Urban Water最新文献

Sewer deposits play a significant role as a source of pollution in combined sewer overflows. The objective of this paper is to identify, using a direct approach on a sewer length, the main source of organic solids among the different deposits and their erosion processes. The different deposits studied were large inorganic solids at the bottom of the sewer, biofilms on the walls of the sewer and organic solids at the water–bed interface. The method applied consisted firstly of analysing very precisely (mass and pollutant loads) the solids in the three types of deposits along a sewer line with a length of 150 m. Then, the deposits were eroded by in situ flushing experiments using tap water. Finally the nature and the mass of particles eroded along the length of the sewer were compared with the nature and the mass of solids in each type of sewer sediment in order to identify the main source of organic solids in the sewers. This comparison indicates that the organic layer at water–bed interface is the main source of eroded solids. An erosion test carried out under continuous observation confirms that the organic layer is actually eroded.

The collection of rainwater from roofs, its storage and subsequent use make a significant saving in the use of potable water. This paper investigates how spatial and temporal fluctuations in rainfall can be incorporated into behavioural models, which simulate the performance of rainwater collectors. Temporal variations are considered at two different time scales, that is daily and monthly intervals. The first model uses a daily time interval to model system performance. A set of rainwater collector performance curves for five geographic locations is developed. From the location-specific curves, a set of average curves is determined which is shown to be sufficiently accurate for estimating rainwater collector performance. The second model uses a larger time interval of one month. The effect of daily fluctuations in rainfall is incorporated into this model using a storage operating parameter. Values of the parameter were determined by matching the output from the daily model with that of the monthly model. Generally the rainwater collector performance predicted by the monthly model using average values of the storage operating parameter is shown to correlate well with the corresponding values determined using a daily time interval model. The monthly model provides a simple and versatile method of modelling the performance of rainwater collectors.

This paper describes a prototype rainwater recovery system that has been fitted within a supermarket. In this system, rainwater is recovered from the roof structure, collected and then used to satisfy part of the domestic cold water requirements of the supermarket (for toilet flushing). The design and commissioning of the system installed is first described. The system has been fitted with a monitoring system, which has been used to record the water usage and to estimate the rainwater recovered for use in the supermarket over approximately an 8-month period. The results are used to calculate the collection efficiency of the system compared to potential gains determined from local rainfall data. This data has also been used to calculate the revenue cost savings for this system. The additional capital cost of this system has been estimated and this has been used to calculate a payback period of 12 years, based upon a collection efficiency of 57.4%. Alternative payback periods for different locations in the UK are also discussed. Finally, this paper considers the effects of alternative roof and tank sizes on system economics. This shows that tank size is critical and that different configurations may be used to achieve payback periods approaching 4 years.

The movement of sediments in sewers has been widely recognised as being strongly linked with poor sewer flow quality. Currently, empirically calibrated transport capacity relationships are used to estimate the movement of in-sewer sediments. The majority of these relationships were developed and calibrated with laboratory data sets that used uniformly sized granular sediment. In many combined sewers, there are both organic and inorganic sediments. The fine-grained organic sediments are thought to be able to develop considerable cohesive strength under certain conditions. This paper describes the results from laboratory experiments in which the erosion of non-homogeneous in-pipe sediment deposits was investigated. The types of sediment mixtures used ensured that a range of cohesive deposit strengths was developed. The measured bed load and suspended load were compared with transport capacity relationships currently used for sewer design. Significant divergence between the transport capacity predictions and experimental observations was discovered. It was seen that it is unwise to model in-sewer deposits as homogeneous and granular and that it is important to take into account the impact of deposit cohesion.

In this study, the development and performance of rainwater utilisation systems in Germany are described. Initially the operational characteristics of the different types of rainwater utilisation systems are explained. The objective of the modelling-based investigations is to quantify the effects of rainwater usage systems on the urban drainage system. On the basis of a long-term simulation of 10 years rain data, the following parameters were calculated: tank volumes, covering efficiency, drinking water savings, overflow occurrence, overflow volumes, overflow reduction, recurrence time of overflows. The water balance of a one-family house and a multi-storey building in Bochum was calculated in a case study.

A previously developed numerical model, able to simulate the erosion from an organic in-pipe deposit, was used to investigate the physical parameters that control the first foul flush in combined sewers. Systematic adjustment of physical parameters indicated that the accurate characterisation of bed properties, i.e. the surface erosional strength and its variation with depth, was more important than the accurate description of the imposed hydraulic conditions.

Figtree Place is a water sensitive urban redevelopment consisting of 27 residential units located in Hamilton, an inner suburb of Newcastle, NSW, Australia. The site uses rainwater tanks, infiltration trenches and a central basin where cleansed stormwater enters the unconfined aquifer for water retention and retrieval. A two-year monitoring programme for roofwater, raintanks, hot water systems and first flush pits has commenced with samples taken from these sources tested for compliance with the Australian Drinking Water Guidelines (1996). Total water saving of around 60% has been shown to be feasible as well as almost complete storm runoff retention.

The existing conventional drainage systems in cities throughout Malaysia have been built mainly to cater for the increase in surface runoff due to rapid development that occurs in the city borders. The drainage system is normally made up of open rigid concrete drain channels susceptible to maintenance problems such as sediment deposition, litter and utility pipes crossing. This paper highlights the results of surveys carried out to determine the sediment size characteristics in urban drains of five cities in Malaysia. A preliminary result from a sediment profile observation at Sungai Raja drainage system, Alor Setar is also described to establish the effect of drain size and slope on deposition trend.