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Radiotracer dispersion studies in the vicinity of a sea outfall
124
Reservoirs, Lakes and Marine Waste Disposal CONCLUSIONS
The models are concluded to have considerable flexibility as tools for the prediction of possible consequences of alternative water quality control actions. These predictions have been reinforced by verification of the hydrodynamic and quality behavior of the model against the prototype under conditions of salinity intrusion and flushing of the estuary. Comparisons of model and prototype performance are given as specific examples. Operating characteristics, input-output requirements, sensitivity, and cost data are given for various classes of simulation runs. A brief description of the adaptation and integration of the models into a comprehensive engineering-economic model of the Bay-Delta System is also provided.
R a d i o t r a c e r dispersion studies in the vicinity o f a sea ouffall. M . J. BARRETT, D . MUNRO a n d A . R. A G o , S t e v e n a g e , E n g l a n d In the United Kingdom (as elsewhere) it is common practice for sewage from coastal communities to be discharged to the sea with little or no preliminary treatment. Knowledge of the concentration of sewage likely to arrive at bathing beaches or to enter sbell-fishery areas is required in deciding on whether a sea outfall is preferable to other forms of sewage disposal and, if so, on the optimum siting of the point of discharge. The Water Pollution Research Laboratory made an intensive study in the vicinity of a sewage ~outfall, extending some 400 m offshore, during two successive summers. The subjects studied fall .conveniently into two parts: the physical dilution of the sewage in the sea, and the distribution of ,coliform bacteria which results from the combined effects of dilution, sedimentation and mortality. Much of the information gained from the latter part has already been published (GhMESONet aL, 1967; 'GAME.SONand SAXON, 1967), and the present paper is concerned with some physical aspects of the problem--dispersion in the top 2 m in an unstratified coastal water, up to 15 m deep, and at distances up to 1 km offshore. The experimental site has a nearly straight shingle beach, offshore of which the bed slopes fairly uniformly at about 1 in 100. The average tidal range is nearly 3 m and the corresponding peak current speed is about 10 m/min. To study the dispersion, a solution containing a few hundred mCi of bromine s2 was added instantaneously to the sea surface and the activity was tracked at three depths for several hours. On seventeen occasions the addition was made in the sewage plume, on the downstream edge of the "boil"; on four other occasions the activity was added at the same point but at times when the sewage was being stored and there was no discharge from the ouffall. Four experiments were also made with the point of addition twice as far offshore, and in one further experiment the activity was added nearly km away from the outfall but at the same distance offshore. At intervals following the addition of bromine a2, the distribution of activity was determined at depths of 0.3, 1 and 2 m by traversing the active area systematically in the laboratory's catamaran, towing submersible streamlined vessels containing gamma scintillation counters. A visual indication of the concentration of activity was provided by logarithmic rate meters in the cabin of the catamaran, and a continuous record of the concentration was obtained by recording the pulses on eight-channel magnetic tape (EDEN and BRIGGS, 1966). The position of the catamaran at the beginning and end of each traverse was fixed by horizontal sextant angles and, at each fix, a coding signal was recorded on one of the magnetic tape channels. The positions at which the concentration had specific selected values were calculated, and after correction for the movement of the water these positions were plotted and isoactivity contours drawn. Digital computers were used for these operations, and the positions were plotted using an off-line microfilm recorder. In all some 100,000 points have been plotted to yield nearly 750 contour diagrams. In FIG. 1, a set of contours is shown for the distribution of activity, at depths of 0'3, 1 and 2 m below the surface, 148 min after the addition of 300 mCi to the vicinity of the sewage boil The track of the catamaran is shown by the lines transccting the contours. A preliminary analysis has been carried out on some of the processed data, with the assumptions that the dispersion is chiefly a result of horizontally isotropic turbulent diffusion, whose horizontal
Reservoirs, Lakes and Marine Waste Disposal
125
diffusivity is so much greater than that in the vertical direction that horizontal diffusion may be considered separately. In the literature it has been suggested that turbulent diffusion can be explained by assuming that diffusivity is a function of either the length of time since the diffusion started or position in the dispersing patch. I.fit is assumed that diffusivity is proportional to some power of the distance, r, from the centre of the patch and some power of the time, t, that has elapsed since the patch was a \
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FIe. 1. Distribution of activity at depths of (a) 0.3, (b) 1, and (c) 2 m, 148 rain after addition of 0.3 Ci to sewage boil. Plain arrow shows tidal velocity (m]min), flighted arrow wind velocity (m/rain). Catamaran's track is indicated by straight lines crossing contours. Numbers above contours are a coding for the concentration of activity as follows: 1, 5 × 10-1o; 2, 1 × 10-9; 3, 2 × 10- 9; 4, 5 × 10-9; 5, 1 × 10-a; 6, 2× 10-8; 7, 5 × 10-a; 8, 1 × 10-7 parts/l, where onepart is the quantity o£ activity added. point then the differential equation of diffusion has an analytic solution, in two dimensions, of the form:
I- arnI
C(r,t) = C(o,t) exp i - - 7 ; - I , q
O)
~
where C(r,t) represents concentration at distance r from the point of maximum concentration at time t, and a, m, and n are independent of r and t. At each depth, for each time, t, that a patch was plotted, an average radius was found for each contour from its area. The maximum concentration C(o,t) was usually taken as being the observed maximum concentration. These measurements were used in various combinations to solve Equation (1) by partial regression analysis for m and n. The calculated values of m and n lie within the range suggested by other workers.
