Key words: wetlands, upland swamp, geomorphology, mapping, Sydney Basin
Effective conservation and management of natural resources requires that we have an understanding of the spatial distribution and physical characteristics of the systems of concern. The results of the THPSS mapping project summarised here provide an essential physical (geomorphological) template atop which a range of other biophysical information on swamp structure, function and condition can be collated and interpreted.
Design. Using a 25 m Digital Elevation Modal (DEM) coupled with orthorectified aerial photography, the THPSS of the Sydney Basin were mapped in ArcGIS. Only valley-bottom swamps were mapped. Hanging swamps or hillslope drapes were excluded. In ArcGIS, the physical attributes of the swamps were attributed and measured. This included swamp area, elevation above sea level, swamp slope, catchment area, swamp and catchment elongation ratio, swamp length and distance to coast.
Results. Five regions of THPSS were mapped (Figure 1); Newnes (Figure 2), Blue Mountains (Figure 3), Budderoo (Figure 4), Woronora (Figure 5) and Gosford (Figure 6). Across these regions there is a total of 3208 individual THPSS. The combined area of these swamps is 101 km2 (10,100 ha) and the combined catchment areas that contain them cover 789 km2. They occur at a median distance of 57 km from the coast, but this is highly varied, ranging from 0.4 – 96 km.
The swamps occur in areas with an average annual rainfall of 1505 mm/year and average annual temperature is 15oC. They occur at a wide range of elevations. Those closer to the coast occur on elevations as low as 160 m ASL, and those further from the coast on plateau country can occur at elevations up to 1172 m ASL. The bulk of these systems occur at median elevations of 634 m ASL. The swamps are elongate in shape, having a median elongation ratio of 0.46. This makes the majority of these systems relatively long (median length is 216 m) and narrow. They occur in relatively elongate catchments with median elongation ratios of 0.61 and median catchment lengths of 488 m. Almost all these valleys terminate at their downstream ends at a valley constriction or bedrock step, making the valleys ‘funnel-shaped’.
Catchment areas draining into the swamps are, on average, 0.25 km2. This means these systems tend to occur in the very headwaters of most catchments in first or second order drainage lines. Each swamp is, on average, 31,537 m2 in area (3.1 ha). These swamps form on deceptively steep slopes. Median minimum swamp slope is 6.2%. The funnel-shaped valleys produce effective constrictions behind which alluvial materials and peat can accumulate, resulting in valley fills forming on relatively steep slopes.
Stakeholders and Funding bodies. This research was funded through the Temperate Highland Peat Swamps on Sandstone Research Program (THPSS Research Program). This Program was funded through an enforceable undertaking as per section 486A of the Environment Protection and Biodiversity Conservation Act 1999 between the Minister for the Environment, Springvale Coal Pty Ltd and Centennial Angus Place Pty Ltd. Further information on the enforceable undertaking and the terms of the THPSS Research Program can be found at www.environment.gov.au/news/2011/10/21/centennial-coal-fund-145-million-research-program. This project was also partly funded by an ARC Linkage Grant (LP130100120) awarded to A/Prof. Kirstie Fryirs and A/Prof. Grant Hose at Macquarie University. We thank Will Farebrother for working on this project. We thank the NSW Land and Property Information for the orthorectified aerial photographs that are used under a research-only license agreement.
Contact information. A/Prof. Kirstie Fryirs, Department of Environmental Sciences, Macquarie University, North Ryde, NSW 2109; +61298508367; firstname.lastname@example.org A/Prof. Grant Hose, Department of Biological Sciences, Macquarie University, North Ryde, NSW 2109; +61298508367; email@example.com