Channel Pattern Changes Research Articles

The river channel pattern change as influenced by the floodplain geoecosystem: an example from the Hongshan Reservoir

The river channel pattern change as influenced by the floodplain geoecosystem: an example from the Hongshan Reservoir

Histologic Correlates of Angiographic Chronic Total Coronary Artery Occlusions: Influence of Occlusion Duration on Neovascular Channel Patterns and Intimal Plaque Composition

Objectives. Age-related changes in histologic composition and neovascular channel (NC) pattern of angiographic chronic total coronary artery occlusions (CTOs) were studied to define histologic correlates of age-related revascularization profiles and neovascular channel formation.Background. Revascularization of CTOs is frequently characterized by inability to cross or dilate the lesion and a high incidence of reocclusion or restenosis but low periprocedural ischemic complication rates. Little is known about the histopathologic basis of these observations.Methods. Ninety-six angiographic CTOs from autopsy studies in 61 patients who had undergone coronary angiography within 3 months of death were studied. Abrupt plaque rupture was excluded. Occlusion segments were analyzed for 1) histologic composition as a function of lesion age; and 2) NC pattern as a function of lesion age and intimal plaque (IP) composition.Results. Cholesterol and foam cell–laden IP was more frequent in younger lesions (p = 0.0007), whereas fibrocalcific IP increased with CTO age (p = 0.008). IP NCs arose directly from adventitial vasa vasorum and were anatomically and quantitatively related in terms of number and size (p = 0.0001) to the extent of IP cellular inflammation. IP cellular inflammation exceeded that found in the adventitia (p < 0.001) or media (p = 0.0001) across all CTO ages. In CTOs <1 year old, the adventitia was associated with a larger number and size of NCs relative to the IP (p = 0.0006 and p = 0.009), media (p = 0.0001 and p = 0.002) and recanalized lumen (p = 0.0001 and p = 0.001). In CTOs >1 year old, the adventitia and IP NC numbers were similar and exceeded NC numbers found in the media (p = 0.0001) and recanalized lumen (p = 0.0001 and p = 0.003).Conclusions. Angiographic CTO frequently corresponds to less than complete occlusion by histologic criteria. Age-related changes in IP composition from cholesterol laden to fibrocalcific may explain the adverse revascularization profile of older CTOs. IP NC growth derived from the adventitia increases with age and is strongly associated with IP cellular inflammation. IP NC formation may protect against the flow-limiting effects of IP growth.(J Am Coll Cardiol 1997;29:955–63)© 1997 by the American College of Cardiology

Reconstruction of the Ocmulgee River, Georgia: 1807-1971

Following European settlement in the late 1700s and early 1800s, the watershed of the Ocmulgee River of Georgia underwent extensive changes in land use. Although the effects of 19th and 20th century changes in land use on stream discharge and the transport of sediments have been well researched, the effect of these variations on stream-channel patterns in the Southern Piedmont and Coastal Plain has not been fully examined. In order to assess historic channel-pattern changes of the Ocmulgee River system, maps of the river channel were prepared from the available data for three time periods—1807, 1903-1910, and 1971. This paper presents the approaches used to reconstruct the Ocmulgee River at these three time periods and to illustrate the application of historical maps in determining fluvial geomorphic change. The 1807 district plats represent some of the earliest documentations of drainage systems in the southeastern United States. Examples of map production quality and tributary mapping, as well as relict riverine features visible on 1941-1969 aerial photography, substantiate the spatial accuracy of the 1807 maps. The evidence indicates that the plat maps are a reliable source of channel-course information and can be used to determine large-scale variations in the position of the Ocmulgee River.

