Archive for Fluvial

Young Danube delta documents stable Black Sea level since the middle Holocene: Morphodynamic, paleogeographic, and archaeological implications

New radiocarbon and optical dates show that the Holocene Danube delta started to build out of a Black Sea embayment 5200 yr ago. Delta lobe development phases differ by as much as 5 k.y. from previously proposed ages. The new chronology allows for a better understanding of the Danube delta paleogeography, including the demise of Istria, the main ancient Greek-Roman city in the region.

Prior reconstructions of sea level in the Black Sea inferred fluctuations to 15 m in range; however, stratigraphy of beach ridges in the delta shows that the relative Black Sea level for the past 5 k.y. was stable in the Danube delta region within 2 m and 1.5 of the current level. Hydroisostatic effects related to a proposed catastrophic reconnection of the Black Sea to the World Ocean in the early Holocene may have been responsible for the sea level reaching the highstand earlier than estimated by models. The new sea-level data suggest that submergence at several ancient settlements around the Black Sea may be better explained by local factors such as subsidence rather than by basin-wide sea-level fluctuations.

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On the evolution of Chilia distributary in Danube delta

Florin Filip, Stefan Constantinescu and Liviu Giosan

Accelerated sea-level rise and anthropogenic stresses on large delta-forming rivers have led to intense pressure on deltas around the world. To address issues of maintenance and restoration natural deltaic processes need to be understood in detail. The evolution of Danube delta was studied by numerous researchers in the last century and a vast majority of these studies were driven by development concerns for navigation, resource exploration, agriculture, and fisheries. In an ongoing study on paleoenvironmental aspects of the Danube delta, we collected a series of sediment cores (1 to 6 m long) along the Chilia distributary. Sedimentological, paleontological, and geochemical analyses combined with AMS radiocarbon on in situ articulated mollusks lead us to suggest that the delta lobes that the Chilia arm built are much younger than previously thought. Furthermore, we can now ascertain that Chilia I lobe grew as a lacustrine delta, whereas Chilia II developed as a bayhead delta with a lagoon. In contrast, the modern Chilia III lobe has been building in the open Black Sea since the 18th Century.

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Evolution of Chilia lobes of the Danube delta: Reorganization of deltaic processes under cultural pressures

Florin Filip, Liviu Giosan

The growth of Chilia deltaic lobes reflects a drastic reorganization of the Danube delta that accompanied its rapid expansion in the late Holocene. Using new cores collected at the apices of the two older Chilia lobes, together with historical maps and satellite photos, we find that a partial avulsion since 1500 years BP led to a gradual rejuvenation of the Chilia distributary. This process led to the successive infilling of a lake and a lagoon and subsequently to the construction of an open coast lobe at the Black Sea coast.

The Chilia branch became the largest Danube distributary, reaching its maximum sediment load in the last 300 years as the southernmost St. George branch lost its previous dominance. Here, we propose that the intensive deforestation of Danube’s lower watershed leading to this delta reorganization has historical cultural causes: an increase in sheep and timber demand associated to the Ottoman Empire expansion in Eastern Europe followed by the adoption of maize agriculture as a result of the Columbian Exchange. Rapid industrialization-driven damming during the Communist Era led to the current generalized sediment deficit for the Danube. Under these conditions, the modern Chilia lobe is rapidly remodeled by waves and may join the Sulina coast to impede navigation on the Sulina canal.

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Maintenance of large deltas through channelization: Nature vs. humans in the Danube delta

Liviu Giosan, Stefan Constantinescu, Florin Filip, Bing Deng

Over the last half century, while the total sediment load of the Danube dramatically decreased due to dam construction on tributaries and its main stem, a grand experiment was inadvertently run in the Danube delta: the construction of a dense network of canals, which almost tripled the water discharge toward the interior of the delta plain. We use core-based and chart-based sedimentation rates and patterns to explore the delta transition from the natural to an anthropogenic regime, to understand the effects of far-field damming and near-field channelization, and to construct a conceptual model for delta
development as a function sediment partition between the delta plain and the delta coastal fringe.

We show that sediment fluxes increased to the delta plain due to channelization counteracting sea level rise. In turn, the delta coastal fringe was most impacted by the Danube’s sediment load collapse. Furthermore, we suggest that morphodynamic feedbacks at the river mouth are crucial in trapping sediment near the coast and constructing wave-dominated deltas or lobes. Finally, we suggest that increased channelization that mimics and enhances natural processes may provide a simple solution for keeping other delta plains above sea level and that abandonment of wave-dominated lobes may be the most long term efficient solution for protecting the internal fluvial regions of deltas and provide new coastal growth downcoast.

