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North American Continental River Drainage Basins The large continental river basins draining North America to the Gulf of Mexico that bound the studied region of the Coastal Plain. As each river approaches the coast it transitions from a broad, dendritic upland catchment area to an aggrading distributary. The coastal plain drainages studied are located in between these distributaries.
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Understanding the detailed structure of landscape topography is important when assessing risks in coastal plain areas susceptible to the combined effects of fluvial, pluvial and coastal flooding. Key to this analysis is the identification and characterization of drainage basins that control surface water flow, but the factors controlling the format...
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... Aquatic vegetation is prevalent in various aquatic environments, including waterways, rivers, lakes, and tidal zones. It plays a crucial role in shaping the morphological evolution of streams and influencing their sediment transport capacity Ielpi et al., 2022;Nepf, 2012a;Swartz et al., 2022). Vegetation exerts a substantial influence on river morphological evolution by introducing additional drag to flow, resulting in reduced flow velocity and energy, consequently affecting the sediment transport capacity of the flowing water (Calvani et al., 2023;Le Bouteiller & Venditti, 2014;Li et al., 2022). ...
Widely distributed in natural rivers and coasts, vegetation interacts with fluid flows and sediments in a variable and complicated manner. Such interactions make it difficult to predict associated drag forces during sediment transport. This paper investigates the drag coefficient for an emergent vegetated patch area under nonuniform flow and mobile bed conditions, based on an analytical model solving the momentum equation following our previous work (Zhang et al., 2020, https://doi.org/10.1029/2020WR027613). Emergent vegetation was modeled with rigid cylinders arranged in staggered arrays of different vegetation coverage ∅. Laboratory flume tests were conducted to measure variations in both the water and bed surfaces along a vegetated patch on a sand bed. Based on the experimental and theoretical analyses, a dimensionless drag model integrating both terms of flow properties and bed effects is proposed to predict the drag coefficient Cd over a mobile bed. The calculated values of Cd exhibit two different trends, that is, nonmonotonically or monotonically increasing along the streamwise direction, due to the combined effect of water surface gradient and bed slope. The morphodynamic response of the mobile bed to nonuniform flow manifests as an evolution in the bed slope within the vegetated patch. Ongoing scouring directs the flow's energy toward overcoming the rising Cd and bed slope, leading to a relatively stable stage with a low sediment transport rate. This study advances the existing understanding of the drag coefficient's role over a mobile bed within nonuniform flows. It also enhances the applicability of vegetation drag models in riverine restoration.
... Drainage basins divide Earth's surface into unique hydrological and geomorphological units separated by their ridgelines. While the shapes of the drainage networks within basins have been extensively studied (Clark et al., 2004;Devauchelle et al., 2012;Howard, 1967;Scherler & Schwanghart, 2020;Swartz et al., 2022;Willett et al., 2014;Yi et al., 2018;Zernitz, 1932), the geometric shape of drainage basins has received much less attention (Castelltort & Simpson, 2006;Castelltort & Yamato, 2013;Castelltort et al., 2009;Daryaei et al., 2012;Sassolas-Serrayet et al., 2018;Shelef, 2018). Because basin shapes reflect how water accumulates across the landscape, they play a crucial role in hydrological responses such as flood propagation or sediment transport (Benda et al., 2004;Hovius, 1996;Kirkby, 1976;Rinaldo et al., 1991Rinaldo et al., , 1995Walley et al., 2018). ...
Drainage basins are fundamental units of Earth's surface, describing how flows accumulate across landscapes. They are direct expressions of how tectonics and climatic forces alter Earth's surface morphology. Here, we measure the width‐to‐length ratios (WLRs) of 386,931 drainage basins (average area ∼157 km²), covering all continents except Antarctica and Greenland. Global variations in WLRs are correlated with climatic aridity, whole‐basin slope, and local topographic roughness. Basins in arid landscapes tend to be narrower, potentially reflecting a higher prevalence of surface runoff and therefore a stronger slope‐parallel component of the transporting flow. Local topographic roughness is associated with wider basins, potentially reflecting greater dispersion of flow directions. Conversely, whole‐basin topographic gradients, potentially reflecting gradients in uplift, are associated with narrower basins. However, steeper basins are also often rougher, so revealing the effects of whole‐basin slope requires correcting for the confounding effects of roughness variations.
