An increase in seawater that experiences high tides can cause tidal flooding. Tidal flooding in the Semarang area requires quick and precise handling, so an emergency dam is needed to deal with seawater overflow or tidal flooding. This study discusses the Knock-Down weir as a practical emergency weir. This study also aims to test the shear stability of the Knock-Down weir model against wall roughness based on variations in soil types, namely: masonry, gravel, sand, and clay. The Knock-Down weirs can be arranged vertically, horizontally, and as needed. The method used is descriptive qualitative. There are four forms of Knock-Down weir arrangement and the safest against wall roughness in various types of soil is prioritized. They are (1) L shape filled with sand + water, (2) Form I filled with sand + water, (3) Form I filled with water, and (4) Shape L filled with water. The results of the research on the safest Knock-Down weirs on shear stability are (1) L shape filled with sand + water, at a height of 1m weirs, shear stability against masonry (3,13), shear stability of gravel (2.09), shear stability to sand (1.67), shear stability against clay (1.25).