Coastal Dynamics 2009
Paper No.

LONGSHORE SEDIMENT MOVEMENT ALONG THE ENSHUNADA COAST
INFERRED FROM FELDSPAR THERMOLUMINESCENCE
Haijiang Liu1, Yuuki Ogawa1, Tomohiro Takagawa1 and Shinji Sato1

Abstract
Investigation on the sediment movement characteristics was conducted in a broad research area with a 150-kilometer
stretch along the Enshunada Coast and the Suruga Bay, Japan based on feldspar thermoluminescence (TL) properties.
River sand grains (primary source) present a higher TL signal than beach sand. Along the nearshore area, local TL
intensity peaks are observed at the river mouth and sample TL intensity gradually deceases with increasing distancefrom the river mouth, which indicates sediment longshore transport features. Far away from the river mouth, thedecreasing trend on TL intensities terminates. Taking the spatial distribution of TL intensities into account, aquantitative estimation on the longshore sediment flux was carried out based on the total river sand discharge. A
sunbath test was implemented to help to distinguish the beach sand constituents. Identification of coastal sand sources
was achieved in terms of the profile and magnitude of the measured TL glow curves.
Key words: longshore sediment movement, thermoluminescence, feldspar grain, sediment source, Tenryu River,
Enshunada Coast

1. Introduction
In the field, both qualitative and quantitative investigation of the nearshore sediment movement is of
critical importance for various coastal applications, such as developing efficient countermeasures against
the coastal erosion problems. In a case study of longshore sediment process within a specified coastal area,
identification of sand source, transport route/amount and the corresponding influential region is necessary.
Therefore, comprehensive studies by considering a rather broad research area with a macroscale stretch are
expected for fully understanding the insight into the general sediment movement mechanism.
Traditionally, the use of fluorescent or dye-marked tracers to study the nearshore sediment transport wasapplied in field works (Voulgaris et al., 1998; McComb and Black, 2005; Hiramatsu et al., 2008). However,such tracer studies suffer from many practical problems in terms of sand sampling and tracer concentration
determination. Artificially injected tracers are different from natural coastal sands in physical and chemical
properties, which may cause unreliable field measurements. Nevertheless, such tracer studies can only beapplied in a rather narrow area within a relative short period, e.g., at a spatial scale of several kilometers
and a temporal scale of several months. On the other hand, in a case study, Yuhi (2008) evaluated the longterm and large-scale morphological changes due to various anthrophogenic impacts based on successive
field survey records. However, such detailed and continuous survey data are usually scarce. At the sametime, further looking at in-situ sediment qualities becomes a useful approach to explore the sediment
movement process. From the sediment size distribution, Liu et al. (2000) estimated the source and the track
path of sediments in a watershed and the nearshore zone. Sato et al. (2004) achieved the long-term changes
in sand movement processes from the distribution of mineral composition. Recently, Rink (1999, 2003) and
Liu et al. (2009) suggested the use of natural residual thermoluminescence (TL) properties of quartz or
feldspar grains as a possible transport indicator in the study of various coastal depositional processes.
Applying this approach, sediment particles constituting the investigated object (natural sands), themselves,are used as self-tracers to monitor the nearshore sand movement. This allows more reliability related to thefield investigation on the nearshore processes. Pioneering studies have been carried out to verify the1

Department of Civil Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
hjliu@coastal.t.u-tokyo.ac.jp; ogawa@coastal.t.u-tokyo.ac.jp; takagawa@coastal.t.u-tokyo.ac.jp; sato@coastal.t.utokyo.ac.jp

Coastal Dynamics 2009
Paper No.
applicability of this new technique under several sediment movement circumstances. However, moredetailed studies and field applications are needed to establish the feasibility of the particle TL properties asa useful tool for examining the nearshore sediment movement under more sophisticated and extended
natural conditions.
In this study, we applied feldspar TL measurements to estimate the sediment movement in a broadresearch area with a 150-kilometer stretch along the Enshunada Coast and the Suruga Bay. Difference
between river and coastal sample TL glow curves was observed. Influence from river sediment discharge tothe nearshore sand constitution was discussed based on the spatial distribution of coastal samples’ TL
intensities. With respect to the measured TL signals, regional longshore sediment process was investigatedfrom both qualitative and quantitative viewpoints. Identification of the coastal sand source was estimated interms of the TL glow curve profile and magnitude. Intercomparison and discussion on the collected sample
TL glow curve and intensity outline a general insight into the longshore sediment movement pattern within
the target area.

