Site modelling methods for detecting hydrologic alteration of flood frequency and flood duration in the floodplain below the carlyle dam,lower Kaskaskia River,Illinois, USA

Reports concerning the influence of dams on river hydrology vary among researchers, interest groups and government agencies. These often contradicting statements may occur because changes in hydrology caused by dams are distinct for each dam and river watershed. The objective of this research was to use site specific techniques to determine if the 1967 installation of the Carlyle Dam, lower Kaskaskia River, Illinois, altered flood frequency and duration within the forested floodplain located below the dam. Results indicated a decrease in flood duration and frequency, and a decrease in annual flood frequency variation at a site 6.4 km below the dam. Pre‐dam versus post‐dam differences in flood frequency and duration at the site 32.2 km below the dam were related to climate rather than dam effects. Although dam impacts are a concern, this research shows that distance downstream from the dam and downstream tributary and watershed characteristics should be considered before assuming that the dam has changed hydrologic parameters for portions of rivers. This research also indicates that areas of the lower Kaskaskia River may still maintain hydrologic ecological integrity, and could be targeted for restoration and adaptive management purposes. Hydrologic modelling combined with river gage and on‐site well measurement techniques presented in this study could provide detailed flood frequency and duration information for land use, sociological and geomorphological questions in focus areas within river floodplains. Copyright © 2008 John Wiley & Sons, Ltd.     

Changes in riparian vegetation communities below a large dam in a monsoonal region: Futase Dam,Japan

This paper examines the effects of a dam reservoir flood control on riparian plant communities in an Asian monsoon area subjected to large summer floods under natural conditions. We compared riparian plant communities downstream of the Futase Dam located on the Arakawa River, with communities on the Nakatsu River, a tributary of the Arakawa River with no dam. Historical changes in spatial distribution of riparian vegetation communities were analysed using aerial photographs. Stand ages and flood history were also examined to analyse the likelihood of tree erosion in scenarios with and without flood control. Comparison of the two reaches shows that the reduced flood peaks below the Futase Dam led to the expansion of riparian forest area and an increase in species diversity. Reduction in the flood peaks below the dam means that the toppling moment of the trees is no longer exceeded. The result is that the riparian forest below the dam is able to develop into later successional stages. Copyright © 2004 John Wiley & Sons, Ltd.     

东江中游河边植被多样性调查评价

植被多样性作为河流健康评价体系的指标之一，反映了植被稳定性对河流健康程度的影响。通过对东江惠州段泗湄洲的植被进行调查分析，采用夏侬-威纳(Shannon-Weiner)多样性和均匀度评价法，对河边植被多样性进行了评价，分析得出了不同高程植被群落的物种组成。亚热带地域河边植被发育较快，植被演替主要决定于淹没频率与高程。从低滩到高滩，植被类型从草本向灌木、最后向木本过渡。植被的多样性也随着高程的增加而提高，高滩植被相对完整、稳定，其生物多样性指数比温带地区的指数高。水位的变化对低滩植被多样性的影响很大。低水位时，低滩散布多种草本植物；而高水位时，部分物种淹没死亡，余下以禾本科和沙草科植物为优势种草本植物群落。     

Identifying the natural flow regime and the relationship with riparian vegetation for two contrasting western Australian rivers

The natural flow regime and the relationship between flows and riparian vegetation are described for sites on both the Blackwood River in south‐western Australia and the Ord River in north‐western Australia. Analysis of long‐term flow data showed the historic mean monthly river discharge for the Blackwood River is strongly seasonal and highly predictable with generally low variability each month. The Ord River showed a strong seasonality of flows with about 92% of the (total) yearly flow occurring between December and March. Flow variability was very high (e.g. coefficient of variation >100% for all months) but highly predictable, with this mostly attributed to low but constant dry‐season flows. Water depth, duration of flood events and the number of flood events per year show a significant correlation with aspects of the riparian vegetation within experimental vegetation plots. Results highlight the strong relationship between floristics, life form structure and population dynamics with stream hydrology. On the Blackwood River, species richness and cover of shrubs reduced with increased duration and frequency of flooding, while cover of exotic species and annual herbs increased with increased flooding. Germination of tree seedlings was not influenced by flood regime but size class of tree species increased with flooding frequency. On the Ord River, species richness was not influenced by flooding regime. However, cover of perennial grasses increased with flooding frequency whilst cover of shrubs decreased. There was no relationship between flooding and seedling establishment whilst tree size class decreased with increased flooding. The methods described here can be used to compare the response of different components of the riparian vegetation to different fluvial regimes (e.g. because of impoundment and abstraction). This technique can be expanded for the management of riparian zones and planning rehabilitation programmes. It may also be useful for improving the ecological knowledge base for setting environmental flows in regulated systems. Copyright © 2001 John Wiley & Sons, Ltd.     

