Measurements of coastal suspended sediment concentrations

Coastal Engineering, 7 (1983) 145- 166 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

145

MEASUREMENTS OF COASTAL SUSPENDED SEDIMENT CONCENTRATIONS

SERGIEI M. ANTSYFEROV', TADEUSZ BASINSKI: and NIKOLAI V. PYKHOV I 1Soviet Academy of Sciences, P.P. Shirshov Institute of Oceanology, Moscow (U.S.S.R.) 2Polish Academy of Sciences, Institute of Hydroengineering, Gdahsk (Poland) (Received February 26, 1982; revised and accepted November 23, 1982)

ABSTRACT Antsyferov, S.M., Basifiski, T. and Pykhov, N.V., 1983. Measurements of coastal suspended sediment concentrations. Coastal Eng., 7: 145--166. Three of the methods available for measurement of suspended sediment concentration were chosen and tested in natural conditions. The equipment included sand traps, a radioisotopic probe and a long-action sampler (bathometer). The working conditions of the equipment were studied and the reliability of data obtained was analyzed. Sources of possible errors have been defined together with requirements for the techniques, and optimum technical parameters have been found. Averaging times, necessary with regard to the reliability of data, have also been determined for the measurements. Calibration and cross-calibration of the measuring devices was carried out. Technological requirements, advantages and areas of applicability are discussed for the techniques. Although they require some modifications, the techniques can already be used in measurements of concentration profiles. The data obtained, and partly shown in this paper, shed light on complex phenomena of sediment suspension. INTRODUCTION P r e d i c t i o n o f s e d i m e n t t r a n s p o r t d u e t o waves is o n e o f t h e m o s t imp o r t a n t tasks o f coastal engineering. M a n y coastal p r o j e c t s require k n o w l edge o f t h e s e d i m e n t t r a n s p o r t rates b o t h o n s h o r e - o f f s h o r e a n d in the longshore d i r e c t i o n . A c c u r a t e c o m p u t a t i o n o f t h e s e d i m e n t b u d g e t is possible o n l y if o n e k n o w s t h e laws o f s e d i m e n t s u s p e n s i o n a n d b e d l o a d across the entire coastal z o n e . So far, this k n o w l e d g e is v e r y limited, m o s t l y because o f scarce field m e a s u r e m e n t s . T h e available t h e o r e t i c a l as well as empirical m o d e l s , w h i c h use b o t h field results a n d l a b o r a t o r y d a t a , yield very d i f f e r e n t values. T h e t h e o r e t i c a l m o d e l s e m p l o y various a s s u m p t i o n s a b o u t t h e vertical profiles o f s e d i m e n t c o n c e n t r a t i o n , l o n g s h o r e c u r r e n t s and mass t r a n s p o r t (Liang a n d Wang, 1 9 7 3 ; F l e m i n g a n d H u n t , 1 9 7 6 ; L e p e t i t and Hauguel, 1978). On t h e o t h e r h a n d , t h e m o d e l s b a s e d o n l a b o r a t o r y tests include so

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146

many experimental coefficients, for fairly narrow ranges of wave and sedim e n t characteristics, t h a t they no longer hold true for natural conditions (Swart, 1976; Stewart, 1976). The global methods derived from field observations of wave energy and sediment characteristics (CERC, 1973; Tanner, 1974, Komar, 1977) are not sufficiently substantiated, as indicated by Greer and Madsen (1978). The scarcity of reliable field data does n o t permit any comparison of the available models, their accuracy or their applicability. Thus, any further progress in this domain depends considerably on the availability of reliable and accurate methods of field measurements and on the a m o u n t of data to be collected by these methods. An international group, represented by the authors, has been established to work out techniques for sand transport computations. The first stage of the programme has dealt with the discussion of the existing methods of field measurements, the choice of the methods promising the best results and their mastery and standardization. This paper presents the work of this group under the joint experiments Lubiatowo '74 and Lubiatowo '76 on the Baltic Sea coast and Kamchiya '77, '78 and '79 on the Black Sea coast. CONDITIONS OF COASTAL MEASUREMENTS