2. Research Area and Methodology
In this section, the theoretical background of sand particle thermoluminescence, together with its
applications in coastal engineering, is briefly introduced. Then, research area and field sampling locations
for this study are specified. After that, laboratory preparation on collected samples and experimental
methods are described.
2.1. ThermoluminescenceThis study applied the use of thermoluminescence (TL) properties of feldspar particles as a tool for theinvestigation of sand transport in the nearshore zone. Constituent mineral grains, e.g., quartz and feldspar,
undergo natural radiation while buried in a sedimentary environment, which builds up the latent
luminescence signal through the effect of exposure to the weak flux of ionizing radiation provided bythorium, uranium and potassium-40 and their daughter products in the sediment, as well as by cosmic rays
and by rubidium-87 to a minor extent. Thermoluminescence is the laboratory-stimulated light emission
from the particle crystal by heating the sample to a certain temperature. The light emission occurs during
the recombination of electrons and holes between traps and luminescence centers in the defect structure of
the quartz or feldspar crystal lattice. Further detailed descriptions can be found in Aitken (1998).
Figure 1 shows a schematic diagram to illustrate the grain TL signal accumulation/release process. The
magnitude of luminescence signals in a grain is proportional to the accumulated energy that has been storedfrom the natural nuclear radiation during depositional burial, i.e., Stage I in Figure 1. After sand particles
are eroded from their depositional spots, sediment transportation along the river or nearshore zone isaccompanied with the sunlight exposure, which reduces the particle luminescence signals by depopulating
the trapped electrons, i.e., Stage II in Figure 1. The more significant the light exposure, i.e., the longer theparticle travelling distance, the smaller the TL signals. Nevertheless, even with long-term subaerial solar
exposure (at a time scale of several years), grains do not lose all their TL signals. This leads to a naturalresidual TL signal. Spooner (1987) found that TL signal generally decreases exponentially with solar
exposure. After a long-time exposure, decrease of the natural residual TL becomes indistinct and tends to asmall, but nonzero asymptote. Thereby, a correlation between sand TL signals and the corresponding
moving distance is established. Consequently, the residual TL signals inherent in natural sand particles canbe used as a transport indictor for describing the nearshore sediment movement process. In the downdrift
direction, sand grain TL signals from a unique source will deplete as a function of travelling time, i.e.,
duration of solar exposure during movement. If sands from other source are supplied into the littoral
process, modification on the local TL signal is expected. By looking at the natural residual TL signal
presenting in stage II, this study focuses on the characterization and identification of nearshore sediment
movement features in the research area.

Coastal Dynamics 2009
Paper No.

TL signal
ErosionSunlight Bleaching
TL DecreaseNon-exposure
TL Increase

Natural Residual TL
Deposition

Stage I

Stage II

Sand BurialTime

Sediment Transportation

Figure 1 Schematic diagram on temporal variation of grain TL signal.

2.2. Research area
In this study, the target research area is the Enshunada Coast, which is located in the west of Shizuoka
Prefecture, Japan, and has a double-arc shoreline profile with Tenryu River mouth extruding in the middle(Figure 2). Tenryu River, considering its large sediment discharge, is assumed to be the original anddominant sediment source for the littoral sands on the Enshunada Coast. This area has been suffered fromcoastal erosion induced by various natural and anthropogenic reasons. Detailed descriptions can be foundin Liu et al. (2007). In order to distinguish the influential area from Tenryu sediment discharge, sample
collection also went eastward to the nearshore region along the Suruga Bay where sand contribution fromthe Ooi River also plays an important role when considering longshore sediment movement.

N 35

Shizuoka Prefecture
Japan

N
10 km

34.8
Research Area

34.7

R1

CF

Coastal Cliff Zone

C30
C35

C25

C1

Ooi River

Oota River

Tenryu River

34.9

R3
C5

R2

Suruga Bay
C10

C22 C20
C15

34.6

C40

Atsumi Peninsula

Enshunada Coast, Pacific Ocean

Omaezaki Cape

34.5
136.75137137.25137.5

137.75138138.25Figure 2. Research area and TL sampling locations for coastal samples (‘●’, C1 to C43),
river samples (‘▲’, R1 to R3) and coastal cliff sample (‘□’, CF).

