Experimental Studies for Monitoring of Bedload using Various Sensors

Experimental Studies for Monitoring of Bedload using Various Sensors

Takahiro ITOH^1*, Ken GOTOH¹, Rei UTSUNOMIYA², Michinobu NONAKA³, Takahiko NAGAYAMA⁴, Daizo TSUTSUMI⁵, Masaharu FUJITA⁶, Shusuke MIYATA⁶

and Takahisa MIZUYAMA⁷

1 Research and Development Center, Nippon Koei Co., Ltd. (2304 Inarihara, Tsukuba, Ibaraki 300-1259, Japan) 2 JFE Advantech Co., Ltd. (7-2-3 Ibukidai-Higashi, Nishi-ku, Kobe 651-2242 Japan)

3 HydroTech Co., Ltd. (876 Kozukeda, Nino-cho, Gamo-gun, Shiga 529-1642 Japan) 4 Nippon Koei Co., Ltd., JAPAN (4-2 Kojimachi, Chiyoda-ku, Tokyo 102-8539, Japan)

5 Disaster Prevention Research Institute, Kyoto University (436-13, Nakao, Okuhida Onsengo, Takayama, Gifu 506-1422 Japan)

6 Disaster Prevention Research Institute, Kyoto University (Yokooji, Fushimi-ku, Kyoto, Kyoto 612-8235, Japan) 7 Graduate School of Agriculture, Kyoto University (Oiwakecho, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan)

*Corresponding author. E-mail: a6556@n-koei.co.jp

In a supercritical flume of Hodaka Sedimentation Observatory of Disaster Prevention Research Institute of Kyoto University in the Ashi-arai-dani River, there are several kinds of hydrophone systems (Japanese pipe hydrophone, a Swiss piezoelectric plate; i.e., Geophone, and Japanese plate-type hydrophone), Reid-type bedload slots and other hydrometric equipments. In order to evaluate characteristics of those sensors, in present study, data obtained by various passive sensors and Reid type bedload slot are compared in flood events on June 19th, 2013. Plate-type hydrophone is sometimes similar with a pipe hydrophone, though the results depend on the watching area, and vibration sensor seems to measure clearly the peak discharge of bedloads. Experimental data by the submerged loadcell system, that is newly developed for the volumetric limitation of measurement by Reid type bedload slot, was collected in July of 2013, are shown and the applicability is confirmed. The loadcell system seems to be able to estimate bedload discharge rate within several percents of errors in flume tests.

Key words: bed-loads monitoring, hydrophone, geophone, Hodaka Sedimentation Observatory

1. INTRODUCTION

Evaluating the sediment transport rate in arbitrary section of a river is important to control and manage the quantity and quality of sediment.

Considerable efforts have been made to continuously monitor bedload discharge in mountainous torrents. It is found that several characteristics such as discontinuity between water discharge and bedload runoff in the flood through several monitoring in mountainous basin. For example, the timing of sediment discharge occurrence does not always correspond to rainfall events [e.g., Mizuyama et al., 1998].

In mountainous torrents, bedloads are quite difficult to measure directly with samplers such as Helley-Smith type sampler, because flow conditions

is usually supercritical and bed roughness is quite large due to coarse boulders on the bed surface, and because it is usually disturbing bed surface condition in measurements. Passive sensors have been developed using characteristics of acoustic [Taniguchi et al., 1992] and vibration wave [Rickenmann et al., 2007]. Especially, in Japan and Europe, the monitoring with those sensors has been conducted [U.S. Geological Survey, 2010].

However, those need a correlation between signals of the passive sensors and sediment discharge rate.

Usually the Reid type bedlad slot [Reid et al., 1980;

Laronne et al., 1992] is installed downstream of the sensors, though a slot can capture sediment until it filled up and give grain size of transported sediment.

The slot has a limitation of capture volume and the data can obtain only in the beginning of stage of flood. In addition, it is pointed out that passive

sensors cannot capture signals due to a lot of collisions to the sensor if a lot of sediment particles move in high shear stress.