The dynamical processes in the coastal zone are more complex and intesive than those in the open sea. The field of coastal engineering extends to sea depths of about 20--25 m; the available data come primarily from this region. The following summary illustrates the authors' experience concerning sandy coastal zones of tideless shelf seas (the Baltic Sea and the Black Sea), cf., Basifiski and Lewandowski (1974), Antsyferov et al. (1976 a~ b). Antsyferov and Kosyan {1977), Kosyan et al. (1978), and Antsyferov et al. (1980 a, b). The offshore zone, seawards of the breaking region of the highest storm waves, is characterized by a calm and slightly varying bed configuration and fairly stable mechanical characteristics of sediments. For a rectilinear shore line and parallel isobaths, it can be assumed t h a t the hydrodynamical conditions are invariable along-shore. The concentration of suspended sand in this zone during storms can reach 1 g 1-~ about 1--3 cm above the sea bed and four orders of magnitude less at the sea surface. The bulk of the suspended matter concentrates mostly in the half-meter thick layer above the bed. In the breaking region of storm waves, the sand bars travel during a storm, bringing about bed-level changes of 1 m. The mechanical characteristics of sediments can vary considerably across this region, by as much as 50% during a single storm. Water circulation systems contribute to the varia tion of h y d r o d y n a m i c factors, n o t only along-shore but also in the offshore -- onshore direction. The concentration of suspended sediment can be 10 g 1-~ at the bed, its vertical gradients being much smaller than in the offshore zone.

147 This is most distinct at the breaking line; according to Kana (1978), the concentration of suspended matter is much higher under plunging than under spilling breakers. In the inshore zone, shoreward of the breaking region, the concentrations can also be as high as 10 g 11, but the variation over vertical distances of 10--20 cm can reach t w o orders of magnitude. Differences also occur between the phases of the oscillatory wave motion {onshore vs offshore}. Ripples are formed in the two first zones during storms. The situation can be more complex due to silt, seaweed and plankton. All these factors put specific requirements on measuring techniques. REQUIREMENTS FOR MEASURING TECHNIQUES Techniques should provide information a b o u t concentration profiles and mechanical characteristics of sediments across the coastal zone. The number of measuring points depends on a specific task. Ten to fifteen elevations should be logged to give accurate vertical profiles of concentration. The lowest elevation should be chosen as close as possible to the bed, while the spacing of measuring devices in the lowermost region should n o t exceed 5--10 cm. The measuring device should discriminate concentrations of 10-4--10 g 1-1, with its sensitivity determined by practical reasons. Supporting structures should n o t disturb the ambient fields, scour included, and the measuring device must not be close to these structures. Design of the measuring devices should account for corrosion, fouling, contamination, organic turbidity, kelp, water aeration and variation of physico-chemical properties of water and sediments. The device should be shock resistant to dynamic load in most severe storms, and it should be relatively inexpensive, thus permitting large-scale use over wide areas and even doubling of individual measuring stations. EXISTING METHODS It must n o t be anticipated that any measuring technique would satisfy all the requirements specified above. Therefore, the basic possibilities of the existing methods are only outlined and their applicability is discussed. The photographic technique permits the taking of photographs of a given volume of water and the counting of sediment particles. It is applied primarily in laboratories, b u t the technology available at present makes it possible also under natural conditions. The m e t h o d itself is expensive, labour consuming, and arbitrary in its stage of densitometric processing. The photoelectric technique is based on light scattering or attenuation in water containing suspended matter. Results of measurements depend not only on quantities of sediment particles b u t also on the size and form of particles and the ambient light. These are the major limitations of the m e t h o d in the natural environment.

148 The radioisotopic technique makes use of the attenuation of the gamma radiation in a medium having a given density. The intensity of the received radiation varies due to changes in density and physico-chemical properties of the medium. The quality of the measurements also depends on source activity and n o n u n i f o r m i t y of radioisotopic decay. The probe devised by Papadopulos and Ziegler (1965) has a sensitivity of 0.5 g 1-~, fairly low as compared with the natural concentrations. The conductance technique employs changes in electrolyte resistance due to decreasing volume of sediment-laden water. The most widespread is the Coulter counter, used since 1953. In this device, the recorded pulse depends on the size of particles. Accordingly, the grain-size curve can be estimated, but only in a very narrow range. Kawana and Tanimoto (1979) have utilized a similar counter for the determination of a grain-size curve in the laboratory. The sampling techniques consist of sampling water containing suspended sediments. They make possible determination of both concentration and grain-size characteristics. (a) Instantaneous samplers, which take samples in about one second, can measure concentrations in different phases of wave motion (crest, trough). They were used by Kana (1978) in the wave-breaking zone. (b) Long-action samplers, pumps, siphons and vacuum devices, work on the suction principle. The duration of sampling and the volume of sample can be controlled. Watts (1953), Schemer and Schubel (1970), Laucht (1971), Fairchild (1972), Bochove (1972), Jensen and Sorensen (1972), Kilner (1976) have contributed to the application of these samplers in the sea. An L-tube suction device installed at a constant depth was used in most cases. The inlet opening is about 1--1.5 cm in diameter. The suction characteristics and overall dimensions of the device are most questionable. Watts (1953) indicated that the suction velocity should be about 5 m sq, however, Fairchild (1972) showed that this velocity brings about deformation of bed if the inlet is located closer than 7--8 cm to the bed. (c) Sand traps force gravitational settling of sand grains penetrating through openings of the traps. The use of the traps was initiated by Fukushima and M izogushi (1958), and then Basiflski and Lewandowski (1974), Antsyferov et al. (1976b). The traps can be installed during periods of fairly calm weather and give average concentrations over entire storm periods. Although somewhat primitive, the m e t h o d has certain advantages, such as simplicity, cheapness and versatility over large areas. Electroacoustic techniques have also emerged recently, such as ultrasound scattering, of Jansen (1978) and Sternberg (1980), and the impact method by Sternberg (1980). They were not known during the preparation of our experiments, so that they could not be taken into account.