Channel pattern change downstream from a reservoir: An example of wandering braided rivers

Reservoir-induced channel pattern change is an issue of significance both in theory and engineering practice. Based on data from three major wandering braided rivers in China, namely, the Yongdinghe, the Hanjiang and the Yellow Rivers, as well as a laboratory experimental study, this paper deals with channel pattern change downstream from reservoirs. Complex response in channel adjustment has been observed in the field, and as a result a three-stage descriptive model has been established to describe the course of channel pattern change. Also, the three stages have been simulated successfully by a laboratory physical model. Although the observed tendency of channel pattern change of the three rivers is quite different, which has been a matter of controversy for many years among Chinese researchers, it can be satisfactorily explained by the present complex response model. Because of different boundary conditions, the duration of the three stages for the three rivers is different, so the channel pattern change of the three rivers shows a different tendency at each specific stage. The present study suggests that Schumm's qualitative model for river channel metamorphosis should be modified when used for predicting reservoir-induced channel pattern change on a wandering braided river. Because the model has not taken into consideration the changing erosional resistance of channel boundary material and therefore the resultant feedback effect, it cannot predict the whole course of channel pattern change over a long period.

Channel metamorphosis, floodplain disturbance, and vegetation development: Ain River, France

The purpose of this paper is to describe and explain channel metamorphosis of the Ain River in east-central France and the effects of this metamorphosis on floodplain disturbance and vegetation development. The Ain River is a 195 km long stream originating in the Jura Mountains which flows into the Rhône River between Lyon, France, and Geneva, Switzerland. The lower 40 km of the Ain River, beyond the mountain front, are situated in a valley of outwash deposits where the floodplain is 0.2 to 1.2 km wide. A complex mosaic of floodplain landscape units has developed. Maps dating back to 1766 and six sets of aerial photographs dated between 1945 and 1991 were used to document changes in channel pattern. Aerial photos and field surveys were used to compile maps of landscape units based on dominant vegetation life-forms, species, and substrate. Six maps dated between 1945 and 1991 were digitized in ARC/INFO and an overlay was generated to determine the changes in landscape units as related to channel disturbance. Change from a braided to a single-thread meandering channel probably took place in the period 1930–1950. The process of river entrenchment has occurred throughout the Holocene but has accelerated in the present century due to shortening of the river course, construction of lateral embankments, and vegetation encroachment following reservoir construction and cessation of wood-cutting and grazing. The increase in horizontal channel stability coupled with channel entrenchment have decreased floodplain disturbance and lowered the water table by approximately one meter. Pioneer and disturbance-dependent landscape units have experienced a more terrestrial-like succession to an alluvial forest. Abandoned channels have also been replaced by alluvial forests. On poorly drained soils, shrub-swamp communities of willow and hydrophytic herbaceous plants have been replaced by mixed forests of ash, alder, black poplar, and oak. On well drained alluvial soils, ash and oak dominated hardwood forests have declined in favor of mesophytic stands of black poplar. All types of vegetation, but particularly dry grasslands-shrublands, have been cleared for mines, campgrounds, agriculture, and other types of development. Using several measures, landscape diversity decreased between 1945 and 1991.

The River Channel Pattern Change Influenced by the Floodplain Geoecosystem: an Example From the Hongshan Reservoir

Since the geoecological approach was widely introduced into geomorphologicalstudies, a new trend characterized by this approach has been formed in thegeomorphological research frontier. Starkel has applied the concept of river drainagebasin geoecosystem to the study of paleo-patterns of rivers and concluded that thechanges in the river channel patterns can be regarded as the expression of the

Longitudinal facies architectural changes of a Middle Holocene anastomosing distributary system (Rhine-Meuse delta, central Netherlands)

