Accumulation of sediments and water quality were investigated in a wet storm-water detention pond in central Sweden. The drainage area surrounding the pond was covered by a section of highway and secondary roads. Sediment samples were collected from the pond and heavy-metal concentrations analysed subsequently in the laboratory. The depth of accumulated sediments was measured at several points around the pond. The investigation showed that during the 18 months that had passed since the pond was constructed, a 5-8 cm layer of sediments had accumulated near the inlet, and a 1.5 cm layer near the outlet of the pond. Storm water passing through the detention pond showed an average reduction rate of 26-84% for total metal content, 67% for total N, 78% for total P and 92% for COD.
The effect of employing demand and pressure management techniques on the cost of water reticulation systems is analysed in this paper. The analysis is based on the cost of supplying a cluster of 4000 households serving a range of hourly demands using pipes of various pressure classes. Demand management reduces costs by 25–45% and pressure management increases savings by a further 20–55%. For demands below 50 l per household per hour there is a cost shift from reticulation infrastructure, to properties, to cover the costs of water storage and fire sprinkler systems. The analysis highlighted the hidden cost within water supply infrastructure to provide fire protection based on street hydrants.
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 (τcd=0.050N/m2) 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 0.12N/m2. 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.
To improve the efficiency of storm drainage networks, many local authorities have invested in network upgrading projects. Many upgrading alternatives can be generated for a given problem. It is the designer's responsibility to choose among the available alternatives. The main objective of the upgrade designs is to reduce flooding of urban areas during extreme storm events. This paper presents an expert system based on fuzzy inference to evaluate the sensitivity of urban areas to network failure. The produced results allow the designer to classify various network upgrading alternatives according to their impacts on urban areas and to introduce this order in a multi-criteria method. A practical application of the expert system is given and its applicability is discussed.
This paper describes conceptual and practical aspects of urban storm drainage performance indicators, based on the authors' experience in developing countries, particularly India. The paper begins by presenting a general framework of objectives and performance indicators as logical intermediate steps between values and the decisions taken to reflect them. The paper then considers practical approaches to performance and indicator measurement, based on field experience in India. General conclusions about drainage performance indicators are then presented, stressing the challenge of finding indicators which are (1) valid indicators of performance, (2) relatively easy to measure, and (3) helpful to the decision-maker.
A contaminant balance for urban residential water systems has been performed for 12 pollutants. The characteristics of the residential site were based on Ellenbrook, a suburb of Perth, Australia. The sources of contaminants were identified and characterised using published literature values. A water balance was used to estimated flow data, and these results were used in conjunction with the contaminant source characteristics to calculate contaminant loads. The contaminants examined were total nitrogen, ammonia, total phosphorus, copper, zinc, lead, cadmium, suspended solids, dissolved solids, chemical oxygen demand, polycyclic aromatic hydrocarbons and oil and grease. Diagrams of contaminant flows through the water, wastewater and stormwater systems are presented. By identifying the sources of contaminants, the diagrams are a useful reference when considering the fate of contaminants in alternative urban water system configurations or how to better handle or reduce these contaminants.
Results of a material balance for nitrogen and phosphorus for Austria will be shown as one example for the use of regional material balances in water quality management. Nutrients in wastewater stem from food and thus from agricultural production to a high extent. The use of sewage sludge from wastewater treatment plants recirculates a part of these nutrients into agriculture. Phosphorus removal at treatment plants is an important step for the improvement of sludge quality. Problems with the reuse of sewage sludge are related to the content of potentially hazardous substances (e.g., heavy metals) in the sludge. Strategies for reduction of heavy metal loadings of sewage sludge have to consider all different sources. As shown in a second example diffuse sources (e.g., corrosion of roofings) highly influence the heavy metal contents of sewage sludge. Additionally, the input of heavy metals via coagulants for phosphorus precipitation must be considered.
The Department of Public Works for the city of Rotterdam manages a complex urban drainage system. The system consists of 30 catchments, collects wastewater discharged by 30 pumping stations, to a total of five treatment plants (1.1 million equivalent population). At present control of all these pumping stations is being centralised. To assess the benefits of central control, a performance index (PI) was developed to classify the actual performance of the system under control, during dry weather conditions and during storm events. The PI is composed of deterministic and heuristic indicators that reflect the quality of the control with respect to different objectives set for the entire water system.
In this paper, we propose a hydraulic reliability index for sewage pumping stations (SPS). This hydraulic reliability index is a measure of the ability of an SPS to fulfill its function in the future in conditions where its pump units (PUs) will be put out of operation occasionally. The reliability index is defined as the ratio of the expected volume of sewage that will not be pumped by SPS, due to possible PU failures, to the expected volume of sewage that will enter the pumping station inlet over the same prediction time. The calculation of the expected volume of unpumped sewage is based on the assumption that the processes leading to PU failures are stochastic and mutually independent. The simple example is used to demonstrate the proposed methodology.