149 SELECTED METHODS All techniques presented in the foregoing have their shortcomings. We have chosen three of them, most promising on the one hand and complementary on the other hand. They include the sand traps, radioisotopic m e t h o d and the suction pump. S a n d traps

Two types of sand traps have been devised (Fig. 1) box traps (type K) and tube samplers (type B). All devices can be installed on bridges or self-contained structures. Further design details are given by Basifiski and Lewandowski {1974), Antsyferov et al. (1976 a, b) and Antsyferov et al. (1980 a, b}. The methodical tests were carried out to answer the following major questions: (a) I~ is possible to compare the results from sand traps installed at different elevations and to give profiles of relative concentration? (b) Does a sand trap catch all natural sand grains and are the granulometric distributions measured in different traps comparable? (c) What is necessary to obtain absolute concentrations from trap mensurements? In order to find the answers, tests were undertaken both in laboratory and under natural conditions: data from sand traps have been compared with measurements by samplers (bathometers). K-type sand traps were tested in the laboratory, together with models, t w e n t y times smaller. The objective was to determine the " e f f i c i e n c y " of K traps for different i-th fractions of sand grains on various levels z. The coefficient of this efficiency is determined as Ki (z) in the formula: Qi (z) = K i (z) S i (z) F T I u (z) L

in which Qi (z) = mass of i-th fraction settled in trap on level z during time interval T Si (z) = local concentration F = projection of trap inlets on the vertical plane normal to wave orthogonal Lu (z) L = local horizontal c o m p o n e n t of water velocity, averaged over time T. The obtained results indicate that K does not depend on z or grain size, and can be assumed a constant value (Antsyferov et al., 1980a). Similar tests, the results of which are shown in Fig. 2, were carried out in the prototype. The velocity field I u (z) I was almost constant over the depth of water, so that the results confirmed the laboratory findings, but have not yielded numerical values for K.

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152 Thus, t h e t w o first questions can be answered, i.e. if o n e has a mass o f the s e d i m e n t e n t r a p p e d and t h e m e a n v e l o c i t y I u (z) I, o n e can d e t e r m i n e vertical profiles o f t h e t o t a l c o n c e n t r a t i o n S(z)/S(c) and o f individual grain f r a c t i o n s Si(z)/Si(c), in w h i c h S(c) d e n o t e s a r e f e r e n c e c o n c e n t r a tion at t h e level z = c. Assuming ] u(z) L~ c o n s t in t h e bed layer u n d e r well-developed waves, one has:

S(z)/S(c) ~-Q(z)/Q(c) R e c e n t studies have s h o w n t h a t the a b o v e relationships also h o l d t r u e f o r B - t y p e sand traps (cf. A n t s y f e r o v et al., 1980a). D a c h e v e t al. ( 1 9 8 0 ) have s h o w n t h a t this m e t h o d gives reliable results differing b y n o t m o r e t h a n 5%, and t h e design o f t h e devices d o e s n o t interfere c o n s i d e r a b l y w i t h t h e f l o w s t r u c t u r e . U n d e r relatively stable h y d r o d y n a m i c c o n d i t i o n s , absolute values o f conc e n t r a t i o n can also be m e a s u r e d , p r o v i d e d a c c u r a t e figures are f o u n d f o r K. This is difficult i n a s m u c h as even f o r K = c o n s t o n a given level zl, t h e r e s u l t a n t Q(z~) d e p e n d s o n t w o variables having d i f f e r e n t values during a storm : p T2

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S(z~, T) I u(zl, T) I dt

Tests were also carried o u t o n t h e d i s t o r t i o n d u e t o piles o f bridges o r d o l p h i n s o n w h i c h t h e traps w e r e installed, cf. A n t s y f e r o v et al. ( 1 9 8 0 a ) . An e x a m p l e o f such m e a s u r e m e n t s at L u b i a t o w o is given in Fig. 3. Z

