An understanding of the movement of a body of water can be considered a prerequisite to any other study whether it be physical or biological. This is particularly so in the case of an estuary where the water movements are complex. The movement of water in an estuary is primarily governed by the tidal and freshwater inputs, the resulting flow being modified by bed and channel configurations, salinity, and siltload variations. The tidal and freshwater inputs are themselves variables, the tidal range varying with the lunar cycle, and the freshwater input varying with the season or rainfall. The salinity variations within an estuary are interlinked with the tidal and freshwater fluctuating inputs. In addition the local and regional weather can modify the tidal response.

SynopsisMeasurements of tidal currents in the outer Tay Estuary, and from the hydraulic model of the estuary, are used to present a tidal atlas of the area and to deduce residual tidal circulation. Additional tests on the model show that the volumetric exchange rate with the sea of the outer estuary can be as high as 58 per cent per tide, but may be lowered to about 35 per cent if multiple tide recirculation is considered. Fresh water discharge into the estuary does not materially affect this exchange rate.

The Melby Wastewater Treatment Plant is located in the municipality of Frederiksværk on the island of Sealand, Denmark. This may be the first full-scale plant in Europe purpose built for biological nutrient removal from diluted wastewater, i.e. weak domestic wastewater mixed with infiltration waters. The relatively strict effluent standards have required the existing treatment plant to be upgraded in capacity, including the design for biological Nitrogen and Phosphorus removal. Due to the weak nature of the influent wastewater, the treatment process that has been adopted includes the application of a primary sludge fermenter to alter the influent characteristics suitable for biological nutrient removal. The treatment process used is the Modified University of Cape Town process utilising a primary sludge fermenter developed at the University of British Columbia in Canada. The combination of these two processes has been successfully applied to meet the strict discharge licence requirements, without the addition of chemicals, despite the unsuitable characteristics of the influent wastewater for biological nutrient removal. The paper describes the operational results for the treatment plant.

This paper presents an analysis of coastal zone colour scanner (CZCS) data for a date for which simultaneous in situ measurements exist.Using CZCS data of 10 July 1979 for the vicinity of Dundee, the inflight slope and intercept for all spectral bands were calculated. Comparison of these results with the pre-flight values show that the deviations of the inflight slopes from the pre-flight slopes for the visible bands are within II per cent, whereas the deviations in the intercepts are found to be rather larger. The contribution to the satellite-recorded radiance from the atmospheric interplay was removed using Sturm's atmospheric correction method which incorporates the iteration procedure described by Smith and Wilson.Many algorithms have been used for comparing the upwelling radiance with the in situ chlorophyll-like pigment concentrations. Although, some of the algorithms gave good correlation coefficients, the constants in the algorithms used turn out to be quite different from the values which have been obtained by other investigators. We have also computed the sea-surface temperatures from the infrared band data and the inflight calibration constants, but no atmospheric correction was applied to the infrared band data.We have used NASA's.chlorophyll algorithms (with given parameters), one for low chlorophyll concentrations and the other for high chlorophyll concentrations for calculating the chlorophyll concentrations for those pixels within which the in situ measurements were made. The low-chlorophyll algorithm gives the chlorophyll concentrations which are smaller by a factor of about 4 than the in situ data. The results obtained from the high-chlorophyll concentration algorithm are within a factor of about 2 of the measured values.The error in the determination of chlorophyll-like pigment concentrations from the CZCS data due to factors hitherto ignored in practice by other workers is shown to be as large as the error due to the inherent signal-to-noise ratio. The factors considered here are (a) the wavelength dependence of the refractive index of seawater, (b) the variation in the temperature and salinity of seawater and (c) the choice of different values of the refractive index of seawater by individual investigators. The results are presented in such a manner that an investigator having no in situ data can estimate the errors due to these factors in the chlorophyll-like pigment concentrations computed from the CZCS data alone.We have also investigated the effect of the revised values of the solar irradiances on the chlorophyll-like pigment algorithm and we recommend that all those algorithms which are based on the original values of the solar irradiances must be revised using the new recommended values of the solar irradiances. If this is not done then the error in the derived product is shown to be about 169 per cent. Downloaded by [Massachusetts Institute of Technology] at 10:05 26 November 2014 756 S. M. Singh et al.

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