**Abstract**

Naturally assembled rocks can be found in the natural rivers with gravel beds, and assembled boulders with large-scale rocks are stable after many floods. This chapter focused on assembled rocks from the point of view of the stability of the structure during many floods and the preservation of the aquatic habitat under normal conditions. In renovated rivers, the installation of hydraulic structures may result in the degradation of the river bed, local scouring behind the structure, bank erosion due to floods, and obstacles in the aquatic migration routes of aquatic animals. A balance between the prevention of disasters and the preservation of aquatic habitats should be maintained. Artificially assembled boulders should be recommended for river engineering technology. Unfortunately, there is no information on the hydraulics of artificially assembled boulders or on the imbrication of boulders in any part of the world. This chapter presents experimental research on the hydraulics of assembled boulders under normal and flooding conditions. A shallow water flow was formed near the water side under normal conditions. The stability of the structure of assembled boulders was confirmed under flooding conditions. These findings were confirmed by field inspection.

**Keywords:** artificially assembled boulders, stability of structure, shallow water flow, normal stage, flood stage
