Locally and globally, mega-hydraulic projects have become deeply controversial. Recently, despite widespread critique, they have regained a new impetus worldwide. The development and operation of large dams and mega-hydraulic infrastructure projects are manifestations of contested knowledge regimes. In this special issue we present, analyze and critically engage with situations where multiple knowledge regimes interact and conflict with each other, and where different grounds for claiming the truth are used to construct hydrosocial realities. In this introductory paper, we outline the conceptual groundwork. We discuss ‘the dark legend of UnGovernance’ as an epistemological mainstay underlying the mega-hydraulic knowledge regimes, involving a deep, often subconscious, neglect of the multiplicity of hydrosocial territories and water cultures. Accordingly, modernist epistemic regimes tend to subjugate other knowledge systems and dichotomize ‘civilized Self’ versus ‘backward Other’; they depend upon depersonalized planning models that manufacture ignorance. Romanticizing and reifying the ‘othered’ hydrosocial territories and vernacular/indigenous knowledge, however, may pose a serious danger to dam-affected communities. Instead, we show how multiple forms of power challenge mega-hydraulic rationality thereby repoliticizing large dam regimes. This happens often through complex, multi-actor, multi-scalar coalitions that make that knowledge is co-created in informal arenas and battlefields.

The contributions to the Special Issue on Contested Knowledges: Water Conflicts on Large Dams and Mega-Hydraulic Development have looked at the politics of contested knowledge as manifested in the conceptualization, design, development, implementation and governance of large dams and mega-hydraulic infrastructure projects in various parts of the world

While national agencies increasingly adopt ‘sustainable’ rhetoric, their policies frequently prioritize bureaucratic legitimacy over local landscape realities. This research examines how Thailand’s development policies shape water and spatial governance in riverine landscapes, focusing on Chiang Mai Province and the Phaya-Kham irrigation system. Despite ambitious sustainable development objectives, implementation is marked by institutional silos, overlapping mandates, and scalar misalignments, resulting in fragmented governance that favors short-term economic gains over long-term ecological health. These dynamics undermine water resource management and exacerbate socio-ecological inequalities. Drawing on archival reviews, policy analysis, mapping, and interviews, the study employs political ecology perspectives and David Mosse’s framework of policy performance to investigate the disjuncture between policy intentions and on-the-ground realities. The Phaya-Kham system illustrates how modernization pressures, urban expansion, and agricultural intensification destabilize community-based water governance. Findings underscore that governance challenges in Chiang Mai are fundamentally political, rooted in struggles over authority and resource control rather than technical shortcomings. Sustainability-oriented policy frameworks may reproduce socio-ecological degradation. Achieving fairer water and landscape governance requires confronting these dynamics, integrating local knowledge, and fostering inter-agency cooperation. By recognizing context-based hydrosocial territories, policies can move toward more socio-environmentally healthy frameworks supporting local riverine communities and landscape realities.