CLIMATE-CHANGE IMPACTS ON RIVER FLOWS IN BRITAIN: THE UKCIPO2 SCENARIOS

This paper describes the implications of the UKCIPO2 climate-change scenarios for river flows in Britain, focusing on mean monthly runoff and Q95 (i.e. the flow which is exceeded for 95% of the time). By the 2020s. mean summer flows will be about 30% lower than the 1961–1990 mean and Q95 will be reduced by approximately 25%. Percentage reductions are particularly large in southern and eastern England. Mean winter flows are modestly increased, with the greatest increases in the north and west. Reductions in the recharge season result in lower flows in groundwater-dominated catchments throughout the year. The climate-change signal is larger than natural multi-decadal variability - even by the 2020s. This natural variability can add +/- 5% to the changes in Q95 due to climate change.
Changes resulting from the UKCIPO2 scenarios are (a) more extreme during summer than those resulting from earlier climate-change scenarios, showing considerably greater flow reductions, and (b) at the drier end of the range in changes arising from the application of scenarios based on other coarser-resolution climate models.     

Coping with COPA II: Actions to Improve Effluent Quality

The paper outlines some of the actions taken by Severn Trent Water to achieve compliance with consent limits since the implementation of the Control of Pollution Act (Part II) in 1985.
Prior to and since 1985, Severn Trent Water has undertaken an extensive programme to analyse the reasons for failure and carry out remedial work. A major feature of this programme, which has been further stimulated by privatization, has been the need to reduce the lead time for carrying out improvements.
The paper discusses the means by which this has been achieved, including the introduction of the 'fast-track'initiative and the 'process matrix'.
Other aspects are outlined including initiatives to develop more robust processes, computerized work scheduling, extensive training programmes and best practice studies.     

A Large-Scale Grid-Based Hydrological Model of the Severn and Thames Catchments

This paper addresses the issues of scale and appropriate model complexity for large-scale hydrological models. A grid-based hydrological model, which employs the UK Meteorological Office Rainfall and Evaporation Calculation System, is applied to the Severn and Thames catchments using a grid scale of 40 km, and is shown to reproduce the observed mean annual runoff over a 10-year period to within 6% with no prior calibration. The variation in the model performance is strongly correlated with the linearity of the annual rainfall/runoff relationship and a climate index. At the monthly scale, runoff routing becomes significant, and the introduction of a two-parameter routeing algorithm significantly improves the monthly runoff simulations giving efficiencies of 90% and 88% for the Severn and Thames respectively. The results provide guidance to climate modellers looking for efficient and robust land-surface parameterizations, and indicate the potential application of such a modelling scheme to water resource managers.     

Refinements to the BOD Test

For about eighty years the biochemical oxygen demand (BOD) has remained one of the major indicators of organic pollution in the water industry.
Whilst many adaptations and refinements have been made over the last 2–3 decades, one of the most significant was to suppress nitrification by the addition of allylthiourea (ATU) at 0.5 mg/1, thus ensuring that only carbonaceous oxidation was measured. Evidence has accrued to show that, for some situations, this concentration is insufficient to fully suppress nitrification.
Poor stability is a problem with biochemical oxygen demand when samples have to be stored prior to analysis, and a method of storage is proposed which minimizes instability. As an empirical bioassay procedure, the accuracy of BOD can be poor compared with alternative methods such as chemical oxygen demand; and problems with incubator and refrigerator temperatures, the preparation of standards, and replacement batteries for dissolved-oxygen probes are discussed.
The aim of this paper is to show that these problems with biochemical oxygen demand can be eliminated, thereby retaining confidence in its use.     