Longitudinal changes in channel planform and facies architecture occur over a 22-km long reach of an anastomosing Middle Holocene distributary system in the Rhine-Meuse delta (central Netherlands). A geological map and a sequence of cross sections show that the channel belt is characterized by sand body width/thickness ratios which decrease within the study area from approximately 25 upstream to well below 10 downstream, accompanied by a change in channel planform as indicated by a downstream increase of the number of crevasse splays.The lithological composition of the sand body is relatively homogeneous, but there is always a well-developed fining-upward sequence from sandy channel deposits to clayey natural levee deposits. Within-channel vertical aggradation appears to have been restricted during most of the period of activity of the distributary system, and since lateral accretion was also limited (especially in the downstream part) rapid accumulation of channel deposits seems to have occurred predominantly during the avulsion stage, leaving a narrow and shallow residual channel as the last remnant.The longitudinal change in channel pattern is mainly attributed to a downstream increase in the rate of (ground)water-level rise that resulted from Holocene sea-level rise. In the Rhine-Meuse delta a rate of (ground)water-level rise of > 1.5 mm yr−1 is required for the creation of fully developed anastomosing fluvial systems (ribbons with a width/thickness ratio of < 15 accompanied by numerous crevasse splays). Values of 1.0–1.5 mm yr−1 enable the formation of fluvial systems with fewer crevasse splays and width/thickness ratios of about 25, which are interpreted as transitional to meandering.

River management and conservation issues on formerly braided river systems; the case of the River Tay, Scotland

Abstract Although the present-day River Tay, Scotland is generally confined to a single course and exhibits limited lateral mobility, historical maps (1747–53) reveal that during the eighteenth and nineteenth centuries a braided river channel pattern was more characteristic of a number of reaches on the piedmont valley floor. Possible explanations of the change in channel pattern include flood embankment construction, flow regulation by impoundment and possibly a change in flood magnitude and frequency, and alterations in sediment supply. Areas of former braiding isolated from the main channel by embankments or incorporated into the floodplain sediments, exhibit a greater susceptibility to erosion and are prone to flood embankment breaches. In contrast, river channel reaches still exhibiting unconfined braiding tendencies have been designated areas of high conservational value due to large expanses of gravel at different stages of vegetation colonization and high plant species diversity. It is suggested that the identification of areas of former braiding and reaches prone to braiding is useful for land use management both for improved flood protection and floodplain habitat conservation.

Physiological Properties of Oligodendrocytes during Developmenta

The electrical properties of oligodendrocytes during their development in cell culture were analyzed by combining two techniques: cell identification with cell-type and stage-specific antibodies and the patch-clamp technique. The transition from the bipotential precursor cell, which can still develop into astrocytes and oligodendrocytes, into an oligodendrocyte results in a marked change in the ion channel pattern. During this developmental transition, voltage-activated Na+ and several types of K+ currents disappear, whereas a comparatively passive, inwardly rectifying K+ current becomes dominant. GABAA receptor-mediated Cl- currents and a pH-activated Na+ current are down-regulated at this transition but are still present at all developmental stages. In contrast, electrical coupling develops only in oligodendrocytes. This change in the channel repertoire could reflect the transition of a cell in a mobile, mitotic, plastic state (the glial precursor) to a more differentiated specialized state (the oligodendrocyte).

Slope‐induced changes in channel character along a gravel‐bed stream: The Allt Dubhaig, Scotland

AbstractChanges in channel character along a small river in the Scottish Highlands are described using measurements in seven reaches over a 3 km length with no significant tributaries but a decline in slope from 0.02 to 0.00015 because of local baselevel control. This decline in slope is associated with rapid downstream fining of the gravel bed followed by an abrupt transition to a sand bed. The channel pattern alters progressively rather than abruptly, in the sequence (1) near‐braided, (2) meandering with active point‐bar chutes, (3) meandering with active outer‐bank talweg, (4) stable equiwidth sinuous. The changes in channel pattern and hydraulic geometry are predicted better by rational approaches based on critical shear stress or other physical concepts than by purely empirical discriminant or trend equations. Measurements in five reaches confirm a downstream decrease in shear stress and the amount and calibre of bedload. It is argued that the downstream changes in channel character in this stream are induced by profile concavity inherited from deglacial conditions, are typical of many streams in mountainous areas and can be understood in terms of slope‐induced changes in hydraulic properties.

