Floodplain Characteristics Research Articles

Morphological Dynamics of the Jamuna River in Kazipur Subdistrict

This study identifies and evaluates the morphologically changing trend and process–response mechanisms of Jamuna River. The study considers the bank erosion, bank-line shifting, rate of erosion, accretion, sedimentation, course changing directions, changes in river width, fluvial landform dynamics, and floodplain features. The lower Brahmaputra–Jamuna River (named Jamuna River) at Kazipur subdistrict, Sirajganj district in Bangladesh are the study area. Multispectral Landsat satellite imageries of dry seasons were used for time series analyses of time periods (1972–2016) to interpret the chronological changes of morphology. The outcomes obtained from the analyse, support the historical westward channel shifting of the river, alluvial material properties, explicate fluvial processes, discharge anabranch instability, erosion, and morphological responses.

Soils of the Lake Baikal Drainage Basin: Results of Research for 1980–2017

Long–term soil research efforts (1980–2017) in the Baikal drainage basin revealed a widespread occurrence of thin layers of skeletal soils in the tundra zone: peat–lithozems, coarse humus and humous and dark–humus lithozems, and petrozems. A variety of complete–profile soils is represented by podburs, peat podburs, gleyic podburs, podzols and gleysols. It is determined that the soil cover of the mountain–taiga zone is nonuniform because of the manifestation of the vertical zonality, the aspects of slopes and permafrost of different types. The main background of the Khangai soils consists of cryosols and podburs; Khentii – sod podburs and dark–humus soils; in the Lake Khovsgol region – cryosols, podburs and sod podburs; the Baikal region – podburs, podzols, peat podburs and sod podzols, and on the windward slopes of the mountain ridges facing Baikal – podburs and coarse humus burozems. The occurrence and development of burozem soils in the Baikal region is confirmed. In the forest–steppe zone of Hangai and Khentii, the soil diversity is presented by cryosols, sod podburs, dark– and grey–humus soils, and in the forest–steppe contact zone by chernozems and castanozems. It is established that in the Selenga middle mountains, the basis for soil cover is provided by sod podburs, and the accompanying soils are grey metamorphic, light–humic and cryoarid soils. We identified a new type of soils, cespitose–grey soils. Psammozems and light–humus soils occur on sands. Chernozems prevail in the steppe zone, and castanozems, cryoarid and, light–humus soils are dominant in the arid steppe zone. It is determined that the floodplain develops soils of different types: immature, alluvial and halophytic. A study is made of the specific character of floodplain soil formation determined by the mountains on the territory, the regional features of floodplain–alluvial processes, the extremely continental climate, and by the functioning of soils in conditions of the combined manifestation of cryodization and aridization. It is emphasized that the 1:5 000 000 soil map of the Lake Baikal drainage basin was created using a unified methodological framework and a unified classification by soil scientists of Russia and Mongolia. It is established that the soils of the Baikal region differ from the soils located at the same latitude of the European territory of Russia. It is found that the mountain zonality has a determining influence on the formation and spatial distribution of soils.

Development of Chute Cutoff in the Lower Course of River Mayo-Inne, Yola South, Nigeria


 
 
 
 The study investigates the development of chute cutoff in the lower course of River Mayo-Inne, Yola South LGA, Adamawa State, Nigeria. The study employed the integrated approach of Remote Sensing, Geographic Information System, Field Survey, Laboratory Analysis, Oral Interview and Personal Observation in examining the influences of some relevant channel planform parameters (Sinuosity Index, Cutoff Ratio and Braiding Index), land use/land cover, channel bank materials, water stage and channel depth on the development of the chute cutoff over a period of Twenty five years (1990-2015). Results revealed the drastic reduction of Sinuosity Index from 1.57 in 1990 to 1.46 in 2015, changing the channel from meandering to the straight pattern. The analysis of changes in cut-off ratio unveiled the development of chute cutoff in bend II, which ultimately separated the river flow, forming a weak braided channel with a braiding index of 0.43. These developments were attributed to incessant flooding in the study area and floodplain characteristics such as floodplain elevation, bank strength and changes in vegetal cover.
 
