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.     

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.     

Trade Effluent Control: Prospects for the 1990s

The proposed privatization of the ten regional water authorities together with the accompanying reorganization of water pollution control responsibilities between the new National Rivers Authority and Her Majesty's Pollution Inspectorate, as well as the ever tightening environmental standards for the aquatic environment emanating from Brussels and from general environmental pressures, means that dischargers of industrial effluents can expect major changes both in the cost of disposing of their effluents and in terms of the legislative controls which will restrict their content.
The paper examines the various factors which will influence the management of trade effluents in the 1990s and endeavours to give some indication of what the future holds both in terms of disposal costs and environmental regulation from the point of view of the discharger.     

The Use of Chemicals in Agriculture

This paper examines the use of agrochemicals in modern agriculture and horticulture. It begins by reflecting on the uncertainties of agricultural and horticultural production prior to the use of synthetic chemicals, then discusses the improved quantity and quality of output which is possible using agrochemicals. The social, environmental and agricultural hazards attendant upon chemical use are also considered. Provided that proper safeguards are observed, the use of agrochemicals is a sine qua non for the majority of farmers and growers in the UK.     

Land Drainage: Agricultural Benefits and Environmental Impacts

The paper reviews the context and contribution of agricultural land drainage in the UK and discusses the design and performance of land drainage improvement and maintenance schemes. The environmental impacts of land drainage are considered, and how drainage activities can be, and are being, modified to meet environmental criteria.     

Physicochemical Aspects of Activated Sludge in Relation to Stable Foam Formation

The presence of stable foams can seriously impair the ability of an activated sludge to produce a high-quality effluent. This paper examines how the physicochemical characteristics of the solids are related to foam formation and describes how the foaming potential of full-scale plants can be assessed. It also confirms that Microthrix parvicella can exhibit a variable morphology and shows that these variations are related to the physicochemical properties that characterize foam-forming solids.     

Burnley Sewage-Treatment Works: Design and Operation of a High-Rate Nitrifying Filter

The paper deals with the planning, construction, operation and performance of the purpose-built nitrifying filter from its commissioning in August 1986 to the present day. Burnley sewage-treatment works consists of inlet screens, Dorr detritors, primary sedimentation tanks, surface-aeration activated sludge units, and final settlement; sludge is digested and tankered to farmland.
The filter was designed and built following the closure of several local works and subsequent diversion of flows to Burnley. It was realized that the increased volume from the extended Burnley works would reduce the dilution of the effluent by the River Calder. This would result in a deterioration in the quality of the river. As a consequence an ammonia standard of 14 mg/l was imposed on the works following the completion of the nitrifying filter.     

Contamination of the Chalk Aquifer by Chlorinated Solvents: A Case Study of the Luton and Dunstable Area

A detailed investigation of contamination by chlorinated solvents of the Chalk Aquifer underlying the towns of Luton and Dunstable was undertaken to assess the extent, causes and mechanisms of pollution. The research programme incorporated land-use surveys, regional groundwater surveys, monitoring of groundwater abstraction points and aquifer profiling by means of the drilling of observation boreholes, the analysis of the recovered core material and the depth sampling of these and other boreholes.
Low-level solvent contamination of the Chalk Aquifer was found to be widespread with 'hotspots'of higher concentrations. At the drilling sites, both the saturated and unsaturated zones were contaminated with solvents, although free product was not observed. The presence of an additional contaminant, oil, at some sites was noted to influence the distribution of solvents within the aquifer.
Clean-up of the aquifer is not a practical option, and treatment of the groundwater at the abstraction points has been adopted.     

Controlling Diffuse Pollution of Groundwater from Agriculture and Industry

The greatest threat of contamination to groundwater resources is posed by pollutants from diffuse sources, yet legislation in the UK has until recently been focused on point sources. The problem of widespread pollution from industrial sources is described and compared with that from agriculture. The legislative controls available under the Water Resources Act 1991 are outlined, and the approach adopted by the National Rivers Authority in its Groundwater Protection Policy is discussed with respect to the concept of groundwater vulnerability.     

Treatment and Disposal Scheme for the Sewage of Athens

The sewage from the Greater Athens area is discharged without treatment to the nearby Saronicos Gulf. Recently the Greek government decided to implement an appropriate treatment and disposal scheme, on the basis of a study of the hydrodynamic behaviour of the Gulf and the fate of the discharged pollutants. The study was conducted with the aid of suitable hydrodynamic and water quality models for a number of alternative treatment schemes, ranging from primary treatment to biological treatment with seasonal nitrogen removal, combined with outfalls of different lengths. The results indicate that, although none of the examined schemes will lead to an immediate substantial impact, the scheme that includes biological treatment with seasonal nitrogen removal can eliminate the danger of serious ecological disturbances at a reasonable cost.