Physical Oceanography, Vol. 20, No. 5, January, 2011 (Ukrainian Original No. 5, September–October, 2010)
FIELD STUDIES OF THE MOTION OF SEDIMENTS IN THE COASTAL ZONE OF THE SEA V. Z. Dykman,1,2 O. I. Efremov,1 and E. V. Man’kovskaya1
UDC 551.465.15
We present the results of measurements carried out with the help of the “Donnaya Stantsiya” complex of equipment in the coastal zone of the Crimean shelf near Evpatoriya and near the southeast end of the Kosa Tuzla Island. For the same intensity of winds in these regions, the intensities of waves and turbulence in the coastal zone near Evpatoriya are much higher and, hence, the fluxes of suspended sediments are more intense. The accumulated data are intended for the correction of the kinetic model used for the evaluation of the characteristics of the field of suspended sediments in the shallow-water areas.
Introduction The upper or coastal part of the shelf is characterized by the fact that it suffers the action of waves of all intensities. The dynamic processes typical of the deep sea are much more intense and available for observations in the shallow-water regions. One of the main problems is connected with the investigation of regularities of the transport of sand sediments in the shallow-water areas under the action of waves. The processes of interaction of the liquid and solid phases are quite complicated and have no rigorous mathematical description up to now. Hence, the main method of investigations is the construction of various physical models of the analyzed phenomenon. The models used for the description of the flows of liquid containing suspended solid particles can be conventionally split into hydrodynamic and kinetic. In the hydrodynamic models, suspensions are regarded as integral objects characterized by the parameters of concentration and sedimentation rate averaged over the granulometric composition. Models of this sort are well developed and successfully applied. As a confirmation, we can mention one of the most significant works [1] in which specific computational schemes and recommendations concerning the prediction of the dynamics of sediments in the coastal zone of the sea are developed on the basis of a vast array of the experimental data combined with the analysis of available theoretical concepts. The practical application of the proposed model gave clear positive results (see, e.g., [2]). At the same time, some important aspects of the motion of sediments, in particular, the distribution of concentration of suspended solid substances over the depth remain poorly studied up to now. In the work [3], the results of the numerical analyses of the vertical distribution of the concentration of suspension performed within the framework of various hydrodynamic models are compared with the experimental data obtained by using of an acoustic profilometer. In the cited work, the authors consider three models: the diffusion model in which the vertical flux of suspension is found as the product of the gradient of its concentration by the coefficient of turbulent viscosity, the convection model in which the vertical transport of particles is realized by separate eddies guaranteeing the formation of a certain mean velocity of convective motion of the suspension in the direction 1 2
Marine Hydrophysical Institute, Ukrainian National Academy of Sciences, Sevastopol, Ukraine. Corresponding author; e-mail:
[email protected].
Translated from Morskoi Gidrofizicheskii Zhurnal, No. 5, pp. 65–80, September–October, 2010. Original article submitted May 26, 2009; revision submitted June 30, 2009. 0928–5105/11/2005–0379
© 2011
Springer Science+Business Media, Inc.