126
Reservoirs, Lakes and Marine Waste Disposal
The shapes of the distributions of activity found in a substantial number of these experiments (see for example FIG. 1) show that differences in the mean velocity of the water in different parts of the patch are also important in dispersion. Mathematical analysis of dispersion in these circumstances is useful where the velocity differences are known or may be predicted: for example, wind causes the mean velocity at depths below the surface to be a function of these depths and of the wind velocity. A theoretical model which takes account of both turbulent diffusion and a non-uniform velocity distribution is described and the results are compared with those obtained from the experimental data. REFERENCES EDEN G. E. and BRIGGSR. (1966) Radioisotope techniques in water pollution studies. Paper presented at Symposium on the Use of Isotopes in Hydrology, International Atomic Energy Agency, Vienna. GAMESOr~A. L. H. and Saxor~ J. R. (1967) Field studies on the effect of daylight on mortality of coliform bacteria. Water Research, 1, 279-295. GA_~m~or4A. L. H., BtrrroN A. W. J. and GOULD D. J. (1967) Studies of the coastal distribution of coliform bacteria in the vicinity of a sea outfall. IVat. Pollut. Control, Lond. 66, 501-523.
On the snrvey and prediction of pollution at the Omuta industrial harbour. SHIGEHISA IWAI, YORITERU INOUE a n d HIDEO HIGUCHI,
Kyoto, Japan
Rapid developments in industries in Japan after World War II have caused many air and water pollution problems. Omuta is one of the most heavily industrialized areas in Japan with coal mines, and factories based on coal utilization. The economical activity of the area called for an enlargement of the harbour and coastal reclamation in order to construct new factories. This alteration of the coastal lines would change the pattern of the marine pollution and would bring on new pollution problems. It has been feared that these changes may affect the production of N o d or the laver, which now in the area exceeds $100,000 a year. Some forecast of the change of coastal current and sea water pollution due to expansion of the area of the harbour was needed for these reasons. Because theories have not yet been established regarding the complicated patterns of current near shore, and because the construction of the harbour is not complete, the only way to estimate the change of coastal current was to use models. As the model might not give the same current patterns as the actual ones, a model showing existing coastal lines was first constructed. A cloud of dye was dosed into the sea and its convection and dispersion were observed by aerial photographs taken from a helicopter. The results were compared with the results obtained from a series of the same dye tests carried out in the model in order to ascertain the reliability of the findings. A new harbour and land to be reclaimed were added to the model, and the coastal currents, after construction of these new lands were observed. FIELD
SURVEY
Omuta Bay has an average length of about 90 km, with 18 km, and depth 20 m. The bottom of the bay consists mainly of fine silts. Twenty kilograms of sodium fluoresceinite were emptied at several points into the bay, inciuding the mouth of the Omuta channel, and its dispersion was observed by aerial photographs as well as the measurements of the concentration of the dye by direct analysis of the sea water. The concentration of the dye, C, after it is dispersed from a point source, may be written as: r2
M
c = 4---~e-
4Dr
where M is the m o u n t of pollutant (or dye) dosed, r is the distance from the centre of the pollutant
Reservoirs, Lakes and Marine Waste Disposal CONCLUSIONS
The models are concluded to have considerable flexibility as tools for the prediction of possible consequences of alternative water quality control actions. These predictions have been reinforced by verification of the hydrodynamic and quality behavior of the model against the prototype under conditions of salinity intrusion and flushing of the estuary. Comparisons of model and prototype performance are given as specific examples. Operating characteristics, input-output requirements, sensitivity, and cost data are given for various classes of simulation runs. A brief description of the adaptation and integration of the models into a comprehensive engineering-economic model of the Bay-Delta System is also provided.
