Surface waters

Research in surface water hydrology made important advances in the areas of river mechanics and streamflow routing, experimental study of overland flow, surface runoff models, partial area processes, effects of land use on surface runoff, and probability, statistics and analysis of uncertainty. In each area there was a fundamental need to apply mathematical and computer methods, and this is reflected in the following review of progress in each of these areas. A broad‐based effort went into developing numerical solutions of the Saint Venant partial differential equations for unsteady flow in open channels. Some papers suggested a numerical procedure; some looked at computational efficiency; some looked at convergence and/or stability properties; some looked at the importance of various terms; some looked at prediction accuracy; and some suggested procedures for branched or looped river networks. These papers offer testimony to widespread use in hydrology practice of models based either on the full Saint Venant equations or on one of many approximations to these equations, including both linear approximations with one or more terms neglected and nonlinear approximations with several terms neglected. Because some of these approximations have the same mathematical structure as certain well‐known hydrologic routing techniques, it is now possible to give clearer physical meaning to the better established hydrologic methods such as the Muskingum method. Hopefully, this will stimulate more intelligent use of all of these techniques (e.g., through new physically based criteria for applying the lag and route model or new criteria for judging when the full nonlinear Saint Venant equations must be used rather than some approximation, etc.). Following is a review of some specific contributions.