Analysis of Flood Risks Upstream from the Imboulou Hydroelectric Dam on the Léfini River, a Tributary of the Right Bank of the Congo River

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. .

Using classification assignment rules to assess land-use change impacts on forest biodiversity at local-to-national scales

Background： Ecosystem representation is one key component in assessing the biodiversity impacts of land-use changes that will irrevocably alter natural ecosystems. We show how detailed vegetation plot data can be used to assess the potential impact of inundation by a proposed hydroelectricity dam in the Mokihinui gorge, New Zealand, on representation of natural forests. Specifically we ask： 1） How well are the types of forest represented Locally, regionally, and nationally; and 2） How does the number of distinct communities （i.e. beta diversity） in the target catchment compare with other catchments nationally？ Methods： For local and regional comparisons plant species composition was recorded on 45 objectively located 400 m2 vegetation plots established in each of three gorges, with one being the proposed inundation area of the Mokihinui lower gorge. The fuzzy classification framework of noise clustering was used to assign these plots to a specific alliance and association of a pre-existing national-scale classification. NationaLly, we examined the relationship between the number of alliances and associations in a catchment and either catchment size or the number of plots per catchment by fitting Generalised Additive Models. Results： The four alliances and five associations that were observed in the Mokihinui lower gorge arepresent in the region but limited locally. One association was narrowly distributed nationally, but is the mostfrequent association in the Mokihinui lower gorge; inundation may have consequences of national importance to its long-term persistence. That the Mokihinui lower gorge area had nearly twice as many plots that could not be assigned to pre- existing alliances and associations than either the Mokihinui upper or the Karamea lower gorges and proportionally more than the national dataset emphasises the compositional distinctiveness of this gorge. These outlier plots in the Mokihinui lower gorge may be unsorted assemblages of species or reflect sampling bias or that native- dominated woody riparian vegetation is rare on the landscape. At a national scale, the Mokihinui catchment has a higher diversity of forest alliances and associations （i.e. beta-diversity） than predicted based on catchment size and sampling intensity. Conclusions： Our analytical approach demonstrates one transparent solution to a common conservation planning problem： assessing how well ecosystems that will be destroyed by a proposed land-use change are represented using a multi-scale spatial and compositional framework. We provide a useful tool for assessing potential consequences of land-use change that can help guide decision making.

Environmental determinants of social wasp diversity and assemblage structure in an Amazonian archipelagic landscape

Hydropower development has become an important driver of habitat loss and fragmentation across lowland tropical forests.Despite ample evidence on the detrimental effects of insular habitat fragmentation on biodiversity,invertebrate taxa,that may be critical to ecosystem functioning,have been overlooked.We assessed the assemblage-level responses of social wasps to forest insularization induced by the Balbina Hydroelectric Dam in Central Brazilian Amazonia.Employing Malaise trapping,we captured wasps on 27 forest islands and three continuous forests.We constructed Generalized Linear Models and employed a model selection approach to examine the impact of local variables(fire severity(FIRE)and basal area of pioneer tree species(PIONEER))and landscape-scale variables(amount of habitat(COVER))on patterns of species richness,composition,and body size of wasps.A total of 374 individuals(29 species)were collected across all sampling sites.COVER was the main predictor of species richness,while PIONEER was the only variable that explained variation in community composition,with a negative effect on body size.Our results add evidence to the pervasive impacts of large hydroelectric dams on tropical forest biodiversity,and suggest that social wasps,among other invertebrates,can be used as bioindicators in infrastructure development projects.