Recent warming of Tonle Sap Lake,Cambodia: Implications for one of the world’s most productive inland fisheries

Tonle Sap Lake in Cambodia is arguably the world's most productive freshwater ecosystems, as well as the dominant source of animal protein for the country. The rapid rise of hydropower schemes, deforestation, land development and climate change impacts in the Mekong River Basin, however, now represent serious concerns in regard to Tonle Sap Lake's ecological health and its role in future food security. To this end, the present study identifies significant recent warming of lake temperature and discusses how each of these anthropogenic perturbations in Tonle Sap's floodplain and the Mekong River Basin may be influencing this trend. The lake's dry season monthly average temperature increased by 0.03°C/year between 1988 and 2018, being largely in synchrony with warming trends of the local air temperature and upstream rivers. The impacts of deforestation and agriculture development in the lake's floodplain also exhibited a high correlation with an increased number of warm days observed in the lake, particularly in its southeast region (agriculture R² = .61; deforestation R² = .39). A total of 79 dams, resulting in 72 km³ of volumetric water capacity, were constructed between 2003 and 2018 in the Mekong River Basin. This dam development coincided with a decreasing trend in the number of dry season warm days per year in the lower Mekong River, while Tonle Sap Lake's number of dry season warm days continued to increase during this same period. The present study revealed that Tonle Sap Lake's temperature trends are highly influenced by temperature trends in the local climate, agriculture development and deforestation of the lake's watershed. Although there were no noticeable impacts observed from upstream dam development in the Mekong River Basin, local‐to‐regional agricultural and land management of the lake's watershed appear to be effective strategies for maintaining a stable thermal regime in the lake in order to facilitate maximum ecosystem health.     

Dynamics of phosphorus fractions and bioavailability in a large shallow tropical lake characterized by monotonal flood pulse in Southeast Asia

This study aims to investigate how the hydrological phase in a flood pulse dominated system, Tonle Sap Lake (TSL), affects the chemical form and bioavailability of P. For this purpose, we conducted extensive field campaigns under different hydrological phases: low-water (LW), rising-water (RW), high-water (HW), and falling-water (FW) phases from December 2016 to September 2017. The TSL ecosystem distinctly exhibited seasonality of the monotonal flood pulse between the low-water and high-water periods, in terms of not only water depth (range 0.5–8.0 m) but also water quality, suspended sediment, P dynamics (concentration, speciation and bioavailability), and trophic status. On an annual basis, the lake retained 56.2% of the external P loads, representing a major sink of P. Seasonally, P dynamics in TSL are determined by internal loading, whereas the annual inflows from the Mekong River basin and lake’s tributaries are important sources of P for TSL. Total particulate phosphorus (TPP) constituted >60% of the total P in LW and decreased to <30% during HW, corresponding to the variation in total suspended solids (TSS). Soluble reactive P predominated the total dissolved P during LW (>70%) and decreased to approx. 30% during HW with decreasing TSS and TPP, suggesting the reduction of bioavailability of P in HW. Our results indicate that the flood pulse plays an important role in the chemical form and bioavailability of P in shallow lakes.     

湄公河与洞里萨湖水量交换特征

洞里萨湖是湄公河最大的连通湖泊,湄公河与洞里萨湖水量交换特征一直是国际社会关注的热点问题,但相关研究成果较少。利用4个河湖控制站的长系列水文资料,分析了湄公河与洞里萨湖水量交换特征,结果表明:湄公河与洞里萨湖的水量交换强度大,洞里萨湖对湄公河径流调峰补枯作用明显,每年汛期5—9月份均会发生倒灌,1995—2011年年均倒灌历时122 d,倒灌水量377亿m³,占湄公河干流同期来水的14.4%,倒灌洪峰流量8 402 m³/s,占干流同期来水的20%,其中7—9月份倒灌水量占全年的88.6%;汛后10月份—次年4月份洞里萨湖向湄公河补水,年均补水历时244 d,补水水量711亿m³,是湄公河倒灌入湖水量的1.96倍,占湄公河下游同期来水的29.9%,其中10月份—次年1月份补水量占全年的83.1%。年倒灌历时、水量与洪峰流量,年补水历时、水量与峰值的年际变化较小,变幅分别为76 d、283亿m³、6 095 m³/s和76 d、474 亿m³、4 677 m³/s,变差系数为0.07～0.24。倒灌、补水水量不仅与湄公河和洞里萨湖的来水大小有关,还受到河湖水位差及洞里萨河水位等因素影响。研究成果可为湄公河三角洲和洞里萨湖区治理提供科学依据。     

