Urban Water最新文献

With increasing global privatisation of water service provision and interest in sustainability, the challenge in setting appropriate measures and targets for performance of both service providers and assets is crucial. The business and regulatory context within which the UK water service providers (WSPs) operate is complex. In the UK performance comparisons for a range of service and other attributes are made by the Regulators. In addition other performance measurement frameworks and indicators, especially in the area of environmental sustainability, have been proposed by bodies external to the WSPs. The emergence of interest in asset serviceability is adding to the complexity of performance measurement and comparison and creates tension between short-run demands of customers and longer-term requirements for sustainability.

Against this background this paper reviews the current framework for measuring and assessing performance of UK WSPs. This review illustrates a number of issues. Firstly the complexity and high levels of performance assessment set by the regulators. Secondly the rapidly changing business and regulatory context in which performance assessment and comparison is made, especially the requirements to measure and demonstrate `serviceability'. Thirdly the problems and difficulty of making meaningful comparisons between WSPs. Fourthly the tension between different areas of performance notably between value for money and customer needs and ecological sustainability.

Three examples are provided in the paper covering the assessment of: the relative sustainability of service provision to deal with sanitary waste; proposals for performance targets for rat control in sewers; a generic framework for including sustainability in decision making for asset management planning. It is concluded that there are major difficulties in the setting of performance indicators. Contextual and institutional aspects appear to control how these are set, with short-term costs and current regulations being the primary drivers. In the UK, this approach appears to discourage WSPs from investing in innovative solutions and whole-life performance of their assets. It is clear that new research is required if the correct balance in devising appropriate performance indicators is to be attained.

It is often assumed that the frequency or volume of combined sewer overflow (CSO) spill is a good indicator of receiving water pollution impact. Whilst this assumption would appear to be true, recently there have been challenges to its veracity. To test this basic premise, an integrated model (SYNOPSIS) has been applied to the urban wastewater system of a semi-hypothetical catchment. By increasing the storage volume at a single downstream tank in the drainage system, the CSO spill frequency and volume was reduced. River water quality criteria, based on UPM standards, were calculated and related to spill frequency and volume over a series of long-term simulation runs. It was found that, up to certain storage volume levels, decreasing overflow frequency improved river DO and BOD and total ammonia. Beyond these volumes, however, there was no further improvement in DO/BOD and an increase in total ammonia. It is concluded that overflow frequency/volume can be used as a performance indicator for receiving water quality, provided its significant limitations are understood.

Two current research projects have recently investigated post-project appraisal and flow measurement at combined sewer overflows. The paper sets out the context in which these projects were carried out and specifically identifies the current performance measures and measurement procedures used within the United Kingdom.

The paper analyses the practical implementation of standards for treated urban wastewater and receiving water bodies with a special focus on the following points of concern for developing countries: (a) typical problems with setting up and implementing standards in developing countries; (b) the need for a stepwise implementation of the measures necessary to achieve the standards; (c) the need for institutional development; and (d) the availability of wastewater treatment technologies. The treatment technologies are presented in a simple and practical way (tabular form), showing their expected effluent quality in terms of important parameters such as BOD, COD, suspended solids, ammonia, total nitrogen, total phosphorus, faecal coliforms and helminth eggs.

Accurate estimation of the control parameters for spatially distributed physically based catchment modelling systems requires considerable work to establish credibility. Presented in this paper is a methodology for estimation of control parameter values based on the application of a decision support system within a hydroinformatic system. The proposed methodology uses information contained within a GIS database together with optimisation techniques to infer spatially variable control parameters for utilisation with a catchment modelling system such as the Stormwater Management Model (SWMM). A case study application of the proposed methodology was undertaken using the Musgrave Avenue Stormwater System in Centennial Park, Sydney. Results from this application suggest that the proposed approach is capable of providing accurate spatially distributed control parameters for implementation with physically based catchment modelling systems.

Transport characteristics of fine sediment deposited in an on-stream stormwater management pond were studied in a rotating circular flume. In deposition experiments, the critical shear stress for deposition $\text{(τ}{}_{\mathrm{<mtext>cd</mtext>}}\text{=0.050}\text{N}\text{/}\text{m}{}^2\text{)}$ and the amount of sediment that would stay in suspension permanently were established. For two consolidation periods, 41 and 138 h, respectively, the critical shear stress for erosion of the surface sediment layer was estimated as $\text{0.12}\text{N}\text{/}\text{m}{}^2$. Finally, empirical relationships were developed to estimate the sediment deposition and erosion as a function of bed-shear stress and recommended for future modelling of fine sediment transport in the pond studied.