Planform Changes Research Articles

Controls on channel planform changes in rivers of the Atlantic Coastal Plain: Findings from the Congaree river valley (South Carolina, USA)

Rivers shaped the landscape of the Atlantic Coastal Plain during the last tens of thousands years. However, their spatial and temporal evolution is understudied. We conducted geophysical, geological and remote sensing surveys in the Congaree River valley, characterized by numerous traces of palaeochannels preserved in the floodplain. The age of the former channels was determined by AMS radiocarbon dating. The main goal of our study was to identify factors controlling the river planform changes and compare the findings with other rivers of the Atlantic Coastal Plain. We found that the Congaree floodplain was shaped by single-thread channels characterized by formation of levees and floodbasins at least 34,000 cal. BP. Large-scale meanders were active between 16,000 and 12,000 cal. BP. They were replaced by meandering channel belts shifting by avulsions between 12,000 and 3,000 cal. BP. Compound meanders have been formed during the last 3000 years. Traces of these channel planforms are also present in other rivers of the Atlantic Coastal Plain. The abandonment of the large-scale meanders was caused by increase in climate humidity, changes in vegetation cover, and inundation of the coastal plain by the ocean level rise, resulting in base-level rise. The avulsions of meander belts in the Early and Middle Holocene were formed in conditions of a humid climate, a series of flooding periods, and continued base-level rise. A relatively drier climate in the Late Holocene caused a change in the meanders’ evolution from the channel belts shifting by avulsions to compound meanders evolving by cutoffs. The last 200 years were dominated by a huge delivery and deposition of fines, caused by deforestation and land-use changes in the river valleys.

Quantitative Analysis of Planform Changes in the Lower Mahaweli River, Sri Lanka

ABSTRACT The development of hydraulic structures has impacted the river discharge and sediment transportation, thus highlighting the river planform changes. Among 103 river catchments in Sri Lanka, the Mahaweli River is the longest river with the largest basin. Many development projects over the years diversely impacted the changes in river masks. However, no study has been conducted to quantify the planform changes in the lower Mahaweli River. Therefore, a comprehensive study was conducted to analyse the river planform changes over 30 years (1991-2021) from Damanewewa to Trincomalee. Freely available remotely sensed satellite data with 30 m resolution were used in the analysis. These images were processed using the QGIS mapping tool and RivMAP toolbox in MATLAB. Major changes were identified at the downstream part of the river and an oxbow lake formation was also observed. The average width for the entire reach (Wra) was identified as 14.83 m and channel width average (Wavg) was noted as 18.09 m. In addition, erosion and accretion rates were calculated, and the cumulative sequence of these rates was increased over the years affecting the change in channel width. Furthermore, the migration rates were also computed with generated river centerline. Highest migration rate reached about 400 m/yr, in the downstream which finally leads to severe meandering. Results revealed that this methodology can be applied to similar river planform analysis. Further, these results showcase the potential importance of analyzing channel stability as well as for water resource management.

Unveiling Stage Zero Conditions in the New Forest National Park: A UAV‐Based Structure‐From‐Motion Photogrammetry and LiDAR Approach for Reconstructing an Anastomosing Wet Woodland at the Avon Water

ABSTRACTIn recent years, there have been significant technological advances in uncrewed aerial vehicles (UAVs) and in particular the use of lightweight consumer‐grade ‘drones’. This combined with the development of structure‐from‐motion (SfM) technology has provided river restoration practitioners with a new tool that can be used to give an affordable, repeatable and objective assessment of river restoration projects. In this study, a combined SfM photogrammetry and LiDAR approach is utilised on a section of the Avon water, a small watercourse in the New Forest National Park. Victorian‐era straightening and channelisation has significantly altered the ecological and morphological state of the river system, but recent river restoration projects aim to reverse these effects. Whilst historic maps may be used as a guide to reveal the former alignment, changes in river planform occurred much earlier and these maps may not represent the natural course of the river. High‐resolution orthophotos and 3D photogrammetric models of the site are created that reveal a palaeolandscape consisting of a mosaic of anabranching channels. These are interpreted to represent a former anastomosing wet woodland and ‘Stage Zero’ of the river system. It is inferred that early human habitation and associated land clearance altered hydrological and hydrogeological conditions, reducing floodplain connectivity and promoting single‐threaded planform configurations. This was then followed by the most recent Victorian‐era straightening. The palaeolandscape revealed by the study provides a guide for future Stage Zero river restoration in the New Forest and elsewhere, demonstrating an application of low cost, UAV‐derived photogrammetry in river restoration research.