洞里萨湖水位与面积和容积的关系研究

洞里萨湖是东南亚最大的且颇具国际影响的淡水湖。基于洞里萨湖湖区不同来源的地形资料,构建了不规则三角网TIN,量算得到不同水位下具有0.1m梯度的洞里萨湖面积和容积。对比分析和水文学法复核结果表明本次构建的洞里萨湖水位与面积和容积的关系是合理的,描绘出了洞里萨湖"低水似湖、高水湖相"的自然景观特点。以洞里萨湖甘邦隆站和出湖控制站波雷格丹站为代表,建立了洞里萨湖水位-面积(容积)关系与实测湖水位的响应关系。结果表明洞里萨湖面积、容积与甘邦隆站水位呈非线性一一对应关系,与波雷格丹站水位成绳套关系,绳套两侧分别对应汛期湄公河向洞里萨湖倒灌和汛后洞里萨湖向湄公河补水。基于河湖关系构建了不同时期不同河湖水位差下的洞里萨湖面积、容积与波雷格丹站水位的相关关系,该精细化的洞里萨湖水位-面积(容积)量算成果可为防汛抗旱精准预报提供科技支撑。     

Tonle Sap Lake,Cambodia: A perspective on its transborder hydrological and resources governance

Tonle Sap Lake is the largest freshwater lake in South East Asia, being situated at the heart of the Mekong River Basin. Governance of the lake over the recent past has been weak and overly complex, and the basin governance structure has changed over time in terms of its fisheries management framework. The governance framework initially focused on the commercial exploitation of fish resources, but has more recently switched to a community‐based fisheries management, biodiversity conservation and open access model. This study discusses how the water flows occurring between the Mekong River and Tonle Sap Lake complicate the governance of the lake, and particularly its fisheries, biodiversity, land and water management activities. The establishment of the Tonle Sap Authority (TSA) in 2007 sought to address the governance challenges facing the lake. The current study concludes, however, that the TSA alone is not sufficient and that global, regional and national stakeholders must make an effort to ensure the water flows between the lake and the Mekong River are themselves considered a core governance issue for the Tonle Sap.     

湄公河干流径流变化及其对下游的影响

湄公河水资源丰富,径流时空变化大.在阐述湄公河水资源及其开发利用状况的基础上,分析了下湄公河干流径流变化及其对洞里萨湖和湄公河三角洲的影响.研究表明:影响湄公河干流径流的水量主要来自老挝,对湄公河干流径流贡献最大的是巴色―上丁段;流域水电开发和水资源利用,改变了下游水文条件,主要使下游汛期洪水威胁减小,枯季径流增加;湄公河水倒灌进入洞里萨湖,在雨季蓄积大量洪水,对湄公河金边以下径流起着天然调节作用,减缓了湄公河三角洲海水入侵和洪水影响,提高了旱季农业灌溉保证率.     

