Towards a better integration of local populations in the design of projects to manage the massive aggradation of rivers stemming from mining activity in Thio, New Caledonia

Abstract

Nickel mining in New Caledonia has largely contributed to the supply of sediment to watercourses, so that some of the main watercourses of the island are considerably aggraded. One of the consequences of this massive aggradation is the elevation and widening of river beds and creeks, thus increasing the flood hazard and the associated risks for people and goods. In addition, it changes the aquatic ecosystems, deteriorates the quality of drinking water supplies, causes the deposit of mud on crops during floods, damages communication networks and affects customary practices and activities.In this context, remediation measures are needed on a local level and they are required to consider technical aspects as well as social and cultural ones. Because of these requirements, the CNRT "Nickel and Environment" funds an applied and interdisciplinary research project with both physical and social sciences in order to (a) better understand local dynamics, and to (b) identify key factors for implementing remediation measures.In addition to physical observation and the modelling of aggradation, observations and experiences concerning river and creek aggradation were collected from the inhabitants of six tribes (Kanak villages) in the Thio Valley. It was equally important to record their perception regarding possible remediation measures, some of which having already been put in practice. In these testimonies, people often referred to ‘water holes’ in the rivers. These are socially important for inhabitants, and their sedimentary dynamics are well known to local people and could represent interesting markers of morphodynamic evolution.Linking lessons learned from both the physical and the social sciences approaches has led to the elaboration of a methodological guide dedicated to the management of sedimentary heritage from mining. This guide was presented to various actors in New Caledonia in 2018. Through the example of water holes as ‘shared objects’, this paper describes why and how the involvement of the inhabitants in the design and implementation of observations and monitoring is necessary and discusses the need to fully integrate people's perceptions into the project design.