In this chapter, modeling of the unsteady open channel flow using one-dimensional approach is considered. As this question belongs to the well-known and standard problems of open channel hydraulic engineering, comprehensively presented and described in many books and publications, our attention is focused on some selected aspects only. As far as the numerical solution of the governing equations is considered, one can find out that essentially there are no problems with provided accuracy. Usually, the implementation of the Saint Venant equations (i.e. the full dynamic wave model) for any case study is successful as long as the basic assumptions introduced during their derivation are fulfilled. Otherwise, some computational difficulties can occur. For this reason we would like to draw the readers’ attention only to such situations when special computational tricks or simplification of the governing equations should be applied.