洞里萨湖的水位和面积变化特征

洞里萨湖是湄公河最大的连通湖泊,其水位、面积变化对洞里萨湖的结构和功能产生重要影响,辨识水位、面积演变规律对洞里萨湖区与湄公河三角洲防汛抗旱和生态环境保护具有重要指导意义。基于金边港、波雷格丹和甘邦隆站长系列的日均水位数据及湖区地形资料,定量分析了洞里萨湖水位、面积的年际与年内变化特征。结果表明:洞里萨湖水位涨落缓慢,涨水天数少于退水天数,涨水率高于落水率。洞里萨湖年际水位波动频繁,年平均水位、年最高水位、年水位极差值、年洪水历时、年平均洪水位、日涨水率年际变化总体呈小幅下降趋势,年最低水位、退水天数、日落水率年际变化呈上升趋势。洞里萨湖水位、面积年内呈单峰型变化,5月份最低,平均水位1.51 m,相应面积2 487 km²,实测最低水位1.11 m,相应面积2 053 km²;10月份最高,平均水位8.70 m,相应面积12 768 km²,实测最高水位为10.54 m,相应面积15 261 km²,多年平均年内水位变幅7.63 m,面积变幅10 628 km²。研究成果为下一步洞里萨湖区的综合治理规划奠定了基础。     

Tonle Sap Lake: Current status and important research directions for environmental management

Tonle Sap Lake (TSL) in Cambodia is the largest freshwater body in South‐East Asia and one of the most productive ecosystems in the world. The lake and its ecosystems are widely under threat, however, due to anthropogenic activities occurring inside and outside its basin (e.g., water infrastructure development; land use change), being poorly understood in most aspects. This study provides an updated review of the state of knowledge of the TSL ecosystem, as well as important research directions for sustainable lake environmental management of Tonle Sap Lake by focusing on four major topics, including climate change and hydrology, sediment dynamics, nutrient dynamics and primary and secondary production. The findings of this study suggest anthropogenic activities in the TSL basin, as well as the Mekong, in combination together with climate changes, are key contributing factors in the degradation of the TSL ecosystem. Insufficient accurate data, however, precludes quantitative assessment of such impacts, making it difficult to quantitatively assess and accurately understand the ecosystem process in the lake ecosystem. More efforts are recommended in regard to environmental monitoring in all sub‐basins around TSL, assessing seasonal changes in nutrient and sediment inputs corresponding to water level and flow changes, assessing cumulative impacts of water infrastructure and climate change on the ecosystem dynamics, and elucidation of ecosystem processes within the lake's internal system.     

Potential effects of a major navigation project (Paraguay–Paraná Hidrovía) on inundation in the Pantanal floodplains

The Pantanal wetland of Brazil, a vast complex of seasonally inundated floodplains along the Paraguay River, is renowned for its outstanding biological resources. A proposed navigation project known as the Paraguay–Paraná Waterway (or Hidrovía) would deepen the Paraguay River channel to facilitate year‐round navigation through the Pantanal. The possibility of decreases in river levels (stage) has aroused concerns in relation to the potential environmental impacts, however the poor understanding of the hydrological relationships between rivers and floodplains has hampered evaluation of these impacts. The present study evaluates the potential impact of river modifications on adjacent floodplains by examining the relationship between the Paraguay River stage and the extent of floodplain inundation. Satellite observations of flooded area (from passive microwave emission; monthly data for 1979–1987) are plotted against river stage from several stations throughout the region to show the stage–inundation relationships for eight subregions along the Paraguay River. Scenarios in which the Paraguay River stage is decreased from the 20th and 80th percentile values reveal large potential impacts on inundation. For stage decreases of 0.10 and 0.25 m, the total flooded area is reduced by 1430 and 3830 km² at low‐water, and by 2410 and 5790 km² at high‐water, respectively. The floodplains of the two northernmost subregions appear to be most susceptible to reductions in flooding, losing more than half of their flooded area with a 0.25‐m decrease in the low‐water stage. The ecological impacts of these reductions in flooded area may be particularly severe at low water, when the few areas that typically remain flooded throughout the dry season serve as important refuges for aquatic animals. These results underscore the need for better understanding of the hydrology of the integrated river floodplain systems in the Pantanal before river channel modifications are carried out. Copyright © 1999 John Wiley & Sons, Ltd.     

