Extent Of Floodplain Inundation Research Articles

Dynamics of Surface‐Water Connectivity in a Low‐Gradient Meandering River Floodplain

AbstractHigh‐resolution topography reveals that floodplains along meandering rivers in Indiana commonly contain intermittently flowing channel networks. We investigated how the presence of floodplain channels affects lateral surface‐water connectivity between a river and floodplain (specifically exchange flux and timescales of transport) as a function of flow stage in a low‐gradient river‐floodplain system. We constructed a two‐dimensional, surface‐water hydrodynamic model using Hydrologic Engineering Center's River Analysis System (HEC‐RAS) 2D along 32 km of floodplain (56 km along the river) of the East Fork White River near Seymour, Indiana, USA, using lidar elevation data and surveyed river bathymetry. The model was calibrated using land‐cover specific roughness to elevation‐discharge data from a U.S. Geological Survey gage and validated against high‐water marks, an aerial photo showing the spatial extent of floodplain inundation, and measured flow velocities. Using the model results, we analyzed the flow in the river, spatial patterns of inundation, flow pathways, river‐floodplain exchange, and water residence time on the floodplain. Our results highlight that bankfull flow is an oversimplified concept for explaining river‐floodplain connectivity because some stream banks are overtopped and major low‐lying floodplain channels are inundated roughly 19 days per year. As flow increased, inundation of floodplain channels at higher elevations dissected the floodplain, until the floodplain channels became fully inundated. Additionally, we found that river‐floodplain exchange was driven by bank height or channel orientation depending on flow conditions. We propose a conceptual model of river‐floodplain connectivity dynamics and developed metrics to analyze quantitatively complex river‐floodplain systems.

Ecological Conditions of Watercourses in the Middle Amur Lowland in the Areas of Drainage Reclamation

The effect of land reclamation on the migration and accumulation of heavy metals and some pollutants in small rivers is determined. The study was conducted in the Middle Amur lowland in different phases of hydrological regime and at different extent of floodplain inundation. The formation of the hydrological regime in small rivers in this area is governed by the irregular annual runoff distribution. The seasonal character of flood periods requires water samples to be taken before spring flood (April) and after floods have passed (September–October), and at various extent of floodplain inundation. The field studies of water-courses were carried out in 2009–2014. The water samples were analyzed to determine the concentrations of heavy metals (iron, manganese, copper, nickel, cobalt, lead and zinc), suspended substances, organic carbon (total, dissolved, and suspended), humic and fulvic acids, and volatile organic compounds. The mobility of heavy metals in surface watercourses was shown to reflect the effect of drainage and surface runoff from soil horizons, an increase in the concentrations of suspended and organic compounds, especially, fulvic acids, which enhance their geochemical mobility. During floods, an increase in heavy metals washout from floodplain soils and the dilution of their concentrations causes the formation of a single-type concentration series of heavy metals. In addition, the processes of pollutants migration show an effect of changes in the geomorphological characteristics of floodplain–channel complexes and a decrease in flow velocity in watercourses in the areas where land reclamation was applied. Thus, all factors mentioned above lead to a decrease in water pollution index in the river.

The winter storms of 2013/2014 in the UK: hydrological responses and impacts

This paper outlines the hydrological aspects of the 2013/2014 winter flooding in the UK, as well as the impacts. The episode is considered in a long-term historical context and wider issues raised by the flood events are discussed briefly.

Managing and researching floods: sustainability, policy responses and the place of rural communities