Agricultural land abandonment linked to pipe collapse and gully development: Reconstruction from archival SfM and LiDAR datasets

Land use and land cover changes such as agricultural land abandonment along with soil erosion are perceived to be important factors that add to land degradation worldwide. In this study, we used aerial imagery, archival-Structure from Motion (SfM) reconstruction and airborne-LiDAR surveys to reconstruct land abandonment along with pipe collapse and gully development in a semi-arid Mediterranean catchment area of the Ebro Valley (Spain) during 1957–2021. Agricultural land dynamics were analysed from the study of planform changes to field crops. Land degradation associated to pipe collapse and gully development was inferred from the geomorphic change detection deduced from the comparison of topographic models obtained from archival-SfM and LiDAR datasets. Through spatial correlation analysis, we identified that higher, steeper, and more hydrologically connected field crop areas were the first to be abandoned. Additionally, the extent of pipe collapses and gullying processes was significantly correlated with the degree of land abandonment over the duration of the study period. Our findings reveal that approximately 20 % of agricultural lands within the study area were abandoned during said study period, with up to 15 % of the abandoned area directly impacted by pipe collapse and gullying processes. Erosion rates associated with these processes within the catchment, implied erosion areas of 3.9 ha and 1.5 ha for the period 1977–2009 and 2009–2021, ranging between 120 Mg/ha yr−1 and 203.2 Mg/ha yr−1, respectively. Our study highlights that abandonment in said area is predominantly conditioned by land degradation resulting from pipe collapses and gully development. The recognition and protection of piping and gully affected areas as geodiversity sites is presented as an alternative at a local level to mitigate the economic impacts of soil degradation. Understanding the effects that pipe collapse and gully development have on arable lands over long-term study periods (i.e., >50 years) is essential in order to shed light on the interconnected factors influencing land productivity and agricultural sustainability. This ultimately guides us to make informed policy decisions that mitigate these detrimental effects.

Reach scale channel planform dynamics of transboundary River Jaldhaka within Himalayan Foreland Basin

ABSTRACT The slopes of Himalayan piedmont and foothill plain are being modified by the Himalayan origin river systems. In this study, spatiotemporal dynamics of channel planform of braided River Jaldhaka have been estimated using United States Army Map (1956) and landsat satellite images (1980-MSS, 1990-TM, 2000-TM, 2010-ETM+ and 2022-OLI) for the delineation of banklines, channel length, sinuosity index, braiding index, channel widths, identification of partial channel avulsion sites and bankline migration using Digital Shoreline Assessment System (DSAS) toolbar. Linear Regression Rate, Net Bankline Movement and End Point Rate were also calculated. Results revealed that the lower reach is more sinuous (maximum average channel sinuosity 1.65) compared with reach-I (1.29) and II (1.11)). The maximum channel width was in the year 2022 (968.6 m) and minimum average channel width was in 1956 (239.87 m). The maximum BI value (3.55) has been calculated in the sub reach-2 (SR-2, reach-I). Similarly, DSAS output shows maximum average EPR values (6.43 m/year) in lower reach which was most erosion prone bank. Bank facies study showed that non-cohesive bank materials accelerate rapid rate of channel avulsion and bank erosion. The variation of discharge, velocity, presence of vegetation and anthropogenic interventions controls the nature of planform changes of Jaldhaka River.