... Compared to complex branching and meandering tidal channel systems [20][21][22] , we observe that the geomorphology of parallel channel systems differs notably in several aspects. First and foremost, these systems commonly develop on open-coast tidal ats or along the anks of major tidal channels, with individual branches being similar in size and nearly parallel to each other. ...
Tidal channel systems arising from morphodynamic interactions exhibit a suite of diverse morphological configurations. A prevalent type is represented by linear dendritic channels formed by single-thread streams aligned roughly parallel or subparallel to each other in the cross-shore direction. Despite their ubiquity, the processes driving the formation of these parallel channel systems remain elusive. We conducted a morphological analysis of 275 parallel tidal channels from 20 different locations worldwide and found that the angle between individual parallel branches and the parent stream, from which they develop, consistently falls within the range of 80-100º. We employed numerical modeling to shed light on the underlying mechanisms governing their formation, revealing that alongshore uniformity in bed topography and the strength of tidal currents condition the alignment of parallel channels. Cross-shore parallel channels can be formed by alongshore tidal currents, and the channel orientation is largely governed by the shape of the bed profile. Straight and shore-normal parallel branches tend to form where the bed profile changes sharply around the mean sea level, while linearly sloping profiles lead to oblique parallel branches. By unraveling the physics underlying the formation of these striking but poorly understood geomorphic features, our results bear significant ramifications for the understanding and management of valuable tidal ecosystems.
... With sedimentation rates on floodplains being a function of distance from the channel (Pizzuto, 1987), the highest elevations on alluvial plains are often located along channel margins (Hassenruck-Gudipati et al., 2022), forming topographic features containing channels called alluvial ridges. This lateral variability in sedimentation builds relief, developing basins which channel belts can be routed into (Aslan & Blum, 1999;Speed et al., 2022;Swartz et al., 2022). These alluvial-ridge basins often develop well-defined tributary drainage networks despite their relatively low relief Fig. 1). ...
... To compare with the channel belts, we similarly measured the orientation of the modern coastal drainage network located near the seismic volume (Fig. 1B). We used channel centerlines downloaded from the USGS National Hydrography Dataset (e.g., Swartz et al., 2022, their Fig. 1). ...
... The channel belts in this volume may represent the shingling and stacking of belts in anywhere from 14 to 25 distinct basins. With the channel-belt interval being between 142 and 177 m thick, if we assume Pleistocene alluvialridge basins were similar in relief to the modern (about 7 -10 m deep; Swartz et al., 2022), then the belts in the volume must represent this process of alluvial-ridge basin creation and filling many times over, indicitating it is a common process in coastal alluvial settings. It is not clear whether preservation in alluvial-ridge basins must occur within a coastal backwater zone. ...
The fluvial sedimentary record is largely composed of deposits from relatively common flow events, rather than more catastrophic scour-and-fill events. At the scales of bedforms, such deposits are preserved within the stratigraphic record because they rapidly accumulate within, and are protected by, morphodynamic topographic depressions that occur naturally in the fluvial system as a result of feedbacks between flow, sediment transport, and topography. Examples include the preservation of ripples in front of dunes, dunes in front of bars, and bars within channels. Here, we used 3D seismic data that images preserved channel belts to test the hypothesis that alluvial-ridge basins, morphodynamic depressions formed between raised channel beds due to decreasing sedimentation rates away from channels in alluvial settings, are a source of topography driving channel-belt-scale preservation. Using the 3D seismic data, we measured the stratigraphic positions of channel belts, as well as their lengths, widths, sinuosities, and centerline orientations in the 3D seismic dataset. Results are consistent with well-preserved channel belts steered by alluvial-ridge-basin topography. Further, the thickness of the channel-belt interval exceeds the relief of any one alluvial-ridge basin, suggesting the volume records the filling of multiple alluvial-ridge basins and that the process is common. Characterizing the stratigraphic signature of alluvial-ridge basins is necessary for understanding contrasting fluvial architectures where external forcings prevented their formation.
... Though alluvial settings have low gradients, they are not flat. On Earth, several m of relief may form due to the decrease in sedimentation rates on a floodplain with increasing distance from an active channel (Aslan & Blum, 1999;Hassenruck-Gudipati et al., 2022;Swartz et al., 2022). It has been hypothesized that the ridge systems instead represent fluvial reworking of draped volcanic ash (Kerber & Head, 2010), but this is inconsistent with the evidence that rivers were important pathways of sediment into the basin. ...