The unprecedented rainfall in southern parts of Britain this winter (with 2014 the wettest January since records began in 1910; UKMO, 2014) have brought widespread flooding. “January [2014] was notable for the persistence and spatial extent of floodplain inundation, particularly from large, slowly responding rivers and in low-lying areas such as the Somerset Levels.” (CEH, 2014: 1). But is persistent rainfall the only cause of flooding? In the most devastated areas, tensions have been running high as residents, politicians, scientists and the regulator (the Environment Agency) have debated the causes of the flooding and the appropriate solutions to it. It has quite quickly turned into a ‘wicked problem’ (Nie, 2003) characterised by societal, political and environmental complexity. In the Somerset Levels, one of the worst affected areas, this has been contested most forcefully as an issue of dredging. Many local residents, farmers and politicians point to the reduction in dredging works undertaken or permitted by the Environment Agency. Dredging, they argue, is necessary to maintain the capacity of watercourses and to permit more rapid conveyance of floodwaters. The Environment Agency, on the other hand, argues that dredging would not have prevented the current flooding and maintains that dredging has its own negative consequences (such as increasing flood risk further downstream – in often larger towns and cities – and damaging aquatic biodiversity). In this commentary, we transcend hydrology and social sciences and use the current floods in southern Britain as an exemplar to explore the interactions between (social) scientific knowledge, conceptualisations of sustainability and the uneven distribution of impacts on affected communities in managing physical effects, human consequences and responses to these extreme hydrological events. We reflect on the role of hydrologists in providing critical responses to flood events and suggest they have a greater role to play in directing more socially responsible flood research.

Towards an operational SAR monitoring system for monitoring environmental flows in the Macquarie Marshes

Multi-frequency synthetic aperture radar (SAR) data was acquired over the Macquarie Marshes Nature Reserve in north central New South Wales (NSW), Australia, to demonstrate the potential of imaging radar for mapping and monitoring wetland extent and inundation patterns in an inland, semi-arid wetland environment. A sequence of ALOS PALSAR and TerraSAR-X images acquired between January 2007 and April 2008 captured the wetlands in three successive phases: dry, wet and transitional. Visual observation of multi-temporal and multi-frequency SAR backscatter data confirmed the capacity of SAR to respond to changes in surface water, soil moisture and biomass. Longer wavelength L-band SAR provides a tool for discriminating wetlands, mapping surface water and detecting below-canopy inundation. Shorter wavelength X-band SAR provides a tool for detecting flushes in growth of vegetation in response to higher soil moisture from flooding. PALSAR data demonstrated a high capacity for discrimination of different wetland classes, while TerraSAR-X data was less suited to discriminating between cover types. The integration of X- and L-band data revealed the extent of floodplain inundation and presence of aquatic vegetation in ponded areas. Given a stable, well-calibrated time-series of SAR data, change analysis provides a mechanism for understanding the hydrological and/or ecological change in an area. In the longer term, it is envisioned that radar will provide a valuable tool within an operational system for monitoring the impact of environmental flows in NSW inland wetlands.

DEM-based modification of pixel-swapping algorithm for enhancing floodplain inundation mapping

Floodplain inundation plays a key role in riparian ecosystems. Remote sensing provides an advanced technology for detecting floodplain inundation, but the trade-off between the spatial and temporal resolutions of remotely sensed imagery is a well-known issue. Sub-pixel mapping is an effective way to mitigate the trade-off by improving the spatial resolution of image classification results while keeping their temporal resolution. It is therefore useful for improving the mapping of highly dynamic flood inundation using coarse-resolution images. However, traditional sub-pixel mapping algorithms have limitations on delineating the extent of floodplain inundation that reveals linear and complex characteristics. A modified pixel-swapping (DMPS) algorithm which is based on a digital elevation model (DEM) is thus developed in this study. It is built on the widely accepted pixel-swapping (PS) algorithm and one of its derivatives, the linearized pixel-swapping (LPS) algorithm. A Landsat image recording a significant flood inundation event in the Chowilla Floodplain of the Murray–Darling Basin in Australia was used as a case study. The results show that the DMPS algorithm outperformed the original PS and LPS algorithms both in accuracy and rationality of the resultant map. It improves the accuracy and the kappa coefficient by about 5% and 0.1, respectively, in comparison with the PS algorithm. The spatial pattern of inundation derived from the DMPS algorithm reveals fewer breakpoints and errors along the river channels. Moreover, it is observed that the DMPS algorithm is less sensitive to some critical parameters compared with the PS and LPS algorithms. It is hoped that the proposed DMPS algorithm will broaden the application of coarse-resolution sensors in floodplain inundation detection, which would thereby benefit the ecological studies in floodplains.

