21
C3 General Concepts Physically-based conceptual model based on physical concepts that describe water movement trough a watershed Lumped versus distributed models Continuous versus event-based models Two-layer soil model Presented by Dr. Fritz Fiedler COMET Hydromet 00-1 Tuesday, 26 October 1999

General Concepts

  • Upload
    meris

  • View
    29

  • Download
    0

Embed Size (px)

DESCRIPTION

General Concepts. Physically-based conceptual model based on physical concepts that describe water movement trough a watershed Lumped versus distributed models Continuous versus event-based models Two-layer soil model. Presented by Dr. Fritz Fiedler COMET Hydromet 00-1 - PowerPoint PPT Presentation

Citation preview

Page 1: General Concepts

C3

General Concepts Physically-based conceptual model

– based on physical concepts that describe water movement trough a watershed

Lumped versus distributed models

Continuous versus event-based models

Two-layer soil model

Presented by Dr. Fritz FiedlerCOMET Hydromet 00-1Tuesday, 26 October 1999

Page 2: General Concepts

C3

Design Considerations Conceptual approach provides means to assess changes

in watershed morphology

Detailed modeling of the many actual watershed processes was too complex for operational application

Detailed modeling required more data than available

System developed that integrates primary physical processes without excessive data and/or computational needs

Essentially based on basic water balance equation:

Runoff = Rainfall - Evapotranspiration - Soil Moisture Changes

Page 3: General Concepts

C3

Sacramento Soil Moisture Accounting Model

Represents soil moisture characteristics such that:

– Applied moisture is distributed in a physically realistic manner within the various zones and energy states in soil

– Rational percolation characteristics are maintained

– Streamflow is simulated effectively

Page 4: General Concepts

C3

Sacramento Model Components Tension water

Free water

Surface flow

Lateral drainage

Evapotranspiration

Vertical drainage (percolation)

Page 5: General Concepts

C3

Soil Tension and Free Water

Page 6: General Concepts

C3

Sacramento Soil Moisture Accounting Model

Page 7: General Concepts

C3

Sacramento Model Structure

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

Surface Runoff

Interflow

Supplemental Base flow

Side Subsurface Discharge

LZSK

LZPK

Upper Zone

Lower Zone

EXCESS

UZK

RIVA

PCTIM

ADIMP

Total Channel Inflow

Distribution Function Streamflow

Total Baseflow

Page 8: General Concepts

C3

Model ParametersPXADJ Precipitation adjustment factorPEADJ ET-demand adjustment factorUZTWM Upper zone tension water capacity (mm)UZFWM Upper zone free water capacity (mm)UZK Fractional daily upper zone free water withdrawal ratePCTIM Minimum impervious area (decimal fraction)ADIMP Additional impervious area (decimal fraction)RIVA Riparian vegetation area (decimal fraction)ZPERC Maximum percolation rate coefficientREXP Percolation equation exponentLZTWM Lower zone tension water capacity (mm)LZFSM Lower zone supplemental free water capacity (mm)LZFPM Lower zone primary free water capacity (mm)LZSK Fractional daily supplemental withdrawal rateLZPK Fractional daily primary withdrawal ratePFREE Fraction of percolated water going directly to lower zone free water storageRSERV Fraction of lower zone free water not transferable to lower zone tension waterSIDE Ratio of deep recharge to channel baseflowET Demand Daily ET demand (mm/day)PE Adjust PE adjustment factor for 16th of each month

Page 9: General Concepts

C3

State Variables

ADIMC Tension water contents of the ADIMP area (mm)UZTWC Upper zone tension water contents (mm)UZFWC Upper zone free water contents (mm)LZTWC Lower zone tension water contents (mm)LZFSC Lower zone free supplemental contents (mm)LZFPC Lower zone free primary contents (mm)

Page 10: General Concepts

C3

Percolation Rate Under Saturated Conditions

Lower zone

Water balance of lower zone

Out

In

Page 11: General Concepts

C3

Percolation Rate Continued... Water balance of lower zone

In

Out

Page 12: General Concepts

C3

Percolation Curve

Page 13: General Concepts

C3

Percolation Characteristics PBASE

– The continued percolation rate under saturated conditions

– A function of the lower zone capacities and the lower zone withdrawal rates

– PBASE = LZFSM • LZSK + LZFPM • LZPK

ZPERC

– The number of PBASE units that must be added to the continuing saturated percolation rate to define the maximum percolation rate

REXP

– The exponent which defines the curvature in the percolation curve with changes in the lower zone soil moisture deficiency.

Page 14: General Concepts

C3

Effect of Soil-Moisture Parameters on Model Response

Volume

– Altering these parameters changes volume, but not the relative breakdown of runoff among various non-impervious components

UZTWM, LZTWM, ET (Demand curve), PE (Adjustment curve)

Timing

– Altering these parameters changes the relative breakdown of runoff between various non-impervious components; always causes timing changes and (in some cases) can cause significant overall volume changes

UZFWM, LZFPM, LZFSM, UZK, LZPK, LZSK, ZPERC, REXP

Page 15: General Concepts

C3

Effect of Soil-Moisture Parameters on Model Response (continued)

Impervious runoff

– Altering these parameters determines how much of the rain + melt goes directly to runoff; both have a volume and timing effect, though PCTIM mainly affects volume, and ADIMP primarily affects timing

PCTIM, ADIMP

Baseflow volume

– Altering these parameters primarily changes the amount of baseflow volume while having little or no effect on other runoff components

SIDE, RIVA, PFREE

Minor effect

– Generally has little effect on model response

RSERV

Page 16: General Concepts

C3

Volume Effects

0

200

400

600

800

1000

12/29 2/17 4/8 5/28 7/17

Me

an

Da

ily F

low

(C

FS

)

Small Tension Water Zones Large Tension Water Zones

Page 17: General Concepts

C3

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

Surface Runoff

Interflow

Supplemental Base flow

Side Subsurface Discharge

LZSK

LZPK

Upper Zone

Lower Zone

EXCESS

UZK

RIVA

PCTIM

ADIMP

Total Channel Inflow

Distribution Function Streamflow

Total Baseflow

Sacramento Model Structure

Page 18: General Concepts

C3

Evapotranspiration ET Demand: Evapotranspiration from land surface when

soil moisture is not limiting (tension water at capacity)

Potential Evaporation: Evaporation from free water surface (lakes, wet grass)

PE Adjustment Curve: Seasonal curve reflecting type and activity of vegetation

ET Demand = PE * PE Adjustment

Page 19: General Concepts

C3

Hydrograph Produced Mainly by Surface Runoff (Runoff Breakdown: Surface 64%, Interflow 15%, Supplemental 21%)

Page 20: General Concepts

C3

Hydrograph Produced by Mixed Runoff ( Runoff Breakdown: Surface 27%, Interflow 33%, Supplemental 40%)

Page 21: General Concepts

C3

Hydrograph Containing No Surface Runoff(Runoff Breakdown: Interflow 17%, Supplemental 83%)