Combining Spectral Water Indices and Mathematical Morphology to Evaluate Surface Water Extraction in Taiwan

Rivers in Taiwan are characterised by steep slopes and high sediment concentrations. Moreover, with global climate change, the dynamics of channel meandering have become complicated and frequent. The primary task of river governance and disaster prevention is to analyse river changes. Spectral water indices are mostly used for surface water estimation, which separates the water from the background based on a threshold value, but it can be challenging in the case of environmental noise. Edge detection uses a canny edge detector and mathematical morphology for extracting geometrical features from the image and effective edge detection. This study combined spectral water indices and mathematical morphology to capture water bodies based on downloaded remote sensing images. From the findings, this study summarised the applicability of various spectral water body indices to the surface water extraction of different river channel patterns in Taiwan. The normalised difference water index and the modified normalised difference water index are suitable for braided rivers, whereas the automated water extraction index is ideal for meandering rivers.

Braiding together student and supervisor aspirations in a struggle to decolonize

In this study, we explore a student-supervisor relationship and the development of relational and reflexive research identities as joint actions towards decolonizing management knowledge and practice. We frame a specific case of PhD supervision through he awa whiria the braided rivers metaphor, which emerges from Māori traditions. This metaphor recognizes a plurality of knowledge streams that can start from different sources, converge, braid and depart again, from the mountains to the sea. In this metaphor, each stream maintains its own autonomy and authority, but knowledge is created at an interface in partnership. We use this framing metaphor to illustrate the tensions between co-creating knowledge with an Indigenous community that a research student has kinship ties with and feels a strong affinity to, and navigating the institutional requirements for a PhD within a UK university. We surface two contributions that open up future possibilities for supervision, research and practice. The first is the use of the metaphor to frame the student-supervisor partnership and strategies for decolonizing management knowledge more broadly. The second is the requirement for relational and reflexive research identities in decolonizing management knowledge.

The Paleoproterozoic Kombolgie Subgroup (1.8 Ga), McArthur Basin, Australia: Sequence stratigraphy, basin evolution, and unconformity-related uranium deposits following the Great Oxidation Event

ABSTRACT Proterozoic continental sedimentary basins contain a unique record of the evolving Earth in their sedimentology and stratigraphy and in the large-scale, redox-sensitive mineral deposits they host. The Paleoproterozoic (Stratherian) Kombolgie Basin, located on the Arnhem Land Plateau, Northern Territory, is an exceptionally well preserved, early part of the larger McArthur Basin in northern Australia. This intracratonic basin is filled with 1 to 2 km-thick, relatively undeformed, nearly flat-lying, siliciclastic rocks of the Kombolgie Subgroup. Numerous drill cores and outcrop exposures from across the basin allow sedimentary fabrics, structures, and stratigraphic relationships to be studied in great detail, providing an extensive stratigraphic framework and record of basin development and evolution. Tectonic events controlled the internal stratigraphic architecture of the basin and led to the formation of three unconformity-bounded sequences that are punctuated by volcanic events. The first sequence records the onset of basin formation and is comprised of coarse-grained sandstone and polymict lithic conglomerate deposited in proximal braided rivers that transported sediment away from basin margins and intra-basin paleohighs associated with major uranium mineralization. Paleo-currents in the upper half of this lower sequence, as well as those of overlying sequences, are directed southward and indicate that the major intra-basin topographic highs no longer existed. The middle sequence has a similar pattern of coarse-grained fluvial facies, followed by distal fluvial facies, and finally interbedded marine and eolian facies. An interval marked by mud-rich, fine-grained sandstones and mud-cracked siltstones representing tidal deposition tops this sequence. The uppermost sequence is dominated by distal fluvial and marine facies that contain halite casts, gypsum nodules, stromatolites, phosphate, and “glauconite” (a blue-green mica group mineral), indicating a marine transgression. The repeating pattern of stratigraphic sequences initiated by regional tectonic events produced well-defined coarse-grained diagenetic aquifers capped by intensely cemented distal fluvial, shoreface, eolian, and even volcanic units, and led to a well-defined heterogenous hydrostratigraphy. Basinal brines migrated within this hydrostratigraphy and, combined with paleotopography, dolerite intrusion, faulting, and intense burial diagenesis, led to the economically important uranium deposits the Kombolgie Basin hosts. Proterozoic sedimentary basins host many of Earth's largest high-grade iron and uranium deposits that formed in response to the initial oxygenation of the hydrosphere and atmosphere following the Great Oxygenation Event. Unconformity-related uranium mineralization like that found in the Kombolgie Basin highlights the interconnected role that oxygenation of the Earth, sedimentology, stratigraphy, and diagenesis played in creating these deposits.