... However, system 5 does not feature a lobate pattern on the other side of the neck (i.e., on the second half of the hourglass), which we interpret to have been mostly lost to erosion based on the deep trough located there ( Figure 5). On Earth, erosional drainage networks made of tributaries, rather than distributaries, can develop along meters of relief in depositional coastal settings due to direct rainfall runoff (Swartz et al., 2022;Willett et al., 2014). How these drainage networks come to be filled with sediment in over time is unknown, but perhaps the tributary pattern is inherited by the depositional rivers that eventually occupy these locations as the basin fills. ...
The evidence for an ancient ocean in Mars' northern hemispheric basin during the Noachian/Hesperian is contentious. Much of the work is based on the modern topography by assuming that erosion has not significantly reshaped the Martian surface over the last 3.5 billion years, despite evidence to the contrary. Here, we provide new evidence for a northern ocean or large sea based on stratigraphic analysis of sedimentary basin fill exposed at Aeolis Dorsa. We mapped over 6,500 km of fluvial ridges, grouped them into 20 systems, and present evidence that they are the eroded remnants of river deltas or submarine‐channel belts, together defining the stratigraphy of an ancient ocean margin. We used Context Camera stereo‐pair elevation models to measure the stratigraphic positions of each system and used branching directions to determine paleoflow directions. By grouping landforms based on stratigraphic position and paleoflow directions, we reconstructed the paleogeography at Aeolis Dorsa over 5 timesteps; all cases differ from the modern topography. We tracked the initial regression and later transgression of a shoreline during at least 900 m of sea‐level rise, a scale consistent with a northern ocean on a warm and wet early Mars.
... However, accurately reconstructing geomorphic processes and palaeo-landscapes from the stratigraphic record in these settings necessitates quantitative linkages between the geomorphic form of modern coastal plains and their resultant stratigraphic expression, as well as methods for determining the degree of lateral and vertical preservation achieved. While significant work has focused on the geomorphic and topographic expression and depositional architecture of coastal plain fluvial landscapes (Galloway, 1981;Amorosi et al., 2008;Clement et al., 2010;Shiers et al., 2019;Swartz et al., 2022), an improved understanding of the coastal response and stratigraphic preservation of geomorphic forms on coastal plains during marine transgression is greatly needed (Hein et al., 2014). ...
... Analysis of the chirp data reveals the presence and architecture of what are interpreted as very well-preserved Late Pleistocene to Holocene coastal plain fluvial geomorphic forms, namely a fluvial channel belt, numerous floodplain channels (as defined in the Terminology section) and abandoned channel fills. While there is acknowledgement of the importance of floodplain channels in sediment transport and regulating surfacewater connectivity between river and floodplain (Lewin & Ashworth, 2014;Czuba et al., 2019), and several key studies explore the morphology and controls on their formation (Trigg et al., 2012;David et al., 2017David et al., , 2019Swartz et al., 2022), there is a relative dearth of research detailing the stratigraphic architecture and preservation associated with channelization and channel fills within the floodplain. Moreover, recognition criteria for coastal plain floodplain channels and the architecture of their sedimentary fills in the stratigraphic record have not been established to date. ...
... Moreover, recognition criteria for coastal plain floodplain channels and the architecture of their sedimentary fills in the stratigraphic record have not been established to date. This study interprets the presence of coastal floodplain channels based on their observed seismic stratigraphic relationships in conjunction with the main channel belt, as well as their map-view configuration in the subsurface compared to the modern Gulf Coastal Plain highlighted by Swartz et al. (2022). Based on these results, direct linkages are established between the stratigraphic record and the geomorphic expression of the nearby coastal plain, and new criteria are proposed for the seismic stratigraphic recognition of the form and fill of coastal floodplain channels. ...
