Verification of STIV analysis of flood discharge at Nakano Observatory
in the Ota river by flow analysis using ALB data
Keisuke YOSHIDA1, Shinya NIGO2, Shiro MAENO1, Koji Mano3, Mitsutaka NAKANO2Introduction

1 Okayama University, Japan, 2 Chugoku Regional Development Bureau, MLIT, Japan, 3 Pasco Corporation, Japan

Background: Recent severe flood conditions that surpass planned severity pose newchallenges for the earlier type of flood river discharge measurement using floating rods. For
such practical issues, non-contact type measurement methods including space-time image
velocimetry (STIV, Fujita et al., 2007) using cost-efficient devices and improved algorithms
for flow analysis have been developed and attracting hydraulic engineers. Nevertheless,their applicability must be verified and improved for various river conditions.
Objective: We conducted flow measurements using STIV analysis at Nakano Observatory in
the lower Ota River in Japan (Fig.1, Fig.2). Our targeted flood occurred during the heavy
rainfall event in early July 2018. Then, we examined the accuracy of the dischargehydrography by means of the present STIV analysis, comparing observations of flooded
water levels with numerical simulations results that used the discharge hydrograph.

3.5 m/s
Figure 2. Left-side infrared camera image
superimposed with corresponding STIV result at
19:00 on July 6 at the targeted cross-section: green
lines, searching lines for STIV analysis; red vectors,surface velocity vectors.

Figure 3. Land cover classification for thetargeted river reach using the ALB dataobtained after flooding in 2018.

Table 1. Discharge conditions for numerical tests.
DischargehydrographCase 1lveg

Case 2

Approximate value of peakdischarge during flooding

Stage–discharge 3000 (m3/s)
relation (H‐Q)
STIV
2600 (m3/s)

Figure 1. (left)Study site: Nakano Observatory and Ota River basin in Hiroshima, Japan.
(right) Targeted cross-section and observation setup at Nakano Observatory (17.8 KP).

Methodology

Figure 4. Targeted river reach and water levels
measured at four points during flooding.

 We obtained data of river bed elevation, land-cover classification using airborne
laser bathymetry (ALB) data (Fig.3) for flooded river simulations.
 We measured water levels at four locations during flooding (Fig.4).
 We set up two cases for numerical simulations (Table 1).

Key Results
 Longitudinal profiles of the simulated water levels using the present dischargehydrograph are approximately consistent with the observations (Fig.5).
 Simulated water levels in Case 1 (H-Q relation) are overestimated by an average ofapproximately 50 cm compared with observations. Simulated results obtained forCase 2 (present STIV-derived hydrograph) are consistent with observations (Fig.6).

Reference
Fujita et al. (2007). Development of a non-intrusive and efficient flow monitoring technique:
The space-time image velocimetry (STIV). Intl. J. River Basin Management, 5(2):105-114.

Figure 5. Longitudinal distribution of simulated waterlevels along the reach for Case 2 with observation: H.W.L.,
high water level; MinBedElev, minimum bed elevation;Sim., simulation results; Obs., observation results.

Figure 6. Time variation of observed andsimulated water levels along the reach:left, Case 1; right, Case 2.