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from the bottom upward, and the combined convection-diffusion model in which the process of lifting of the suspended solid substance is determined by the total action of the diffusive and convective flows. It was indicated that the results of calculations performed according to the diffusion model are in good agreement with the data of observations for the waves of high intensity and do not agree with the data of observations for weak waves, whereas the convection model, on the contrary, “works” better for low energies of the waves and the riffle structure of the bottom. Nevertheless, the illustrative material presented in this work shows that the results of calculations performed for all three models are, strictly speaking, not satisfactory in the case of weak waves. The analysis of the problem of motion of the sediments performed by using the kinetic model in which the suspension is regarded as a collection of discrete particles characterized by certain distribution functions over the sizes is, in some aspects, better than the hydrodynamic description. In the process of sedimentation in turbulent flows, the particles of suspension acquire, due to their inertia, a nonoscillating mean component of acceleration P directed against the gravitational force. In the subsurface layer, the indicated pulsating deceleration of particles of the suspension constitutes a small fraction of the reduced gravitational acceleration g p and may increase directly near the bottom by more than an order of magnitude due to the high frequency of turbulent fluctuations of the velocity in this region. As a result of reasonable simplifications of the descriptions of the processes of sedimentation and lifting of terrigenous particles in the turbulent flow, it is possible to determine the equilibrium probability distribution function (W ) of suspended solid particles over their hydraulic coarseness W (the rate of sedimentation in immobile water) [4]. The distribution functions of particles of the suspension constructed for the coastal region of the sea depend on two parameters. Namely, the variance of turbulent fluctuations of the velocity specifies the location of the interval of sharp drop of the distribution function in the region of large diameters and the exponent 2q = = p /g p characterizes the slope of the segment of the function with power dependence in the region of small hydraulic and geometric sizes. The combined method for the determination of the characteristics of suspension in the coastal region of the sea combines (in addition to the constructed probability distribution functions of particles) the kinetic model of the intensity of wind-induced waves with the spectral model of subsurface turbulence generated by waves and the semiempirical model of pulsating turbulent bottom boundary layer [5, 6]. It is worth noting that the improvement and confirmation of the reliability of kinetic and hydrodynamic models of motion of the sediments in the coastal zone require the analysis of the input data obtained under the field conditions. The Donnaya Stantsiya complex of equipment developed at the Marine Hydrophysical Institute of the Ukrainian Academy of Sciences should remove the deficiency of these data. This complex is intended for measuring the characteristics of the hydrodynamic and lithodynamic processes in the chosen regions of the sea for various hydrometeorological conditions. Equipment of the Donnaya Stantsiya Complex Our investigations are mainly based on the use of the “Donnaya Stantsiya” complex (Fig. 1) including – the module of meters of the dynamic parameters, namely, a meter of pulsations of three components of the vector of current velocity u , v , and w , a meter of temperature T and conductivity C , a meter of hydrostatic pressure, and a meter of heel, trim, and vibroaccelerations along three axes; – the module of a meter of the attenuation coefficient of collimated light, i.e., a transparency meter; – the module of three accumulating meters of the suspension (traps) with a possibility remote reading of the amount of suspended substances;
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Fig. 1. Structure of the Donnaya Stantsiya measuring complex. – the module of the central unit containing the central processor with flash memory, adapters of the measuring modules, the transceiver, and the transformer of feeding voltages. In addition, the station is equipped with the coastal data-reception unit connected with a personal computer. The detailed description of the structure and principles of operation of measuring channels can be found in [5]. The complex is connected with the data-reception unit by a special cable with caprone braid: two wires of the telephone cable and three filaments of polypropylene. It is also possible to use a cable rope. In the course of the field experiments, we did not use the electromagnetic meter of horizontal components of the current velocity and the hydroacoustic wavegraph because they were in the stage of laboratory testing. In the absence of the electromagnetic meter of horizontal components, the data on the velocities and directions of bottom currents were obtained by using a hydrometric vane (VG-1-120/70). Prior to the expedition, the vane was upgraded at the Department of Shelf Hydrophysics of the Marine Hydrophysical Institute of the Ukrainian Academy of Sciences by installing an additional electronic block and microelectronic compass used for the realization of the algorithm of vector averaging of the results of measurements and accumulation of large data arrays in a flash-memory unit. The vane was mounted near the Donnaya Stantsiya complex on a submerged buoy in the course of the experiments carried out near the Kosa Tuzla Island and on a special pyramidal structure in the course of measurements performed in the coastal zone near Evpatoriya. The results of data processing show that the data averaged over 5-min intervals give reliable estimates of the velocity and direction of the current even for a significant wave component and a low mean transfer rate. The operative data on the velocity and direction of the wind were obtained with the help of a portable meteorological station (Wireless Weather Station) guaranteeing the possibility of indication of all current values of the parameters, as well as the values averaged over 10-min periods.
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Fig. 2. Spectra S (m2/sec) of pulsations of the components of the vector of current velocity (—) u , (•••) v , and (---) w (a) and the coherence function uw (b) typical of the shallow-water area near the southeast end of the Kosa Tuzla Island.
