Lumped_VSA_model: Lumped Variable Source Area (VSA) Watershed Model
In EcoHydRology: A Community Modeling Foundation for EcoHydrology

Description Usage Arguments Details Value Warning Note Author(s) References See Also Examples

This model calculates streamflow and approximate saturated area percentage contributing to overland flow. It was developed in saturation-excess dominated watersheds, and is based on the Thornthwaite-Mather water budget and SCS Curve Number approach for overland runoff.

Lumped_VSA_model(dateSeries, P, Tmax, Tmin, Depth = NULL, SATper = NULL, AWCper = NULL, 
percentImpervious = 0, no_wet_class = 10, Tp = 5, latitudeDegrees = 42.38, albedo = 0.23, 
StartCond = "avg", PETin = NULL, AWC = Depth * AWCper, SAT = Depth * SATper, SW1 = NULL, 
BF1 = 1, PETcap = 5, rec_coef = 0.1, Se_min = 78, C1 = 3.1, Ia_coef = 0.05, 
PreviousOutput = NULL, runoff_breakdown = RunoffBreakdown(Tp, HrPrcDelay = (Tp/2 - 4)))

`dateSeries`	Daily date series in the format "2013-05-21"
`P`	Rain + Snowmelt (mm)
`Tmax`	Maximum daily T (C)
`Tmin`	Minimum daily T (C)
`Depth`	Average watershed soil depth (mm) Not needed if SAT and AWC depth entered directly
`SATper`	Porosity of the soil (volumetric fraction, 0-1) Not needed if SAT (porosity depth) entered directly
`AWCper`	Available water capacity, Field capacity - wilting point (volumetric fraction, 0-1) Not needed if AWC entered directly
`percentImpervious`	Percent of the watershed that is impervious (percentage, 0-100
`no_wet_class`	Number of wetness classes to distribute runoff over. Default is 10.
`Tp`	Time to peak of hydrograph (hours)
`latitudeDegrees`	latitude (degrees)
`albedo`	Average surface albedo, defaults to average 0.23
`StartCond`	Watershed conditions before first day of run (options are "wet", "dry", "avg")
`PETin`	# User has the option to enter PET values (mm/day), otherwise this will be estimated from Priestley-Taylor equation, estimating radiation from temperature
`AWC`	# AWC depth (mm)
`SAT`	Porosity depth (mm)
`SW1`	Soil water on the first day (depth, mm)
`BF1`	Baseflow on the first day (mm/day)
`PETcap`	Cutoff for maximal PET allowed per day (mm)
`rec_coef`	Baseflow recession coefficient
`Se_min`	Minimal daily CN S value. (mm)
`C1`	Coefficient relating daily Curve Number S to soil water
`Ia_coef`	Initial abstraction coefficient for CN-equation. (range ~ 0.05 - 0.2)
`PreviousOutput`	If the model is run repeatedly, previous output can be provided so that the model only needs to calculate from that point forward.
`runoff_breakdown`	The proportion of runoff that reaches the outlet on a given day after the storm event. Can be calculated from Tp

The model expects continuous input on a daily time-step, since the soil-water is calculated over time, and affects the amount of runoff that will be generated after a storm. Also, note that precipitation values are actually Rain + Snowmelt (mm). Users can use the snowmelt function to determine this if needed.

Returns a data frame with modeled streamflow, baseflow, ET, and maximum wetness class generating runoff for all dates. Soil water and other modeled intermediate results are also returned. All flow values (modeled_flow, baseflow, OverlandFlow, ShallowInterflow, totQ, quickflow_combined, impervRunoff, excess) are in depth of flow per day (mm/d)

This function cannot handle NA values in input, and can only be run for a daily time-step. If Tx < Tn for any day, this will produce an error. Currently, the crop coefficients used to estimate PET are specific for deciduous northeastern USA.

This function is under development and might change substantially in further versions.

Josephine Archibald

Archibald, J.A., B.P. Buchanan, D.R. Fuka, C.B Georgakakos, S.W. Lyon, M.T. Walter. (in press) A simple, regionally parameterized model for predicting nonpoint source areas in the Northeastern US. Journal of Hydrology: Regional Studies

Schneiderman EM. Steenhuis TS, Thongs DJ, Easton ZM, Zion MS, Neal AL, Mendoza GF, Walter MT. 2007. Incorporating variable source area hydrology into a curve-number-based watershed model. Hydrological Processes. 21: 3420-3430

Shaw, SB, MT Walter. 2009. Improving runoff risk estimates: Formulating runoff as a bivariate process using the SCS curve number method. Water Resources Research. 45

Thornthwaite CW, JR Mather. 1957 Instructions for computing potential evapotranspiration and water balance. Publ Climatol 3: 183-311

United States Department of Agriculture (USDA). (1986). SCS publication Technical Release 55: Urban Hydrology for Small Watersheds. Natural Resources Conservation Service

Weiler K. Unpublished. Determination of the Linear Bedrock Coefficient From Historical Flow Data

PET_fromTemp

## Not run: 
data(OwascoInlet)
# First get rain and snow-melt input: 
rsm <- SnowMelt(Date=OwascoInlet$date, precip_mm=OwascoInlet$P_mm, Tmax_C=OwascoInlet$Tmax_C, 
Tmin_C=OwascoInlet$Tmin_C, lat_deg=42.66)
# Calculate streamflow based on watershed characteristics:
Results <- Lumped_VSA_model(dateSeries = OwascoInlet$date, 	P = rsm$Rain_mm+rsm$SnowMelt_mm, 
Tmax=OwascoInlet$Tmax_C, Tmin = OwascoInlet$Tmin_C, latitudeDegrees=42.66, Tp = 5.8, Depth = 2010, 
SATper = 0.27, AWCper = 0.13, StartCond = "wet")
#  View results:
hydrograph(streamflow=ConvertFlowUnits(cms=OwascoInlet$Streamflow_m3s, WA=106, AREAunits="mi2"), 
timeSeries=OwascoInlet$date, streamflow2=Results$modeled_flow, precip=rsm$Rain_mm+rsm$SnowMelt_mm)

## End(Not run)