Channel planform and land cover changes on a mined river floodplain: Amite River, Louisiana, USA (original) (raw)
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Channel planform and land cover changes on a mined river floodplain
Applied Geography, 1997
The Amite River in southeastern Louisiana, USA, is a disturbed floodplain and channel, where combined gravel and sand extraction has exceeded 10 million tons per year. To examine relationships between mining and channel change along this river, land cover data from a 55-km floodplain reach with variable mining intensity were compiled from photographic, map and documentary sources for two different time periods. These data were manipulated using a geographic information system and analysed using nonparametric statistics, producing statistically robust, moderate correlations between the degree of floodplain mining and change in channel position. The approach and results have application in research, planning and management concerning floodplain disturbances and channel instability.
Floodplain and instream mining are activities that generally increase channel change or instability. To quantify this effect, it is necessary to have some idea of natural or baseline rates of change in rivers in the same region where stream have similar topography, climate, geologic units and vegetation. The Pascagoula River and its tributaries traverse a number of geologic units and the basin shows a diverse set of land cover and land uses, including two streams with considerable historical and recent mining activity. This study quantifies the rates of change in the Pascagoula and some of its tributaries, suggesting at which point planform changes are clearly modified, directly or indirectly, more so by human action. This is done by digitizing the larger and mined tributaries of this system in a GIS using varied sources of data (aerial photographs, topographic maps and digital ortho quarter quadrangles). Polygon areas derived from overlays characterizing changes (areas of erosion, deposition, no change, and areas between channels) in channel position and planform were extracted from the GIS and normalized for scale, so that larger rivers could be compared with the headwaters, as well as smaller rivers and creeks. This study provides insights into the natural factors and anthropogenic activities that influence channel changes in this basin, and thus where future change might be expected to occur. Those insights, in turn, can be applied to management and engineering in the basin.
Pit avulsions and planform change on a mined river floodplain: Tangipahoa River, Louisiana
Physical Geography, 2011
Floodplain mining creates a vulnerable landscape comprised of pits, bare land and stock piles with minimal vegetation. During floods, when stages can exceed bankfull by several meters, all or part of the channel may divert into a pit, re-routing the flow and transforming the planform and profile of alluvial landscapes. Using geospatial data from the mined Tangipahoa River floodplain for 1980 to 2004, the objectives of this study are to (1) assess if pit characteristics, proximity to channel, and size affect the potential for diversion; and (2) interpret relationships between pit diversions, channel changes, and floods. Of the 56 pits mapped in the floodplain in 1980, six had been captured by 2004. Captured pits were closer to the main channel than those which were not captured, but the areas of captured and noncaptured pits were not significantly different. However, avulsions into large pits caused more channel planform change than those into smaller pits. Other findings are that point bar areas increased 72% overall, more so in the mined reach, and that degradation exceeded 6 m in the mined reach, in contrast with aggradation of 1 m roughly 20 valley km downstream. Results will be useful in understanding landscape vulnerability and can be applied to river management and restoration. [
Physical Geography, 2011
This set of eight papers, four in this special issue of Physical Geography and four in the forthcoming issue (Vol. 32, No. 6), resulted from a special session on the geomorphology and physical geography of medium-sized watersheds at the meeting of the Southeastern Division of the Association of American Geographers (SEDAAG) held in November 2010 in Birmingham, Alabama. Medium-sized rivers are generally large enough to contain multiple zones, in which different geomorphic processes may be dominant. In their headwaters, known as Zone 1, low-order streams dominate and have a unique signature in terms of water quantity, water quality, hillslope sediment, and nutrients provided from local contributing areas . As tributaries converge into higher-order rivers, the Zone 2 or transfer zone takes on greater relative importance. Geomorphic investigations in this zone require integration of multiple inputs from the larger drainage area and consideration of lag times, from initial landscape disturbance to changes in sediment delivery and channel and floodplain morphology. Generally, sediment input can equal output if a stream is stable in the transfer zone, but it is usually disrupted when anthropogenic disturbances are prevalent, a theme that is explored in a number of the papers in this issue.
