EcoHydRology (version 0.4.1)

Lumped_VSA_model: Lumped Variable Source Area (VSA) Watershed Model

Description

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.

Usage

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)))

Arguments

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

Value

• 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)

Warning

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.

Details

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.

References

Archibald, J.A., B.P. Buchanan, D.R. Fuka, C.B Georgakakos, S.W. Lyon, M.T. Walter. A simple, regionally parameterized model for predicting nonpoint source areas in the Northeastern US. Submitted to 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

See Also

PET_fromTemp

Examples

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)