土木学会第55回年次学術講演会（平成12年9月）
Ⅲ-B362 Multi-layers Effect on Evaporation Rates from Unsaturated Sandy Soil
HASHEM M*., MOHAMED A. A. , WATANABE K*.,
ALI N. A., MOHAMED A. A., and ABDEL-LAH A. K.
*
JSCE members
Saitama University, Japan
Assiut University, Egypt
1. Introduction:
Evaporation is an important parameter on upward solute transport, hydrological and other
environmental matters. In arid and semi-arid zones the downward movement of the pollutants near the soil surface
rarely occurs, the evaporation is the main factor which can cause the upward pollutant migration. Most of the areas of
the arid zones are desert, covered by a surface of sandy soil. Three experiments were carried out under the same
conditions to estimate the values of the evaporation rate in three types of soil as, fine sand, coarse sand and multilayered sandy soil.
2. Measuring apparatus :
All dimensions in cm
The schematic view of the measuring
apparatus is shown in Fig. 1. It is mainly
consists of two units: Ventilated chamber
and an evaporation measuring equipment
developed by Mohamed et al. (1998). The
main idea of the equipment is, if some
parts of the ground surface are covered by
a box made of transparent sheet and the
air is injected into one side and exhausted
from the other side, the absolute humidity
of the air increased when the vapor is
coming out from the ground surface by
evaporation or evapo-transpiration.
Air
Suction pump
F
T
T
Instrument port
Computer
Air
Air
10
10
80
3. Experimental work: Three laboratory
experiments were carried out on three
types of sand. All the experiments were
carried out under the same conditions. The
average air temperature was 25.5 oC and
its relative humidity was 59.0 %. The
ventilated chamber was placed over a soil
box which has the same horizontal area.
A constant level of groundwater
was kept through the groundwater supply
tank for each experiment.
Soil
Outlet
50
100
Compartment
Central
Compartment
F A flow meter
T A pair of
humidity and
temperature sensors
Inlet
Compartment
Fig. 1. Schematic view of the measuring apparatus
For unsaturated fine sand depth (dFS) was 60 cm while the coarse sand depth (dCS) was 25 cm. The physical
properties of each type of sand are given in Table 1. In the two layers experiment, the coarse sand was placed as the
upper layer and the fine sand as the lower layer, dCS = 25 cm and dFS = 35 cm.
4. Discussion and analysis of results: During the time of each experiment the temperature, relative humidity, air
flow rate and the surface area of the soil column (constant for all experiments) were used to calculate the evaporation
(Brutseart, 1982). Transient changes of the evaporation rate and the average value for all types are shown as in Figs.
2, 3, and 4.
5. Conclusions: The Evaporation rate could be calculated during all experiments for each type of soil. The average
values of the evaporation rate (shown in the figures) were different according to sand type. The evaporation rate from
the surface of the fine sand was found to be larger than that from the coarse sand, even the groundwater table was
__________________________________________________________________________________________________
Keywords: Multi-layers, Unsaturated Sandy Soil, Evaporation.
Hydroscience & Geotechnology Lab., Civil and Envir. Eng. Dept., Graduate School of Science and Eng., Saitama University.,
255 Shimo-okubo, Urawa-Shi, Saitama 338-8570, Japan.
Tel: 048-858-3568
Fax: 048-855-1378
土木学会第55回年次学術講演会（平成12年9月）
Ⅲ-B362 more deeper in the first case than that in the second case. In the case of multi-layers soil, when the coarse sand was
the upper layer, the evaporation rate was found to be less than from each type of soil.
Table 1. Properties of both fine and coarse sand used in this study.
Mean diameter
Sp.
Bulk density
Porosity
Sat. Hyd. conductivity
3
(mm)
gravity
(g/cm )
(%)
(cm/s)
0.19
2.653
1.42
44.5
0.029
1.34
2.47
1.50
39.6
0.047
3.5
Average Value = 2.15 mm/day
3
2.5
2
1.5
1
0.5
90
84
78
72
66
60
54
48
42
36
30
24
18
12
6
0
0
Evaporation rate (mm/day)
Sand
type
Fine
Coarse
Time in days
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
73
70
68
65
62
59
56
53
51
48
45
42
39
37
34
31
28
25
23
20
17
14
11
8
6
3
Average value = 0.5 mm/day
0
Evaporation rate (mm/day)
Fig. 2. Transient change of the evaporation rate for fine sand experiment.
Time in days
Fig. 3. Transient change of the evaporation rate for coarse sand experiment.
Average value = 0.35 mm/day
0.6
0.5
0.4
0.3
0.2
0.1
120
115
110
105
101
96
91
86
82
77
72
67
62
58
53
48
43
38
34
29
24
19
14
10
5
0
0
Evaporation rate (mm/day)
0.7
Times in days
Fig. 4. Transient change of the evaporation rate for multi-layers experiment.
References:
1. Brutseart, W., 1982. “Evaporation into the atmosphere”. Kluwer Academic Publisher.
2. Mohamed, A. A., K. Watanabe, and T. Sasaki 1998. “Ventilated Chamber system for continuous
recording of both the evaporation rate and the heat balance at the bare soil surface.” Journal of
Groundwater Hydrology. 40(2): 185-202.