High-water Level River Discharge Measurement Method in Japan

Flood River Discharge
Measurement Method in Japan
Hydrologic Engineering Research Team
Hydraulic Engineering Research Group
Public Work Research Institute (PWRI)

Contents
1. Overview of River Discharge
Observation in Japan
2. Standard Flood Discharge
Measurement Method in Japan
3. Other Flood Discharge Measurement
Method in Japan
1. Non-Contact Surface Current meter
2. Pressure-flood current meter
3. Measurement using ADCP

Feature of River in Japan
• Catchment area is small
• Rivers have very steep bed
slope
• Annual precipitation is big
Japan
Annual precipitation[mm/year]
Other countries
Most of Floods are Flash Floods
in Japan

River Discharge Observation
framework in Japan
Oversee
River Bureau,MLIT
PWRI
Technical Support
Manual Preparation
Regional Bureaus
Check the data ,has responsibility in
the data.
Local Work offices
Order observation
Local survey company
Observed data
River
Discharge
Observation
Flood
Discharge
Measurement
Low-flow
discharge
Measurement

Feature of Flood River Discharge
Measurement in Japan
Problem
• There are a lot of debris flows.
• Current velocity is high.
Contact current meter is almost impossible
Measurement using Floats has become
standard in Japan.

Historical back ground of Flood Discharge
Measurement in Japan
Ministry of construction staffs observed by themselves often
using bamboo which grow naturally around observatory at its
early period
Increased observatory(about 1400
place in Japan for MLIT)
Decreased staffs
Local construction office can’t
observe discharge by itself
Since an office cannot apply a large
amount of cost, the quality of data
may have fallen off.
ex:Discharge and WL observatory
relevant to Tone River basin (We
can see a lot of observatory )

Measurement using Floats
• Characteristic
1. Standard method of Flood River Discharge
Measurement to make rating curve
2. Plunge floats from a bridge

Operational Problem of Measurement
using Floats.1
• It is difficult to observe the WL raising time or peak time.
• Decreasing expert observers (It became impossible to contract with
one contractor who have know-how for long time,because bid system
was changed)
The example by
which the data of a
rise term is not
observed

Technical Problem of Measurement
using Floats.1
• Now averaged (max.&min.) conversion factor
for each type of float is as follows:
1) Surface float: 0.85 ( valid for h 0.7m )
2) 0.5 m float: 0.88 ( valid for h = 0.7 1.3m )
3) 1 m float: 0.91 ( valid for h = 1.3 2.6m )
4) 2 m float: 0.94 ( valid for h = 2.6 5.2m )
5) 4 m float: 0.94 ( valid for h 5.2m )
This standard was decided about 40 years ago, Then, research was
progressed and the problems mentioned later was pointed out. So,we
should re-check these factors.
We are going to check these factors
from this year to next year

Technical Problem of Measurement using
Floats.2(Hypothesis on Disturbed flow in the downstream of bridge piers)
Actual discharge value:Q
Q
Non-back flow field
Back flow field
Discharge observed value based on the current standard Q’
Q 1 =A 1
Q 2 =A 2 V 2
Non-back flow field
Q 1 Discharge of non-back flow field ,A 1 river area of non-back flow field,
V 1 average velocity of non-back flow field,
Q 2 Discharge of back flow field,A 2 river area of back flow field,
V 2 average velocity of back flow field
V 1
Q=Q 1 +Q 2
=A 1 V 1 +A 2 V 2
Q 1 =A 1 V 1
Q
Non-back flow field
Q 1
=A 1
(V 1
+V
)
Back flow field Q 2
=A 2
(V 1
+V
)
Q’= Q 1
+Q 2
=(V 1
+V
)(A 1
+A 2
)
Non-back flow field Q 1
=A 1
(V 1
+V
)
Q 1 Discharge of non-back flow field,A 1 river area of non-back flow field,V 1 average velocity of non-back flow field,
V acceleration by aboideau rising effect,Q 2 Discharge of back flow field,A 2 river area of back flow field
comparison of Discharge observed value of current standard and Actual discharge observed value
Q’=Q+(V 1 -V )A 2 +V (A 1 +A 2 )
Discharge observed value based on the current
standard has overestimates the river discharge
The part become exorbitance
caused bythe underline part
Tone River downstream construction office
Tone River downstream part river bed and discharge observation research report in 1999

Hypothesis on Disturbed flow in the downstream of
bridge pies
vertically averaged current velocity [m/s]
It is shown that current velocity become low around the
bridge piers.
transverse direction distance [m]
Vertically averaged current velocity observation data by
ADCP (10/3/2003 at Isikariohasi observatory)

Technical Problem of Measurement using
Floats.3
(Hypothesis on parallel spiral flow)
‘Parallel spiral flow’
is created in the
downstream of bridge
basements. Floats are
apt to be concentrated
in the lines. Velocity
is about +10% more
than the average.”
According to Dr. Ryosaku
KINOSHITA (1998) A
discussion on the flood
discharge measurement in the
downstream of river, Journal of
Japan Society of Hydrology &
Water Resources, vol.11, No.5,
pp.460-471 471 (in Japanese).