R a d i o t r a c e r dispersion studies in the vicinity o f a sea ouffall. M . J. BARRETT, D . MUNRO a n d A . R. A G o , S t e v e n a g e , E n g l a n d In the United Kingdom (as elsewhere) it is common practice for sewage from coastal communities to be discharged to the sea with little or no preliminary treatment. Knowledge of the concentration of sewage likely to arrive at bathing beaches or to enter sbell-fishery areas is required in deciding on whether a sea outfall is preferable to other forms of sewage disposal and, if so, on the optimum siting of the point of discharge. The Water Pollution Research Laboratory made an intensive study in the vicinity of a sewage ~outfall, extending some 400 m offshore, during two successive summers. The subjects studied fall .conveniently into two parts: the physical dilution of the sewage in the sea, and the distribution of ,coliform bacteria which results from the combined effects of dilution, sedimentation and mortality. Much of the information gained from the latter part has already been published (GhMESONet aL, 1967; 'GAME.SONand SAXON, 1967), and the present paper is concerned with some physical aspects of the problem--dispersion in the top 2 m in an unstratified coastal water, up to 15 m deep, and at distances up to 1 km offshore. The experimental site has a nearly straight shingle beach, offshore of which the bed slopes fairly uniformly at about 1 in 100. The average tidal range is nearly 3 m and the corresponding peak current speed is about 10 m/min. To study the dispersion, a solution containing a few hundred mCi of bromine s2 was added instantaneously to the sea surface and the activity was tracked at three depths for several hours. On seventeen occasions the addition was made in the sewage plume, on the downstream edge of the "boil"; on four other occasions the activity was added at the same point but at times when the sewage was being stored and there was no discharge from the ouffall. Four experiments were also made with the point of addition twice as far offshore, and in one further experiment the activity was added nearly km away from the outfall but at the same distance offshore. At intervals following the addition of bromine a2, the distribution of activity was determined at depths of 0.3, 1 and 2 m by traversing the active area systematically in the laboratory's catamaran, towing submersible streamlined vessels containing gamma scintillation counters. A visual indication of the concentration of activity was provided by logarithmic rate meters in the cabin of the catamaran, and a continuous record of the concentration was obtained by recording the pulses on eight-channel magnetic tape (EDEN and BRIGGS, 1966). The position of the catamaran at the beginning and end of each traverse was fixed by horizontal sextant angles and, at each fix, a coding signal was recorded on one of the magnetic tape channels. The positions at which the concentration had specific selected values were calculated, and after correction for the movement of the water these positions were plotted and isoactivity contours drawn. Digital computers were used for these operations, and the positions were plotted using an off-line microfilm recorder. In all some 100,000 points have been plotted to yield nearly 750 contour diagrams. In FIG. 1, a set of contours is shown for the distribution of activity, at depths of 0'3, 1 and 2 m below the surface, 148 min after the addition of 300 mCi to the vicinity of the sewage boil The track of the catamaran is shown by the lines transccting the contours. A preliminary analysis has been carried out on some of the processed data, with the assumptions that the dispersion is chiefly a result of horizontally isotropic turbulent diffusion, whose horizontal
Reservoirs, Lakes and Marine Waste Disposal
125
diffusivity is so much greater than that in the vertical direction that horizontal diffusion may be considered separately. In the literature it has been suggested that turbulent diffusion can be explained by assuming that diffusivity is a function of either the length of time since the diffusion started or position in the dispersing patch. I.fit is assumed that diffusivity is proportional to some power of the distance, r, from the centre of the patch and some power of the time, t, that has elapsed since the patch was a \
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FIe. 1. Distribution of activity at depths of (a) 0.3, (b) 1, and (c) 2 m, 148 rain after addition of 0.3 Ci to sewage boil. Plain arrow shows tidal velocity (m]min), flighted arrow wind velocity (m/rain). Catamaran's track is indicated by straight lines crossing contours. Numbers above contours are a coding for the concentration of activity as follows: 1, 5 × 10-1o; 2, 1 × 10-9; 3, 2 × 10- 9; 4, 5 × 10-9; 5, 1 × 10-a; 6, 2× 10-8; 7, 5 × 10-a; 8, 1 × 10-7 parts/l, where onepart is the quantity o£ activity added. point then the differential equation of diffusion has an analytic solution, in two dimensions, of the form:
I- arnI
C(r,t) = C(o,t) exp i - - 7 ; - I , q
O)
~
where C(r,t) represents concentration at distance r from the point of maximum concentration at time t, and a, m, and n are independent of r and t. At each depth, for each time, t, that a patch was plotted, an average radius was found for each contour from its area. The maximum concentration C(o,t) was usually taken as being the observed maximum concentration. These measurements were used in various combinations to solve Equation (1) by partial regression analysis for m and n. The calculated values of m and n lie within the range suggested by other workers.
