Uncertainty Analysis of Routed Outflow in Rockfill Dams

Detention rockfill dams are an easy and common tool for flood control. Due to their coarse pores, the flow in void spaces is turbulent and non-Darcy. Different relationships introduced by researchers are used to define the hydraulics of the flow within the rockfill materials. The present research is aimed at gaining a better understanding of the difference among these relationships and the sources of uncertainty associated with the different parameters of each of the relationships. To examine the importance of various factors on the uncertainty of the outflow hydrograph, sensitivity analysis was conducted. For this purpose, a rockfill mass was provided, fifteen random samples of the mass selected, and then the physical characteristics of the material were measured or estimated. Also, some flood routing tests have been conducted. In these tests a physical model of a dam was installed and downstream water level was measured for different outflow rates. While the downstream water level was considered as certain variable but other parameters were seen as stochastic (stochastic parameters are considered as random variables) and outflow discharge as an output uncertain parameter. Uncertainty analysis has been conducted for different points of the outflow hydrograph by employing available methods. The results show that the Samani et al. and McCorocoudale et al. relationships have the lowest and highest uncertainty, respectively. The sensitivity analysis demonstrates different levels of sensitivity accompanied each of the relationship parameters which results in different effects on the total uncertainty of the relationships.