Estimate of river-bed variation and pier scour by using a non-contact surface velocity radar.

Jian-Hao Hong, Po-Hung Yeh, Han-Chung Yang, Chih-Chiang Su

Tuesday 30 june 2015

12:54 - 12:57h at Oceania (level 0)

Themes: (T) Sediment management and morphodynamics, (ST) River morphodynamics, Poster pitches

Parallel session: Poster pitches: 5B. Sediment - River

Scour around bridge piers and along river reaches has long been an intrigue topic for researchers. Its development, especially during floods or some other large hydrological events, has particularly received plenty of attention. Most research focuses on either building a prediction model or developing a scour monitoring system. However, due to the difficulties in obtaining scour measurements during floods or spontaneous simulations from numerical models, it always poses a great challenge for the administrators or agencies in the right timing for bridge closure or re-opening. This study conducted field measurements of bridge pier and channel bed scour at Mingchu Bridge which crosses the middle section of the Choshui River in Taiwan. Numbed bricks and wireless tracers were used to measure the maximum scour depth and temporal variations of the scour depths during floods. A surface velocity radar and a water-level gauge were also installed on the bridge deck to obtain flow information. Scour data were collected separately during a monsoon and Typhoon Matmo in 2014, with the respective peak flow discharges of 1,446 and 4,980m3/s. The corresponding maximum general and pier scour depths reached 1.76 m and 2.53 m during the monsoon, and 3.245 m and 4.125 m during the typhoon. A quick estimation algorithm for temporal variations of general scour depth was developed, based on the effectively cumulative stream power concept and calibrated by using the field data. Temporal variations of total pier scour depth then could be determined by superimposing the estimation on the local pier scour depth. By examining with the data from these two events, the results showed reasonable agreement with the field measurements. With the quick estimation developed in this study, it would be possible to install guidelines for river and bridge management. More field data are needed to further test the reliability and capability of the proposed method, and a more robust scour monitoring system shall be developed in the future.