A bivariate copula-wavelet analysis approach for quantifying compound runoff-sediment risks under cascade reservoirs

Area of Science:

• Hydrology
• River Basin Management
• Water Resource Engineering

Background:

• Managing river basins with cascade reservoirs requires understanding complex runoff and sediment dynamics.
• Cascade reservoirs significantly alter natural hydrological processes, necessitating advanced risk assessment tools.

Purpose of the Study:

• To develop and apply a bivariate copula-wavelet risk analysis (BCWRA) approach for assessing synchronous and asynchronous runoff-sediment risks.
• To quantify the impact of cascade reservoir operations on runoff-sediment dynamics in the Upper Yellow River Basin (UYRB).

Main Methods:

• Trend detection and periodicity analysis of hydrological data.
• Copula-based joint probability modeling and joint return period estimation.
• Application of the BCWRA approach to four hydrological stations in the UYRB.

Main Results:

• Reservoir operations reduced synchronous runoff-sediment events by 17.74% and increased asynchronous events by 18.25%.
• Midstream stations showed heightened risks of sediment retention and channel erosion.
• Reservoir regulation decreased runoff variability and sediment transport, shortening return periods for extreme events.

Conclusions:

• The BCWRA approach effectively assesses compound runoff-sediment risks in regulated river basins.
• Adaptive management strategies are proposed to mitigate risks associated with altered hydrological dynamics.
• The study provides a generalizable framework for managing compound hydrological hazards in regulated rivers.