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)

Watershed Modeling Approaches: CASC-2D

Watershed Modeling Approaches: CASC-2D

Watershed Modeling Approaches

Soil Moisture Routing Model (Cornell)

• subsurface: 2-D Darcy’s Law / water balance, topography driven• evapotranspiration• deep percolation

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

jijiji Tq ,,, tan

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

Watershed Modeling Approaches: KINEROS2

Watershed Modeling Approaches: KINEROS2

Watershed Modeling Approaches: KINEROS2

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

tanzfo ef

Kq

K0 = surface conductivity, f = decay coef., = ground slope

Upslope contributing area a

Stream line

Contour line

Watershed Modeling Approaches: Topmodel

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)

• Tension water (unsaturated)• Free water (saturated)• Surface flow• Lateral drainage• Evapotranspiration• Vertical drainage (percolation)

Watershed Modeling Approaches: SAC-SMA

Components:

Watershed Modeling Approaches: SAC-SMA

Watershed Modeling Approaches: SAC-SMA

E T Demand

Impervious Area

E T

E T

E T

E T

Precipitation Input

Px

Pervious Area

E T

Impervious Area

Tension Water

UZTW Free Water

UZFW

PercolationZperc. Rexp

1-PFREE PFREE

Free WaterTension Water P S

LZTW LZFP LZFS

RSERV

Primary Baseflow

Direct Runoff

SurfaceRunoff

Interflow

Supplemental Base flow

Side SubsurfaceDischarge

LZSK

LZPK

Upper Zone

Lower Zone

EXCESS

UZK

RIVA

PCTIM

ADIMP

TotalChannelInflow

DistributionFunction Streamflow

TotalBaseflow

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