Flood Fighting Drill in Japan

Flood Fighting (the fight against flooding).

Suikou deployment team and Opening ceremony.

Compared with among other types of disaster, flood often occurs anywhere but timely forecasted. Thus, it is available for giving an early flood warning or making flood fighting arrangement.

In Japan, by the law it's required to conduct the flood drills annually in order to provide understanding of the type of flood fighting activities by involving local residents, private companies, local disaster managers and students.

The benefits from this activity are raising public awareness on flood fighting (i.e. enhancement of public preparedness) and implementing school based flood disaster education (i.e. capacity development). Public awareness is the basis for flood fighting and it is essential for public to be proactive and look for the problems and causes before floods happens. Meanwhile, within the education sector it urges to create curriculum on disaster management to educate school children and students in the flood fighting techniques.




Flood drills (banks protection in Fujikawa).


Rescue and evacuation demonstration.


Experiencing of making sandbags.

山梨発 水と緑を考える 大学・地域・産業連携国際シンポジウム

STOP PRESS !!

Day of Defense - Completing a Doctoral Dissertation

Two weeks ago, She turned to sweat although she could handle everything elegantly (well done, Congrats !! ).

Absorbing (non-reflecting) boundary condition

An absorbing BCs has been formulated and applied to SUIKOU2D in conjunction with MacCormack and TVD schemes. The inclusion of the boundaries is very important in the successful application of any numerical techniques. Hyperbolic equations are particularly sensitive because errors introduced at the boundaries are propagated and reflected throughout the grids. This, in many cases, may results in instability or incorrect flow values.

Numerical modeling of inundation flow often involves computational domains that are very large. Discretizing the entire domain and solving the flow equations turn out to be a tedious jobs in term of times and memory. Therefore, the physical domain has been truncated by introducing a pseudo boundary. Here, the use of pseudo boundary as open boundary aids in reducing the size of computational domain and and emphasizes the interest area only.

There are two possible flow conditions may occur in the pseudo boundary; sub-critical or super-critical flows accompanied with shocks where it needs special treatment on each. An ideal pseudo boundary condition should meet the following criteria:
(i) it should be compatible with physical conditions of the nature.
(ii) it should not degrade/defect the numerical solutions.
(iii) it should absorb the outgoing waves to avoid any reflections.

Several established methods are available for pseudo boundary. The simplest approach is by implementing two ways, including
1. extrapolation of flow variables from the interior node (Froude >=1);
2. solved by MoC (Froude <1).

Test Case

A 10m height of water in reservoir in upstream part of computational domain. It is assumed some buildings in the downstream part as represented by random blocks. Initially, it is dry in the downstream. Suddenly the reservoir partially bursts and inundates downstream part.

The simulations are carried out on the basis of;
a. The first case, all of outer BCs of the computational domain is considered as wall.
There is no incoming/outcoming flux through walls. The shocks will be reflected as they hit the walls.
b. Second, the downstream part is truncated by pseudo BC.
All incoming/outcoming shocks will be absorbed as represented flows pass through the downstream wall without any reflections.

The animations of water surface during 1200 seconds after breach are as shown below.
(click on the image to run animation)

a. case no.1 (walls BC).

b. case no 2. (non reflecting BC).


c. Water depth along x-axis at center of breach.

Obviously seen, the lowering water depth in reservoir occurs in case no. 2 since there is out flowing flux through pseudo BC, whilst no.1 is reflected back.

to be continued....

Making Space for Water

Afflux and Backwater

As water engineers we often know terms of 'backwater' rather than 'afflux'. Why?. Don't be confused!
In hydrology, afflux is defined as a rise in the water level immediately upstream of and due to a natural or artificial obstruction. Backwater is a consequence of afflux, in other words the afflux brings 'backwater effect'.