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ABSTRACTIn recent years, the use of models and scoring surveys for assessing the environmental impacts associated with river‐engineering works has increased. This paper discusses the circumstances in which modelling may be needed, and gives details of some of the models currently in use and under development. River corridor surveys, HABSCORE, RIVPACS (River Invertebrate Prediction and Classification System), SERCON (System for Evaluating Rivers for Conservation) and QUASAR (Quality Simulation Along Rivers) are described, and more detailed information is given on the IFIM (Instream Flow Incremental Methodology using PHABSIM), the physical habitat simulation approach being tested for the National Rivers Authority and the Ministry of Agriculture, Fisheries and Food.

This article presents one method for building computer models that focus on understanding and resolving complex, or "wicked," environmental issues. The method is designed to promote cooperative decision-making and consensus among stakeholders, scientists, and managers. The article argues that there are only two ways to resolve "wicked" environmental issues: regulation by conflict or regulation by consensus. It points out that regulation by conflict leads to coercion and further conflict. In contrast, regulation by consensus leads to acceptable and durable decisions. The article concludes that cooperation and consensus are superior to conflict and coercion. The method presented is illustrated with a successful project to develop a Habitat Conservation Plan (HCP) to protect the northern spotted owl in California.

Prime Minister Margaret Thatcher's 1984 privatization of British Telecom was a landmark moment for neoliberalism. It served to popularize and vindicate the sale of state utilities around the world. This article shows how computer models of the future were central for British telecommunications', and thus for Britain's, transition from social democracy to neoliberalism, from monopoly to market. The British telecommunications network was a key interest in both the social democratic and neoliberal British state's plans for the digitalization of Britain. I argue that computers were crucial to the rise of neoliberalism, both as a managerial tool that simulated futures of free markets and as a technology that symbolized and supported the contraction of the British state. This article traces the history of the British telecommunications system's Long Range Planning Department, which was at the heart of British Telecom's privatization. In doing so, it argues that the history of technology is in a unique position to study how tools such as computers both forecast and symbolize the political power of the future.

Typically, detailed quantitative and computer models of human operators performing real world tasks cannot easily be developed. We propose a technique that more easily allows for that development. We propose that when a cognitive task analysis has been carried out, a computer simulation model useful for approximations of task completion time is often within reach. The first step is to construct an activity network or order-of-processing diagram from the task analysis. Second, activity durations are found in the literature or approximated through multidimensional scaling. Finally, equations are written for calculating task completion time, or a program is written for simulations to estimate this time. Resulting models can be useful for optimizing system design. The approach is illustrated with an activity network by W. D. Gray, B. E. John, and M. E. Atwood (1993) for a telephone operator task. Simulations demonstrate the feasibility of using multidimensional scaling to obtain approximate activity durations. The approach is also illustrated with an order-of-processing diagram representing drivers reading roadside message displays. We point out that if a more detailed picture of unobservable mental processes in a task is needed, techniques have been developed for this through analysis of response times. Actual or potential applications of this research include system design, human-computer interaction, message comprehension, and simulation of information-processing tasks.

In Urban Dynamics, Forrester presents a computer model capable of projecting the growth and decay of cities. The author defends the use of computer models by making the strong epistemological claim that causal analysis of complex social systems is doomed to failure because the way such systems work is counterintuitive. It is my contention, however, that counterintuitive results of a computer model have only heuristic value. Such results by themselves do not constitute valid knowledge.