{"id":111,"date":"2026-02-25T13:29:56","date_gmt":"2026-02-25T12:29:56","guid":{"rendered":"https:\/\/traceclimate.cerege.fr\/?page_id=111"},"modified":"2026-03-03T14:13:31","modified_gmt":"2026-03-03T13:13:31","slug":"bathymetric-sediment-budget","status":"publish","type":"page","link":"https:\/\/traceclimate.cerege.fr\/?page_id=111","title":{"rendered":"Bathymetric sediment budget"},"content":{"rendered":"\n

Global sediment budget<\/strong><\/h2>\n\n\n\n

Bathymetric data reveal areas of deposition and erosion (Fig.\u202f5). After river-mouth shifts, remaining mouths and prodeltaic lobes generally erode. The Petit Rh\u00f4ne prodeltaic lobe erodes continuously throughout the study period.<\/p>\n\n\n\n

Bathymetric data reveal areas of deposition and erosion (Fig.\u202f5). After river-mouth shifts, remaining mouths and prodeltaic lobes generally erode. The Petit Rh\u00f4ne prodeltaic lobe erodes continuously throughout the study period.<\/p>\n\n\n\n

Since 1841, sediment has accumulated mainly in the Beauduc Gulf and along the Espiguette and Beauduc spits. The Gracieuse spit appeared in 1895. The Grand Rh\u00f4ne mouths form a sedimentary belt about 1.5\u202fkm wide.<\/p>\n\n\n\n

Bathymetric data are available only for 1872\u20131895 and 1895\u20131974. Both periods show a positive overall sediment budget, but it decreases sharply from +11.10 to +1.47 \u00d7 10\u2076\u202fm\u00b3\u202fyr\u207b\u00b9.<\/p>\n\n\n\n

Changes in prodeltaic lobes<\/strong><\/strong><\/h2>\n\n\n\n

Net accumulation at the Grand Rh\u00f4ne lobes declines over time, from 12.63 to 3.40 \u00d7 10\u2076\u202fm\u00b3\u202fyr\u207b\u00b9 between 1841\u20131872 and 1895\u20131974. Petit Rh\u00f4ne and offshore areas show increasing erosion, from \u22120.53 to \u22121.34 \u00d7 10\u2076\u202fm\u00b3\u202fyr\u207b\u00b9.<\/p>\n\n\n\n

All relict prodeltaic lobes erode once the river ceases to discharge. Erosion rates generally decrease over time, as seen in the Bras de Fer lobe. Pi\u00e9manson and Roustan lobes eroded after artificial closure, stopping only after Roustan reopened in 1892. Westward mouth shifts subsequently caused erosion of the P\u00e9goulier lobe.<\/p>\n\n\n\n

Changes in the shoreface<\/strong><\/strong><\/strong><\/h2>\n\n\n\n

The shoreface budget was calculated for the western Grand Rh\u00f4ne zone, dominated by waves. Eastern areas influenced by river input were excluded. Petit Rh\u00f4ne is included due to its erosional regime.<\/p>\n\n\n\n

During the first period, the shoreface budget is positive (+2.73 \u00d7 10\u2076\u202fm\u00b3\u202fyr\u207b\u00b9). In the second period, it becomes negative (\u22121.94 \u00d7 10\u2076\u202fm\u00b3\u202fyr\u207b\u00b9). This change is due to increased erosion and decreased accumulation.<\/p>\n\n\n\n

Upper shoreface (0\u201310\u202fm) shows slight net accumulation initially (+0.34 \u00d7 10\u2076\u202fm\u00b3\u202fyr\u207b\u00b9), then minor erosion (\u22120.28 \u00d7 10\u2076\u202fm\u00b3\u202fyr\u207b\u00b9). Lower shoreface initially gains sediment (+2.39 \u00d7 10\u2076\u202fm\u00b3\u202fyr\u207b\u00b9) but shifts to strong erosion (\u22121.66 \u00d7 10\u2076\u202fm\u00b3\u202fyr\u207b\u00b9).<\/p>\n\n\n\n

Overall, sediment accumulation has become more limited over time. Relict lobes and shoreface zones illustrate the combined influence of river-mouth dynamics and wave processes. The data show that shifts in river mouths directly affect prodeltaic lobes and the adjacent shoreface. Sediment supply from active mouths is crucial for maintaining deltaic accretion. Areas cut off from river input experience progressive erosion. Wave-dominated zones are particularly sensitive to long-term sediment redistribution.<\/p>\n\n\n