In the Hodaka Sedimentation Observatory of the Disaster Prevention Research Institute of Kyoto University, which is abbreviated as Hodaka Obs.

DPRI, bedload monitoring with Japanese pipe hydrophone started in the supercritical flume of the Ashi-arai-dani River in the 1990s and Reid type bedload slot was installed in the 2000s, and flume data of the sediment runoff due to rainfall has been collected in event to event [Mizuyama et al., 2011].

Recently, in November of 2012 to June of 2013, several kinds of sensors were installed to compare with data obtained by them. Those sensors newly installed are the geophone in Europe, the plate-type hydrophone with the vibration meter which has two kinds of iron plate such as 800 mm in width, 200 mm in length (1,600 cm²) and 500 mm in width, 400 mm in length (2,000 cm²). Those sensors, Japanese pipe hydrophone and Reid type bedload slot are located centered in the flume, and data obtained by all sensors are compared each other.

As seen in debris flow monitoring [McArdell et al., 2007], the measurement with loadcells can be useful for large bedload particles due to development of loadcell sensor. If sediment particles of bed load are submerged, those weights are reduced by buoyancy force driven to those particles on the bed. If the weight of bedload can measure on the bed using some plane plate such as steel plate, it can be measured continuously without disturbing bed surface condition. A small, automatically recording submerged loadcell system with two pin-type loadcells, a pressure sensor for flow depth and electromagnetic velocity meter were developed by Nippon Koei Co., Ltd. and JFE Advantech Co., Ltd. and installed in the right bank side of the flume. The system was installed in November, 2012 at same section of the experimental flume to compare with the measured bedload weight for Reid-type bedload slot and the trial experiment

has been conducted.

In present study, data obtained by passive sensors and Reid-type bedload slot are compared in flood events in 2013. Experimental data by the submerged loadcell system, which has conducted in 2012 and 2013, are shown. Characteristics of those sensors are discussed through comparisons of data obtained in observation flume in Ashi-arai-dani River.

2. OUTLINE OF AN OBSERVATION FLUME

Ashi-arai-dani has a total watershed area of 6.5 km², and is a mountain torrent which actively moves sediment from the accumulated volcanic outflow of Mt. Yake-dake. Tributaries which join the Ashi-arai-dani River are the Hiru-dani River (0.85 km²), the Wari-dani River (1.11 km²), Shiramizu-dani River (2.1 km²) and Kuro-dani River (1.2 km²). The downstream reach of the main channel of the Ashi-arai-dani River is named as Fuka-dani where the supercritical flume is located as shown in Fig. 1. Measurement system consisted of a Japanese pipe hydrophone (the length= 0.35 m), a level gauge for flow water depth and Reid type bedload slot (the inlet width= 0.2 m) was installed in the flume. The bed slope is 1/20, flow width is 5 m, channel length is 15 m and channel depth is 1.0 m in the flume.

Japanese pipe hydrophone amplified the acoustic wave if bedload particles collided with the sensor using a six rank-amplifier, in which the gain is 2, 4, 16, 64, 256, and 1016 times. Output of each number of signals recorded as an impulse and the time-averaged acoustic wave data. The impulse data is accumulated during one minute and the acoustic wave is recorded by time averaged data within one second during one minutes. Those data for all rank impulses and an acoustic wave are recorded.

Flow water depth is observed at upstream of middle of the flume. Hourly rainfall is observed at Tochio meteorological station, which is located at around 3 km of downstream from the flume. After installing those sensors, there were six rainfall

Fig. 1 Instruments for bedload monitoring in an observation flume of the Ashi-arai-dan River

Flow

Load cell box (Submerged load cell)

Electromagnetic velocity meter

Pressure sensor (in loadcell box) 5.0m in width, 1/20 in bed slope

Reid-type automatically recording bedload slot

Pipe hydrophone

Fig. 2 Schematics and photo of submerged loadcell system

Rubber plate Force plate 1.0m

0.5m

0.7m

1.0m 0.5m

0.07m Force plate

Pin-type loadcell (Waterproofing)

events in 2013; e.g., on 19th June, on 7th to 11st July, on 23rd to 25th Aug., on 30th Aug. to 4th Sep., on 16th Sep. and on Oct. 26th. Monitoring data on 19th to 23rd June are shown in present study.

