Cuspate Delta Research Articles

Coastal Erosion Caused by River Mouth Migration on a Cuspate Delta: An Example from Thanh Hoa, Vietnam

Coastal erosion poses a significant threat to the infrastructure of the coastal community at the mouth of the Ma River in Thanh Hoa Province, Vietnam. In response, emergency solutions such as hard, protective structures are often implemented. However, this approach exacerbates the problem as the underlying mechanisms of coastal erosion are not adequately investigated and understood. In this study, the long-term configuration of the mouth of the Ma River in Thanh Hoa Province, Central Vietnam, is investigated using Landsat imagery spanning from 1987 to 2023. An analytical solution of a one-line model for shoreline change was also used to examine the sand discharge from the Ma River and the diffusion coefficient for the sand transported along the shore by breaking waves. The results showed an asymmetric configuration of the mouth of the Ma River over the past 37 years. The supply of sand from the Ma River is around 350,000 m3/year. The majority of sand (ranging from 55% to 75%) is mainly transported to the northern beach of the Ma River delta. This uneven distribution of sand from the Ma River has led to the asymmetrical morphology of the delta apex in which the northern part of the Ma River delta is experiencing northward movement while the southern part of the Ma River Delta is moving southward and landward. The asymmetrical morphology of the delta at the mouth of the Ma River has recently been identified as the cause of severe coastal erosion. The diffusion coefficient value determined for the transportation of longshore sand along the deltaic lobes of the Ma River delta corresponds to 90 m2/day. This study offers a practical method for investigating morphological changes in cuspate deltas, especially when measured field data are limited.

The interaction of buoyant coastal river plumes with mangrove vegetation and consequences for sediment deposition and erosion in a tidal environment

To identify the drivers of sediment deposition within a mangrove-lined river delta, we developed a three-dimensional numerical model in an idealized domain. Our model system is based on the Firth of Thames, a modern flat-fronted, bay-head deltaic system, in the Hauraki Gulf, in the North Island of New Zealand. The interactions of the buoyant river plume with mangroves are examined, including sediment deposition and erosion patterns. The morphological study presented here is restricted to cohesive sediments, whose patterns are observed after 4 months of morphological evolution. For the non-vegetated case, represented by a spatially uniform roughness, sediment deposited throughout the central model domain with a formation of a cuspate delta at the river mouth. However, in the vegetated case (with vegetated areas represented by an enhanced and spatially varying roughness coefficient), sediment deposition occurred in the regions of forests and flats, whereas the fringe areas experienced erosion. The sediment deposition patterns along cross-sections were qualitatively consistent with field observations from the Firth of Thames. Analysis of the across-transect and along-transect momentum balances demonstrates that the predominant balance between the bottom shear stress and baroclinic pressure gradient largely controls the sediment deposition in the riverine sections of the domain. However, close to the center of the plume, vertical advection promotes suspension of the sediments in the fringe region during the flood tide.

Palaeogeography and evolution of the Godavari delta, east coast of India during the Holocene: An example of wave-dominated and fan-delta settings

We investigated the Holocene evolution of the Godavari delta along the east coast of India, by analyses of landforms and 11 borehole cores collected from the delta plain during 2010–2013 with 113 14C dates. The Godavari delta covering an area of 5820km2 is one of the world's largest wave-dominated deltas fringed by a ~30km wide beach-ridge plain. Our analysis of sediment facies and their ages indicated that the Holocene marine sequence thickens seaward from ~10m to more than 50m and that the local relative sea level rapidly rose from 43.5m to 7.5m below the present sea level during 10.9–8.0calkyBP followed by a slow rise up to its current level around 5calkyBP. Spatio-temporal variations in sediment accumulation rates and palaeo-shorelines for the last 6ky revealed successive changes of the main depocentre (delta lobe). We recognised six stages of delta evolution with distinct cyclic shifts of delta lobes controlled by avulsions. A linear beach ridge located 12–14km inland from the present shoreline, which separates the first three lobes from the last three, represents the effect of coastal erosion of past cuspate delta lobes, as does the current linear shoreline of the central part of the delta. Our study documents continuous net progradation during the Holocene on millennial to centennial time scales. However, a considerable decrease of sediment discharge due to dam construction and water diversion since the 1970s has exacerbated coastal erosion, resulting in shrinking of the Godavari delta plain and tipping it into a persistent destruction phase.

