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Assessing and improving sustainablilty of urban water resources and systems

Risultati finali

The POSI program is based on a simple one-dimensional model of the steady state infiltration of surface water through an unsaturated soil to the water table. The soil is treated as a layered medium with two homogeneous layers. This model should provide a reasonable approximation to infiltration over large, open areas. In particular, it will give an estimate of the typical time for a small sample of water to travel from the surface to the water table.
The report summarizes the direct measurements of leakage rates in the cities of Rastatt and MtGambier. It describes various methods for leakage quantifications including their application and pitfalls. It is the basis for the parametrisation of leakage models. The report will act as a resource for future scientific publications.
The leakage models combined as NEIMO is a tool that provides exfiltration and infiltration data on a network scale using input data generally available to water authorities or accessible from public institutions. Individual exfiltration and infiltration models were based on the Darcy law on fluid flow through porous media. NEIMO simulates defects, such as cracks and displaced joints, on each pipe asset in the network, the wastewater flow through the system, the position of groundwater relative to the pipe and determines the leakage from (exfiltration) or into (infiltration) for each asset. The size and distribution of defects are related directly or indirectly to CCTV damage inspection reports. The wastewater flow simulation is obtained from UVQ, which allows PLM to track the contaminant loads in the exfiltrating or infiltrating water. The output from NEIMO is passed for subsequent assessment by an unsaturated flow model, treating leakage as point sources of contamination. Validation of the model has been challenging, especially as direct measurement of exfiltration is an inexact science. In view of the many assumptions made in model development and defect size estimation the uncertainty in the leakage computed is conservatively estimated at 50%.
The background case study cities reports are developed as the first work package within the AISUWRS project, which aims to assess and improve the sustainability of urban water resources and systems with the help of computer tools. The overall scope of the project is to develop an innovative system to quantify and manage the problems from sustainable urban water systems and to assess the impact of pollution on the urban groundwater resources. Therefore, four case study cities with different hydrogeological and hydro-logical settings in Germany (Rastatt), England (Doncaster), Slovenia (Ljubljana) and Australia (Mt. Gambier) have been selected due to their significantly different approaches to the management of the existing urban water systems. This background study compiles data about the urban water and groundwater systems in Rastatt and aims to identify the principal problems the urban water management is facing. The studies contain a detailed description of the economic and demographic profile of the different cities as well as information on the geological and hydrological setting and the aquifer vulnerability. An overview of the city’s water infrastructure are provided together with data about groundwater quality and a short description of existing numerical groundwater models is given. The overall work program of AISUWRS is based upon the development of a number of models that will allow prediction of the effects of urban infrastructure on ground water contamination. Six models are currently developed: - UVQ model. - Pipeline leakage model. - Unsaturated flow model (UFM) to predict water transport to the aquifer. - Unsaturated transport model (UTM) to predict the transport of contaminants to the aquifer. - Groundwater flow and transport model to predict transport within the aquifer. - DSS to compare the costs of infrastructure rehabilitation with the costs of aquifer contamination.
The AISUWRS DSS was set up for all case studies. It demonstrates the causal directions in urban water management and allows the fast comparison of different scenarios. Within the project, scenarios of climate change, demand change, decentralised rainwater infiltration, greywater reuse and different strategies for sewer rehabilitation were assessed. The reports on the set up of the Urban Volume and Quantity Model are freely available to the case study cities. Additional results are documented in the AISUWRS book.
The AISUWRS Socio-Economic analysis reports detail the actual situation in the case study cities and may be used freely by the local stakeholders. Stakeholders have different perspectives looking on the water system, and considering the impacts on the environment, the social situation, and the economy. In order to come to a practical assessment, a set of indicators has been developed and applied in the project. This socio-economic analysis does not intend to analyse all urban problems. The analysis strictly centres around aspects under consideration within the AISUWRS approach (as e.g. leakage from urban waste water systems) and the models developed within the project. The analysis primarily considers the water system as a black box that interacts with the “Urban System”. In this context the Urban System consists of water users (as e.g. private households and businesses), people with their way of life (e.g. consumption pattern), urban settlements, architectural constructions, traffic and businesses of different kinds that give employment and wealth to the population. (Business is here defined as all kinds of activities and employments, regardless of private or public ownership, including: Farmers, Public services for swimming pools, beaches, sport arenas, parks & gardens, Public Administrations, Industries etc.).
The SEESAW Model has, as far as possible, been applied to the four AISUWRS case study cities of Ljubljana, Slovenia, of Mount Gambier, South Australia, of Rastatt, Germany, and of Doncaster, England. Unfortunately not the whole intended scope of the approach could be implemented, applied and approved during the project: data availability was scarce due to either sensitivity problems with regard to commercial water utilities (Doncaster), non-existence of data in the case study city’s utility (Ljubljana) or similar problems. The decision orientation of the approach was partly confronted with political constraints related to the action scenarios defined for model application (Rastatt). And the final decision workshop in the four case study cities was not applicable, as on one side for all the cities the action scenarios were found to be not relevant for actual decision making, and on the other side, results with regard to the impact of improvement measures were delayed and thus caused further delays for the subsequent workshops that could thus not be planned as early in advance to win the stakeholders for participation.
