**Ahmed M. A. Sattar 1,2, Hossein Bonakdari 3,\*, Bahram Gharabaghi 3,\* and Artur Radecki-Pawlik <sup>4</sup>**


Received: 27 November 2018; Accepted: 1 February 2019; Published: 6 February 2019

**Abstract:** Open channel levees are used extensively in hydraulic and environmental engineering applications to protect the surrounding area from inundation. However, levees may fail to produce an unsteady flow that is inherently three dimensional. Such a failure may lead to a destructive change in morphology of the river channel and valley. To avoid such a situation arising, hydraulic laboratory modeling was performed on an open channel levee breach model capturing velocity, in x, y and z plans, at selected locations in the breach. Sandbags of various shapes and sizes are tested for incipient motion by the breach flow. We found that a prism sandbag has a better hydrodynamic characteristic and more stability than spherical bags with the same weight. Experimental results are then used to evaluate existing empirical equations and to develop more accurate equations for predicting critical flow velocity at the initial stage of sandbag motion. Results showed the superior predictions a few of the equations could be considered with an uncertainty range of ±10%. These equations explained the initial failed attempts of the United States Army Corps of Engineers (USACE) for breach closure of the case study, and confirmed the experimental results are simulating the case study of breach closure.

**Keywords:** breach closure; levee breach; channel side flow; sandbags; open channel flow; critical velocity; incipient motion