Historical and contemporary drivers of knickpoint retreat and morphological evolution along Bayou Pierre, Mississippi

AbstractChannel incision in rivers can cause marked ecological and economic damages. This phenomenon is abundant and generally well documented along impacted streams in the loess hills adjacent to the Lower Mississippi River valley. Bayou Pierre, an ecologically important small tributary of the Mississippi River, is currently incising but causes are not well understood. In this study, we examine diverse data sources to: (1) reconstruct a history of erosional stimuli and possible origins and (2) examine effects of contemporary controls. Review of long‐term planform and land use data for the Mississippi River revealed episodic foreshortening events followed by episodic deforestation and reforestation. Hydrologic data suggest an increase in rainfall over the last few decades. Estimates of knickpoint retreat place origins prior to Mississippi River channel straightening (1929–1944). Planform analysis in three focal reaches of Bayou Pierre demonstrates slow change prior to 1982, but accelerated changes after those periods. Mean rainfall and 3‐day storm intensity correlate to some planform changes; however, the storm of 1983 may be a better explanation of sudden planform change. We found some evidence of potential internal feedback loops in patterns of bar growth. Together, our analyses provide a synthesis of stimuli experienced by Bayou Pierre over the last ~200 years and suggest both channel migration events before straightening of the Mississippi River and more recent hydrologic events have influenced patterns of geomorphic change in Bayou Pierre.

Channel morphological change monitoring using high-resolution LiDAR-derived DEM and multi-temporal imageries

Natural processes and human activities both cause morphological changes in channels. Remote sensing products are often used to assess planform changes, but they tend to overlook vertical changes. However, considering both planform and vertical changes is crucial for a comprehensive evaluation of morphological changes. Using spatiotemporal aerial imagery and topographic data, remote sensing plays a vital role in evaluating channel morphological changes and flood-carrying capacity. This study aimed to investigate the morphological changes of a creek in an urban catchment using very high-resolution remote sensing products. In this study, we developed a new framework for investigating overall channel morphology change by employing very high-resolution aerial imagery and a LiDAR-derived digital elevation model (DEM). By digitizing channel boundaries using ArcGIS Pro 3.0, and analyzing various morphological parameters, erosion, and deposition patterns, we examined the impact of urban expansion and infrastructure development on channel adjustments. Channel adjustments have been performed in the case study catchment (Dry Creek, South Australia, Australia) due to urban expansion and development of infrastructure in the downstream reaches. Our findings revealed a significant southwest shift in the planform of the channel, with a maximum shift of 478 m and an average shift of 217 m since 1998. This alteration resulted in an increase in the sinuosity index reaching 1.2. Over the period from 2018 to 2022, the channel experienced a net deposition depth of 3.4 cm to 3.6 cm in downstream reaches. The annual deposition volume in the downstream reaches was 1963 m3, necessitating regular desilting to prevent channel capacity loss and flooding in the surrounding environment. This study also highlights the incremental growth of riparian vegetation within the channel, which affects surface roughness, channel slope, and carrying capacity. These findings provide a valuable baseline for future investigations into stream channel morphology changes and emphasize the importance of implementing appropriate measures such as desilting and vegetation management to mitigate deposition levels, reduce flood risks, and enhance the overall health and functionality of Dry Creek. The framework used in this study can be applied to other case studies employing reliable and high-resolution remote sensing data products.

Wing flexibility effect on aerodynamic performance of different flapping wing planforms

Uniform downwash of a revolving or flapping wing is a key indicator of aerodynamic efficiency. Although the slack-angle of flexible wings can significantly alter the downwash due to the inherent aerodynamic twist, its effect on the downwash distribution for a change in planform remains unknown. In this study, the effect of wing flexibility (slack-angle β) on the unsteady aerodynamic characteristics is investigated using three wing planforms. The study reveals that ββ > 5° can suppress the wing planform effect, leading to the generation of the same amount of lift at mid-stroke. To emphasize on the role of wing flexibility, further comparisons are made with rigid cases for each change in planform. A change in planform for the rigid cases significantly affects the position of the tip vortices (TiVs). But, the TiV positions of the flexible wings remained unchanged, helping to generate a wider downwash area to enhance the lift in contrast to that of the rigid-wing counterparts. The study found that the flexible and rigid wings can generate two distinct downwash patterns, which are respectively near uniform and tip-oriented, during the flapping motion. The ability of the flexible wings to sustain the wider near uniform downwash irrespective of the selected planform is paramount for enhanced aerodynamic performance.

