Flood River Discharge Measurement Method in Japan

Transcription

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

2 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

3 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

4 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

5 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.

6 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 )

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

8 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

9 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 = m ) 3) 1 m float: 0.91 ( valid for h = m ) 4) 2 m float: 0.94 ( valid for h = m ) 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

10 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 V 1 Q=Q 1 +Q 2 Q 2 =A 2 V 2 =A 1 V 1 +A 2 V 2 Q 1 =A 1 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 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

11 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)

12 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 (in Japanese).

13 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.

14 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

15 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)

16 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.

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

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

19 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.

20 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

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

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

23 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

24 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)

25 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 3 4m/s)

26 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

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

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