In addition, we used data of stationary meteorological stations located at the border post of the Kosa Tuzla Island and on the territory of the Ukraina paralympic complex. Note that our investigations of the shallowwater areas were carried out near this complex. The inquiry frequency for the channels of the module of meters of the dynamic parameters and the transparency meter was equal to 100 Hz. At the same time, for the module of traps of suspension, it was equal to 1 Hz. Due to the large volumes of the data, the operation of the Donnaya Stantsiya was realized in the interruption mode by blocks with the duration of records from 10 to 30 min. The vane and meteorological station were operating continuously.
Experimental Procedure and the Analysis of the Accumulated Data In 2008, the measurements were carried out in the course of two expeditions: in the shallow-water areas near the Kosa Tuzla Island on 22–25.08.2008 and on the west coast of the Black Sea near Evpatoriya (Zaozernoe) on 02–03.10.2008. In the first expedition, the works were carried out for four days on the southeast end of the island characterized by the most intense destruction of the coast: Since the time of interruption of construction of the dam on the Russian side, the Kosa Tuzla Island became shorter by 800 m.
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Fig. 3. Spectra of pulsations of the longitudinal component of the vector of current velocity u' for various wind velocities near the southeast end of the Kosa Tuzla Island.
Fig. 4. Time dependences of the variances of fluctuations of three components of the vector of current velocity, sums of these variances, and the wind velocity according to data of measurements on August 23, 2008 near the Kosa Tuzla Island.
The Donnaya Stantsiya complex was located at a distance of ~10 m from the coastal line of the southeast end of the spit at a depth of 1.5 m in the strait between the island and the dam on a thin layer of bottom sediments lying above protecting plates. The adjustments of the Donnaya Stantsiya complex and the hydrometric vane were made by hand without application of any floating means. All apparatus were taken off in the evening and adjusted at the same place in the morning. The Donnaya Stantsiya complex was oriented in such a way that the components of measured velocity fluctuations which are longitudinal and transverse relative to the device coordinates corresponded always, respectively, to the meridional and zonal components of the current velocity. A gage of the meter of pulsations of three components of the current velocity vector and a transparency meter were located at a distance of 0.25 m from the bottom, and three sand traps were at levels of 0.25; 0.5; and 0.75 m. During the expedition, we obtained totally 35 blocks of data recordings at winds of mainly the north directions. During the experiment, we did not observe southern and southeast winds on the Kosa Tuzla Island.
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Fig. 5. Dependence of the sum of variances of fluctuations u , v , and w on the wind velocity according to the data of observations on August 23, 2008 in the shallow-water areas near the Kosa Tuzla Island (straight line is a linear trend).
Fig. 6. Response of the system of waves to changes in the wind direction according to the data of observations on August 24, 2008 in the shallow-water areas near the Kosa Tuzla Island.
In Fig. 2, we show a characteristic example of the spectral processing of data of the meter of pulsations of three components of the current velocity vector. We chose a 10-min interval of recordings containing about 60,000 readings in each channel. These data were averaged over five points, so that the maximum frequency in the spectrum was equal to 10 Hz. The spectra of pulsations of the components u', v', and w' and the coherence between the longitudinal u and vertical w components were calculated by the FFT method. The spectra in Fig. 2 are characterized by the presence of a maximum of wave velocities at a frequency of 0.5 Hz, where the coherence between the components attains a value of 0.75. On the turbulence segment from 1 to 10 Hz, we did not register a significant coherence. The turbulence energy level (Fig. 2b) is much less than the energy level on the wave segment (Fig. 2a). Therefore, we may assume that the variance calculated for a series of observations is mainly determined by fluctuations of velocities of the wave origin. The levels of spectra depend significantly on the wind velocity at the time moment of measurements, as shown in Fig. 3. There, we present the spectra of fluctuations of the longitudinal component of the current velocity u at various wind velocities. We note that the difference in levels in the wave region approximately by one and a half order does not cause a significant change in the frequency of the maximum.
