Recent developments in sedimentmonitoring in Japanese rivers

Shusuke Miyata

Kyoto University

Free University of Bozen-Bolzano

Taro Uchida

National Institute for Land and Infrastructure Management, MLIT, Japan

Sediment monitoring in Japanese rivers

Standardized 60 monitoring stations have been established by the Japanese government.

Sediment related issues in mountain areas

DisastersLandslideLandslide

Flood caused by deposits in channels

Can we know impacts of mass movement in the upper reach during storm?

Sediment related issues in mountain areas

Watershed management Quantity and quality of sediment from

mountain streams are critical. Even in a basin, tributaries show different

characteristics of sediment runoff.

Sediment runoffSevere Mild

Why sediment monitoring in mountain rivers?

Why not numerical simulations?

✓ In general, mountain rivers are under supply-limited conditions.

✓ Field data is insufficient to validate the simulations.

✓ Mountain rivers include inherent complex geometry.

Contents of monitoring

◼ Water level gauge -> discharge◼ Turbidity sensor -> suspended load◼ Japanese pipe hydrophone

(pipe microphone) -> bedload

JPH

WL gauge

Turbidity sensor

Raw waveform

Bedload transport

Flow

MicrophoneΦ=272 mm

Filtered waveform

Acoustic energy Suzuki et al. (2010)

Suspended transport

Optical backscatter type turbidity sensor

Max measurement: 0 – 4000 NTU-> 0 – 5 (or 10) g/l for mud

-> 0 – 50 (or 100) g/l for sand

Sensor

Outcome of standardized monitoring

Sparse forest

After Tamura et al. (2014) After Tamura et al. (2016)

Forested catchmentForested catchment

Forest

SS [

m3/s

]

Discharge [m3/s]

Sparse forest

m3/k

m2/y

0

50

100

150

200

SS Bedload Total SS Bedload Total0

2000

4000

6000

8000

10000

Annual amounts of sediment transport

Forest Sparse forest

• Monitoring results revealed remarkable impact of plantation and erosion control works.

• Bedload transport was dominant in the sparse forest, while SS was dominant runoff process in the forested catchments.

Problems of monitoring: Bedload

1. Noise of the stream water hides signals of fine particles.

2. Multiple bedload hitting a pipe can cause underestimation of the measured transport rate.

3. Saltating bedload potentially results in underestimation.

4. A single pipe is insufficient to involve cross-sectional distribution of bedload transport.

Combination of vertical and horizontal pipes

𝑅ℎ𝑣 = ൘𝐴𝑣𝐻

𝐴ℎ𝐿

Tsutsumi et al. (2018)

𝐴𝑡 = 𝑅ℎ𝑣𝐻

𝐻𝑝𝐴ℎ

Homogeneous distribution

Practical distribution

Ratio of Acoustic energy by vertical and horizontal pipes

Total acoustic energy through the cross section

Effects of the combination

Tsutusmi et al. (2018)

This approach can calculate total acoustic signal by bedload transport including saltating bedload.

Problems of monitoring: Suspended sediment

I. Common turbidity sensors are effective to wash-load. Courser suspended load is not reasonably measured by the turbidity.

II. Monitoring of a single turbidity sensor can not catch vertical distributions of concentration.

III. Frequent elevations changes of riverbed and stream surface in mountain rivers may cause malfunction of sensors.

Application of TDR (time domain reflectometry) to sediment concentration measurement

Cable-tester

Sensor probe

Apparent length

Ref

lect

ion

co

effi

cien

t

TDR waveform

ε𝑜𝑏𝑠 =𝐿𝑎𝐿𝑉𝑝

2

La

Probe length L

1. Measurement of dielectric constant εobs using TDR

2. Calculation of ratios of water (εw=80) and sand (εs=3)

𝜀𝑜𝑏𝑠 = 1 − 𝜃 𝜀𝑤 + 𝜃 𝜀𝑠 〈Dobson et al. (1985)〉

CT

DR [

-]

0.0

0.1

0.2

C [-]

0.0 0.1 0.2

CT

DR [

-]

0.0

0.1

0.2

(a) d=0.2 mm

(b) d=0.0004 mm

Lab. experiment for validation

Deionized water (60L)

Cable tester

Data logger

Multi-plexer

5 coil-type probes & a 3-rod probe

Average

Monitoring at the sparse forest catchment

Sediment concentration by TDRHeights of 0.03 - 0.23 m

Sampling at various heights for suspended load

Heights of 0.02 - 0.15 m

Water level, Turbidity

TDR sensors

Pipe-hydrophone

Sampling

∅25mm

0:00 4:00 8:00 12:00 16:00

Rai

nfa

ll [

mm

/h]0

10

20

30

Dis

char

ge

[m3/s

]

0

1

2

3

Comparisons between sampling and TDR during a storm in June 2017

Sediment concentration: TDR > Sampling.Vertical profiles (higher at the bottom) were found.

C [-]

0.00 0.05 0.10

z [m

]

0.0

0.1

0.2

0.3 (a) 5:20

Sampling

TDR

C [-]

0.00 0.05 0.10

z [m

]

0.0

0.1

0.2

0.3 (b) 5:40

C [-]

0.00 0.05 0.10

z [m

]

0.0

0.1

0.2

0.3 (c) 6:00

C [-]

0.00 0.05 0.10

z [m

]

0.0

0.1

0.2

0.3 (d) 6:40

C [-]

0.00 0.05 0.10

z [m

]

0.0

0.1

0.2

0.3 (c) 6:00

0.001 0.01 0.1 1 10

Per

cen

tag

e p

assi

ng

th

ou

rgh

0

20

40

60

80

100

5:206:006:40

(a) h=0.12 m

Diameter [mm]

0.001 0.01 0.1 1 10

(b) h=0.07 m

Diameter [mm]

0.001 0.01 0.1 1 10

Per

cen

tag

e p

assi

ng

th

ou

rgh

0

20

40

60

80

100(c) h=0.02 m

Particle size distributions of sampled suspensions

The sediment concentrations by the TDR method was the sum of wash-load and suspended sediment.

