Transcript Sacramento Soil Moisture Accounting Model

National Weather Service
River Forecast System
Sacramento Soil Moisture Accounting Model
COMET
Hydromet 00-2
7 March 2000
2290 East Prospect Road, Suite 1
Fort Collins, Colorado 80525
Sacramento Soil Moisture
Accounting Model
 Physically-based
 Conceptual
 Lumped (versus distributed)
 Continuous (versus event-based)
C3
Sacramento Soil Moisture
Accounting Model
 Represents soil moisture characteristics such that:
– Applied moisture is distributed properly in various
depths and energy states in soil
– Rational percolation characteristics are maintained
– Streamflow is simulated effectively
C3
Sacramento Model Components
 Tension water
 Free water
 Surface flow
 Lateral drainage
 Evapotranspiration
 Vertical drainage (percolation)
C3
Soil Tension and Free Water
C3
Sacramento Soil Moisture
Accounting Model
C3
Sacramento Model Structure
E T Demand
Precipitation Input
Px
Impervious
Area
ET
PCTIM
Pervious Area
Upper Zone
EXCESS
ET
Direct Runoff
ADIMP
Impervious Area
Surface
Runoff
Tension Water
Free Water
UZTW
UZFW
UZK
ET
Interflow
Percolation
Zperc. Rexp
Total
Channel
Inflow
RIVA
ET
1-PFREE
Distribution
Function
Streamflow
PFREE
Lower Zone
Tension Water
ET
LZTW
Free
P
Water
S
LZFP
LZFS
LZSK
Supplemental
Base flow
RSERV
LZPK
Primary
Baseflow
C3
Total
Baseflow
Side
Subsurface
Discharge
Model Parameters
PXADJ
PEADJ
UZTWM
UZFWM
UZK
PCTIM
ADIMP
RIVA
ZPERC
REXP
LZTWM
LZFSM
LZFPM
LZSK
LZPK
PFREE
RSERV
SIDE
ET Demand
PE Adjust
C3
Precipitation adjustment factor
ET-demand adjustment factor
Upper zone tension water capacity (mm)
Upper zone free water capacity (mm)
Fractional daily upper zone free water withdrawal rate
Minimum impervious area (decimal fraction)
Additional impervious area (decimal fraction)
Riparian vegetation area (decimal fraction)
Maximum percolation rate coefficient
Percolation equation exponent
Lower zone tension water capacity (mm)
Lower zone supplemental free water capacity (mm)
Lower zone primary free water capacity (mm)
Fractional daily supplemental withdrawal rate
Fractional daily primary withdrawal rate
Fraction of percolated water going directly to lower zone free water storage
Fraction of lower zone free water not transferable to lower zone tension water
Ratio of deep recharge to channel baseflow
Daily ET demand (mm/day)
PE adjustment factor for 16th of each month
State Variables
ADIMC
UZTWC
UZFWC
LZTWC
LZFSC
LZFPC
C3
Tension water contents of the ADIMP area (mm)
Upper zone tension water contents (mm)
Upper zone free water contents (mm)
Lower zone tension water contents (mm)
Lower zone free supplemental contents (mm)
Lower zone free primary contents (mm)
Percolation Rate Under Saturated
Conditions
 Water balance of lower zone
In
Lower zone
C3
Out
Maximum Percolation Rate
 Water balance of lower zone
In
Out
C3
Percolation Curve
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.
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
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
C3
Volume Effects
Mean Daily Flow (CFS)
1000
800
600
400
200
0
12/29
2/17
Small Tension Water Zones
C3
4/8
5/28
Large Tension Water Zones
7/17
Hydrograph Produced Mainly by Surface Runoff
(Runoff Breakdown:
C3
Surface 64%, Interflow 15%, Supplemental 21%)
Hydrograph Produced by Mixed Runoff
( Runoff Breakdown: Surface 27%, Interflow 33%, Supplemental 40%)
C3
Hydrograph Containing No Surface Runoff
(Runoff Breakdown: Interflow 17%, Supplemental 83%)
C3