Weili LIANG, Ken’ichirou KOSUGI and Takahisa MIZUYAMA
Lab. of Erosion Control, Division of Forest Science Graduate School of Agriculture
Kyoto University,JapanStudy background and purposeStudy background and purpose
Soil water dynamics around a treeSoil water dynamics around a tree
Precipitation in forest is intercepted by canopies and partitioned into throughfall and stemflow that result in spatial and temporal variability of rainfall infiltration processes. However, these heterogeneous phenomena in the redistributed process was usually disregarded or dealt with homogeneously.
The purpose of this study is to clarify effects of a tree stand on rainfall infiltration processes at a forested hillslope based ondetailed observations of soil moisture distributions and groundwater table variation.
Study area and measurementStudy area and measurementThe study site is located on a hillslope at Kamigamo experimental station of Kyoto University. I selected a Tall Stewartia (Stewartiamonadelpha) as an observed tree.
Soil water contentI monitored soil water contents at depths of 10, 20, 30, 40, 50 cm at 10 locations from upstream to downstream of the tree by
capacitance meters. (Sentek, EasyAG-5p).
Pore water pressureTensiometers have been set on the same locations adjacent to capacitance meters. Each tensiometer has been installed above bedrock, so shallow groundwater table variation can be measured.
Horizontal distance (cm)
-200 -150 -100 -50 0 50 100 150 200 250
Vertical depth (cm
)
-400
-350
-300
-250
-200
-150
-100
-50
0No.1
No.2
No.3No.4
No.5
No.6No.7
No.8
No.10 Tree
No.9
Bedrock: Sandstone，Clay stone
Soil: Brown forest soil Downstream
Upstream
Q1 : What happened around the tree during wetting processes?
In the case of high rainfall:
Amount of rainfall : 194 mm, Duration of event : 51.5 hr.
In the case of low rainfall:
Amount of rainfall : 14 mm, Duration of event : 6.3 hr.
Q2 : What happened around the tree during drying processes?
Q3 : How much rain-water was stored around the tree?
Accumulated rainfall (mm)
0 10 20 30 40 50 60
Max. of soil storage change (m
m)
0
10
20
30
40
50
60
1:1
Dry antecedent condition
Wet antecedent condition
Accumulated rainfall (mm)
0 10 20 30 40 50 60
Max. of soil storage (mm)
0
20
40
60
80
100
120
140
160
Dry antecedent condition
Wet antecedent condition
∆Smax.—A.R.∆∆SSmaxmax..——A.R.A.R.
soil storage (S) =
soil water content × spatial scale
ΔS = Srain - Sinitial
In the case of 2D scale :
Smax.—A.R.SSmaxmax..——A.R.A.R. No. 10 9 8 7 6 5 4 3 2 1
Mesh for storage cal.
Depth (cm)
-50
-40
-30
-20
-10
0
In the case of 1D scale :
No. 10 9 8 7 6 5 4 3 2 1
Mesh for storage cal.
Depth (cm)
-50
-40
-30
-20
-10
0
No.1No.2No.3No.4No.5
0
20
40
60
80
100
120
No.6
0 10 20 30 40 50 60
No.7
0 10 20 30 40 50 60
No.8
0 10 20 30 40 50 60
No.9
0 10 20 30 40 50 60
1:1
No.10
Accumulated rainfall (mm)
0 10 20 30 40 50 60
Soil storage change (m
m)
0
20
40
60
80
100
120
Dry antecedent condition
Wet antecedent condition
No.1No.2No.3No.4No.5
0
50
100
150
200
250
No.6
0 10 20 30 40 50 60
No.7
0 10 20 30 40 50 60
No.8
0 10 20 30 40 50 60
No.9
0 10 20 30 40 50 60
No.10
Accumulated rainfall (mm)
0 10 20 30 40 50 60
Max. of soil storage (m
m)
0
50
100
150
200
250
Dry antecedent condition
Wet antecedent condition
∆Smax.—A.R.∆∆SSmaxmax..——A.R.A.R.
Smax.—A.R.SSmaxmax..——A.R.A.R.
dry wet
dry wet
HomogeneityHomogeneity
HeterogeneityHeterogeneity
In the case of each point :
No.10
Percentage of soil storage change (%)
0 5 10 15
Depth (cm
)
-50
-40
-30
-20
-10
No.1No.2No.3No.4No.5
-50
-40
-30
-20
-10
No.6
0 5 10 15
No.7
0 5 10 15
No.8
0 5 10 15
No.9
0 5 10 15
5.9%5.7%4.8%5.1%2.9%
42.6%19.6%5.3%3.8%3.9%
No. 10 9 8 7 6 5 4 3 2 1
Mesh for storage cal.
Depth (cm)
-50
-40
-30
-20
-10
0
∆Smax.—depth∆∆SSmaxmax..——depthdepth
Time (hour)0 6 12 18 24 30 36 42 48
Rainfall
(mm/10min) 0
2
4
6
7/17 07:00 (before rainfall)
Soil water content change
Depth
(cm)
-50
-40
-30
-20
-10
0.00
0.05
0.10
0.15
0.20
0.25
Groundwater table variation
Depth
(cm)
-100
0
100
200
300
Soil
Bedrock
No. 10 9 8 7 6 5 4 3 2 1
7/17 10:20 (rained for 3.3 hour)
Soil water content change
Groundwater table variation
Soil
Bedrock
10 9 8 7 6 5 4 3 2 1
7/18 10:20 (rained for 27.3 hour)
Soil water content change
Groundwater table variation
Soil
Bedrock
10 9 8 7 6 5 4 3 2 1
7/19 06:20 (rained for 47.3 hour)
Soil water content change
Groundwater table variation
Soil
Bedrock
10 9 8 7 6 5 4 3 2 1
Time (hour)0 1 2 3 4 5 6 7 8Rainfall
(mm/10min) 0
2
4
6
7/05 01:30 (before rainfall)
Soil water content change
Depth
(cm)
-50
-40
-30
-20
-10
0.00
0.05
0.10
0.15
0.20
0.25
Groundwater table variation
Depth
(cm)
-100
0
100
200
300
Soil
Bedrock
No. 10 9 8 7 6 5 4 3 2 1
7/05 04:20 (rained for 2.8 hour)
Soil water content change
Groundwater table variation
Soil
Bedrock
10 9 8 7 6 5 4 3 2 1
7/05 05:00 (rained for 3.5 hour)
Soil water content change
Groundwater table variation
Soil
Bedrock
10 9 8 7 6 5 4 3 2 1
7/05 07:50 (rained for 6.3 hour)
Soil water content change
Groundwater table variation
Soil
Bedrock
10 9 8 7 6 5 4 3 2 1
Time (day)0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Rainfall
(mm/10min) 0
2
4
6
7/30 13:00 (1 day after rain-stop)
Soil water content change
Depth
(cm)
-50
-40
-30
-20
-10
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
Groundwater table variation
Depth
(cm)
-400
-200
0
200 Soil
Bedrock
No. 10 9 8 7 6 5 4 3 2 1
8/04 01:00 (5.5 day after rain-stop)
Soil water content change
Groundwater table variationSoil
Bedrock
10 9 8 7 6 5 4 3 2 1
8/08 01:00 (9.5 day after rain-stop)
Soil water content change
Groundwater table variationSoil
Bedrock
10 9 8 7 6 5 4 3 2 1
8/12 01:00 (13.5 day after rain-stop)
Soil water content change
Groundwater table variationSoil
Bedrock
10 9 8 7 6 5 4 3 2 1
