Sand dams for sustainable water management: Challenges and future opportunities.

Sand dams are impermeable water harvesting structures built to collect and store water within the volume of sediments transported by ephemeral rivers. The artificial sandy aquifer created by the sand dam reduces evaporation losses relative to surface water storage in traditional dams. Recent years have seen a renaissance of studies on sand dams as an effective water scarcity adaptation strategy for drylands. However, many aspects of their functioning and effectiveness are still unclear. Literature reviews have pointed to a range of research gaps that need further scientific attention, such as river corridors and network dynamics, watershed-scale impacts, and interaction with social dynamics. However, the scattered and partially incomplete information across the different reviews would benefit from an integrated framework for directing future research efforts. This paper is a collaborative effort of different research groups active on sand dams and stems from the need to channel future research efforts on this topic in a thorough and coherent way. We synthesize the pivotal research gaps of a) unclear definition of "functioning" sand dams, b) lack of methodologies for watershed-scale analysis, c) neglect of social aspects in sand dam research, and d) underreported impacts of sand dams. We then propose framing future research to better target the synthesized gaps, including using the social-ecological systems framework to better capture the interconnected social and biophysical research gaps on sand dams, fully utilizing the potential of remote sensing in large-scale studies and collecting sand dam cases across the world to create an extensive database to advance evidence-based research on sand dams.

Reconstructing Ancient Hohokam Irrigation Systems in the Middle Gila River Valley, Arizona, United States of America.

We explore the concept of scales to examine emerging irrigation realities, i.e., connecting more agents within larger spaces - relates to the complexity of irrigation systems. Modern hydraulic models allow the inclusion of emerging multi-scale issues over time, including social issues related to different spatial and temporal scales. We show that the time needed to manage irrigation efficiently relates to the size of a system. By reconstructing ancient Hohokam irrigation systems in Arizona, we identify how longer-term extension of spatial scales created management problems beyond the scope of available technology. This approach allows greater understanding of how stresses in daily irrigation management may have impacted longer-term societal stability.