A flexible modeling package for topographically based watershed hydrology

An OBJect-oriented TOPographic-based (OBJTOP) hydrological model with a graphical user interface (GUI) was created using object-oriented design (OOD) methods and the objected-oriented programming (OOP) language-C++. OBJTOP presents an array of alternative TOPMODEL hydrological processes of (1) saturation excess or the mixture of infiltration/saturation excess overland flow, (2) exponential or power law decay of hydraulic conductivity with soil depth, (3) topographic index (TI) or soil topographic index (STI) weighting of run-off likelihood, and (4) simulations with or without channel routing, to explain watershed response and increase flexibility and applicability. OBJTOP utilized an object-oriented design (OOD) approach, including the ‘inheritance’ concept to study individual objects (or processes) at multiple levels, and the ‘aggregation’ concept to study the interactions of objects (or processes). Further, OOD readily provides for model extension, creating a description of hydrologic processes in a natural, direct, concise, and adaptable manner distinct from procedurally designed and implemented models. The OBJTOP GUI provides an efficient tool for data input, parameter modification, simulation scheme selection and model calibration with three objective functions, including Nash-Sutcliffe. Graphical outputs include time series plots of precipitation depth, partitioned run-off volumes, watertable depth (average or TI/STI based), and map graphics of TI, STI, and depth to watertable. Applications illustrating OBJTOP ability and flexibility include simulation of the TOPMODEL standard Slapton Wood, UK dataset, and simulation of Ward Pound Ridge, NY a small forested catchment with power function decay of hydraulic conductivity and extensive impervious surfaces.