 
 

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.

Substantial soil organic carbon retention along floodplains of mountain streams

AbstractSmall, snowmelt‐dominated mountain streams have the potential to store substantial organic carbon in floodplain sediment because of high inputs of particulate organic matter, relatively lower temperatures compared with lowland regions, and potential for increased moisture conditions. This work (i) quantifies mean soil organic carbon (OC) content along 24 study reaches in the Colorado Rocky Mountains using 660 soil samples, (ii) identifies potential controls of OC content based on soil properties and spatial position with respect to the channel, and (iii) and examines soil properties and OC across various floodplain geomorphic features in the study area. Stepwise multiple linear regression (adjusted r2 = 0.48, p < 0.001) indicates that percentage of silt and clay, sample depth, percent sand, distance from the channel, and relative elevation from the channel are significant predictors of OC content in the study area. Principle component analysis indicates limited separation between geomorphic floodplain features based on predictors of OC content. A lack of significant differences among floodplain features suggests that the systematic random sampling employed in this study can capture the variability of OC across floodplains in the study area. Mean floodplain OC (6.3 ± 0.3%) is more variable but on average greater than values in uplands (1.5 ± 0.08% to 2.2 ± 0.14%) of the Colorado Front Range and higher than published values from floodplains in other regions, particularly those of larger rivers.

The spatial organization of ecosystem services in river‐floodplains

AbstractRiver‐floodplains are hotspots for many ecosystem services (ES), and thus, understanding how these services are spatially organized along river systems is essential. General principles from river‐floodplain ecology may provide guidance for understanding these spatial patterns, yet such concepts have rarely been incorporated into spatial assessments of ES. Using a lens of riverine concepts, we contrasted how floodplain ES capacity and diversity (orchard production, forage production, carbon storage, paddle route quality, fish capacity) vary with longitudinal river‐floodplain position. High spatial resolution aerial photography (2006) facilitated detection of floodplain features contributing to the production of ES. We also determined how river reach types are linked to production of ES. We found that ES capacity varied considerably with longitudinal position and reach type. Agricultural capacity was concentrated in lower reaches, high‐quality paddle routes in middle‐lower reaches, and fish capacity and carbon storage in upper reaches. Furthermore, the highest diversity of ES was concentrated in the lowland floodplain reaches. Our results suggest river‐floodplain concepts can improve spatial assessments of ES, increase our understanding of the relationships among biological features and ES, and thus help us better manage some of the key ES trade‐offs.

Floodplain morphodynamics and distribution of trace elements in overbank deposits, Vistula River Valley Gorge near Solec nad Wisłą, Poland

AbstractGeological and geochemical investigations were carried out in the floodplain of the Vistula River Valley gorge near Solec nad Wisłą (Małopolska Gorge of the Vistula River). Geological mapping was supported by DEM and remote sensing analysis. Sediment samples were taken from depths of 0.5 m and 1.5 m from all geomorphological features identified. The geochemical analysis included determination of Cr, V, Sr, Ba, Ni, Cu, Co, As, Pb and Zn concentrations. Results indicate that the main factors affecting the pattern of features in the floodplain of this area are (1) the highly dynamic flood flow in the narrow section of the gorge and (2) the relief of the top surface of the sub-alluvial basement. The variable concentrations of trace elements are closely related to the floodplain features. Their concentrations can be considered as valuable geochemical proxies that enable a more thorough reconstruction of the sedimentary evolution of the Vistula River Valley and other similar river valleys, especially in gorge sections.

