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Fragmentation and flow regulation of rivers by large dams are known to obstruct the longitudinal dispersal of waterborne plant propagules between impoundments, and to affect plant community composition. However, even several decades after a dam has been built, impoundments may still have a relatively species‐rich riparian flora. We hypothesized that free‐flowing tributaries act as the major gene pools for such impoundments, thus alleviating the fragmenting effect large dams have on the main channel. The importance of tributaries as seed sources was tested by releasing wooden seed mimics in three different‐sized (0.22–6.93 m3 s?1) tributaries of an impoundment in the Ume River in Northern Sweden. In each tributary seed mimics were released, during the spring flood peak, from three points approximately 1, 2 and 3 km upstream the outlet in the impoundment. The importance of a tributary as a seed source increased with tributary size. Of the 9000 released seed mimics 1.5% reached the impoundment; 1.2% of the 9000 originated from the largest tributary and 0.3% from the middle‐sized one. The smallest tributary retained all its mimics. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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小浪底水库拦沙初期泥沙输移及河床变形研究 总被引:3,自引:0,他引:3
应用物理模型试验对小浪底水库运行初期的泥沙输移和河床变形进行了一系列的研究预测,结果表明水库运用初期基本上为异重流排沙;库区干流淤积形态为三角洲且不断向下游推进;支流淤积主要是干流倒灌的结果,在沟口可形成拦门沙;库水位大幅下降,干流河床将产生溯源冲刷和沿程冲刷,支流淤积面随之下降。水库投入运用以来的实测资料分析表明,尽管预报试验所采用的水沙条件与水库运用以来的实际情况不尽相同,但两者在输沙流态、淤积形态及变化趋势方面基本一致,从而证明了模型试验得出的结论是符合实际的。 相似文献
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介绍浩坤水电站库区水文地质、工程地质条件及喀斯特发育特征,结合连通试验成果和水位观测资料,对浩坤水电站库区喀斯特渗漏问题进行分析论证,提出防渗处理措施,评价是否具备成库条件。 相似文献
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水库蓄水会对周围工程与地质环境造成较大的影响,严重时甚至会引起岸体滑坡。基于空间计量学全局和局部空间自相关系数及其相关分析方法,以向家坝坝体下游坝后左岸人工高边坡为例,在传统研究只考虑二维坐标的情况下,进一步考虑不同测点的三维空间坐标,建立了考虑空间坐标的空间权重矩阵,计算了各个蓄水时段高边坡不同测点的外观变形数据的全局和局部空间自相关系数;对比了不同蓄水时段下游边坡外观变形的空间聚集性态,从而定位高边坡变形监测关键测点。研究结果表明:2种空间自相关系数可以有效探测变形数据的聚集程度,识别聚集区域;水库蓄水会在下游坡形成明显的空间聚集性变形,尤其是在蓄水初期变化最为剧烈,需要在该阶段加强观测。 相似文献
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The biomass and frequency of occurrence of aquatic macrophytes observed during 1975 and 1991 in Navigation Pool No. 8 of the upper Mississippi River were compared. Samples were collected from contiguous backwater, isolated backwater and impounded habitat types. Overall declines were observed in both frequency and biomass between the two years. Changes in depth, water clarity and bed sediment texture were also observed. About 50% of the samples collected in 1991 had no vegetation, compared with 20% in 1975. The greatest reduction in frequency occurred among submergent taxa (77% in 1975 to 31% in 1991), whereas only slight declines were observed for emergent taxa. However, the mean biomass of both lifeforms decreased substantially (48 to 1 g/m2 for submergent and 61 to 27 g/m2 for emergent lifeforms). The mean total biomass declined from 114g/m2 in 1975 to 35 g/m2 in 1991. Declines were most evident in the impounded habitat, where the frequency of occurrence of submergent taxa decreased from 83% in 1975 to 11% in 1991, and mean biomass decreased from 90 to 1 g/m2. Similar but less extensive reductions in frequency and biomass of submergent taxa were observed in the contiguous backwater habitat. In contrast, both the frequency and biomass of floating-leaved macrophytes increased slightly in contiguous backwater habitats. Changes in frequency and biomass of macrophytes in isolated backwater habitats were neligible between 1975 and 1991. It is hypothesized that changes in the macrophyte community structure may be related to physical changes associated with 57 years of impoundment. 相似文献
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水库蓄水会对周围工程与地质环境造成较大的影响,严重时甚至会引起岸体滑坡.基于空间计量学全局和局部空间自相关系数及其相关分析方法,以向家坝坝体下游坝后左岸人工高边坡为例,在传统研究只考虑二维坐标的情况下,进一步考虑不同测点的三维空间坐标,建立了考虑空间坐标的空间权重矩阵,计算了各个蓄水时段高边坡不同测点的外观变形数据的全局和局部空间自相关系数;对比了不同蓄水时段下游边坡外观变形的空间聚集性态,从而定位高边坡变形监测关键测点.研究结果表明:2种空间自相关系数可以有效探测变形数据的聚集程度,识别聚集区域;水库蓄水会在下游坡形成明显的空间聚集性变形,尤其是在蓄水初期变化最为剧烈,需要在该阶段加强观测. 相似文献
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水布垭水库初期蓄水时机决策研究 总被引:1,自引:0,他引:1
结合清江梯级上游水布垭水库导流洞封堵时机选择中涉及到的各种影响因素,对工程及流域防洪安全、下游水库发电效益、河道断流时间等问题进行了研究分析。经多年历史实测资料演算,建议在2006年9月下旬封堵导流洞。该方案有助于减少断流时间,从而减少对下游的负面影响,以获得最大的经济效益。 相似文献
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沙市河段是上荆江河势较为复杂的河段之一,也是航道治理的重点河段之一。根据三峡水库蓄水以来沙市河段实测地形资料以及沙市水文站的实测水文资料,从来水来沙、深泓平面、洲滩、深槽以及横断面变化等方面系统分析了沙市河段的近期河道演变特性。结果表明:(1)三峡水库蓄水后,沙市河段整体呈现冲刷的趋势,深泓平面摆动集中在分汊段,沿程洲滩冲刷萎缩,横断面冲淤时有发生,20 m深槽冲刷发展,接近贯通。(2)受到沿程护岸工程以及洲滩守护工程等的影响,该河段总体河势基本稳定,但局部河段内仍会有所调整。(3)河段尚未达到冲淤平衡,未来一段时间内,河段仍将以冲刷为主,若无人工干预,滩槽演变趋势将延续近期的变化,由此对防洪、航运等方面带来的影响值得关注。 相似文献