3. POSSIBILITY OF BEDLOAD MEASUREMENTS ON THE BED

3.1 Principle of measurement using loadcells Figure 2 shows schematics and photo of submerged loadcell system, and especially the structure of the frame is shown. A steel plate (force plate) and submerged loadcell system with two pin-type loadcells can theoretically measure moving solid materials on the bed surface. If we know the value of the time lag,  , obtained by temporal changes of both loadcells, the velocity can be estimated using the distance of both loadcells. Using the weight measured at upstream/down steam section, the flux of mass, Qmass, which is synonymous with the sediment discharge rate, Qb, is calculated by the following equations.









t s t

s t

mass

l w w dt

v dt w v dt Q

M 2

2

1 (1)

in which Ml is the mass measured by loadcell in unit width, Qmass is the flux of mass in unit width, w is the averaged weigh by loadcells in unit width, w1 is the measured value by the loadcell located in upstream side (in unit width), w2 is the measured value by the loadcell located in downstream side (in unit width) and vs is the velocity of solid particles.

The time lag,  , can estimate to make the cross-correlation function, Cw1w2, take the maximum value. The cross-correlation function, Cw1w2, is defined as follows.

 



   



 ²

2 1 2

2 1

lim

w

w w t w t dt

C  T  (2)

 L

v_s  ⁽³⁾

in which t is the time, T is the period with long

time sale for time-integration and L is the distance (= 0.7 m) between two loadcells on the force plate.

3.2 Laboratory tests

Laboratory tests in factory were conducted to evaluate effects of the moving weight on the measurements using loadcells in JFE Advantech Co., Ltd. Figure 3 shows the relation between input and output weight estimated using following Eqs.

(1) and (2) and schematics of procedure for those tests. The several kinds of iron material were used for those tests such as prisms and balls with different diameters. Tests were conducted by making those iron materials move on the steel plate in the air, which was shown in Fig. 3, by giving iron materials speed using a slope. In the figure, for example, “Ball A: Forty iron balls (0.025kg×40)”

means tests using forty iron balls A (weight= 0.025 kg)” and “Mixed ball: A= Forty, B= Twenty” means tests using forty iron balls A (weight= 0.025 kg) and twenty iron balls B (weight= 0.050 kg) mixture.

In the calculation, velocity was calculated using images taken by digital camera. Data measured by loadcells was collected by 100 Hz of sampling rate, and was converted using the low-pass filter and the converter (LCT-160A: JFE Advantech production).

Estimations on a force plate in an air can explain well input data for one, two, many iron materials and those mixtures.

3.3 Flume tests in an observation flume

Submerged loadcell system, which was constituted of a pressure sensor for flow depth and electromagnetic velocity meter, was installed in the right bank side of the flume in November, 2012.

The trial experiment has been conducted, and the system was installed at same section of the experimental flume to compare with the measured bedload weight for Reid-type bedload slot.

Flume tests were conducted in the supercritical

a) Relation between input and output weight estimated by loadcell system b) Schematics of procedure for laboratory tests

Fig. 3 Relation between input and output weight estimated in the air and schematics of procedure for laboratory tests

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

推定した通過重量（kg）

投入重量（kg）

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

推定した通過重量（kg）

投入重量（kg）

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

Input weight (kg)

Estimation (kg)

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

推定した通過重量（kg）

投入重量（kg）

角柱0.5kg1個 角柱1.0kg1個 角柱1.0kg2個 鋼球A(0.025kg)40個 鋼球B(0.05kg)20個 鋼球C(0.1kg)20個 鋼球D(0.2kg)10個 鋼球A40個B20個 鋼球C20個D10個 鋼球B20個C20個D10個 鋼球A40個B20個C20個D10個 A prism (0.5 kg)

Two prism (0.5 kg×2)

