Valley infill swamps on sandstone Formed where peat material several metres thick has been deposited on a sandstone base and where the hydraulic gradient within the swamp is controlled by the gentle dip of the valley floor and the slow migration of water through the swamp. Valley infill swamps on alluvium Formed where a layer of peat material has been deposited in a broad valley that is not directly on top of sandstone but is instead on sand, talus or other alluvial material so that the watertable in the swamp is integral to the groundwater system in the surrounding terrain rather than perched above it on a sandstone rock base. Headwater swamps—formed where a typically thinner layer of peat and other organic material has been deposited in the base of the broad valley upstream of a waterfall or other rock feature that substantially influences the hydraulic gradient through the swamp; Hanging swamps or valley side swamps—formed where sandstone rock strata is exposed at or near the surface on the side of a valley and the swamp relies on the integrity of the underlying rock strata and a combination of rainfall and groundwater infiltration for recharge. Valley infill swamps Valley infill swamps on sandstone The key characteristics of a valley infill swamp on sandstone are illustrated in Figure 2.2. Sandstone strata form the base of the swamp, much as it does elsewhere along the stream channel. However, the stream gradient is low enough in the area of the peat swamp for peat to accumulate sufficiently thick to support an ecological community that is distinctly different to elsewhere along the stream channel, thereby defining the extent of the peat swamp. Water flowing in the stream channel upstream and downstream of the swamp typically flows in one or more channels across the surface of the peat so that the watertable within the peat swamp is near the surface and well above the level of the sandstone base. Flat Rock Swamp on the Waratah Rivulet was an example of this type of swamp before the bushfire in 2001. Figure 2.2 Illustration of key characteristics of a valley infill peat swamp. Figure 2.3 is a photograph of this type of swamp in a tributary of Waratah Rivulet, west of Helensburgh on the Woronora Plateau. The extent of the swamp is evident in the base of the valley by the change in vegetation. © Copyright, Ken Mills
Valley infill swamps on sandstone Formed where peat material several metres thick has been deposited on a sandstone base and where the hydraulic gradient within the swamp is controlled by the gentle dip of the valley floor and the slow migration of water through the swamp. Valley infill swamps on alluvium Formed where a layer of peat material has been deposited in a broad valley that is not directly on top of sandstone but is instead on sand, talus or other alluvial material so that the watertable in the swamp is integral to the groundwater system in the surrounding terrain rather than perched above it on a sandstone rock base. Headwater swamps—formed where a typically thinner layer of peat and other organic material has been deposited in the base of the broad valley upstream of a waterfall or other rock feature that substantially influences the hydraulic gradient through the swamp; Hanging swamps or valley side swamps—formed where sandstone rock strata is exposed at or near the surface on the side of a valley and the swamp relies on the integrity of the underlying rock strata and a combination of rainfall and groundwater infiltration for recharge. Valley infill swamps Valley infill swamps on sandstone The key characteristics of a valley infill swamp on sandstone are illustrated in Figure 2.2. Sandstone strata form the base of the swamp, much as it does elsewhere along the stream channel. However, the stream gradient is low enough in the area of the peat swamp for peat to accumulate sufficiently thick to support an ecological community that is distinctly different to elsewhere along the stream channel, thereby defining the extent of the peat swamp. Water flowing in the stream channel upstream and downstream of the swamp typically flows in one or more channels across the surface of the peat so that the watertable within the peat swamp is near the surface and well above the level of the sandstone base. Flat Rock Swamp on the Waratah Rivulet was an example of this type of swamp before the bushfire in 2001. Figure 2.2 Illustration of key characteristics of a valley infill peat swamp. Figure 2.3 is a photograph of this type of swamp in a tributary of Waratah Rivulet, west of Helensburgh on the Woronora Plateau. The extent of the swamp is evident in the base of the valley by the change in vegetation. © Copyright, Ken Mills
peat-swamp-subsidence.docx