Survey of Sāmoa’s LiDAR dataset reveals an extensively human-modified environment consisting of networks of ditches and terraces that extend from the coast to the remote interior. This system served to control flooding and subsequent soil saturation while also supporting agricultural production. As a component of niche construction, these drainage networks further maintained the integrity of the island’s soils and ecosystem by regulating water flow and reducing erosion, allowing for long-term stability. Additionally, the expanded extent of these features was likely implemented in conjunction with the evolution of social complexity in Sāmoa, playing a key role in the growth of pre-colonial Sāmoa’s population and chiefly system. Through the examination of the similarities and differences between three study areas in the eastern Atua province of ‘Upolu Island, this research suggests that prehistoric Sāmoans not only knew how to target specific soils for agricultural production, but also recognized the importance of drainage to maximize agricultural production. Revitalizing such traditional ecological knowledge and land management practices intends to simultaneously draw further connections to related Polynesian communities and promote an adaptation strategy for other indigenous island and coastal communities in crisis. Sāmoa’s prehistoric agricultural system provides an example of indigenous people within a socio-ecological system building resilience through collective action. Understanding how and why ancestral Sāmoans so intensely modified their environment provides a model for modern communities eager to live more sustainably, especially as Pacific Islander communities support efforts to do so in preparation for increasingly powerful and more frequent rainfall events due to a rapidly changing climate.