Paul F. Hudson

Channel migration and meander-bend curvature in the lower Mississippi River prior to major human modification

Channel migration and meander-bend morphology are examined for the lower Mississippi River between 1877 and 1924, prior to channel cutoffs, revetments, and change in sediment regime. The spatial pattern of meander-bend migration coincides with differences in flood-plain deposits. Migration of meander bends averaged 45.2 m/yr in the upper alluvial valley, where there are numerous clay plugs, but increased to 59.1 m/yr in the lower alluvial valley, where there are fewer clay plugs in contact with the channel. The highest migration rates occurred with meander bends having a curvature, r m / W m (ratio between meander-bend radius to channel width) between 1.0 and 2.0, which is a departure from previous models. Results from this study suggest that rivers with complex flood-plain deposits exhibit patterns and relationships that deviate from models derived in homogeneous flood-plain deposits.

Event sequence and sediment exhaustion in the lower Panuco Basin, Mexico

Abstract Although large tropical river systems transport the majority of the worlds runoff and sediment, few studies have examined the dynamics of suspended sediment transport in this setting. This includes Mexico, which contains two of the larger river basins draining into the Gulf of Mexico. This study provides a detailed analysis of discharge (Q) and suspended sediment transport dynamics for the lower Panuco basin (98,227 km2) of eastern Mexico, including the lower Moctezuma, lower Tamuin, and Panuco rivers. Daily values of discharge and suspended sediment concentration (SSC) are examined for three stations, spanning from the late 1950s to early 1990s. Although the Panuco is a large basin, the relationship between discharge and suspended sediment concentration represents a departure from the oft-reported study by Heidel [Trans. - Am. Geophys. Union 37 (1956) 56]. Instead of sediment lagging discharge, the sediment wave precedes discharge by an average of 1.7 days, displaying pronounced clockwise (positive) hysteresis. This may be due to the sources of runoff and sediment, which are derived primarily in the lower reaches of the basin because of precipitation patterns, geology, and basin morphometry. The distinct differences in lithology between the Tamuin and Moctezuma basins, which join in the coastal plain to form the Rio Panuco, allow the influence of geologic setting to be considered. Q–SSC relations display positive hysteresis where the sediment is derived from erodible Tertiary shale deposits in the Moctezuma basin. In contrast, Q–SSC relations in the Rio Tamuin, which transports less suspended sediment because of its karstic setting, are more linear due to these relations being dependent on the entrainment of bed material. Consideration of the sequence of events during the rainy season suggests that much of the hillslope-derived sediment is flushed through the system by early events, which would occur because of exhaustion of hillslopes sediments. Q–SSC relations are increasingly linear during later events in the Rio Panuco, which is likely due to these events transporting a higher proportion of sediment entrained from the channel. This is manifest by a reduction in lead times, as the number of days between peak SSC and peak Q for early and late events significantly decreases from 2.6 to 0.9, respectively. Large events (>750 m3/s) in the latter part of summer and early fall having high suspended sediment concentrations could be due to the replenishment of hillslope sediments, or due to the contribution of sediment from source areas that were not previously exhausted. The findings from this study are likely common to most drainage systems having seasonal bimodal streamflow regimes, whereas the seasonal signature of Q–SSC relations is likely enhanced in those settings where agriculture is a major component of the landscape.

Flood delineation in a large and complex alluvial valley, lower Pánuco basin, Mexico

Determining the extent of flooding is an important role of the hydrological research community and provides a vital service to planners and engineers. For large river systems located within distant settings it is practical to utilize a remote sensing approach. This study combines a remote sensing and geomorphic approach to delineate the extent of a large hurricane generated flood event in the lower Panuco basin (98,227 km2), the seventh largest river system draining into the Gulf of Mexico. The lower Panuco basin is located within the coastal plain of eastern Mexico and has a complex alluvial valley. Data sources included a Landsat 5TM and Landsat 7ETM+ scene, and topographic and particle size data from fieldwork and laboratory analysis. The Landsat 5TM image was acquired after the peak of a large flood event in 1993, whereas the Landsat 7ETM+ scene was acquired during the dry season in 2000. The increasing number of days between flood crest and the date of flood image acquisition along the river valley provided the opportunity to examine several methods of flood delineation and to consider differences in floodplain geomorphology. Backswamp environments were easily delineated in flooded reaches within the Panuco and Tamuin valleys, whereas in the Moctezuma valley more sophisticated methods were required because of the greater time between image acquisition and flood peak, and the complex floodplain topography. This included Principal Component (PC) analysis and image classification. Within the floodplain, residual Holocene terraces complicated flood mapping. Classification of both images allowed consideration of the influence of permanent standing water. Although the flooded areas were greater in the lower reaches of the study area, because this portion of the valley contained large floodplain lakes, the amount of inundation was actually lower. Remote sensing offers the ability to examine large alluvial valleys in distant settings but does not imply that geomorphic criteria should be excluded. Indeed, because of heterogeneous floodplain topography this study illustrates the importance of including field based geomorphic analysis so that the complexity of distinct floodplain environments are considered. The findings from this study are significant because most remote sensing data obtained for the purpose of flood mapping will not coincide with the flood crest. Thus, this study provides an appropriate method for mapping flood inundation in large and complex floodplain settings after flood crest recession.

