Finessing 1-D Hydraulic Models into 2-D Performance

The majority of the applications of hydraulic models are performed in 1 spatial dimension. Although nature "operates" in 4 dimensions (3 spatial dimensions and the time dimension), hydraulic engineers often fearlessly model 4-dimensional phenomena with 1-dimensional (1-D) models (sometimes in unsteady mode) knowing fully that the model is just a crude approximation of the real world. These engineers do this not because they willfully want to ignore the other dimensions but rather because of many practical and legitimate reasons. In certain applications where a 2-dimensional (2-D) depth-averaged model might be warranted, an experienced engineer can sometimes finesse a 1-D model and extend its capabilities such that the model can reasonably emulate 2-D phenomena or use an external application that can be used to adjust the 1-D results for 2-D application. This paper presents such techniques and also explains the cautions/limitations of the techniques. The paper will use HEC-RAS as the example model since it is the most widely used 1-D model.