1. No category

Research Trends and Results
Preparation of Sediment Balance Map by Grain Size Group for
Promotion of Comprehensive Sediment Management
HATTORI Atsushi (Ph.D.), Head; FUKUSHIMA Masaki (Ph.D.), Senior Researcher;
KOBAYASHI Katsuya, Researcher; MASUYA Shigekazu, Guest Research Engineer
River Division, River Department
Keywords: sediment transport system, sediment balance, grain size group
decreasing for the same. Accordingly, for example, in
mountainous area (including branch rivers), the amount
of transfer to a river channel is obtained by deducting the
amount of "blue" from "red."
With this method, it is possible to grasp the relations
between sediment balance in a river channel and the
amount of transfer between areas. In the figure, for
gravel, gravel extraction from the river channel is
estimated to have a greater effect on degradation of the
riverbed
compared
with
dam
sedimentation.
Furthermore, for sand and silt / clay, gravel extraction
from the river channel has little effect and dam
sedimentation is estimated to have a direct effect on the
amount of transfer to coastal areas.
In the future, we plan to prepare sediment balance
maps for each of the 109 river systems with analyses
similar to above and utilize them for promoting
≪土砂収支図≫
comprehensive
sediment management for each river.
≪土砂収支図≫
≪土砂収支図≫
3
単位：【千m 3/年】
単位：【千m3 /年】
/年】
単位：【千m
評価期間： S33 ～
H18
評価期間： S33
S33 ～
～ H18
H18
Downstream
1958
～ 2006 / Coastal
(西暦)： 1958
1958 ～
～ 2006
2006
(西暦)：
area
評価期間：
River
channel
(西暦)：
河道部
Branch
支川river
礫
の
土
砂
収
支
図
礫の
の土
土砂
砂収
収支
支図
図
礫
1,200
1,200
1,200
下流・海岸部
Legend
凡例
Amount of
河道部への
transfer to river
受け渡し量
channel
：
：
400
上
400 上
400
流
流
200
200
200
か か
ら000 ら
下
下
-200
-200
-200
流
流
-400
-400
-400
へ
へ
の の
1,200
1,200
1,200
土 土
1,000
砂
砂
1,000
1,000
受
受
800
800
800
け
け
600
600 渡
渡
600
し
400
400 し
400
量
量
200
200 を
200
を
増000 減
加
少
-200
-200
-200
さ
さ
-400
-400 せ
せ
-400
る
る
1,200
1,200
1,200
方 方
1,000
1,000
向 向
1,000
に
800
800 に
800
働
働
600
600
600
く
く
400
も
400 も
400
の
の
200
200
0
00
-200
-200
-200
-400
-400
-400
砂
の
土
砂
収
支
図
砂の
の土
土砂
砂収
収支
支図
図
砂
1,200
1,200
1,200
砂
400
400
400
200
200
200
0
00
-200
-200
-200
-400
-400
-400
シ
ル
ト
・
粘
土
の
土
砂
収
支
図
シル
ルト
ト・
・粘
粘土
土の
の土
土砂
砂収
収支
支図
図
シ
1,200
1,200
1,200
1,000
1,000
1,000
800
800
800
600
600
600
400
400
400
200
200
200
0
00
-200
-200
-200
-400
-400
-400
[千m3/年]
[千m3/年]
[千m3/年]
土
砂
生
産
域
土砂
砂生
生産
産域
域
土
～
ダ
ム
流
域
～ダ
ダム
ム流
流域
域
～
支
川
群
支川
川群
群
支
河
道
容
積
変
化
量
河道
道区
区域
域
河
（
直
轄
管
理
区
間
）
（直
直轄
轄管
管理
理区
区間
間）
）
（
下
流
へ
の
給
砂
量
下流合流点又は
下流合流点又は
Sand feeding to
下流合流点又は
海岸への供給量(-)
海岸への供給量(-)
海岸への供給量(-)
downstream
河
道
外
搬
出
入
量
河道区域
in river
Changes
実質的な
実質的な
実質的な
channel volume
河道容積増加量(+)
河道容積増加量(+)
河道容積増加量(+)
Gravel
extraction
砂利採取量(-)
砂利採取量(-)
砂利採取量(-)
砂
利
採
取
量
Amount of transfer
河道搬出(入)量(-)
河道搬出(入)量(-)
河道搬出(入)量(-)
river channel
outside
支
川
等
堆
砂
量
SG境界等堆積量
Sedimentation
SG境界等堆積量in
SG境界等堆積量
(-)
(-)
river, etc.