Ba ll A: Forty iron ba lls (0.025 kg×40) Tota l: 1 kg Ba ll B: Twenty iron ba lls (0.050 kg×20) Ba ll C: Twenty iron ba lls (0.100 kg×40) Ba ll D: Ten iron ba lls (0.200 kg×10) Mixed Ba ll: A=Forty, B=Twenty Mixed Ba ll: C=Twenty, D=Ten Mixed Ba ll: B=Twenty C=Twenty, D=Ten A prism (1.0 kg)

Mixed Ba ll: A=Forty, B=Twenty C=Twenty, D=Ten Tota l: 1 kg Tota l: 4 kg Tota l: 2 kg : Tota l: 2 kg : Tota l: 4 kg

: Tota l: 5 kg

: Tota l: 6 kg

Slope Moving steel materials

(Inlet) Force plate (Inlet)

Moving steel materials

Force plate Loadcell system

Slope

flume of Hodaka Obs. DPRI on November 23th in 2012. Tests were conducted for the movement of one boulder. Data by loadcells are collected by 100 Hz and the flow depth and velocity are measured by 10 Hz. In those tests, the flow depth in the channel was around 0.1 m. The value measured weight is analyzed using the time moving-average with every 50 samples.

Figure 4 shows temporal changes obtained by the loadcells and flow depth in the flume tests in case of one large boulder. Raw data (100 Hz of sampling rate) are also show in the figure. The velocity estimated using Eqs. (2) and (3) is 1.07 m/s for one boulder. Estimated weight of a boulder is 1.98 kg and there is a discrepancy of 3.9 % for the input value, 2.06 kg.

4. VARIOUS SENSORS FOR BEDLOAD MONITORING

4.1 Comparison of data obtained by sensors Figures 6 and 7 show the monitoring data

obtained by various sensors, which are shown in Fig. 5, at Ashi-arai-dani River basin in flood events on June 19th to 23rd, 2013.

4.1.1 Characteristics of field data measured by sensors

Figure 5 shows temporal changes of observed data obtained by plate-type hydrophone (500 mm in width and 400 mm in length, 800 mm in width and 200 mm in length), Japanese pipe hydrophone (350 mm in length) and Geophone. Those data also are compared with data by electromagnetic sensor for velocity, Reid type bedload slot and rainfall intensity (Tochio station). In Fig. 6, the impulse data are shown by the accumulated impulses in one minutes, and the voltage values of acoustic waves and vibration data are shown in Fig. 7 by the time-averaged data in one second in every one minutes.

In the plate hydrophone, as described above, there are two kinds of iron plate size: Area of the plate is 2,000 cm² and 1600 cm², respectively. It is well known impulse of Japanese pipe hydrophone,

Fig. 4 Temporal changes of flow depth and estimated weight by the loadcell system in flume tests (One boulder) 0

0.02 0.04 0.06 0.08 0.1 0.12

-6 -4 -2 0 2 4 6

14:02:05.00 14:02:06.00 14:02:07.00 14:02:08.00

水位

出力値

上流側ﾛｰﾄﾞｾﾙ 下流側ﾛｰﾄﾞｾﾙ 上流側ﾛｰﾄﾞｾﾙ(生data) 下流側ﾛｰﾄﾞｾﾙ(生data) 通過土砂量 水位

時間差から粒子移動速度を推定

投入礫重量2.06kg 推定通過重量

移動平均(n=50)データ を使用

Flow depth (m)

Moving average (n=50) Upstream

loadcell

Estimated weight (kg)

Flow depth 0.65 sec.

Estimated weight (kg)

Downstream loadcell

time (h:min:s) Estimation= 1.98 kg [Input weight= 2.06 kg]

Fig. 5 Instruments for water discharge and bedload monitoring in the supercritical flume of Ashi-arai-dani River (1) (2)

(3)

(4) (5) (6) (7) (8)

(9)

[Sensors]

(1) Rader water level meter (2) Web camera

(3) Electromagnetic velocity meter (4) Swiss-type’ geophone

(5) Plate-type hydrophone (6) Plate-type hydrophone (7) Pipe hydrophone (8) Reid-type bedload slots (9) Submerged loadcell and

Electromagnetic velocity meter [Location]

*(1) and (2) are centered at 9.5m from upstream end.

