1. Watershed Modeling Approaches Distributed: CASC-2D (CSU, U Conn, WMS) overland flow: 2-D diffusion wave with explicit FD channel flow: 1-D diffusion wave with explicit FD, or 1-D dynamic wave with implicit Preissmann scheme infiltration: Green-Ampt equation with redistribution evapotranspiration, interception, erosion (overland and channel)

2. Watershed Modeling Approaches: CASC-2D

4. Watershed Modeling Approaches Soil Moisture Routing Model (Cornell) subsurface: 2-D Darcy’s Law / water balance, topography driven evapotranspiration deep percolation

5. Watershed Modeling Approaches DHSVM Grid-based subsurface routing, hydraulic gradient = ground slope Power law subsurface hydraulic conductivity (transmissivity) function Unit hydrograph distribution of excess runoff (travel time for each pixel) Muskingum-Cunge network/channel routing

7. Watershed Modeling Approaches KINEROS2 (USDA-ARS) overland flow: 1-D kinematic wave, 4-pt implicit FD; wetted area factor in recession channel flow: 1-D kinematic wave, 4-pt implicit FD infiltration: Smith-Parlange, layered soils, redistribution, interactive (plane to plane), sub-grid effective parameters erosion and sedimentation: 4-pt implicit FD interception

8. Watershed Modeling Approaches: KINEROS2

11. Watershed Modeling Approaches TOPMODEL Topographically Driven: slope, contributing area, convergence Saturated zone hydraulic gradient assumed to be equal to slope Exponential decrease of hydraulic conductivity with depth Watershed outflow related to mean depth to water table Saturation and infiltration excess runoff generation Evapotranspiration Channel routing: kinematic wave K 0 = surface conductivity, f = decay coef.,  = ground slope

12. Upslope contributing area a Stream line Contour line Watershed Modeling Approaches: Topmodel

13. Watershed Modeling Approaches SAC-SMA (part of NWSRFS) Physically-based conceptual model –based on physical concepts that describe water movement trough a watershed Lumped Continuous Two-layer soil model (upper and lower zones)

14. Tension water (unsaturated) Free water (saturated) Surface flow Lateral drainage Evapotranspiration Vertical drainage (percolation) Watershed Modeling Approaches: SAC-SMA Components:

15. Watershed Modeling Approaches: SAC-SMA

17. Watershed Modeling Approaches SAC-SMA is a component of NWSRFS Snow models available Runoff over a time step distributed to watershed outlet using UH Channel routing: lumped methods, distributed methods