三峡水库蓄水以来水库淤积和坝下冲刷研究

为了分析三峡工程对库区及坝下长江中游河势的影响,基于实测资料,较为系统地研究了三峡水库蓄水运用以来水库泥沙淤积和坝下游河床冲刷特性。研究表明,1991年以来长江干流各站径流量变化不大,输沙量明显减小;三峡水库蓄水运用后的2003～2011年入库沙量继续大幅减少,仅为原设计值的40%,水库年均淤积泥沙1.40亿t,也仅为论证阶段的40%左右,且绝大部分淤积在常年回水区和死库容内;受上游来沙减小和三峡水库蓄水拦沙影响,坝下游输沙量大幅减小,悬移质泥沙颗粒也明显变粗,长江中游原有的冲淤相对平衡状态被打破,河床发生沿程冲刷,2002年10月至2010年10月,宜昌至湖口河段总冲刷量为9.79亿m3,河床冲淤形态转变为“滩、槽均冲”,主要冲刷发生在宜昌至城陵矶河段。     

长江中游水文情势变化及对鱼类的影响分析

为分析三峡水库蓄水后长江中游河道水文情势变化情况及其对鱼类产卵繁殖的影响,采用水文变化指标体系和变动范围法,对宜昌站水文情势变化进行了定量分析,得出了变化程度较为剧烈的水文参数。通过对照典型鱼类的历史产卵量与历史流量过程,归纳了典型鱼类四大家鱼的生态水文需求,得出了影响鱼类产卵繁殖的主要水文参数。提出了水文情势变化影响鱼类产卵繁殖过程的概念性模型。在分析的基础上,揭示了长江中游水文情势变化对鱼类产卵繁殖的影响。     

三峡库区消落带植被恢复重建模式探讨

消落带特点、成因、生态特征等决定植被遴选和生境培育,是三峡库区消落带植被恢复重建的关键问题。通过系统回顾三峡库区消落带植被恢复重建研究进展,总结植被遴选成果及经验,基于重建原理将现有植被恢复重建模式分为水位变动适应型和土壤基质加固型。最后,从改善消落带植被立地条件出发,提出生态环保、技术可行的基于土壤固化的植被恢复重建模式,并通过河道生态修复的成功实践论证了其在三峡库区消落带植被恢复重建中的可行性和重要应用意义。     

洪门水库坝基顺河断层灌浆处理及质量评价

土坝坝基断层渗透破坏的治理备受关注,本文介绍了洪门水库土坝坝基顺河断层的处理方法,并对处理结果进行了分析评价.     

Cloud-Verhulst hybrid prediction model for dam deformation under uncertain conditions

Uncertainties existing in the process of dam deformation negatively influence deformation prediction. However, existing deformation prediction models seldom consider uncertainties. In this study, a cloud-Verhulst hybrid prediction model was established by combing a cloud model with the Verhulst model. The expectation, one of the cloud characteristic parameters, was obtained using the Verhulst model, and the other two cloud characteristic parameters, entropy and hyper-entropy, were calculated by introducing inertia weight. The hybrid prediction model was used to predict the dam deformation in a hydroelectric project. Comparison of the prediction results of the hybrid prediction model with those of a traditional statistical model and the monitoring values shows that the proposed model has higher prediction accuracy than the traditional statistical model. It provides a new approach to predicting dam deformation under uncertain conditions.     

三峡升船机船厢室段和下闸首二次开挖施工技术

三峡升船机的船厢室段和下闸首的二次开挖,面临着工期紧、场地狭窄、结构强度要求高的难题,如何解决开挖施工进度和质量控制之间的矛盾,并在开挖过程中有效控制爆破规模,避免爆破施工影响临近建筑物的安全,是施工单位必须解决的问题。介绍了边坡开挖的施工顺序以及针对不同开挖部位的施工方案,同时阐述了不同施工方案的钻爆工艺及爆破控制参数。相关经验可供类似工程施工借鉴。     

