沙漠研究 19-1, 269- 272 (2009 )Journal of Arid Land Studies“Desert Technology IX ”
Refereed Paper

The Influence of Sediment Heterogeneity on Percolation in Sand Dune
Takayuki KAWAI1, Hiroshi YASUDA1, Tadaomi SAITO1, Yasuyuki TADA2
Abstract: In this research, we aimed to clarify the phenomenon of vertical soil moisture
movement in dune. Moreover, the dominant factor of soil moisture movement was checked.
Research area was Tottori sand dune, Japan. We set an observation point for soil moistureprofile and an artificial outcrop for the sedimentary structures and the detailed soil moistureprofile. As the observation result, the soil moisture inside the dune was heterogeneous andhad a layered structure. However, this observation point consisted of almost fine sand fromthe grain mechanical analysis. There was no remarkable difference of sediment. Then wechecked the sedimentary structures to the last detail by artificial outcrop. Under surface, there
was a compound cross lamina structure. Additionally, the soil moistures on each cross lamina
borders were constantly higher than other depths. These results showed that the laminastructures controlled the soil moisture movement of sand dune.
Keywords: Lamina structure, Sediment heterogeneity, Sand dune, Soil moisture

1. Introduction
When we worked around water problems in sandy area, especially in natural dune, the percolation
phenomenon was generally analyzed on the assumption that the sand sedimentary structure washomogeneous. Actually, sandy soils were formed with a uniform material compared with other soils.
Therefore, the percolation analysis with a simple soil layer model was widely used for environmental andirrigation problems in sandy area. However, it was not verified enough whether the actual percolation
phenomenon to the deep was the same as the homogeneous model. The objectives of this research were
(1) to clarify the actual percolation feature by soil moisture observation in a natural dune, (2) to consider
the factors that control percolation form.
2. Materials and Methods
The research site was located in Tottori coastal dune,Tottori, Japan (35˚32’N, 134˚12’E, Altitude 12−55 m). The
mean annual precipitation was 1905 mm. Two-observation
plots were set about 1 km inland from the coastline. Bothpoints were bare soil surface and had few sand movements.
Point 1: The topological condition of point 1 was flat
surrounded by windbreak forest. Soil moisture profile wasmeasured by ADR sensors (Theta Probe-ML2, DELTA-T)
during the years 2003−2007. The ADR sensor had aresistance characteristic for salinity, as Nakajima et al. (1998).
Therefore, it was suitable for continual soil moisturemeasuring at seashore. The observation depth was 0.05, 0.2,0.4, 1.0, 1.5, 2.0, 3.0, 4.0, 5.1, 6.3, 7.5, 8.7 and 9.9 m (Fig. 1).
To excavate for each depth, we used a simple vacuum methodwith a dust collector, as Kawai et al. (2006). This evacuation
method was convenient to dig deep holes in sandy soil. In
addition, the groundwater level was about 10 m deep at thisarea from the preliminary examination (Fig. 1). The annual
groundwater level changed about 1 m.
For other soil physicality, sand grain size and soil-moisture retentivity were measured at intervals of 50 cm.
12Soil Water Observation Depth ( m )1.0 m2.0 m
3.0 m
4.0 m

0.05
0.2
0.4
1.0
1.5
2.1
3.0
4.0

5.0 m

5.1

6.0 m

6.3

Observation wellSurface

UnsaturatedZone

7.0 m

7.5
8.0 m
9.0 m

8.7

10.0 m9.9High Gro und water Level

11.0 m
12.0 m
13.0 mLo w Gro undwater Level

Saturated Zone

14.0 m
15.0 mBedrockFig. 1. Observation depth - point1.

Arid Land Research Center, Tottori University, 1390. Hamasaka, Tottori, Japan.
Forestry and Forest Products Research Institute, 1. Matunosato, Tukuba, Japan.

270

Point 2: The topological condition of point 2 was steep slope face to west. An artificial outcrop(2×3 m) was made in the slope and detailed sand sedimentary structures were confirmed by visualevaluation. Additionally, the soil moisture profile (2−5 cm intervals) was measured by WET sensor(DELTA-T).
3. Results and Discussion
3.1. Soil moisture (point 1)
The observation result of soil moisture was shown in Figure 2. This figure consisted of percolationand soil moisture graph. At the soil moisture graph, the longitudinal axis showed depth and the horizontal
axis showed time. The color strength showed the volumetric water content. The soil moistures wererelatively high ranging 8−15% because of much annual precipitation in Tottori area. Only the shallow
depths (upper 20 cm), the soils were highly dried ranging 1−3% water content under the summer condition.
The soil moistures of 2.0 and 6.0 m deep were constantly high compared with other depths. This showedthat the soil moisture of vados zone was heterogeneous situation and had a layered structure. In addition,Fig. 2. Soil moisture profile and Precipitation.

