Extension of the QUASAR River-Water Quality Model to Unsteady Flow Conditions

A modification of the well-known water-quality model 'quality simulation along river systems'(QUASAR) is presented in order to extend its ability, so that it may be considered applicable under unsteady-flow conditions. An aggregated dead-zone travel-time parameter, based on (a) the kinematic wave velocity (celerity) of the flow wave and (b) the behaviour of the solute within so-called 'dead zones', has been incorporated into the existing model formulation. This extends the current continuously-stirred tank reactor-based model process to account for the behaviour of solute under unsteady-flow conditions. The enhanced water-quality model has been validated by application to the Colorado River.     

Durban's Newest Water Resource - The Inanda Dam

The Inanda Dam is one of a series of reservoirs constructed to utilize the water resources of the Umgeni River, which rises in the Natal midlands and reaches the Indian Ocean at Durban, South Africa. The structure exploits the local topography and geology, with mass concrete founded on the granite forming the right bank and river bed, and a clay core earth embankment on the weaker left bank. Due to high ambient temperatures, the placing temperature of the concrete had to be controlled to avoid crack formation. Mix designs were modified by the addition of blast-furnace slag, and the mix water was cooled using liquid nitrogen to reduce the placing temperature of the concrete. Major floods also occurred, and although they caused little damage to the structure itself serious damage was sustained by the existing water-supply infrastructure, resulting in a review of the operational strategy of the system. The reservoir is to be operated initially as a river regulator with downstream abstraction. However, in order to provide additional security, a tunnel aqueduct linking the reservoir directly to the water-treatment works is under construction.     

Colour Removal in a Reservoir and the Dredging and Dewatering of the Deposited Waterworks Sludge

T he A lbert R eservoir of the Yorkshire Water Authority was built in the 1850s as the final raw water storage in the chain of impounding and storage reservoirs which feed Halifax, Brighouse, and Elland in West Yorkshire (Fig. 1).
This paper describes the problems encountered with increasing raw water colour since the mid1970s, the action taken to pretreat the water at the Albert reservoir prior to pressure filtration at the Thrum Hall Water Treatment Works (WTW), and the resulting problems with the deposited alum sludge in Albert reservoir.     

The Use of Different Conveyance Calculations for Modelling Flows in a Compact Compound Channel

Flow measurements have been taken for steady and unsteady flows on a reach of a river having a compact compound channel. The 'single channel', 'divided channel' and 'lateral' distribution methods have been used to calculate conveyances for use in a one-dimensional unsteady flow model of the reach. Comparisons with measured flows show that the divided channel method and the lateral distribution method both underestimate floodplain flow depths. The lateral distribution method gives the closest accuracy in the relative depth range 0.15 ≤ Yr < 0.40. For large flow depths the single channel method becomes more accurate and slightly over-estimates flow depths.
The accuracy of unit width discharge distributions, calculated from the lateral distribution method are assessed by comparison with observed distributions for overbank flows.     

The Effect of Ozonation on Particle Removal in Drinking-Water Treatment

The effect of the introduction of additional process stages in a surface-water treatment plant was studied in order to investigate how particle removal could be optimized. Particle counting is considered to be a useful indicator of treatment performance. This paper is based on results which were obtained from trials on a water-treatment plant treating surface water; these consisted of a combination of modifications to existing full-scale plant and a specially constructed pilot plant.     

The East Kent Chalk Aquifer during the 1988-92 Drought

Groundwater resources of Chalk aquifers may become depleted during drought periods; major causes of this depletion include reductions in the aquifer transmissivity and the interaction between aquifers and rivers. In the East Kent aquifer there are certain catchments where difficulties are encountered in maintaining yields but, in other catchments, drought periods have little effect on the available resources. A mathematical model is developed to help understand the flow processes within the aquifer system, and the model is used to predict the consequences of possible abstraction scenarios.     

Thermal Drying of Sewage Sludge

Over the next decade the UK will experience significant, imposed changes in the quantity of sewage sludge produced and in the means available for its disposal. Existing practices are being reappraised and new technologies are being explored to cope with a predicted 40% increase in the quantity for disposal. Thermal drying of sludge undoubtedly has a role to play in coping with this demand.
The two principal process types, i.e. direct and indirect heat application, are appraised in depth and a comparison is drawn. A case study is identified to examine the energy demands of the process, including the potential for heat recovery and for resource reuse. The environmental impact of a typical process is also examined.     

Maintaining Groundwater Supplies during Drought Conditions in the Brighton Area

The very low level of recharge to the chalk of the South Downs, which provide Brighton with its water supply, has meant that the groundwater levels are very low. Despite this, no restrictions have been necessary since February 1991. This is perhaps due to the instigation of public information campaigns, together with media coverage of the drought, as well as a successful programme of leakage control. This paper looks at how the growth of public water supply has been accommodated operationally while ensuring that groundwater quality is maintained. Options for the future expansion of supply, and their cost-effectiveness, are also considered.     

Development of the Sludge Thermal-Drying Option for South West Water

Sewage-sludge production in South West Water is predicted to more than double, to about 50000 dry tonnes per annum, by the turn of the century. Staff of South West Water Services have carried out a strategic review of sludge utilization and treatment options, and have developed a strategic planning computer model to assist in the financial evaluation of the many options which are available. The strategy allows for the provision of new raw sludge thermal-drying facilities for the anticipated increase in sludge production.
Trials were carried out with an indirect dryer system to develop and investigate the operational issues and use of the dried raw product. The initial trial produced a fluffy, low-density material with poor storage and handling characteristics, apparently associated with the high-fibre content of the sludge. The process has been modified to include pelletization.     

The Lower Colne Improvement Scheme: Environmental Costs and Benefits

ABSTRACT The Lower Colne improvement scheme, on a river system to the west of London, was the first in the Thames region to give equal importance to environmental and engineering aspects in a feasibility study which was carried out in the early 1980s. This resulted in a scheme proposal comprising sixty elements of discrete work, rather than a continuous new channel or embankments, which reduced the impact on the environment. Many of these separate elements comprise environmental mitigation and enhancement features. This paper focuses on (a) examples of different types of scheme, (b) the environmental advantages and disadvantages, and (c) the costs of incorporating such features into flood-defence works.