The SEESAW Model, being an Excel-application, is available in English and German, other languages may be added via language tables. The SEESAW Model consists of Input-Forms with regard to the city related basic input, the situation from point of view of the water utility and groundwater modellers, the action scenario description, the questionnaires to private households, experts and businesses etc.; Service tables such as language tables, scenario administration files and statistical analysis files for the questionnaire analysis; Output Forms including evaluation sheets acting as reporting tables. They report e.g. on the assessment of the actual urban water situation from a technical point of view on consequences to the action scenarios, on the expectations and valuations of water users compared to the action scenario improvements, on new water prices related to improvement measure implementation etc. The AISUWRS Deliberator is a special tool to explain the action scenarios valuation of different stakeholders considering the relevant decision criteria in a three dimensional cube with the dimensions Stakeholders, Actions, and Decision Criteria.
An important final dissemination product that is underway at the time that this summary is being produced is the production of a book, sponsored by the IWA that will describe the AISUWRS process in detail, illustrate its application in the case-study cities, demonstrate the socio-economic aspects of the water management process and provide guidelines for those wishing to develop these prototype tools for operational use. The book is to be A4 format, colour, about 350 pages in length and is currently scheduled to be completed and published during early 2006.
While the field studies and monitoring programmes in the four case study cities were essential as a validation to the AISUWRS modelling exercises, the field studies also produced substantial new scientific knowledge, especially in thee provision of hard facts and new monitoring strategies. The reports are used for further work in the case studies, as examples for other cities and as a resource for future scientific publications.
Urban Volume Quality (UVQ) is a conceptual, daily time step, urban water and contaminant balance model that simulates an integrated urban water system and estimates the contaminant loads and the volume of water flowing throughout the water systems from source to discharge point. As an integrated urban water system it considers the total urban water cycle, comprising the water supply, stormwater and wastewater systems. The urban water system is defined here to be the delivery of water to residential, commercial, industrial and other users within an urban area, and management of the wastewater and stormwater generated within that same area. UVQ has been designed to provide flexibility in the manner in which water services are represented and provides the ability to represent a wide range of conventional and emerging techniques for providing water supply, stormwater and wastewater services to either an existing urban area or a site which is to be urbanized.
The recently developed pseudo-transient model UL_FLOW (Mohrlok, 2005) based on a steady state analytical solution and a simple time dependent water balance was used to simulate the one-dimensional infiltration from a real sources and to compute residence times of a non-reactive solute within the soil profile between the source and the groundwater table. This model has been documented in the deliverable D14 (Mohrlok, 2005). A sensitivity study was prepared in order to investigate the effect of different soil types, coarse sand and sandy loam, and soil thicknesses on the groundwater recharge rates and residence times for two different infiltration rate time series selected from neighbourhood 11 and 23 defined for UVQ simulations of Rastatt case study. Particularly, the influence of the time step sizes, i.e. the temporal averaging, has been in the focus of that investigation. The developed extension to the model UL_FLOW_UVQ (Mohrlok, 2005) allows the calculations directly based on the UVQ output files and the neighbourhood data sets and produces output for all neighbourhoods. It has been applied to the Rastatt case study data sets and produced spatially varying time series of groundwater recharge rates and residence times. The model was developed by Dr.Ulf Mohrlok (IfH).
The DSS links the individual models together and supports the selection and comparison of predefined scenarios. The DSS enables users to track potential groundwater contaminants from the source, such as a leaking sewer, and the attenuation and movement of contaminants through the unsaturated zone until they reach the aquifer. The major benefit from the application of the DSS is to provide a holistic urban water system tool that enables water services to be represented in a flexible manner and provides the ability to represent and investigate the implications of a wide range of conventional and emergent techniques for providing water supply, stormwater and wastewater services. Users are also able to explore the likely implications of critical uncertainties such as changes to water consumer behaviour or climate change. The DSS allows for the processing of predefined scenarios, and the quantification of key indicators for scenario evaluation. This will allow end-users to develop best practice response to different scenarios based on the potential for groundwater contamination. For example; modifying customer preferences, groundwater treatment or introducing system improvements that minimise contamination. A comprehensive output summary table is produced for each scenario. The output of the DSS is then available for further implementation into numerical groundwater flow and transport models.
Water and contaminants, either from direct infiltration through pervious surfaces or from point contamination sources which are typically from leaks in pipes, may pass through the soil to reach the groundwater. SLeakI considers leaks from pipes. It is assumed that each leak occurs in a pipe that is bedded in sand in a trench. It is further assumed that a colmation layer will be formed below the leak. This colmation layer serves to limit the rate of flow from the leaks and also removes a high proportion of the microbes. The flow path of water leaking from the pipe will be determined, among other things, by soil texture. Necessary inputs to SLeakI include soil properties and the flow rate from the leak. The leak data in the AISUWRS study is provided by the NEIMO output (leak volume and contaminant concentration) of each asset in the pipe network. These data are used to estimate the path through each soil layer, and the residence time of water in that layer.