Landscape Scale Assessment of Floodplain Inundation Frequency Using Landsat Imagery

In large river ecosystems, the timing, extent, duration and frequency of floodplain inundation greatly affect the quality of fish and wildlife habitat and the supply of important ecosystem goods and services. Seasonal high flows provide connectivity from the river to the floodplain, and seasonal inundation of the floodplain governs ecosystem structure and function. River regulation and other forms of hydrologic alteration have altered the connectivity of many rivers with their adjacent floodplain – impacting the function of wetlands on the floodplain and in turn, impacting the mainstem river function. Conservation and management of remaining floodplain resources can be improved through a better understanding of the spatial extent and frequency of inundation at scales that are relevant to the species and/or ecological processes of interest. Spatial data products describing dynamic aspects floodplain inundation are, however, not widely available. This study used Landsat imagery to generate multiple observations of inundation extent under varying hydrologic conditions to estimate inundation frequency. Inundation extent was estimated for 50 Landsat scenes and 1334 total images within the Gulf Coastal Plains and Ozarks Landscape Conservation Cooperative (GCPO LCC), a conservation science partnership working in a 730 000‐km² region in the south central USA. These data were composited into a landscape mosaic to depict relative inundation frequency over the entire GCPO LCC. An analytical methodology is presented for linking the observed inundation extent and frequency with long‐term gage measurements so that the outcomes may be useful in defining meaningful critical thresholds for a variety of floodplain dependent organisms as well as important ecological processes. Published 2015. This article is a U.S. Government work and is in the public domain in the USA     

DISCONNECTING THE FLOODPLAIN: EARTHWORKS AND THEIR ECOLOGICAL EFFECT ON A DRYLAND FLOODPLAIN IN THE MURRAY–DARLING BASIN,AUSTRALIA

Globally, dams and water extractions are well‐recognised disruptors of flow regimes in floodplain wetlands, but little is known of the hydrological and ecological impacts of floodplain earthworks constructed for irrigation, flood mitigation and erosion control. We mapped the distribution of earthworks with high‐resolution SPOT (Système Probatoire d'Observation de la Terre) imagery in an internationally recognised Ramsar wetland, the Macquarie Marshes of the Murray–Darling Basin, Australia. There were 339 km levees, 1648 km channels, 54 off‐river storages and 664 tanks (0.5–5 m high), detected within the 4793 km² floodplain study area. Earthworks reduced localised flooding compared with undeveloped sites. The most pronounced disconnection of the original floodplain (73.0%) occurred where earthworks were most concentrated compared with areas with few earthworks (53.2%). We investigated relationships between hydrological connectivity and mortality of the perennial flood‐dependent river red gum Eucalyptus camaldulensis at 55 floodplain sites (225 × 150 m). Over half of the river red gums were dead at 21.8% of the sites. Earthworks blocked surface flows to flood‐dependent vegetation and drowned vegetation in artificially inundated off‐river storages. Mortality was due to impacts of earthworks and potentially exacerbated by effects of river regulation, water extraction and climate. River red gums were healthiest in narrow river corridors where earthworks confined flows and flows could recede freely. Rehabilitation of flood‐dependent ecosystems should focus on reinstating lateral connectivity and protecting environmental flows. Copyright © 2011 John Wiley & Sons, Ltd.     

Habitat loss as the main cause of the slow recovery of fish faunas of regulated large rivers in Europe: the transversal floodplain gradient

In large European rivers the chemical water quality has improved markedly in recent decades, yet the recovery of the fish fauna is not proceeding accordingly. Important causes are the loss of habitats in the main river channels and their floodplains, and the diminished hydrological connectivity between them. In this study we investigate how river regulation has affected fish community structure in floodplain waterbodies of the rivers Rhône (France), Danube (Austria), Rhine and Meuse (The Netherlands). A typology of natural and man‐made aquatic habitats was constructed based on geomorphology, inundation frequency and ecological connectivity, along the transversal river–floodplain gradient, i.e. perpendicular to the main stream of the river. Fish species were classified in ecological guilds based on their flow preference, reproduction ecology and diet, and their status on national red lists was used to analyse the present state of the guilds and habitats. Ecological fish guilds appear to be good indicators of ecological integrity and functioning of river–floodplain systems. A transversal successional gradient in fish community structure that bears some resemblance to the gradient found in natural rivers can still be discerned in heavily regulated rivers. It resembles the longitudinal river gradient; even some predictions of the River Continuum Concept are applicable. Overall, richness and diversity of species and ecological guilds decrease with decreasing hydrological connectivity of floodplain waterbodies. Anthropogenic disturbances have affected fish species unevenly: guilds of specialized species that are highly adapted to specifically riverine conditions have declined far more than generalist species. Fish habitats in the main and secondary channels have suffered most from regulation and contain the highest percentage of threatened species. Rheophilic fishes have become rare because their lotic reproductive habitats are severely degraded, fragmented, absent or unreachable. Limnophilic fishes have become rare too, mainly as a result of eutrophication. Eurytopic fishes have become dominant everywhere. Copyright © 2003 John Wiley & Sons, Ltd.     

