{"id":6384,"date":"2020-11-25T10:36:23","date_gmt":"2020-11-25T09:36:23","guid":{"rendered":"https:\/\/dev.asleman.org\/?post_type=60_secondes&amp;p=6384"},"modified":"2020-11-25T10:36:23","modified_gmt":"2020-11-25T09:36:23","slug":"n61-le-delta-du-rhone","status":"publish","type":"60_secondes","link":"https:\/\/asleman.org\/en\/60_secondes\/n61-le-delta-du-rhone\/","title":{"rendered":"No.61: The Rh\u00f4ne delta"},"content":{"rendered":"<p>Do you know why the Rh\u00f4ne, so opaque at Bouveret, emerges from Lake Geneva almost translucent?<\/p>\n\n\n\n<p>The answer to this question lies in the \ud835\uddf1\ud835\uddf2\ud835\uddf9\ud835\ude01\ud835\uddee \ud835\uddf1\ud835\ude02 \ud835\udde5\ud835\uddf5\ud835\uddfc\u0302\ud835\uddfb\ud835\uddf2. The milky colour of the Rh\u00f4ne is due to the presence of suspended sediments. At the mouth of the Rh\u00f4ne, these particles settle to the bottom of the lake, forming what is known as a delta.<\/p>\n\n\n\n<p>Like the Nile delta (probably the best known), deltas are distinguished by a triangular shape close to the Greek letter \u0394 (delta), from which they take their name. \ud835\udddc\ud835\uddf9\ud835\ude00 \ud835\uddf7\ud835\uddfc\ud835\ude02\ud835\uddf2\ud835\uddfb\ud835\ude01 \ud835\ude02\ud835\uddfb \ud835\uddff\ud835\uddfc\u0302\ud835\uddf9\ud835\uddf2 \ud835\uddfa\ud835\uddee\ud835\uddf7\ud835\uddf2\ud835\ude02\ud835\uddff \ud835\uddfd\ud835\uddfc\ud835\ude02\ud835\uddff \ud835\uddf9\ud835\uddee \ud835\uddef\ud835\uddf6\ud835\uddfc\ud835\uddf1\ud835\uddf6\ud835\ude03\ud835\uddf2\ud835\uddff\ud835\ude00\ud835\uddf6\ud835\ude01\ud835\uddf2\u0301 by offering habitat conditions sought after, particularly by many bird species.<\/p>\n\n\n\n<p>As well as providing a natural transition zone, the Rh\u00f4ne delta is very important \ud835\uddf1\ud835\uddee\ud835\uddfb\ud835\ude00 \ud835\uddf9\ud835\uddf2 \ud835\uddfd\ud835\uddff\ud835\uddfc\ud835\uddf0\ud835\uddf2\ud835\ude00\ud835\ude00\ud835\ude02\ud835\ude00 \ud835\uddf1'\ud835\uddfc\ud835\ude05\ud835\ude06\ud835\uddf4\ud835\uddf2\u0301\ud835\uddfb\ud835\uddee\ud835\ude01\ud835\uddf6\ud835\uddfc\ud835\uddfb for the different layers of water in Lake Geneva.<\/p>\n\n\n\n<p>As we mentioned in a previous 60 seconds, Lake Geneva is divided into three layers, from top to bottom: Epilimnion, metalimnion and hypolimnion. Warmer for most of the year, the surface waters are less dense than those in the depths. This difference in density explains the \ud835\ude00\ud835\ude01\ud835\uddff\ud835\uddee\ud835\ude01\ud835\uddf6\ud835\uddf3\ud835\uddf6\ud835\uddf0\ud835\uddee\ud835\ude01\ud835\uddf6\ud835\uddfc\ud835\uddfb \ud835\uddf1\ud835\ude02 \ud835\uddf9\ud835\uddee\ud835\uddf0.<\/p>\n\n\n\n<p>When it enters Lake Geneva, the Rh\u00f4ne flows through the metalimnion (interflow process). In fact, the temperature of its water is similar to that of this layer. It can also happen that the Rh\u00f4ne water, loaded with sediment, is denser than the hypolimnion, producing \ud835\ude02\ud835\uddfb \ud835\uddf0\ud835\uddfc\ud835\ude02\ud835\uddff\ud835\uddee\ud835\uddfb\ud835\ude01 \ud835\uddf1\ud835\uddf2 \ud835\uddf3\ud835\uddfc\ud835\uddfb\ud835\uddf1 (underflow).<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img decoding=\"async\" src=\"https:\/\/dev.asleman.org\/wp-content\/uploads\/2020\/11\/delta-du-rhone-fb-2-1024x538.jpg\" alt=\"\" class=\"wp-image-6385\"\/><\/figure>\n\n\n\n<p>\ud835\udddf\ud835\uddf2\ud835\ude00 \ud835\uddff\ud835\uddee\ud835\ude03\ud835\uddf6\ud835\uddfb\ud835\ude00 \ud835\ude00\ud835\uddfc\ud835\ude02\ud835\ude00-\ud835\uddf9\ud835\uddee\ud835\uddf0\ud835\ude02\ud835\ude00\ud835\ude01\ud835\uddff\ud835\uddf2\ud835\ude00 \ud835\uddf1\ud835\ude02 \ud835\uddf1\ud835\uddf2\ud835\uddf9\ud835\ude01\ud835\uddee \ud835\udde5\ud835\uddf5\ud835\uddfc\u0302\ud835\uddfb\ud835\uddf2 have been formed by these bottom currents for over 1,000 years. These currents carry the water from the Rh\u00f4ne down to the bottom of the lake, providing oxygen to the water, which is struggling to be replenished by natural mixing.