Change of flooding patterns in the upper Amazon as a consequence of river regime change, a case study of Iquitos city

Abstract:

Since the 1980s the Amazon basin has experience an intensification of hydrological extreme events, which particularly affects the Andean Rivers. Particularly, the precipitation in the Peruvian Amazon area where Iquitos city is located shows the largest precipitation increment since the 1990s. Rain patterns show larger periods of droughts with more intense rains during the wet season. Recently, this region of the Peruvian Amazonian has experiment the most extreme flooding event since 1970, as a consequence of the change of regime in the rivers, where the extremes have become more pronounced. The extreme flood event that occurred in April 2012 inundated a considerable area of the city, setting a new water surface elevation record of the Amazon River in the zone. To study the impact in the floodplains and nearby Iquitos city, caused by the change of regime in the upper Amazon River, we analysed and simulated the past events to find patterns of inundation during floods. Data utilized for doing so, is based on the compilation and correlation of geological, and hydrological information related to flooding in Iquitos city. River overbank flow is a complex phenomenon that requires a correct representation of the physics. Actual approaches use algorithms that couple horizontally 1D model for the rivers and 2D models for the flood plains. They use over-simplifications for the interaction between flood plain and main channel and are unable to model the transversal momentum above the main channel. For that reason, we developed an algorithm that couples vertically the in-channel and overbank flows. This new model was validated against experimental results. The numerical results show an accurate approximation to the historical inundations of the city. The analysis and modelling shows that the flooding patterns have an substantial change due to the new regime observed in the upper Amazon River.