Storm-Driven Shoreface Morphodynamics on a Low-Wave Energy Delta: The Role of Nearshore Topography and Shoreline Orientation

An analysis of storm-driven sedimentary changes on the shoreface of a low–wave-energy cuspate delta on the southern coast of Spain is examined. Bathymetric surveys, ranging from 1- to 40-m depth, were collected 2 days before and 9 days after a high-magnitude Levante storm. The storm lasted only 36 hours, with peak wind gusts of 100 km/h (28 m/s) and maximum wave heights of 7.4 m. Storms of similar magnitude have only been recorded four times in the last 20 years along this coast. The deltaic nearshore and shoreface was divided into three main morphologic and morphodynamic zones based on process-response mechanisms following the storm event. The eastern section, characterised by a steep and concave shoreface, only had minor erosion and deposition as a result of the storm. The area seaward of the river mouth, an intermediate zone where the coastline changes orientation, is characterised by a widening surf zone and an irregular shoreface out to 10-m depth before dipping steeply to 40-m depth. Poststorm changes along this transitional area resulted in the deposition of a thin veneer of sediment over a 3 km2 area from 10- to 40-m depth. The western section, a shallow and wide delta front with a double-bar, a trough, and shore-oblique topography, was modified the most by the storm, with significant upper shoreface erosion and shore-oblique erosional scars in 5–7-m depth. Results of spectral wave modelling of wave-induced force match well with observed morphological change; force is minimal along the east coast, more pronounced along the steep shoreface opposite the river mouth, and at a maximum along the west coast. It is suggested that coastal orientation, shoreface morphology (topography, gradients), and storm parameters (wave and wind direction) generated contrasting wind and wave-induced currents on the delta shoreface, resulting in spatial differences in storm response.

Tectonic and climatic controls on historical landscape modifications: The avulsion of the lower Cecina River (Tuscany, central Italy)

Integration of geomorphology, stratigraphy, sedimentology and morphotectonics in the analysis of the lower Cecina River reach, coastal Tuscany, reveals an undocumented historical channel avulsion. Geomorphological evidence and radiocarbon dating support that, from the Last Glacial Maximum until the end of the 16th century, the Cecina River flowed north of the present course and formed a well-developed cuspate delta. Two concurrent factors, active tectonics as a preparing factor and discharge regime as an activation factor, are thus inferred to have favored the avulsion of Cecina River. Fragmentary archaeological and historical records indicate that the late Holocene Cecina River plain was virtually unpopulated until the latest 16th century. This seems the main reason why high-magnitude hydrological events and prominent river channel avulsions were not reported in historical chronicles. From this perspective, geomorphological data may provide important knowledge and understanding of recent dynamics of environmental change when historical record is lacking or missing.

Tectonic Control of High-Frequency Holocene Delta Switching and Fluvial Migration in Lingayen Gulf Bayhead, Northwestern Philippines

Remotely sensed images, maps, charts, and historical accounts document the evolution of the Lingayen Gulf bayhead plain in the northwestern Philippines. Beach ridges and relict channel patterns record delta progradation and switching that, together with meander belt migration, constructed the bayhead plain. The latest delta switching occurred after 1935, when the downstream portion of the Agno River, the largest river discharging into the bayhead, was artificially diverted to a more direct route. The shoreline retreated in the abandoned delta; in contrast, paired sets of beach ridges that diverge toward the new river mouth formed a cuspate delta. In the more landward portions of the coastal plain, similar but older pairs of wedge-shaped beach ridge sets occur between more continuous to parallel sets that also truncate their apical ends. The pair of wedge-shaped sets was used to map paleodelta lobes; the continuous-parallel sets record transgressive events. Within 7 kilometers of the bayhead plain, at least 15 paleodelta lobes were alternately, successively, or simultaneously built by three river systems. These paleodeltas formed during the sea level fall from 2.4 ka to the present. Before this, westward tilting because of movements along the two faults that bound the alluvial plain and switching of the main distributary channel of the Agno alluvial fan caused the lower Agno River to migrate episodically to the southwest. Continued channel avulsions in the alluvial fan changed the sediment loads of the multiple river pathways created by meander belt migration, leading to delta switching downstream. Contemporaneous 220-year recurrences of delta switching and high-magnitude Philippine Fault earthquakes indicate tectonic control of the bayhead plain evolution.

