The geomorphic and hydrological character, behaviour and function of an intact upland swamp, Budderoo Plateau, New South Wales, Australia

Upland swamps are a form of topogenous mire which occur on the plateaux areas of southeastern Australia. These systems are well recognised for their ecological value and their functional role in the hydrodynamics of the catchments in which they occur. However, little is known about the internal hydrological functioning of upland swamps and how this relates to their geomorphic structure and evolution. Upland swamps are currently vulnerable to widespread and ongoing degradation as a result of landuse change, longwall mining, dewatering, peat mining and urbanisation. With this in mind, the aims of this study are to supplement the current knowledge on the geomorphic evolution and physical characteristics of upland swamps of Eastern Australia, and to provide baseline data on their internal hydrological functioning. The sedimentological, geomorphic, hydraulic and hydrological properties of an intact upland swamp on the Budderoo Plateau NSW are investigated. The geomorphic structure of the swamp is simple, and is comprised of four distinct geomorphic zones: the central swamp, the headwater marginal swamp, the valley marginal swamp, and the hillslope zones. The results of this study indicate that the development of the swamp was uniform and consisted of a sequence of mineral deposition (up to 1 m thick overlying bedrock) followed by a subsequent phase of organic accumulation up to 3.3 m thick. The organic accumulation has produced a layer of upper fibric organic fines and lower sapric organic fines. Each of these sedimentary units has different hydrological behaviours (rates of water transfer and discharge) that drive the overall function of the swamp in response to rainfall of various magnitudes and duration. Three hydrological response regimes have been identified in the functioning of this swamp. These regimes are characterised by different peak and recession responses to rainfall. The form of the hydrograph produced is controlled by antecedent water table position (i.e. which sedimentary layers are saturated) and the amount, timing and duration of rainfall. Depending on antecedent moisture conditions, the swamp can be operating either as a store for water or as a rapid conduit for water throughflow and overland flow. It therefore has a dual function in terms of flow generation in response to rainfall. These findings are consistent with those established within the Australian literature on upland swamps and within the broader international peatland literature.