Simulating Spatial and Temporal Dynamics of Soil Moisture and Gully Flow
Using Improved Grid-Xinanjiang Model with a Prior Parameter Estimates
Abstract
To systematically generalize the influence of gullies on floods, a
distributed model named Improved Grid-Xinanjiang (GXAJ), and a priori
parameters estimation scheme based on the Global Digital Soil Mapping
System (SoilGrids) are proposed. Within a watershed divided into a
series of orthogonal cells, shallow furrows and trenches inside the
cells are conceptualized as primary gullies, in which water movement is
simulated by kinematic wave equation considering the gullies density,
and well-developed grooves between cells are considered as main gullies,
where water moves as a kinematic wave and enters the rivers. The
simulation of 27 flood events in the Tunxi watershed of Anhui Province
from 2008 to 2017 was implemented, and the simulation results were
compared with that of Xinanjiang model (XAJ). The relative runoff volume
error and flood peak error of the GXAJ model and XAJ model are 8.4% and
10.7%, 8.9% and 12.1%, respectively. The GXAJ model outperforms in
the simulation of flood peak, and is capable of producing the dynamics
of soil water and gullies flow. The spatial characteristics and the
sensitivity of parameters, free storage capacity and gullies density, at
various phases, that is, initial, rise, peak, fall and tail, have been
analyzed. The value of free storage capacity decreases and then
increases with the increase of altitude and distance from the river. The
gullies density in the bank and ridge area is greater than that in the
middle of the slope segment. Sensitivity analysis shows that gullies
density has the noticeable influence on the relative runoff volume error
and Nash-Sutcliffe coefficient in the rise phase, while free water
storage capacity has a significant effect on the relative runoff volume
error during the flood rise phase and Nash-Sutcliffe coefficient in peak
phase, respectively.