MONITORING PHENOLOGY OF FLOODPLAIN GRASSLAND AND HERBACEOUS VEGETATION WITH UAV IMAGERY

River restoration projects, which aim at improved flood safety and increased ecological value, have resulted in more heterogeneous vegetation. However, they also resulted in increasing hydraulic roughness, which leads to higher flood water levels during peak discharges. Due to allowance of vegetation development and succession, both ecological and hydraulic characteristics of the floodplain change more rapidly over time. Monitoring of floodplain vegetation has become essential to document and evaluate the changing floodplain characteristics and associated functioning. Extraction of characteristics of low vegetation using single-epoch remote sensing data, however, remains challenging. The aim of this study was to (1) evaluate the performance of multi-temporal, high-spatial-resolution UAV imagery for extracting temporal vegetation height profiles of grassland and herbaceous vegetation in floodplains and (2) to assess the relation between height development and NDVI changes. Vegetation height was measured six times during one year in 28 field plots within a single floodplain. UAV true-colour and false-colour imagery of the floodplain were recorded coincidently with each field survey. We found that: (1) the vertical accuracy of UAV normalized digital surface models (nDSMs) is sufficiently high to obtain temporal height profiles of low vegetation over a growing season, (2) vegetation height can be estimated from the time series of nDSMs, with the highest accuracy found for combined imagery from February and November (RMSE = 29-42 cm), (3) temporal relations between NDVI and observed vegetation height show different hysteresis behaviour for grassland and herbaceous vegetation. These results show the high potential of using UAV imagery for increasing grassland and herbaceous vegetation classification accuracy.

MONITORING PHENOLOGY OF FLOODPLAIN GRASSLAND AND HERBACEOUS VEGETATION WITH UAV IMAGERY

Abstract. River restoration projects, which aim at improved flood safety and increased ecological value, have resulted in more heterogeneous vegetation. However, they also resulted in increasing hydraulic roughness, which leads to higher flood water levels during peak discharges. Due to allowance of vegetation development and succession, both ecological and hydraulic characteristics of the floodplain change more rapidly over time. Monitoring of floodplain vegetation has become essential to document and evaluate the changing floodplain characteristics and associated functioning. Extraction of characteristics of low vegetation using single-epoch remote sensing data, however, remains challenging. The aim of this study was to (1) evaluate the performance of multi-temporal, high-spatial-resolution UAV imagery for extracting temporal vegetation height profiles of grassland and herbaceous vegetation in floodplains and (2) to assess the relation between height development and NDVI changes. Vegetation height was measured six times during one year in 28 field plots within a single floodplain. UAV true-colour and false-colour imagery of the floodplain were recorded coincidently with each field survey. We found that: (1) the vertical accuracy of UAV normalized digital surface models (nDSMs) is sufficiently high to obtain temporal height profiles of low vegetation over a growing season, (2) vegetation height can be estimated from the time series of nDSMs, with the highest accuracy found for combined imagery from February and November (RMSE = 29-42 cm), (3) temporal relations between NDVI and observed vegetation height show different hysteresis behaviour for grassland and herbaceous vegetation. These results show the high potential of using UAV imagery for increasing grassland and herbaceous vegetation classification accuracy.

Alien and native plant richness and abundance respond to different environmental drivers across multiple gravel floodplain ecosystems

AbstractAimTo assess whether native and alien plant cover and richness respond similarly to flow regime, propagule pressure, climate and floodplain characteristics in highly dynamic braided river ecosystems.LocationCanterbury, New Zealand.MethodsA regional, multiscale survey was conducted across 19 braided river floodplains in multiple catchments. We measured alien and native cover and richness across gradients of flow regime (flow magnitude, variability and high/low‐flow events), propagule pressure (inferred from land cover), climate and local‐scale floodplain substrate and topography. Boosted regression trees were used to determine the relative and absolute importance of these variables on plant cover and richness.ResultsThe floodplain ecosystems were highly invaded with 154 alien species and only 31 natives. Alien cover was higher in rivers with larger maximum flows, in plots with fine substrate texture, and at higher local river bed elevations. Alien richness increased as the variability of winter flows increased and followed a hump‐shaped relationship with river bed elevation. In contrast, native species richness and cover were both shaped primarily by climate and by land cover, higher in cooler and wetter areas with more adjacent native vegetation.Main conclusionsAlien and native richness and cover were shaped by different variables, so managing the ecosystem (e.g. flow regime) to mitigate aliens would not necessarily promote natives. Promotion of natives will require considerations of propagule supply and whether extant native species are suited to low‐elevation climatic conditions. Aliens were associated with predictors that approximate disturbance processes. Increased flow variability in winter could lead to an increase in the number of aliens; conversely, flow stabilization is likely to allow problematic invaders to increase in cover locally.

