Abstract
The geomorphologic instantaneous unit hydrograph (GIUH) is an applicable approach that simulates the runoff for the ungauged basins. The nash model is an efficient tool to derive the unit hydrograph (UH), which only requires two items, including the indices n and k. Theoretically, the GIUH method describes the process of a droplet flowing from which it falls on to the basin outlet, only covering the flow concentration process. The traditional technique for flood estimation using GIUH method always uses the effective rainfall, which is empirically obtained and scant of accuracy, and then calculates the convolution of the effective rainfall and GIUH. To improve the predictive capability of the GIUH model, the Xin’anjiang (XAJ) model, which is a conceptual model with clear physical meaning, is applied to simulate the runoff yielding and the slope flow concentration, integrating with the GIUH derived based on Nash model to compute the river network flow convergence, forming a modified GIUH model for flood simulation. The average flow velocity is the key to obtain the indices k, and two methods to calculate the flow velocity were compared in this study. 10 flood events in three catchments in Fujian, China are selected to calibrate the model, and six for validation. Four criteria, including the time-to-peak error, the relative peak flow error, the relative runoff depth error, and the Nash–Sutcliff efficiency coefficient are computed for the model performance evaluation. The observed runoff value and simulated series in validation stage is also presented in the scatter plots to analyze the fitting degree. The analysis results show the modified model with a convenient calculation and a high fitting and illustrates that the model is reliable for the flood estimation and has potential for practical flood forecasting.
Highlights
Flood is one of the most devastating natural disasters on earth, which causes immense human safety damage and property loss worldwide [1], especially in some areas with insufficient hydrologic data, the data scarcity has led to the inability of many hydrologic model applications, causing inaccurate flood prediction and failing the prevention of flood disaster
This study presents a flood forecasting approach, applying the XAJ model to calculate the flow generation, partition, and the slope flow concentration, and the optimized geomorphologic instantaneous unit hydrograph (GIUH) based on the Nash model to compute the river flow concentration
It provides a comprehensive simulation of the runoff process, keeping the advantage of GIUH being independent on the observed hydrologic data, which is suitable in ungauged or scantly gauged basins
Summary
Flood is one of the most devastating natural disasters on earth, which causes immense human safety damage and property loss worldwide [1], especially in some areas with insufficient hydrologic data, the data scarcity has led to the inability of many hydrologic model applications, causing inaccurate flood prediction and failing the prevention of flood disaster. Rodriguez-Iturbe et al [2], Valdes et al [3], and Gupta et al [4] initially proposed GIUH to describe the movement of each droplet by using the probability density function. It is based on the Horton–Strahler stream ordering scheme [5,6,7], with a view at the stochastic distribution of water droplet concentration time. Rodriguez-Iturbe and Valdes [2] applied the theory of probability method to hydrological flow concentration and derived the R-V GIUH and the formula of three-order river network, including the reasonably transferring rules of each droplet. Rosso [9] explored the relation between Horton order ratios and the two parameters of the Nash model from in a numerical perspective, explaining the effect of catchment geomorphology on hydrologic response
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