A changing river: Long‐term changes of sinuosity and land cover in the Navasota River Watershed, Texas
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Abstract The Navasota River Basin, itself a tributary of the Brazos River in Texas, is a dynamic watershed undergoing many natural and anthropogenic changes. Local stakeholder involvement in this watershed is quite high, and many landowners in the southern portion of the watershed have concerns regarding the increasing frequency and duration of flooding on private property adjacent to the river, often attributing these impacts to the construction of the Lake Limestone dam. In this study, we examine historical flow data, channel morphology, land use/land cover, and precipitation. Our findings indicate that while there appears to be increasing flow in the northern portion of the watershed, temporal data gaps near the watershed outfall prevent the indication of such a trend in the southern portion of the watershed. Nevertheless, other natural and anthropogenic factors are evident in the watershed that may have a significant influence on downstream flooding. Overall river sinuosity (meandering) declined over the study period, with some river segments encountering significant straightening. Total river length declined by 4.3 km from 1972 to 2020. The number and length of offtake channels also decreased substantially during this period. Land use/land cover use shifted dramatically, with a 39.2% increase in impervious cover and a 12.5% decrease in herbaceous cover since 1972. Finally, yearly precipitation increased, with the change point occurring in 1972. Our findings suggest that the shortening and straightening of the river has reduced its volumetric capacity over time. Coupled with increasing impervious surface cover and precipitation, more water is being delivered downstream at a rate exceeding the watershed's ability to discharge it, thereby contributing to flooding issues expressed by stakeholders. We recommend that bathymetric data and supplemental flow monitoring and modeling within the watershed is needed to fully understand how anthropogenic and natural forces may further affect streamflow in the future.Keywords:
Sinuosity
Impervious surface
Land Cover
Watershed area
This research deals with the surface dynamics and key factors – hydrological regime, sediment load, and erodibility of floodplain facies – of frequent channel shifting, intensive meandering, and lateral instability of the Bhagirathi River in the western part of the Ganga-Brahmaputra Delta (GBD). At present, the floodplain of the Bhagirathi is categorized as a medium energy (specific stream power of 10–300 W m−2), non-cohesive floodplain, which exhibits a mixed-load and a meandering channel, an entrenchment ratio >2.2, width–depth ratio >12, sinuosity >1.4, and channel slope <0.02. In the study area, since 1975, four meander cutoffs have been shaped at an average rate of one in every 9–10 years. In the active meander belt and sand-silt dominated floodplains of GBD, frequent shifting of the channel and meander migration escalate severe bank erosion (e.g. 2.5 × 106 m3 of land lost between 1999 and 2004) throughout the year. Remote sensing based spatio-temporal analysis and stratigraphic analysis reveal that the impact of the Farakka barrage, completed in 1975, is not the sole factor of downstream channel oscillation; rather, hydrogeomorphic instability induced by the Ajay–Mayurakshi fluvial system and the erodibility of floodplain sediments control the channel dynamics of the study area.
Meander (mathematics)
Sinuosity
Bank erosion
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Abstract The braided hydrosystem of the Szigetköz floodplain played a prominent part in the structure of the fish communities in the upper section of the middle river Danube Regulations and flood control measures have modified the natural resources of the area since the 19th century. At the end of 1992, the River Danube was diverted to the by‐pass canal of the Gabcikovo Hydroelectric Power Plant and most of the small tributaries to the river became dry in the floodplain. The juvenile fish assemblages have been monitored since the completion of the Dam of the River Gabcikovo. The monitoring results of parapotamic and plesiopotamic backwaters demonstrate the importance of hydrological connectivity of the floodplain tributaries.