Degradation of the Mitchell River fluvial megafan by alluvial gully erosion increased by post-European land use change, Queensland, Australia

Along low gradient rivers in northern Australia, there is widespread gully erosion into unconfined alluvial deposits of active and inactive floodplains. On the Mitchell River fluvial megafan in northern Queensland, river incision and fan-head trenching into Pleistocene and Holocene megafan units with sodic soils created the potential energy for a secondary cycle of erosion. In this study, rates of alluvial gully erosion into incipiently-unstable channel banks and/or pre-existing floodplain features were quantified to assess the influence of land use change following European settlement. Alluvial gully scarp retreat rates were quantified at 18 sites across the megafan using recent GPS surveys and historic air photos, demonstrating rapid increases in gully area of 1.2 to 10 times their 1949 values. Extrapolation of gully area growth trends backward in time suggested that the current widespread phase of gullying initiated between 1880 and 1950, which is post-European settlement. This is supported by young optically stimulated luminescence (OSL) dates of gully inset-floodplain deposits, LiDAR terrain analysis, historic explorer accounts of earlier gully types, and archival records of cattle numbers and land management. It is deduced that intense cattle grazing and associated disturbance concentrated in the riparian zones during the dry season promoted gully erosion in the wet season along steep banks, adjacent floodplain hollows and precursor gullies. This is a result of reduced native grass cover, increased physical disturbance of soils, and the concentration of water runoff along cattle tracks, in addition to fire regime modifications, episodic drought, and the establishment of exotic weed and grass species. Geomorphic processes operating over geologic time across the fluvial megafan predisposed the landscape to being pushed by land used change across an intrinsically close geomorphic threshold towards instability. The evolution of these alluvial gullies is discussed in terms of their initiation, development, future growth, and stabilisation, and the numerous natural and anthropogenic factors influencing their erosion.

Deltaic floodplains development and wetland ecosystems management in the Ganges–Brahmaputra–Meghna Rivers Delta in Bangladesh

The Ganges delta has a great importance for its exceptional hydro-geological settings and deltaic floodplain wetland ecosystems. The floodplain is formed by the deposition of the Ganges, Brahmaputra and Meghna River. The physical characteristics of floodplains, geographic location, the multiplicity of rivers and the monsoon climate render wetland ecosystems highly vulnerable to natural disaster and anthropogenic activities. Flooding is a natural annual phenomenon of a river system which occupies a unique position in the culture, society and economy of Bangladesh. There are 257 rivers in Bangladesh, from which 59 rivers are transboundary rivers. All of these rivers play a prospective role in the economic development of the country. The deltaic floodplains of the Ganges–Brahmaputra–Meghna Rivers Delta are undergoing rapid hydro-morphological changes due to natural and anthropogenic causes. Historically, these three rivers have played a strong role in formation of deltaic floodplains and wetland ecosystems in the Ganges–Brahmaputra–Meghna (GBM) Rivers Delta. The GBM rivers system is continuously developing the active deltaic floodplains in the coastal region of Bangladesh. The deltaic wetlands are under threat due to extension of agricultural land use, shrimp cultivation, and saline water intrusion in the tidally active delta region. The main reasons of ecosystem degradation are the settlements development, urbanization processes and substantial uses of deltaic natural resources. The study investigated the role of river systems in the formation and development process of delta and salinity intrusion and its impact on wetland ecosystems in the tidally active deltaic floodplains in the coastal region. The objective of this study is to understand the role of river systems in the delta formation process and an analysis of deltaic floodplain and degraded wetland ecosystems of the Ganges–Brahmaputra–Meghna Rivers Delta in Bangladesh.

