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Simple modelling approaches such as a spatially lumped, rainfall-runoff model offer a number of advantages in the management of water resources including the relative ease with which groundwater and surface water accounts can be evaluated at the river-reach scale in data-poor areas. However, rainfall-runoff models are generally not well suited for use in ephemeral river systems because of their inability to simulate abrupt transitions from flow to no-flow periods and the highly non-linear rainfall-runoff relationships that exist in low yielding catchments. This paper discusses some of the challenges of using a rainfall-runoff model to assess the impacts of groundwater extraction on low flows within an ephemeral river system and demonstrates how these challenges were overcome during the development of the IHACRES_GW (Identification of Hydrographs And Component flows from Rainfall, Evaporation and Streamflow data -with Ground Water store) model. Details on the model algorithms, calibration, validation and objective function fits are provided. The performance of the IHACRES_GW model in Cox's Creek (Namoi Valley, Australia), and 13 additional areas investigated, suggests that this simple modelling approach may be of considerable utility for water accounting, especially when attempting to evaluate the impacts of groundwater extraction on low flows in similar systems. K. M. Ivkovic

This paper discusses the integration of hydrology with other disciplines using an Integrated Assessment (IA) and modelling approach to the management and allocation of water resources. Recent developments in the field of socio-hydrology aim to develop stronger relationships between hydrology and the human dimensions of Water Resource Management (WRM). This should build on an existing wealth of knowledge and experience of coupled human-water systems. To further strengthen this relationship and contribute to this broad body of knowledge, we propose a strong and durable "marriage" between IA and hydrology. The foundation of this marriage requires engagement with appropriate concepts, model structures, scales of analyses, performance evaluation and communication -and the associated tools and models that are needed for pragmatic deployment or operation. To gain insight into how this can be achieved, an IA case study in water allocation in the Lower Namoi catchment, NSW, Australia is presented.

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Coastal lakes are ecosystems which provide significant environmental, social and economic values. They are a key habitat for many aquatic species, particularly for juvenile fish and aquatic invertebrates. They are a focus for human activity, including recreation, tourism, and many forms of industry and production such as oyster and commercial fisheries. More and more the foreshore areas of lakes are seen as a desirable place to live, with urban development a key pressure on lake systems. However current development, use and management of these systems mean that these values are already under threat. Environmental managers, urban planners and other decision makers need to make complex decisions about patterns of current and future use of these systems which allow for the trade-offs associated with various activities to be effectively taken into account. Decision support systems (DSS) are seen to have a role to play in supporting these activities.When developed properly, DSS can support decision making processes by providing users with a tool that shows the relationships between drivers of a system and outcomes. Environmental outcomes (e.g. estuary health) are controlled by often complex biophysical, ecological, economic and/or social drivers and processes. In this context a DSS should address uncertainty in data, knowledge and predictions, and allow users to explore the sensitivity of outcomes to controllable drivers (e.g. management actions), uncontrollable drivers (e.g. climate variability) and uncertainty. The DSS development and adoption process also needs to be flexible to a changing decision making environment. Ultimately the success of any DSS will depend not only on its technical capacity, including the robustness of any science underlying it, or the ease of use of any interface but also on the circumstances into which it arrives: the time and money allowed for training, capacity building, incorporation of stakeholder comments and development of trust between DSS developers, scientists and the community; the way in which the DSS is embedded in the decision making process; and the ‘politics’ and constantly changing face of the decision making environment.This chapter will discuss issues regarding the development of a DSS under typical planning timeframes where there are limited resources (time and budgetary) and where current and future management issues may not be certain and/or may change over the planning timeframe. The chapter largely draws on experiences gained during the development and application of the CAPER DSS in the Great Lakes, NSW Australia.

Water Quality Improvement Plans (WQIP) are an ecosystem-based approach to integrated water cycle management. They aim to integrate the best available science for decision making coupled with a strong participatory approach. A WQIP is a comprehensive plan for water quality protection and improvement in the face of pressures from future development. Plan recommendations are developed in consultation with the community to ensure they are feasible, cost effective and will achieve the environmental outcomes required. This paper describes the Catchment Planning and Estuary Response (CAPER) Decision Support System (DSS) which has been designed to support the development of these plans. To date this approach has been or is in the process of being used in the development of ten water quality improvement plans. CAPER integrates metamodels of more detailed catchment and receiving water quality models such as the Source Catchments model, MUSIC model and DELPH-3D model with other empirical and literature based approaches to allow testing of the impact of alternative future land use and land management options. An easy-to-use interface has been developed to allow development of scenarios and exploration of the impacts of alternative options. This paper describes the generic CAPER approach and its application to developing WQIPs for several case studies in the Northern Territory, NSW and Tasmania.

This article examines the role that catchment hydrology plays in modern society: from understanding the behavior of catchments, to providing information for the management of water resources. This is discussed in the context of three classes of hydrological models (empirical, conceptual, and physics‐based), and considers the problems faced by hydrologists: scale, heterogeneity, ungauged catchments, and the impact of change (both land use and climate) on catchment response. This article concludes with discussion on the future directions of catchment hydrology, and the challenges that need to be met.