Hydrological and climate impacts on river characteristics of pahang river basin, Malaysia

The climate, geomorphological changes, and hydrological elements that have occurred have all influenced future flood episodes by increasing the likelihood and intensity of extreme weather occurrences like extreme precipitation events. River bank erosion is a natural geomorphic process that occurs in all channels. As modifications of sizes and channel shapes are made to transport the discharge, sediment abounds from the stream catchment, and floods are triggered dramatically. The aim of this study is to analyze the flood-sensitive regions along the Pahang River Basin and determine how climate and river changes would have an impact on flooding based on hydrometeorological data and information on river characteristics. The study is divided into three stages, namely the upstream, middle stream, and downstream of the Pahang River. The main primary hydrometeorological data and river characteristics, such as Sinuosity Index, Dominant Slope Range and Entrenchment Ratio collected as important inputs in the statistical analysis process. The statistical analyses, namely HACA, PCA, and Linear Regression applied in river classification. The result showed that the middle stream and downstream areas demonstrated the worst flooding affected by anthropogenic and hydrological factors. Rainfall distribution is one of the factors that contributed to the flood disaster. There are strong correlations between the Sinuosity Index (SI) and water level, which indicates that changes occurred at both planform and stream classification. The best management practices towards sustainability are based on the application of the outcomes that have been obtained after the analysis of Pahang River planform changes, Pahang River geometry, and the local rainfall pattern in the Pahang River Basin.

The evolution of meandering rivers in sedimentary basins: Insights from the lower Drava (Hungary/Croatia)

AbstractRivers flowing through sedimentary basins are subjected to a variety of controls. The main goal of our study was to identify the effect of external (e.g. climate changes, tectonics) and internal controls (e.g. sediment transport, deposition, vegetation cover) on the evolution of meandering rivers flowing through sedimentary basins using the example of the lower Drava River (Europe, Hungary/Croatia). Field research was conducted along a 50‐km‐long section of the valley. Sedimentary data from boreholes and corings, 35 km of ground‐penetrating radar surveys and analyses of digital maps were conducted to reconstruct channel planform changes. Traces of four meander belts were identified, and 39 AMS radiocarbon dates were used to distinguish the chronology of the fluvial events. The evolution of the lower Drava River comprised alternating periods of deposition (formation of aggrading meander belt) and avulsions. The channel belts were formed owing to upstream sediment delivery and floodplain storage. Changes in climate humidity and the occurrence of high flows influenced the planform of the meanders within particular channel belts. The oldest channel was active at least ~40 000 cal. BP before being reworked by subsequent meanders active between the Late Pleniglacial (30 000–14 700 cal. BP) and Late Glacial (~11 000 cal. BP) periods. The channel belts shifted to the south in the Holocene, between ~11 000 and 250 cal. BP due to the presence of a thrust fault situated diagonally to the Drava Valley. Results show channel width, channel belt width and the surface area of point bar deposits increased in the succeeding generations of meanders and that the style and sedimentary architecture of the channel belts were dominantly dependent on autogenic controls, that is, sediment delivery, aggradation and erosional events (e.g. formation of chute cut‐offs).