Regulation leads to increases in riparian vegetation,but not direct allochthonous inputs,along the Colorado River in Grand Canyon,Arizona

Dams and associated river regulation have led to the expansion of riparian vegetation, especially nonnative species, along downstream ecosystems. Nonnative saltcedar is one of the dominant riparian plants along virtually every major river system in the arid western United States, but allochthonous inputs have never been quantified along a segment of a large river that is dominated by saltcedar. We developed a novel method for estimating direct allochthonous inputs along the 387 km‐long reach of the Colorado River downstream of Glen Canyon Dam that utilized a GIS vegetation map developed from aerial photographs, empirical and literature‐derived litter production data for the dominant vegetation types, and virtual shorelines of annual peak discharge (566 m³ s^?1 stage elevation). Using this method, we estimate that direct allochthonous inputs from riparian vegetation for the entire reach studied total 186 metric tons year^?1, which represents mean inputs of 470 gAFDM m^?1 year^?1 of shoreline or 5.17 gAFDM m^?2 year^?1 of river surface. These values are comparable to allochthonous inputs for other large rivers and systems that also have sparse riparian vegetation. Nonnative saltcedar represents a significant component of annual allochthonous inputs (36% of total direct inputs) in the Colorado River. We also estimated direct allochthonous inputs for 46.8 km of the Colorado River prior to closure of Glen Canyon Dam using a vegetation map that was developed from historical photographs. Regulation has led to significant increases in riparian vegetation (270–319% increase in cover, depending on stage elevation), but annual allochthonous inputs appear unaffected by regulation because of the lower flood peaks on the post‐dam river. Published in 2010 by John Wiley & Sons, Ltd.     

GEOMORPHOLOGICAL CONTROLS ON VEGETATION RESPONSES TO FLOW ALTERATIONS IN A MEDITERRANEAN STREAM (CENTRAL‐WESTERN SPAIN)

The expected recovery of the natural conditions of large regulated rivers over the distance downstream from a dam is limited by relative tributary size according to the Serial Discontinuity Concept; however, geomorphology may also influence the recovery process. We examined the woody vegetation of the riparian zone in seven river segments distributed along the regulated reach of the Tiétar River in central‐western Spain, which flows through two distinct geomorphic templates. Whereas the annual runoff has decreased by 30% on average along the entire studied reach following the construction of the Rosarito Dam and the initiation of field irrigation in the region, the magnitude and frequency of the peak flows decreased by 30% immediately downstream from the dam but recovered the natural values with the distance downstream. We evaluated the recovery patterns toward the natural riparian conditions by comparing woody species composition, diversity and distribution of vegetation patches established prior to and after dam completion. Our results did not indicate a recovery gradient of any of the analysed vegetation attributes downstream from the dam. Instead, we found that the difference in the slope of the stream channel and banks, the width of the valley and the size of substratum particles among the surveyed patches were factors that significantly mediated dam and tributary effects on vegetation and influenced the degree of vegetation recovery. Hence, the maintenance of the intensity of the flow alteration scheme by the numerous water withdrawals and the low tributary contributions, coupled with differential geomorphological characteristics along the reach, overwhelmed the natural tendency for the river to restore its natural conditions with distance downstream. Improving water management and, particularly, restoring endangered riparian ecosystems require a detailed understanding of existing and potential woody species behaviour across the geomorphological settings of rivers. Copyright © 2012 John Wiley & Sons, Ltd.     