DETERMINATION OF SLUDGE COMPOST QUALITY BY BIOASSAY

The paper reports the progress on a plant germination and growth trial as part of Thames Water's quality-control procedure for sludge composting and recycling. The experiment was conducted by cultivating two types of plants in a greenhouse under controlled environmental conditions, using (a) standard peat-based multipurpose compost, (b) Terra Eco Systems multipurpose compost, and (c) woodchip-amended sludge compost.
Tomatoes and petunias were selected for the trial, and the varieties were first-generation (F) hybrid. Germinated seed counts were used to calculate germination percentages and germination values, to assess compost performance. Calculated germination values for tomato and petunias were 26.52 and 17.76 respectively for the peat-based compost: the values of tomato plants for Woodchip-amended compost and Terra Eco compost were 17.80 and 11.84 respectively; and for petunia, all composts performed similarly, with germination values ranging from 14.00 to 17.76. It was concluded that there were no significant differences between the petunia plants in three composts used in this trial.     

The Microbiology of Lubricants and Oils for Water Supply Applications

Recent work in the US has shown that contact between lubricants and oils and drinking water can promote the growth of heterotrophic micro-organisms. It is unlikely that these species are pathogenic, and therefore harmful to man. However, the hygienic status of water distribution systems could be affected, leading to higher heterotrophic plate counts during routine sampling. Experimental work has been undertaken to study the microbiological impact of a range of lubricants and oils on drinking water. The methods have been based on an existing procedure for the assessment of the growth potential of drinking water, i.e. the 'assimilable organic carbon'test. The results of this work could serve as the basis of a future standard method for the rapid and inexpensive screening of oils and lubricants for their microbiological suitability in potable-water applications.     

Health Risks of Chlorination - is there a Problem?

C hlorine is an effective and reliable disinfectant whose use in the treatment of drinking water has ensured water of high microbiological quality. Although the benefits of chlorination are beyond doubt, the fact that chlorine reacts with many of the organic substances in raw waters forming some substances of potential risk to health has led to concern and has stimulated a series of investigations. These investigations have used a variety of approaches and techniques, including advanced organic analysis, epidemiology, and toxicology. The paper reviews this research and discusses some of the factors affecting the risks associated with drinking chlorinated water.     

Precast Concrete Blocks for High-Velocity Flow Applications

Precast concrete blocks can be used as erosion protection to a surface subjected to high-velocity water, for example a dam spillway.
The paper describes model testing carried out on flat and wedge-shaped blocks in a purpose-designed facility at the University of Salford, where an open channel discharge intensity of 0.5 m²/s can be accelerated to a velocity of 7.5 m/s.
The failure modes of tied and untied flat concrete blocks have been investigated under different laying and bedding conditions. The model results are compared to the findings from prototype studies. Results from experiments on wedge-shaped blocks of a Soviet design are also presented and confirm the Russian experience that the wedge shape is inherently stable at large discharges, a block of 100-m thickness being stable under a discharge intensity of 20 m²/s.     

Excluding Groundwater Infiltration into New Sewers

Much attention has been focused on the need for sewer renovation and rehabilitation of old sewerage systems, but age is not always the reason for sewer failure. Serious problems of performance have also been encountered on sewerage schemes less than 10 years old. This paper considers the problems of groundwater infiltration into new foul sewers, and suggests that deficiencies might exist in some aspects of modern sewer design and construction.
Infiltration is most frequently observed at sewer joints. Results are presented of laboratory tests which show the ability of flexible fixed-ring joints on clay sewers to withstand both internal and external pressures. Damaged polyester fairings on the spigots of these pipes can act as one-way valves, and massive infiltration may result. The standard site water test is shown to be inadequate in detecting some of these types of defect which may result from damaged pipes or poor workmanship.     

Abbeystead Outfall Works: Background to Repairs and Modifications – and Lessons Learned

The explosion at the Abbeystead valve house in May 1984, with its attendant loss of life and injury, forcibly drew the attention of the public to the dangers of methane and other natural gases. It also reaffirmed to the water industry and engineering professions the pervasive nature of the gas and the need to take appropriate measures in the construction, design and operation of any scheme which involves a possible methane presence. The investigations into the source and mechanism of the methane gas ingress, and the design of the permanent repairs and modifications to the scheme, have illustrated many of the risks and problems associated with methane and the measures for dealing with them.
The paper describes the essential repairs and modifications which had to be carried out, the main lessons learned, and the recommendations which are felt to be applicable to new and existing water schemes where methane may be present.