Development of the estuarine conceptual models

The conceptual models in this report are representations of real-world systems, and are a synthesis of the current state of knowledge for each different type of coastal waterway. They summarise key physical, geomorphic, sedimentary, and biological information (emphasising Australian conditions), building upon the initial work undertaken by Heap et al. (2001) for the National Land and Water Resources Audit (NLWRA 2002). The models are intended to represent relatively 'unmodified' conditions, as defined by the NLWRA (2002), rather than impacted or degraded systems.

The conceptual models incorporate biophysical information collated from numerous studies of Australian and overseas estuaries and coastal waterways. They were developed with the assistance of experts from a variety of disciplines, including ecology, biology, oceanography, geomorphology, sedimentology, and geochemistry (acknowledgments). Due to the large number of technical terms necessary throughout this work, a glossary of Terms has been included in the side bar of every pages.

Initially, each class of coastal waterway is briefly described with a general introduction to their geomorphology, physical processes, formation, evolution, and typical sedimentary environments and associated habitats. For each class of coastal waterway, several additional alternatively used names are also provided for reference. Each type of coastal waterway has been illustrated within the same background setting or bedrock 'palaeo-valley'. This is intended to assist in demonstrating how coastal waterways vary with respect to different wave, tide or river flow conditions. Additionally, a sense of coastal waterway evolution can be gained by referring to each of the relevant models; for example, the infilling of an embayment to form a wave-dominated estuary, and subsequently a wave-dominated delta.

For each type of coastal waterway, the following processes are superimposed onto the background geomorphological block diagrams:

  • Hydrodynamics - processes related to water movement and salinity variation. For wave- and tide-dominated estuaries, 'negative' estuary scenarios have been included to depict the hydrodynamics expected in arid, low-rainfall regions or seasons (climate and seasonality).
  • Sediment dynamics - transport pathways and depositional characteristics of fine-grained and coarse-grained sedimentary material.
  • Nutrient dynamics - transport pathways, biological interactions, and key processes that relate to the behaviour of nitrogen, an important nutrient in each system.

The movement or transport of materials or energy is depicted using arrows, with a legend provided where required. Important habitats, and how they relate to the processes in question, are also depicted on the models.

The models are not to scale and have been vertically exaggerated for legibility and communication purposes. As such, the orientation and aspect of the models, while arbitrary, has been standardised, and is not intended to represent any particular region of Australia. Water levels are shown to represent Lowest Astronomical Tide (LAT). The distribution and abundance of habitats are indicative only and do not necessarily represent the actual area or abundance in those systems. While not depicted as such in our models, we recognise that saltmarshes, saltflats, and mangroves are often overlapping habitats whose distributions are determined by biology and climate. They nevertheless exhibit distinct sedimentary characteristics and so are separated in our models for clarity. Saltmarshes are the temperate equivalent of tropical mangrove forests (although the latter often form sparse forests in temperate areas). saltflats saltpans) are more sparsely vegetated and generally occur in arid regions at slightly higher elevations in coastal waterways with large tidal ranges or areas prone to infrequent saltwater inundation.

Regardless of the style of communication, it is unavoidable that some components or aspects of the conceptual models may be inaccurate, due to insufficient information. However, we anticipate the need for review by coastal managers, researchers, and other stakeholders, and we welcome and encourage feedback to our models. The models will be reshaped as the collective knowledge improves, and as the models are tested. We hope that this review process will lead to better long-term model credibility and much improved representations of complex coastal ecosystems.

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