有植被的河道水流紊动特性模型试验研究

通过物理模型试验,研究了有植被的河道水流紊动特性.试验结果表明,在复式断面河道滩地种植柔性植被后,滩地糙率增大,水流紊动更为剧烈,河道水流紊动强度峰值由原先的滩槽交界区转移到滩地区.滩地的水流紊动强度沿程递减;滩槽交界区的水流紊动强度沿程不断增大;主槽的水流紊动强度主要与床面糙率有关,滩地植被影响了滩地水流的归槽时间,使主槽水流流速沿程增大.     

海河流域河道外生态需水研究

水土流失是海河流域较为突出的生态环境问题之一。经对比研究发现，植被覆盖度的变化会通过影响洪充量，土壤侵蚀量等因子，进而改变水土流失的状况。从提高植被覆盖度尤其是低覆盖度草地植被的角度出发，定量研究了为改善流域水土流失状况河道外生态需水的具体数额，得出海河流域现状年河道外生态耗水（降水）385亿m^3。另外，为改善河道外生态环境状况将低覆盖度草地提高地提高至中等覆盖度水平，则需要增加生态需水12．5亿m^3。     

Hyperion, IKONOS, ALI, and ETM+ sensors in the study of African rainforests

The goal of this research was to compare narrowband hyperspectral Hyperion data with broadband hyperspatial IKONOS data and advanced multispectral Advanced Land Imager (ALI) and Landsat-7 Enhanced Thematic Mapper Plus (ETM+) data through modeling and classifying complex rainforest vegetation. For this purpose, Hyperion, ALI, IKONOS, and ETM+ data were acquired for southern Cameroon, a region considered to be a representative area for tropical moist evergreen and semi-deciduous forests. Field data, collected in near-real time to coincide with satellite sensor overpass, were used to (1) quantify and model the biomass of tree, shrub, and weed species; and (2) characterize forest land use/land cover (LULC) classes.The study established that even the most advanced broadband sensors (i.e., ETM+, IKONOS, and ALI) had serious limitations in modeling biomass and in classifying forest LULC classes. The broadband models explained only 13-60% of the variability in biomass across primary forests, secondary forests, and fallows. The overall accuracies were between 42% and 51% for classifying nine complex rainforest LULC classes using the broadband data of these sensors. Within individual vegetation types (e.g., primary or secondary forest), the overall accuracies increased slightly, but followed a similar trend. Among the broadband sensors, ALI sensor performed better than the IKONOS and ETM+ sensors.When compared to the three broadband sensors, Hyperion narrowband data produced (1) models that explained 36-83% more of the variability in rainforest biomass, and (2) LULC classifications with 45-52% higher overall accuracies. Twenty-three Hyperion narrowbands that were most sensitive in modeling forest biomass and in classifying forest LULC classes were identified and discussed.     

河道漫滩及湿地上淹没柔性植物水流的紊流特性

植物在河流生态的修复中起重要作用,因此对含植物明渠水流的紊流机理的研究显得非常重要。将河漫滩及湿地中含淹没柔性植物的水流视为充分发展了的紊流,在实验室中用特定材料模拟柔性植物,通过水槽试验用三维ADV对淹没柔性植物段紊流特性进行了测量研究,对试验结果计算分析表明含淹没柔性植物的垂向流速分布不再符合指数分布;其紊流具有明显的各向异性特性;植物冠层交界处,水流紊动交换强烈,该处紊流强度及雷诺应力出现最大值。     

柔性植物阻流特性研究

河流中的植物不仅影响河流的泄洪能力而且在生态的修复中起重要作用,因此对含植物明渠水流的阻力特性及紊流特性的研究显得非常重要。将河道中含柔性植物的水流视为充分发展了的紊流,在实验室中用特定材料模拟柔性植物,通过水槽试验用三维ADV对淹没柔性植物段紊流特性进行了测量研究,分析了含淹没柔性植物明渠水流的水力学特性及阻力特性并得出其曼宁糙率n的变化规律。对试验结果分析表明,含淹没柔性植物的垂向流速分布不再符合指数分布;其紊流具有明显的各向异性特性;植物冠层交界处,水流紊动交换强烈,该处紊流强度及雷诺应力出现最大值。     

Valley floor landscape change following almost 100 years of flood embankment abandonment on a wandering gravel‐bed river

Critical to restoring the nature conservation value of many river corridors is an understanding of how alluvial landscapes will respond to cessation of river management and land use practices that have previously degraded the environment. This paper analyses changes in valley floor landforms and vegetation patch dynamics, in relation to fluvial disturbance, over a period of almost 100 years following flood embankment abandonment on a wandering gravel‐bed river, namely the River Tummel, Scotland. Such rivers were once typical of many draining upland areas of northern maritime Europe. Prior to abandonment the valley floor landscape was agriculturally dominated and the river for the most part was single thread confined between flood embankments. The pattern of landform change and vegetation patch development over time following a decision in 1903 not to maintain embankments was tracked by geomorphic and land cover mapping utilizing successive sets of aerial photography for the period 1946 to 1994. A historical context for these changes was also feasible because the channel planform in 1900 and earlier channel planform changes dating back to 1753 were known due to the availability of old maps and earlier geomorphic studies. The land cover mapping was validated by comparison of results produced from the interpretation work on the 1994 aerial photographs with the field‐based UK National Vegetation Classification protocol. The findings of the study illustrate that bordering the River Tummel fluvial landforms and vegetation patch mosaics, presumably resembling those that occurred before valley floor land use intensification, evolved in less than 50 years after flood embankment abandonment with a resultant increase in habitat diversity. The change relates primarily to flood‐induced channel planform change and moderate levels of fluvial disturbance. The general significance of this change to plant species diversity on the valley floor of the River Tummel and elsewhere is discussed as is possible implications of the upstream impoundment and scenarios for climatically induced changes in flood frequency and magnitude. The overall outcome is the strong possibility that simple changes in river management and land use practices could result in re‐establishment of the nature conservation value of similar river corridors in Europe over the medium term without active restoration efforts. Copyright © 2002 John Wiley & Sons, Ltd.     