An Evaluation of MODIS Daily and 8-day Composite Products for Floodplain and Wetland Inundation Mapping

Wetland and floodplain inundation is well-known for its hydrological, ecological and environmental importance. Satellite remote sensing provides an effective and efficient tool for detecting inundation extent. This study compares and validates inundation maps derived from NASA’s Moderate Imaging Spectroradiometer (MODIS) imagery. The comparison was performed between MODIS daily and 8-day composite products; and the validation was conducted using Landsat Thematic Mapper (TM) images. Two floodplain wetlands in the Murray-Darling Basin in Australia were selected as case studies, and inundation extents corresponding to the peak flows of significant flood events were extracted using the Open Water Likelihood (OWL) algorithm and the modified Normalised Difference Water Index (mNDWI) for MODIS and TM images, respectively. The accuracy of the inundation maps derived from different images were assessed spatially and statistically. The evaluation results show that both MODIS products may provide a reasonable estimate of the dynamic extent of floodplain inundation at the regional scale. The accuracy of inundation mapping is mainly due to the spatial and spectral characteristics of MODIS imagery and has nothing to do with the type of products chosen, thus the 8-day composite images can be used as a surrogate for daily images for the purpose of inundation delineation.

Spatial and Temporal Patterns in Fish Assemblages Following an Artificially Extended Floodplain Inundation Event, Northern Murray-Darling Basin, Australia

Water extraction from dryland rivers is often associated with declines in the health of river and floodplain ecosystems due to reduced flooding frequency and extent of floodplain inundation. Following moderate flooding in early 2008 in the Narran River, Murray-Darling Basin, Australia, 10,423 ML of water was purchased from agricultural water users and delivered to the river to prolong inundation of its terminal lake system to improve the recruitment success of colonial waterbirds that had started breeding in response to the initial flooding. This study examined the spatial and temporal patterns of fish assemblages in river and floodplain habitats over eight months following flooding to assess the possible ecological benefits of flood extension. Although the abundances of most fish species were greater in river channel habitats, the fish assemblage used floodplain habitats when inundated. Young-of-the-year (4-12 months age) golden perch (Macquaria ambigua) and bony bream (Nematalosa erebi) were consistently sampled in floodplain sites when inundated, suggesting that the floodplain provides rearing habitat for these species. Significant differences in the abundances of fish populations between reaches upstream and downstream of a weir in the main river channel indicates that the effectiveness of the environmental water release was limited by restricted connectivity within the broader catchment. Although the seasonal timing of flood extension may have coincided with sub-optimal primary production, the use of the environmental water purchase is likely to have promoted recruitment of fish populations by providing greater access to floodplain nursery habitats, thereby improving the ability to persist during years of little or no flow.

The hydrological characteristics of the Berg River

This study aimed to provide a comprehensive description of the natural and present-day hydrology of the Berg River, focusing on the hydrological importance of the upper river, i.e., the subcatchment to be dammed by the Berg River Dam, to its lower reaches. Considerable between-year variability was demonstrated in all aspects of flow, including baseflows and the range of different magnitudes of floods. Flood frequencies are high (average of 7 to 8 floods above a disturbance threshold per annum; range 3–15). Flooding is strongly seasonal with very low levels of flooding from November to April, alongside a period characterised by high flood frequencies, from May to September, with one or more floods occurring on average per month. This pattern of seasonal disturbance has a fairly high predictability (52%), based on Colwell's measures. However, within the flood season, flood frequency per month is unpredictable (17%). Colwell's Contingency, or the measure of how repetitive the pattern is, is particularly low. Floods constituting disturbance events in the Berg River show intra-annual variability in their timing and inter-annual variability in the frequency (number per year) and periodicity (number per month). The upper Berg River plays a critical role in contributing to both base flows and small floods in the lower river, contributing on average 72% of the flood peak in the lower reaches, for floods <20 m3/s and contributing disproportionally to all intra-annual flood events in the lower reaches. Base flow level has a major influence on the extent of floodplain inundation achieved by floods in the estuary. The disproportionate contribution of this subcatchment is a reflection of both its natural characteristics (high rainfall, water-producing area within the catchment) but also, and importantly, a consequence of the extent of development elsewhere in the catchment that has removed orreduced smaller flood flows. This contribution of the upper river to floods in the lower reaches appears to be substantially greater during drought years. The Berg River Dam is likely to diminish this contribution of the upper catchment to base flows and smaller floods along the full length of the river and will quite probably remove this ‘flood buffer’ provided by the upper river during dry or drought years.

