盐池地区不同下垫面输沙率特征

Characteristics of sediment discharge in different underlying surface in the Yanchi area

为探究宁夏盐池地区输沙率年内与年际变化特征以及风速与输沙率关系,测量刘窑头风蚀实验站2010—2019年5种下垫面风蚀样地(流动沙丘、半固定沙丘、固定沙丘、灌木林地和荒草地)的输沙率(Q)及风速(V),计算集中度(R_(CD))和集中期(R_(CP))、年际变差系数(S_(v))与年际极值比(S_(w)),并将输沙率与风速进行函数拟合。结果表明:1)下垫面影响Q的大小及均匀性,灌木林地平均输沙率最小,年内输沙率集中程度最高,R_(CP)集中在5、6月。10 a间固定沙丘年内最大输沙率出现的时间日期前移,荒草地年最大输沙率出现的日期逐渐后移。2)S_(v)和S_(w)均表明流动沙丘输沙率年际变异程度高于灌木林地。3)指数函数能更好地反映半固定沙丘(R^(2)=0.843)输沙率响应风速特征,其他下垫面为幂函数最佳。4)一元三次函数较好表达各年平均输沙率与风速关系,拟合公式为:Q=65.42-93.36V+42.55V^(2)-6.00V^(3)(R^(2)=0.800)。存在2个风速临界值(1.74和2.99 m/s),改变输沙率对风速的响应。结果可用于盐池地区风沙治理措施建设实践中,可为盐池地区的风蚀综合治理提供科学依据与技术支撑。

[Background]The ecological environment of the Yanchi area is fragile,and sand erosion will affect the ecological environment and sustainable development of the region.Changes in wind erosion environments can be detected through a quantitative analysis of the dynamic wind erosion processes.Characteristics of changes in sediment discharge over long time scales affect to varying degrees the planning and implementation of sand management measures in arid regions.Quantitative analyses of sediment discharge and wind speeds on different underlying surfaces in the study area are of reference value for the deployment of wind and sand control projects on different underlying surfaces in the study area.[Methods]The wind speeds and monthly and annual weights of sand accumulation were measured at the Liuyaotou wind erosion experimental station,and the sediment discharge was calculated using the sediment discharge equation.The data was from five types of wind erosion samples(moving dune,semi-fixed dune,fixed dune,shrub-land and barren grassland)at the Liuyaotou wind erosion experimental station from 2010 to 2019.Immediately,sediment discharge concentration(R_(CD)),sediment discharge concentration period(R_(CP)),sediment discharge inter-annual variation coefficient(S_(v)),and sediment discharge inter-annual extremum ratio(S_(w))were calculated.We also fitted the sediment discharge and wind speed by regression analysis to explore the response of sediment discharge to wind speed variation.[Results]1)The underlying surface affected the magnitude and the uniformity of the sediment discharge,and there were some differences in the concentration and concentration period values of sediment discharge on five kinds of different underlying surfaces.The smallest average value of content and concentration was in shrub-land,indicating that the stable intra-annual variation occurred in the shrub-land.And the corresponding months of the concentration period were in May and June in shrub-land.The maximum annual sediment discharge in fixed dunes shifted forward over the course of the 10-year period.While the annual maximum sediment discharge in barren grassland shifted back in time.2)Both the research on the inter-annual variation coefficient and the inter-annual extremum ratio indicated a higher degree of inter-annual variability of sediment discharge from the moving dune than from the shrub-land in the study area.The instability of the inter-annual variation coefficient from the moving dune was extremely high,and it was small from shrub-land.3)The exponential function better reflected the relationship between sediment discharge and wind speed for the semi-fixed dune,for which the R^(2) was 0.843,while the best fit of sediment discharge and wind speed for the other underlying surfaces was the power function.4)A cubic function was a good expression of the relationship between the average sediment discharge in each year and the wind speed in each year.The fitting formula was:Q=65.42-93.36V+42.55V^(2)-6.00V^(3)(R^(2)=0.800).There were two wind speed thresholds(1.74 and 2.99 m/s)that caused the response of the sand transport rate to wind speed to change.[Conclusions]There is an effect of underlying surface type on the variation coefficient and extremum ratio of sediment discharge.Meanwhile,there are critical values where the sediment discharged in response to wind speed.The results of this study could be used in the construction of wind and sand measures in the Yanchi region,providing a scientific basis and technical support for the comprehensive management of the Yanchi wind erosion region.