Abstract:Measurements of evapotranspiration from contrasting stands of Phragmites australis [ET(Reed)] were obtained over several years at three sites within England between 1994 and 1998. A comparison with published ET(Reed) values showed the UK rates to be considerably lower than those measured in continental Europe. From the ET(Reed) data monthly crop coefficients [K c (Reed)] have been developed, which when used with Reference Crop Evapotranspiration will enable reedbed water use to be determined. Due to the differences in study site characteristics, values for K c varied widely, and it was not considered appropriate to combine results to produce a single set of monthly mean values. However, suggestions are made regarding the application of the K c (Reed) values to wetland design.

Recently, research has shown that a settling process is an efficient treatment for the removal of suspended solids from storm sewage. In order to design settling tanks, there is a need to determine the settling velocity characteristics of these solids. Devices and test methods for measuring settling velocities of solids in storm sewage have been developed by researchers. A literature review has revealed that the settling velocity profiles obtained with some methods (Chebbo, 1992), (Michelbach and Wohrle, 1993) and (Tyack et al., 1993) are very different. In order to explain why the results are different and to quantify the influence of the experimental procedure on the settling velocity grading curves, we have compared the selected methods when tested with the same sample and we have studied the effects of the conservation of the sample before the test, of the concentration of solids in the device and of the nature of the water on the settling velocity profiles. The results of the comparative tests indicate that the settling velocities are significantly lower with both the Cergrene and Aston methods than with the UFT test procedure. Moreover, the study has shown that the settling characteristics of solids change with time, that the use of sewage liquor rather than demineralised water or drinking water can change the results of the measurement and that the higher the concentration of solids, the greater the velocity of settled particles.

In order to optimise the design and the management of sewer networks and settling tanks, there is a need to determine the settling velocity characteristics of sewage and stormwater solids. Devices and test methods for measuring settling velocities of these solids have been developed (Chebbo, 1992), (Michelbach and Wohrle, 1993) and (Tyack et al., 1993). In order to quantify the influence of the experimental procedure on the settling velocity grading curves, we have compared three selected methods (Cergrene, Aston, Camp) when tested with the same sample with the method developed by UFT (Michelbach and Wohrle, 1993). The results of the comparative tests indicate that the settling velocities are significantly higher with the UFT test procedure than the other methods. This is mainly explained by the fact that the UFT method takes only settleable solids into account. When the calculations of the four methods are made with the total mass of SS, the study has shown that the settling velocity curves of the same samples are different. The differences vary between the nature of the samples and the test procedures which were compared. The influence of the experimental procedure for separating a sample by settling velocities fractions is demonstrated. In conclusion, we explain the need to develop an international test procedure in order to be able to compare the results.

A broad-based approach has been used to assess the impacts of discharges to rivers from 47 surface water severs, with the objective of determining whether such discharges are damaging to stream quality. In order to study as many sites as possible, sampling, laboratory and data analysis techniques were designed to be as simple and rapid as possible. This broad approach was deliberately chosen to contrast with other UK studies in which a small number of sites have been investigated in detail. Three parameters were studied, all of which could reflect the effects of intermittent pollution on stream quality during dry weather. These were the numbers and types of benthic nacroinvertebrates upstream and downstream of the outfalls, the concentrations of metals in algae upstream and downstream of the outfalls, and the concentrations of metals in sediments upstream and downstream of the outfalls. Information relating to the study catchments has been collected from local authorities and by observation at the time of sampling. This information includes catchment areas, land uses and receiving stream quality. Methods used for site selection, sampling, analysis and data interpretation are described. Results show that there is a small but significant fall in biological water quality downstreap of outfalls, but no consistent detectable impact on the concentrations of metals in sediments or algae. The biological effects are compared with the catchment characteristics to identify the factors governing the impact, and upstream water quality is found to be an important factor. Other factors influencing the impact are sewered catchment area and land use.

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