Abstract
The determination of characteristic flow velocity is a hydrodynamic problem needs to be solved in the application of geomorphologic instantaneous unit hydrograph (GIUH) for runoff simulation in areas with no or limited data. In this study, 120 watersheds are collected to construct a regression model; 85 of these basins are used for regression analysis, and the 35 remaining basins are utilized to verify the feasibility of the constructed model. Random forest algorithm is applied to screen out important geomorphologic factors from the 16 extracted factors that may affect flow velocity. Multivariate regression is used to establish the numerical relationship between velocity and the selected factors. Sensitivity analysis of each adopted factor in the constructed model is conducted using the LH-OAT method. The rationality and feasibility of the regression model are validated by comparing the flow velocity calculation with a previous approach, which is also calculated based on geomorphological parameters. Subsequently, the runoff simulation based on the GIUH model is evaluated using the proposed technique. Results demonstrate that the proposed formula possesses high fitting accuracy and can be easily used to calculate flow velocity and generate GIUH.
Highlights
Nash[13,14] derived a mathematical formula of the unit hydrograph (UH), which contains fewer parameters but is applicable in practical conditions based on the hypothesis that the effects of watershed storage can be simulated by several linear reservoirs in series connection
The shape of the IUH can be changed in response to the change in scale, that is, area size is a decisive factor in GIUH generation[7]
The accuracy of the GIUH method largely relies on the calculation of the characteristic flow velocity estimation
Summary
Nash[13,14] derived a mathematical formula of the unit hydrograph (UH), which contains fewer parameters but is applicable in practical conditions based on the hypothesis that the effects of watershed storage can be simulated by several linear reservoirs in series connection. Where u(t) stands for the UH ordinate; index a is the shape parameter that reflects the number of conceptual free water reservoirs; and k is the scale parameter, which is a constant reservoir storage that delineates the average watershed flow time of concentration. In previous literature[17], the shape parameter a relies on H–S geomorphologic characteristics RA, RB, and RL10–12 of a watershed, and k depends on geomorphology and on the flow velocity. Croley applied a numerical solution to obtain a against RA, RB, and RL as Eq (2), and the normal ranges of H–S geomorphologic numbers from 3 to 6, 2.5 to 5, 1.5 to 4.1 are proposed by investigating the features of a natural river network[32].
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