Scientific Investigations Report, 2006
A multiscale geomorphic classification was established for three segments of the Missouri River on the border of South Dakota and Nebraska: the 39-mile and 59-mile segments of the Missouri National Recreational River administered by the National Park Service, and an adjacent segment, Kensler's Bend. The objective of the classification was to define naturally occurring clusters of geomorphic characteristics that would be indicative of discrete sets of geomorphic processes (process domains), with the intent that such a classification would be useful in river-management and rehabilitation decisions. The statistical classification was based on geomorphic characteristics of the river collected from 1999 digital aerial orthophotography. Persistence of classified units was evaluated by comparison with similar datasets for 2003 and 2004. Changes in channel location and form were also explored using imagery and maps from 1993 to 2004, 1941, and 1894. The multivariate classification identified a hierarchy of naturally occurring clusters of reach-scale geomorphic characteristics. The simplest level of the hierarchy divides the river from segments into discrete reaches characterized by single and multithread channels. Additional hierarchical levels established 4-part and 10-part classifications. The utility of the classifications was established by exploring persistence of classified units over time and by evaluating variation of bank erosion rates by geomorphic class. The classification system presents a physical framework that can be applied to prioritization and design of bank-stabilization projects, design of habitat-rehabilitation projects, and stratification of monitoring and assessment sampling programs.
Channel and Floodplain Change Analysis over a 100-Year Period: Lower Yuba River, California
Remote Sensing, 2010
Hydraulic gold mining in the Sierra Nevada, California (1853-1884) displaced ~1.1 billion m 3 of sediment from upland placer gravels that were deposited along piedmont rivers below dams where floods can remobilize them. This study uses topographic and planimetric data from detailed 1906 topographic maps, 1999 photogrammetric data, and pre-and post-flood aerial photographs to document historic sediment erosion and deposition along the lower Yuba River due to individual floods at the reach scale. Differencing of 3 × 3-m topographic data indicates substantial changes in channel morphology and documents 12.6 × 10 6 m 3 of erosion and 5.8 × 10 6 m 3 of deposition in these reaches since 1906. Planimetric and volumetric measurements document spatial and temporal variations of channel enlargement and lateral migration. Over the last century, channels incised up to ~13 m into mining sediments, which dramatically decreased local flood frequencies and increased flood conveyance. These adjustments were punctuated by event-scale geomorphic changes that redistributed sediment and associated contaminants to downstream lowlands.
Wetlands, 2009
Human alterations along stream channels and within catchments have affected fluvial geomorphic processes worldwide. Typically these alterations reduce the ecosystem services that functioning floodplains provide; in this paper we are concerned with the sediment and associated material trapping service. Similarly, these alterations may negatively impact the natural ecology of floodplains through reductions in suitable habitats, biodiversity, and nutrient cycling. Dams, stream channelization, and levee/canal construction are common human alterations along Coastal Plain fluvial systems. We use three case studies to illustrate these alterations and their impacts on floodplain geomorphic and ecological processes. They include: 1) dams along the lower Roanoke River, North Carolina, 2) stream channelization in west Tennessee, and 3) multiple impacts including canal and artificial levee construction in the central Atchafalaya Basin, Louisiana. Human alterations typically shift affected streams away from natural dynamic equilibrium where net sediment deposition is, approximately, in balance with net erosion. Identification and understanding of critical fluvial parameters (e.g., stream gradient, grain-size, and hydrography) and spatial and temporal sediment deposition/erosion process trajectories should facilitate management efforts to retain and/or regain important ecosystem services.