Multi‐annual contemporary flood event overbank sedimentation within the vegetated lower Orinoco floodplain,Venezuela

Multi‐annual contemporary flood event overbank sedimentation rates were quantified on the World's third largest river in terms of discharge, the tropical lower Orinoco. We discuss the role of variables at the basin and reach scales that contributed to the complexity of spatio‐temporal overbank sediment deposition patterns. Monitored in situ plots were characterized by distance to the main channel, hydroperiod, different geomorphological units, and vegetation cover. Flood event sedimentation rates showed a high spatial variability ranging from the absence of sediment deposition up to 225.46 kg m^‐2 yr^‐1. Banks and levees received relatively high amounts of sediment (39.6 kg m^‐2 yr^‐1), whereas observed mean sedimentation rates on the more distant floodplain and backswamps tended to be lower (17.7 kg m^‐2 yr^‐1). Significant differences in sedimentation rates were observed in two major vegetation types: dense herbaceous and shrubby vegetation (42.2 kg m^‐2 yr^‐1) and floodplain forest (12.7 kg m^‐2 yr^‐1). However, overbank sedimentation patterns also reflected imbricated hydrosedimentary and biogeomorphological vegetation feedbacks that co‐construct fluvial landforms. The incidence of an El Niño–Southern Oscillation–La Niña episode during the study period on sediment availability and floodplain sedimentation suggests that within whitewater rivers, where suspended sediment concentrations are naturally high, hydrological connectivity seems to be more important for floodplain sedimentation than variations in suspended sediment concentrations. These results may provide a good basis for future biogeomorphological investigation projects using complementary methodologies, in order to better anticipate global change and fluctuations in the occurrence, strength or duration of El Niño–La Niña episodes in the tropical zone and their consequences for flood discharge and sediment dynamics during channel–floodplain exchanges.     

Ecological connectivity in alluvial river ecosystems and its disruption by flow regulation

The dynamic nature of alluvial floodplain rivers is a function of flow and sediment regimes interacting with the physiographic features and vegetation cover of the landscape. During seasonal inundation, the flood pulse forms a ‘moving littoral’ that traverses the plain, increasing productivity and enhancing connectivity. The range of spatio-temporal connectivity between different biotopes, coupled with variable levels of natural disturbance, determine successional patterns and habitat heterogeneity that are responsible for maintaining the ecological integrity of floodplain river systems. Flow regulation by dams, often compounded by other modifications such as levee construction, normally results in reduced connectivity and altered successional trajectories in downstream reaches. Flood peaks are typically reduced by river regulation, which reduces the frequency and extent of floodplain inundation. A reduction in channel-forming flows reduces channel migration, an important phenomenon in maintaining high levels of habitat diversity across floodplains. The seasonal timing of floods may be shifted by flow regulation, with major ramifications for aquatic and terrestrial biota. Truncation of sediment transport may result in channel degradation for many kilometres downstream from a dam. Deepening of the channel lowers the water-table, which affects riparian vegetation dynamics and reduces the effective base level of tributaries, which results in rejuvenation and erosion. Ecological integrity in floodplain rivers is based in part on a diversity of water bodies with differing degrees of connectivity with the main river channel. Collectively, these water bodies occupy a wide range of successional stages, thereby forming a mosaic of habitat patches across the floodplain, This diversity is maintained by a balance between the trend toward terrestrialization and flow disturbances that renew connectivity and reset successional sequences. To counter the influence of river regulation, restoration efforts should focus on reestablishing dynamic connectivity between the channel and floodplain water bodies.     

