The analysis of the risk of flooding upstream
from the Imboulou hydroelectric dam on the Léfini River in the Republic of
Congo-Brazzaville, focused on the evolution of annual rainfall and flow in the
study area during the period from 1970 to 2020 before and after the building of
the dam in 2005, by applying statistical methods. These methods were used to
analyse the spatial and temporal evolution of rainfall and flow at the unique
hydrometric station located at the RN2 (National Road N°2) bridge in the
village of Mbouambé in the Pool region. This work has shown that rainfall is
not the cause of flooding in the Léfini catchment area. The monthly flow
coefficient (MFC) showed exceptional
flooding from November and December onwards after the dam was built, resulting
in a variability of flows, with periods of high and low water. In addition, the
annual average flow (AAF) and the maximum average flow (MAF) increased after
the dam was built. Maximum average flows (MAF) were higher than annual average
flows (AAF) throughout the period of study (1970-2020). The annual and monthly
rainfall-runoff relationship showed changes after the dam was built,
particularly from 2009 and during the months of November and December.
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