2005
A variety of fluvial geomorphic assessment methods, such as TMDL development, biological habitat quality assessment, and overall channel characterization, have been developed and are being adopted by organizations for use in assessing stream conditions for a variety of purposes. This paper first summarizes available stream geomorphic assessment methods, detailing their strengths and weaknesses. Then we describe an actual project conducted by Tetra Tech in Griffin, Georgia to show how assessment methods were selected to suit a particular application and how the results were presented to maximize usefulness to the client. The stream channel stability study was conducted on Shoal Creek for the City of Griffin, Georgia, Public Works and Stormwater Department. The focus of the study was to qualitatively assess the potential availability of sediment from channel sources so that the findings could be used to address downstream sedimentation issues. Time and funding constraints led to choosing a qualitative rapid geomorphic assessment method whereby channel evolution and other easily observable field data were collected for the entire watershed. Assessed reaches were then classified by degree of channel stability with results presented as a set of correlated maps, data tables, photographs, and reach narratives. This data set enabled stormwater management decision makers for the City of Griffin to prioritize the specific erosion hot spots for mitigation.
Earth Surface Processes and Landforms, 2003
A digital elevation model (DEM) of a fluvial environment represented landform surface variability well and provided a medium for monitoring morphological change over time. Elevation was measured above an arbitrary datum using a ground-based three-dimensional tacheometric survey in two reaches of the River Nent, UK, in July 1998, October 1998 (after flood conditions) and June 1999. A detailed geostatistical analysis of the elevation data was used to model the spatial variation of elevation and to produce DEMs in each reach and for each survey period. Maps of the difference in elevation were produced and volumetric change was calculated for each reach and each survey period. The parameters of variogram models were used to describe the morphological character of each reach and to elucidate the linkages between process and the form of channel change operating at different spatial and temporal scales.The analysis of channel change on the River Nent shows the potential of geostatistics for investigating the magnitude and frequency of geomorphic work in other rivers. A flood modified the channel features, but low magnitude and high frequency flows rationalized the morphology. In spite of relatively small amounts of net flux the channel features changed as a consequence of the reworking of existing material. The blocking of chute entrances and redirection of the channel had a considerable effect on the behaviour of the channel. Such small changes suggested that the distributary system was sensitive to variation in sediment regime.Plots of the kriging variances against sampling intervals were used to quantify the temporal variation in sampling redundancy (ranging between −11 per cent and +93 per cent). These curves illustrated the importance of bespoke sampling designs to reduce sampling effort by incorporating anisotropic variation in space and geomorphic information on flow regime. Variation in the nugget parameter of the variogram models was interpreted as sampling inaccuracy caused by variability in particle size and is believed to be important for future work on surface roughness. Copyright © 2003 John Wiley & Sons, Ltd.
Can an annual flood induce changes in channel geomorphology?
Natural Hazards
The present study has been a pioneering effort examining the role of an annual flood as a potent stimulus inducing changes in channel geomorphology of the Mayurakshi River, India. Twenty cross sections have been considered for the measurement of various hydrogeomorphic attributes of the river in both the pre-and post-flood conditions in 2018. The study sensed an escalating trend for channel width, width/depth ratio, and wetted perimeter while the reverse was also detected for average depth, maximum depth, cross-sectional area, and hydraulic radius. For example, the width/depth ratio recorded an increase of ~ 11%, and the hydraulic radius depicted a decrease of ~ 8%. Furthermore, channel asymmetry, bed asymmetry and bed relief index experienced a decrease after the flood. The sudden hydraulic impulse during monsoon flood as manifested in velocity, discharge, specific stream power, Reynolds number, Froude number increases the erosivity of the fluid. Besides the hydraulic factors, bank material (massive sandbank susceptible to hydraulic action and mixed bank constituted by alternate bands of sand and silt, and vulnerable to failure by piping action) brings substantial changes in channel morphology. Moreover, anthropogenic interventions such as sand mining are found to play a significant role in channel behaviour. The role of the multiple factors driving the morphological changes of the cross sections has been unpacked using canonical component analysis.