Examinando por Materia "delta"

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    Discharge diversion in the Patía River delta, the Colombian Pacific: Geomorphic and ecological consequences for mangrove ecosystems
    (PERGAMON-ELSEVIER SCIENCE LTD, 2013-10-01) Restrepo, Juan D.; Cantera, Jaime R.; Universidad EAFIT. Departamento de Geología; Ciencias del Mar
    In the Patía River delta, the best-developed delta on the western margin of South America, a major water diversion started in 1972. The diversion of the Patía flow to the Sanquianga River, the latter a small stream draining internal lakes from the Pacific lowlands, shifted the active delta plain from the south to the north and changed the northern estuarine system into an active delta plain. The Sanquianga Mangrove National Park, a mangrove reserve measuring 800km2, lies in this former estuary, where major hydrologic and sedimentation changes are occurring. Overall, major environmental consequences of this discharge diversion in terms of geomorphic changes along distributary channels and ecological impacts on mangrove ecosystems are evidenced by: (1) distributary channel accretion by operating processes such as sedimentation, overbank flow, increasing width of levees, sedimentation in crevasses, interdistributary channel fill, and colonization of pioneer mangrove; (2) freshening conditions in the Sanquianga distributary channel, a hydrologic change that has shifted the upper estuarine region (salinity <1%) downstream; (3) downstream advance of freshwater vegetation, which is invading channel banks in the lower and mixing estuarine zones; (4) die-off of approximately 5200ha of mangrove near the delta apex at Bocas de Satinga, where the highest sediment accumulation rates occur; and (5) recurrent periods of mangrove defoliation due to a worm plague. Further analyses indicate strong mangrove erosion along transgressive barrier islands on the former delta plain. Here tectonic-induced subsidence, relative sea-level rise, and sediment starving conditions due to the channel diversion, are the main causes of the observed retreating conditions of mangrove communities. Our data also indicate that the Patía River has the highest sediment load (27×106tyr-1) and basin-wide sediment yield (1500tkm-2yr-1) on the west coast of South America. Erosion rates from the Patía catchment have been more pronounced during the decades of 1970-1980 and 1990-2000, as a result of land degradation and deforestation. The high sediment and freshwater inputs into the mangrove ecosystem create additional stress (both at ongoing background levels and, occasionally, at dramatic levels), which may periodically push local environmental parameters beyond the thresholds for mangrove survival. The future environmental state of the Sanquianga Mangrove National Reserve deserves more scientific and governmental attention. © 2011 Elsevier Ltd.
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    Human induced discharge diversion in a tropical delta and its environmental implications: The Patía River, Colombia
    (ELSEVIER SCIENCE BV, 2012-03-06) Restrepo, Juan D.; Kettner, Albert; Universidad EAFIT. Departamento de Geología; Ciencias del Mar
    The Patía River, the number one in terms of sediment yield ~1500tkm -2yr -1 draining the western South America, has the most extensive and well developed delta on the Pacific coast, measuring 1700km 2. During the Holocene, nature forced the Patía delta to the south; however, a major water diversion, starting in 1972, diverted the Patía flow to the Sanguianga River, the latter, a small stream draining internal lakes from the Pacific lowlands. This human induced discharge diversion shifted the active delta plain back to the north and changed the northern estuarine system into an active delta plain. Overall, major environmental consequences of this discharge diversion in terms of morphological changes along the delta coast and distributary channels, are evidenced by: (1) coastal retreat along the abandoned delta lobe; 63% of the southern shoreline is retreating at maximum rates of 7myr -1, with a corresponding coastal land loss of 106myr -1; (2) transgressive barrier islands with exposed peat soils in the surf zone; (3) abandonment of former active distributaries in the southern delta plain with associated closing of inlets and formation of ebb tidal deltas; (4) breaching events on barrier islands; and (5) distributary channel accretion in the northern delta plain by morphological processes such as sedimentation (also in crevasses), overbank flow, increasing width of levees, interdistributary channel fill, and colonization of pioneer mangrove. The Sanguianga Mangrove National Park (SMNP), the largest mangrove reserve in Colombia, measuring 800km 2, lies in this former estuary, where major hydrologic and sedimentation changes are occurring. Observed environmental changes in the SMNP, include (1) seaward advance of the sub-aqueous delta front at the Sanquianga inlet evidenced by an increase in tidal flat area from 5.4Mm 2 in 1986 to 14Mm 2 in 2001; (2) freshening conditions in the Sanguianga distributary channel, a hydrologic change that has shifted the upper estuarine region (salinity <1psu) downstream; (3) downstream advance of freshwater vegetation, which is invading channel banks in the lower and mixing estuarine zones; (4) die-off of approximately 5200ha of mangrove near the delta apex at Bocas de Satinga; and (5) recurrent periods of mangrove defoliation due to a warm plague. Further analysis indicate that during the past two decades, processes such as mangrove erosion in the delta shore, are the result of a short-term relative sea-level rise of 5.1mmyr -1 for the 1984-2006yr-period, after the devastating tsunami of 1979. In the Patía catchment, erosion rates have been more pronounced during the 1970-1980 and 1990-2000 decades, as a result of land degradation and deforestation. Preliminary results indicate that relative resent anthropogenic influences on the Patía River drainage basin have altered the deltaic environment and beyond significantly. © 2011 Elsevier B.V.
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    Late Holocene evidence of coseismic subsidence on the San Juan delta, Pacific coast of Colombia
    (COASTAL EDUCATION & RESEARCH FOUNDATION, 2001-01-01) Gonzalez, JL; Correa, ID; Universidad EAFIT. Departamento de Geología; Ciencias del Mar
    The San Juan delta of Colombia formed under a complex physical setting. Among the unusual factors that controlled the delta formation are: its location in an area with one of the highest precipitation rate anywhere in the world, highly variable river discharge and high sea levels of short duration, both associated with El Niño-La Niña climatic disturbance, and high mesotidal range combined with a medium to low wave energy. Of all the aspects that make the physical setting complex, the high seismicity produced by the subduction of the Nazca plate under the South American plate, has perhaps, been the most important controlling factor in the Late Holocene development of the delta. Coring on its SW island retrieved soils buried, 1.2-1.5 m by intertidal deposits; the sharp contact between the soils and the mantling deposits, implies large sudden submergence, which is most simply explained as being coseismic, associated with the high seismicity of the area. Timing of the earthquake that caused subsidence, is placed around 500 years BP. Evidence from recent earthquakes along the South central Pacific coast of Colombia indicates that - subsidence > 1 m requires a M 7.9 or greater earthquake.