Floodplain forests of the Iberian Peninsula: Vegetation classification and climatic features

AbstractAimsTo produce a formalized classification of floodplain forests in the Iberian Peninsula and to assess their main bioclimatic gradients.LocationIberian Peninsula.MethodsA data set with more than 3000 vegetation plots of floodplain forests was compiled from vegetation‐plot databases, while climatic data were derived from a digital climatic atlas. After filtering of plots according to their area and geographic stratification, 1892 plots were used to build a typology from association to order level using multivariate classification methods (Fuzzy C‐means, agglomerative hierarchical clustering). The phi fidelity index was used to determine the diagnostic species of the syntaxa in the proposed classification. Main climatic gradients were explored using non‐metric multidimensional gradient analysis, and ANOVA was carried out in order to define the bioclimatic features of Iberian floodplain forests.ResultsA total of 41 floodplain forest associations were distinguished for the Iberian Peninsula, grouped in nine suballiances, four alliances and two orders. Mediterraneity (summer aridity) was the main climatic driver, as it separates the temperate floodplain forests of the order Alno‐Fraxinetalia from the Mediterranean forests of the Populetalia albae. Continentality and precipitation were mainly relevant at alliance level, as they separated both the temperate alliances Alnion and Hyperico‐Alnion, the latter more oceanic, and the Mediterranean alliances Populion and Osmundo‐Alnion, the latter from more rainy areas. Temperature was an important driver at association level, as the associations included in the same suballiance or alliance differed regarding their thermicity index.ConclusionsOur study develops the first formalized classification of Iberian floodplain forests and provides their bioclimatic diagnosis. One new alliance, Hyperico‐Alnion, is proposed for floodplain forests of the Cantabrian watershed. Mediterraneity, continentality and precipitation drive floodplain forest diversity at broad scale, while temperature is the main bioclimatic driver at fine scale. The proposed classification provides the scientific basis for the conservation of this habitat type, with high conservation priority, in southern Europe.

Conceptual hydrogeological model for a landfill in a floodplain environment: case study of the JV Industries and Fairway Landfill, Shxwhá:y Village First Nation, Chilliwack, B.C.

The characteristics of floodplains of major rivers are of interest to many shoreline communities due to issues related to flooding, water demand, and land use. Studies of the hydrogeological conditions within these environments can improve our understanding of these settings. The case study of the JV Industries and Fairway Landfill, located within the floodplain of the Fraser River, highlights the complex groundwater flow dynamics in such an environment. In particular, the study examined the potential for substantial changes to both groundwater flow and groundwater quality during or immediately following the spring freshet due to the presence of permeable, extensive, and hydraulically well-connected floodplain deposits. During spring and early summer, groundwater flow across the landfill is controlled primarily by the Fraser River freshet and the direction of flow varies spatially across the site. During the winter, groundwater flow is controlled primarily by regional topography and is directed to the southwest towards the nearest topographic depression, the remnant Coco-oppelo Slough. In the intervening months, the flow directions are transitional between the winter and spring – early summer flow patterns. The changes in the groundwater flow patterns were inferred to temporally affect the groundwater quality downgradient of the landfill.

Spatio-temporal patterns of major bacterial groups in alpine waters.

Glacial alpine landscapes are undergoing rapid transformation due to changes in climate. The loss of glacial ice mass has directly influenced hydrologic characteristics of alpine floodplains. Consequently, hyporheic sediment conditions are likely to change in the future as surface waters fed by glacial water (kryal) become groundwater dominated (krenal). Such environmental shifts may subsequently change bacterial community structure and thus potential ecosystem functioning. We quantitatively investigated the structure of major bacterial groups in glacial and groundwater-fed streams in three alpine floodplains during different hydrologic periods. Our results show the importance of several physico-chemical variables that reflect local geological characteristics as well as water source in structuring bacterial groups. For instance, Alpha-, Betaproteobacteria and Cytophaga-Flavobacteria were influenced by pH, conductivity and temperature as well as by inorganic and organic carbon compounds, whereas phosphorous compounds and nitrate showed specific influence on single bacterial groups. These results can be used to predict future bacterial group shifts, and potential ecosystem functioning, in alpine landscapes under environmental transformation.