Dynamic vegetation model as a tool for ecological impact assessments of dam operation

This study presented the results of an application of a floodplain dynamic model to the Nakdong River, South Korea. At the Nakdong River, high flows are reduced by dams and the river bed is degraded. Both changes contribute toward the same result: the floodplain is hydraulically disconnected from the main channel and the morphology of the river has been modified. Such changes brought also to a deep modification in the riparian vegetation distribution, abundance and composition. The focus of the study is on the relationship between the hydrology alterations induced by dams and the successional changes in riparian vegetation. More in detail, the study attempts to adapt an existing dynamic floodplain vegetation model to the Nakdong ecosystem characteristics in order to single out what were the effects of the dam operations that led to a change in the riparian landscape. The dynamic model is targeted on Monsoon floodplain vegetation, it is developed upon a custom developed geoprocessing framework and supported by a standalone user interface. It simulates dynamics of floodplain vegetation communities based on different physical parameters. The general concept of the model is that a vegetation community will either undergo toward a maturation stage or will be destroyed (recycling or retrogression) if the magnitude of key physical parameters is greater than the threshold value for a specific community. The model has been calibrated using hydraulic data spanning the time period 1952–2007. The calibration results have been also used to investigate the impacts on the riparian vegetation given by dams operations. The findings of the research highlight that consecutive years of reduced maximum discharge allowed consistent vegetation colonization of riverine areas that were bare before the dam construction.     

水电开发影响下河岸带植被结构和生物量分布

为了解水电开发不同阶段对河岸带植被的影响差异,在澜沧江中下游小湾电站、漫湾库区、漫湾坝下、大朝山库区、大朝山坝下、景洪电站河岸带设置6个样带进行植被结构指标和生物量空间分布特征调查分析。结果表明:澜沧江中下游河岸带植被以乔木为主体,乔木层结构指标以已建库区和坝下样带较高,灌木层和草本层结构指标以在建电站和坝下样带较高;已建库区、坝下和在建电站样带乔木层和群落生物量的最高值分别出现在距离河岸100,50 m和200 m处;乔木层生物量以库区样带最高,灌木层生物量以坝下样带最高,草本层生物量以在建电站样带最高;库区和坝下样带群落生物量大致相当,高于在建电站样带;漫湾库区及其坝下乔木层结构指标以及群落生物量相对变化幅度小于大朝山库区及其坝下样带,小湾样带小于景洪样带。研究区植被结构和生物量的分布格局反映了库区植被恢复程度的差异和电站施工影响强度的差异。     

库什塔依水电站工程枢纽布置及主要设计特点

针对库什塔依水电工程的地形地质条件,选择了符合工程实际的坝型、枢纽布置方案、泄洪建筑物进口高程和规模以及泄水建筑物消能形式,并对工程主要设计特点进行了说明。     

Predicting Long‐Term Changes in Riparian Bird Communities in Floodplain Landscapes

As anthropogenic impacts on riverine ecosystems expand, both aquatic and terrestrial ecosystems are influenced over large spatiotemporal scales. We predicted how riparian bird communities changed in response to long‐term changes in floodplain landscapes such as woodland expansion (i.e. rapid increases in vegetation cover on gravel bars and the progress of vegetation succession due to a decrease in the frequency and magnitude of flood disturbance). To test the hypothesis that woodland expansion after dam construction reduces the abundance of gravel bar‐nesting birds and increases the abundance of forest‐nesting birds, we estimated historical changes between past and present bird abundances using species distribution models across multiple rivers that were either unregulated or regulated by dams. We created past and present vegetation maps from remote sensing images and used habitat quantities as explanatory variables in the species distribution models. As we hypothesized, the estimated abundance of gravel bar‐nesting birds decreased and that of forest‐nesting birds increased because of woodland expansion in some regulated rivers. This suggests that anthropogenic alterations of riverine conditions (e.g. dam construction) can affect terrestrial ecosystems (e.g. riparian bird communities) through changes in floodplains (e.g. woodland expansion). In addition, our findings highlight the efficacy of combining spatial and temporal analyses when examining long‐term ecological dynamics. Copyright © 2013 John Wiley & Sons, Ltd.     

