Research Trends and ResultsRiver Tsunami Simulation Experiment with Large
Hydraulic Model
HATTORI Atsushi (Dr. Eng.), Head; FUKUSHIMA Masaki (Dr. Eng.), Senior Researcher;
MATSUURA Tatsuro, Senior Researcher
River Division, River Department
Keywords: river tsunami, flood, water level

2. River tsunami simulation experiment using alarge model
In order to deepen the understanding of suchcharacteristics of river tsunami, we conducted asimulation experiment 1) by running water up a large scalemodel of an actual river to obtain data on various tsunami
scales and terrains, in addition to the data on the actual
tsunami caused by the Great East Japan Earthquake. We
made a 1:330 model of the area of 10 km x 11 km, as
shown in the Photo, which includes the protected
lowland up to the point about 10 km upward from themouth of Kitakami River.
Digging a sand bar or flood plane was expected tofacilitate the run-up of tsunami and consequently raise
upstream water level, which was, however, not observedin the simulation, and the water level was lower than
before digging at some points.

River levee (upstream)
Spur close to the levee

Flood planeRiver levee(downstream)

Sandbank Flow direction

Coastal levee

Water gauge

River levee
Water gauge

Wave-making device

River-mouthbarDirection of tsunami
propagation

Photo: Overview of Model Waterway
Maximum tsunami water level/ Levee height T.P (m)1. Characteristics of River Tsunami to Consider
in Studying Measures
The water level of tsunami is essential information inconsidering various measures for tsunami disasters, suchas determination of levee height and discussion on town
development / evacuation. Water levels in rivers or
flooded areas are generally obtained through tsunami
analysis by tracing a series of events including arrival at
the coast and run-up along the river channel. In suchtracing, characteristics of rivers should be taken intoconsideration.
One of such characteristics is topographic changes inriver channel. As flood control measures, a sand bar
and other areas where river bed is high may be dug down
to lower the water level in case of flood or flood plane
may be dug to widen the river. If such digging causes
any change to tsunami water level, it should beconsidered in determining the height of levee.
Another characteristic is that whether tsunami water
could overtop from the river or magnitude of tsunami
may change according to the condition of levee breakage.
The reason for mentioning this is that if tsunami water
breaks the levee and overtops and floods, the level ofwater that further runs upward from the breakage point
may be lowered. Since such events occur in various
ways, it is important to consider them and observe thecondition of flood at various points in the upstream anddownstream.

Protruding area ofthe spur

Height of right sideleveeWith levee
Remove thedownstream levee

Mountain side

Mountain side

Distance from River Mouth (km)Figure: Measurement of Maximum Water Level ofRun-up Tsunami

To simulate a situation where the downstream levee
shown in the Photo was broken, we also conducted theexperiment by removing the same levee. The result
showed the water overtopped about 1 m from the levee
upstream the river in the protruding area of the spur,
while the water overtops about 2 m in the experiment
simulating a situation where no breakage of the leveeoccurs (see the Figure).
3. Future study
It is not yet clarified what conditions of tsunami andtopography cause such phenomena but they would
suggest the necessity of study under various conditions
according to locations, scales of topographic changes, etc.
In order to study such issues more simply and accurately,
we are further considering with tsunami experts aiming
for further improvement of analytical methods andpresentation of how to set conditions.
[Reference] Masaki FUKUSHIMA, Tatsuro MATSUURA,
Atsushi HATTORI, "Experimental Study on the Characteristicsof River Tsunami," Journal of Japan Society of Civil Engineers,
Ser. B2 (Coastal Engineering), Vol. 60, No. 2, pp. I_261-265,2013.