Updrift river mouth migration on cuspate deltas: two examples from the coast of Tuscany (Italy)

The configuration of the Arno and Ombrone deltas (Italy) is evaluated. The terminal courses of the rivers forming these deltas face the dominant wave orthogonal. This configuration came about during rapid delta progradation as a consequence of increased river sediment input due to widespread deforestation within the catchment area, a prevailing phenomenon from the Early Middle Ages to the XVIII century. The rivers attained and maintained their directions as the result of the increased accretion rate on the less exposed downdrift side of the delta. On the more exposed updrift side, delta growth caused the shoreline to gradually rotate so that it directly faced the waves approaching the coast. Here, due to the lower refraction, wave energy per shore unit increased whilst accretion rate decreased. This rotation of the shoreline-induced longshore inversion on the updrift side, whereas today cusp erosion is restoring the original drift direction.

Holocene deltaic sequence in the Saloum estuary, Senegal

The 2250 km 2 Saloum delta, south of Dakar, Senegal, consists of a Holocene sedimentary sequence deposited during five evolutionary stages: submerged postglacial ria, funnel-like estuary, barred estuary, cuspate delta, and reverse estuary. The passage from one stage to another was marked by the deposition of sedimentary units consisting of shelly sands, silty or sandy clays, and an extensive thick green mud. Muds in the lower strata, dating between 6130 and 3500 yr B.P., were deposited on a subtidal mudflat, while fine sands and silty clays characterize intertidal deposits. A drastic change in sedimentation patterns, resulting in the accumulation of a series of beach barriers, likely was associated with a major climatic change. The regional climate was then very dry, and silt and sand were trapped in the water behind the barriers in two stages, from 1990 to 1510 and 1020 to 600 yr B.P. Each event was accompanied by construction of shell middens that demonstrate the presence of humans who exploited newly available shallows and banks. Relative sea level did not change significantly between 6000 yr B.P. and the present. Morphological and sedimentological changes observed in the late Holocene sequences were apparently induced by a constraining climatic background.

Rates, Controls, and Sand-Body Geometries of Transgressive-Regressive Cycles: Cretaceous Moosebar and Gates Formations, British Columbia

The Moosebar and Gates Formations (Lower Cretaceous) in northeastern British Columbia consist of seven transgressive-regressive sequence. Nonmarine sediments are thickest in the south and pinch out northward. The sequences are laterally persistent, extending east from the foothills for 240 km (150 mi). The orientation of maximum transgressive and regressive limits in five cycles occurs within an east-west-trending zone 30-40 km (19-25 mi) wide. A recurring, northward-bulging sediment depocenter near the Alberta-British Columbia border was fed by a series of stacked, northerly flowing rivers. The rivers were a major source of sediment for gravel beaches to the north and east. Isopach maps of marine sandstone and conglomerate show a series of west-northwest-east-southeast-o iented sand bodies 60-70 km (37-43 mi) wide, parallel with the shorelines. Each coastline prograded northward as a shoreline-attached strand plain and a series of arcuate or cuspate deltas. Gates Formation marine-nonmarine cyclicity is a series of fourth-order cycles superimposed on a major third-order cycle. The cyclicity and lateral extent of the sequences can be explained as a result of tectonic thrusting and loading superimposed on the trend of the Peace River arch. The influence of eustatic sea level variations and sedimentologic switching of point sources had minimal effect. Coastal retreat ranged from 437 to 875 m/1,000 years (1,433 to 2,780 ft/1,000 years). Coastal progradation ranged from 218 to 437 m/1,000 years (175 to 1,433 ft/1,000 years). The duration of several transgressive-regressive cycles was 103,000-275,000 years.

Geometry and Facies of Latest Cretaceous Deltaic and Submarine Fan Systems, Southern Sacramento and Northern San Joaquin Basins, California: ABSTRACT