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Fig. 7 . External view of the optical module, i.e., a meter of the attenuation coefficient of collimated light (transparency meter). This means that the frequency of the basic wave in the region under study at north winds is determined by the run length, and the intensification of a wind induces only an increase in the steepness of waves. The spectrum level in the turbulence segment varies at a greater degree by approximately two orders. In Fig. 4, we present the time dependences of the variances of fluctuations of three components of the current velocity vector, the sums of these variances, and the velocity of a wind of the north direction which intensified during the day of August 23, 2008. Since the contribution of the turbulence is small, we observe the dominance of the tendency to the growth of the velocity of waves at an increase in the wind velocity. This tendency is clearly seen in Fig. 5, where we give the dependence of the total variance of fluctuations of three components of the current velocity vector on the wind velocity. In the available range of wind velocities, this dependence can be interpreted as a linear one. We can conclude already by Fig. 4 that changes of the energy of waves occur almost synchronously with variations of the wind velocity. The data obtained on August 24, 2008 illustrate the reaction of the system of waves on a change of the wind direction (Fig. 6). It is worth noting that the fast change of the wind direction from the north to east one happened from 11 till 12 h was accompanied by a corresponding increase in the zonal component v of the motion of waves. Most likely, the time of a reaction of the system of waves in the region under study near the Kosa Tuzla Island to the variability of winds of the north directions does not exceed 1 h. The examination of traps of a suspension showed that the amount of a material in the lower trap (0.25 m) that was accumulated for three days is very small (a layer of about 5 mm, ~ 8 cm3). It consisted mainly of organic substances of different origin (a vegetable material, to a significant extent), whereas the amount of a mineral suspension is insignificant (about 2 mm, ~ 3 cm3). We can conclude that, during the expedition, the suspension included mainly particles of organic origin formed in the Tamanskii Bay. Such particles have a less density, are deposited with a lower velocity, and fill the traps with a lower efficiency as compared with a sand suspension. For the alternative determination of parameters of a substance suspended in water, the Donnaya Stantsiya complex is equipped by a meter of the attenuation coefficient of collimated light, a transparency meter (Fig. 7). A method of determination of characteristics of a dispersion medium (the mean size of particles and their concentration) by fluctuations of its transparency is described in [7, 8] in detail. A technical realization of the method of fluctuations is simple, and it is expedient to apply this method for the development of in-process systems of observation of the dynamics of a large dispersed suspension in the coastal zone and its transport along a shore. The essence of the method of fluctuations consists in the following. Let a light beam with small diameter pass through the dispersion medium. Due to the chaotic motion of particles, their number in the beam varies, and the medium transparency fluctuates.
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Fig. 8. Typical examples of measurements of the transparency of seawater in the shallow-water areas (output voltage Uout of the measuring unit of the transparency meter) for different hydrometeorological conditions: (a) calm, (b) waves of strength 3.
The theory of this phenomenon indicates that the optical density of a medium and the variance of its transparency D depend on the mean size and the concentration of particles. The characteristics of a dispersion medium can be calculated by fluctuations of its transparency with the help of the formulas [7, Chap. 6.3]
s0 =
D S , I 0 2 ()
r=
s0 ,
n=
, ls0
= ln
I , I0
(1)
where s0 is the mean cross-section of particles, D is the variance of the light beam intensity for the time interval of measurements, I 0 is the initial intensity of a light beam passing through the dispersion medium, S is the cross-section of a light beam passing through the dispersion medium, is the optical density of the medium in the light beam, () is a special function, r is the mean radius of particles, n is the concentration of particles with a given radius, l is the distance passed by the light beam in the dispersion medium, and I is the mean intensity for the time interval of measurements of a light beam which passed through the dispersion medium. The special function
() = 2e
2
( sin ) 1 sin d
exp 0
connects the variance D with the optical density of the medium and the mean number of particles in the transilluminated volume N . Its calculation is performed in [7, Table 6.3]. The method of fluctuations described in the above-mentioned works for a suspension consisting of spherical particles can be also applied to nonspherical particles such as particles of a suspension in the sea. In this case, the mean cross-section of particles in a light beam should be calculated. As an example, we mention work [9], where suspensions containing particles of kaolin and cellulose fibers with nonspherical complicated shapes were studied.
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Fig. 9. Variations of the parameters of suspended substance (man radius of the particles, their number, and mass concentration) corresponding to the increase in the wind velocity according to the data of observations on August 22, 2008 near the Kosa Tuzla Island (the straight lines are linear trends).