E 138.5

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In total, 43 surface samples (about 10 cm beneath the ground surface) were collected at the top ofintertidal zone in the target coastal area, named as C1 to C43 starting from east to west as shown in Figure
1. Among those, samples C3 and C22 were collected at the Ooi and the Tenryu River mouth, respectively.
Sample collections were carried out with a spatial interval of several kilometers. Detailed sampling was
conducted in the vicinity of river mouth or coastal structures to reveal the local changes in TL properties. In
order to identify the sand source, riverbed surface samples (about 5 km upstream of the river mouth) werealso extracted along three major rivers within this research area, i.e., the Tenryu River, the Oota River andthe Ooi River with sample name R1, R2 and R3, respectively. Field samples, named as ‘CF’, were alsocollected from the coastal cliff located at the west side of the Enshunada Coast to recognize the nearby
beach sand sources. During field sampling, dark film cases, together with black bags, were used to store thesand samples to prevent natural light exposure.
2.3. Sample pre-treatment and TL measurement
Laboratory preparation of the collected samples was conducted in semidarkness (under subdued orange
light) to avoid the underestimation of luminescence signals. Sample pretreatment was conventional(Wallinga et al., 2000). All samples were water washed and subsequently treated with 15% H2O2 and 18%
HCL to remove the organic material and carbonates. Then, the K-feldspar rich fraction was obtained by adensity separation in sodium-polytungstate at a density of 2.58 g/cm3. The grain size fraction of 180-300µm was used for further studies. Subsequently, a monolayer aliquot, with each disk retaining about several
hundreds of feldspar grains, was applied in measurement to avoid the possible inhomogeneous features inluminescence signals from individual grains. Luminescence measurements were performed on a Risø 48sample automated TL/OSL Reader with an internal 90Sr/90Y beta irradiation source. Sample TL signals were
measured up to 5000C using a heating ramp rate of 50C/s. A detection filter combination of a Schott BG39
and Corning 7-59 filter was used with a TL signal transmission window between 320 and 480 nm.
Measurements were performed based on the TL test protocol proposed in Liu et al. (2009), in which
natural TL measurement was carried out after a preheat of 1800C for 10 s to remove the unstable TL signals.
To compare the samples collected at different locations, normalization of the natural TL signal is needed tocompensate the inherent difference in samples, such as aliquot mass. Normalization was realized using an
artificial test dose stimulation of 60 s (10.8 Gy dose). The normalized feldspar TL signal (after the averageof four aliquots for every sample) was used in the following discussions.

3. Results and Discussions
3.1. TL glow curves for river samples
Sediment supply from the river discharge in a fluvial system is the dominant sand source for the adjacentcoastal sediment cell. Therefore, consideration of river sand properties is necessary for investigation on thenearshore sediment movement. Figure 3 presents the normalized TL glow curves for three river samples(R1, R2 and R3) and one typical coastal sample (C22). It is found that all three river sample TL signals
have much larger values, with a normalized TL peak value over ten, than that of coastal sample. Sand
grains originating from the river upstream area have large TL signals since they undergo short travelling
time and distance from their depositional burial stage under which TL signals are accumulating in particle
crystal lattice. During the transport process, sand particles have the opportunity to exposure to sunlight anddeplete their stored TL signals. Hence, large and small TL signals are expected for river and beach samples,
respectively, as demonstrated in Figure 3. This is consistent with the result from Liu et al. (2009) in which
they only investigated samples from the Tenryu River.
3.2. TL glow curves for coastal samples
Along the nearshore region and away from the river mouth (sand source), a decreasing trend in grain TL
would be anticipated for a single sediment source condition because grain particles experience increasing
light exposure during transport process. Figure 4 illustrates normalized feldspar TL glow curves from five
coastal samples as shown in Figure 2, in which sample C22 was collected at the Tenryu River mouth andCoastal Dynamics 2009
Paper No.
samples C19, C18, C17 and C16 were from the east side of the Enshunada Coast with an increasing
distance from the Tenryu River mouth. It is found that the normalized natural residual TL signals gradually
decrease with increasing distance from their primary source at the Tenryu River mouth. This is inagreement with the result from Rink (2003) who conducted TL measurements on nearshore samples along
the coast of Israel. During the longshore sediment movement, sand particles undergo light exposure withrespect to the moving time and distance, thus depopulate their stored TL signals in this process. Hence, adecreasing trend of TL signal is expected in the downdrift direction.

Normalized TL

20

16

R3, Ooi River

12

R1, Tenryu River

R2, Oota River

8

C22, Coast
4

0
0

100

200

300

400

500

Temperature (ºC)
Figure 3. Normalized TL glow curves for three river samples (R1 at Tenryu River, R2 at Oota River and R3 at Ooi
River) and one coastal sample (C22 at the Tenryu River mouth).

5

C22

Normalized TL

4

C19

3

C18
2
C17
C16

1

0
0

100

200

300

400

500

Temperature (ºC)
Figure 4. Normalized TL glow curves for coastal samples along the east side of the Enshunada Coast.

Coastal Dynamics 2009
Paper No.

