Analysis of the model for a 5.97 m flood The reference year is 2006 with a flood height of 5.97m at the Mopti gauge, which can also be compared to the year 1996 with 5.95m at the Mopti gauge (but no images available). In 2006, the flood recorded at Ké Macina matches that of the model; at Sofara on the Bani the flood is a little higher. On the contrary, the resulting flood at Akka is lower than expected, with above all a very fast propagation speed which reduces the flooding in Akka. Unfortunately, the repeatability of the Landsat images in 2006 is not satisfactory and the spatial coverage is incomplete. The only image 198_050 (10/5/2006) of the extreme southwest of the Delta is not fully usable because it is very noisy; however, it shows that the flood is already largely declining in south of the Delta while the north is not yet completely flooded and / or vegetated. With a flood height of 5.97m at the Mopti gauge, the area potentially flooded on NIV_597 totals 1,192,890 ha. After integration within the limits of Veg7 and reintegration of errors related to the smoothing of the matrix, the flooded area calculated by the model at 5.97m (shape NIV_597_Veg7) is 1,152,745 ha. On the Landsat images of 11/23/2006 (plus the image of Oct. 30 for the south of the Delta) the flooded area within the limits of Veg7 reaches 1,091,847 ha. - shape (VEG7_SF_2006)-. However, fully flooded or highly vegetated areas extend over 887,004 ha while the partially flooded area extend over 204,843 ha. The common area - shape (Commun_597_2006) - between NIV_597_Veg7 and VEG7_2006 extends over 987 844 ha. The ratio between this common area and the area calculated by the model thus reaches 85.6%. Analysis of the differences between the flooded area calculated by model and observed on Landsat images (see the synthesis map: synthèse_597_2006) . Ultimately, the synthesis_597-2006 map shows the malfunctions of the model, with the southern part of the Delta poorly supplied in flood (in red and pink on the synthesis map) and the central and north west Delta better flooded than expected (in green on the map). The flood extends around the large basins of the center and north west of the Delta, Toggere Koumbe, Kadial and Kakagnan basins, as is also highlighted on the map of these large basins (Inon_plus_597). This “better than expected” flood might be related to the peculiar longitudinal profile of the Diaka (as explained for the 4.40 m flood analysis in 1984).

The classification of the Landsat image of 11/23/2006 (tiles 197_050 and 197_049) with test sites and maximum likelihood criteria (as described on page 42) highlights two types of vegetation associations , strongly differentiated, as figured on the extract located in the northwest of the Delta. 1 –In dark green: a densely green flooded vegetation, fringed by open water (in blue) 2 –In light green: a scanty green vegetation observed in some places within the Delta and on the Delta margins. These vegetation units, which were not flooded in November 2006, still had notable green vegetation in late October (South) and late November. Yet these areas were not included in the flooded areas observed on Landsat and compared with flooded areas calculated by the model.

1 - the areas calculated as flooded by the model but which are not flooded on Landsat at the end of November 2006 extend over 165,492 ha , of which 36,886 ha are vegetation mosaics of “ambiguous” flood status, while 128,606 ha are vegetation usually flooded by river flood. The "ambiguous" flooded vegetation associations (flooded by local run-off and / or combining floodable with unflooded associations) are located in Peru Dialoubé, at the edge of the Delta and on the right bank of the Bani, north of the erg of Femaye. They are therefore doubly marginal, because of their flooding status and because of their location at the edge of the flood plains. The flood-prone vegetation units that were not flooded in 2006 are located partly in Dialloubé Peru but mainly extend in the south of the Delta. The flood dysfunctions in the southwest of the Delta between Ké Macina and Diafarabé, and in the south, between the right bank of the Niger and the Bani, already noted in the analysis the 6.21m flood, are amplified in floods which only reach around 6m in height at the Mopti gauge, confirming the poor flood provision this "upstream part of the Delta". 2 - Flooded areas according to the Landsat images of November 2006 and which are not flooded by the model extend over approximately 102,845 ha. Distribution of fully or partly flooded areas on the Landsat images of November 2006 and not flooded by the model according to the flood depth of vegetation associations.

597_2006.rar

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