资料短缺地区径流模拟研究

以柬埔寨洞里萨湖流域为对象,基于多源降水信息分析、水文模型构建及适应性分析、参数移植研究及检验等,探讨了资料短缺地区的径流模拟问题。结果表明:气候再分析资料集Ag MERRA在洞里萨湖地区的精度较高,VIC模型在该区域的适应性较好,可以用来进行水文模拟;水文模型参数与流域气候和下垫面因子的相关性较好,拟合优度R2都在0. 65以上,移植的可信度较高;在3个验证流域的实测径流过程对比分析表明,基于参数移植方案构建的水文模型能较好地模拟资料短缺地区的流域水文过程。     

The effect of altered flow regime on the frequency and duration of bankfull discharge: Murrumbidgee River,Australia

On meandering rivers with well‐developed floodplains, bankfull stage has geomorphological and ecological significance because it approximates the level of connection between the channel and the floodplain. As a river rises to bankfull stage, sediment begins to be deposited on the floodplain, wetlands are progressively inundated and organisms migrate between the channel and floodplain habitats. On many rivers large headwater dams have reduced the frequency and duration of floodplain inundation downstream. However, the lack of reliable pre‐regulation flow data has made it difficult to quantify the effects of river regulation. This study used historical regulated and modelled natural flow data to determine the effects of regulation on the frequency and duration of bankfull flows on the Murrumbidgee River, one of Australia's largest and most heavily regulated rivers. In combination with floodplain surveys the flow data show that regulation has halved the frequency and duration of bankfull flows. This reduction in channel–floodplain connection has implications for the ecological health of the Murrumbidgee River. Copyright © 2005 John Wiley & Sons, Ltd.     

Spatial Pattern of Phytoplankton Based on the Morphology‐Based Functional Approach along a River–Floodplain Gradient

Current efforts to yield an appropriate method that would simplify the use of phytoplankton in the ecological evaluation of freshwaters resulted in different approaches based on clustering phytoplankton organisms. In this study, we applied the morphology‐based functional group (MBFG) concept to determine the spatial changes of phytoplankton in the natural riverine floodplain of the alluvial reaches of the Danube River along the horizontal gradient from the river towards the floodplain habitats. The obtained results showed that the magnitude of environmental changes depended on alternations in hydrological variables (hydropattern and water level) that influenced changes in the physical and chemical conditions. High‐intensity flood pulses caused environmental homogenizations and nitrate enrichment of the floodplain habitats. Phytoplankton dynamics were strongly associated with the environmental changes, and using the MBFG approach, two basic hydrological conditions were identified: inundation phase dominated by diatoms (GVI) and isolation phase dominated by filamentous cyanobacteria (GIII). Total diatom biomass decreased along the floodplain gradient with a diminishing of physical constraints, and site‐specific variables became more important in favouring diatom assemblages. The different response of cyanobacterial species to mixing regime was of particular significance for species successions during bloom period. Altogether, classifying very diverse diatoms (centrics and pennates and planktonic and benthic) and cyanobacterial taxa into single groups represents a weakness of the MBFG approach, which might make it impossible to reflect all the ecological differences governed by environmental constraints along river–floodplain gradients. Copyright © 2014 John Wiley & Sons, Ltd.     

