The Catchment Modelling Toolkit folks at eWater have released a development of their E2 modeling framework known as WaterCAST.
"The intent of WaterCAST is to provide managers of predominantly rural, and peri-urban, catchments with the capability to make informed decisions as to how changes in catchment management influence the quantity and quality of runoff to receiving waters. It is especially helpful for looking at water balance and for managing the factors affecting movement of sediments, nutrients and salts across catchments and in streams."
"WaterCAST differs from most catchment models in that it does not have a fixed structure and set of algorithms. It is actually a flexible framework that requires the user to consider and select a combination of models best suited to the problem at hand. So the user builds the specific modelling tool he or she wants according to the level of complexity appropriate to the problem and the available data and knowledge."