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AbstractThe fluvial system in the upper Val Roseg in the Swiss Alps is characterized by a complex glacial floodplain. To analyze the changes in floodplain morphology between 1947 and 1999, a period during which the two main glaciers lost 700 to 1600 m in length, ten sets of aerial images were rectified and channel network and active floodplain area were digitized into a Geographic Information System (GIS). Changes mainly included an increase in the active floodplain width in the upper part of the floodplain. In the 100- to 500-m wide floodplain, the average lateral shift of the main channel ranged from 2 to 10 m yr−1. While the channel network was continuously renewed at a turnover rate of 25% per year, the overall structure of the Roseg floodplain remained relatively constant, despite rapid glacial retreat that increased the availability of glacial sediments potentially susceptible to fluvial transport. The sinuosity index averaged 1.15 ± 0.01 and the braiding index 4.6 ± 1.2. Only the connectivity index showed high variation (6.6 ± 5.0), about 34% of which may be attributed to variation in discharge.
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Causal model for the percentage of trans links (% trans) along such streams. Analyses of 40 stream reaches indicate (1) that 81 percent of the variation in the percentage of tributaries on the concave side (outside) of bends (% CVT) can be explained by the mean number of tributaries per bend (N ~T~ ), valley sinuosity (P), and the rate of bend migration; and (2) that 72 percent of the variation in % trans can be accounted for by % CVT, N ~T~ and P. The variable N ~T~ represents both the availability of space on the convex (inside) of bends relative to that required for a tributary to form and the ratio of the mean bend length to mean chain length, which affects the convergence and divergence of runoff down valley sides. Locations of tributaries along main streams can be understood largely in terms of four factors: spatial requirements of tributaries, sinuosity of the main valley, lengths of the valley bends, and rate of bend migration.\--Modified journal abstract.
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Divergence (linguistics)
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Drainage basin geometry was analyzed in the lower portion of the Big Black River, Mississippi. The study was centered on a reach of the Big Black River that encompasses an anomalous straight reach (ASR) and has morphometric characteristics that differ from those of upstream and downstream reaches. The study area was divided into three reaches, defined by alluvial valley and active floodplain width, sinuosity, and slope. Tributary streams with confluences in the three study reaches were investigated for evidence of surface tilting, and channel and valley slopes and sinuosity were measured. The average stream channel and valley slopes within the middle reach are nearly double those of the upper and lower reaches. Lateral stream migration within the tributary basins was quantitatively analyzed by measuring the asymmetry factor (AF) and transverse topographic symmetry factor (T) indices. While AF results suggest minimal to no lateral migration within the tributaries, the T results show some shifting. The results are inconclusive regarding the possible effect of neotectonic activity in the study area near the ASR. The mean southward migration may indicate a preferred migration direction relative to the general dip of the coastal plain and plunge of the Mississippi Embayment.
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Alluvial fan
Confluence
Alluvial plain
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An analysis of 40 winding streams and valleys reveals that a higher proportion of large tributaries than small ones occurs on the concave (out) side of bends. The principal reason for this is that large tributaries experience greater difficulty than small ones forming in the limited amount of space on the convex (in) side of bends. The proportions of small and large tributaries on the concave side of bends are determined largely by the spatial requirements of tributaries, valley sinuosity, mean valley bend length, and mean rate of bend migration. In addition, the proportion of large tributaries on the concave side of bends is affected by junction angle adjustments that deflect a main stream toward a large tributary, thereby creating a bend with the large tributary on its concave side. These adjustments increase the proportion of large tributaries on the concave side of bends, especially along low‐sinuosity headwater streams.
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Abstract The process of channelization on river floodplains plays an essential role in regulating river sinuosity and creating river avulsions. Most channelization occurs within the channel belt (e.g. chute channels), but growing evidence suggests some channels originate outside of the channel‐belt in the floodplain. To understand the occurrence and prevalence of these floodplain channels we mapped 3064 km 2 of floodplain in Indiana, USA using 1.5 m resolution digital elevation models (DEMs) derived from airborne light detection and ranging (LiDAR) data. We find the following range of channelization types on floodplains in Indiana: 6.8% of floodplain area has no evidence of channelization, 55.9% of floodplains show evidence (e.g. oxbow lakes) of chute‐channel activity in the channel belt, and 37.3% of floodplains contain floodplain channels that form long, coherent down‐valley pathways with bifurcations and confluences, and they are active only during overbank discharge. Whereas the first two types of floodplains are relatively well studied, only a few studies have recognized the existence of floodplain channels. To understand why floodplain channels occur, we compared the presence of channelization types with measured floodplain width, floodplain slope, river width, river meander rate, sinuosity, flooding frequency, soil composition, and land cover. Results show floodplain channels occur when the fluvial systems are characterized by large floodplain‐to‐river widths, relatively higher meandering rates, and are dominantly used for agriculture. More detailed reach‐scale mapping reveals that up to 75% of channel reaches within floodplain channels are likely paleo‐meander cutoffs. The meander cutoffs are connected by secondary channels to form floodplain channels. We suggest that secondary channels within floodplains form by differential erosion across the floodplain, linking together pre‐existing topographic lows, such as meander cutoffs. Copyright © 2016 John Wiley & Sons, Ltd.
