Several of the world's largest deltas have recently been conceptualized as social-ecological delta systems. Although such conceptualizations are valuable in emphasizing complex interaction between social actors and ecological processes in deltas, they do not go into specific dynamics that surround technological developments in the hydraulic domain. By drawing from concepts originating in socio-technical systems research, we stress the importance of technology, particularly the domain of hydraulic engineering, in shaping a delta's future. Based on two geographically distinct cases of flood management infrastructure in the Dutch delta, we demonstrate the influence of existing hydraulic works, in mutual interaction with social responses and environmental processes, on the development of the congregated delta system over time. The delta trajectory concept is introduced as a way to understand the interplay between social, ecological, and technological systems in deltas. We discuss options to realign unsustainable pathways with more desirable ones. Adaptive delta management presents a policy environment where these messages may be picked up.