小溶江水利枢纽坝址选择

从地形地质条件、淹没影响实物指标、施工条件、枢纽建筑工程投资等方面对小溶江水利枢纽上、下坝址进行综合比选,经分析后认为下坝址综合条件优于上坝址,在可行性研究阶段推荐下坝址方案。     

多头小直径深层搅拌截渗墙在南四湖湖西大堤加固中的应用

南四湖湖西大堤加固工程采用了水泥土截渗墙施工技术,即运用多头小直径深层搅拌截渗桩机,把水泥浆喷入土体并搅拌形成多桩相割搭接的水泥土墙,用水泥土墙作防渗墙,从而达到截渗目的。该技术具有造价低、防渗效果好、功效高、取材方便等优点,可供类似工程借鉴。     

FINE SEDIMENT INFILTRATION DYNAMICS IN A GRAVEL‐BED RIVER FOLLOWING A SEDIMENT PULSE

Pulses of fine sediment in gravel‐bedded rivers can cause extensive fine sediment infiltration (FSI) into void spaces in coarse bed material, potentially altering river morphodynamics and aquatic ecosystems. Previous work suggests a conceptual model of FSI whereby FSI occurs to a limited depth as a function of the relative grain size of bed sediment compared with infiltrating sediment and is influenced by fine sediment supply and local flow dynamics. Our study applies this conceptual model to a complex reach of a wandering, medium‐sized, gravel‐bed river to investigate the spatial and temporal controls on FSI. To constrain the timing of FSI, we use the release of contaminated sediment from an upstream dam removal and complementary field methods (bulk sampling, freeze cores and infiltration bags) to capture sediment across varied depositional settings. Our results indicate that, even in a morphologically complex reach, fine‐sediment content in the bed does not vary significantly among deposition settings or vertically below the bed surface. We also found that the most contaminated fine sediments released into our study river by a dam removal are not present within the bed material and that substrate has likely been reworked over the period between the release of contaminated sediment and sampling. Our observations also suggest that seals of fine sediment causing void pore space at depth, which have previously been associated with FSI, are not evident in our field area. This suggests that in natural systems, high sediment supply and mobile beds may limit seal formation and persistence. Copyright © 2013 John Wiley & Sons, Ltd.     

ASSESSMENT OF RIPARIAN VEGETATION SENSITIVITY TO RIVER HYDROLOGY DOWNSTREAM OF A MAJOR TEXAS DAM

Dams may impact the health of downstream riparian vegetation communities through flow modifications such as decreased flood frequency and duration. Without historical vegetation data, however, it is difficult to relate changes in vegetation composition to hydrology patterns downstream of dams. We studied bottomland hardwood forests downstream of Toledo Bend Dam on the Sabine River in Texas and Louisiana to determine their sensitivity to minor changes in river hydrology with a particular focus on floods. Current riparian vegetation was characterized within three topographic zones at three selected sites below the dam. Using 80 years of hydrologic records from two gauging stations downstream of the dam, we evaluated trends in flood frequency, flood duration, peak discharge and total flood discharge in those periods before (1926?1965) and after (1971?2005) dam construction, as well as related flood stage to floodplain elevations to link topography to flood frequency. Plant species diversity in this system is highly dependent on minor changes in elevation, and the proportion of wetland‐dependent species changes rapidly with only a few centimeters difference in elevation. Although 50% of trees, shrubs and herbs in the sloughs were wetland adapted, their numbers were only 21% in the levees (74–284 cm higher in elevation) and 14% in the mid‐floodplains. Since dam construction, total flood discharge and duration at the most upstream gauge on the Sabine River decreased by 49%. At both gauges, mean discharge was also altered with higher summer flows. Patterns of tree regeneration point to less recruitment by wetland‐dependent species in the years following dam construction. These results suggest that minor changes in flood magnitude might limit occurrence of wetland species to the lowest topographic zones and illustrate the need to analyse sensitivity of plants to minor changes in flood characteristics when historical data for the vegetation community are lacking. Copyright © 2012 John Wiley & Sons, Ltd.