Multiscalar Assessment of Mining in River Floodplains of the Southeastern United States

The mining of sediment is a profitable activity involving clearing and digging out large tracts of land and transformation of the topography. Often, these mines, as well as the pits, ponds, and piles of sediment are near or within the floodplains of a fluvial system. During flood events, the river can overtop and erode riparian areas that separate it from the mine, flowing into the pit and causing planform changes including avulsions. The United States Geological Survey (USGS) has mapped mining sites across the United States, but there are still multiple omissions. Google Earth Pro was used to collect geospatial point data on mines that are within the floodplain boundaries of rivers and creeks in the southeast, a region of high biodiversity. Google Earth extracted data were compared to USGS data using ArcGIS Pro, and their proximity to floodplains and channels was analyzed. Distances between the channels and pits prior to avulsion were referenced from literature (Mossa & Marks, 2011) and used to assess potential risk for other sites. It was found that out of the 1,856 total pits from USGS and Google Earth data, 25.9% were omitted from the USGS data set. This supported the conclusion that current data sets, while thorough, are still incomplete and that a better understanding of site location can reduce the risk of avulsions, which can impact infrastructure, property boundaries, flood risk, and ecological health.

Investigation of rivers planform change in a semi-arid region of high vulnerability to climate change: A case study of Tigris River and its tributaries in Iraq

In this paper, the planform changes of rivers in a semi-arid region, which are particularly vulnerable to the impacts of climate change, were investigated. This research provides valuable insights into the adaptation and mitigation efforts necessary for effective climate change risk management in this area. A comprehensive analysis was carried out using satellite images and GIS to investigate the changes in the planform of the Mosul-Makhool reach of the Tigris River and its Lesser Zab and Greater Zab tributaries as a case study. To date, no studies have examined the impact of dam construction and climate change on the planform changes of these rivers. A survey was conducted to analyze the channel planform from 1979 to 2021. Various channel planform features were computed, including sinuosity index, braiding index, erosion and accretion, migration rate, confluence point, and junction angle. Results demonstrated that the Tigris River has low meandering features, the Lesser Zab has moderate meandering features, and the Greater Zab has the highest sinuosity index value of 1.95, which indicates very high meandering features. The change in the sinuosity index was fairly small. Generally, the rivers tended slightly towards deposition rather than erosion. The migration rate of the meandering rivers was high, with the highest value recorded in the Tigris River and Greater Zab. The average movement rate of the Greater Zab-Tigris River confluence was 31.81 m/year, and the Lesser Zab-Tigris River confluence moved 20.2 m/year. The study results demonstrate that climate change and dam construction significantly impact the rivers' planform in semi-arid regions. This investigation holds significant importance in evaluating morphodynamic changes in river systems worldwide with great detail and accuracy using satellite data.

Spatio-Temporal Dynamics of Sediment Transport Pathways: Sand Apron Bars and Islands of Tokelau and Kiribati, Central Pacific

Although there is general agreement that global change will influence low-lying atoll islands, considerable uncertainty remains concerning the nature, rates, and causes of morphological change (or, conversely, the stability) of islands. As the net geomorphical product of sediment erosion, transport, and accumulation, islands are intimately tied to reef flat sedimentological processes. Recognizing the morphodynamical linkages between reef flats and islands, the purpose of this study is to examine the nature and controls on spatial and temporal variations in sediment transport pathways on reef flats and their relation to island planform changes or stability on atolls of Tokelau and Kiribati. GIS analysis of historical aerial images and high-resolution remote-sensing data capture patterns of reef flat change up to 72 years in duration with up to weekly temporal resolution. Data reveal how granular materials that make up bars and islands on reef flats respond to physical oceanographic processes via sedimentary-geomorphical change across temporal scales, from “instantaneous” impacts of cyclones or swell events to seasonal to multi-decadal shifts. Each of these shifts is manifest as migration of sediment of island beaches and bar forms, but the character varies markedly—bars form new islands, others erode and disappear; some changes are cyclic, others are directional, still others are hybrid; sediment can be transported lagoonward, oceanward, along the reef flat, or in combinations thereof; and migration rates reach up to 10 s of m/month. Although sea-level change likely plays a modulating role, much of the considerable spatial and temporal variability relates to differences in energy controlled by seasonal change in swell direction and climate shifts. Nonetheless, sedimentary response to these external forcings at any specific location also is shaped by local factors, such as trade wind-generated lagoonal waves and currents, atoll lagoon size and depth, margin width and orientation relative to waves, and autogenic processes such as attachment of migrating bars. Collectively, these influences shape the spatially and temporally heterogeneous sediment flux to and from islands, and thus the variable response of islands to ongoing sea-level change. Understanding such local influences is requisite to predictive understanding of how global change might impact these sensitive seascapes.