Relations (1) were deduced in the case where the light beam of a transparency meter passing through the dispersion medium is attenuated only by particles present in the medium, rather than the medium itself [7, Chap. 6.3]. Such a medium is, for example, air characterized by a very small light attenuation coefficient. In the case where the medium containing suspended particles is sea water, the attenuation of light occurs due to water itself (which attenuate light significantly, especially in the long-wave region, where the measurements of fluctuations of the transparency of the dispersion medium are carried out) and due to the presence of a dissolved organic substance (yellow substance) and a suspension composed by small-sized and large-sized particles. Fluctuations of the water transparency are induced by large-sized particles with radii of the order of at least 10 μm . The remaining substances are a nonfluctuating “optical background” which should be taken into account. The method of calculations of parameters of a substance suspended in a seawater is presented in [10]. In Fig. 8, we show some examples of typical realizations of the output voltage U out of the measuring unit of a transparency meter under calm and stormy conditions that allowed us to calculate the parameters of a suspension under the described field studies. In Fig. 9, we present the results of processing of records of the transparency meter that were obtained near the Kosa Tuzla Island. During August 22, 2008, the wind velocity increased from 2.5 to 5.9 m/sec. We indicate the increase of the mass concentration and the mean radius of particles of a suspension, as well as the decrease in the number of registered particles in unit volume, in the course of time. Thus, the approximately double increase in the mean radius of particles compensates the double decrease in their number. After the change of the wind direction on August 25, 2008 and a decrease in its velocity, we note another tendency: the number of particles and the mass concentration of a suspended substance become simultaneously to decrease at an insignificant decrease in the mean radius. The second expedition on October 2–3, 2008 near Evpatoriya (Zaozernoe) was executed with the same apparatus composition. A small change of the procedure consisted in the use of a special pyramidal structure to hang a modified hydrometric vane instead of a submerged buoy, which was made due to significant velocities of the wave-induced motion in the bottom layer. The Donnaya Stantsiya complex was placed at a somewhat less depth (1 m).
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Fig. 10. Long-wave segments of the spectra of pulsations of the components of current velocity (—) u , (•••) v , and (---) w according to the data of measurements at the southeast end of the Kosa Tuzla Island (curves 1) and in the shallow-water area near Evpatoriya (curves 2).
Fig. 11. Hydrometeorological situation near Evpatoriya on October 2, 2008. On the first day at a steady wind velocity of about 7.5 m/sec, the station was mounted near a shore in the zone of surfs. On the second day, when the wind velocity became small, the apparatus was placed at the same depth significantly further from the shore, where the regular white-capping was practically absent. Totally, we obtained 30 blocks of records of data during the second expedition. The region near Zaozernoe is open for southern and southwest winds and is characterized by a different hydrodynamic situation as compared with that near the Kosa Tuzla Island.
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Fig. 12. Changes in the level of accumulated suspension in the lower (at a level of 0.25 m) and medium (0.5 m) traps according to the data of observations on October 2, 2008 in the coastal zone of the sea near Evpatoriya.
Fig. 13. Changes in the concentration of suspension revealed by the data of the traps located at depths of 0.25 and 0.5 m according to the data of observations on October 2, 2008 in the shallow-water area near Evpatoriya (straight lines are linear trends).
In Fig. 10, we give characteristic spectra obtained by processing the data of a meter of pulsations of three components of the current velocity vector for these regions at close values of the wind velocity. The wave segment of the spectrum calculated for a region near Evpatoriya occupies a wider region, and its maximum is shifted to the side of lower frequencies. Respectively, waves turn out longer, and the turbulence generated in the subsurface layer decays more slowly, as the depth increases. As a result, the turbulence intensity registered at a distance of 0.25 m from the bottom on a coastal area near Evpatoriya turned out approximately by one order higher than that near the Kosa Tuzla Island. The hydrometeorological situation during the day of October 2, 2008 is illustrated by Fig. 11. We note that the variances of all components of the velocity on the wave segment of the spectrum are practically invariable in the course of time under a steady wind of the southwest direction. The concentration of a suspension calculated according to the data of the accumulating meters of a suspension, i.e., traps with remote read-out, is represented in Fig. 12. There, we show the plots demonstrating the increasing levels of the accumulated suspension in the lower (a level of 0.25 m) and medium (0.5 m) traps.
