Flooding dynamics on the lower Amazon floodplain: 2. Seasonal and interannual hydrological variability

Abstract

[1] We analyzed seasonal and interannual variability in hydrological fluxes and inundation dynamics of a large floodplain unit (2440 km 2 ) along the lower Amazon River over a period of 15 years (1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010). Floodplain inundation was simulated using LISFLOOD-FP, which combines one-dimensional river routing with two-dimensional overland flow, and a local hydrological model. Dominant sources of inflow varied seasonally among direct rain and local runoff (November), Amazon River (December to August) and seepage (September and October). Shifts in timing of dominance among the water balance components occurred conform variations in annual peak stage. The period of dominance of river inflow over total floodplain influxes began about 1 month earlier and ended 1 month later in the 2009 high flood year compared to the 1998 low flood year. On average, river to floodplain discharge represented 0.75% of the Amazon River discharge at Obidos and 82% of the annual hydrological influxes to the floodplain. We observed an up to ninefold variation in riverfloodplain annual discharge. Relatively small increments in main stem peak discharge cause disproportionately large changes in the flow routed through the floodplain. Despite the higher frequency of years with lower minimum stages, the intensification of the hydrological cycle of the Amazon Basin is causing substantially greater amounts of riverine water to flow across floodplain environments.

Recent increase of river–floodplain suspended sediment exchange in a reach of the lower Amazon River

“…The average annual inflow from the Amazon River was 72.6 ± 45.6 km 3 . Annually, the floodplain acted as a net source of water to the river due to 4.7 ± 2.5 km 3 of local hydrological inputs (Rudorff et al ., ).…”

“…Seasonal growth and decomposition of grasses and other aquatic plants are linked to the inundation dynamics (Silva et al ., ). Floodplain inundation originates mainly from Amazon River water with additional contributions from direct precipitation, runoff from the local upland ( terra firme ) catchments (total drainage area of 1370 km 2 ), and groundwater (Rudorff et al ., ). The river stage varies on average by 6.7 ± 1.0 m (1995–2014) annually with the peak of the hydrograph between May and June and the trough between October and December.…”

“…Rudorff et al . () analyzed seasonal floodwater pathways, summarized as follows. Before the beginning of the rising hydrograph around December, the two main eastern channels are the only active connections between the floodplain and the Amazon River, and they drain floodplain water into the river (Figure B).…”

Implications of scatter corrections for absorption measurements on optical closure of Amazon floodplain lakes using the Spectral Absorption and Attenuation Meter (AC-S-WETLabs)

“…Water flow and mixing patterns over the Curuai floodplain are complex. Rudorff, Melack, & Bates (2014a, 2014b examined its hydraulic controls of flooding and hydrological variability. At peak discharge, approximately 97% of river water enters the floodplain as diffuse overbank flow and is routed subparallel to the Amazon River.…”

Correction of Interferometric and Vegetation Biases in the SRTMGL1 Spaceborne DEM with Hydrological Conditioning towards Improved Hydrodynamics Modeling in the Amazon Basin

“…Water in the floodplains also comes from local runoff, groundwater seepage and direct rainfall, whose contributions vary seasonally and inter-annually [13][14][15]. The seasonal contribution and the mixture of these different water sources could be a key driving factor of biochemical and ecological processes in floodplains [16,17].…”