黄河流域多沙粗沙区植被覆盖变化与减水减沙效益分析

通过遥感手段和数字流域模型,研究了黄河流域多沙粗沙区近10来年的植被覆盖变化及其减水减沙效益。研究表明,多沙粗沙区90年代末期与80年代末期相比,植被覆盖度增加区域大约占50%,植被覆盖度没变化区域约占48%。植被覆盖度的变化导致了流域水沙条件的变化,90年代末期植被覆盖条件下,植被措施的减水减沙百分比不高;不同的降雨过程,植被措施的减水减沙效益有一定的差别;从不同降雨过程多年平均看,近10来年植被措施年均减水2.63亿m3,减沙1.13亿t,减水减沙比为2.75,即减1亿t沙的同时减水2.75亿m3,减水百分比为7.61,减沙百分比为10.56,减沙效益大于减水效益。     

TTI hydraulics and erosion control laboratory research field performance of erosion-control blankets

Storm water management issues facing the Texas Department of Transportation in the late 1980s led to the development of a coordinated research program with the Texas Transportation Institute. Researchers developed methodologies for evaluating the field performance of various erosion control technologies of the most widely used products within the Department's construction and maintenance operations. From these methodologies, the Hydraulics and Erosion Control Laboratory was designed and constructed. Currently, participants include private industry (manufacturers of erosion control products), transportation researchers (TTI), and the public sector (TxDOT).The results reported in this paper reflect 2 years of erosion-control blanket research. The study objectives were to determine the effectiveness of erosion-control blankets on the growth of warm-season perennial grasses and their ability to prevent sediment loss in a sloped condition.The laboratory simulates the highway environment with the sloped plots (6 m in width) located on an earthen embankment that is 300 m in length and 6.75 m in height (94 ft. by 22 ft., vertically). A randomized experimental design was replicated on two soil types (sand and clay) for each slope condition (3:1 or 2:1) with a control.In general, the results indicate better combined results relating to sediment retention and vegetation establishment performance for erosion-control blankets on sandy soils (noncohesive) regardless of slope condition (3:1 or 2:1) or material type. A minimum of 50% more sediment was retained on the sandy treatment plots and a 45% more vegetation coverage was achieved compared with the control plots. When analyzed by material type related to performance, excelsior, synthetic blends, and straw/coconut blends performed the best. For clay soils (cohesive), regardless of slope condition (3:1 or 2:1), the combined results indicate a minimum of 75% more sediment was retained and a minimum of 5% more vegetation establishment was achieved compared with the control plots. When analyzed by material type related to performance, excelsior, straw, and straw/coconut blends performed the best.     

近20年塔里木河干流生态环境变化遥感监测分析

针对塔里木河流域综合治理后生态环境的变化状况及植被的恢复状况等热点问题,基于遥感时空变化分析方法从土地利用、地表水体和植被覆盖度的时空变化方面分析了近20年来塔里木河干流生态环境的变化状况。结果表明:(1)塔里木河干流土地利用受到人类活动的影响显著,自2000年以来,塔里木河干流耕地面积增加显著,净增2 229 km~2,草地面积整体下降,萎缩3 157 km~2;(2)综合治理以来,下游河段2009—2018时段水体出现频率明显高于2000—2008时段,水体出现频率提高约15%;(3)2000年以来,塔里木河流域的植被覆盖度持续增加,特别是下游河段植被覆盖度增加明显,覆盖度增加18%。但中、上游流域的植被覆盖度的增加趋势主要贡献来源于耕地,中上游地区耕地的增加仍会对塔里木河流域的生态保护和恢复造成一定的影响。     

基于MODIS数据的浙江省植被覆盖度时空变化分析

以浙江省为研究区,基于2009—2018年MODIS_NDVI数据,采用MVC最大值合成法获取逐月NDVI值,利用改进的像元二分模型估算2009—2018年植被覆盖度,结合DEM数据及《浙江省林地保护利用规划》(2010—2020年)中的林地分区,分析浙江省植被覆盖度的时空变化情况。结果表明:①2009—2018年浙江省植被覆盖度总体处于高盖度级别,存在缓慢降低的趋势。②2009年和2018年的植被覆盖度空间格局基本一致,即浙南山地区、浙西山地丘陵区>浙中丘陵盆地区、浙东沿海丘陵海岛区>浙北平原区;植被覆盖度变化以稳定为主,占总面积的62.79%,退化区域面积大于改善区域面积,退化趋势以浙北平原区最为严重,占总面积的6.73%,改善趋势以浙南山地区最为明显,占总面积的4.87%。③各地形因子范围内的植被覆盖度变化均相对稳定;不同高程范围内,明显退化区域在高程100 m以下,明显改善区域在高程200 m以上;不同坡度范围内,退化最明显区域为坡度[0°,5°)范围,明显改善区域为坡度15°以上;不同坡向间,植被变化的差异并不明显。研究成果可为该地区的生态环境建设和水土流失防治提供理论依据。