Sandstone body character, river styles, and geomorphology of the lower Eocene Willwood Formation, Bighorn Basin, Wyoming, USA

The lower Eocene Willwood Formation of the intermontane Bighorn Basin, Wyoming, USA, is an alluvial red bed succession with a sand content of ca. 20%-25%. The formation has been studied intensively for paleontology, paleoclimate, and sedimentary reconstruction. However, alluvial sandstone bodies and their corresponding river styles remain little characterized and documented. Here, efforts are made to study the characteristics and river styles of sandstone bodies through ca. 300 m of alluvial stratigraphy in the McCullough Peaks outcrop area based on the field data and a georeferenced 3-D photogrammetric model. Four channel facies associations are recognized, and they are ascribed to four river planform styles: distributary channel, massive trunk-shaped channel, braided channel, and sinuous channel, with the latter two styles being the more abundant. The channel sandstone bodies that show the character of sinuous rivers and those of braided rivers differ significantly in average thickness (6.1 m versus 9.0 m) and insignificantly in average width (on average 231 m) and paleoflow directions (on average N003). Braided-character dominated and sinuous-character dominated river styles are seen to alternate in the outcrop, while they show no spatial dependency in the 10 km2 study area. Bighorn Basin margins varied in the early Eocene, with differing tectonic, geological, and topographic characteristics. The observed mixture of river styles may be attributed to differential influences of axial and transverse river systems and/or climate change that controls water discharge and sediment load. An early Eocene geomorphologic reconstruction is constructed summarizing these new and earlier results.

A study of the hydraulic parameters and ecological significance of braided rivers under flow variations

Numerical modeling of braided channels showed no significant differences in the number of cross-sectional branches between different water periods in the middle reaches of the Yarlung Tsangpo River. During most of the year (wet, normal and dry periods), flow velocities in the higher-branching (HB) channels were significantly lower than in the other two branching categories, while the overall distribution of depth in the higher-branching channels maintained a high degree of consistency with the moderate-branching channels (MB), which partly explains why the HB channels are important habitats for fish spawning, nursery and baiting (lower flow velocity distribution with a wider range of depth). Based on the examination of the water surface width, the water surface width may not be a limiting factor for fish habitat within braided rivers. Simulation of the hydrodynamic parameters of the fish-spawning grounds revealed that the average cross-sectional flow velocity and water depth fluctuated the least at different flows during the fish-spawning period for the HB channels. By counting the hydraulic parameters of the spawning grounds during the spawning period, it can be seen that the most preferred flow velocity for fish in the braided river in the study section was 0.1-0.4 m/s, and the water depth was 0-1.2 m. This article analyses the characteristics of the hydraulic parameters of the braided river and provides theoretical support for the restoration of fish habitats in braided rivers.

Monitoring Dynamic Braided River Habitats: Applicability and Efficacy of Aerial Photogrammetry from Manned Aircraft versus Unmanned Aerial Systems

Despite growing interest in using lightweight unmanned aerial systems (UASs) for ecological research and conservation, review of the operational aspects of these evolving technologies is limited in the scientific literature. To derive an objective framework for choosing among technologies we calculated efficiency measures and conducted a data envelopment productivity frontier analysis (DEA) to compare the efficacy of using manned aircraft (Cessna with Aviatrix triggered image capture using a 50 mm lens) and UAS (Mavic Pro 2) for photogrammetric monitoring of restoration efforts in dynamic braided rivers in Southern New Zealand. Efficacy assessment was based on the technological, logistical, administrative, and economic requirements of pre (planning), peri (image acquiring) and post (image processing) phases. The results reveal that the technological and logistic aspects of UASs were more efficient than manned aircraft flights. Administratively, the first deployment of UASs is less efficient but was very flexible for subsequent deployment. Manned aircraft flights were more productive in terms of the number of acquired images, but the ground resolution of those images was lower compared with those from UASs. Frontier analysis confirmed that UASs would be economical for regular monitoring of habitats—and even more so if research personnel are trained to fly the UASs.

