Bathymetry of Zipingpu Reservoir by earthquake and flood induced turbidity currents

A field measurement to assess the bathymetry was conducted in Zipingpu Reservoir from 2007 to 2013, Min River, China. The Wenchuan (Ms = 8.0) earthquake (2008) took place in the upper reach and sedimentation by flood induced turbidity currents changed reservoir bathymetry in a short time.

The Zipingpu Reservoir effectively controls the 98% sediment inflow and 90% torrential rain area of upstream reaches, which the average annual flow is 469m³/s. It meets irrigation and municipal water supply of Dujiangyan irrigation project and Chengdu, balancing flood control, power generation and environmental protection, etc.

All data obtained from multi-beam echo sounder system (MBES) are used to analyses the changes of bathymetry. It consists of acoustic, auxiliary, data collection and visualization system, which was mounted on a vessel. The similarities of compassion with reservoir section measurement suggest that high resolution (1.25 cm) and superior performance of MBES can accurately detect the characteristics of bathymetry by transmitting fan-shape pulses perpendicular to cover bottom, as shown in Figure 1. Figure 1 Measurement results by MBES. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315623207/4fbc492d-6678-4a12-aaf6-5c2b8ea38e5f/content/fig215_1.jpg"/>

A natural barrier induced by landslide is found in a distance of 6.95 km upstream of the dam, which had been raised for 33.84 m. The volume of the landslide in reservoir is estimated about 5.3 × 10⁶ m³. A flushing cone formed close to the dam because of turbidity currents. Figure 2 shows that the most severe deposition occurs behind the barrier formed, with area loss ratio reaching to 40%. Figure 2 Comparison of thalweg. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315623207/4fbc492d-6678-4a12-aaf6-5c2b8ea38e5f/content/fig215_2.tif"/> Figure 3 Distribution of section area loss ratio. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315623207/4fbc492d-6678-4a12-aaf6-5c2b8ea38e5f/content/fig215_3.jpg"/>

Triangulated Irregular Network method was used for creating 3D terrain model and analyzed storage capacity. The results show that the storage capacity loss ratios are 17.07% at lowest level and 12.23% at flood limit water level compared to 2008.