Reconstruction of the characteristics of a natural alluvial river–floodplain system and hydromorphological changes following human modifications: the Danube River (1812–1991)

Based on detailed historical surveys from 1812, the natural riverine landscape of a 10.25‐km‐long reach of the Danube River in the Austrian Machland region prior to channelization is analysed. Anthropogenically induced changes of fluvial dynamics, hydrological connectivity and aquatic habitat composition are discussed, comparing the situations following channelization (1925) and flow regulation (1991). In 1812 the alluvial river–floodplain system of the Danube River comprised a highly complex channel network, numerous gravel bars and extensive islands, with the main channel and side arms (eupotamon) representing about 97% of the entire water surface at low flow. The floodplain was characterized by relatively flat terrain and numerous natural trenches (former active channels) connected to the main channel. These hydromorphological conditions led to marked expansion/contraction of the water surface area at water level fluctuations below bankfull (‘flow pulse’). The high degree of hydrological connectivity enabled intensive exchange processes and favoured migrations of aquatic organisms between the river and floodplain habitats over a period of approximately 90 days per year. Overall in 1812, 57% of the active zone (active channels and floodplain) was inundated at bankfull water level. Channelization and construction of hydropower plants resulted in a truncated fluvial system. Consequently, eupotamal water bodies decreased by 65%, and gravel/sand bars and vegetated islands decreased by 94% and 97%, respectively, whereas the area of the various backwaters doubled. In 1991 the former ‘flow pulse’ was halved due to artificial levees and embankments, greatly diminishing hydrological connectivity and decoupling large areas of the floodplain from the main channel. Active overflow, formerly playing an important role, is now replaced by backwater flooding and seepage inflow in isolated water bodies. Copyright © 2003 John Wiley & Sons, Ltd.     

Modelling floodplain inundation on a regulated river: integrating GIS,remote sensing and hydrological models

The lower River Murray in South Australia is highly regulated through weirs and water extraction for irrigation. Management of the river for environmental purposes requires an understanding of the extent of floodplain inundation from various flows and weir manipulations. This study aimed to produce a floodplain inundation model for the 600 km long and 1–5 km wide portion of the River Murray in South Australia from the New South Wales border to Lake Alexandrina. The model was developed using a Geographical Information System (GIS), remote sensing and hydrological modelling. Flood inundation extents were monitored from Landsat satellite imagery for a range of flows, interpolated to model flood growth patterns and linked to a hydrological model of the river. The resulting model can be analysed for flows ranging from minimum flow to a 1‐in‐13‐year flood event for any month and weir configuration and has been independently tested using aerial photography to an accuracy of approximately 15% underestimate. The results have proven the approach for determining flood inundation over a large area at approximately one‐tenth of the cost of detailed elevation and hydrodynamic modelling. The GIS model allows prediction of impacts on infrastructure, wetlands and floodplain vegetation, allowing quantitative analysis of flood extent to be used as an input into the management decision process. Copyright © 2005 John Wiley & Sons, Ltd.     

Coupled Hydrological/Hydraulic Modelling of River Restoration Impacts and Floodplain Hydrodynamics

Channelization and embankment of rivers has led to major ecological degradation of aquatic habitats worldwide. River restoration can be used to restore favourable hydrological conditions for target species or processes. However, the effects of river restoration on hydraulic and hydrological processes are complex and are often difficult to determine because of the long‐term monitoring required before and after restoration works. Our study is based on rarely available, detailed pre‐restoration and post‐restoration hydrological data collected from a wet grassland meadow in Norfolk, UK, and provides important insights into the hydrological effects of river restoration. Groundwater hydrology and climate were monitored from 2007 to 2010. Based on our data, we developed coupled hydrological/hydraulic models of pre‐embankment and post‐embankment conditions using the MIKE‐SHE/MIKE 11 system. Simulated groundwater levels compared well with observed groundwater. Removal of the river embankments resulted in widespread floodplain inundation at high river flows (>1.7 m³ s^?1) and frequent localized flooding at the river edge during smaller events (>0.6 m³ s^?1). Subsequently, groundwater levels were higher and subsurface storage was greater. The restoration had a moderate effect on flood peak attenuation and improved free drainage to the river. Our results suggest that embankment removal can increase river–floodplain hydrological connectivity to form a more natural wetland ecotone, driven by frequent localized flood disturbance. This has important implications for the planning and management of river restoration projects that aim to enhance floodwater storage, floodplain species composition and biogeochemical cycling of nutrients. © 2016 The Authors. River Research and Applications Published by John Wiley & Sons Ltd.