The Architectural Surfaces Characteristics of Sandy Braided River Reservoirs, Case Study in Gudong Oil Field, China

The architecture analysis of the different orders sedimentary bodies is of great significance to the efficient development of oil and gas fields. In order to investigate the effects of the architectural interfaces on reservoir quality and heterogeneity, this study takes the Gudong oil field as a case to investigate the architectural characteristics of hierarchical bounding surfaces using detailed descriptions of core and wireline logs. Architectural models from the 7th-order to the 3rd-order are analyzed, and the developmental characteristics of the 5th-order braided river, 4th-order single sandstone, and 3rd-order accretion are summarized. The interlayer between two braided rivers is floodplain mud deposition, with poor physical properties, stable thickness, and strong blocking capacity. Two models of interlayers are found in the 4th-order deposition. The first interlayer is between the braided filling channel and midchannel bar, which is composed of generally fine-grained sediments with calcium cementation and poor physical properties. The second interlayer is a transformation belt between two midchannel bars and is generally composed of gravel-scoured deposition with penetration capability. The 3rd-order surfaces are defined as the surfaces of accretions within midchannel bars. Two models of interlayers are also found in the 3rd-order surfaces of accretions. The paleocurrent of the sandy braided river is reconstructed by synthesizing the core data, well logging data, and production performance data. A total of 1 fluvial system (7th-order), 2 compound braided rivers (6th-order), 11 braided rivers (5th-order), 41 midchannel bars (4th-order), and 96 accretions (3rd-order) are developed in the study area.

Effects of grid scale and resulting initial bed disturbance differences on the evolution of braided rivers

<p>Physics-based models have been increasingly developed in recent years and applied to simulate the braiding process and evolution of channel units in braided rivers. Braided rivers are the river network system characterized by the staggered distribution of bars and channels. In the numerical calculation, the grid scale affects the behavior process and morphological description of braided rivers. In this paper, a 2D numerical model is used to simulate the evolution of the braided rivers where the transport of load bed sediment plays a dominant role. In the natural scale braided rivers evolution modeling, the difference of the braided rivers' morphological characteristics under different grid scales is discussed, and the influence of different distribution of topographic disturbance caused by grid scale difference on the morphological characteristics of braided rivers is discussed. The study shows that the grid scale does not affect the description of braided rivers evolution process, and braided rivers evolve in the same way regardless of grid scale (within a reasonable range). However, the statistical characteristics of braided rivers are greatly affected by the grid scale. The braiding index increases as the grid scale decreases, but when the grid scale decreases to a certain extent (20m in this paper), the braiding index no longer increases. The number and average height of bars in braided rivers increase with the decrease of grid scale, and the average area of bar near riverbed also increases with the decrease of grid scale, but the average area of bar near water surface does not change with the change of grid scale. In general, the higher the grid resolution is, the more similar the bar morphology in the numerical model is to that in natural rivers. In addition, the different distribution of topographic disturbance caused by the grid scale difference has an influence on the braiding intensity and the bar morphology of the braided rivers, but the influence degree is much smaller than that caused by the grid scale difference.</p>

Impact of vegetation control measures on the bedform of braided gravel-bed river

<p>Braiding is among the most dynamic landscape on Earth. It provides diverse habitats for freshwater creatures. Unfortunately, the number of braided rivers is reducing affected by human activities in the Anthropic period. The increase of the vegetation cover within the river corridor is one important factor, which is induced by flow regime change, land-use change, or alien vegetation invasion. Vegetation clearance could be a promising measure to mitigate vegetation overexpansion. Several previous research suggested vegetation clearance may induce geomorphological metamorphosis. However, quantitative prediction of the morphological change resulted from the vegetation clearance is still an open question to date. We simulated the river morphological response of vegetated braided river with gravel bed to the vegetation clearance using the Nays2DH model combined with a vegetation module. Except for vegetation removal, the developed conceptual model considered vegetation colonization and the destruction induced by floods. Multiple scenarios have been tested, considering two vegetation types (strong and weak vegetation), two clearance methods (full clearance and partial clearance), and two maximum discharge. The full clearance scenario stood for the removal of above-ground and underground biomass simultaneously, and the partial clearance scenario stood for the removal of above-ground biomass. Braided rivers had developed for both no vegetation and river with weak vegetation cover. The bedform affected by strong vegetation coverage consisted of a main channel and small channels on the floodplain, which was consistent with previous experimental results. The distinctive morphology of developed bed form depended on the dominant factor in the vegetation-geomorphology interaction: vegetation dominant or physical process dominant. River morphology responded differently to the vegetation control measure based on the dominating factor. For the vegetation dominated river, the developed main channel tended to be braiding after the vegetation removal, and the river morphology change was sensitive to the vegetation clearance method. By contrast, river morphology changed insignificantly by vegetation colonization and after vegetation removal if the river physical process was dominant. We also found that the small channels on the floodplain promoted sediment transport from the floodplain to the main channel after the vegetation clearance. Thus, the morphological response to the vegetation clearance method was also affected by the reduction of maximum discharge because the connectivity between floodplain and channel was reduced. To improve vegetation clearance effectiveness, we recommend increasing the connectivity between the floodplain and the main channel, such as excavating small channels on the floodplain.</p>