Sinuosity
Overbank
Meander (mathematics)
Channelized
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The fluvial system in the upper Val Roseg in the Swiss Alps is characterized by a complex glacial floodplain. To analyze the changes in floodplain morphology between 1947 and 1999, a period during which the two main glaciers lost 700 to 1600 m in length, ten sets of aerial images were rectified and channel network and active floodplain area were digitized into a Geographic Information System (GIS). Changes mainly included an increase in the active floodplain width in the upper part of the floodplain. In the 100- to 500-m wide floodplain, the average lateral shift of the main channel ranged from 2 to 10 m yr−1. While the channel network was continuously renewed at a turnover rate of 25% per year, the overall structure of the Roseg floodplain remained relatively constant, despite rapid glacial retreat that increased the availability of glacial sediments potentially susceptible to fluvial transport. The sinuosity index averaged 1.15 ± 0.01 and the braiding index 4.6 ± 1.2. Only the connectivity index showed high variation (6.6 ± 5.0), about 34% of which may be attributed to variation in discharge.
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The present study aims to investigate the evolution of river networks and floodplain geomorphological features of river Raidak within the dynamic Himalayan foreland basin regime over 65 year's timescale (1955–2020). High resolution satellite images and old maps have been used to prepare the floodplain geomorphological maps. Additionally, field verification technique has been adopted to improve the accuracy of floodplain landforms mapping. Sedimentary log analysis was conducted in order to identify the floodplain types and fluvial architectural elements in the floodplain. The nature of channel oscillation has been assessed using different parameters (channel length, channel width, sinuosity, bank line migration and erosion-accretion area). Results showed that progressive migration of meander bends and channel shifting on a recent past time-scale have resulted into many floodplain geomorphic features such as cut-offs, palaeochannel, backswamps, abandoned channel and meander scroll bar on Holocene floodplain surface. These floodplain landforms are more prominent on the middle and lower part of the floodplain. Numerical investigation showed variation in channel sinuosity of the middle and lower reach of river Raidak-I (1.85, 1.64 and 1.73 during the year 1955, 1987 and 2020 respectively) suggesting channel lengthening and shortening during different time period through mender development and cut-offs formation. Result also shows spatiotemporal variation in channel width and increasing trend of erosion-accretion area during the period 1987–2020. The sedimentary log analysis suggests non-cohesive medium energy (specific stream power varies between 10 and 300 Wm-2) floodplain of principal class B characterized with meandering and braided channel pattern, multiple sequence of Holocene sediments and existence of different floodplain landforms. Different natural processes (variable discharge, frequent floods, active tectonics, meander migration and channel shifting) and human interferences (channelization, mining activities, construction of cross-sectional structures and land use changes) have been responsible for evolution and morphological modification of Raidak river system and their floodplains.
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Palaeochannel
Meander (mathematics)
Landform
Stream power
Point bar
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The presence of floodplain channels on the Highland Water is dependant on overbank flow brought about by a connection between the channel and the floodplain. High channel sinuosity and hydraulically effective debris dams also promote floodplain channel development. In reaches which are deeply incised due to channelisation flow does not reach the floodplain, hence floodplain channels are absent (Table 1).
Overbank
Sinuosity
Meander (mathematics)
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