ADCP流量観測/ADCP Discharge Measurements

(Written by Ms. Takigami, Translated to EN by AI)

月に一回程度、千葉県の利根川水系鹿島川の羽鳥地点において、ADCP（音響ドップラー流速計）を用いた流量観測を行っています。本研究では、印旛沼で実施されている循環灌漑を、治水分野にも適用できる可能性について検証しており、循環灌漑によって農業用水の使用料を削減することで、豪雨時に必要な印旛沼のバッファーを増加させ、洪水被害を低減させることを目指しています。研究の過程で、羽鳥地点の流出量のシミュレーションを行っており、羽鳥地点の観測流量が必要になっています。

観測では、ADCPを取り付けたボートを橋の上から川へ降ろし、ロープで曳航しながら橋の端から端まで移動させます。ADCPは水中に超音波を発信し、水中を流れる粒子からの反射波を利用して流速を測定する機器です。川幅方向に移動しながら水深ごとの流速を連続的に計測することで、流速分布や断面形状を把握し、川全体を流れる流量を高精度に算出できます。これにより、河川をどれだけの水が流れているかを定量的に把握でき、シミュレーションの再現性向上だけでなく、流域の水循環や洪水時の流出特性を評価するための重要なデータが得られます。（観測にあたっては、中央大学手計研究室の学生さんにもご協力いただいています。この場を借りて感謝申し上げます。）

(AI-translated )

Approximately once a month, we conduct river discharge measurements using an Acoustic Doppler Current Profiler (ADCP) at the Hatori monitoring site on the Kashima River, which is part of the Tone River system in Chiba Prefecture.

This study examines the potential application of the cyclic irrigation system currently practiced around Lake Inbanuma to flood management. By reducing agricultural water withdrawals through the reuse of irrigation water, the study aims to increase the water-storage capacity available in Lake Inbanuma during heavy rainfall events, thereby reducing the risk of flood damage. As part of this research, we are simulating river discharge at the Hatori site, for which observed discharge data are essential.

During each survey, a small boat equipped with an ADCP is lowered from a bridge onto the river. The boat is then towed by rope from one side of the bridge to the other. The ADCP emits ultrasonic signals into the water and measures flow velocity using signals reflected by particles moving with the current.

By continuously measuring flow velocity at different depths while moving across the width of the river, the instrument captures both the velocity distribution and the shape of the river cross-section. These measurements allow us to calculate the total volume of water flowing through the river with a high degree of accuracy.

The resulting data provide a quantitative understanding of river flow conditions. They are important not only for improving the accuracy and reproducibility of our simulations, but also for evaluating the water cycle within the watershed and the characteristics of runoff during flood events.

We would also like to express our sincere appreciation to the students of the Tebakari Laboratory at Chuo University for their assistance with the field measurements.