Effects of stormwater management and stream restoration on watershed nitrogen retention

Restoring urban infrastructure and managing the nitrogen cycle represent emerging challenges for urban water quality. We investigated whether stormwater control measures (SCMs), a form of green infrastructure, integrated into restored and degraded urban stream networks can influence watershed nitrogen loads. We hypothesized that hydrologically connected floodplains and SCMs are “hot spots” for nitrogen removal through denitrification because they have ample organic carbon, low dissolved oxygen levels, and extended hydrologic residence times. We tested this hypothesis by comparing nitrogen retention metrics in two urban stream networks (one restored and one urban degraded) that each contain SCMs, and a forested reference watershed at the Baltimore Long-Term Ecological Research site. We used an urban watershed continuum approach which included sampling over both space and time with a combination of: (1) longitudinal reach-scale mass balances of nitrogen and carbon conducted over 2 years during baseflow and storms (n = 24 sampling dates × 15 stream reaches = 360) and (2) 15N push–pull tracer experiments to measure in situ denitrification in SCMs and floodplain features (n = 72). The SCMs consisted of inline wetlands installed below a storm drain outfall at one urban site (restored Spring Branch) and a wetland/wet pond configured in an oxbow design to receive water during high flow events at another highly urbanized site (Gwynns Run). The SCMs significantly decreased total dissolved nitrogen (TDN) concentrations at both sites and significantly increased dissolved organic carbon concentrations at one site. At Spring Branch, TDN retention estimated by mass balance (g/day) was ~150 times higher within the stream network than the SCMs. There were no significant differences between mean in situ denitrification rates between SCMs and hydrologically connected floodplains. Longitudinal N budgets along the stream network showed that hydrologically connected floodplains were important sites for watershed nitrogen retention due to groundwater–surface water interactions. Overall, our results indicate that hydrologic variability can influence nitrogen source/sink dynamics along engineered stream networks. Our analysis also suggests that some major predictors for watershed N retention were: (1) streamwater and groundwater flux through stream restoration or stormwater management controls, (2) hydrologic residence times, and (3) surface area of hydrologically connected features.

Bifurcation instability and chute cutoff development in meandering gravel-bed rivers

Chute cutoffs reduce sinuosity of meandering rivers and potentially cause a transition from a single to a multiple channel river. The channel bifurcation of the main channel and the mouth of the incipient chute channel controls sediment and flow partitioning and development of the chute. Recent channel bifurcation models suggest that upstream bend radius, gradient advantage, inlet step, and upstream sediment supply at the bifurcation are important factors in the evolution of bifurcations. Our objective is to unravel the relative importance of these factors for chute cutoff success and development. We compare results from a morphodynamic three-dimensional (3D) model and a one-dimensional (1D) model with nodal-point relation with field observations of chute cutoffs in a meandering gravel-bed river. The balance between increased gradient advantage and flow curvature upstream of the chute channel bifurcation was systematically investigated with the 1D model. The 3D model runs and the field observations show the development of two types of chute cutoffs: a scroll-slough cutoff and a bend cutoff. The morphodynamic 3D model demonstrates that chutes are initiated when flow depth exceeds the floodplain elevation. Overbank flow and a significant gradient advantage result in a bend cutoff. The outcome of the 1D model shows that channel curvature at the bifurcation determines the success or failure of the chute cutoff when the chute channel is located at the inner bend, as in the case of scroll-slough cutoffs. We conclude that chute initiation depends on floodplain characteristics, i.e., floodplain elevation, sediment composition, and the presence of vegetation. Chute cutoff success or failure is determined by the dynamics just upstream of the channel bifurcation and location of the chute channel in the bend, which determines channel curvature and gradient advantage. These findings have ramifications for the prediction of chute cutoff in a wide range of rivers under natural and managed conditions and for the understanding of stratigraphy and architecture of deposits.