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153

Radioisotopic probe Based on the tests by Papadopulos and Ziegler (1965) and Florkowski and Cameron (1965), in 1970 we initiated studies aiming at a p r o t o t y p e radioisotopic probe for measurements of the concentration o f suspended sediment in the sea. The above authors confined themselves primarily to rivers while measuring techniques for marine conditions did not exist. In 1975, 24'Am probe was designed with a radiation intensity of 100 mCi (Fig. 4), and previous experience was utilized. Subsequent tests included

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determination of the o p t i m u m distance between source of radiation and receiver, supply voltage, electric stability, the effect of temperature variation on electronic circuitry, recurrence of results, and a cycle of calibrations. All these tests are described b y Basiflski et al. (1980b). The probe was calibrated b y different methods because it is sensitive to various factors and no single m e t h o d proved sufficiently accurate. The cali-

154 bration was conducted in fresh water, taken as reference, and then in salt solutions with different densities. Two tanks were prepared; in one of them, aluminium plates of various thickness (Fig. 5a), or a sand layer between plastic plates, were placed between the source and the receiver. In the other tank (Fig. 5b), forced circulation of sea water with quartz sand was em-

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ployed. Using data on physical properties of various materials as in Table I, calibration was also extended to different mixtures o f qcartz and water. The formula by Shvartsman (1976) was used: In ( N o / N ) = S L p (Pms/Pw - #mw/Ps)

155 TABLE I Physical properties of materials Compound

Specific weight g c m -3

H=O SiO 2 NaC1 Al

1.00 2.65 2.20 2.70

Mass coefficient of attenuation of gamma quanta with energy E = 60 keV 0.190 0.240 0.310 0.245

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= a m o u n t o f g a m m a q u a n t a passing t h r o u g h thickness L; = a m o u n t o f g a m m a q u a n t a passing t h r o u g h = concentration of suspended sediment; = bulk weight of sediment; = bulk weight of water; = mass c o e f f i c i e n t o f g a m m a a t t e n u a t i o n b y = mass coefficient of gamma attenuation by

a water layer with a water-sand mixture;

suspended sediment; water.

T h e r e s p e c t i v e values w e r e t a k e n f r o m T a b l e I. T h e m a j o r e r r o r o f r a d i o i s o t o p i c m e a s u r e m e n t s is i n c l u d e d in t h e statistical e r r o r e d u e t o h e t e r o g e n e i t y o f t h e r a d i o i s o t o p i c d e c a y o f t h e i s o t o p e e = 2 oN/X/N

= k/x/IT

in w h i c h I = intensity of radiation flux recerded by receiver = averaging t i m e f o r m e a s u r e d p a r a m e t e r k = 1.94, c o e f f i c i e n t f o r a s = 0 . 3 5 T h e f o r m u l a s h o w s t h a t t h e statistical e r r o r o f N can b e d e c r e a s e d f o r longer t i m ~ s T a n d higher intensities. H o w e v e r , since a l o n g e r t i m e o f m e a s u r e m e n t m a k e s r e c o r d i n g o f f a s t fluct u a t i o n s o f c o n c e n t r a t i o n i m p o s s i b l e , a n d b e c a u s e increasing t h e i n t e n s i t y a b o v e 100 m C i is n o t safe, o n e has t o find a r e a s o n a b l e c o m p r o m i s e . This can be a c h i e v e d b y m e a s u r e m e n t o f high c o n c e n t r a t i o n s o v e r s h o r t t i m e s o f averaging or, a l t e r n a t i v e l y , l o w c o n c e n t r a t i o n s o v e r l o n g t i m e s . T h e o t h e r errors o f c o n c e n t r a t i o n m e a s u r e m e n t s (Table II) - - d u e t o variable salinity, t e m p e r a t u r e a n d d e n s i t y o f w a t e r , variable c h e m i c a l c o m p o s i t i o n o f s e d i m e n t s a n d s u b s t a n c e s dissolved in w a t e r , d i f f e r e n t grain sizes,

156 TABLE II Sources of measurement errors Sand traps Variable water salinity Variable water temperature Variable chemical composition of solutions in water Variable chemical composition of sediment Grain size Fine organic suspension Suspended seaweed and algae + Aeration of water Bottom level changes + Unequal decay of radioisotope -

Long-action sampler

Radioisotopic probe

+ -

(+): it has an effect. (-): it has no effect.

and t h e p r e s e n c e o f organic m a t t e r - - can be e l i m i n a t e d b y c o m p a r a t i v e calib r a t i o n in local c o n d i t i o n s . A e r a t i o n o f w a t e r and seaweed can r e n d e r the m e a s u r e m e n t s impossible. T h e m i n i m u m averaging t i m e s h o u l d be c h o s e n each time, d e p e n d i n g o n t h e c o n c e n t r a t i o n s m e a s u r e d . It is f o u n d t h a t 100 s is t h e s h o r t e s t averaging t i m e f o r c o n c e n t r a t i o n s o f I g 1-~ m e a s u r e d with 241Am (cf. Basiflski et al., 1 9 8 0 b ) . As a result o f t h e tests, t h e r a d i o i s o t o p i c p r o b e can m e a s u r e sand d e n s i t y in t h e b e d l a y e r and f l u c t u a t i o n s o f high c o n c e n t r a t i o n s a n d it can be used as a reference.