Braidplain Evolution in the Pennsylvanian South Bar Formation, Sydney Basin, Nova Scotia, Canada

ABSTRACT The South Bar Formation is a 1 km-thick alluvial succession in the Pennsylvanian Morien Group of the Sydney Basin, Nova Scotia that fines upward from conglomerate to pebbly sandstone to sandstone facies assemblages. The conglomerate assemblage comprises mainly massive to horizontally stratified conglomerate and planar cross-stratified sandstone, attributed to deposition in proximal braided rivers confined between bedrock ridges. The sandstone assemblage shows uniformity of facies and paleocurrents across the basin, and is interpreted as a distal braidplain deposit; the pebbly sandstone assemblage is transitional between the other two. Both sandstone assemblages are dominated by trough cross-stratified sandstone formed by dune migration in channel tracts about 4 m deep. This succession differs markedly from Platte River and Icelandic sandy braidplain deposits, which are mainly planar cross-stratified sands formed by broad, shallow flow. The South Bar sandstones are more like South Saskatchewan River deposits, but differ in 1) greater abundance of trough sets and 2) rarity of planar sets and other components of shallow water channel fill. These features are ascribed to 1) inheritance of relatively deep channels from confined upstream reaches, 2) maintenance of deep flow in active tracts by local confinement between temporary banks, and 3) rapid avulsive abandonment of active tracts, which inhibited development of channel-fill sequences. Evidence for local temporary confinement is preserved as in situ and slumped channel-margin mudrock units. Lateral and vertical transitions from the upper South Bar Formation to the mud-rich Waddens Cove and Sydney Mines Formations are ascribed to changes in channel pattern from braided to meandering. The former is attributed to decreased slope, the latter to eustatic rise in sea level.

CHANNEL PATTERN CHANGES ALONG THE LOWER OCONEE RIVER, GEORGIA, 1805/7 to 1949

Historical maps and aerial photographs of a stretch of the Oconee River channel above its junction with the Ocmulgee indicate that as erosive land use in the basin changed following European settlement so did the pattern of the river channel. Between 1805/7 and 1910, as erosive land use increased, channel sinuosity increased from 1.24 to 1.55, the number of islands in the river increased from 1 to 21, and meander wavelengths, amplitudes, and radii of curvature all decreased. The decrease in erosive land use in the period 1910 to 1949 was accompanied by a slight decrease in channel sinuosity to 1.50, a reduction in the number of islands to 9, and a slight increase in meander wavelengths and radii of curvature. The channel pattern changes may have been a response to changing river discharge and sediment transport characteristics brought about in part by land use changes in the basin. Higher peak and annual discharges in the late 1800s and early 1900s together with higher concentrations of suspended sediment...

Land use, floods, and channel changes: Upper Middle Fork Willamette River, Oregon (1936–1980)

Flow trends and channel characteristics from 1936 to 1980 were evaluated for the Middle Fork Willamette River, which drains a 668‐km2 forested watershed in the Cascade Mountains of western Oregon. An inventory of aerial photographs from 1959 to 1972 shows that landslides associated with roads and in clearcuts were 27 and 23 times more frequent, respectively, than in forested areas. Numerous landslides unloaded sediments directly into the drainage system; most landslides appear to have been initiated during a large flood (return period greater than or equal to 100 years) of December 22, 1964. Analysis of precipitation and peak flows (greater than 100m3 s−1) from 1958 to 1980 by means of power function models suggests a trend of increasing flows as timber harvesting and road building expanded in the basin. Changes in channel pattern, documented from aerial photographs, show major increases in channel width from 1959 to 1967 and a trend of decreasing width from 1967 to 1980. During summer low flows in 1979 and 1980, 65 cross sections of the channel were surveyed to provide detailed measurements of existing channel conditions. Channel widths of 62% of the aggraded reaches were significantly greater (α=0.05) than those for nonaggraded reaches.