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Fig. 14. Changes in the parameters of suspended substance (mean radius of the particles, their number, and mass concentration) under the action of stable wind according to the data of observations on October 2, 2008 in the coastal zone of the sea near Evpatoriya (straight lines are linear trends).
Fig. 15. Characteristics of currents during a storm in the coastal strip near Evpatoriya according to the data of observations on October 2, 2008.
Since the traps, like the entire Donnaya Stantsiya complex, were switched-on in the interruption mode, we indicate jumps on the plots corresponding to the accumulation for periods of “silence.” In other words, the information about the accumulation of a suspension is laid in a change of readings in the process of measurement. We note that the rate of accumulation of a suspended substance increases in both traps during a day. The concentration of a suspension C tr by readings of the traps is determined by the formula [11]
C tr = K tr
dm , dt
(2)
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Fig 16. Spectra of pulsations of the longitudinal component of the vector of current velocity according to the data of measurements on October 2, 2008 (curve 1) and October 3, 2008 (curve 2) in the coastal zone of the sea near Evpatoriya.
Fig. 17. Time dependences of the variances of fluctuations of the components of the vector of current velocity u , v , and w in the frequency range 0.1–50 Hz according to data of measurements on October 3, 2008 in the shallow-water areas near Evpatoriya (straight lines are linear trends).
where K tr is the calibrating coefficient and dm/dt is the rate of accumulation of a suspension in a trap. The values of the concentration of a suspension calculated by formula (2) are given in Fig. 13. Despite a great dispersion of values of the derivatives dm/dt , we note the stable difference in the concentrations at both levels and a remarkable trend to increasing the concentration of a suspension during the day of October 2, 2008. In Fig. 14, we show the variability of the characteristics of a suspension during October 2, 2008 calculated by readings of a transparency meter. The mean radius of suspended particles and their number per unit volume increase slowly, whereas the mass concentration of a suspension increases relatively rapidly.
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Fig. 18. Time dependences of the variances of turbulent fluctuations of the components of the vector of current velocity u , v , and w in the frequency range 1.0 – 50 Hz (straight lines are linear trends).
Fig. 19. Time dependences of the amount of accumulated suspension and its concentration in the case of weakening of the wind according to the data of the trap located at a depth of 0.25 m on October 3, 2008 in the shallow-water areas near Evpatoriya (the straight line is a linear trend and the continuous line is a polynomial trend).
In Fig. 15, we present characteristics of a current in a coastal strip near Evpatoriya obtained with the help of a hydrometric vane in the first day of measurements during a storm. The current was directed along the shore with an approximately constant velocity. We emphasize that the concentration of a suspension stably increases at the practical constancy of all hydrometeorological parameters according to the data of a transparency meter and traps of a suspension. This phenomenon will be discussed in the Conclusions. On the second day, October 3, 2008, the meteorological situation changes, the weak wind with a velocity of about 2 m/sec was unsteady in direction, and, respectively, wind-induced waves were absent. In Fig. 16, we give the spectra of pulsations of the longitudinal component of the current velocity vector for the first and second days of the Evpatoriya expedition.
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Fig. 20. Variations of the parameters of suspended substances (mean radius of the particles, their number, and mass concentration) under the conditions of sharp decrease in the wind velocity and changes in the direction of the wind according to the data of observations on October 3, 2008 in the coastal zone of the sea near Evpatoriya (the straight lines are linear trends).
Note that the spectrum in the wave segment became narrower on the second day, and the turbulence intensity significantly decreases. During the day, the intensity of swell monotonically decreased. In Fig. 17, we demonstrate the time dependence of the variances of fluctuations of three components of the current velocity in the whole frequency range from 0.1 to 50 Hz. These plots can be interpreted as a change in the energy of waveinduced motions, since the contribution of turbulence is small in this case. Assuming that the waves decay exponentially after the termination of the action of a wind and using the data in Fig. 17, we can approximately evaluate the duration of a decrease t w of the energy of waves Ew by the formula
Ew (t) = Ew (0)e
t / tw
.