Long-action bathometer T h e device illustrated in Fig. 6 and described in detail b y Basi~ski et al. ( 1 9 8 0 a ) has an a n n u l a r s u c t i o n nozzle. T h e s u c t i o n velocities along t h e p e r i p h e r y o f t h e disc are relatively small, so t h a t t h e y d o n o t d i s t u r b t h e f l o w field b u t y e t e n t r a i n t h e sand grains s u s p e n d e d at the nozzle. The c a p a c i t y o f t h e settling t a n k (50 l) p e r m i t s m e a s u r e m e n t s over a few m i n u t e s . T h e design m a k e s it possible t o m e a s u r e c o m p l e t e vertical profiles o f c o n c e n t r a t i o n . T w o t y p e s o f t h e b a t h o m e t e r s have b e e n d e v e l o p e d : r e m o t e - c o n t r o l a u t o m a t i c sampling, a n d m a n u a l sampling f r o m bridges. The objectives o f t h e respective m e t h o d i c a l tests were t o d e t e r m i n e : (a) W h a t is t h e o p t i m u m s u c t i o n v e l o c i t y a n d w h a t kind o f d i s t u r b a n c e s are i n t r o d u c e d b y t h e s u c t i o n n o z z l e ? (b) W h a t time averaging is n e c e s s a r y f o r reliable results? (c) D o t h e d a t a give a b s o l u t e c o n c e n t r a t i o n s ? T h e tests carried o u t b y P y k h o v et al. ( 1 9 8 2 ) w i t h s u c t i o n velocities at t h e

157

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Fig. 6. Long-action sampler (bathometer) -- dimensions and assembly. 1 = water pump; 2 = water pipe; 3 = settling tank; 4 = water level gauge; 5 = electric wire; 6 = test tubes; 7 = winch. V1 = 16--88 cm s-~; V~ = 52--292 cm s-l;a = 5--15 m m ; d = 11--25 ram.

disc p e r i p h e r y o f a b o u t 8 - - 8 0 c m s-~ h a v e n o t d i s p l a y e d t h e e f f e c t o n c o n c e n t r a t i o n . T h e r e f o r e , s m a l l s u c t i o n v e l o c i t i e s o f several c m s -~ h a v e b e e n c h o s e n . T h e s e v e l o c i t i e s d i d n o t b r i n g a b o u t e n t r a i n m e n t o f b e d grains even if t h e n o z z l e w a s v e r y c l o s e t o t h e b e d . T h e y also p r e v e n t c l o g g i n g b y seaweed. Series of l a b o r a t o r y tests on the flow structure a r o u n d the nozzle have s h o w n t h a t t h e d i s t u r b a n c e s are m i n o r . R e p e a t i n g r e s u l t s c a n b e o b t a i n e d f r o m 1 0 - m i n series o f m e a s u r e m e n t s , which c o r r e s p o n d to 1 0 0 - - 1 2 0 waves or 250 1 of water p u m p e d b y conventional pumps. I t c a n b e a s s u m e d t h a t t h e d a t a m e a s u r e d give a b s o l u t e c o n c e n t r a t i o n s b u t t h i s c o n c l u s i o n m u s t b e v e r i f i e d in f o r t h c o m i n g t e s t s . EXAMPLES OF MEASUREMENTS

The techniques described above have been e m p l o y e d t h r o u g h o u t the field e x p e r i m e n t s L u b i a t o w o ' 7 4 , L u b i a t o w o '76 ( t h e B a l t i c Sea) a n d K a m c h i y a

158

'77, Kamchiya '78 (the Black Sea). All results of these experiments have been published b y Antsyferov et al. (1976 a, b), Antsyferov and Kosyan (1977), Kosyan et al. (1978), Antsyferov et al. {1980 a, b), Pykhov et al. (1980 a, b). Some examples are presented here to illustrate these results. Figure 7 shows distributions of the sediment mass caught in traps situated in the offshore zone at Lubiatowo. The data are taken for a 54-hour storm, having a 15°hour phase of stabilization.

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Fig. 7. Distribution o f (a) suspended mass Q (gram) and (b) sand fraction above 0.1 ram, during 54-hour s t o r m at L u b i a t o w o .

