Challenges in Physical Modeling of Erosion

The methods used in the design of a physical model of a bed erosion in a large pond downstream of a tailrace
outfall structure are discussed. The model was a laboratory simulation of a free surface flow from a hydropower
tunnel into a large pond with the aim of reducing discharge into a downstream river. A significant part of
the investigation was the laboratory reproduction of a damaging erosion process below a large concrete
apron. Four challenges in the design and operation of the physical model were dealt with: (1) providing for
sufficient erosion depth below the rigid bed floor, (2) choosing a proper scaling ratio for sediment grain size,
(3) continuously accessing the study area without disturbing the flow or the bed topography, and (4) making
quick measurements of the bed topography at the end of each test. The methods employed and the lessons
learned could enhance the laboratory skills of physical modelers of movable bed projects.