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.

Spatial and temporal variation in fish-assemblage structure in isolated waterholes during the 2001 dry season of an arid-zone floodplain river, Cooper Creek, Australia

Spatial and temporal variation in fish-assemblage structure within isolated waterholes on the floodplains of Cooper Creek, Australia, was studied during the 2001 dry season, a period of natural drought in this arid-zone river. Spatial variation in fish-assemblage structure and the abundance of five species in disconnected waterholes early in the dry season (April 2001) were related to the extent of floodplain inundation 14 months previously, and to the interconnectedness of waterholes and waterhole habitat structure. As the dry season progressed, waterhole volumes decreased owing to evaporative water loss and structural habitat elements (anabranches, bars, boulders) became exposed. Marked changes in fish assemblage structure between the early (April) and late (September) dry season were related to habitat loss but not to water chemistry. Interactions between flow and habitat across a nested hierarchy of spatial scales (the floodplain, the waterhole and habitat patches within waterholes) were crucial to the persistence of fish assemblages through the 2001 dry season. We conclude that the magnitude, timing and frequency of floodplain inundation and natural variations in waterhole volume must be maintained if we wish to sustain the distinctive habitats and fish assemblages of this arid-zone floodplain river.

Effects of Flow Regulation on Shallow‐Water Habitat Dynamics and Floodplain Connectivity

Abstract Our study examined the effects of flow regulation on the spatiotemporal availability of shallow habitat patches with slow current velocity (SSCV patches) and floodplain inundation in the unregulated Yellowstone River and the regulated Missouri River in Montana and North Dakota. We mapped representative sites and used hydraulic models and hydrograph data to describe the frequency and extent of floodplain inundation and the availability of SSCV habitat over time during different water years. In the Yellowstone River the distribution, location, and size of SSCV patches varied but followed an annual pattern that was tied to the snowmelt runoff hydrograph. There was less variation in patch distribution in the Missouri River, and the pattern of habitat availability was influenced by flow regulation. Regulated flows and their effects on channel morphology and patterns of vegetation establishment resulted in 3.0–3.5 times less area of inundated woody vegetation during normal and dry years in the Missouri...

Controls on Patterns of Coarse Organic Particle Retention in Headwater Streams

Organic matter retention is an integral ecosystem process affecting C and nutrient dynamics and biota in streams. Influences of discharge (Q), reach-scale channel form, and riparian vegetation on coarse particulate organic matter (CPOM) retention were analyzed in 2 headwater streams in northeastern Oregon. Ginkgo biloba leaves were released in coniferous forest reaches and downstream floodplain meadow reaches during spring high flow and summer baseflow. Transitional reaches were also analyzed during summer baseflow. Paper strips, simulating sedge blade retention, were released in meadow reaches during high flow. Mean transport distances (S_P) were calculated as the inverse of the longitudinal loss rate (k) of leaves in transport. The metrics S_P, width-specific discharge (Q_W = Q/stream width), and the mass transfer coefficient (v_dep=Q_W/S_P) were used to investigate retention. Values of S_P (0.9-97 m) were 2 to 11 times longer during high flow than baseflow. Mean S_P in forest reaches (29.3 m) was significantly shorter than in meadow reaches (68.9 m) during high flow but not during baseflow. Standardizing k for the scaling effects of Q by analyzing the relationship between Q_W and S_P, in which the slope equaled the inverse of mean v_dep of all Ginkgo releases, indicated times when v_dep was higher or lower than predicted by Q. Values of S_P were driven largely by Q, yet most experiments in which values of v_dep exceeded those predicted by Q_W occurred during high flow. Values of v_dep (0.3-32 mm/s) across experiments were generally inversely related to S_P but did not differ between forest and meadow reaches during high flow. Unlike meadow reaches, mean v_dep in forest reaches was higher during high flow (5.2 mm/s) than baseflow (1.1 mm/s). Values of v_dep were positively related to large wood volume and negatively related to the extent of floodplain inundation during high flow. Yet, in the meadow reach that had lower relative channel constraint, paper strips were transported farther onto the floodplain as Q rose, resulting in long-term (∼1.5 mo) retention. Despite downstream increases in Q, there were no differences in mean baseflow S_P or v_dep among reaches in either stream, indicating some longitudinal compensation in retention. Alternating associations between retention metrics and structural elements of the stream channels between flow periods suggests dynamic reach-scale hydrologic-retention thresholds in response to changes in Q. Analysis of v_dep across experiments indicated that channel morphology, stream wood, and riparian vegetation are major controls on CPOM retention.

