Analysing the Flood Warning of Negro River in Manaus

Abstract

The magnitude of the Amazon basin, associated with geological, geomorphological and hydrological factors, as well as the distribution of rainfall, contribute to the existence of large rivers, both in extension and flow, such as the Negro and Solimões rivers, which are selected to be evaluated in this study. Manaus city is bathed by the Negro river, near the confluence of the two rivers, in which the water level of Negro river is controlled by Solimões river level. This study proposes to analyse a project named Negro River Flood Warning System that presents a river level or stage forecast about Negro river by the Geological Survey of Brazil in Manaus since 1989, where the annual flood and ebb monitoring process is performed in the Solimões, Negro and Amazonas hydrological system. Flood forecasting models are important for the composition of extreme events alerts, as well as for the knowledge of decision-makers, representatives of public agencies and affected communities. Many factors contribute to the flooding event: how the various tributaries are integrated down the river main stem and how the basin behaves during the six months of flooding in the rainy season. For the forecast, it is important to monitor the evolution of the level of rivers such as Negro and Solimões, understanding the dynamics of the basin and also the events associated with major floods that have already occurred, as recorded in the historical series of the port of Manaus, all this combined with a statistical methodological approach. In the Manaus alert system, linear regression analysis is used. According to results obtained for the past 15 years, the flood forecast interval reveals that the forecast in 87% of cases has fulfilled the objective of presenting a stage very close to the water level peak. Furthermore, it was noticed that a height of 27 m in Negro river turned to be an alert quota with a return period of 10 years. Once the river water level reaches a height of 29 m, it can be considered a ‘severe flood water level’ with a return period of 17 years.