Analysis of the model for a 5.10 m flood The reference for a 5.10 m flood at the Mopti gauge is the 1990 flood. Landsat images are available for October 1, October 10 and November 27. The 1990 flood is very peculiar, with higher flood than expected for a flood height of 5.10 m at the Mopti gauge in Sofara and Ké Macina but with an atypical time lag between the Niger and Bani floods and a bimodal flood at Sofara. The flood at Akka is significantly lower than expected with 5.10 m at Mopti. According to J.P. Lamagat's model, a 5.10 m flood at Mopti should correspond with 4.24 m in Ké Macina, while 4.41 m were actually recorded, a level corresponding to a 5.30 m flood height at Mopti. Similarly the flood height at Sofara should be 3.89 m while 4.28 m were actually recorded, corresponding to a flood height close to 5.40 m at Mopti. The low flood height at Mopti in 1990 is explained by the bimodal flood at Sofara and by the very unusual flood peak offset between Sofara and Mopti which also explains the abnormally low value in Akka. The flooded area calculated by the model for 5.10 m - shape (Niv_510) - extends over ​​747,325 ha, which overestimates the area actually flooded quite significantly. This is explained in particular by the overflows of the matrix at level 55, which precisely correspond to the 5.10 m flood height. After integration into Veg7, the shape file Niv_510_Veg7 shows a flooded area reaching ​​664 827 ha, the value retained for comparison with Landsat. This value is very close to that obtained by directly taking into account on Veg7 only the vegetation associations whose flood depth is below -1.50 m (664 953 ha). The map above (left) figures the flooded areas according to the model for a water height of 5.10 m at the Mopti gauge. While for a flood of 5.97 m, the Delta still presented a continuous body of flood water, for one of 5.10 m the body is fragmented, suggesting the large deep basins of the Delta (see page 49). The map also shows areas with scanty flooding, in particular the upper Niger River downstream from Ké Macina as well as downstream along the Niger and Diaka separation, and also the southern Delta. The map drawn from the analysis of Landsat images shows flooded/vegetated areas extending over ​​623,138 ha, rather close to the flooded area calculated by the Niv_510 model (664,827ha) but with a somewhat different distribution, as shown in the synthesis map - shape (synthesis_510_1990) - which groups together the shape files (commun_1990_510, inon_plus_1990 and inon_ moins_1990) The comparison of the flooded areas calculated by the model with flooded areas observed in the Landsat images leads to the following remarks: 1 - The flooded and heavily vegetated area common to the ​​Landsat images and the flooded area calculated by the model extends over 496,775 ha . Thus the ratio of common area / flooded area of ​​the model reaches 74.7% , showing that confidence in the model calculations decreases with the lower floods. 2 - The summary map figures (in red) areas calculated by the model as floodable but not flooded on Landsat extending over 167,534 ha ; and, conversely, areas flooded on Landsat which are not flooded according to the model figure (in purple and mauve) : they extend over 126,101 ha 3 - The effectively non-flooded areas (in red) are located in four places: on the right bank of the Niger river upstream from Mopti, confirming the poor flood water provision of this region of the Delta with the flood almost disappearing from the Pondori basin; the south of the Ténenkou Basin; the surroundings of the Peru Dialloubé and the northwest of the Delta in connection with the lower than expected flood at Akka at the exit of the Débo lake. 4 - The areas totally or partially flooded on Landsat and not flooded according to the model are mainly located: • In the MB2 vegetation mosaic units along the Niger and Bani, which according to the model have a flood depth of -1.40m, and are therefore not flooded at 5.10 m; yet in reality, they are composed of banks at the 0 m level and a series of levees and channels whose flood depth ranges as low as - 2.80 m; • In and around the Toggere Coumbe, Kakagnan and Kadial basins, highlighting the influence of the peculiar longitudinal profile of the Diaka defluent and the limits of its influence in relation to the Débo lake (see details on page 47).

510_1990.gdb contain two shape files - Niv_510 : The raw calculated model -Synthèse_510_1990 with the following items: sigle : acronym of vegetal associations niveau : level of vegetal association profond : submersion depth of vegetal associations Val_rast : 0 = non flooded 1 = totally flooded 2 = partially flooded Val_rast come from the analysis of Landsat Images Synthèse : 1 = commun_510_1990 2 = inon_plus_1990 3= inon_moins_1990

510_1990(EN).rar

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