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–Parana Waterway (or Hidrovia) 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.

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

AbstractThe 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.

Endangered ecosystems: a review of the conservation status of tropical Asian rivers

Tropical Asian rivers are characterized by their flow seasonality. One (sometimes two) peaks in discharge cause temporary declines in phytoplankton, zooplankton and zoobenthos biomass, but lead to inundation of river floodplains and significant land-water interactions. Fishes undertake lateral or longitudinal breeding migrations within the river system during the flood season, which is marked also by intensive feeding upon allochthonous inputs. Among the diverse human influences upon tropical Asian rivers, three threats stand out. Firstly, degradation of drainage basins (particularly through deforestation and overgrazing) leads to increased suspended sediment loads and extensive flooding. Excessive floodplain siltation alters habitats causing species decline or disappearance. The second threat — river regulation and control — has been practised widely in the region for centuries but, with the planned development of massive projects on the Yangtze and Mekong Rivers, the potential for environmental damage has increased. Flow regulation reduces flood-season peaks, changing the magnitude and extent of floodplain inundation and land-water interactions. Fish breeding migrations may be disrupted, because dams block migration routes or changed flow regimes fail to stimulate reproduction. River pollution is pervasive throughout the region, and constitutes the third threat. Untreated sewage is a particular problem in densely-populated areas, and pollution by industrial effluents and mining wastes is becoming more important. The effects of pollution in tropical Asian rivers are essentially the same as those recorded in north-temperate regions. However, biological understanding has yet to be matched by an ability to halt or limit river degradation. Together, the three threats have led to declines and range constrictions of aquatic animals and those terrestrial species associated with riparian corridors and floodplains. River dolphins and certain crocodilians are particularly threatened, but declines in species of waterfowl, floodplain deer, a host of fishes, macrophytes, and invertebrates have been documented. Reversing the trend is difficult as pollution, flow regulation, and drainage-basin degradation have non-additive detrimental effects on river ecosystems, and enhance the success of exotic invasive species. Moreover, our ability to predict the outcome of man-made changes is hampered by a lack of knowledge of species' life histories and a paucity of data on the trophic basis of production. Despite a lack of detailed information, conservation of tropical Asian rivers will be effected only if limnologists move beyond the bailiwick of science. Ecologically viable management strategies for tropical Asian rivers will succeed only if the socioeconomic context of development plans is taken into account. A failure to rise this challenge will result in the further degradation of these endangered ecosystems.

The use of Landsat multispectral scanner data for the analysis and management of flooding on the river Severn, England

Remote sensing has emerged as one of the major techniques for the analysis and delineation of large floods. This analysis can provide data invaluable for the hydrological management of large river systems. A need for information on the extent of floodplain inundation for the lower reaches of the largest river in the UK was met by a search through Landsat images of floods and the analysis of the best example recorded. Automated classification of the Landsat imagery of this flood on the river Severn in 1977 was used to provide estimates of the extent and spatial distribution of inundation. Flood images were generated using the Plessey IDP 3000 image processor, and the maps derived accorded well with aerial photography and qualitative flood information. Three distinct floodplain environments were delineated and flood images produced by different spectral bands compared. Specific questions prompted by flood hazard management and concerning the processes and extent of flooding were answered by the Landsat data analysis. Management of the flood risk of large rivers is expensive and remote sensing data is a relatively cheap and effective way of monitoring control works and providing data for the prediction of the effects of future hydrological works. Remote sensing is a practical way in which spatial information concerning the behavior of large dynamic systems can be obtained both quickly and relatively cheaply.