Regional cross sections and net-sand isopach maps depict the geometry and genetic relations of Maestrichtian deltaic and submarine fan depositional systems in the southern Sacramento and northern San Joaquin basins. The six Starkey sands are multilobed cuspate to lobate deltas with east-west or northeast-southwest axes and apices near Sacramento and Stockton. The overlying sand (Bunker, 3rd Massive, etc) in the Sacramento Valley is an elongate delta with north-south axes and multiple apices. Submarine fans (lower and upper Winters, Tracy, Blewett, and Azevedo sands) are elongate northwest-southeast, parallel to the basin axis. Most fan shapes are distorted owing to onlap on basin slopes or the cross-valley sill termed the Stockton Arch, but less confined fans show the expected fan shape. Initially the slope was fault controlled, but the deltas prograded the slope, constricting the basin. Five deltas overtook the prograding slope and fed sand over the shelf edge or through shallow slope channels to the fans. Deltas were abandoned during cyclic sea level rises; during the succeeding progradations, mud was swept out of the deltas and draped over the slope and previous fan. Thus, five cycles of delta progradation, fan growth, delta retreat, and fan abandonment are preserved. As the basin filled and water depth decreased, deltas became larger and fans grew smaller. Local cross sections show facies relations and lithologies. Cuspate deltas consist mainly of coarsening-upward prodelta mud-delta front/shoreface sand. Elongate deltas are largely delta-plain marsh and channel facies. Fans are mainly thick-bedded (amalgamated) massive to fining-upward sand; bed thickness and grain size decrease in a narrow periphery where fans onlap basin slopes or grade to basin-plain shale. Gas is produced from both suprafans and fan margins. End_of_Article - Last_Page 910------------

Late Pleistocene and Holocene evolution of the North Adriatic continental shelf (Italy)

During the Würm regression the present North Adriatic continental shelf was a wide fluvio-lacustrine plain, where rivers with rather high dynamics coexisted with swamps and bogs characterized by calm water and formation of peat soils. The Flandrian marine transgression covered the plain, reworking the continental deposits. The advancing sea affected the study area in two stages; the first at about 6000 yr BP, the second, corresponding to the maximum Holocene marine ingression, at 2000–3000 yr BP. At this time the Po River began to form cuspate deltas from an almost straight coastline. This process continued until about 1600 AD when deforestation and the construction of levees increased the sedimentary load carried by the river, causing the building up of modern lobate deltas.

The bathymetry and sedimentation of Cape San Blas shoal and shelf off Saint Joseph Spit, Florida

ABSTRACT A total of 144 bottom dredge samples were collected on Cape San Bias Shoal and vicinity, west of Apalachicola Bay, Florida, in the Northeast Gulf of Mexico. On the basis of this investigation, four bathymetric-sedimentary provinces can be distinguished: (1) The Cape San Blas Shoal extends southwest approximately 14.5 km into the Gulf from the Cape. Characterized by a very rough ridge-and-swale topography, it can be divided into two general units by sediment type, mean grain size, and standard deviation. (2) A basin, located northeast of Cape San Blas Shoal and extending south to about 12.8 km offshore, contains very fine-grained sediments derived from the Apalachicola River. (3) To the south of this basin, and southeast of Cape San Blas Shoal is the ridge-and-swale province composed of a mixture of shell hash, medium to coarse sand and a low percentage of silt. (4) The shelf to the west of the shoal is basically composed of very-well sorted fine sand and shelly fine sand with some coarse sand on a smooth, gently seaward sloping topography. Thin mud layers, originating in Apalachicola Bay and transported around the shoal, overlie the sand in certain areas of the shelf. The doublet of geomorphic provinces consisting of Cape San Blas Shoal and the ridge-and-swale province are interpreted as a shoal-retreat massif. It was initiated as a cuspate delta of an Apalachicola River distributary during a low stand of seal level. At the present time it is maintained 'in line' through wave refraction, although sediment-budget calculations indicate that a shift to the east is taking place. The shoal grows landward through accretion at the base. Prominent cross-cutting depressions were initiated as spillways by hurricane-generated currents. Hurricane waves and surge-generated currents largely determine the ultimate shape of these provinces. Surface features of selected quartz grains were studied by differential-interference and scanning electron microscopy. The coarser grains of the shoal, ridge-and-swale and north shelf provinces, show V-shaped impact features and grooves characteristic of high-energy environments. The fine grained shelf and basin sands are smooth and relatively featureless. The sediments in the study area generally consist of a minor contribution of modern mud and shell hash, but mainly of quartz-sand which was originally laid down as a subaerial deposit during a low stand of the sea. Nearshore processes have produced from the original material the nearshore modern well-sorted, fine sand. This material is most prominent in, but not restricted to either the nearshore or the shoal regions of the study area. Lower Cape San Blas Shoal and the ridge-and-swale province consist of coarser sands with notable admixtures of shell hash. Although such sand is often referred to as relict, textural considerations and some (ill-developed) associations between textural parameters and topography suggest that the sediment continues to undergo transportational and depositional episodes, largely in response to hurricane conditions. The term 'palimpsest' is more properly applied to this kind of material.