*(3) and (4) are centered at 11.4m from upstream end.

*(5), (6), (7) and (8) are centered at 12.2m, 12.9m, 15.3m and 15.3m, respectively.

*(9) is in right hand side at 17.0m from upstream end.

Upstream

Flow

(9) (8)

Fig. 6 Monitoring data, in which hydrophones show impulses, obtained by various sensors at Ashi-arai-dani River basin (On June 19th to 23rd, 2013)

0 1000 2000 3000 4000

2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00

-1 -0.5 0 0.5 1

6/19 6/20 6/21 6/22 6/23

電圧値(mV)

水位(m)

水位―ジオフォン 上流水位 水路水位 ｼﾞｵﾌｫﾝ

0 500 1000 1500 2000

2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00

-1 -0.5 0 0.5 1

6/19 6/20 6/21 6/22 6/23

パルス数(回/5min)

水位(m)

水位―ﾊﾟｲﾌﾟﾊｲﾄﾞﾛﾌｫﾝ ^{上流水位 水路水位 増幅率1016倍 増幅率256倍 増幅率64倍 増幅率16倍 増幅率4倍 増幅率2倍} 0 500 1000 1500 2000

2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00

-1 -0.5 0 0.5 1

6/19 6/20 6/21 6/22 6/23

パルス数(回/5min)

水位(m)

水位―ﾌﾟﾚｰﾄ型ﾊｲﾄﾞﾛﾌｫﾝ200×800mm 上流水位 水路水位 増幅率1016倍 増幅率256倍 増幅率64倍 増幅率16倍 増幅率4倍 増幅率2倍 0 500 1000 1500 2000

2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00

-1 -0.5 0 0.5 1

6/19 6/20 6/21 6/22 6/23

パルス数(回/5min)

水位(m)

水位―ﾌﾟﾚｰﾄ型ﾊｲﾄﾞﾛﾌｫﾝ400×500mm 上流水位 水路水位 増幅率1016倍 増幅率256倍 増幅率64倍 増幅率16倍 増幅率4倍 増幅率2倍

2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00

0 10 20 30 40

6/19 6/20 6/21 6/22 6/23

雨量(mm/h)

雨量(栃尾) 雨量(白馬)

0 1000 2000 3000 4000

2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00

-1 -0.5 0 0.5 1

6/19 6/20 6/21 6/22 6/23

電圧値(mV)

水位(m)

水位―プレート型ハイドロフォン400×500mm 振動センサー ^{上流水位 水路水位} ﾌﾟﾚｰﾄ型ﾊｲﾄﾞﾛﾌｫﾝ400 音響ｾﾝｻｰ

0 1000 2000 3000 4000

2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00

-0.5 0 0.5 1 1.5

6/19 6/20 6/21 6/22 6/23

捕捉土砂重量(kg)

水位(m)

水位―捕捉土砂重量 _{ピット水位 捕捉土砂重量}

0 1 2 3 4

2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00

-1 -0.5 0 0.5 1

6/19 6/20 6/21 6/22 6/23

底面流速(m/s)

水位(m)

水位―底面流速 _{上流水位 上流水位 底面流速}

Rain fall (mm/h)Flow depth (m)Flow depth (m)

1016 (Gain) 64 (Gain)

16 (Gain)

Flow depth (m)

Pipe hydrophone (350 mm in length)

Flow depth (m)

Geophone in Europe

Vibration sensor in plate type hydrophone (500 mm in width, 400 mm in length)

Flow depth (m) Out put (mVolt)

Flow depth (Upstream) Flow depth (In channel) Flow depth (Upstream) Flow depth (In channel)

Flow depth (m)

Electromagnetic sensor for velocity

Velocity (m/s)

Flow depth (Upstream) Flow depth (In channel)

Flow depth (m) Trapped sediment weight (kg)

