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Tema: Crecidas controladas: experiencia en el Cañón del Colorado

  1. #1
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    Predeterminado Crecidas controladas: experiencia en el Cañón del Colorado

    Aupa gente!!

    Ya en algunos otros hilos he defendido la importancia ambiental (y económica!) de las crecidas de los ríos.

    Buscando información sobre las Zonas de Inundabilidad Controlada, he encontrado esta otra técnica relativamente novedosa, y ambientalmente interesante: la generación controlada de crecidas -gracias a desembalses-, que permite acercar al río a su régimen natural de caudales.

    Las webs principales del experimento:
    http://www.gcmrc.gov/
    http://walrus.wr.usgs.gov/grandcan/

    Controlled Flooding of the Colorado River in Grand Canyon: the Rationale and Data-Collection Planned

    Controlled flooding of the Colorado River by releases from Glen Canyon Dam has been proposed as a way to manage sediment and other resources in the Grand Canyon. Floods are a natural occurrence of rivers and, in the case of the Colorado River, the architect of the Grand Canyon landscape. Scientists have proposed a controlled flood in response to resource managers' request for ways to restore some of the pre-dam resource conditions. Floods are expected to suspend sand moved to the river bottom by lower flows and deposit it along the river banks where it will be above water after the flood recedes. In this way, the limited sand resources can be utilized to preserve habitat for plants and animals and for use by river runners and campers. Because some effects of a clear water flood from Glen Canyon Dam are uncertain, the U.S. Geological Survey (USGS), in cooperation with the Bureau of Reclamation and the National Park Service, has planned a short period of controlled flooding to provide information for science-based decision-making.


    Background

    Glen Canyon Dam began to store water in 1963. The dam made possible the production of electricity and the irrigation of crops and created new opportunities for recreation. By many measures, life in the Southwest has been improved. But the presence of the dam and regulation of flow have greatly reduced the size and frequency of floods, the amount of sediment in the river, and the annual variation in water temperature.

    The river environment changed within Glen Canyon National Recreation Area, Grand Canyon National Park, and tribal lands of the Navajo, Havasupai, and Hualapai people--in other words, areas set aside for the preservation of the cultural and natural resources. Concern about the environmental effects of the dam and its operation caused the Bureau of Reclamation to initiate a series of studies known as the Glen Canyon Environmental Studies (GCES). Efforts by concerned parties resulted in the enactment into law of the Grand Canyon Protection Act of 1992 and the completion of an Environmental Impact Statement (EIS). The Act and the EIS provide for use of Glen Canyon Dam to manage the resources of the river corridor, including the use of periodic controlled flooding.


    Controlled-Flood Rationale

    Before 1963, melting snow in the upper Colorado River basin produced high flows that raced through the Grand Canyon each spring. An average peak discharge of 93,400 cubic feet per second (cfs) scoured large volumes of sediment from the river bottom. Later in the summer, receding floodwaters deposited this scoured sediment and also sediment carried in from tributaries. This annual scour and fill process maintained large sand bars along the river banks, kept sand bars clear of vegetation, and kept debris fans--deposits of cobbles and boulders that form at the mouths of tributaries--from constricting the river. Reduced frequency of flooding since flow regulation began has reduced the size of sand bars and allowed vegetation to encroach on the channel, debris fans to build up, and backwater areas used by native fish to fill in.

    The last decade of study has greatly expanded scientists' understanding of the Colorado River in Grand Canyon. On the basis of this knowledge, scientists predict that periodic high flows can be used to retain sand in the canyon by depositing it along river banks. Sand submerged in the river is not stationary but is slowly being moved downstream along the river bottom. Floods have the hydraulic energy necessary to suspend sand and to form bars higher up the river banks. These sand bars are less subject to erosion and more useful for camping than bars formed by lower flows. Backwater areas will be scoured of accumulated fine sediments and vegetation. This cleaning or rejuvenation process will recreate low-velocity habitat for fish. Debris fans will be eroded and the character of the rapids changed.

    A controlled flood from Glen Canyon Dam is proposed to rebuild sand bars along the river banks and to provide data needed to predict the movement of water and sediment during floodflows. Methods for predicting the movement of water and sediment were developed and successfully applied by USGS and other scientists at lower discharges. Measurements at floodflows are needed to extend the usefulness of these methods. Once tested with data from a wide range of flow conditions, methods can be used to predict how flow and sediment would be affected by a wide range of dam releases.



    [...]
    http://water.usgs.gov/wid/FS_089-96/FS_089-96.html




    EDIT: Y aquí los primeros datos, obtenidos entre 1996 y 1999...
    http://www.gcmrc.gov/files/pdf/gcmrc...e_sediment.pdf

    Ea, a seguir recabando info!
    Última edición por Salut; 02-feb-2010 a las 03:23

  2. #2
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    Predeterminado

    Se ve que sólo han podido crear unas pocas crecidas artificiales.

    Controlled Flood in the Grand Canyon Planned For Next Month
    The flooding aims to help restore the Colorado River ecosystem to its pre-dam conditions, but many remain skeptical of the plan


    The AP is reporting that next month the U.S. Geological Survey will stage a controlled flood of the Colorado River in the Grand Canyon via the Glen Canyon Dam in order to learn whether they can approximate the natural conditions of the river.

