the nws s i mp lified d am b rea k model smpdbk model

The NWS The NWS SSiimpmplified lified DDam am BBreareakk Model Model

SMPDBK ModelSMPDBK Model

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.

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

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


r

a

BS

23.4C 3

df

robmaxhCt

C3.1BQQ

/60/

PEAK OUTFLOW:

Qbmax corrected for tailwater submergence and dynamic effects

Depths computed from Manning Eq. for a known discharge


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


)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

QQ

ROUTED FLOW:


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


fop

fppfld t

QQQQ

tt

bff haQ

Time to Flooding and Deflooding of Elevation hf:

op

fpf

op

rpdefld QQ

QQt

QQVOL24.2tt

the nws s i mp lified d am b rea k model smpdbk model

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