Flow depth (in bedload slot) Reid type bedload slot

Out put (mVolt)Impulse (pulses/ 1min)Impulse (pulses/ 1min)Impulse (pulses/ 1min)

Flow depth (Upstream) Flow depth (In channel) Flow depth (Upstream) Flow depth (In channel)

Gain times: 1016, 256, 64, 16, 4, 2 Gain times: 1016, 256, 64, 16, 4, 2 Gain times: 1016, 256, 64, 16, 4, 2

16 (Gain)

64 (Gain) 1016 (Gain)

Plate type hydrophone (800 mm in width, 200 mm in length) Rain fall (Tochio Station)

Plate type hydrophone (400 mm in length, 500 mm in width)

0 500 1000 1500 2000

2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00

-1 -0.5 0 0.5 1

6/19 6/20 6/21 6/22 6/23

パルス数(回/1min)

水位(m)

水位―ﾌﾟﾚｰﾄ型ﾊｲﾄﾞﾛﾌｫﾝ400×500mm 上流水位 水路水位 増幅率1016倍 増幅率256倍 増幅率64倍 増幅率16倍 増幅率4倍 増幅率2倍

Flow depth (In channel) Flow depth (Upstream)

16 (Gain): Blue colored 64 (Gain): Yellow colored 1016 (Gain): Gray colored

Fig. 7 Monitoring data, in which hydrophones show voltage output, obtained by various sensors at Ashi-arai-dani River basin (On June, 19th to 23rd, 2013)

0 1000 2000 3000 4000

2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00

-1 -0.5 0 0.5 1

6/19 6/20 6/21 6/22 6/23

電圧値(mV)

水位(m)

水位―ジオフォン 上流水位 水路水位 ｼﾞｵﾌｫﾝ

0 100 200 300 400

2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00

-1 -0.5 0 0.5 1

6/19 6/20 6/21 6/22 6/23

電圧値(mV)

水位(m)

水位―パイプハイドロフォン 音響センサー ^{上流水位 水路水位} ﾊﾟｲﾌﾟﾊｲﾄﾞﾛﾌｫﾝ

0 100 200 300 400

2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00

-1 -0.5 0 0.5 1

6/19 6/20 6/21 6/22 6/23

電圧値(mV)

水位(m)

水位―プレート型ハイドロフォン200×800mm 音響センサー ^{上流水位 水路水位} ﾌﾟﾚｰﾄ型ﾊｲﾄﾞﾛﾌｫﾝ200 音響ｾﾝｻｰ 0 100 200 300 400

2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00

-1 -0.5 0 0.5 1

6/19 6/20 6/21 6/22 6/23

電圧値(mV)

水位(m)

水位―プレート型ハイドロフォン400×500mm 音響センサー ^{上流水位 水路水位} ﾌﾟﾚｰﾄ型ﾊｲﾄﾞﾛﾌｫﾝ400 音響ｾﾝｻｰ

2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00

0 10 20 30 40

6/19 6/20 6/21 6/22 6/23

雨量(mm/h)

雨量(栃尾) _{雨量(白馬)}

0 1000 2000 3000 4000

2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00

-1 -0.5 0 0.5 1

6/19 6/20 6/21 6/22 6/23

電圧値(mV)

水位(m)

水位―プレート型ハイドロフォン400×500mm 振動センサー ^{上流水位 水路水位} ﾌﾟﾚｰﾄ型ﾊｲﾄﾞﾛﾌｫﾝ400 音響ｾﾝｻｰ

0 1000 2000 3000 4000

2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00

-0.5 0 0.5 1 1.5

6/19 6/20 6/21 6/22 6/23

捕捉土砂重量(kg)

水位(m)

水位―捕捉土砂重量 _{ピット水位 捕捉土砂重量}

0 1 2 3 4

2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00 20:00 23:00 2:00

-1 -0.5 0 0.5 1

6/19 6/20 6/21 6/22 6/23

底面流速(m/s)

水位(m)

水位―底面流速 _{上流水位 上流水位 底面流速}

Rain fall (Tochio Station)

