The hydro-geomorphologic complexity of the lower Amazon River floodplain and hydrological connectivity assessed by remote sensing and field control

Abstract Hydrological connectivity processes along the lower Amazon River floodplain at Lago Miratuba Floodplain (LMF) were analyzed based on remote sensing and field measurements. Connectivity processes are related to 12 geomorphic sub-units of the floodplain that are interconnected at different stage thresholds through channelized and overbank flow paths, while lakes act as reservoirs for flood waters, local rainfall, and water table saturation-seepage. Hydrological connectivity processes along the floodplain happen through complex internal routings of water flows over space and time, mainly along floodplain channels and breached levees. The contribution of local recharge (mainly rainfall) was decoupled from river recharge (river hydrological connection to floodplain) because precipitations and local runoff also recharge the floodplain. The hydrological connectivity of the 12 geomorphic units varied significantly from each other, because the inundation and the floodplain connections with the river were initiated at specific river stage thresholds for each sub-unit. An interesting finding is that connections with the river for all units were initiated through channelized flows below the bankfull stage of the Amazon River. The connectivity processes over different geomorphic units are also not correlated with their minimum distance (shortest lines) from the river. This implies that a “flood pulse” model largely concerned with lateral connectivity (mostly through overbank diffusion) only partially explains the complex hydrological connectivity processes at a regional scale along the complex lower Amazon River floodplain. Thus, for hydrological connectivity assessments in the Amazon River floodplain, reach-by-reach scale studies have to be carried out, relating the hydro-geomorphologic processes (channelized flow routing paths, overbank diffusion, and local recharge) to the internal geomorphic variability and complexity of the floodplain.