SEDIMENT DYNAMICS IN THE RESTORED REACH OF THE KISSIMMEE RIVER BASIN,FLORIDA: A VAST SUBTROPICAL RIPARIAN WETLAND

Historically, the Kissimmee River Basin consisted of a broad nearly annually inundated riparian wetland similar in character to tropical Southern Hemisphere large rivers. The river was channelized in the 1960s and 1970s, draining the wetland. The river is currently being restored with over 10 000 hectares of wetlands being reconnected to 70 river km of naturalized channel. We monitored riparian wetland sediment dynamics between 2007 and 2010 at 87 sites in the restored reach and 14 sites in an unrestored reference reach. Discharge and sediment transport were measured at the downstream end of the restored reach. There were three flooding events during the study, two as annual flood events and a third as a greater than a 5‐year flood event. Restoration has returned periodic flood flow to the riparian wetland and provides a mean sedimentation rate of 11.3 mm per year over the study period in the restored reach compared with 1.7 mm per year in an unrestored channelized reach. Sedimentation from the two annual floods was within the normal range for alluvial Coastal Plain rivers. Sediment deposits consisted of over 20% organics, similar to eastern blackwater rivers. The Kissimmee River is unique in North America for its hybrid alluvial/blackwater nature. Fluvial suspended‐sediment measurements for the three flood events indicate that a majority of the sediment (70%) was sand, which is important for natural levee construction. Of the total suspended sediment load for the three flood events, 3%–16% was organic and important in floodplain deposition. Sediment yield is similar to low‐gradient rivers draining to the Chesapeake Bay and alluvial rivers of the southeastern USA. Continued monitoring should determine whether observed sediment transport and floodplain deposition rates are normal for this river and determine the relationship between historic vegetation community restoration, hydroperiod restoration, and sedimentation. Published in 2011 by John Wiley & Sons, Ltd.     

基于数字高程模型DEM的溃坝生命损失风险分析

数字高程模型DEM作为基础空间数据,在众多领域有着广泛的应用。本文在油罗口水库大坝缺乏下游实测地形数据资料的情形下,以地形图数据和ArcGIS软件平台获取的计算域下游所需地面高程等信息为基础,应用BREACH软件及River2D水动力学模型模拟了水库下游溃坝洪水演进,采用Graham法估算了水库下游溃坝生命损失,初步得出油罗口水库大坝遭受重现期为5000a一遇洪水时,副坝发生管涌破坏溃决导致的生命损失风险是不可容忍的。由此也可以让水库管理决策人员对水库溃坝洪水可能造成的后果做到心中有数,做好日常的防洪调度及应急预案编制工作,最大程度保障水库下游人民群众生命安全,防止灾害的发生。     

Restoration of Hydrochory Following Dam Removal on the Elwha River,Washington

Hydrochory, seed dispersal by water, affects riparian vegetation by contributing to downstream community composition and diversity. However, dams can block hydrochory, reducing downstream species diversity and fragmenting riparian corridors. Dam removal is becoming more prevalent for economic and ecological reasons and is expected to restore hydrochory; however, this has never been documented in rivers. The largest dam removal project to date was the 2011 to 2014 removal of the Glines Canyon and Elwha dams on the Elwha River in Washington. Prior to dam removal, hydrochory was lower below Glines Canyon Dam compared with an upstream reach; our objective was to test the hypothesis that dam removal would restore downstream hydrochory to levels observed in the upstream reach. To test this, we collected seeds in nets above and below the dam during three sample periods (early July, late July and early August), growing out seeds in a greenhouse and comparing seed abundance and species richness above and below dams, before and after dam removal. We found that after dam removal, the average number of hydrochorous seeds and species increased below Glines Canyon Dam to levels similar to or higher than that of the upstream reach; hydrochory levels in the upstream reach did not change. This study is the first to document the restoration of hydrochory in rivers following removal of a large dam. Restoration of hydrochory may ultimately increase downstream vegetation diversity and play a role in the recolonization of reservoir sediments deposited in the riparian zone in the years following dam removal. Copyright © 2016 John Wiley & Sons, Ltd.     