Flow depth (m)Rain fall (mm/h)Flow depth (m)Flow depth (m)Flow depth (m)Flow depth (m)Flow depth (m)Flow depth (m) Velocity (m/s)Trapped sediment weight (kg)Out put (mVolt)Out put (mVolt)Out put (mVolt)Out put (mVolt)Out put (mVolt)

Plate type hydrophone (400 mm in length, 500 mm in width)

Flow depth (Upstream) Flow depth (In channel)

Plate type hydrophone (800 mm in width, 200 mm in length)

Flow depth (Upstream) Flow depth (In channel)

Pipe hydrophone (350 mm in length)

Flow depth (Upstream) Flow depth (In channel)

Vibration sensor in plate type hydrophone (500 mm in width, 400 mm in length)

Flow depth (Upstream) Flow depth (In channel)

Geophone in Europe

Flow depth (Upstream) Flow depth (In channel)

Electromagnetic sensor for velocity

Flow depth (Upstream) Flow depth (In channel)

Reid type bedload slot Flow depth (in bedload slot)

whose area on the bed is 16.8 cm², is sensitively obtained. The watching area of the plate-type hydrophone is larger than that of Japanese pipe hydrophone. Plate-type hydrophone in high gain (1016 times) measured in case of less than 500 impulses in one minute, and, however, it seems that measured impulses take some constant values if the impulse of high gain in one minute exceeds more than around 750 impulses. Impulses of middle gain (e.g, 16 times) are measured more for Plate-type hydrophone in comparison to Japanese pipe

hydrophone. In Japan, there are several monitoring sites with Japanese pipe hydrophone and some monitoring data propose that there are maximum threshold for high gain and those values are around 2500 to 4000 impulses in five minutes (500 to 800 impulses/min) for gain: 16 to 1016 times [Tsunakawa et al., 2013]. In addition, 2500 impulses in five minutes for maximum threshold (gain: 256 to 1016 times) was measured for rainfall events on 16th July, 2004, in monitoring at Ashi-arai-dani River [Mizuyama 2008; Mizuyama et al., 2012]. Herein, we will examine the threshold value of Japanese pipe hydrophone in next section, supposing that the value could be 2500 to 3750 impulses in five minutes (500 to 750 impulses/min).

The impulse of the plate-type hydrophone is more than that of Japanese pipe hydrophone in small magnitude of flood due to the watching area.

The data of vibration sensor and geophone are similar each other because of measurement by vibration sensor. As seen in the temporal changes of Reid type bedlod slot, there are almost two peak of sediment capture time at around 11:00 and 17:00 on June 19th until the slot is filled by sediment. In comparison with the output of acoustic waves of hydrophone, geophone, vibration sensor in the plate-type hydrophone, the peak of sediment

a) Comparison of several sensors for Japanese pipe hydrophone

b) Comparison of several sensors for Reid type bedload slot

Fig. 8 Comparisons of acoustic wave data obtained by Japanese hydrophone, Geophone, Plate type hydrophone (Data obtained in rainfall events on June 19th and July 29th, 2013 ate used.)

Geophone in Europe (mVolt)

Japanese pipe hydrophone (mVolt)

Plate type hydrophone of 400 mm in width (mVolt)

Japanese pipe hydrophone (mVolt)

Plate type hydrophone of 800 mm in width (mVolt)

Japanese pipe hydrophone (mVolt)

Reid type bedload slot (kg/5 min)

Japanese pipe hydrophone (mVolt) Plate type hydrophone

of 800 mm in width (mVolt) Plate type hydrophone

of 500 mm in width (mVolt)

Reid type bedload slot (kg/5 min)

Reid type bedload slot (kg/5 min)

◇

◆29th, July event 19th, June event

◇

◆29th, July event 19th, June event

◇

◆29th, July event 19th, June event

Fig. 9 Japanese pipe hydrophone versus Geophone in Europe for the voltage values (mVolt)

Geophone in Europe (mVolt)

Japanese pipe hydrophone (mVolt) 150

Linear correlation

movements can watch by vibration sensor and geophone, and two peaks are clearly measured. On the other hand, hydrophone can observe continuous time of sediment, and especially, the plate-type hydrophone (800 mm in width and 200 mm in length) seems to watch both peak and continuous time of sediment movements.

