughout the whole catchment is analysed and assessed, thus, allowing for future strategies and plans to be developed ensuring sustainable water and land resources within a catchment.
This blog entry will include a summary account of the ICM prepared on the catchment study area. It will provide information on the interaction of the studied catchment with the biophysical features of the natural environment and also the way in which human activity influences this interaction. It will also identify relevant issues within the catchment and address the good management strategies and develop clear implementation procedures to solve these problems.
Catchment Study Area:
The Pakuranga Catchment is located in Manukau City, within the Auckland eastern suburbs of Pakuranga and Howick. The total area of the Pakuranga catchment covers approximately 3000 hectares of land . The catchment site is less than 40m above sea level with topographic conditions of relatively flat and low lying (70% of the area) to gently sloping land. Slope on the northern and eastern side of the catchment is steeper (6°-15°) while it is flatter on the south and western side (2°-5°). The Pakuranga catchment consists of a main water body which is the Pakuranga Creek. The Pakuranga Creek consists of several branches of streams feeding into the Tamaki River. The main channel length of the Pakuranga Creek is 4.3km.
The Pakuranga Catchment was mostly of rural farmlands mainly for pastoral farming prior to the 1960 urbanisation. During the 1960’s, high levels of urban development occurred, averaging 1.5 % of the total catchment area being urbanised each year from 1960-1995. Urbanisation in the Pakuranga catchment has brought substantial environmental changes in terms of the land surface, natural flow of water bodies and water quality. Increased sediment loads and contaminants getting into Pakuranga Creek and its tributary arms have caused the water quality to degrade and have also impacted the terrestrial and aquatic ecology within the study catchment. In addition to that, some streams have been altered from their natural condition through the straightening of meanders, piping of water for residential use and lining of channel base with concrete.
Key Issues and Management Options:
Issue 1: Intensification of Land Use
The increasing demand for accommodating population growth has led to the intensification of land use within the catchment. The areas within the catchment that is currently experiencing urban intensification are in Pakuranga and Howick while Botany is currently undergoing Greenfield development. Land use intensification is the main issue that contributes largely to the other issues that will be addressed in the next sections. Impacts of increasing urban development within the catchment include the ecological and physical changes to the water body, increase in stream flows, destruction of stream ecosystem and water quality degradation. It is therefore important to accommodate growth within the study area in a sustainable manner that avoids further degradation of the catchment.
Issue 2: Water Quality Degradation
The degradation of water quality within the catchment is caused by point source and non-point source pollution. The main point source pollution in the Pakuranga creek and stream are of industrial spillages, sewage and storm water overflows and old landfill sites while non-point sources are caused by run-off from roads and storm water discharge. The increase of impervious surfaces within the catchment due to land use intensification accumulates pollutants that further degrade the waterways. According to van Roon and Knight, increasing impervious surfaces in urban catchment result in high flood flows that create a ‘first flush’ effects, “whereby city streets are washed clean and receiving waters are deluged with a slug of sediment-associated contaminants that cannot settle”. It is therefore important to develop practical solutions to improve water quality within the catchment.
Issue 3: Loss of Biodiversity
The intensification of land use has impacted habitat destruction and the bioaccumulation of nutrients in the water body, which in turn resulted in the loss of aquatic and terrestrial biodiversity within the Pakuranga catchment. Increased urbanisation within the catchment has caused the loss of riparian strips along the streams, fragmentation of forests and the channeling and channeling and piping of natural streams. Riparian vegetation and natural streams provide important diverse habitats for flora and fauna and therefore improve the likelihood of biodiversity being maintained. Increasing urbanisation also results in increase impervious surfaces, which then impacts the bioaccumulation of nutrients in the natural streams. Excessive nutrients on streams can stress some aquatic species and therefore their ability to survive. It is therefore important to address the biodiversity loss issue with appropriate management options to enhance and improve aquatic and terrestrial biodiversity within the catchment. Habitat destruction and further degradation of streams should be avoided.
Issue 4: Increased Sedimentation
The increasing intensification of land use has increased sedimentation within the Pakuranga catchment. Earthworks, construction and the removal of vegetation during urbanisation have increased the likelihood of erosion and sediment being transported by storm water to streams and creeks. On the other hand, stormwater excess causes souring of stream banks and sedimentation, thus, affecting the survival of aquatic biodiversity. It is therefore important for developers to avoid further soil loss into sensitive streams through adapting adequate construction practices.
Issue 5: Changed Hydrology
The increase in impervious surfaces, the channeling and piping of streams and the discharge of storm water has caused changes to the hydrological regime. Impervious surfaces prevent the natural absorbing and storing of rainfall, ground water replenishment and produce quick run-off responses to rainfall events. In order to maintain the hydrological balance within the catchment, it is important to impose measure on discharging of stormwater, prevent further channeling and piping of natural streams and apply LIUDD techniques to decrease impervious surface ratios.
Here is a link for the document that summarises management options for each issue:
No comments:
Post a Comment