Geoscience Reference
In-Depth Information
volcano lavas with high permeability distribute widely in Leizhou Peninsula,
forming very good hydrological conditions for groundwater. In the study
area, the surface was covered by 2.5-3 m thick of red soil underneath the
basalt. Since the red soil has a high hydraulic conductivity ranging from
6
.
16
10
−
2
cm/s, and crack often can be found at the
surface when the soil at top layer dries up in the shiny days, rain water can
very easy to infiltrate to the ground. As a result, there is no river in the
study area and groundwater is the only source for agriculture and drinking.
Its annual average temperature is over 23
◦
C. In dry season (from October
to March), water shortage problem is very serious since the high evapora-
tion and wilted point occurred often at the top soil layer. The height of the
study area is 80 m above the sea level.
Measurements for soil water, groundwater as well as overland flow have
been conducted in four year period start from June 2000. In order to
measure the water balance in the study area, five TDR sensors (CS610,
Campbell) have been set at the depth of 10, 30, 60, 100, and 200 cm, respec-
tively. At the same time, tensiometers were set at the same depths as the
TDR sensors. Rainfall was measured by rain gauge. All data of rainfall and
TDRs were recorded in a dataloger CR10 (Campbell) with the interval of
10 min. Also, the overland flow and the water table were measured in the
interval of 10 minutes.
10
−
5
×
and 1
.
11
×
3. Results and Discussions
3.1.
Variations of soilwater during the events
Figure 2 shows the vertical profile of soil water change during July 25-29,
2001 with total rainfall of 261 mm, where we set 0:00 on July 25 as the start-
ing point. There was a rain from 28 h to 33 h 50 min. Before the rain event,
soil volumetric water content at 10 cm in depth was 30.2%, and responded
quickly to the rain. It changed to 48.3% at 28 h 50 min and reached the
peak of 67.5% at 30 h 30 min. The changes of soil volumetric water content
at 30, 60, 100, and 200 cm in depth began at 29 h 30 min, 30 h 20 min, 30 h
30 min and 30 h 40 min, respectively. As a result, soil water increased at
all depths and had their maximum water contents ranging from 63.8% to
72.8% during the rainfall period. After the rain, soil volumetric water con-
tent at 10 cm in depth decreased continually, and reached to 50.2%, 40.1%,
and 30.9% at 36 h, 64 h, and 144 h, respectively. However, soil volumetric
water content at other depths returned to their values before the event at
about 130 h. During this event, overland flow occurred.