Hydrologic and geomorphic processes in the Colville River delta, Alaska

The Colville basin drains the North Slope of Alaska and is one of several large Arctic river systems located within permafrost. The timing and style of fluvial processes in the earths permafrost regions differ from those occurring in midlatitude settings. Moreover, in comparison to temperate-zone systems, rivers located entirely within permafrost perform most of their work during relatively short periods of time. This paper examines river ice hydrology and the resulting geomorphic processes that occur within the Colville delta, Alaska. Fluvial processes and landform development within the Colville delta occur after the flood-pulse is initiated by the breakup of river ice. During this 4-month period, the geomorphic processes are largely influenced by the movement of ice. The flood-pulse and accompanying river ice influences erosional and depositional processes and results in unique styles of sediment transport, deposition, and riverbank erosion.

Local- and watershed-scale controls on the spatial variability of natural levee deposits in a large fine-grained floodplain: Lower Panuco Basin, Mexico

This study examines spatial variations in natural levee deposits within the lower reaches of a large coastal plain drainage system. The Panuco basin (98,227 km 2 ) drains east-central Mexico, and is an excellent setting to examine the influence of watershed and local controls on the morphology and sedimentology of natural levees. Although many fluvial systems in the U.S. Gulf Coastal Plain have been investigated, the rivers in the Mexican Gulf Coastal Plain have received comparatively little attention. Lateral and downstream characteristics of natural levee morphology and sediment texture are considered within the context of meandering river floodplain deposits. Data sources include total-stations surveying, sediment samples of surficial levee deposits, topographic maps (1:50,000), and aerial photographs (1:40,000). The slope of natural levees average 0.0049 m/ m, whereas the texture (D84) of levee deposits averages 0.12 mm. Natural levee characteristics vary due to local- and watershed- scale controls. The lateral reduction in levee height displays a curvilinear pattern that coincides with an abrupt change in sediment texture. The downstream pattern of natural levee texture exhibits the influence of local-scale perturbations superimposed upon a larger watershed-scale trend. Disruption to the fining trend, either by tributary inputs of sediment or reworking of Tertiary valley deposits, is retained for a limited distance. The influence of the channel planform geometry on levee morphology is examined by consideration of the radius of curvature (Rc) of meander bends, and is inversely related to natural levee width. This suggests that the planform geometry of river channels exerts a control on the dispersal of flood sediments, and is responsible for considerable local variability in the floodplain topography. The average width of natural levees increases with drainage area, from an average of 747 m in the Moctezuma to an average of 894 m in the Panuco. However, in the lower reaches of the Panuco valley the width of natural levees rapidly decreases, which is associated with fining of the suspended sediment load. Thus, the reduction in natural levee width signifies an abrupt change in the directionality of cause- effect relationships at the watershed-scale. Findings from this study elucidate linkages between meandering river channels and floodplains for a large lowland alluvial valley. D 2003 Elsevier Science B.V. All rights reserved.

23 – Rivers of Mexico

This chapter discusses the physical and biological features of five major Mexican rivers—the Rio Panuco, Usumacinta–Grijalva rivers, Rio Candelaria, the Yaqui, and the Rio Conchos. Five additional rivers—the Chihuahuan Deserts Rio Salado; the Rio Tamesi, which joins the Rio Panuco near its mouth; the Rio Fuerte, which flows through some of the continents largest canyons in the Sierra Madre Occidental to the Gulf of California south of the Yaqui and Mayo rivers; the Ayuquila–Armeria river system, which empties into the Pacific Ocean; and the Rio Lacanja, a small mountainous tributary of the Usumacinta—are also briefly reviewed. The history of human impacts on Mexicos rivers includes many groups of prehistoric inhabitants. Mexicos major rivers are highly exploited. Construction of dams, primarily for crop irrigation in otherwise desert environments, is one of the major factors. Water pollution from discharge of domestic wastes, high salinity, and nutrients from irrigation returns, mining, and industrial wastes is widespread throughout Mexico. With the increase in population and associated land-use change and generally limited resources available for conservation of natural resources the scenario of the rivers are becoming much worse.

Landscape Complexity and Remote Classification in Eastern Coastal Mexico: Applications of Landsat‐7 ETM+ Data

Abstract This paper addresses multiple semi‐automated methods for discriminating landuse/landcover (LULC) classification in the absence of field data. The study site comprises a heterogeneous mixture of physiographic landscape elements in a remote area of eastern Mexico. Classification of modified Tasseled Cap transformations as well as a hybrid unsupervised‐supervised classification technique were employed using a Landsat 7ETM+ scene; the panchromatic band was reserved for accuracy assessment. Using a random stratified sampling scheme, overall accuracies ranged from 61.5% to 83.3% and Khat accuracies varied from 56% to 81.1%. The classifications derived from modified Tasseled Cap transformations did not appropriately discriminate landscape components, possibly owing to landscape heterogeneity. Classification results were improved through the use of landscape stratification in the attribution phase in the hybrid classification procedure, recommended for complex environments. Lastly, this work underscores the emerging importance of reserving Landsat 7ETM+ panchromatic information for accuracy assessment when field data are lacking.