10

TL intensity

8

Tenryu River

C5

Oota River

6

C1

C20

4
Atsumi Peninsula
C40

2

C30

Ooi River

C25

Omaezaki

C35

C15

C10

0
-80

-60
West

-40

-20

0

20

40

Longshore distance from Tenryu River mouth (km)

60

80
East

Figure 5. Spatial distribution of residual TL intensity in the research area.

3.3. Spatial distribution of natural residual TL intensity
Spatial distribution of the natural residual TL intensity in terms of the longshore distance away from the
Tenryu River mouth is illustrated in Figure 5. Here, an eastward direction from the Tenryu River mouth isassumed to be positive. TL intensity is evaluated by considering average of the normalized TL glow curve
over temperature range of 260-3800C, which covers dominant TL signals as shown in Figure 4. It is foundthat TL intensity goes to a local peak value in the vicinity of the Tenryu River mouth. Influence from theriver sand contribution can be observed which elevates the adjacent coastal TL intensity since river sands
contain larger TL values as shown in Figure 3. Away from the Tenryu River mouth, TL intensity gradually
decreases on both sides of the nearshore zone. This agrees with the scenario that during longshore sediment
movement process, sand particles experience sunlight exposure which induces a decrease on grain TL
signals as also seen from the TL glow curves shown in Figure 4. Spatial distribution of TL properties in thisregion reveals the TL signal decreasing process specified in stage II of Figure 1. In the nearshore downdrift
direction, grain TL decreases as a result of continuous solar exposure during sediment transport process.
Local TL intensity variation can also be observed around the Ooi River mouth. However, such phenomena
can not be detected around the Oota River mouth. This is attributed to the small sediment discharge fromthe Oota River with a river length of 44 km and a catchment area of 488 km2. Comparing with the Tenryu
River with a length of 213 km and a catchment area of 5090 km2 (10 km west of the Oota River), influenceon the coastal sample TL intensity from Oota River originated sands, although they also present a large TL
signal (Figure 3), can be neglected. Hence, considering the coastal sand constituents along the Enshunada
coast, predominant contribution from Tenryu River is confirmed through the measured TL signal. This isregardless of the particle size, mineral components and sand color, which were used in the previous studies(Liu et al., 2000; Sato et al., 2004; Liu et al., 2007).
Another interesting phenomenon is that around the river mouth, there exists certain fluctuation on themeasured TL intensity, which is more obvious for Tenryu River mouth. Within a range of ±5 km, clear
variation on measured TL intensities is observed. Away from this area, modification on the coast sample TL
intensity is rather smooth. This is owing to sediment inherent characteristics from the river sand supply. Liuet al. (2009) found that particle TL signal heterogeneity is rather significant for river samples since
sediment movement caused by the unidirectional river flow, thereby, the TL signal bleaching by sunlight, isoccasional and irregular (mainly during flood events) under river environment. Nevertheless, under coastenvironment, especially in the dynamic swash zone where field samples were collected, sand particles are
frequently mobilized and exposure to sunlight by the continuous wave uprush and downwash motions. This
induces a more uniform TL signal for coast samples. In the vicinity of river mouth, both mechanisms exist.
Mixing process between river sands and original coast sands occurs. Hence, variation on TL signal inducedby the non-uniform river sand appears around the river mouth. In case of a larger river sediment discharge,such spatial TL variation extends to a wide range. With respect to this point, it can be assumed that sand

