Towering hydroelectric concrete dams and flood-protection embankments attempt to ‘control and tame’ rivers within nation-state led security framings of their natural transboundary flows. This originates from a very ‘masculinist’ outlook of national hydrocracies to be able to engineer rivers, materializing and embedding concrete border walls on the river basin, through large-scale ‘infrastructure development’ and ‘hydraulic-mission’ paradigms. This work explores the idea of riparian infrastructure development as an extension of the nation-state’s bordering practices, deploying national-security discourses and narratives towards legitimizing such interventions. Such bordering practices have political, ecological, and economic impacts on the international scale and, at the same time, have layered effects within the nation-state. This chapter will employ examples from South Asia to demonstrate such bordering effects on transboundary river basins, particularly in the context of the major Himalayan river basins. The construction of mega hydropower dam projects by China and India has been viewed as projects of national pride and importance and serves as ‘sovereignty markers’ on their respective stretches of shared river basins. The flood-protection embankments within their territorial limits make for additional bordering effects upon upstream and downstream riparian communities, accentuating politics of economic inclusion and exclusion, and engineering flood-related disasters over time. The understanding of dams and embankments as border walls makes for an analysis of the ecological ruptures that such riparian infrastructure development has inflicted on transboundary rivers.