Honduran Reef Island Shoreline Change and Planform Evolution over the Last 15 Years: Implications for Reef Island Monitoring and Futures

Assessing the vulnerability of low-lying coral reef islands is a global concern due to predictions that climate and environmental change will increase reef island instability and cause reef island populations to be among the first environmental refugees. Reef islands in the Pacific and Indian Oceans are highly dynamic environments that morphologically adjust to changing environmental conditions over annual-decadal timescales. However, there is a paucity of reef island shoreline change data from the Caribbean where sea-level rise, ecological and environmental disturbance and hydrodynamic regimes are considerably different than in other oceans globally. Here we present shoreline change analysis of 16 reef islands in northern Honduras, at the southern end of the Mesoamerican Barrier Reef. Satellite imagery from a maximum period of 12.4 years from Utila (2006–2019), and 2.4 years from Cayos Cochinos (2018–2021) was analysed to quantify island shoreline change and planform morphological adjustments. We identified accretion as the dominant island behaviour in Utila, where 5 of 7 islands increased in area and 61.7% of shorelines accreted, contributing to an overall net area increase of 9.4%. Island behaviour was more variable in Cayos Cochinos, where 55.7% of shorelines eroded, 5 of 9 islands remained stable, and net island area change was insignificant (2%). Conversely, the 4 smallest Cayos Cochinos islands (all <1500 m2) experienced significant shoreline change, potentially highlighting a new size threshold for considering reef island evolution. Across both sites, reef islands demonstrated a range of modes of planform change, including lateral accretion and erosion, and migration. Consequently, we provide the first empirical evidence of the dynamic nature of Caribbean reef islands during a period coincident with sea-level rise and highlight the heterogeneous nature of reef island evolution between and within two neighbouring sites at timescales relevant for island adaptation efforts.

Multidecadal changes in planform morphology of the confluence of River Niger and River Benue, West Africa

Analysis of 35 years (1987–2022) of time-lapse data derived from Landsat imagery and SRTM DEM has revealed significant changes in planform morphology at the confluence of the River Niger and River Benue in Lokoja, West Africa. In the study area, the Niger is flanked by high elevation plateaus of ca. 400 m altitude and low-lying floodplains on its western bank. The Benue is characterized by more abundant intra-channel and bank-attached bars relative to the Niger. Over the 35-year period, a net downstream migration of 880 m was observed at the junction, its angle decreased from ca. 175° in 1987 to 50° in 2006 and to ca. 16° in 2022 and showed varied segmentation patterns. We establish a linkage between this decrease in confluence angle and increase in annual runoff in the study area. Expansion along the banks of the Niger, Benue, and post-confluence channels was found to be low and non-uniform, suggesting varied resistance of the banks to erosion, which is linked to the abundance of vegetation. These decadal changes in confluence planform are important for understanding river confluence dynamics in major river systems around the world.

Understanding the Planform Complexity and Morphodynamic Properties of Brahmaputra River in Bangladesh: Protection and Exploitation of Riparian Areas

The Brahmaputra River (BR) is a heavily braided river, due to various intricate paths, high discharge variability and bank erodibility, as well as multi-channel features, which, in turn, cause huge energy dissipation. The river also experiences anastomosing planform changes in response to seasonal water and sediment waves, resulting in a morphology with extreme complexity. The purpose of this study was to provide detailed and quantitative insights into the properties of planform complexity and dynamics of channel patterns that can complement previous studies. This was achieved by investigating the applicability of the anastomosing classification on the Brahmaputra river’s planform, and computing disorder/unpredictability and complexity of fluctuations using the notion of entropy and uniformity of energy conversion rate by the channels, by means of a power spectral density approach. In addition, we also evaluated their correlation with discharge as a dynamic imprint of river systems on alluvial landscapes, in order to test the hypothesis that river flow may be responsible for the development of anastomosing planforms. The analysis suggests that higher discharge values could lead to less complex planform and less fluctuations on the alluvial landscape, as compared to lower discharge values. The proposed framework has significant potential to assist in understanding the response of complex alluvial planform under flow dynamics for the BR and other similar systems.