Coastal Dynamics 2009
Paper No.
discharge from the Tenryu River is larger than that from the Ooi River. According to MLIT (2006), the total
sediment discharge from the Tenryu River is around 9.7×105 m3 per year (including slits with size less than
0.106 mm, sands with size between 0.106 and 0.85 mm and gravels with size larger than 0.85 mm), and thedischarge from the Ooi River is about 1.45×105 m3 per year. This argument can also be distinguished withrespect to the nearshore extension where coastal sand TL signal is affected/enhanced by the relevant river
supply. In case of the Tenryu River, it covers a range of about ±30 km as shown in Figure 5. Within thisrange, increase in sample TL intensity is observed. TL intensity keeps a rather uniform, but small value
beyond this area. As for the Ooi River, its effect is rather limited, i.e., about 65±5 km in Figure 5. This
demonstrates sediment supply from the Tenryu River is greater than that from the Ooi River. Anotherscenario is that the longshore sediment movement is predominant around the Tenryu River; whereas,
certain offshore sediment movement exists for the Ooi River discharge. From the measured nearshore
bathymetry data, it is confirmed that the seabed has a steeper nearshore topography in the Suruga Bay (OoiRiver) than that of Enshunada Coast (Tenryu River), which implicates the hypothesis that Ooi Riversupplied sands may go directly into the offshore zone. Accordingly, longshore sand movement inferredfrom the measured TL intensity presents just in the limited area of the Ooi River mouth. As for the Tenryu
River, longshore sand movement extends to a wide region indicated from the TL measurement.
Up to now, analyses on the longshore sediment movement based on coastal sample TL measurement are
qualitative. At the same time, quantitative discussion on the longshore sediment flux around the rivermouth can also be estimated from the spatial distribution of the measured TL intensity. Considering thatcoastal sands lose their inherent TL signals during longshore movement owing to the sunlight exposure, thelonger distance away from the river mouth results in the smaller sand grain TL signal comparing to thesample TL collected at the river mouth. The decrease in particle TL intensity is proportional to the time
duration of sunlight bleaching, that is, inversely proportional to the longshore sediment movement velocity
in case of the same longshore travelling distance. After river-supplied sediments reach the nearshore zone,
question on how and how much these sands will be distributed along the coastal area becomes important.
Understanding on it can help us to develop efficient countermeasures against costal erosion problems.
Traditionally, such nearshore sediment distribution is estimated from the measured bathymetry data. In thisstudy, through the longshore distribution of sand sample TL intensities in the vicinity of river mouth, we
can evaluate the proportional relationship of sand moving velocities between two sides of the river mouth,
thus, estimation of the longshore sediment flux can be carried out based on the total river sediment
discharge. According to the inclination of TL intensity profile presented in Figure 5, longshore sediment
flux originating from the Tenryu and the Ooi River discharges was quantitatively estimated and listed inTable 1. As for TL intensity-based estimation, offshore sand loss was not included in the calculation.
Inferred from TL intensity distribution, it is found that the Tenryu-contributed sands are almost equallydistributed to both sides, which induced a nearly symmetric TL intensity profile around the Tenryu Rivermouth as illustrated in Figure 5. In case of the Ooi River, a rather asymmetric longshore sediment flux isestimated with most of sands (1.32×105 m3/y, about 90% of the total river discharge) go to the left side of
the river mouth. This is in agreement with the estimation from measured bathymetry data (1.37×105 m3/y to
the left side). Such asymmetric longshore flux distribution is caused by the nearshore wave direction in thetarget area. Predominant wave direction in this area is from south to north. Considering the Ooi River,shoreline along the Suruga Bay is in the northeast-to-southwest direction, hence, most of sands aretransported to the north, i.e., the left side of the river mouth, due to the wave-induced longshore currents. In
case of the Tenryu River and taking into account that the Enshunada Coast is in the east-west direction, asymmetric distribution on Tenryu-contributed sands can be expected on two sides of the river mouth.
Consequently, measured TL intensity distribution can be used as an indicator to quantitatively estimate theriver-contributed sediment longshore distribution. Although the estimation is brief, this approach provides arather simple and efficient way comparing with the traditional method based on the variation of measured
seabed bathymetry data.
Table 1. Longshore sediment flux estimated from TL intensity distribution.

