基于HEC-RAS模型的无定河万年尺度洪水水文学研究

对无定河流域进行深入调查研究，在其下游SJGT河段发现夹有古洪水滞流沉积物的全新世剖面。古洪水SWD厚度30 cm，含有微薄平行层理，且直接覆盖在东汉文化层之上。古洪水SWD粒度以粉沙为主且分选良好，磁化率低，具有与2012年洪水SWD相似的沉积学特征，是全新世大洪水地质学记录。对东汉文化层OSL测年显示，古洪水发生在1 900~1 700 a B.P.。运用HEC-RAS模型法恢复其流量为15 460 m3/s。同时用相同方法和水文参数模拟了2012年洪水洪峰流量，与水文站实测值误差为1.0%，说明参数选择与洪峰流量恢复合理准确。将古洪水水文数据加入实测洪水与历史洪水序列中，建立万年尺度洪水洪峰流量与频率关系，将百年一遇、千年一遇洪水由外延转变为内插，提高了洪水频率分析的精度。研究结果对无定河流域水利工程、交通工程等设计洪水提供了重要水文资料。

Study on Flood Hydrology at Ten Thousand Years Scale in the Wuding River Based on HEC-RAS Model

The Holocene profile with palaeoflood slackwater deposit was found in the SJGT reach downstream of the Wuding River basin after a thorough investigation. The palaeoflood SWD is 30 cm thick and contains thin parallel bedding, which directly covers the Eastern Han culture layer. The grain size of palaeoflood SWD is mainly silt with good sorting and low magnetic susceptibility. The mode (Md) and mean (Mz) of palaeoflood SWD are 31.88 and 35.71 μm respectively, which belong to coarse silt. The mode (Md) and mean (Mz) of 2012 flood SWD are similar to those of palaeoflood, and both belong to coarse silt. The sorting coefficients of paleofloods SWD and 2012 floods SWD are smaller, 0.79 and 0.65 respectively, which indicates that they are better sorting in the process of sediment transport. Palaeoflood SWD has sedimentary characteristics similar to those of the 2012 floods and is a Holocene flood geological record. OSL dating of the Eastern culture layer indicates that the palaeoflood occurred between 1 900 and 1 700 a B.P., which is the result of regional response to global climate change. The stage of palaeoflood is 765.86 m by using SWD thickness and sediment concentration method, and the discharge is 15 460 m3/s by using HEC-RAS model method. At the same time, the same method and hydrological parameters (such as roughness coefficient and gradient) are used to simulate the error between the peak discharge of flood and the measured value of hydrological station in 2012, which shows that the selection of parameters and the restoration of peak discharge are reasonable and accurate. The hydrological data of paleoflood are added to the measured flood and historical flood series to establish the relationship between flood peak discharge and frequency at the scale of ten thousand years. The once-in-a-century and once-in-a-thousand floods are transformed from extension to interpolation, which improves the accuracy of flood frequency analysis. Flood peak discharge of once-in-a-century, once-in-a-thousand and once-in-a ten thousand floods in Wuding River Basin are 7 070, 10 820 and 15 710 m³/s, respectively. The results provide important hydrological data for design floods of water conservancy and traffic engineering in the Wuding River Basin.