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Early Anthropogenic Transformation of the Danube-Black Sea System

Over the last century humans have altered the export of fluvial materials leading to significant changes in morphology, chemistry, and biology of the coastal ocean. Here we present sedimentary, paleoenvironmental and paleogenetic evidence to show that the Black Sea, a nearly enclosed marine basin, was affected by land use long before the changes of the Industrial Era. Although watershed hydroclimate was spatially and temporally variable over the last ,3000 years, surface salinity dropped systematically in the Black Sea.

Sediment loads delivered by Danube River, the main tributary of the Black Sea, significantly increased as land use intensified in the last two millennia, which led to a rapid expansion of its delta. Lastly, proliferation of diatoms and dinoflagellates over the last five to six centuries, when intensive deforestation occurred in Eastern Europe, points to an anthropogenic pulse of river-borne nutrients that radically transformed the food web structure in the Black Sea.

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Evolution of Sulina mouth bar (Danube river)

This paper studies the dynamics of the Sulina branch mouth by analyzing the influence of human intervention on sediment deposition at the point at which the Danube river empties into the sea. The surface and volume of the bar and southern spit at the Sulina branch mouth are calculated for the first time using advanced techniques.

The methodology consisted in georeferencing and vectoring the maps produced by the European Commission of the Danube (ECD), followed by a morphometrical separation of the bar and southern spit in the resulting models (from a 5 m depth to the surface). The ECD performed the first improvement works in the Danube Delta; the role of the jetties was to exceed the length of the bar which, in its natural state, extended over the entire mouth. The highest bar development rate was recorded between 1920 and 1925, when the volume of sediments in front of the jetties reached ~2.5 mil. m3. After 1930, both the surface and volume of the sediment deposition rates sharply decreased, due to the change in jetty direction and intensive dredging at the mouth.

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Fluvial landscapes of the Harappan civilization

The collapse of the Bronze Age Harappan, one of the earliest urban civilizations, remains an enigma. Urbanism flourished in the western region of the Indo-Gangetic Plain for approximately 600 y, but since approximately 3,900 y ago, the total settled area and settlement sizes declined, many sites were abandoned, and a significant shift in site numbers and density towards the east is recorded. We report morphologic and chronologic evidence indicating that fluvial landscapes in Harappan territory became remarkably stable during the late Holocene as aridification intensified in the region after approximately 5,000 BP. Upstream on the alluvial plain, the large Himalayan rivers in Punjab stopped incising, while downstream, sedimentation slowed on the distinctive mega-fluvial ridge, which the Indus built in Sindh. This fluvial quiescence suggests a gradual decrease in flood intensity that probably stimulated intensive agriculture initially and encouraged urbanization around 4,500 BP.

However, further decline in monsoon precipitation led to conditions adverse to both inundation- and rain-based farming. Contrary to earlier assumptions that a large glacier-fed Himalayan river, identified by some with the mythical Sarasvati, watered the Harappan heartland on the interfluve between the Indus and Ganges basins, we show that only monsoonal-fed rivers were active there during the Holocene. As the monsoon weakened, monsoonal rivers gradually dried or became seasonal, affecting habitability along their courses. Hydroclimatic stress increased the vulnerability of agricultural production supporting Harappan urbanism, leading to settlement downsizing, diversification of crops, and a drastic increase in settlements in the moister monsoon regions of the upper Punjab, Haryana, and Uttar Pradesh.

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Tipuri de produse cartografice specifice Gurii Sulina

Geographia Napocensis Anul VII, Nr. 2, 2013

MARIUS BUDILEANU
Abstract:- The paper aim is the indexing and ranking of all types of cartographic materials produced by European Commission of the Danube (ECD), 85 unique pieces being already identified from a total of 365.

This first step is important for the next analisys approach regarding the evolution of the Sulina mouth, based on the bathymetrical numerical models. ECD had been asigned (between 1856-1939) the fullfilling of all activities required for the navigation on the Sulina mouth and in the Danube Delta. Another very significant component of ECD activity consisted in the bathymetrical measurments and making maps and plans of the Sulina mouth. In 1861, parallel to the finalisation of the temporary jetties, Sulina mouth first triangulation was made. After this, all maps prior to 1861 have been modified, while on the newer ones a new grid of 500 to 500 feet was represented. The bathymetrical measurements had a seasonly frequence, having as main goal the understanding of coastal dynamics.

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