Tenryu
River
Ooi
River

Left
Right
Left
Right

TL spatial distribution
from Figure 5(TL/km)
0.13
0.13
0.17
1.75

Estimated longshore
sediment flux
(×105 m3/y)
4.75
4.95
1.32
0.13

Total river discharge from
MLIT (2006)(×105 m3/y)
9.7
1.45

Coastal Dynamics 2009
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3.4. Identification of sediment source
Further look at Figure 5, it reveals that in the area far away from the Tenryu River mouth, e.g., 30 km away,
TL intensity decreasing trend terminates for both sides of the Enshunada Coast. Sand samples keep a rather
constant TL intensity over there. However, a certain difference between the constant TL intensity values fortwo sides of the Enshunada Coast can be observed, i.e., about 1.6 on the west side and 0.7 along the eastside. It is proposed that the natural residual TL intensity from the same sand primary source will be
depleted and achieve the same constant TL intensity value finally. This constant value implicates the hardto-bleach TL component remained in feldspar grains, which cannot be thoroughly depleted under naturalenvironment. This remaining TL signal represents the nonzero asymptotic value at the final state of theparticle TL bleaching curve, i.e., the late part of stage II shown in Figure 1. Under this stage, grain TL
almost keeps a constant value even under long time solar exposure. Further longshore sand movement does
not remove the remaining unbleachable TL signal. As a result, there has no significant change on themeasured natural residual TL intensity after a certain distance from the river mouth. Nevertheless, sandsamples on the west side keep a higher residual TL intensity than the east side one. Considering the above
mechanism, it suggests that these sands may not reach the final unbleachable stage. Further decrease on TL
signals can be expected to achieve a smaller natural residual TL intensity equal to the final value on theeast side. At the same time, such high, but uniform TL distribution on the west side was detected, whichshould come from other external reasons except the sediment contribution from the Tenryu River.
In order to confirm these assumptions, sunbath test was performed using two coast samples, C13 on theeast side and C36 on the west side. These two samples were selected considering that they are located in
the TL-constant zone as shown in Figure 5. In order to provide a homogeneous laboratory lighting
condition for data comparison, sunbath test was conducted using indoor fluorescent lamp to bleach thefield samples with different time durations (10s, 1 min, 1 hour, 1 day and 1 week in this study). Afterward,
TL intensity was measured and compared with the original natural residual TL intensity, i.e., without any
sunbath. Ratio between these two TL intensities is named as relative TL intensity. Figure 6 illustrates thesunbath test results with a logarithmic scale on sunbath time. For sample C13, even after long-time andsuccessive light exposure, there is no clear change in the sample TL intensity. Measured results after
various sunbath tests on sample C13 demonstrate a nearly constant TL value for sample C13, which is notdepleted by further sunlight exposure. Hence, on the east side of the Enshunada Coast, after longshoretransport from the Tenryu River mouth, sand particles lose their TL signal and in deed, reach a stable stage
with a approximately constant TL feature. However, in case of sample C36, a decreasing trend is observed
after one week light exposure. This means under continuous sunshine conditions, sand sample on the westside can be further bleached to a smaller TL intensity value (almost equal to that of C13) if there is no othersand supply to this area. Nevertheless, the fact that TL intensity keeps a higher constant value on the westside indicates other sand supplying source with a large TL intensity exists over there besides sedimentcontributed from the Tenryu River transported by the longshore sand movement.
On the west side of the Enshunada Coast, there exists a series of coastal cliffs. Figure 7(a) shows a photoof these coastal cliffs. It is understood that due to the short distance between cliff and shoreline (few tens ofmeters), these cliffs are suffering from erosion problems under episodic storm or typhoon conditions.
Eroded cliff particles are transported to the nearby area and mixed with the coastal sands located at the
Enshunada Coast. Consequently, coastal cliff serves as another sand source. From the geological viewpoint,these cliff sands were buried long time ago and excluded from sunlight exposure. Hence, they contain large
TL signals. In order to verify this argument, sand samples were also collected from the coastal cliff, i.e.,sample CF (Figure 1) which is near to coastal sample C36. Figure 7(b) presents the normalized TL glow
curve measured from the cliff sample, CF. Comparing to the corresponding coastal sample result, C36, it isclear that cliff sands hold a rather large TL intensity. After erosion and movement, cliff sands lose certain
part of their inherent TL signals. However, due to the short travelling distance (short light exposure time),
they still contain a relatively large TL features. With respect to the quantity of nearshore transported sands,
eroded cliff sands only has a small amount due to the relatively occasional storm erosion events. Then,these sands mix with Tenryu-borne coastal sands of low TL intensities after an extensive longshore
movement. As a result, sand samples along the west side of Enshunada Coast can keep a relatively highand constant natural residual TL signal. As shown in Figure 1, the coastal cliff zone extends to a wide range
along the west side of Enshunada Coast. Taking results of Figure 5 into account, it is found that the stretch

Coastal Dynamics 2009
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of coastal cliff zone just matches with the area where the TL intensity keeps a constant value. Hence,
mixing process in this region from two different sediment sources, i.e., Tenryu-contributed sands
transported from far distance and cliff sands eroded from nearby area, was observed and confirmed after
the TL measurement.

1.1
C36

1
0.95

0.85

1 week0.9

1 day

1 hourC13

1 min

Relative TL intensity

1.05

0.8
1

10

100

1000

10000

1000001000000

Sunbath time (s)Figure 6. Sunbath test results for samples C13 and C36.

(a)

80

(b)

Enshunada
Coast

Normalized TL

60
Coastal Cliff

Cliff sample, CF
40

20
Eroded Cliff Spot

Coastal sample, C36
0
0

100

200

300

400

500

Temperature (ºC)

Figure 7. (a) Photo of coastal cliff along the west side of the Enshunada Coast.
(b) Normalized TL glow curves for coastal cliff sample, CF, and nearby coastal sample, C36.