大坝运行过程中泄水对坝下游生态系统的影响分析及控制

大坝运行过程中泄水会对坝下游生态系统产生负面影响,体现在河道生态环境、洪泛区生态环境和河口生态环境中水文水力情势、河道形态和地貌、水质、原有生物生存和繁衍环境等发生变化,生物种类和数量减少,生物多样性降低。因此有必要对河道区、洪泛区和河口区进行水文水质监测、地下水水位监测、鱼类及水生生物监测、动植物种类和生境调查等;同时,确保大坝下游河段环境流量、制定合理的泄水调度方案和实施坝下游生态系统恢复,以期控制负面影响,使坝下游生态系统逐渐呈良性循环。     

Novel plant communities limit the effects of a managed flood to restore riparian forests along a large regulated river

Dam releases used to create downstream flows that mimic historic floods in timing, peak magnitude and recession rate are touted as key tools for restoring riparian vegetation on large regulated rivers. We analysed a flood on the 5th‐order Green River below Flaming Gorge Dam, Colorado, in a broad alluvial valley where Fremont cottonwood riparian forests have senesced and little recruitment has occurred since dam completion in 1962. The stable post dam flow regime triggered the development of novel riparian communities with dense herbaceous plant cover. We monitored cottonwood recruitment on landforms inundated by a managed flood equal in magnitude and timing to the average pre‐dam flood. To understand the potential for using managed floods as a riparian restoration tool, we implemented a controlled and replicated experiment to test the effects of artificially modified ground layer vegetation on cottonwood seedling establishment. Treatments to remove herbaceous vegetation and create bare ground included herbicide application (H), ploughing (P), and herbicide plus ploughing (H + P). Treatment improved seedling establishment. Initial seedling densities on treated areas were as much as 1200% higher than on neighbouring control (C) areas, but varied over three orders of magnitude among the five locations where manipulations were replicated. Only two replicates showed the expected seedling density rank of (H + P) > P > H> C. Few seedlings established in control plots and none survived 1 year. Seedling density was strongly affected by seed rain density. Herbivory affected growth and survivorship of recruits, and few survived nine growing seasons. Our results suggest that the novel plant communities are ecologically and geomorphically resistant to change. Managed flooding alone, using flows equal to the pre‐dam mean annual peak flood, is an ineffective riparian restoration tool where such ecosystem states are present and floods cannot create new habitat for seedling establishment. This problem significantly limits long‐term river and riparian management options. Copyright © 2010 John Wiley & Sons, Ltd.     

Toledo Bend reservoir and geomorphic response in the lower Sabine River

Downstream geomorphic responses of stream channels to dams are complex, variable, and difficult to predict, apparently because the effects of local geological, hydrological, and operational details confound and complicate efforts to apply models and generalizations to individual streams. This sort of complex geomorphic response characterizes the Sabine River, along the Texas and Louisiana border, downstream of the Toledo Bend dam and reservoir. Toledo Bend controls the flow of water and essentially prevents the flux of sediment from three‐quarters of the drainage basin to the lower Sabine River. Although the channel is scoured immediately downstream of the dam, further downstream there is little evidence of major changes in sediment transport or deposition, sand supply, or channel morphology attributable to the impoundment. Channels are actively shifting, banks are eroding, and sandbars are migrating, but not in any discernibly different way than before the dam was constructed. The Sabine River continues to transport sand downstream, and alluvial floodplains continue to accrete. The relatively small geomorphic response can be attributed to several factors. While dam releases are unnaturally flashy and abrupt on a day‐to‐day basis, the long‐term pattern of releases combined with some downstream smoothing creates a flow regime in the lower basin which mimics the pre‐dam regime, at least at monthly and annual time scales. Sediment production within the lower Sabine basin is sufficient to satisfy the river's sediment transport capacity and maintain pre‐dam alluvial sedimentation regimes. Toledo Bend reservoir has a capacity: annual inflow ratio of 1.2 and impounds 74% of the Sabine drainage basin, yet there has been minimal geomorphic response in the lower river, which may seem counterintuitive. However, the complex linked geomorphic processes of discharge, sediment transport and loads, tributary inputs, and channel erosion include interactions which might increase as well as decrease sediment loads. Furthermore, if a stream is transport‐limited before impoundment, the reduced sediment supply after damming may have limited impact. Copyright © 2003 John Wiley & Sons, Ltd.     