Anthropogenic amplification of geomorphic processes on fluvial channel morphology, case study in Gilgel Abay river mouth; lake Tana Sub Basin, Ethiopia

As a result of ongoing human induced or natural factors acting on river channels, banks, and within a catchment, alluvial river systems change their course and morphology over time. The base level changes and the backwater effects affect rivers entering a static water body. For coastal rivers, the planform changes are highly pronounced at the fluvial deltas and flood plains. Aggradation, degradation, progradation, meandering, and formation of islands and distributary channels are common processes on coastal rivers. This study investigates planform changes and landscape responses of Gilgel Abay river about 36 km stretch starting from the bridge, near Chimba, to its entrance to Lake Tana by using historical images for the last 60 years (1957–2020) and field observation. The study reach was divided in to three parts based on feature characteristics. For data preparation and analysis, image analysis software's; ENVI, ERDAS IMAGINE, and ArcGIS were used. From land use land cover classification, the land use pattern near the river flood plain and delta area changed significantly. The overall planform results (sinuosity, width, and island) show that, Gilgel Abay River within the study reach has shown little change in its planform for the last 60 years. However, the landscape of alluvial delta formed at the mouth of the river has shown huge change. Accretion-erosion result map shows, a maximum of 18.73 ± 1.97 m/y accretion and −12.48 ± 1.44 m/y erosion at the right side (eastward) and a maximum of 50.06 ± 1.44 m/y accretion and lost only 3.95 ± 1.97 m/y westward. The delta area analysis shows in the last five decades, 17.13 ha/yr of land has formed disproportionally out of which over 56% is added at the right shore of the river. In general, for the planform changes that occurred in Gilgel Abay river channel and fluvial delta, human-induced factors have a great contribution. Increasing interest for new settlements inside delta flood plain, productive agricultural land and artificial lake level rise changes the river planform and the delta appearance. Quantitative and qualitative mapping of river and delta coupling with feeding basins and floodplains is important to enhance and understand the socioeconomic influences on river morphology and needs an integrated management framework.

Monitoring and Modelling Morphological Changes in Rivers Using RS and GIS Techniques

River geomorphological investigation issues have received little attention in most countries of the world. Such processes become a pressing necessity due to climate change and anticipated events of extraordinary surges and dry seasons, which may debilitate the security of adjacent and downstream cities, particularly in locales that are exceedingly delicate and influenced by climatic changes. Al-Abbasia reach is a river that runs through the middle of the Euphrates River and is known for its numerous bends and meanders. The study of hydraulic structures such as barrages can provide important information about their influences on morphological processes in river reaches near the barrage upstream and downstream. Hydraulic analysis is made of the river behavior in u/s and d/s of hydraulic structures like barrages as a result of sediment deposition and erosion in u/s and d/s. A study, i.e., research on the impacts of the Abbassia barrage on the river system, has been conducted to address this issue using multi-temporal Landsat satellite data from 1976 to 2022 provided by the USGS. The study reach is located 5 kilometres upstream and 5 kilometres downstream of the Abbassia reach. Following the construction of the barrage, which had an impact on the sedimentation and geometry of the river, morphological variations took place in this part of the Al Abbassia reach. In this study, morphological changes throughout 49 years between 1976 and 2022 were investigated utilising remote sensing (RS) and geographic information system (GIS) approaches. Additionally, four image groups from three separate decades were used to perform change detection (1990–2000, 2000–2010, and 2010–2022). In this study, a monitoring system using Landsat-3 MSS: 1985, Landsat-5 TM: 1990, 1995, 2000, 2005, and Landsat-8 OLI: 2010, 2011, 2015, 2021, 2022 were employed to map river planform changes. The long-term comparison of this series of satellite images and historical maps for the period 1976–2022 indicates a continuation of change in the reach study with a rate of approximately 56, 33, 97, and 55% for upstream and 19%, 26%, 3%, and 45% for downstream for the width, area, deposition, and erosion, respectively. Furthermore, it is observed that there is a shift in river course within 200 m downstream of the barrage for the period of 1985–1990. The findings of this study, which monitor river morphological change at finer temporal and spatial resolutions, are crucial for promoting sustainable river management. They also aid in the investigation of river behaviour, which is necessary for providing the best management possible and overcoming the difficulties posed by this important research issue. Doi: 10.28991/CEJ-2023-09-03-03 Full Text: PDF