Subsurface fluvial deposits in coastline‐proximal settings record the spatiotemporal evolution of the coastal landscape and may be viable repositories of sediment for future coastal restoration projects. However, quantitative linkages between the geomorphic form and stratigraphic expression of coastal plain fluvial elements remain lacking, complicating coastal stratigraphic interpretations and subsurface resource assessment. This study explores the expression and preservation of fluvial coastal plain geomorphic features through outcrop‐scale seismic stratigraphic analysis of ultra‐high‐resolution chirp acoustic reflection data from the north‐western Gulf of Mexico inner continental shelf, offshore the Brazos River, Texas, USA. The chirp data exhibit decimetre‐scale vertical resolution within the upper 35 m of the shelf, evincing the preservation of two distinct types of coexisting fluvial channel‐forms: Type 1, a 1 km wide and 9 m deep single‐storey channel belt filled with sand‐rich lateral accretion deposits and channel fills; and Type 2, numerous 10 to 800 m wide and 1 to 20 m deep incisional floodplain channels filled with extensive drapes of overbank‐derived sediments. The chirp data resolve fluvial geomorphic elements including lateral accretion surfaces, levées, floodplain deposits, and abandoned channel fills. Rollover of lateral accretion surfaces, widespread draping of seismic reflectors within channel fills, and quantitative comparison between the interpreted stratigraphic forms and analogous features on the nearby Texas Coastal Plain suggest near‐complete stratigraphic preservation of the geomorphic form of both channel belt and floodplain channel elements. Rapid aggradation of the coastal plain by the Brazos River in this region during the Holocene transgression is hypothesized as a mechanism for the high degree of preservation achieved. This study proposes the first recognition criteria for the seismic stratigraphic expression of coastal floodplain channels and provides direct linkages between the geomorphic and stratigraphic expression of a coastal plain fluvial landscape, promoting improved coastal stratigraphic interpretations and assessment of subsurface lithofacies distributions.
The size and geometry of river channels play a central role in sediment transport and the character of deposition within alluvial basins across spatiotemporal scales spanning the initiation of grain movement to the filling of accommodation generated by subsidence. This study compares several different approaches to estimating palaeoflow depths from fluvial deposits in the early Palaeogene Willwood Formation of north‐west Wyoming, USA. Fluvial story heights ( n = 60) and mud plug thicknesses ( n = 13) are statistically indistinguishable from one another and yield palaeoflow depth estimates of 4 to 6 m. The vertical relief on bar clinoforms ( n = 112) yields smaller flow depths, by a factor of ca 0.3, with the exception that the largest bar clinoforms match story heights and mud plug estimates. This observation is consistent with modern river data sets that indicate unit bar clinoforms do not capture the reach‐mean bank‐full flow depths except in rare circumstances. Future studies should use story heights (i.e. compound bar deposits) and mud plugs to estimate bank‐full flow depths in alluvial strata. Additionally, the thickness of multi‐storied fluvial sandbodies ( n = 102) and overbank cycles composed of paired crevasse splay and palaeosol deposits ( n = 45) were compared. The two depositional units display statistically indistinguishable mean and median values. Building upon previous depositional models, these observations suggest basin rivers aggraded approximately one flow depth prior to major avulsion. This avulsion process generated widespread crevasse splay deposition across the floodplain. Once the main river channel stem was reestablished, overbank flooding and palaeosol development dominated floodplain settings. The depositional model implies river aggradation autogenically generated topography in the basin that was effectively filled during the subsequent avulsion. This constitutes a meso‐timescale (10 ³ –10 ⁴ years) compensational pattern driven by morphodynamics that may account for the high completeness of fossil and palaeoclimate records recovered from the basin.
Subsidence alone is often too slow to provide the necessary relief to preserve channel belts continuously over 10s of km, as is often observed in outcrop on Earth and Mars, as well as subsurface seismic volumes. A significant source of topographic relief was recently recognized along coastal plains of the US Gulf of Mexico and Atlantic, regions generally considered flat. Alluvial ridges, built from aggraded river-channel beds, bound topographically lower regions which develop tributary drainage networks initiating at the bounding ridges and draining seaward. This relief is capable of driving variability in fluvial sedimentation, thus controlling the way coastal river-channel belts accumulate and become preserved in the rock record. To show this, buried fluvial channel belts are mapped in a 3D seismic volume offshore of the Brazos river delta, Texas, USA. Well-preserved fluvial channel belts are consistently mapped on top of surfaces possessing shorter channelized features. Horizons defined by short channelized features are interpreted as basal surfaces hosting the erosional channels of coastal tributary basins. The belts sitting above these surfaces record the occupation and filling of these basins following avulsions of major, sandy river systems. Both the focused sedimentation and the protection offered by the basin prevent the reworking of these belts, resulting in well-preserved belts recording ‘strangely ordinary’ transport conditions.
