Characterization of vertical unsaturated flow reveals why storm runoff responses can be simulated by simple runoff-storage relationship models
Characterization of vertical unsaturated flow reveals why storm runoff responses can be simulated by simple runoff-storage relationship models
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DOI：
10.1016/j.jhydrol.2020.124982
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发表时间：
2020-09-01
影响因子：
6.4
通讯作者：
Kojima, Nagahiro
中科院分区：
文献类型：
--
作者：
Tani, Makoto;Matsushi, Yuki;Kojima, Nagahiro
采用理查兹方程进行了垂向非饱和流数值试验，以研究构造活动区山区流域暴雨径流响应为何可以用具有径流-蓄量幂律关系的简单径流模型模拟的物理基础。通过垂直非饱和流传输的压头传播可以产生快速响应的流出从底部的土柱，无论固有的土壤水力学特性，类似于在一个山坡上观察到的暴雨径流响应在一个“恒定分配期”，当一个大的恒定部分的降雨分配给暴雨径流。另外，还进行了两个试验，一个是降雨强度增加时向下通量增加的阶段，另一个是无降雨的衰退阶段，以研究垂向非饱和流的详细特征。增水阶段湿润锋的形成延迟了出流的增加，但在恒定的分配期内，这种延迟很小。在整个衰退阶段的流出率和土壤柱的总存储量之间的相互依赖的关系近似的幂律方程来自总存储量和恒定的流出量之间的关系在稳态条件下。幂律方程的指数随着柱长的减小而趋于最大值，随着柱长的增加而趋于最小值。出流率与总存储量的相互依赖关系通常只在非饱和带中检测到，可能会导致出流响应的土壤水力特性的异质性的敏感性较低，证明了简单的径流模型在异质山区流域的应用。
Numerical experiments on vertical unsaturated flow using the Richards equation were conducted to examine the physical basis of why storm runoff responses from mountainous watersheds in tectonically active regions could be simulated by simple runoff models with a runoff-storage power-law relationship. Pressure head propagation transmitted through vertical unsaturated flow could produce a rapid response of the outflow from bottom of the soil column, regardless of the inherent soil hydraulic properties, similar to storm runoff responses observed on a hillslope in a 'constant allocation period' when a large constant portion of rainfall is allocated to storm runoff. Additional experiments were conducted both for an increasing stage of downward flux in response to increasing rainfall intensity and for a recession stage without rainfall, to investigate the detailed characteristics of vertical unsaturated flow. The creation of a wetting front during the increasing stage delayed the increase of outflow, but this delay was small during a constant allocation period. An interdependent relationship between the outflow rate and the total storage of the soil column throughout the recession stage was approximated by a power-law equation derived from relationships between total storage and constant outflow under steady-state conditions. The exponent of the power-law equation approached a maximum of unity as the column length decreased, and it approached the minimum value obtained from the intrinsic relationship between soil hydraulic conductivity and volumetric water content as the column length increased. The interdependence of the outflow rate with the total storage generally detected only in the unsaturated zone might cause a low sensitivity of outflow responses to the heterogeneities of soil hydraulic properties, justifying the application of simple runoff models in heterogeneous mountain watersheds.