A First-Principle, Physics-Based Watershed Model [chapter]

David Richards, Hsin-Chi Lin, Hwai-Ping Cheng, Fan Zhang, Guobiao Huang, Earl Edris, Gour-Tsyh Yeh
2005 Watershed Models  
The approaches to watershed-scale modeling can be classified into three broad groups: parametric methods, stochastic approaches, and physics-based mathematical models. In the past 30 years, the watershed modeling communities have employed parametric-based models (the most famous one is the HSPF [1]; all other parametric models are similar to HSPF, e.g., SWMM [2], CREAMS [3], STORM [4], ANSWERS [5], SWRRBWQ [6]) for watershed management and assessment including ecological exposure assessments
more » ... TMDL calculations. Evolved from the pioneer model STANFORD WATERSHED IV [7] , HSPF has dominated watershed simulations for more than 20 years. Physics-based, process-level chemical transport and hydrological models have been practically nonexistent until recently. It is easy to understand that only the physics-based, process-level fluid flow and thermal, salinity, sediment, and biogeochemical transport models have the potential to further the understanding of the fundamental biological, chemical and physical factors that take place in nature. It is precise for this reason that EPA ecological research strategies [8] had clearly stated that the first-principle, physics-based models should be used in ecological system assessment on a watershed scale. Progresses in the development of first-principle, physics-based models for individual processes of infiltration, evapotranspiration, recharge, moisture redistribution in vadose zone, groundwater flow, surface runoff, and river flow have been remarkable. These individual processes must be dynamically coupled over various spatial and temporal scales. In the past, each individual process was often investigated assuming other coupling and influencing processes were a priori. For example, to model overland flow (surface runoff), it was often implicitly assumed that the infiltration was known and the feedback from groundwater flow and river flow were not explicitly enforced. Integrated approaches to modeling coupled processes have gained momentum recently. Many integrated models have achieved the coupling via external or internal linkage of individual process level models. As a result, these models often have to introduce undue empiricism. This chapter specifically focuses on a first-principle, physics-based model, WASH123D [9] . The development of an integrated numerical model of the aforementioned processes is presented. A rigorous coupling of these hydrological and biogeochemical processes is achieved by imposing the continuity of fluxes and state variables. In this integrated model, any process between two media is the natural consequence of interaction and feedback between processes occurring in individual
doi:10.1201/9781420037432.ch9 fatcat:67n426ffjrhyhilkqkrm3nys3y