David Nijssen

The relationship between diversity profiles, evenness and species richness based on partial ordering

Problems with the notion of evenness, such as ambiguity, proliferation of indices, choice of indices, etc. can be overcome by a more fundamental, mathematical approach. We show that the Lorenz curve is an adequate representation of evenness. The corresponding Lorenz order induces a partial order in the set of equivalent abundance vectors. Also diversity can adequately be studied through a partial order and represented by a curve derived from the classical Lorenz curve. This curve is known as the intrinsic diversity profile (or k-dominance curve) and was introduced by Patil and Taillie (1979) and Lambshead et al. (1981).

Application of Scenarios and Multi-Criteria Decision Making Tools in Flood Polder Planning

Effectiveness of technical flood control measures depends strongly on multiple characteristics of floods. Copulas can be applied for multivariate statistical descriptions of flood scenarios. However, the parameterisation of these multivariate statistical models involves many uncertainties. With regard to these known unknowns the multivariate statistical characteristics of flood scenarios can be handled as imprecise probabilities. Such imprecise probabilities can be specified by Fuzzy Numbers and integrated in a Multi Criteria Decision Making framework. Their application in a Multi Criteria Decision Making framework, which was developed for flood retention planning in a river basin, is demonstrated here with a case study.

Nature development along the river Scheldt: Combining ecosystem functions in the Kruibeke-Bazel-Rupelmonde polder

In the wake of current water management problems, new legislation and a rising public awareness concerning environmental problems, new opportunities for nature development arise. The ecosystem management concept of restoring native ecosystems and rehabilitating original ecosystem functions and processes (such as nutrient cycles and hydrological processes) is being applied along the river Scheldt. Based on analysis and estimates of current and future problems in both the valley and the estuary, a conceptual rehabilitation model with a long-term vision is developed to tackle these problems. This vision is then translated into concrete plans and implementations trying to combine safety measures against flooding as much as possible with ecological rehabilitation and the creation of sustainable river related nature. The entire process from vision building, problem analysis and model making to concrete nature development plans is outlined in this article for the example of an ambitious nature development project in the Kruibeke-Bazel-Rupelmonde polder. The entire landscape (over 500 ha) will be rehabilitated, not by restoring the ecological patterns, but mainly by creating opportunities for ecological processes to take place, such as tides, inundation, seepage and grazing.

Handling uncertainties of hydrological loads in flood retention planning

The efficiency of technical measures for flood protection depends on the specifications of their design flood. If actual floods deviate from this design flood, the performance may differ significantly. To evaluate the remaining risk, a comprehensive hydrological analysis of flood conditions becomes essential. If multiple flood characteristics are considered, critical loads have to be characterized with multivariate statistics, providing an unprecedented wealth of information regarding the hydrological variability. However, such a characterization involves many uncertainties. Using imprecise probabilities, these known unknowns can be integrated into the planning process. In this paper, the importance of multivariate imprecise probability data in flood protection planning is shown and a methodology to integrate this information into existing decision support frameworks is presented. To alleviate the utilization of those data in the planning process, we propose a plausibility approach to filter the amount of possible flood scenarios and to improve the data accessibility. The application in a multi-criteria decision-making framework, which was developed for technical flood retention planning in a river basin, is demonstrated with a case study.

Aggregating spatially explicit criteria: avoiding spatial compensation

Abstract Since the shift from safety-oriented planning towards risk-based flood management planning, both hydrology/hydraulic research as well as operations research have made remarkable progress. Unfortunately, in the transfer of information between both areas of expertise, valuable spatial information is being lost, which may lead to flawed decision-making. Spatial aggregation of positive or negative criteria score across cells as is customary holds a major pitfall: spatial compensation at the river basin scale. If one cells benefits outweigh another cells detriments, these detriments are lost in the spatial aggregation process. However, not all variables are commensurable. A decision-maker might reasonably object to an alternative that generates additional damage, even if they are amply compensated elsewhere. Current aggregation procedures have more of a tendency to veil these problems then to deal with them. Moreover, valuable information defined as spatial equity is also often lost in the decision matrix. In this paper, classical criteria are changed and new criteria are selected to inhibit the abundant spatial compensation, add the variable of spatial equity and provide decision-makers with non-ensconced and therefore more accurate results. The shortcomings and error-proneness of the established frugal summation procedures are outlined by intuitive simplified examples. These examples also serve to illustrate and test the logical performance of the proposed methodology. To test their applicability, they are used in an actual test case, selected for the problems intricacy.