| 刘晓燕,党素珍,高云飞,杨胜天.黄土丘陵沟壑区林草变化对流域产沙影响的规律及阈值[J].水利学报,2020,51(5):505-518 |
| 黄土丘陵沟壑区林草变化对流域产沙影响的规律及阈值 |
| The rule and threshold of the effect of vegetation change on sediment yield in the loess hilly region,China |
| 投稿时间：2019-12-11 |
| DOI：10.13243/j.cnki.slxb.20190867 |
| 中文关键词: 黄土丘陵区 流域产沙 林草有效覆盖率 影响 规律 阈值 |
| 英文关键词: loess hilly region sediment yield effective vegetation coverage influence rule threshold |
| 基金项目:国家重点研发计划项目（2016YFC0402403） |
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| 中文摘要: |
| 围绕植被变化与土壤侵蚀的关系，已有海量研究成果，但提出的植被盖度~土壤侵蚀量响应规律多是基于坡面小区上的观测成果，反映的是植被变化在"本地"的水沙响应，不能反映植被变化对小区下游的坡面、沟谷和河道的"异地"效应。在近20年黄河来沙锐减的背景下，如何在较大的流域尺度上，评价林草植被变化对流域产沙量的影响，已经成为亟待解决的重大科学问题。本文在对黄土丘陵区地貌和产沙特点分析的基础上，引入了易侵蚀区、林草有效覆盖率（Ve）和产沙指数（Si）等新概念，利用黄土丘陵区流域实测的林草、降雨和水沙数据，分析了林草植被变化与流域产沙能力之间的响应规律及其机制，提出了可基本遏制流域产沙的林草阈值。研究结果表明，流域的产沙指数均随林草有效覆盖率Ve的增大而减小，二者呈指数关系；当Ve ≤ 40%~45%时，产沙指数随Ve增大而迅速降低，不过在Ve<20%时改善植被的减沙作用不太稳定；Ve>40%~45%后，改善植被导致的产沙指数递减速率越来越小。流域的林草植被覆盖程度越差，产沙强度对雨强越敏感；当Ve>50%~60%后，决定流域产沙量的首要因素是有效雨量，雨强次之。林草植被改善是通过对流域产洪量和含沙量的共同减少、以及地表径流输移阻力的增大，实现对流域产沙量的削减；削减洪水和增大阻力均将导致黄丘区地表的水蚀动力降低，含沙量降低则是地表物质补给困难的直接反映。对于黄土丘陵区的第1~4副区，要实现流域产沙模数≤ 1000 t/（km2·a）的目标，林草有效覆盖率应达55%~65%以上，该阈值自东向西递增。对于黄土丘陵区的第5副区，当林草有效覆盖率Ve>45%~50%后，流域产沙量也趋于稳定，但因产沙机制特殊，即使林草梯田有效覆盖率达到60%以上，仍难以基本遏制流域的产沙；而且，河（沟）床产沙占比越高，依靠林草植被改善而削减产沙的难度越大。该成果可为认识近20年黄土高原植被改善与黄河泥沙锐减的关系，提供理论依据。 |
| 英文摘要: |
| There has been much research on the relationship between vegetation change and soil erosion, but the proposed response of vegetation cover on soil erosion is mostly based on the observation data of slope plots, which is the local response of vegetation change and cannot reflect the effect of vegetation change on lower slopes,gullies and river channels downstream of the runoff plots. How to evaluate the im-pact of vegetation change on the sediment yield of the Yellow River basin on a large scale has become an important scientific problem to be solved in the context of the sharp decrease in sediment discharge in the past 20 years. Based on the analysis of topography and sediment yield characteristics in the loess hilly re-gion, this paper introduces some new concepts, such as the erosion-prone area, the effective vegetation coverage (Ve) and the sediment yield index (Si), and uses the measured vegetation, rainfall, runoff and sediment data of the basins in the loess hilly region,analyzes the response pattern and mechanism of vege-tation change on sediment yield capacity at the watershed scale,and proposes the effective vegetation cover-age threshold that can basically curb sediment yield in the basin. The results show that the sediment yield capacity of the basin decreases exponentially with increasing Ve. When the Ve ≤ 40-45%, the Si decreases rapidly with the increase in Ve, but the effect of vegetation improvement on sediment reduction is not sta-ble when the Ve <20%. When the Ve >40-45%, the decreasing rate of the Si caused by vegetation im-provement becomes smaller. The worse the vegetation coverage, the more sensitive the sediment yield is to the concentration degree of rainstorms. When the Ve is greater than 50-60%, the primary factor determin-ing sediment yield in the basin is effective rainfall, followed by the concentration degree of rainstorms. Im-provement in vegetation can reduce the sediment yield by reducing the flood yield and sediment concentra-tion and increasing the resistance to surface runoff transport. The reduction in floods and increase in resis-tance will lead to a decrease in water erosion power on the surface of the loess hilly region. The decrease in sediment concentration is a direct reflection of the difficulty of replenishing the surface materials. For the 1st to 4th subregions of the loess hilly region, to achieve the target of sediment yield modulus ≤ 1000 t/(km2·a), the threshold of the Ve should be greater than 55-65%, increasing from west to east. For the 5th subregion of the loess hilly region,when the Ve is greater than 45-50%,the sediment yield of the ba-sin tends to be stable. However,due to the special sediment yield mechanism,it is still difficult to basical-ly curb the sediment yielding in the basin even when the Vet >60%. Moreover, the higher the proportion of the sediment yield produced by the riverbed,the more difficult it is to reduce the sediment yield by im-proving vegetation. The results provide a theoretical basis for understanding the relationship between vegeta-tion improvement in the Loess Plateau and sediment decrease in the Yellow River in the past 20 years. |
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