    The flood will release 41,000 cubic feet per second of water for nearly three days. This is the third experimental flood since 1996, part of an on-going study the results of which have yet to be released. Environmental opponents argue that the flooding needs to occur in regular intervals that mimic more closely the natural cycle of flooding, and that the data already shows this to be true.

    Rivers depend on natural cycles of flooding in order to replenish nutrients and to create specialized habitats for plants and animals. As a river flows, it brings sediment from its upper reaches to its lower, distributing food and minerals along the way.

    When a river floods, it collects an abundance of nutrients from the land and deposits them in the water, which its populations have come to depend on over time. Flooding also creates backwater habitats in which aquatic animals breed, as well as favorable conditions for riparian vegetation (plants that live along a river's edge).

    When a river is dammed, all those benefits are lost. The steady bounty of sediment and debris is caught in the dam's reservoir (and builds up over time, leading to the failure of some dams). The effect is to starve the river below. When water is released to simulate flooding, it is unfortunately not the same water it was before. A reservoir is stagnant and so the temperature stratifies, becoming progressively colder toward the bottom. The coldest water is what is usually released. When it flows out of the dam, it is devoid of sediment; so instead of feeding the river, it actually works in the opposite direction by washing away what little sediment remains and disrupting animal populations that rely on an established calendar of water temperature.

    The scientists behind the Glen Canyon Dam project will study the effects on the river after this flooding with the hope that they can more closely approximate the natural cycle that once was. By flooding more frequently, they aim to replicate the naturally occurring patterns of the river. Whether it will work is still very much a matter of debate.
    http://www.popsci.com/scitech/articl...ned-next-month

  3. 15-abr-2010, 16:48

    Razón
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  4. #3
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    Predeterminado

    Creo que esas experiencias se deberían aplicar al caso español, cuyos ríos tradicionalmente tienen crecidas que son vitales para la dinámica del río.
    Última edición por jasg555; 15-abr-2010 a las 17:19

  5. #4
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    Predeterminado

    ^^ Efectivamente!! Ojalá se introduzcan algún día, pero eso conllevaría una mejor gestión de la llanura aluvial... me se de dos colectivos bastante poderosos (agri&ladri) que la liarían parda, en defensa de su comodidad (que no su beneficio a largo plazo).


    En fin, para quienes no dominen la lengua inglesa, traduciremos algunas ideas:
    Scientists have proposed a controlled flood in response to resource managers' request for ways to restore some of the pre-dam resource conditions. Floods are expected to suspend sand moved to the river bottom by lower flows and deposit it along the river banks where it will be above water after the flood recedes. In this way, the limited sand resources can be utilized to preserve habitat for plants and animals and for use by river runners and campers.
    Los científicos han propuesto una crecida controlada en respuesta a la solicitud, por parte de los gestores de recursos, de medios para recuperar las condiciones previas a la construcción del embalse. Se espera que las crecidas eleven las arenas desde el fondo del río (a donde fueron arrastradas por los bajos caudales) y las depositen en los bancos a lo largo del río, donde estarían por encima del nivel de las aguas una vez se retire la crecida. De esta manera, los recursos limitados de arena pueden ser utilizados para preservar el habitat para plantas y anumales, y para su uso por parte de excursionistas fluviales y campamentos.

    the presence of the dam and regulation of flow have greatly reduced the size and frequency of floods, the amount of sediment in the river, and the annual variation in water temperature.
    La presencia del embalse y la regulación del caudal han reducido grandemente la importancia y la frecuencia de las crecidas, la cantidad de sedimentos en el río y la variación anual de la temperatura del agua.

    Reduced frequency of flooding since flow regulation began has reduced the size of sand bars and allowed vegetation to encroach on the channel, debris fans to build up, and backwater areas used by native fish to fill in.
    La menor frecuencia de crecidas desde que empezó la regulación de caudales ha reducido el tamaño de los bancos de arena, y permitido a la vegetación invadir el canal, la formación de acumulaciones de residuos, y la colmatación de zonas de aguas tranquilas utilizadas por la ictofauna (peces) autóctona.

    Floods have the hydraulic energy necessary to suspend sand and to form bars higher up the river banks. These sand bars are less subject to erosion and more useful for camping than bars formed by lower flows. Backwater areas will be scoured of accumulated fine sediments and vegetation. This cleaning or rejuvenation process will recreate low-velocity habitat for fish. Debris fans will be eroded and the character of the rapids changed.
    Las crecidas tienen la energía hidráulica necesaria para elevar la arena y formar bancos de arena a un nivel superior al del río. Estos bancos estan menos expuestos a la erosión, y más útiles para acampar que los bancos formados por caudales más bajos. Las zonas de aguas tranquilas se verían limpiadas de los sedimentos finos acumulados y de vegetación. Este proceso de limpieza y rejuvenecimiento recrearía los hábitats de aguas tranquilas para peces. Las acumulaciones de residuos se verían erosionadas y el caracter de los rápidos modificado.
    Última edición por Salut; 27-abr-2010 a las 22:55

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