branch
(-)
ダ
ム
堆
砂
量
ダム堆砂量(-)
土砂生産量(+)
土砂生産量(+)
yield
Sediment
土砂生産量(+)
土
砂
生
産
量
sedimentation
Dam
ダム堆砂量(-)
ダム堆砂量(-)
3
シ
ル
ト
・
粘
土
[千m3/年]
[千m3/年]
m /year
thousand
[千m3/年]
Silt / clay
3
[千m3/年]
[千m3/年]
[千m3/年]
m /year
thousand
1,000
1,000
1,000
800
800
800
600
600
600
海
岸
・
合
流
点
海岸
岸・
・合
合流
流点
点
海
200
0
00
-200
-200
-200
-400
-400
-400
砂利採取量
砂利採取量
砂利採取量
(特定採取)(-)
(特定採取)(-)
(特定採取)(-)
3
[千m3/年]
[千m3/年]
m /year
thousand
[千m3/年]
800
800
800
600
600
600
400
400
400
200
200
200
: Decrease in the amount of sediment transfer from upstream to downstream
1,200
1,200
1,200
1,000
1,000
1,000
800
800
800
600
600
600
1,000
1,000
1,000
砂利採取量
砂利採取量
砂利採取量
(指定区間)(-)
(指定区間)(-)
(指定区間)(-)
礫
Sand
黒
部
川
水
系
黒部
部川
川水
水系
系
Mountainous
黒
山地部
area
砂防土砂流出
砂防土砂流出
砂防土砂流出
抑制量(-)
抑制量(-)
抑制量(-)
Gravel
黒
部
川
水
系
黒部
部川
川水
水系
系:::
黒
: Increase in the amount of sediment transfer from upstream to downstream
1. Importance of organization of basic information
for comprehensive sediment management
Comprehensive sediment management means to take
drastic measures that connect different areas from a
viewpoint of "sediment transport system," i.e., a group of
areas connected in terms of sediment transfer, by
removing the limitation of area-specific measures, such
as for mountains, river channels, and coastal areas with
regard to sediment-related issues including disaster
prevention and environmental conservation.
This
concept was proposed a long time ago but is not yet
established in the practice of river management.
One reason for that is that it takes much time to collect
and organize the data from previous surveys and analyses,
and identify sediment movement for the scale of a
sediment transport system that is based comprehensive
sediment management. The circumstances giving rise to
such reason are as follows.
1) Record periods, resolutions (spatial / temporal
observation intervals, data acquisition methods, etc.), and
quality (e.g. planned value or actual value) of the
observations and other data are not unified mainly
because different entities performed projects in different
areas, and the scale and location of projects changed
according to social, economic, or other situations.
2) Under such constraints, it requires experience to
organize and analyze data with an approach to identifying
the relevance between each issue and sediment
movement according on the scale of a sediment transport
system.
Therefore, we decided to collect relevant data in a
retrospective and comprehensive manner, and create a
sediment balance map that reflects the status of sediment
transfer in mountainous area (including dams) and coastal
areas based on the sediment balance of river channels
connected to those areas in the 109 river systems
managed by the country.
2. Preparation of sediment balance map by grain
size group as basic information
A sediment balance map indicates dam sedimentation,
branch river sedimentation, transfer of sediment from the
river channel in river development or maintenance, gravel
extraction, increase in channel volume calculated from
changes in river channel shape, and sediment yield
estimated from geology, etc. Each of these quantities is
classified according to grain size groups (gravel, sand, silt
/ clay) and indicated as an annual average value. When
the color of a bar indicating the amount is "red," it means
increasing transfer from mountain to river channel or
from river channel to coast, and when "blue," it means
Fig.: Example of Sediment Balance Map by Grain
Size Group