Glacially conditioned specific stream powers in low-relief river catchments of the southern Laurentian Great Lakes

Fluvial systems of the southern Laurentian Great Lakes region are carved into a complex glacial landscape shaped by continental ice and meltwater of the late Pleistocene. These glacially conditioned river catchments are typically small with drainage areas <104km2. A 10-m digital elevation model (DEM) is used to map the spatial distribution of stream gradient for 22 major river catchments of peninsular southern Ontario, which drain to base levels in the lower Great Lakes (Huron, St. Clair, Erie, and Ontario). Raw data from the DEM show stream gradients that exhibit multiscale variance from real and from artifact sources. Based on a vertical slice and multiple-pass moving-window averaging approach, slope data are generalised to the river reach scale (1–2km) as a representative spatial scale for fluvial processes operating over Holocene timescales. Models of specific stream power are then compared with glacial landform and surface geology mapping. Inherited glacial signatures in river slope appear as deviations in a stream length-gradient index (SL/K index), where river reaches are frequently oversteepened or understeepened. Based on a slope–area analysis, and complementary to theories of channel pattern discrimination, constant stream power curves (with power-law exponent of −0.4) provide a first-order approach to stratify river reaches in terms of glacial conditioning and expected planform morphologies. However, multiple-channel planform types are rare and localised in southern Ontario, indicating that oversteepened reaches with high stream powers may often be moderated by (1) sediment calibre, with cobble-beds from inherited glacial sediments; and/or (2) relative bank strength, with limited channel widening particularly in gravel and sand-bed channels. Further discrimination of glacially conditioned fluvial process domains will ultimately require consideration of alluvial floodplain characteristics in addition to general observations of river morphology and channel pattern.

Integrative Method for Quantifying Floodplain Habitat

AbstractRestoring functional, self-sustaining floodplain habitats requires explicit consideration of the flow dynamics that once created healthy floodplain ecosystems. This paper describes a new method for quantifying the benefits of river projects by linking the spatial and temporal characteristics of floodplains to define the functional habitat they create. Combining standard hydrologic and hydraulic analysis, habitat can be quantified using area-duration-frequency (ADF) curves for several durations and across multiple frequencies of flood occurrence. From this, a value can be created for expected annual habitat (EAH) analogous to expected annual damages (EAD) used in flood risk analysis. To illustrate this method, a modeling case study was conducted on the Lower San Joaquin River in California. The case study shows that a levee setback to restore floodplain connectivity could benefit splittail fish populations but not rearing salmonids. The development of ADF curves and EAH values is a transparent and ...

TerEx Toolbox for semi‐automated selection of fluvial terrace and floodplain features from lidar

ABSTRACTTerraces and floodplains are important indicators of near‐channel sediment dynamics, serving as potential sediment sources and sinks. Increasing availability of high resolution topography data over large areas calls for development of semi‐automated techniques for identification and measurement of these features. In this study we introduce a novel tool that accommodates user‐defined parameters including, a local‐relief threshold selected by a variable‐size moving window, minimum area threshold, and maximum distance from the channel to identify and map discrete terrace and floodplain surfaces. Each of the parameters can easily be calibrated for a given watershed or reach. Subsequently, the tool automatically measures planform area, absolute elevation, and height relative to the local river channel for each terrace polygon. We validate the tool in two locations where terrace maps were previously developed via manual digitization from lidar and extensive field mapping campaigns. The tool is also tested on six different types of rivers to provide examples of starting selection parameters, and to test effectiveness of the tool across a wide range of landscapes. Generally, the tool provides a high quality draft map of terrace and floodplain surfaces across the wide range of environmental conditions for which it has been tested. We find that the tool functions best in catchments where the terraces are spatially extensive, with distinct differences between the terrace and floodplain. The most challenging environments for semi‐automated terrace and floodplain mapping include steep catchments with dense riparian vegetation, and very small terraces (~10 m2 in areal extent). We then apply the tool to map terraces and floodplains in the Root River watershed, southeastern Minnesota and generate exceedance plots for terrace heights. These plots provide a first pass analysis to indicate the tributaries and reaches of the river where terraces constitute a significant source of sediment. Copyright © 2013 John Wiley &amp; Sons, Ltd.