Abstract
Abstract The construction of check dams in northwestern China has resulted in nonstationary changes in flood peak discharge series; the stationary assumption of the conventional hydrological frequency analysis is no longer satisfied. According to the characteristics of the construction and operation of check dams, the nonstationarity of flood peak discharge series are largely induced by changes in the effective runoff generation area (i.e., the basin area minus the area controlled by check dams). Knowing the power function relationship between the flood peak discharge and the basin area, we can remove the influence of the effective runoff generation area and convert the original nonstationary series into a stationary series. This de-nonstationarity method can achieve stationarity in the first and second moments simultaneously. Therefore, we can calculate the design value of the reconstructed series using the conventional frequency analysis method. According to the effective runoff generation area under design conditions, we can then obtain the corresponding design flood of the original series. We applied this method to the Mahuyu River basin to obtain the design flood under nonstationarity. Due to the consideration of the deterministic influence of check dams during the de-nonstationarity process, the uncertainty analyzed by the bootstrap method is obviously small.
Highlights
Design flood estimation plays an important role in water project design, water resources planning, and flood risk control
We inferred that nonstationarity in the flood peak discharge series is caused by changes in the effective runoff generation area in the presence of check dams
As a kind of engineering measure for water and soil conservation, lead to the nonstationary changes in the flood peak discharges series. This nonstationarity creates unreliable design flood values when they are calculated with the conventional hydrological frequency analysis method
Summary
Design flood estimation plays an important role in water project design, water resources planning, and flood risk control. It is usually obtained using frequency analysis which is a technique of fitting a probability distribution to a series of observations for defining the probabilities of future occurrences of some events of interest, e.g., an estimate of a flood magnitude corresponding to a chosen risk of failure (Khaliq et al ). For the flood peak discharge Q with distribution FQ(Qjθ), we generally assume that the series is stationary, and that the distribution parameters θ are time invariant. In the context of the construction of thousands of check dams, the stationarity of the flood peak discharge series gradually disappears. The nonstationary flood frequency analysis has become a point of concern for engineers and local managers
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