Up to now, we focus on the magnitude of sample TL glow curves for discussions. Further considering
the profile of TL glow curves can provide more information related to the sediment movement. Figure 8
demonstrates 3 normalized TL glow curves sampled in the vicinity of the Ooi River. Comparing with the
TL glow curves around the Tenryu River as shown in Figure 4, there exists a clear difference in terms ofglow curve profiles. In general, TL glow curve presents two local peaks within the temperature range. One
is around temperature of 2800C, and the other is around 3600C. As for TL glow curves around the Tenryu
River, the low temperature TL peak has a larger value than the high temperature TL peak; whereas, adifferent result, with the 2800C TL peak being smaller than the 3600C TL peak, is confirmed for TL glow

Coastal Dynamics 2009
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curves around the Ooi River. This represents different sand natural TL characteristics from different
sediment sources. During sediment movement, sand particles experience various bleaching process under
different circumstances. This also induces local features on the grain TL signal. Hence, identification ofsand source and judgment on a specified river-affected region can be implemented based on theseproperties of TL glow curves.

10

Normalized TL

8

C3

C1

6

C2

4

2

0
0

100

200

300

400

500

Temperature (ºC)
Figure 8. Normalized TL glow curves along east side the Ooi River.

10
C5, Yoshida
Harbor North

Normalized TL

8

C4, Ooi South6

4
C6, Yoshida
Harbor South2
C7, Shizunami
0
0

100

200

300

400

500

Temperature (ºC)
Figure 9. Normalized TL glow curves for samples C4, C5, C6 and C7 around the Yoishida Harbor.

Coastal Dynamics 2009
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Figure 9 illustrates the normalized TL glow curves for 4 samples collected at the right (south) side of the
Ooi River mouth, along the shoreline of Suruga Bay. Samples C5 and C6 were collected on two sides of
the Yoshida Harbor with a rather short distance in between, i.e., about 1 km. However, there is a sudden
drop on the measured TL signal between C5 and C6. Sudden decrease on the TL intensity between C5 andC6 can also be observed from Figure 5. Going further north by considering TL glow curve of sample C4(about 2 km north of sample C5), which was collected at south of the Ooi River mouth, it presents a similar
TL profile as that of C5; whereas, going further south and looking at sample C7 (Shizuname, about 3 km
south of sample C6), its glow curve shows an analogous shape as that of C6. Taking TL signal magnitude
into account, two groups can be classified, i.e., C4/C5 with large TL intensity and C6/C7 with small one.
Further looking at the TL glow curves between C4/C5 and C6/C7 and considering Figures 4 and 8, it isindicated that samples C4 and C5 are originated from the Ooi River with high temperature peak being
larger than low temperature peak; whereas, samples C6 and C7 present curve profiles similar to that fromthe Tenryu River with high temperature peak being smaller than low temperature peak, which implicatesthat these sands are originated from Tenryu sediment discharge. It reveals the following scenario that due tothe significant sediment supply from Tenryu River in the old days, a certain amount of sand particles fromthe Tenryu River goes eastward, bypasses the Omaezaki Cape and affects the nearshore beach constitution
along the Suruga Bay. Such nearshore transport can extend as north as the location of the Yoshida Harbor,which is the physical boundary between Tenryu-originated sands and Ooi-originated sands. Therefore,
identification on coastal sand sources is realized. Such Tenryu sand bypass movement pattern is also
consistent with the finding from Liu et al. (2007), in which they tracked the sand movement based on thesand sample color and magnetic properties.

4. Conclusions
Longshore sediment movement along the Enshunada Coast and the Suruga Bay was investigated based on
the feldspar thermoluminescence (TL) properties. Laboratory measurements on sand natural residual TL
signals reveal the following conclusions:
1. As sediment primary source for the nearshore area, river sands present a higher TL signal than coastal
sands. The latter experiences the TL signal depleting process during movement.
2. Owing to the river sand discharge with large TL features and gradual bleaching during longshore
sediment movement, measured coastal sand TL signals present a local peak value around the rivermouth and a decreasing trend with an increasing distance from the river mouth.
3. In the vicinity of river mouth, there exist certain fluctuations in terms of the coastal sand TL intensity,
which is ascribed to the river sand supply with rather heterogeneous particle TL signals.
4. Comparing to the Tenryu River and the Ooi River, sediment discharge from the Oota River is fairly
insignificant. Inferred from TL measurement, Tenryu-contributed sands are transported to a wider
longshore region than that from the Ooi River.
5. Considering the spatial distribution of natural residual TL intensities, quantitative estimation on thelongshore sediment flux based on the total river sand discharge was carried out. Eastward andwestward sediment fluxes are almost equal in case of Tenryu River; whereas, predominantly northward
sediment movement (about 90% of the total river discharge) is recognized for Ooi river supplied sands.
6. The decreasing trend on TL intensity terminates with uniform values being observed far away from the
Tenryu River mouth. The constant residual TL intensity on west side is larger than east one. On eastside of the Enshunada Coast, it is attributed to the unbleachable feldspar natural residual TL
characteristics. Along the west side, mixing process between Tenryu-contributed sands transported
from far distance and coastal cliff sands eroded at nearby area was undergoing and confirmed after thesunbath test and relevant TL measurements. This induces a relatively larger constant TL intensity valueon the west side than the east side of the Enshunada Coast.
7. Further looking at the profile and magnitude of sample TL glow curves, identification on coastal sandsources was implemented. It is found that the Tenryu-originated sands can bypass the Omaezaki Capeand affect the beach constitution as far as the south of the Ooi River. Interface between these two sandcontributions is detected around the Yoshida Harbor.