黄河下游冰坝形成条件分析

黄河下游河道由于特定的地理位置,河道形态和水文、气象条件的组合,常常造成凌讯期部分河道卡冰结坝。通过对黄河下游河道冰坝的形成机理、冰坝的类型、冰坝的生消演变规律的分析,对进一步开展黄河下游河道冰坝的预测预报,搞好黄河下游防凌工作有着重要意义。     

玛尔挡水电站泄洪雾化数学模型研究

玛尔挡水电站地处高山峡谷地区、两岸岩体地质情况较差,挑流泄洪雾化可能对两岸边坡及交通安全产生不利影响。为准确预测泄洪雾化水流的影响范围和程度,结合蒙特卡罗方法考虑环境风和地形因素的随机喷溅数学模型,对玛尔挡水电站在水舌风和汛期最不利自然风两种情况下3个典型工况的雾化情况进行了计算和分析。研究结果表明:泄洪雾雨主要沿边坡竖向爬升,只考虑水舌风时,下游雾化降雨范围最远到达坝下1 021 m,横向左扩散至3 190 m高程,横向右扩散至3 160 m高程。水舌风和自然风共同作用时,各泄洪组次雾化范围沿自然风向偏移,左右岸影响范围收窄。根据暴雨分布范围,建议适当增加下游两岸边坡的防护长度和高程。雾化降雨对省道S101没有影响,但左岸导流洞出口导墙段区域和右岸进厂交通洞口位于薄雾降雨区,泄洪时应禁止通行。     

浯溪口水利枢纽溃坝洪水模拟

浯溪口水利枢纽位于昌江干流中游,是一座以防洪为主的水利工程,其溃坝洪水研究对于下游景德镇市防洪风险管理具有十分重要的意义.应用TELEMAC-2D建立了浯溪口水利枢纽二维溃坝洪水演进数学模型.模型模拟范围以60 m等高线为界,坝址为上游边界,下游出口距坝址62 km.模型采用非结构化三角形网格划分,局部加密.应用昌江河水面线和樟树坑水位流量过程线的实测值对模型合理性进行了验证,模型计算值与实测值基本吻合,说明TELEMAC-2D能较好地模拟河流洪水演进.进而取用不同入库洪水重现期在漫顶溃坝情况下的溃决流量过程作为洪水演进的上游边界条件,模拟计算出不同溃坝流量下浯溪口大坝下游洪水水力特性参数(水深、流量和淹没范围等),为浯溪口溃坝风险图绘制及大坝下游城市防洪管理提供了科学依据.     

Vegetation community response to hydrologic and geomorphic changes following dam removal

Dam removal can restore fish passage, natural flow regimes, sediment transport in streams, dispersal of organic matter, and drift of aquatic insects. However, dam removal also impacts the riparian vegetation, with both immediate and delayed responses. In this study, we measure vegetation change at the Merrimack Village Dam site on the Souhegan River in Merrimack, NH, USA. The August 2008 removal caused a ~3‐m drop in water level and rapid erosion of impounded sediment, with ~50% removed in the first 3 months. Terrace, floodplain, and wetland communities were surveyed in summer 2007, 2009, 2014, and 2015. Temporal change was quantified using Analysis of Similarity on the Bray–Curtis dissimilarity matrix. Only herbaceous vegetation closest to the river channel and in the off‐channel wetland changed significantly. The herbaceous plots directly adjacent to the impoundment eroded to bare sand in 2009, but by 2014, the original riparian fringe community had re‐established in the newly developed floodplain. Between 2007 and 2014, the off‐channel wetland area changed from aquatic species to a stable terrestrial community that persisted without significant change in 2015. The vegetation response was greatest in areas with the largest geomorphic and hydrologic change. These included the channel margin where erosion and bank slumping created an unstable scarp. The mid‐channel island and off‐channel wetland were strongly affected by the lowered water table. However, large unvegetated areas never persisted nor did the areal coverage of invasive species expand, which are two frequent concerns of dam removal stakeholders.