Mean wave height and period with a 6-m depth of water were 0.71 m and 5.85 s, respectively. It is clear that the intensity of suspension decreases with increasing distance from the sea bed, with exception o f the depth of 8 m, where the waves are most intensively transformed, just prior to breaking. Figure 8 contains t w o vertical profiles of relative concentration, for t w o storms of different force in the Black Sea. Waves approached the shore perpendicularly. During storm I the highest waves broke at P4, the most frequent breaking t o o k place at P2, while some waves also collapsed at P~. During the weaker storm II, the highest waves broke at P2, while wave breaking was most often encountered at P~. Sediment characteristics are given in Table III.

159

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T A B L E III S e d i m e n t c h a r a c t e r i s t i c s in t e s t s h o w n in Fig. 8 S t a t i o n No.

Depth, m

M e a n grain diameter, mm

Mean standard deviation mm

1 2 3 4 5

1.1 1.7 4.0 2.3 7.0

0.303 0.319 0.157 0.304 0.312

0.098 0.182 0.113 0.161 0.131

160

The results show t h a t vertical profiles of concentration are exponential in the region o f the prevailing wave breaking. The measured values are highest, and the bed to middepth ratios are one order of magnitude. This type of concentration profile corresponds to constant eddy diffusivity for sand grains over the entire depth of water. In the zone of strong deformation of waves, offshore o f the breaking region, the Sz curves display a clear-cut bed layer having a thickness of 0 . 4 - 0 . 5 m. The concentrations in the bed layer and above it differ by 2--3 orders of magnitude.

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Figure 9 illustrates sediment mass distributions in traps during various phases of a storm. The traps were situated at 15--25 levels, the lowest of which was 8--10 cm above the sea bed. At the beginning of the storm, at the time tl, the highest intensity of suspension was encountered about profiles 1 and 2, where the waves broke. On the offshore side of this region, the suspension was observed only at the bed. The greatest suspension was

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162

observed at the time G, associated with the highest waves. At this time the waves broke most frequently between the profiles 2 and 3, while the highest waves plunged between the profiles 4 and 5. U p o n attenuation of the storm at times t4, ts, t6, the concentration profiles varied as shown in the drawing. The variation of the sand mass in traps and of the mean grain diameter in vertical profiles, during various phases of the storm, are depicted in Fig. 10. It can be inferred that in the offshore zone (profiles 4 and 5) the significant Profite

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Fig. 1 1 . E x a m p l e s o f a b s o l u t e c o n c e n t r a t i o n s m e a s u r e d w i t h (a) r a d i o i s o t o p i c p r o b e o f f L u b i a t o w o ; ( b ) a n d ( c ) l o n g - a c t i o n b a t h o m e t e r at K a m c h i y a . S = c o n c e n t r a t i o n in gl-~, = m e a n grain d i a m e t e r in m m . W a v e h e i g h t , / 4 , w a v e p e r i o d , T, a n d w a t e r d e p t h , h: ( 1 ) - - / 7 = 0 . 6 4 m , T = 3 . 8 s, h = 3 . 6 m; ( 2 ) - - / 4 , 0 . 6 1 m , T = 4 . 5 s, h = 3 . 6 m; ( 3 ) - - / ~ = 0 . 6 6 m , T = 4 . 0 s, h = 3 . 6 m .

163

suspension occurs for wave heights greater than 0.8 m and wave periods longer than 4 s. Under weaker waves the sand suspension (i.e. very low concentrations) are measured only at the sea bed. Closer to the shore, higher concentrations appear in the phases o f storm development and decay, as primary wave breaking takes place here. Three maxima of q isolines are seen in profile 3. The first and the third maxima coincide with the maxima in profiles 1 and 2, which correspond to strong deformation o f most waves passing through profile 3 and to the breaking of the highest waves at this point. The highest maximum in profile 3 coincides with the maxima in profiles 4 and 5, which correspond to frequent wave breaking in these profiles. An opposite tendency is observed in profile 1 -- the maximum of d isolines coincides with the minima of q isolines. This can be coupled with the washout of the finest fractions of sediments and their displacement or, alternatively, with the deposition of coarser grains from other regions. Figure 11 shows examples of the vertical profiles of sediment concentration measured with the radioisotopic probe and the long-action bathometer. The radioisotopic profile in Fig. l l a was taken at a depth of 3.5 m off Lubiatowo, in the Baltic Sea. The measurements were accompanied by the scouring process at the measuring dolphin structure, and thus by significant turbulence and high concentration of suspended sediment. The time of averaging was 200 s; each data point results from averaging of 5--7 primary data. Figures l l b and l l c give similar data at a depth of 3.6 m at Kamchiya, in the Black Sea, taken with a long-action b a t h o m e t e r in different storm phases. It m a y be seen that, for almost identical mean wave height, the concentration increases with growing mean wave period. The distribution of the mean grain diameter does n o t display this effect. CONCLUSIONS

