SPILLWAY RATINGS SPILLWAY RATINGS andand

STABILITY DESIGN PROCEDURESSTABILITY DESIGN PROCEDURES

____________________________________________________SITES 2005SITES 2005

INTEGRATED DEVELOPMENT ENVIRONMENTINTEGRATED DEVELOPMENT ENVIRONMENTfor

WATER RESOURCE SITE ANALYSIS

OBJECTIVE

Provide understanding of:• Principal spillway rating

• Auxiliary spillway rating

• Permissible velocity approach

• Allowable stress approach

• Cover discontinuities

The first elevation entry in the table must correspond to the spillway crest elevation. The first discharge entry must be zero, and the subsequent discharge entries must increase with increasing elevation.

Inlet

Conduit

EXAMPLE HELP

the rating for the auxiliary spillway may be entered at the structure table

AUXILIARY SPILLWAY RATINGAUXILIARY SPILLWAY RATING

FEATURESFEATURES

• VARIABLE FLOW RESISTANCEVARIABLE FLOW RESISTANCE (by reach)

• MIXED VEGETAL AND NON-VEGETAL MIXED VEGETAL AND NON-VEGETAL flow resistance

• SEEKS HYDRAULIC CONTROL SECTIONSEEKS HYDRAULIC CONTROL SECTION

Auxiliary Spillway ProfileAuxiliary Spillway Profile

InletNaturalGround

ConstructedInlet Channel Constructed

Exit Channel

Exit Natural Ground

Tie

Sta

.

X

SPILLWAY PROFILE

Avoid short steep slopes between mild slopes!Avoid short steep slopes between mild slopes!

The program identifies the hydraulic control as the upstream end of the first reach downstream of the crest that flows supercritical at the discharge in question. Reach length is not checked. Therefore, short steep reaches that may be submerged by mild slope reaches downstream may cause improper rating.

CCII = 5.6 = 5.6

n = 0.04n = 0.04

AUXILIARY SPILLWAYAUXILIARY SPILLWAYSTABILITY ANALYSISSTABILITY ANALYSIS

SITESSITES

SITESSITES

STABILITY ANALYSISSTABILITY ANALYSIS

TECHNOLOGY OPTIONSTECHNOLOGY OPTIONS• PERMISSIBLE VELOCITYPERMISSIBLE VELOCITY• ALLOWABLE STRESSALLOWABLE STRESS

COMPUTATIONAL OPTIONSCOMPUTATIONAL OPTIONS

• ENTER BED WIDTHENTER BED WIDTH - COMPUTE STRESS LEVEL• ENTER ALLOWABLE STRESS LEVEL ENTER ALLOWABLE STRESS LEVEL - COMPUTE BED WIDTH

VEGETAL EROSION PROTECTIONVEGETAL EROSION PROTECTION

PERMISSIBLE VELOCITY PERMISSIBLE VELOCITY

COVER SLOPE %

EROSION RESISTANT

EASILY ERODED

Bermudagrass 0-55-10>10

876

654

Kentucky Bluegrass0-55-10>10

765

543

Weeping Lovegrass 0-5 3.5 2.5

(ft/s)(ft/s)

VEGETAL COVER FACTORVEGETAL COVER FACTORused to compute

EFFECTIVE STRESSEFFECTIVE STRESS

COVERCOVER FACTOR

Bermudagrass

Kentucky Bluegrass

Weeping Lovegrass

0.9

0.87

0.5

CF

AH 667TP 61

ORDINARY FIRMORDINARY FIRMLOAMLOAM

SILT LOAMSILT LOAM

SANDY LOAMSANDY LOAM

EROSION RESISTANT

EASILY ERODED

FLOW DEPTH, ft

AV

ER

AG

E V

EL

OC

I TY

, ft/

s

MAINTENANCE CODEMAINTENANCE CODE

1 - UNIFORM COVER OR SURFACE1 - UNIFORM COVER OR SURFACE

2 - MINOR DISCONTINUITIES2 - MINOR DISCONTINUITIES

3 - MAJOR DISCONTINUITIES3 - MAJOR DISCONTINUITIES

EFFECTIVE STRESSEFFECTIVE STRESS

• Maintenance code effectMaintenance code effect

e= ds(1-Cf) (ns/n)2

If MC=2, Cf0

If MC=3, Cf0 and n ns

AUXILIARY SPILLWAYAUXILIARY SPILLWAYSTABILITY ANALYSISSTABILITY ANALYSIS

SITESSITES

SUMMARYSUMMARY

• BASED ON PEAK OF SDHBASED ON PEAK OF SDH• APPLIED TO EXIT CHANNELAPPLIED TO EXIT CHANNEL• VELOCITY OR STRESS calculationsVELOCITY OR STRESS calculations• COMPUTE V, COMPUTE V, ee, or BED WIDTH, or BED WIDTH• MAINTENANCE CODE for stress MAINTENANCE CODE for stress calculationscalculations