The Influence of the El Niño Southern Oscillation on Suspended Sediment Load Variability in a Seasonally Humid Tropical Setting: Panuco Basin, Mexico

ABSTRACT Although large tropical rivers transport the majority of suspended sediment to the oceans, because of a lack of adequate data there have been few detailed studies of sediment transport and its relationship to drainage basin processes. This study examines sediment transport variability in the lower Panuco basin of east‐central Mexico using daily values of streamflow and suspended sediment load spanning from the late 1950s to early 1990s. These data are used to estimate sediment yield, and in considering the influence of El Niño and La Niña events on geo‐morphic processes. Annually, the Rio Panuco transports an average of 56267×103 tons of sediment. Substantial differences in sediment transport between the Rio Moctezuma and Rio Tamuin, large basins that join to form the Rio Panuco in the Gulf Coastal Plain, are related to lithologic variability. The Panuco basin has a sediment yield of 74.1 tons (km2/yr). However, sediment load varied considerably during the period of analysis due to the influence of the El Niño Southern Oscillation (ENSO). Although a number of studies have considered the hydrologic significance of ENSO events, few have systematically considered the geomor‐phic implications of both El Niño and La Niña events. Results from this study are significant because, in comparison to adjacent regions that are dominated by El Niño events, in the Panuco basin La Niña events are more significant in terms of streamflow and sediment production. In comparison to El Niño events, stream‐flow and sediment loads are 45% and 120% greater during summer La Niña events, respectively. This suggests that increases in runoff associated with wetter La Niña conditions result in disproportionate geomorphic responce. In comparison to the Tamuin basin, sediment loads are much greater in the Moctezuma basin, which illustrates that the influence of ENSO is greater in regions underlain by clastic deposits rather than limestone. This study is significant because it systematically illustrates the significance of ENSO events to geomorphic processes within a large basin located within the seasonally humid tropics.

POOL-RIFFLE MORPHOLOGY IN AN ACTIVELY MIGRATING ALLUVIAL CHANNEL: THE LOWER MISSISSIPPI RIVER

This study analyzes the pool-riffle morphology of the Lower Mississippi River within the context of an actively migrating meandering river. Historic hydrographic surveys (1:20,000) from the late 1800s and early 1900s document the natural channel morphology of the Lower Mississippi, and are used to construct a 1225-km profile of the channel thalweg. Previous studies suggest that pools and riffles are limited to gravel bed channels. This study documents their occurrence within a large fine-grained channel, and illustrates the importance of these features within the context of meandering processes. The channel width at riffles is significantly greater than at pools, and the spacing of pools is scale dependent, averaging 7.2 channel widths. Extreme values occur where heterogeneous channel deposits control the channel alignment. Meander-bend radius of curvature and pool depth is inversely related, which would occur because of the enhancement of helical flow and channel bed shear stress associated with sharper meander-bend curvature. The migration of meander bends increases with pool depth. However, the adjustment of pool depth is inversely related to meander-bend migration. Higher rates of lateral migration are associated with a reduction in pool depth, while meander bends that were less active laterally were more effective at scouring the channel and thereby increasing the depth of pools. The results of this investigation of a large and complex alluvial channel provides linkages with detailed studies that document the mechanisms of meander-bend processes within individual channel reaches and laboratory flumes. Findings suggest that the pool-riffle adjustment of meander bends occurs synchronously with planform adjustment, and as suggested by Keller and Melhorn (1978), represents meandering in the vertical dimension.

Overbank sedimentation from the historic A.D. 2011 flood along the Lower Mississippi River, USA

In this study, we document sedimentary characteristics of overbank flood deposits associated with the epic A.D. 2011 flood along the Lower Mississippi River (southern USA) and directly compare the findings to sedimentation from a comparable flood event in 1973, with the general purpose of understanding how extreme floods contribute to floodplain depositional patterns and accretion rates of embanked fluvial systems. The thicknesses of the 2011 flood deposits averaged 138 mm along natural levee crests, 9 mm on meander scrolls, and 3 mm in backswamps. These thicknesses are considerably less than those documented for the 1973 flood, sampled at the same locations. We contend that less sedimentation in 2011 occurred because the flood was not supplied with much upstream sediment from the Missouri River. Further, the 2011 sediments are coarser than in 1973, indicating that the higher 2011 flood levels were associated with more energetic overbank flows that flushed fine-grained sediments downstream within the narrow embanked floodplain corridor. The largest recorded flood in North American history is only marginally preserved in the embanked floodplain stratigraphy of the alluvial valley of Earth’s third largest fluvial system.