Long-term geomorphic adjustments following the recoupling of a tributary to its main-stem river

River restoration and rehabilitation projects are widespread, but rarely include the data needed to fully evaluate if they are successful in achieving their goals or how long the process of readjustment takes before a new ‘recovered’ regime state is reached. Here we present a seven-year post-project dataset detailing the morpho-sedimentary responses of a river to the reconnection of a formerly diverted tributary, and relate observed changes to conditions in the river prior to the reconnection. We describe changes in the tributary and main-stem channels, including changes in channel planform, morphology, and the export of coarse and fine sediment from the tributary to the main-stem river. We use the data to develop a conceptual model of the system's response to the reconnection.Marked geomorphic changes occurred within the first two years after the reconnection. Changes during this ‘shock phase’ included dramatic erosion and subsequent deepening and widening of the tributary channel, rapid development of a confluence bar and an increase in fine sediment delivered to the main-stem. After this shock phase, and despite the continued occurrence of high magnitude flow events, the rate of geomorphic change in the tributary began to decrease, and the rate of growth of the confluence bar slowed. Fine sediment volumes in the main-stem also decreased steadily. After an adjustment phase lasting a total of approximately 4.5 yr (including the initial 2-yr shock phase), the tributary to mainstem system appeared to reach a new dynamic equilibrium that we consider the adjusted regime state. This new regime state was characterised by, among other things, an increase in geomorphic heterogeneity in the tributary and main-stem channels.Changes in both fluvial processes and forms indicate that within 4.5 yr the project was successful in achieving its goal of augmenting sediment and increasing geomorphic heterogeneity. Our conceptual model of adjustment mirrors that developed by Petts and Gurnell (2005), with the river passing through a complex and dynamic adjustment phase before reaching a new regime state. However, unlike the responses to impoundment represented by Petts and Gurnell, our model of river response to rehabilitation charts increases in dynamism and heterogeneity.

Exploring willow decline in an over-greening riparian corridor (River Jarama, Spain)

The analysis of willow forest decline in the Jarama River has been assessed through the study of morphological river conditions in three periods (1956, 1998 and 2018) together with active channel mobility ratios and changes in channel planform and vegetation coverage. Species composition of current riparian corridors at river segment scale and monitored natural recruitment of pioneer species at local scale have been studied. Jarama River has changed from wide active wandering towards narrower meandering channels with dense and continuous riparian over-greening corridors, in which willow formations are threatened, and drought-tolerant species have colonised it. Landform evolution shows an intensive ‘maturation’ associated with ‘anthropisation’ processes during the first period, while stability dominates nowadays. Results show a generalised aging and progressive mortality of shrub willows and the expansion of forests dominated by Fraxinus angustifolia, likely associated to the progressive reduction of channel mobility and the lack of bare gravel bars for pioneer recruitment. The dominant willow species is Salix salviifolia, a drought tolerant willow that has been able to withstand the processes of 'maturation’ and channel narrowing being widely distributed throughout the riparian section. On the other hand, other strict pioneer willows such as Salix eleagnos and Salix purpurea are very rare and are found in the few gravel banks that remain on the shore. Results predict a gradual disappearance of willows in the Jarama River as there is no significant recruitment, and they would last as long if those old specimens may survive.