Causative classification of river flood events.

A wide variety of processes controls the time of occurrence, duration, extent, and severity of river floods. Classifying flood events by their causative processes may assist in enhancing the accuracy of local and regional flood frequency estimates and support the detection and interpretation of any changes in flood occurrence and magnitudes. This paper provides a critical review of existing causative classifications of instrumental and preinstrumental series of flood events, discusses their validity and applications, and identifies opportunities for moving toward more comprehensive approaches. So far no unified definition of causative mechanisms of flood events exists. Existing frameworks for classification of instrumental and preinstrumental series of flood events adopt different perspectives: hydroclimatic (large-scale circulation patterns and atmospheric state at the time of the event), hydrological (catchment scale precipitation patterns and antecedent catchment state), and hydrograph-based (indirectly considering generating mechanisms through their effects on hydrograph characteristics). All of these approaches intend to capture the flood generating mechanisms and are useful for characterizing the flood processes at various spatial and temporal scales. However, uncertainty analyses with respect to indicators, classification methods, and data to assess the robustness of the classification are rarely performed which limits the transferability across different geographic regions. It is argued that more rigorous testing is needed. There are opportunities for extending classification methods to include indicators of space-time dynamics of rainfall, antecedent wetness, and routing effects, which will make the classification schemes even more useful for understanding and estimating floods. This article is categorized under:Science of Water > Water ExtremesScience of Water > Hydrological ProcessesScience of Water > Methods.

A robust optimization technique for analysis of multi-tracer experiments.

Fate and transport of solutes in heterogeneous porous media is largely affected by diffusive mass exchange between mobile and immobile water zones. Since it is difficult to directly measure and determine the effect in the aquifers, multi-tracer experiments in combination with mathematical modeling are used to obtain quantitative information about unknown system parameters such as the effective mobile and immobile porosity, and the diffusive mass exchange between mobile and immobile water zones. The Single Fissure Dispersion Model (SFDM) describing nonreactive transport of solutes in saturated dual-porosity media, has been employed as a modeling approach to explain dual-porosity experiments in the field and laboratory (column experiments). SFDM optimization with conventional methods of minimization was immensely difficult due to its complex analytical form. Thus, previous studies used a trial and error procedure to fit it to the experimental observations. In this study, a rigorous optimization technique based on the newly developed scatter search method is presented that automatically minimizes the SFDM to find the optimal values of the hydrogeologically related parameters. The new program (OptSFDM) is accompanied with an easy-to-use graphical user interface (GUI) that is flexible and fully integrated. The program usability is showcased by a few, previously presented experimental case studies, and compared against the currently available, trial-and-error based, command-line executable, SFDM code.