In real-time control (RTC) of combined urban and rural water systems the so-called centralised control requires information from different locations in the water system and hence sensitive to the communication network breakdown during extreme storm runoff events. Optimisation algorithms used in advanced forms of centralised control require considerable computing times and thus may be impractical for RTC. To overcome these problems, the application of machine learning methods is proposed, using artificial neural networks and fuzzy adaptive systems. Results obtained in a realistic case study show that the trained controllers, can replicate centralised control behaviour quite accurately and rapidly, while using only local data sources.
The in-service strength degradation, as a result of corrosion, of cast iron water distribution pipes has been investigated. The strengths of 1 m lengths of pipe extracted from the ground have been measured in either 3- or 4-point bending and the size of the controlling defect has been estimated by visual examination of the fracture surface. The application of Weibull statistics to the bend test data demonstrates that there is bimodal behaviour which suggests that there are two populations of flaws present. It is postulated that the larger flaw size population is associated with corrosion pits that form during the process of graphitisation, while the smaller flaw size population is associated with the inherent flaws within the (brittle) cast iron pipe material. A critical pit depth is identified at the transition between the two competing flaw populations, where there is a change in slope on the Weibull plot. It is shown also that the residual strength/pit depth data are described equally well by either of the two conventional analyses, i.e. loss of section and fracture mechanics.
An understanding of pollutant characteristics on impervious surfaces is essential to estimate pollutant washoff characteristics and to design methods to minimise the impacts of pollutants on the environment. This paper presents data on surface pollutant characteristics on an urban road surface in Melbourne, Australia, from samples collected over a 36 day period. The data indicate that buildup over the dry days occurs relatively quickly after a rain event, but slows down after several days as redistribution occurs. The surface pollutant also becomes finer over the dry days as it is disintegrated. The washoff of surface pollutant is dependent on the rainfall and runoff characteristics, but the results here show that common storms only remove a small proportion of the total surface pollutant load. The data also show that street sweeping may have an adverse impact on pollutant washoff because the street sweeper releases the finer material but only removes some of them, making the fine sediment available for washoff by the next storm. The data also show that most of the nutrients are attached to the finer sediments, and to effectively reduce nutrient loads in particulates, treatment facilities must be able to remove the finer particles (down to 50 μm for TP and down to 10 μm for TN), and not just the total sediment or suspended solid load.
Based on previous observations of the 45° junction manhole for supercritical flow in the main and lateral branches, the hydraulics of the more common 90° junction manhole were explored. Using a selected manhole geometry involving: (1) a short straight piece in the lateral branch to inhibit full development of the bend wave, and (2) the addition of the junction extension as used in previous designs for the bend manhole, the present study gives results that are in basic agreement with those collected in the 45° junction manhole. This surprising result thus allows for a design basis independent of the junction angle.
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.
Source control measures include rainwater tanks, infiltration trenches, grassed swales, detention basins and constructed wetlands that can be used in housing allotments and subdivisions. A methodology for evaluating the regional economic benefits due to implementation of source control measures is presented and illustrated for two case studies in the Lower Hunter and Central Coast regions of New South Wales, Australia. It is demonstrated that use of rainwater tanks to supplement mains water supply for toilet, hot water and outdoor uses can very significantly reduce demand on mains water supply. Reductions in regional water demand will enable deferment of water supply headworks augmentation, while reductions in peak mains water demand will extend the life of water supply distribution infrastructure. In addition, substantial reduction of stormwater discharge from allotments can be realised. For the Lower Hunter region with an urban population of about 450,000 it is shown that construction of new water supply headworks infrastructure can be delayed by up to 34 years. Compared with the traditional provision of mains water and stormwater disposal, the use of rainwater tanks along with other source control measures can produce present worth savings to the Lower Hunter region conservatively estimated to be up to $67 million. Similar results were found for the Central Coast region.
Sustainability challenges us to reflect on wastewater treatment differently. Instead of focussing on end-of-pipe-treatment for emission prevention, attention shifts towards optimal resource utilisation, favouring the development of decentralised systems. But are these systems more sustainable than centralised wastewater treatment systems? What aspects determine sustainability? In an extensive literature review we give an overview of sustainability assessment methods and currently used indicators. Based on this we propose a general assessment methodology that builds on multi-objective optimisation and a complete set of sustainability indicators, yielding insight into the trade-offs made when selecting sustainable wastewater treatment systems.
The objective of the paper is to investigate the attitudes and preferences of the residential water users of the city of Thessaloniki, in order to evaluate the demand management aspects of the urban water policy. A field survey has been conducted in the city of Thessaloniki and investigated among others the reliability of the utility’s services and infrastructure, the acceptability of various water demand options, the willingness to pay of the consumers and the level of public awareness. Straightforward comparisons with the results of a similar survey five years ago help extract useful remarks and conclusions concerning the shift of the urban water policy towards integrated and therefore more sustainable directions.
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.
