图特河北汊对圣海伦斯火山爆发响应过程的模拟

Simulation of channel response of North Fork Toutle River to the eruption of Mount St.Helens

受1980年圣海伦斯火山爆发的影响,图特河北汊(North Fork Toutle River)河道被掩埋深度达140多米,重新发育河道在时空上均表现出冲淤交替的调整特点。以往研究方法仅能模拟河床高程单调上升或下降的变化趋势,而不能模拟火山爆发后30多年间河道冲淤交替的动态调整过程。本文收集了图特河北汊近30年来的水沙资料和断面形态资料,采用河床演变的滞后响应模型,对图特河北汊的河床高程及河道冲淤过程进行了模拟。结果表明,滞后响应模型的不同计算模式均能较好地模拟图特河北汊对火山爆发的响应调整过程,模型计算精度较高。由于滞后响应模型考虑了前期水沙条件对河道演变的累计影响,因此该模型能够较好模拟河道由扰动后的非平衡状态向平衡状态调整的全过程,可用于模拟和预测河流受突发剧烈扰动后的动态调整路径。

Severely affected by the eruption of Mount St. Helens in 1980, the channel of North Fork Tout le River was buried with a maximum depth of 140m. The readjustment of the channel has presented alterna tive aggradation and degradation both with time and in space during the last 30 years after the eruption. Previous method can only reproduce the asymptotic increasing or decreasing of the channel bed elevation and cannot simulate the dynamic adjustment processes of channel erosion and deposition. In this study, we collected 30year series of data on the water and sediment conditions and channel geometry of the river. The aggradation and degradation processes of the channel bed were simulated by the delayed response mod el. The results show that different modes of the delayed response model can well simulate the relaxation paths of the channel bed of the North Fork Toutle River. Because the delayed response model considers the cumulative effects of the water and sediment conditions on the evolution of the river, it is able to simu late the adjustment processes of the river from a perturbed state after the eruption to a certain steadystate. The model provides an effective method for quantitatively studying or simulating the relaxation processes of the fluvial system affected by instantaneous and significant disturbances.