the nws s i mp lified d am b rea k model smpdbk model
DESCRIPTION
The NWS S i mp lified D am B rea k Model SMPDBK Model. SMPDBK Model Description. The NWS SMPDBK model computes the dam break outflow from a simplified equation and routes the outflow base on curves generated with the NWS DAMBRK model. Flow depths are computed based on Manning’s equation. - PowerPoint PPT PresentationTRANSCRIPT
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The NWS The NWS SSiimpmplified lified DDam am BBreareakk Model Model
SMPDBK ModelSMPDBK Model
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SMPDBK Model DescriptionSMPDBK Model Description
The NWS SMPDBK model computes the dam break outflow from a simplified equation and routes the outflow base on curves generated with the NWS DAMBRK model. Flow depths are computed based on Manning’s equation.
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SMPDBK LimitationsSMPDBK Limitations
Backwater effects ignored
No special effects included (e.g. bridges, dams, constrictions, etc.)
Error range: 0 - 10% Relative to NWS DAMBRK (when used within its limitations)
Rapid, easy, low cost, emergency situations
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Qo = Spillway Flow
Br = Breach Width (avg.)
tf = Time of Failure (hour)
hd = Height of Dam
As = Avg. Surface Area of Reservoir in Top Portion of Reservoir
SMPDBK ModelSMPDBK Model
r
a
BS
23.4C 3
df
robmaxhCt
C3.1BQQ
/60/
PEAK OUTFLOW:
Qbmax corrected for tailwater submergence and dynamic effects
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Depths computed from Manning Eq. for a known discharge
SMPDBK ModelSMPDBK Model
SBAAn
1.49Q 2/3
FLOW DEPTH:
The slope (S) is dependent on the upstream and downstream reach:
If both subcritical, use average slope;
If both supercritical, use upstream slope;
If upstream slope is supercritical & downstream slope is subcritical, hydraulic jump present – compute two depths;
If upstream slope is subcritical & downstream slope is supercritical, use critical slope (Sc;
1/3
2
c Dn77000S
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SMPDBK ModelSMPDBK Model
)0.54(1A
6VOLX1mc
Routing of peak discharge via empirically derived relationships (using DAMBRK model) as represented via dimensionless parameters Qp/Qbmax, X/Xc, V*, and Fr.
cc
*
XAVOLV
cc
cr
/BgA
VF
c
*
XXX
bmax
p*
Q
ROUTED FLOW:
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SMPDBK ModelSMPDBK Model
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SMPDBK ModelSMPDBK Model
cxtT fp
1mm
32
35V0.682c
ix
2/3xn
1.49x ii
DSV
Time to Peak (Tp):
1mh
xref
iD
ii xx
*ref D,A,Sn,,Qfh
Manning Equation: SDAn
1.49Q 2/3
103.0QQ 2/
* mx
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SMPDBK ModelSMPDBK Model
fop
fppfld t
QQQQ
tt
bff haQ
Time to Flooding and Deflooding of Elevation hf:
op
fpf
op
rpdefld QQ
QQt
QQVOL24.2tt