<\/p>\n\n\n\n<p>Over the last 150 years, \ud835\uddf1\ud835\uddf2\ud835\ude02\ud835\ude05 \ud835\uddf4\ud835\uddff\ud835\uddee\ud835\uddfb\ud835\uddf1\ud835\ude00 \ud835\uddfd\ud835\uddff\ud835\uddfc\ud835\uddf7\ud835\uddf2\ud835\ude01\ud835\ude00 \ud835\uddf1'\ud835\uddf6\ud835\uddfb\ud835\uddf3\ud835\uddff\ud835\uddee\ud835\ude00\ud835\ude01\ud835\uddff\ud835\ude02\ud835\uddf0\ud835\ude01\ud835\ude02\ud835\uddff\ud835\uddf2 have greatly narrowed the Rh\u00f4ne delta. First of all, the first correction of the Rh\u00f4ne canalised the river, making it follow the course we know today by draining the other six arms of its delta. Subsequently, the growth of hydraulic dams reduced the supply of alluvium necessary for the delta's ecosystem and the oxygenation of the lake bed.<\/p>\n\n\n\n<p>Today, the ecological role of the delta is better recognised. As a result, work to correct the Rh\u00f4ne River is set to leave more room for the natural functioning of the river by 2025.<\/p>\n\n\n\n<p>Photos: JM Zellweger &amp; <a href=\"https:\/\/map.geo.admin.ch\/?lang=fr&amp;topic=ech&amp;bgLayer=ch.swisstopo.pixelkarte-grau&amp;layers=ch.swisstopo.zeitreihen,ch.bfs.gebaeude_wohnungs_register,ch.bav.haltestellen-oev,ch.swisstopo.swisstlm3d-wanderwege,ch.swisstopo.swissbathy3d-reliefschattierung&amp;layers_opacity=1,1,1,0.8,1&amp;layers_visibility=false,false,false,false,true&amp;layers_timestamp=18641231,,,,&amp;E=2538074.96&amp;N=1134701.94&amp;zoom=4\" data-type=\"URL\" data-id=\"https:\/\/map.geo.admin.ch\/?lang=fr&amp;topic=ech&amp;bgLayer=ch.swisstopo.pixelkarte-grau&amp;layers=ch.swisstopo.zeitreihen,ch.bfs.gebaeude_wohnungs_register,ch.bav.haltestellen-oev,ch.swisstopo.swisstlm3d-wanderwege,ch.swisstopo.swissbathy3d-reliefschattierung&amp;layers_opacity=1,1,1,0.8,1&amp;layers_visibility=false,false,false,false,true&amp;layers_timestamp=18641231,,,,&amp;E=2538074.96&amp;N=1134701.94&amp;zoom=4\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">Map.Geo<\/a><\/p>\n\n\n\n<p>\ud835\udc12\ud835\udc28\ud835\udc2e\ud835\udc2b\ud835\udc1c\ud835\udc1e\ud835\udc2c :<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li><a href=\"https:\/\/www.letemps.ch\/sciences\/mysteres-reveles-fond-lac-leman\" data-type=\"URL\" data-id=\"https:\/\/www.letemps.ch\/sciences\/mysteres-reveles-fond-lac-leman\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">Le Temps<\/a>(14 September 2016)<\/li><li><a href=\"https:\/\/www.letemps.ch\/suisse\/un-delta-lacustre-biodiversite-lembouchure-rhone\" data-type=\"URL\" data-id=\"https:\/\/www.letemps.ch\/suisse\/un-delta-lacustre-biodiversite-lembouchure-rhone\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">Le Temps<\/a>(7 September 2017)<\/li><li><a href=\"https:\/\/dev.asleman.org\/60_secondes\/n16-un-leman-a-trois-etages\/\" data-type=\"URL\" data-id=\"https:\/\/dev.asleman.org\/60_secondes\/n16-un-leman-a-trois-etages\/\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">Une info en 60' n\u00b09 <\/a>Un L\u00e9man \u00e0 trois \u00e9tages\".<\/li><li>LOIZEAU (1991), \u201cLa s\u00e9dimentation r\u00e9cente dans le delta du Rh\u00f4ne, L\u00e9man: processus et \u00e9volution\u201d, PhD thesis: Univ. Geneva. <a href=\"https:\/\/archive-ouverte.unige.ch\/unige:47526\" data-type=\"URL\" data-id=\"https:\/\/archive-ouverte.unige.ch\/unige:47526\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">(online)<\/a><\/li><\/ul>\n\n\n\n<p><\/p>\n\n\n\n<p><\/p>","protected":false},"featured_media":6386,"template":"","mots-cles":[],"class_list":["post-6384","60_secondes","type-60_secondes","status-publish","has-post-thumbnail","hentry"],"acf":[],"_links":{"self":[{"href":"https:\/\/asleman.org\/en\/wp-json\/wp\/v2\/60_secondes\/6384","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/asleman.org\/en\/wp-json\/wp\/v2\/60_secondes"}],"about":[{"href":"https:\/\/asleman.org\/en\/wp-json\/wp\/v2\/types\/60_secondes"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/asleman.org\/en\/wp-json\/wp\/v2\/media\/6386"}],"wp:attachment":[{"href":"https:\/\/asleman.org\/en\/wp-json\/wp\/v2\/media?parent=6384"}],"wp:term":[{"taxonomy":"mots-cles","embeddable":true,"href":"https:\/\/asleman.org\/en\/wp-json\/wp\/v2\/mots-cles?post=6384"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}