The Simulation Software on the Extension and Extinction of Vegetation
Organization
DepartmentAuthors

TEL /FAX /e-mailNational Institute for Land and Infrastructure Management
River Environment Division, Environment Department

Koh-ichi FUJITA, Katsuhiro ONUMA, Yutaka INOUETEL :029-864-2587
FAX :029-864-7221
e-mail : kakan@nilim.go.jp【INTRODUCTION】
We developed the software on the expansion and extinction of vegetation. In this software, we focused on the destructionof vegetation by floods, the sedimentation of fine grained soil by vegetation and the expansion and extinction of vegetation
caused by the changes in the condisions of location. Here, the process shown in the next page "Scenario on the expansion
and extinction of vegetation" is called the expansion and extinction of vegetation. we divided vegetation into three stages
according to the condisions of location.
The plant communities can't be forecast because the vegetation is divided into only three stages. And we consider only
the action of the river and the conditions of location in this software. However, the user can examine the influence on
vegetation by changing in physical environment (flood frequency, tractive force, etc). It is useful in the river management
to examine roughly the tendency; the bare ground kept or vegetation growing thickly. For instance, you can use for thefollowing purpose. So this software is practical and useful supporting tool.
【Analysis of the factor of stable vegetation growth】
Inputting the discharge caused actually, the user can examine the effects of the floods on the expansion and extinction ofvegetation. So you can analyze the factor of stable vegetation growth.
【Planning river improvement】
Inputting the arbitrary cross-sectional views, the user can examine how the relative height influences on the sedimentationof fine grained soil causing stable vegetation growth. So you can discuss the appropriate cutting down elevation wherevegetation don't grow thickly.

【DEVELOPMENT HISTORY】
・This software was made based on the thesis on Tama-river, the following publishing.
・We calculate on various rivers, and examining the applicable conditions and limits of this software.
・We improve the operation of this software.

【MODEL FEATURES】
・This software targets the segment-1 reach.
・Quasi two-dimensional uniform flow analysis is adopted.
・The operation is very simple; the user can calculate only by inputting constants (for example coefficient of roughness),a cross-sectional view, discharge, etc.
・The secular changes of the expansion and extinction vegetation can be examined, for the calculation is done byinputting the flow discharge actually caused.
・The changes of the coefficient of roughness according to the shift of vegetation can be considered.
・The sedimentation of fine grained soil by vegetation can be considered.
・The calculation result can be output to Excel, so you can analyze easily.
・Vegetation is divided into three stages, and the cycle shown in the next page "Scenario on the expansion and extinctionof vegetation" can be expressed. (The following number shows the process of the number in figure. )①The bare ground or the vegetation which is possible to grow on a severe conditions like the gravel-bed
reaches is assumed. This stage is named Type-Ⅰ.
②After a certain period passes, the vegetation change. This stage is named Type-Ⅱ.
Type-Ⅱ grow denser than Type-Ⅰ, so the vegetation deposit fine grained soil during floods.
③After some floods and fine grained soil deposited to some thickness, stable vegetation areas is formed.
This stage is named Type-Ⅲ.
④Type-Ⅱ and Type-Ⅲ returns to Type-Ⅰ through the extinction by big floods.

【PROJECT REFERENCES】
We apply this software to the following river and examine tha applicability in cooperation with Foundation of River andWatershed Environment Management.
Tyubetsu-river, Watarase-river, Kanna-river, Nakatsu-river, Ooi-river, Tenryu-river, Mibu-river, Tedori-river, Ozeriver, Hiji-river【REFERENCES】
Koh-ichi Fujita et al : Mechanism and Simulation of the Expansion and Extinction of Stable Vegetation Areas in a GravelBed Alluvial Fan River, Journal of Hydraulic, Coastal and Environmental Engineering, No.747 ⅱ-65, pp.41-60, 2003.11

Development of the simulation software on the extension and extinction of vegetation
10 years before dam construction

5 years after dam construction

current direction

current direction

The Simulation Softwareon the Extension and Extinction of Vegetation

Before dam construction it was bare ground.
After dam construction vegetation grew thickly.

This software was developed as the supporting tool to examine
the process of the expansion and extinction of vegetation.

・What is the cause?
Decrease in disturbance frequency by flood control?
Or no flood by chance?
・Will stable vegetation areas be formed?
Or it will return to bare ground?
・What is the proper characteristics of the expansion
and extinction of vegetation in this river?
・How was the expansion and extinction ofvegetation while aerial photograph didn't exist?

【Features】
・The effect of the sedimentationof fine grained soil can be considered.
・The expansion and extinction of vegetation isquantitatively predictable.
・The operation is very simple.
・The calculation result can be output to Excel.

Scenario of the expansion
and extinction of vegetation

Calculation flow
inputing parameter (cross-sectional view, discharge, vegetation, etc.)： dimensionless tractive force
applied to the examination split.
τ*cs(i) : dimensionless tractive force
Type-i can be washed out(Type-i is Type-Ⅰ,Type-Ⅱ or Type-Ⅲ)
It is possible to set t*cs(i) at each vegetation stage.
τ*loopdischarge read in

Development of vegetation

hydraulic accounting
How is the tractive force?
τ*＜τ*cs(i)Sedimentation of fine grained
soil by vegetation at floods

No
Destruction of vegetation

Yes
Type judgment

Type-Ⅰ

Type-Ⅱ

Yes

Have regulatedyears passed?

Type-ⅢNo①②often③③

Is thickness of finegrained soil more thana regulated value?

Is thickness of finegrained soil more thana regulated value?
Nooccasionally

No

Yes

Ⅰ

ⅢA

seldomⅢA

cross-sectional view fixed

④Yes

Ⅱ

loop
end

ⅢA→ⅢB→ⅢC

Ⅰ

Type-Ⅲ is changed by elapsed years,
from Type-ⅢA to ⅢB, Type- from Type-ⅢB to Type-ⅢC.
The parameter(τ*cs(i), coffecient of roughness, etc) canbe set at each stage.

The example of calcutation result 〜at the cross-section of red line in above aerial photograph 〜

distance [m]40

inputteddischarge[m3/s]

200200400600800
1000
inputted crosssection view

The vegetation
had grown before
dam construction.

If there were no dam,the vegetation may
return bared groundagain by floods.

The stable
vegetation area
has been formed.

60
80
100
120
140
160

48

50

52

elevation [m]

-8

dam
+2
construction
years before and after dam constructiona) with flood control-6：Type-Ⅰ-4-2：Type-Ⅱ+4：Type-ⅢA-8

dam+2
construction
years before and after dam constructionb) without flood control-6：Type-ⅢB-4-2：Type-ⅢC+4