Scientific data

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DIDEM flyer during a workshop, Ankarafansika, Madagascar @ IRD DIDEM Rijasolo

Madagascar

Identification, localization and numbering of islets and geomorphological units of the Betsiboka delta (northwestern Madagascar) on Sentinel 2 satellite images (2020, 2021)

Authors : Hervé, Dominique; Randrianatoandro, Ravakiniaina; Delaitre, Eric; Robison, Laurent; Razanaka, Samuel; Ratiarson, Venot

DOI : https://doi.org/10.23708/COLVLV

Long time series (more than a century) are difficult to construct but they are useful for understanding hydro-geomorphological phenomena that take place over the long term and anticipating future risks.
The Betsiboka River into which the Ikopa flows from Antananarivo, capital of Madagascar, is characterized by hyper-sedimentation which gives it a red color. Downstream, at Mahajanga, the river forms a delta nested in its estuary and influenced by the tides, which becomes blocked over the years, then flows into Bombetoka Bay and the Mozambique Channel. This clogging takes the form of islets which are colonized by the mangrove, once emerged. Monitoring a population of islets and their cover by mangroves makes it possible to evaluate the sedimentation speed of the delta and the dynamics of the mangroves (colonization, growth, mortality).
These data - and the associated article - illustrate the stages of constructing a map representing all of these islets, located and numbered in 2021 (Satellite Sentinel 2 image of 04/28/21, low tide = -1.86) , the delimitation of the nested delta, the location of the islets according to an upstream-downstream gradient, finally the contours and numbering of each islet. This inventory can thus serve as a reference, as an end point for historical studies, or as a starting point for multi-year monitoring enabled by the Sentinel 2 satellite.