黄土丘陵沟壑区第五副区产沙机制初步分析

The sediment producing mechanism of the No.5 sub-region of the Loess Hilly Region in the Loess Plateau

黄土丘陵沟壑区第五副区主要分布在黄土高原西北部,是黄河流域的主要产沙区之一。通过实地调查,结合下垫面、降雨和水文实测数据,本文分析了该区泥沙来源、产沙特点及其影响因素,揭示了该区的产沙机制。实地调查表明,黄土丘陵沟壑区第五副区大体是黄土丘陵和黄土台塬的结合产物,地表光滑的黄土丘陵群包围着一片黄土盆地或阶地是其地形特点,土壤疏松、植被稀疏是其地貌特点,雨量和雨强小、蒸发强是其气候特点。该区泥沙不仅产自周边丘陵,且相当部分来自中部盆地的河(沟)岸崩塌或滑坡,是黄土高原河沟侵蚀最剧烈的地方,有些河流的河沟产沙占比甚至高达2/3;从支毛沟,到干沟和河道,随着汇入水量的增加,产沙强度逐级增大。周边丘陵所产洪水是河(沟)岸崩塌或滑坡的主要动力,其植被覆盖或梯田规模是影响产洪的关键因素。该区产洪能力偏低,但洪水的含沙量高、且很难显著降低。

The No.5 Sub-region of the Loess Hilly Region located mainly in the Northwest Loess Plateau is one of the major sediment source areas in the Yellow River Basin. Based on the results of field surveys and the observed data of underlying surface and rainfall and hydrology, this paper analyzed its sediment source, sediment yielding characteristics and influence factors, and the sediment yielding mechanism were revealed. The results proved that No.5 Sub-region of the Loess Hilly Region is a combination of Loess Hilly Region type and Loess Plateau-gully Region type, and it is characterized with a stretch of loess ba- sin surrounded by groups of loess hills, and possesses loose soil, sparse vegetation, and light rainfall amount and intensity. The sediment sources of this region are not only from the surrounding hilly area, but also from the riverside-bank or the gully-bank of the middle plateau area by a significant amount. The ero- sion intensity of riverside-bank and gully-bank is most severe in the Loess Plateau, the sediment amount produced from river-or-gully bank in some area even comprises two-thirds of the total sediment yield in the basin, and the intensity would increase with the increase of water joining from mini-ditch to stem-ditch and to river. Floods produced by surrounding hills are main driving force of the bank collapse and slide, and the key influence factors affecting the flood production are vegetation coverage degree and terrace area. The flood yielding ability of the No.5 Sub-region is rather low, but the sediment concentration is high and difficuh to reduce notably.