Fredrik Huthoff

Theoretical Analysis of Wing Dike Impact on River Flood Stages

The question of whether wing dikes (bank-perpendicular river training structures or groynes) cause higher flood levels has been debated in the United States for many years. Some researchers point to empirical data that show large stage increases which are associated with wing dike construction, whereas other researchers have suggested that such increases are contrary to engineering theory. In a recent report, the U.S. Government Accountability Office (USGAO) presented this question as a priority to be resolved by engineers and scientists. As a first step to better understand the connection between navigation structures and flood levels on the Middle Mississippi River (MMR), a simplified theoretical analysis is presented to test the assertion (made in the USGAO report and elsewhere) that such increases are contrary to hydraulic theory. This analysis predicts that wing dike construction may lead to water level lowering for in-bank flows and to water level increases for out-of-bank (flood) flows. This confirms that, in principle, wing dikes may have contributed to the observed flood water level trends in the MMR. More detailed follow-up studies are required to accurately quantify the impact of wing dikes on flood levels. DOI: 10.1061/(ASCE)HY.1943-7900.0000698.

Stone Stability under Stationary Nonuniform Flows

AbstractA stability parameter for rock in bed protections under nonuniform stationary flow is derived. The influence of the mean flow velocity, turbulence, and mean acceleration of the flow are included explicitly in the parameter. The relatively new notion of explicitly incorporating the mean acceleration of the flow significantly improves the description of stone stability. The new stability parameter can be used in the design of granular bed protections using a numerical model for a large variety of flows. The coefficients in the stability parameter are determined by regarding the measured low-mobility entrainment rate of rock as a function of the stability parameter. Measurements of flow characteristics and stone entrainment of four different previous studies and many configurations (uniform flow, expansion, contraction, and sill) are used. These configurations have different relative contributions of mean flow, turbulence, and stationary acceleration. The coefficients in the parameter are fit to all ...