History of Apalachicola River Delta Area, Florida: ABSTRACT

The Apalachicola River and its tributaries have delivered significant quantities of sediment into the northeastern corner of the Gulf of Mexico since early Tertiary time. The location of a major drainage outlet in the Alabama-Florida-Georgia tri-state area must be a matter of structural control, inasmuch as well-developed Cretaceous cuestas across southern Alabama and Georgia divert important drainages either toward the east (Atlantic Ocean) or the west (Alabama River system, draining into Mobile Bay). The early Tertiary predecessor of the Apalachicola River may have been located about 75 km. east of the present river. The modern gorge of the Apalachicola has been occupied since perhaps middle Miocene time, when a previous estuary (in an important graben or half-graben) was completely filled with sediment. The Mio-Pliocene river built three or four cuspate deltas, at elevations of about 80, 50, 35, and perhaps 25 m. Three of these still exhibit relic offshore-flat, barrier-island, and drained lagoon topography. Clear evidence is present in the area for Pleistocene sea-levels at 9, 6, 0, and -2 m. During the Pleistocene, the Apalachicola dammed the mouth of the Chipola River with sediment, forming Dead Lake, and almost completely filled a large estuary near the village of Apalachicola, leaving Lake Wimico and East Bay as remnants. Many of the features of the modern cuspate delta (including offshore shoals) have been formed, and reworked, as sea-level moved up and down during the Pleistocene. One of these features, an as yet inadequately explored and filled channel perhaps 35-40 m. deep, is under the present course of the river. The low wave-energy level in the northeastern corner of the Gulf of Mexico--much like that along geosynclinal coasts of the past--is responsible for preservation of many delta characteristics which probably would have been eliminated if breaker heights had been typical of an open ocean. Subtle structural deformation, still continuing in the delta area, partly controls the overall delta outline as well as many of the details. The prime structural trend in the area is N. 50°E.; there is less evidence for linears striking approximately N. 70°W. End_of_Article - Last_Page 1756------------

A Resume of River Delta Types: ABSTRACT

Deltas and deltaic sediments are produced by the rapid deposition of stream-borne materials in relatively still-standing bodies of water. Notwithstanding the effects of subsidence and water level movements, most deltaic sediments are deposited off the delta shoreline in the proximity of the river's mouth. As these materials build upward to the level of the still-standing body of water, the remainder of deltaic sediments are deposited on shore, within the delta's flood plains, lakes, bays, and channels. Nearly 2,500 years ago, Herodotus, using the Nile as an example, stated that the land area reclaimed from the sea by deposition of river sediments is generally deltoid in shape. The build-up and progradation of deltaic sediments produces a distinct change in stream gradient from the fluvial or alluvial plain to the deltaic plain. Near the point of gradient change the major courses of rivers generally begin to transport much finer materials, to bifurcate into major distributaries, and to form subaerial deltaic plains. The boundaries of the subaerial plain of an individual delta are the lateral-most distributaries, including their related sediments, and the coast line. Successively smaller distributaries form subdeltas of progressively smaller magnitudes. Deltas may be classified on the basis of the nature of their associated water bodies, such as lake, bay, inland End_Page 334------------------------------ sea, and marine deltas. Other classifications may be based on the depth of the water bodies into which they prograde, or on basin structure. Many delta types have been described previously. Most of these have been related to the vicissitudes of sedimentary processes by which they form. Names were derived largely from the shapes of the delta shorelines. The configuration of the delta shores and many other depositional forms expressed by different sedimentary facies appear to be directly proportional to the relative relationship of the amount or rate of river sediment influx with the nature and energy of the coastal processes. The more common and better understood types, listed in order of decreasing sediment influx and increasing energy of coastal processes (waves, currents, and tides), are: birdfoot, lobate, cuspate, arcuate, and estuarine. The subdeltas of the Colorado River in Texas illustrate this relationship. During t e first part of this century, the river, transporting approximately the same yearly load, built a birdfoot-lobate type delta in Matagorda Bay, a low-energy water body, and began to form a cuspate delta in the Gulf of Mexico, a comparatively high-energy water body. Many deltas are compounded; their subdeltas may be representative of two or more types of deltas, such as birdfoot, lobate, and arcuate. Less-known deltas, such as the Irrawaddy, Ganges, and Mekong, are probably mature estuarine types. Others, located very near major scarps, are referred to the Gilbert type, which is similar to an alluvial fan. End_of_Article - Last_Page 335------------