Fluvial Hydraulics of Deltas and Alluvial Fans

Delta formation and its associated steam channel hydraulics have been studied using data obtained in a large laboratory flume. The findings for deltas are generally applicable to alluvial fans. Delta or fan shape is directly related to the pattern of stream flow, its loci, and mode of deposition. In response to a change in water discharge, sediment feeding rate or base level, stream channel adjustments on the delta are characterized by the formation of a single channel or multiple distributary channels. The changes in channel pattern are associated with large changes in channel width and stream power expenditure. Stream channel changes are related to the stream’s tendency to seek equal power expenditure along the channel; they also provide delicate adjustments in velocity and sediment load to favor restoration of channel’s equilibrium.

Proglacial Aggradation and Changes in Braided Channel Patterns During a Period of Glacier Advance: An Alpine Example

Studies of the morphological changes exhibited by an Alpine proglacial valley-train over a six-year period of glacier advance have provided quantitative evidence of initial degradation and subseque...

The role of multispectral imagery in elucidation of recent channel pattern changes in middle ganga plain

The mapability of Landsat images has opened up a new potentiality for study of channel pattern changes which was earlier not so easy due to nonavailability of suitable evidences at different timespans. Middle Ganga plain covering largely the northern part of Bihar and parts of eastern Uttar Pradesh is in a slate of perpetual flux due to large scale channel migration and avulsion resulting in devastating floods. Mosaic of three Landsat images has helped to study the channel changes which have occurred since 1935. The course of the river Ganga has beeh digitised along a basal line and two dimensional coordinates are taken at as many as more than fifty sample points for studying the magnitude and direction of channel changes during 1935–1975 period. The analysis shows that the main multiple channel river Ganga is under the huge hydrostatic thrust to be shifted towards south of its basin annually at a very high rate of 100 Meter per year all along the course except at its upstream near Ghazipur and at Monghyr where the shifting is towards north. The northward bend at Monghyr may be due to the presence of the Precambrian outliers here. For the multi-and single channelld tributaries of Ganga in channel behaviour is mainly in three directions—the lower water channels in the floodplain of Ganga are shifting to the south in conformity with that of their parent stream, the tributaries in Gogra-Gandak doab are shifting towards east but the shifting of the Kosi-Mahananda group of tributaries in the eastern part of the basin is towards west These channel pattern changes thus known at the interregional scale from the Landsat images may further be integrated with the study in hydrogeomorphology and their pertinent environmental impact.

Proglacial Aggradation and Changes in Braided Channel Patterns during a Period of Glacier Advance: An Alpine Example

Proglacial Aggradation and Changes in Braided Channel Patterns during a Period of Glacier Advance: An Alpine Example

Experimental Study of Channel Patterns

A series of experiments was performed in a large flume to determine the effect of slope and sediment load on channel patterns. Sediment loads and slopes were closely related, and as slope and sediment loads increased, threshold values of these variables were encountered, at which channel patterns altered significantly. At a very low slope and sediment load, the channels remained straight, but at a discharge of 0.15 cfs, a meandering-thalweg channel formed at slopes greater than 0.002. With increased slope and sediment loads, thalweg sinuosity increased to a maximum of 1.25. At slopes greater than 0.016, a braided channel formed. The model channels responded to increased sediment loads by maintaining steeper gradients and by major channel pattern changes, but at very gentle slopes and at steep slopes, the channel could not be forced to develop a meandering thalweg. These experiments suggest that landforms may not always respond progressively to altered conditions. Rather, dramatic morphologic changes can occur abruptly when critical erosional and (or) depositional threshold values are exceeded. The meandering-thalweg channel was not a meandering channel. A truly meandering channel with a sinuosity of 1.3 formed when a suspended-sediment load (3 percent concentrations of kaolinite) was introduced into the flow. The clay stabilized the alternate bars, and scour and deepening of the thalweg resulted. This in turn lowered the water level at constant discharge, and the alternate bars emerged o t form point bars. A meandering-thalweg channel was thus converted to a meandering channel by the type of sediment load change that has accompanied climatic and hydrologic changes of the recent geologic past.