The h y d r o d y n a m i c processes taking place in the offshore zone, breaking region and inshore zone differ considerably and put different requirements on measuring techniques. While designing the measuring facilities and data processing one has to take into account the research objectives, the number and layout of measuring stations, measurement interval from 10 -4 to 10 g 1-1, streamlining about a facility and its supports, corrosion, fouling, contamination, organic turbidity, kelp, water aeration, the variation of physicochemical properties of water and sediment, and financial potentials (Table IV). Each o f the measuring techniques has its o w n drawbacks, b u t the three tested thoroughly, i.e. sand traps, radioisotopic probe and long-action bathometer, are possible to use under Table IV conditions. Nonetheless, even these three techniques, should be further developed. The measurements carried o u t hitherto b y the methods described have

164 TABLE IV Technical data of the instruments

Main dimensions Calibration

Distance between measurement points Minimum distance from the b o t t o m Real sensivity Sediment measured Integration time

Determination of sediment composition Cost Application

Sand traps

Suction sampler

Radioisotope probe

Fig. 1 Laboratory and field calibrations to determine relatire concentrations 5--10 cm

Fig. 6 Chosen parameters do not produce any significant deviations

Fig. 4 Calibrated in different ways

1--2 cm

1--2 cm

10--20 cm

2--3 cm

2--3 cm

A few grams Sand Hours

1 mg 1-1 Sand About 100 waves

Possible

Possible

103 mg l-l Sand About 100 waves for mean concentration. 1-100 s for instantaneous concentration (1 s only for high concentrations) Not possible

Low Relative measurements in any coastal zone conditions

Moderate Absolute measurements of mean concentration from piers or platforms

High Absolute measurements of instantaneous high concentration from piers or platforms

permitted concentration profiles to be found across coasts during storm cycles, together with absolute values of suspended sediment concentrations. REFERENCES Antsyferov, S., Basifiski, T., Kosyan, R. and Onishchenko, E., 1976a. Investigation of suspended sediment distribution over coastal slope. Results of the international project " L u b i at o wo - 7 4 " , Inst. of Fishery, Gdynia, Poland. Antsyferov, S., Basifiski, T. and Onishchenko, E., 1976 b. Method of field measurements of concentration and composition of suspended sediments. Results of the international project " L u b i at o w o - 7 4 " , Inst. of Fishery, Gdynia, Poland. Antsyferov, S. and Kosyan, R., 1977. Issliedovanije dwizenija wzwiesonogo oblomotshnogo materiala moristie zony walow, Okieanologia, 17(3), Moscow (in Russian)

