High rates of sedimentation in Governors Bay, Whakaraupō, New Zealand have led to the expansion of mesotidal mudflat and shallowing of the bay. This has been identified as a significant issue for local mana whenua, recreational activities, and fishing in the bay. Previous research has identified that this sediment is most likely drawn from the catchment immediately surrounding Governors Bay. This study aims to identify the source of the sediment in Governors Bay, better constrain its location within Governors Bay, and provide solutions in the form of possible remediation scenarios to enact to reduce erosion rates across the catchment. This was achieved through the acquisition and analysis of an 84 cm sediment core in Governors Bay as well as 36 sediment samples from the catchment to determine sediment provenance. This information was combined with InVEST sediment delivery ratio modelling software to identify areas of greatest concern in terms of sediment erosion as well as the land use types which contribute the most to sediment erosion and the types which can best be used to prevent it.

Geochemical, total organic carbon and grainsize analysis of the sediment core and samples from the catchment identify the primary sediment source entering the bay as being that found below the 200 m contour in the catchment. This area corresponds to loess and loess colluvium stratigraphy and loess derived soils. Modelling of sediment erosion in the catchment suggests that the highest rates of erosion are found on hill slopes with grassland cover and in areas of urban development. Areas with the lowest rates of sediment erosion are found to be those with relatively flat topography and native forest cover.

A remediation scenario is proposed to restore native forest to Governors Bay. The initial focus is suggested to be areas of grassland below the 200 m contour, with simultaneous removal of pests and weeds that would threaten native forest growth. Focus can then shift to reforesting the entire catchment in native forest over the long term apart from urban development. This scenario provides an effective option to reduce overall sediment erosion rates in the catchment, slow the expansion of the mesotidal mudflat to near natural growth levels, and to restore and prolong the cultural health of Governors Bay as well as securing future accessibility to the waters of the bay for the local community.