The calculation yields t w 10 h. In Fig. 18, we present the time dependences of the variances of turbulent fluctuations of three components of the current velocity vector in the frequency range from 1 to 50 Hz which are obtained by the corresponding filtration of the input series. According to the calculation by data given in Fig. 18 (analogously to the calculation for Fig. 17), the decay time tT of the turbulence energy ET is tT 7.7 h . We can consider that the turbulence decays somewhat faster than waves. The variation of the calculated concentration of a suspension according to the data of the lower trap (0.25 m) on the second day of measurements in the Evpatoriya expedition in shown in Fig. 19. At a significant dispersion of the values obtained, the observed decrease in the concentration C tr can be characterized by the calculated time constant ttr 7.5 h, which is practically coincides with tT . In Fig. 20, we give the corresponding variability of the characteristics of a suspension calculated by data of a transparency meter on October 3, 2008. We note that, at a practically constant number of particles, the drop of their concentration occurs due to a decrease in their mean radius. The computed time constant tT for the drop of concentration CT by the data of measurements of transparency is tT 10.5 h, i.e., close to the value of t w .
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The above-presented brief analysis of data of field observations executed in 2008 with the help of the Donnaya Stantsiya complex does not include the consideration of the results of measurements of the temperature, electrical conduction, heel, trim, and vibroaccelerations along three axes. For relatively low wind loads, the values of heel, trim, and vibroaccelerations turned out to be insignificant, which confirms the reliability of structure of the station. CONCLUSIONS The Donnaya Stantsiya complex of equipment is developed with an aim of accumulation of the in-situ data not only for their storage with subsequent construction of the empirical dependences but mainly for the verification of the numerical kinetic models and improvement of their prognostic properties. It is also important to study the dynamics of wave-induced and turbulent processes in the coastal zone in connection with the variations of the characteristics of motion of suspensions. The solution of these problems is promoted by the high mobility of the complex, simplicity of its installation, and the possibility of carrying out measurements under various geographic conditions in various hydrometeorological situations. The measurements performed near the Kosa Tuzla Island show that, for small fetches, the system of waves and the characteristics of transparency of waters fairly rapidly respond (for at most 1 h) to changes in the wind situation. The intensity of turbulence varies in broader limits than the energy of surface waves which turns out to be proportional to the wind velocity. For the north winds, as an additional characteristic of this region, we can mention the presence of large amounts of organic suspensions delivered from the Tamanskii Bay. The flux of the sand suspension is weak because the short waves formed in this case can be characterized solely by the relatively low values of the bottom wave velocities and bottom turbulence even for significant winds. In the coastal zone of the sea near Evpatoriya, the southwest wind leads to the generation of much longer waves characterized by high levels of the bottom velocities and bottom turbulence in the shallow-water regions. As the wind action terminates, the wave energy, the energy of bottom turbulence, and the concentration of suspension decrease much slower than for the north winds near the Kosa Tuzla Island. Hence, the time constants computed for the former case are higher by about an order of magnitude. On October 2, 2008 (the first day of the Evpatoriya expedition), the measurements carried out in the zone of surfs revealed a stable noticeable growth of the concentration of sand suspension for stable levels of the wave and turbulent energies and an almost constant longshore current. This growth cannot be explained by the transfer caused by the horizontal inhomogeneities of the field of transparency because the autochthonous sand suspension at a depth of 1 m suffers rapid sedimentation for ~ 2 min and the corresponding space scale for a current velocity of 0.3 m/sec has the order of 30 m. Thus, the level of concentration of the sand suspension is a local parameter of the medium and must correspond to the dynamics of wave-induced and turbulent motions in the coastal zone. Most likely, the regular event of white-capping in the region of the surfs may lead to changes in the internal structure of turbulence with preservation of its energy parameters. In general, the results of field studies obtained with the help of the Donnaya Stantsiya measuring complex represent a valuable material for the correction and improvement of the kinetic schemes of computation of the characteristics of motion of sediments in the coastal regions of the sea. REFERENCES 1. V. A. Ivanov and A. E. Mikhinov, Prediction of the Dynamics of Sediments in the Coastal Zone (Practical Recommendations and Parameters of Calculations) [in Russian], Preprint, Marine Hydrophysical Institute, Ukrainian Academy of Sciences, Sevastopol (1991).
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