Hydrosedimentary monitoring of the Hydrothiem observatory, Eastern tropical coast of New Caledonia (SW Pacific)

Study region: The eastern coast of New Caledonia (SW Pacific).Study focus: The HydroThiem hydrological observatory is devoted to the study of the impact of invasive ungulate species and bushfires on water resources, erosion and water quality in a catchment used for drinking water. It includes (1) three 100 m2 plots located on characteristic land surfaces, i.e. a woody savanna submitted to bushfires every few years, a healthy forest and a forest strongly degraded by deer and wild pigs, (2) two watersheds covering areas of 25 200 m2 and 3.1 km2. The first watershed includes mostly savanna while the second one is mostly constituted of humid forest. Available data include rainfall, soil moisture, discharge, and sus-pended matter concentration.New hydrological insight: Discharge and erosion rates exhibit striking differences between the three plots: the healthy forest presents a 3 % runoff and almost no erosion, the degraded forest being characterized by a 90 % runoff and large erosion, the savanna presenting intermediate values of runoff and erosion. The largest watershed present a 64 % runoff and an erosion rate amounting to 72 % of the one of the degraded plot. This emphasizes the role of subsurface flow and of gully erosion, respectively. Results from the Hydrothiem observatory can be used for a comparison with similar watersheds and may suggest guidelines for restoration and conservation strategies.

Automated summary

The HydroThiem hydrological observatory in the eastern coast of New Caledonia studied the impact of invasive ungulate species and bushfires on water resources, erosion, and water quality in a catchment used for drinking water. By comparing three different land surfaces, it was found that the healthy forest had the lowest runoff and erosion rates, while the degraded forest had the highest. The savanna had intermediate values. The largest watershed showed significant runoff and erosion, highlighting the role of subsurface flow and gully erosion. The results can be used for comparison and guidance in restoration and conservation strategies.