The observation by ADCP (19/12/2000,Mashimo discharge observatory)
Hypothesis of parallel spiral flow
The figure which changed the depth to
width into 1 to 1
:uv component Contour diagram
:w component Contour diagram
Upstream
Downstream
From upstream and downstream the periodic structure
appeared regularly.
we can guess the existence of a parallel spiral flow.

Technical Problem of Measurement
using Floats.4(other problem)
When vegetation flourish on flood channel, floats don’t
run properly
• It is difficult to use floats in the middle
water level or on the river terrace.
Not flow floats
these area

Other flood River Discharge Measurement
Methods
In order to supplement the drawback of float observation,
we need to develop and put other techniques in operational.
Development of other flood River Discharge
Measurement Methods in Japan
. Non-Contact Surface Velocity Measurement
(supplement method for Measurement using floats)
. Pressure-type Flood Current Meter
( for investigation use only)
. ADCP
(under investigation for high water)

Non-Contact Surface Velocity
Measurement
Characteristic
1. Measure river surface velocity (estimate cross-sectional
total discharge by summing up each of the cross-sectional areas.
Vertically averaged velocity is calculated using a conversion factor )
2. 4 types of Non-Contact Surface current meter
were developed(The PWRI and other six private
companies developed them for four years. The current
meters are attached on bridge or bank of river,
and we can observe automatically even from a
remote office.

Assortment of Non-Contact Surface
Current Meter1
• Doppler type
1. Radio wave-type current meter
2. Ultrasonic-type current meter

Assortment of Non-Contact Surface
Current Meter2
• Image processing type
1. PIV current meter
2. Optical Flow current meter

Problem of Non-Contact Surface
Velocity Measurement
1. Conversion factor is subject to change
We decided conversion factor from observed
data at Uono-River and Tone-River,
We must get more data and verify the factor
using the data.
Discharge by Non-Contact
Surface Current Meter [m3/s]
Discharge by float observation[m3/s]
The Discharge by Non-contact
Surface Current Meter using the
conversion factor made from
Uono-River and Tone-River data
are settled in less than about 5%
of float observation discharge.

Problem of Non-Contact Surface
Velocity Measurement
1. Correction of Wind Effect.
We made the algorithm to eliminate wind current and
tested the effect in an indoor experiment, but we haven’t
developed method to eliminate the effect of windswell.
The relative error of discharge measured
value[%]
Radio
wave
Ultra
Sonic
PIV
Optical
flow
With no influence
compensation of a
wind
With influence
compensation of a
wind

Problem of Non-Contact Surface
Velocity Measurement 3
1. Cost is expensive

Out look of Non-Contact Surface Current
Meter
We will get data from new 6 sites in this year

Pressure-type Flood Current Meter
• Characteristics
1. Used for turbulence 2D constitution research
mainly
2. hanged from a bridge
3. Measure vertical water velocity profile

Problem of Pressure-type Flood
Current Meter
1. Cost is expensive
(about ¥100,000,000$850,000)
2. Possibility of miss by flowing objects
or when current velocity is fast (more
4m/s)

Measurement using ADCP(by radiocontrolled
boat)
• Characteristics
1. Used for turbulence 3D structure of turbulence in
river flow
2. Measure vertical water velocity profile precisely
3. We can use it if current velocity is not so fast (less
than 34m/s)

Problem of Measurement using
ADCP(by radio-controlled boat)
1. Steering of radio-controlled boat is difficult.
(Substantially only one company has the operation
technology.)
2. It is difficult to use if current velocity is high

Conclusion
• Float observation is standard in Japan
• In order to supplement the drawback of float
observationNon-Contact Surface Velocity
Measurement, Pressure-type Flood Current
Meter, Measurement using ADCP are now
being developed.

Our interest
• How to rating curve management
• The other possibility of using Non-Contact
Surface Velocity Measurement
• The other possibility of using ADCP