2710-0.5Pass mass percentage ( % )100

1.0-1.5
2.0-2.580

3.0-3.5
4.0-4.560

5.0-5.5
6.0-6.540

7.0-7.5
8.0-8.520

9.0-9.5
10.0-10.5

00.0100.100
Grain diameter ( mm )1.000

Fig. 3. Grain size in vados zone.
600m
2.0m
4.0m
6.0m
8.0m

150

Suction ( cm )the soil moisture around 9 m deep increased
rapidly in the winter of 2005 and 2006 years.
This was because that the groundwater level
moved upwards and the sensor area became
saturated zone.
Generally, heterogeneity of the soil
moisture depends on the sediment structure.
Then, the sand grain size and soil-moistureretentivity (water retention curve) of this point
were measured to evaluate the sediment layered
condition (Figs. 3 and 4).
From Figure 3, all grain size distribution
curves were sigmoid curve that was the feature ofhomogeneous sand. This result showed thevados zone consisted of fine sand and of single
sediment. From Figure 4, all water retention
curves showed the characteristic of sand that thewater retentivity decreased rapidly by 30−50 cmsuction. However, there was a slight differencein each line: especially within the range of 20−60
cm suction (enlarged view of Fig. 4). For
example, the 8.0 m deep sand retained 0.23
cm3/cm3 soil moisture under 40 cm suction. On
the other hand, the 6.0 m deep sand retained 0.07
cm3/cm3 soil moisture under 40 cm suction.
These results suggested followings: In this vadoszone, the homogeneous sands formed somemicroscopic sediment structures and thesesediment structures had some influences on thesoil -moisture retentivity.

401000.00.1

0.2

5000.00.1

0.2

0.3

0.4

0.5

Water content ( cm3/cm3 )Fig. 4. Water retention curve at each 2 m depth.

3.2. Sand sedimentary structures and soil moisture profile (point 2)
With the artificial outcrop, we made detailed observation of sand sedimentary structures and soil
moisture profile. The result was shown in Figure 5. From the visual evaluation, it was understood thatthe observation point had a compound cross lamina sedimentary structure. Here, lamina is the thinsedimentary structure (several mm-thickness) formed with dune growth, as Fritz and Moore (1988). And
compound cross lamina has the incommensurate structure; each lamina set overlapped with no horizontalcontinuousness. Lamina set is formed with a number of laminae that deposited at same age. At thisobservation point, there were 6 clear unconformity borders of lamina set. Especially, the unconformity
was remarkable of 190 cm deep. Upper lamina set deposited with 8° W and under lamina set deposited
with 18−36˚W.
The soil moistures varied by depth. These variations correlated well with each lamia set. And thesoil moistures were relatively high on all sedimentary borders. Especially, the soil moisture on the 190
cm deep border was 5 % higher compared with up-and-down layers. This observation results suggested
that the lamina structures controlled the vertical soil moisture movement in dune.
Moreover there were 7 nondistinctive volcanic ash layers. Nevertheless these ash layers had only
1−20 mm thickness; the soil moistures were relatively high on all borders. At 167 cm deep, there was thethickest ash layer (20 mm) and the soil moisture was relatively high compared with other ash borders.
Additionally, there was a definite irony sand layer in 230 cm deep. This layer also had a highly soil
moisture condition. However, the WET sensor measured a relative permittivity to obtain volumetricwater content and the iron sand had an effect on the sensor-output value. These results indicated that themicroscopic sediment also controlled the vertical soil moisture movement as lamina structure.

272

Volumetric water content ( % )0(a) Compound Cross Lamina Structure1515202025253030Soil moisture
Unconformity

353505050

Volcanic ash layer
Irony sand layer 50100100100150150150200200200250250250

Depth ( cm )10100(b) Soil Moisture Profile

Fig. 5. Compound cross lamina structure and Soil moisture profile.

4. Conclusions
We clarified the vertical soil moisture movement in sand dune. As the observation result, the soilmoisture inside the dune was heterogeneous and had a layered structure. Then we checked thesedimentary structures finely by artificial outcrop. As the result, there was a compound cross laminastructure. The soil moistures on each cross lamina borders were constantly higher than other depths.
Also, some volcanic ash and an irony sand layer were detected. The soil moistures on these layers wererelatively high. Thus it became clear that the lamina structures and other microscopic sedimentary
successions controlled the water movement of sand dune.
Acknowledgments
This research was partially supported by Grant-in-Aid for Scientific Research (Grant No. 20580281)
and JSPS Global COE Program “Dryland science.”
References
Fritz W.J., Moore J.N. (1988): Basic of physical stratigraphy and sedimentology. John Wiley & Sons. Inc.
Kawai T., Kamichika M., Kimura R., Tada Y., Kodama Y., Sakura Y. (2006): The New simple excavation method at sandy field withdust collector. Sand dune research, 52(3): 91-102.
Nakajima M., Inoue M., Sawada K., Nichol C. (1998): Measurement of soil water content by Amplitude domain reflectometry,Method and its calibration. Japanese association of groundwater hydrology, 40(4): 509-519.