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.     

Post-Construction Effects of the Cameroonian Lagdo Dam on the River Benue

This paper examines the immediate and long-term effects of the Lagdo dam on the Upper Benue river basin in Nigeria. From routine monitoring of the River Benue, it was found that some immediate deleterious effects were (a) siltation of the river bed and channel, (b) frequent flooding events, and (c) reduction in flow. Consequently, these factors have constrained irrigation, navigation and fishing activities which were formerly undertaken along the river. Similarly, water-supply intake structures and irrigation abstraction facilities along the river have either been silted up or threatened. Allowing for assumptions on a real-time operational schedule of the dam, coupled with future water demands in north Cameroon, longterm effects of the dam on the Benue basin within Nigeria are predicted.     

Sludge Bulking Control with Ozone

O zonation was studied as a non-specific means of sludge bulking control. Direct ozonation at 6 g/m³ influent, i.e. 4 gO₃/kg sludge per day into the aeration basin of a 150 l/d Phoredox system controlled the growth of filamentous organisms and improved the settleability of the sludge. Bulking control with ozone is not significantly more expensive than with chlorine or with larger settler capacity.     

SOLVING AN URBAN RIVER EROSION PROBLEM ON THE TILMORE BROOK, HAMPSHIRE (UK)

The Tlimore Brook, In Hampshire, typifies the Impact of new housing development that has taken place In phases over the past 20 years or so, on a river corridor. However, the issue is not one of flooding, because the channel itself had been straightened and deepened in historical times and had been adjusted further by down-cutting; thereby forming an over-large channel sufficient to contain flood flows. Perhaps rarely for lowland Britain, the key problem was that of erosion, threatening adjacent properties. This paper describes the nature of the erosion problem and the subsequent geomorphological design to mitigate it. A key unique feature of this project was the extent of backfilling required, over the entire length, to raise the over-deep channel bed. The project was constructed in 2003.     

Performance of the Burwarton Estate Waste Stabilization Ponds

The Burwarton Estate waste stabilization ponds, near Bridgnorth, Shropshire, serve a population of 150. There are three ponds in series: a facultative pond, and two equal maturation ponds, followed by two parallel and alternately used constructed wetland ditches. This paper describes the design of the ponds and reports upon their performance during the first two years of operation.     

Ozone Treatment of Sewage Works' Final Effluent

This paper describes a laboratory-based study which was designed to investigate (a) the changes in selected physico-chemical properties of a sewage-works' final effluent after ozonation, and (b) the effect of ozone on the concentration of organic halides and effluent toxicity and mutagenicity. Different conditions were studied involving the application of ozone concentrations up to 13.5% w/w and the ozonation of the effluent under both constant and variable ozonation rates.     

The Effect of Overbank Flow in a Meandering River on its Conveyance and the Transport of Graded Sediments

A large-scale model hydraulic study of inbank and over-bank river flow, using a regular sinuous river channel with a mobile bed, was carried out in the Flood Channel Facility at HR Wallingford, UK. The selected sediment had a wide range of particle sizes present over the 'fine sand to coarse sand'range. Flow velocity, local and global sediment transport rates, and channel conveyance were all measured. The resulting bed forms were determined and used to explain the secondary circulation in the sinuous channel as well as the size sorting of the sediment. The paper gives an early overview of this major project.     

A Methodology for Monitoring the Performance of Combined Sewer Overflows

The authors have been involved with the field monitoring of combined sewer overflows and screens over a number of years. During this period they have developed a monitoring methodology which ensures reliability, consistency and accuracy of results. The paper recommends appropriate equipment to be used for monitoring the qualitative and quantitative performance of combined sewer overflows and gives recommendations on location and installation thereof. Particular reference is made to methods for cross-correlating data amongst monitors and for proper interpretation of the results. The recommended methods have been proven in the field on a variety of working project.     

Locating Outfalls on Meandering Channels to Optimise Transverse Mixing

Many sources of river pollution approximate steady-state conditions and, under such conditions, the rate of transverse mixing is critical in determining the impact of pollutants. Results are presented from transverse-mixing experiments which were carried out on a large-scale laboratory channel with meander planform geometry of natural cross-section, generated by flow over a mobile bed. Dye-tracer measurements below three point sources within one cross-section are presented and compared, together with hydrodynamic measurements. The results show the importance of locating outfalls to maximise mixing rates, hence minimising pollution impact (depending on the environmental need). A release on the outside of a bend is shown to result in a faster rate of transverse mixing than a release on the inside of a bend.