Erick Boehmler NERFC
21
6/3/2010 ER FFG Conference An Overview of Gridded Flash Flood Guidance; A Spatially Distributed Runoff and Threshold-Runoff Based Approach Erick Boehmler NERFC
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An Overview of Gridded Flash Flood Guidance; A Spatially Distributed Runoff and Threshold-Runoff Based Approach. Erick Boehmler NERFC. Eastern Region Flash Flood Guidance. Goals of Gridded FFG Development. - PowerPoint PPT Presentation
Transcript of Erick Boehmler NERFC
6/3/2010 ER FFG Conference
An Overview of Gridded Flash Flood Guidance; A Spatially Distributed Runoff and Threshold-Runoff Based Approach
Erick BoehmlerNERFC
6/3/2010 ER FFG Conference
Eastern Region Flash Flood Guidance
6/3/2010 ER FFG Conference
Goals of Gridded FFG Development
Produce a flash flood guidance product at a resolution closer in scale to basins in FFMP that:Reflects the spatial variability of the physical
characteristics that impact the susceptibility of a location to flash flooding
Uses freely available (or easily derived) data with nationwide coverage
Requires minimal calibration effortFits seamlessly into the existing RFC and WFO
operational flash flood warning infrastructure
6/3/2010 ER FFG Conference
Gridded Flash Flood Guidance
Advantages of GFFG approach are: Improves the spatial resolution of soil-moisture
conditions and flash flood thresholdsApplies a spatially consistent soil-moisture
accounting model across RFC areas and independent of RFC forecast basins
6/3/2010 ER FFG Conference
Gridded Flash Flood Guidance
6/3/2010 ER FFG Conference
Gridded Flash Flood Guidance Gridded FFG has a significant precedence
It is an accepted and operationally utilized method for FFG grid displays from Southern Region RFCs beginning in 2007
6/3/2010 ER FFG Conference
Arkansas-Red Basin River Forecast Center
Gridded FFG
OHD RDHM Soil Moisture
Dynamic NRCS Curve Number
VariableThreshold
Runoff
Gridded Flash Flood Guidance Model
SlopeLength to
divide
Static CNArea
Duration2-yr, 3-hr DDF
Gridded Runoff
How much rain to produce runoff
How much runoff to produce flash
flooding
6/3/2010 ER FFG Conference
Soil Moisture Accounting with a Distributed Hydrologic Model
4km gridded soil moisture products
UZTWC UZFWC
LZ
TW
C
LZ
FS
C
LZ
FP
C
Sacramento Model
Storages
Upper ZoneSaturation Ratio
National Weather ServiceOffice of Hydrologic Development
Research Distributed Hydrologic Model
Arkansas-Red Basin River Forecast Center
4km gridded temperature
4km gridded precipitation
6/3/2010 ER FFG Conference
Upper Zone Saturation
Upper zone saturation, 5/1/2009 Upper zone saturation, 6/1/2009
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Runoff ComputationDevelopment of Dynamic Curve
NumberCombined to create an average (ARCII)
Curve Number grid at HRAP scale 30m National Land Cover Dataset1000m NRCS Hydrologic Soil Groups
Utilized upper zone saturation ratio from RDHM output with NRCS curve number model (NEH Part 630, chap. 10) to formulate an automated curve number adjustment Convex of average for wet conditionsConcave of average for dry conditions
6/3/2010 ER FFG Conference
Arkansas-Red Basin River Forecast Center
Varying Curve Numbers by Antecedent Soil Moisture Conditions
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60 70 80 90 100
WET
NORMAL
DRY
Average Curve Number
So
il M
ois
ture
Ad
just
ed C
urv
e N
um
ber
*
75% Upper Zone Saturation
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NRCS Curve Number Graphic
Arkansas-Red Basin River Forecast Center
6/3/2010 ER FFG Conference
Threshold Runoff ComputationDevelopment of Variable
Threshold Runoff (Thresh-r)Thresh-r is estimated at the HRAP scale
Ratio of flood flow, Qs to peak flow, Qp of the unit hydrograph.
Qs is approximated by the annual return period flow, Q2
Qp is derived through the use of NRCS’ triangular unit hydrograph method
Adjustment for runoff anticipated within the next 6-hours from rainfall in progress through latest available MPE grid
6/3/2010 ER FFG Conference
NRCS Triangular Unit-graph Variables
CN = NRCS Curve Number
y = average watershed slope
Known Variables
Calculated Variables
pR tDT 2/
50
7080
1900
1.
.)(
y
Slp
.
t
Qp = peak discharge from unit hydrograph
tp= lag time (time from center of mass of rainfall to Qp)
TR = time to Qp from beginning of rainfall
S = Abstraction = (1000/CN)-10
l = length to divide
A = drainage area
Rp T
AQ
*484
D = duration of rainfall ( 1 Hour for unit Hydrograph)
Arkansas-Red Basin River Forecast Center
6/3/2010 ER FFG Conference
NERFC Area Computed Thresh-r
Qs = f (design storm,
slope, curve number)
=
Qp = f (slope, curve number)
Thresh-r
6/3/2010 ER FFG Conference
Arkansas-Red Basin River Forecast Center
GFFG System FFG Calculation
2
44.0 2 QSQQSFFG
S = (1000/CN)-10 Q = ThreshR
6/3/2010 ER FFG Conference
Limitations of the GFFG systemGFFG system limitations include:
No projection of snow-melt runoff within applicable duration of FFG value
RDHM modeled SWE 1/25 12Z MPE 12 hours ending 1/25 12Z
SCHOHARIE COUNTY SWE about 3 inches Approaching rainfall
6/3/2010 ER FFG Conference
Limitations of the GFFG system GFFG system limitations include:
No projection of snow-melt runoff within applicable duration of FFG value
GFFG system 1/25/2010 00Z GFFG system 1/25/2010 12Z
SCHOHARIE COUNTY 00Z 3-hr FFG = 1.9 12Z 3-hr FFG = 1.8
6/3/2010 ER FFG Conference
Limitations of the GFFG system GFFG system limitations include:
No projection of snow-melt runoff within applicable duration of FFG value
Legacy system 1/25/2010 00Z Legacy system 1/25/2010 12Z
SCHOHARIE COUNTY 00Z 3-hr FFG = 2.0 12Z 3-hr FFG = 1.4
6/3/2010 ER FFG Conference
Limitations of the GFFG system
GFFG system limitations include:CN adjustment for runoff response is
consistently overestimated during cool season monthsRDHM models upper zone tension water at
capacityUpper soil zone contents to capacity ratio remains
high
6/3/2010 ER FFG Conference
Questions / Contacts
John Schmidt(918) [email protected]
Tony Anderson(918) [email protected]
James Paul(918) [email protected]
Erick Boehmler(508) [email protected]