The sampled suspensions were almost wash-load (<0.1mm).

Concentration:

TDR > sampling*Remarkable at the bottom.

samplingTDR

C[-

]

2017/10/22-23

00:00 06:00 12:00 18:00 00:00 06:00 12:00

0.00

0.05

0.10

0.150.00

0.05

0.10

0.15 0.00

0.05

0.10

0.15

0

10

20

300

1

2

3

0

2000

4000

TDR P-3 (h=0.13 m)

TDR P-2 (h=0.08 m)

TDR P-1 (h=0.03 m)

Dis

char

ge

[m3/s

]

Rai

nfa

ll

[mm

/h]

Tu

rbid

ity

[NT

U]

C[-

]

C[-

]

Heavy storm event in Oct. 2017

Precipitation: 144 mmMax intensity: 12 mm/h

Deposition on the probe

00:00 06:00 12:00 18:00 00:00 06:00 12:00

Rai

nfa

ll [

mm

/h]0

10

20

30

Dis

char

ge

[m3/s

]

0

1

2

3

Vertical profiles of concentration

0.00 0.02 0.04 0.06 0.08 0.10

z [m

]

0.0

0.1

0.2

0.3

0.00 0.02 0.04 0.06 0.08 0.10

0.0

0.1

0.2

0.3(a) 10/22 17:40 (b) 10/22 20:30

0.00 0.02 0.04 0.06 0.08 0.10

0.0

0.1

0.2

0.3

C [-]

0.00 0.02 0.04 0.06 0.08 0.10

z [m

]

0.0

0.1

0.2

0.3

(c) 10/22 20:50

(d) 10/22 21:20

C [-]

0.00 0.02 0.04 0.06 0.08 0.10

0.0

0.1

0.2

0.3

C [-]

0.00 0.02 0.04 0.06 0.08 0.10

0.0

0.1

0.2

0.3(e) 10/22 21:30 (f) 10/22 21:50

Modelling of concentration profile

Measured conc. at the bottom

Near-bed concentration Ca

Vertical profile of concentration

Rouse distribution

Garcia & Parker (1991)

Water level, Particle size

height=0.03[m]（height of the probe）

Height = 5% of water level(= about 0.01m)

Ashida & Michiue (1970)

*Theories for movable bed

0.00 0.05 0.10

z [m

]

0.0

0.1

0.2

0.3

0.00 0.05 0.10

0.0

0.1

0.2

0.3(a) 10/22 17:40 (b) 10/22 20:30

0.00 0.05 0.10

0.0

0.1

0.2

0.3

C [-]

0.00 0.05 0.10

z [m

]

0.0

0.1

0.2

0.3

(c) 10/22 20:50

(d) 10/22 21:20

C [-]

0.00 0.05 0.10

0.0

0.1

0.2

0.3

C [-]

0.00 0.05 0.10

0.0

0.1

0.2

0.3(e) 10/22 21:30 (f) 10/22 21:50

Calculated and measured profiles

Rouse distribution with the measured near-bed concentrations showed better fitting with the observation.

Measured

Ashida &

Michiue

(1970)

Garcia &

Parker

(1991)

TDR at

0.03 m

For Ca

0.00

0.05

0.10

0.15P-1 (h=0.03 m)P-2 (h=0.08 m)P-3 (h=0.13 m)Average

0

10

20

300

1

2

3

2017/10/22-23

00:00 06:00 12:00 18:00 00:00 06:00 12:00

0.00

0.02

0.04

0.06

Runoff of suspended sediment during the event

Averaged concentration and SS transport can be calculated when concentrations at the near-bed height were obtained.

Dis

char

ge

[m3/s

]

Rai

nfa

ll

[mm

/h]

C[-

]S

usp

end

ed s

edim

ent

[m3/s

] 509 m3（=1349 t）

Summary

In Japanese mountain rivers, standardized sediment monitoring systems are established.

Sediment runoff data in 60 stations have been collected and analyzed to understand characteristics of each catchment and/or detect mass movement in the upper reach.

Monitoring methods of bedload and suspended load are improved.

W0/u*

0.01 0.1 1 10

Ca

0.01

0.1

1

W0/u*

0.01 0.1 1 10

W0/u*

0.01 0.1 1 10

W0/u*

0.01 0.1 1 10

Ashida & Michiue (1970) Garcia & Parker (1991) TDR at 0.03 m

(a) d=0.1 mm (b) d=1 mm (c) d=2 mm (d) d=10 mm

Measured (TDR) and calculated Cas

*W0/u* was calculated using hydraulic conditions at each time.

Effects of particle size

The profiles during the high discharges were well simulated with d=

1.0 mm.

0.00 0.05 0.10

z [m

]

0.0

0.1

0.2

0.3

0.00 0.05 0.10

0.0

0.1

0.2

0.3(a) 10/22 17:40 (b) 10/22 20:30

0.00 0.05 0.10

0.0

0.1

0.2

0.3

C [-]

0.00 0.05 0.10

z [m

]

0.0

0.1

0.2

0.3

(c) 10/22 20:50

(d) 10/22 21:20

C [-]

0.00 0.05 0.10

0.0

0.1

0.2

0.3

C [-]

0.00 0.05 0.10

0.0

0.1

0.2

0.3(e) 10/22 21:30 (f) 10/22 21:50

d=0.1 mm d=1.0 mm

d=2.0 mm