Coastal Dynamics 2009
Paper No.
Acknowledgements
We would like to thank Mr. T. Yoshii, the University of Tokyo, for helps during field TL sample collection.
This study is a part of Tenryu-Enshunada Project, “Dynamic sediment management and coastal disasterprevention by advanced technologies” supported by the Special Coordination Funds for promoting Scienceand Technology of Ministry of Education, Culture, Sports, Science and Technology, Japan.

References
Aitken, M.J., 1998. An Introduction to Optical Dating: The Dating of Quaternary Sediment by the Use of PhotonStimulated Luminescence. London, Oxford Science Publications, 267p.
Hiramatsu, H., Tomita, S., Sato, S., Tajima, Y., Aoki, S. and Okabe, T., 2008. Sediment movement mechanism aroundthe Magome River mouth based on color sand tracer experiments. Proceedings of Coastal Engineering, JSCE,
55(1), 696-700. (in Japanese)Liu, H., Sato, S., Tajima, Y., Huang, G. and Fujiwara, H., 2007. Investigation on the historical evolution of alluvial
deposits along the Tenryu River and the Enshu Coast. Proceedings of the 4th Asian and Pacific Coastal
Engineering Conference, Nanjing, China, 1139-1150.
Liu, H., Kishimoto, S., Takagawa, T., Shirai, M. and Sato, S., 2009. Investigation of the sediment movement along the
Tenryu-Enshunada Fluvial system based on feldspar thermoluminescence properties. Journal of Coastal Research,
In press.
Liu, J.T., Huang, J.-S., Hsu, R.T. and Chyan, J.-M., 2000. The coastal depositional system of a small mountainous river:
A perspective from grain-size distributions. Marine Geology, 165, 63-86.
McComb, P. and Black, K., 2005. Detailed observations of littoral transport using artificial sediment tracer, in a highenergy, rocky reef and iron sand environment. Journal of Coastal Research, 21(2), 358-373.
MLIT, 2006. Documents on Sediment management, Basic Policy for River Maintenance, Tenryu River Fluvial System
and Ooi River Fluvial System, http://www.mlit.go.jp/river/basic_info/jigyo_keikaku/gaiyou/seibi/, Ministry ofLand, Infrastructure, Transport and Tourism, Japan. (in Japanese)
Rink, W.J., 1999. Quartz luminescence as a light-sensitive indicator of sediment transport in coastal processes. Journalof Coastal Research. 15(1), 148-154.
Rink, W.J., 2003. Thermoluminescence of quartz and feldspar sand grains as a tracer of nearshore environmental
processes in the southeastern Mediterranean Sea. Journal of Coastal Research. 19(3), 723-730.
Sato, S., Kajimura, T., Abe, M. and Isobe, M., 2004. Sand movement and long-term beach evolution in a fluvial systemcomposed of the Samegawa River and the Nakoso Coast. Coastal Engineering Journal, 46(2), 219-241.
Spooner, N.A., 1987. The Effect of Light on the Thermoluminescence of Quartz. M.Sc. thesis, Dept. of Physics,
University of Adelaide, Australia.
Voulgaris, G., Simmonds, D., Michel, D., Howa, H., Collins, M.B. and Huntley, D.A., 1998. Measuring and modelingsediment transport on a macrotidal ridge and runnel beach: an intercomparison. Journal of Coastal Research, 14(1),315-330.
Wallinga, J., Murray, A. and Wintle, A., 2000. The single-aliquot regenerative-dose (SAR) protocol applied to coarsegrain feldspar. Radiation Measurements, 32, 529-533.
Yuhi, M., 2008. Impact of anthropogenic modifications of a river basin on neighboring coasts: case study. Journal of
Waterway, Port, Coastal, and Ocean Engineering, 134(6), 336-344.