●Research Trends and Results

Sediment discharge and flow discharge observations
in mountain rivers to contribute to general sedimentmanagement
UCHIDA Taro (Dr.(Agriculture)), Senior Researcher
SUZUKI Takuro (Dr.(Agriculture)), Researcher
Research Center for Disaster Risk Management, Erosion and Sediment Control Division(Key words) Sediment discharge observation, suspended sediment, bedload, hydrophone

2. Outline of sediment discharge and flow
discharge observations
Flow rate, suspended sediment discharge, andbedload discharge are observed. Flow rate is obtainedby measuring the water level with a water level gauge
and solving a water level – flow rate relational
equation. The suspended sediment discharge isobtained by multiplying flow rate by suspended
sediment concentration measured by a turbidity meter.
The bedload discharge sensor is described in the next
section.
3. Method of analyzing observed data obtained bya bedload discharge sensor (hydrophone)
The device used as a bedload discharge sensor,
which is a steel pipe containing a microphone, iscalled a hydrophone (Photo 1). The sound pressure
value is calculated from the impact sound wave of thebedload, then converted to sediment discharge rate1).
The sound pressure value is the averaged value of theamplitude of the impact sound waves and it can beused in much the same way as the sound volume.
When a sand or gravel particle impacts thehydrophone individually, the sound pressure value is
proportional to the volume of a particle. When a groupof particles impact it, the more particles, the larger thesound pressure value. However it is not proportional
to the total volume. This is because the sound pressure
value is reduced due to the destructive interference ofsound waves. The reduction rate is large when thenumber of particles per unit of time is large. Forexample, even if particles with the same volume
impact the hydrophone, the smaller each particle, themore the sound pressure volume decreases because thenumber of particles becomes larger (Fig. 1). Bedload
discharge is calculated based on these relationships by
a numerical calculation.

Steel pipe
金属管Internal
マイク内蔵
microphone

Photo 1. Hydrophone
0.5Sound pressure
音圧値value

1. Introduction
In order to resolve various problems related to damsedimentation, aggradation and degradation ofriverbeds, shoreline erosion, and other sediment
movement, it is necessary to perform general sedimentmanagement as part of a sediment transport system.
Therefore, it is important to clarify the quantities andthe characteristics of flow discharge and sediment
discharge from the mountains where sediment isproduced.
The Ministry of Land, Infrastructure, Transport andTourism has been performing nationwide sediment
discharge and flow discharge observations andimproving this observation system since 2009. TheErosion and Sediment Control Division providestechnological support for observation methods, hasdeveloped a method of converting observed data tosediment discharge rate, and has developed a databasesystem.

砂礫径毎のExperimental
results bysand
and gravel
実験結果
dit

Large diameter sediment砂礫径大0.42mm3mm
5mm
7mm
砂礫径毎のCalculation
results bysand
and gravel
数値計算結果diameter
2mm‐cal3mm‐cal5mm‐cal
7mm‐cal0.30.20.1

Small diameter
砂礫径小
sediment

00102030

403Sediment
discharge3rate(cm /sec)
流砂量(cm/sec)

Figure 1. Sediment Discharge Rate - Sound Pressure
Value Relationship (Experimental Results andCalculation Results)
4. Future plans
The observed data will be used for general sedimentmanagement and crisis management. And it is stored
in a data base system. The improvement of the methodof converting observed data to bedload discharge rateis planned, through the verification of measurement
accuracy in field observations.
[Reference]
1) T. Suzuki, H. Mizuno, N. Osanai, R. Hirasawa, Y.

●Research Trends and Results
Hasegawa (2010): Basic study on sediment ratemeasurement with a hydrophone on the basis ofsound pressure data, Journal of the Japan Societyof Erosion Control Engineering, Vol. 62, No. 5, p.
18-26, 2010.