165 Antsyferov, S., Kosyan, R., Onishchenko, E. and Pykhov, N., 1980 a. Use of sand traps in measurement of concentration and composition of suspended sediment. Results of the international project " L u b i a t o w o 76", Hydrotechn. Trans. No. 41, Inst. of Hydroeng., Gdafsk, Poland. Antsyferov, S., Basifiski, T., Kosyan, R., Pykhov, N. and Pustelnikov, O., 1980 b. Distribution of suspended sediment over coastal zone of Lubiatowo. Results of the international project "Lubiatowo 76", Hydrotechn. Trans. No. 41, Inst. of Hydroeng., Gdafisk, Poland. Basifiski, T. and Lewandowski, A., 1974. Field investigation of suspended sediment, Proc. 14th Coastal Eng. Conf., Copenhagen. Basifiski, T., Kasperowicz, Z. and Onishchenko, E., 1980 a. Continuous-suction sampler for measuring concentration of suspended sediment. Results of the international project " L u b i a t o w o 76". Hydrotechn. Trans., No. 41, Inst. of Hydroeng. Gdafisk, Poland. Basifiski, T., Onishchenko, E., Pykhov, N. and Oktaba, L., 1980 b. Radioisotopic probe for measurement of concentration distribution of suspended sediment in coastal zone. Results of the international project "Lubiatowo 76". Hydrotechn. Trans., No. 41, Inst. of Hydroeng., Gdafisk, Poland. Coastal Engineering Research Center (CERC), 1973. Shore Protection Manual, U.S. Army Corps of Engineers, 3 vols. Coulter, W.H., 1953. U.S. Patent 265650B. Dachev, W., Kosyan, R. and Pykhov, N., 1980. Izpolzuvanie na batomietri nanosoulowitieli za izutchawanie na plavashchtite nanosy w morski uslovija. Okieanologija, 6, Sofia (in Bulgarian). Fairchild, I.C., 1972. Longshore transport of suspended sediment, Proc. 13th Coastal, Eng. Conf., Vancouver. Fleming, C.A. and Hunt, J.N., 1976. Application of sediment transport model, Proc. 15th Coastal. Eng. Conf., Honolulu. Florkowski, T. and Cameron, T.E., 1965. A simple radioisotope X-ray transmission gauge for measuring suspended sediment concentrations in rivers. Radioisotopes Instruments in Industries and Geophysics, Symp. IAEA, Warsaw. Fukushima, H. and Mizogushi, Y., 1958. Field investigation of suspended littoral drift, Coastal Eng. in Japan, 1. Greer, M.N. and Madsen, D.S., 1978. Longshore sediment transport data: a review. Proc. 16th Coastal Eng. Conf., Hamburg paper No. 93. Jansen, R.H.I., 1978. The in situ measurement of sediment transport by means of ultrasound scattering. Delft Hydraulics Laboratory, publ. No. 203. Jensen, J.K. and Sorensen, T., 1972. Measurement of sediment suspension in combinations of waves and currents. Proc. 13th Coastal Eng. Conf., Vancouver. Kana, T.W., 1978. Surf zone measurement o f suspended sediment. Proc. 16th Coastal Eng. Conf., Hamburg. Kawana, K. and Tanimoto, T., 1979. Suspended particles near the b o t t o m in Osaka Bay, J. Oceanogr. Soc. Jap., 35(2). Kilner, F.A., 1976. Measurement of suspended sediment in the surf zone. Proc. 15th Coastal Eng. Conf., Honolulu. Komar, P.D., 1977. Beach sand transport distribution and total drift. J. Waterway, Port, Coastal Ocean Div., Proc. of ASCE, 103(WW 2). Kosyan, R., Pykhov, N. and Filippov, A., 1978. Vertikalnoje rozpriedielenije koncentracji i sostava wzwieshennyh nanosow w zonie razrushenija woln, Okieanologia, 18(6) Moscow (in Russian). Laucht, H., 1971. Entwicklung eines automatischen Schwebstoffmessger~ites filr Brandungsbereich, Forchungsbericht: Sandbewegung im Kilstenraum, Deutsche Forchungsgemeinschaft, Bonn. Lepetit, J.P. and Hauguel, A., 1978. A numerical model for sediment transport.. Proc. 16th Coastal Eng. Conf., Hamburg, paper No 103. -

-

166 Liang, S.S. and Wang, H., 1973. Sediment transport by wave action. Techn. Rept., No. 26, College of Marine Studies, Univ. Deleware. Papadopulos, I. and Ziegler, C.A., 1965. Radioisotope technique for monitoring sediment concentration in rivers and streams, Radioisotopes Instruments in Industries and Geophysics. Symp. I.A.E.A., Warsaw. Pykhov, N., Dachev, W., Kosyan, R. and Nikolov, H., 1980 a. Issliedovanie polia srednei za storm koncentracji vzvieshonogo oblomotchnogo materiala i iego sostava w bieriegovoi zonie moria. Results of the international experiment "Kamchiya '77", Sofia (in Russian). Pykhov, N., Dachev, W. and Kosyan, R., 1980 b. Ismientchivost polia koncentracji vzvieshennyh nanosov w zonie deformacji i rozrushenija voln vo vriemia storma, Results of the international experiment "Kamchiya '77", Sofia (in Russian). Pykhov, N.W., Antsyferov, C.M., Dachev, W.Z. and Kosyan, R.O., 1982, Izmierenije absolutnych znaczenii koncentracji wzwieszennyh nanosow w stormowych uslowijah. Riezultaty eksp. "Kamchiya 78", Sofia (in Russian) (in press). Schemer, E.W. and Schubel, I.R., 1970. A near-bottom suspended sediment sampling system studies of resuspension. Limnol. Oceanogr., 15(4). Shvartsman, A.O., 1976. Issliedovanije i rastchiet mutnosti w pribreznoj zonie wodohranilistcha. Tr. Gos. Gidrol. Inst., 124 (in Russian). Sternberg, R.W., 1980. Suspended sediment studies. The NSTS (Nearshore Sediment Transport Study) program for 1981 and 1982. Scripps Institution of Oceanography, California. Stewart, D.H., 1976. Predictive equations regarding coastal transport. Proc. 15th Coastal Eng. Conf., Honolulu. Swart, D.H., 1976. Coastal sediment transport, computation of longshore transport, Delft Hydraulics Laboratory, Rap. No. R 968. Tanner, W.E., 1974. Sediment transport in nearshore zone, Proc. Symposium 26/I Florida State University. Van Bochove, G., 1972. Measurements in the surf zone, Rijkswaterstad, memo 72-24, The Netherlands. Watts, G.M., 1953. Development and field test of a sampler for suspended sediment in wave action, Beach Erosion Board, Techn. Mem., No. 34.