4.1.2 Differences in measurements using between vibration and acoustic sensors

Figures 8a) and 8b) shows the relation in the output of acoustic wave and vibration wave of between the Japanese pipe hydrophone and the geophone and the plate-type hydrophone, and the relations in the output of between the acoustic wave by plate-type/Japanese pipe hydrophone and Reid type bedload slot.

As mentioned above, the threshold of Japanese pipe hydrophone is estimated at around 500 to 750 impulses. In Fig. 7, the peak for the voltage of acoustic wave is observed at around 17:00 on 19th June, 2013 and the value takes around 150 mVolt.

On the other hand, impulses of Japanese pipe hydrophone take around 700 impulses (gain: 16 times) and 900 impulses (gain: 256 times).

Plate-type hydrophone of 800 mm in width and 200 mm in length measured high voltage data and the 1:2 inclinations can find in Fig. 8a). The hydrophone of 500 mm in width and 400 mm in length measures similar data to Japanese pipe hydrophone and the 1:1 inclination can find in Fig.

8 a) and 8b).

Figure 9 shows the relation in the voltage between Japanese pipe hydrophone and geophone in Europe, taking into account the maximum threshold of Japanese pipe hydrophone measurements. In Fig 8b), a limitation in the relation of Japanese pipe hydrophone versus Reid type bedload slot is not seen, because the bedload slot is almost filled up and the sediment volume is not obtained in case of around 150 mVolt of Japanese pipe hydrophone. For the relation of plate-type hydrophone versus Reid type bedload slot, there is steep inclination of output voltage to the slot and it seems that there is a linear correlation without a limitation in a range less than 150 mVolt.

Reid-type bedload slot cannot measure total sediment volume in one flood event due to the limited measurement volume, through the monitoring data on 19th to 23rd June, 2013 as indicated by Mizuyama [2012]. In flood events on 19th to 23rd June of 2013, correlations between the sediment volume and the voltage of acoustic waves are not fully obtained. The results emphasize, for example, necessity of the submerged loadcell system with plat plate on the bed surface, and the

system was developed and installed to obtain continuous data of bedload. In next section, we will introduce the system and the accuracy for the measurement. Data of flume tests are shown because monitoring data on 19th to 23rd June of 2013 cannot obtain due to electric trouble for data accumulations.

4.2 Bedload monitoring with submerged loadcells In order to confirm bedload measurements with the loadcell system, flume tests were conducted in observation flume of Hodaka Obs. DPRI on July 5th to 6th in 2013. Tests in July of 2013 were for several kinds of uniform sediment particles. In the submerged loadcell system, the data is collected by 100 Hz and the flow depth and velocity are measured by 10 Hz. In those tests, the flow depth in the channel was around 0.1 m.

Let us see data obtained in July of 2013. Three kinds of uniform sediment were used as shown in Table 1. The grain size distribution and the material are shown in Fig. 10 and Fig. 11. The sediment was supplied from upstream of 5 m as shown in Fig. 12.

The supplying sediment is set as equilibrium sediment concentration for the bed slope: Material G1=3.07 kg/s, G2=2.98 kg/s and G3=3.07 kg/s, which are specified in the air. Sediment supply time is specified as 50 seconds. The equilibrium sediment discharge rate (flux of mass discharge), Qb, is calculated based on the knowledge of sediment discharge rate [e.g., Japan Society of Civil Engineering, 1999]. In tests, the flow depth in the channel was around 0.1 m.

Figure 13 show temporal changes obtained by the loadcell, flow depth and clear water velocity on the bed in the flume tests in case of the materials G1. Figure 14 shows cross-correlations for the materials G1, G2 and G3 in flume tests. Sediment discharge

Table 1 Physical parameter of sediment particles Material d₆₀ (mm) Specific weight

G1 17.0 2.63

G2 30.0 2.65

G₃ 59.7 2.63

Fig. 10 Grain size distribution of sediment used in flume tests