126
Reservoirs, Lakes and Marine Waste Disposal
The shapes of the distributions of activity found in a substantial number of these experiments (see for example FIG. 1) show that differences in the mean velocity of the water in different parts of the patch are also important in dispersion. Mathematical analysis of dispersion in these circumstances is useful where the velocity differences are known or may be predicted: for example, wind causes the mean velocity at depths below the surface to be a function of these depths and of the wind velocity. A theoretical model which takes account of both turbulent diffusion and a non-uniform velocity distribution is described and the results are compared with those obtained from the experimental data. REFERENCES EDEN G. E. and BRIGGSR. (1966) Radioisotope techniques in water pollution studies. Paper presented at Symposium on the Use of Isotopes in Hydrology, International Atomic Energy Agency, Vienna. GAMESOr~A. L. H. and Saxor~ J. R. (1967) Field studies on the effect of daylight on mortality of coliform bacteria. Water Research, 1, 279-295. GA_~m~or4A. L. H., BtrrroN A. W. J. and GOULD D. J. (1967) Studies of the coastal distribution of coliform bacteria in the vicinity of a sea outfall. IVat. Pollut. Control, Lond. 66, 501-523.
On the snrvey and prediction of pollution at the Omuta industrial harbour. SHIGEHISA IWAI, YORITERU INOUE a n d HIDEO HIGUCHI,
Kyoto, Japan
Rapid developments in industries in Japan after World War II have caused many air and water pollution problems. Omuta is one of the most heavily industrialized areas in Japan with coal mines, and factories based on coal utilization. The economical activity of the area called for an enlargement of the harbour and coastal reclamation in order to construct new factories. This alteration of the coastal lines would change the pattern of the marine pollution and would bring on new pollution problems. It has been feared that these changes may affect the production of N o d or the laver, which now in the area exceeds $100,000 a year. Some forecast of the change of coastal current and sea water pollution due to expansion of the area of the harbour was needed for these reasons. Because theories have not yet been established regarding the complicated patterns of current near shore, and because the construction of the harbour is not complete, the only way to estimate the change of coastal current was to use models. As the model might not give the same current patterns as the actual ones, a model showing existing coastal lines was first constructed. A cloud of dye was dosed into the sea and its convection and dispersion were observed by aerial photographs taken from a helicopter. The results were compared with the results obtained from a series of the same dye tests carried out in the model in order to ascertain the reliability of the findings. A new harbour and land to be reclaimed were added to the model, and the coastal currents, after construction of these new lands were observed. FIELD
SURVEY
Omuta Bay has an average length of about 90 km, with 18 km, and depth 20 m. The bottom of the bay consists mainly of fine silts. Twenty kilograms of sodium fluoresceinite were emptied at several points into the bay, inciuding the mouth of the Omuta channel, and its dispersion was observed by aerial photographs as well as the measurements of the concentration of the dye by direct analysis of the sea water. The concentration of the dye, C, after it is dispersed from a point source, may be written as: r2
M
c = 4---~e-
4Dr
where M is the m o u n t of pollutant (or dye) dosed, r is the distance from the centre of the pollutant