HY8:Outlet Control Computations

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Outlet control means that the amount of water the culvert barrel can carry is limited by the barrel and/or tailwater conditions downstream. As a result, the flow in the barrel is subcritical, and the energy equation may be used to find the upstream headwater depth. Several flow profiles are possible and are shown below and on page 32 of HDS-5. The following correlations apply to HY-8: Type A in HDS-5 is Type 4 in HY-8, Type B in HDS-5 is Type 3 in HY-8; Type C in HDS-5 is Type 6 in HY-8, Type D in HDS-5 is Type 7 in HY-8, and Type E in HDS-5 is Type 2 in HY-8. Descriptions of these flow types may be found in HY-8 by selecting the “Flow Types” button from the Culvert Summary Table. The logic for determining flow type and the headwater elevation due to outlet control is shown below from the HY-8 help file.


File:HY8image38.gif


STEP

  1. Compute critical depth (dco)
  2. Compute normal depth (dno)
  3. Compute fullflow if nomograph solution assumed "6-FFt or FFc".
  4. If dco > rise, assume fullflow "6-FFc".
    If oh < ih, compute S2 curve, "5-S2n" if submerged, else "1-S2n"
  5. If dco < dno, assume mild slope.
    A. If tailwater (twh) >= So(L) + rise, compute fullflow "4-FFt".
    B. If twh >= rise, outlet submerged, assume inlet unsubmerged
    i. Pipe flows partially full, compute M1 curve "3-M1f".
    Length of curve = L - (twh - rise) / So
    Outlet DEPTH = rise.
    ii. If inlet submerged, full flow "6-FFt".
    C. If twh >= dco, outlet depth = twh.
    i. If twh is >= dno, calculate M1 curve "3-M1t"
    If depth = rise, fullflow from that point. "7-M1t"
    ii. If twh is < dno, calculate M2 curve "3-M2t"
    If depth = rise, fullflow from that point. "7-M2t"
    D. If twh is < dco, outlet depth = dco.
    i. Calculate M2 curve "2-M2c".
    If depth = rise, fullflow from that point. "7-M2c"
  6. If dco >= dno, assume steep slope.
    A. If twh is >= So(L) + rise, assume fullflow "4-FFt".
    B. If twh is >= rise, outlet submerged, assume inlet unsubmerged.
    i. Steep channel-hydraulic jump forms
    ii. Calculate fullflow headwater (oh) "6-FFt or FFc"
    iii. If oh < rise, then inlet is unsubmerged.
    a. Length full = (twh - rise) / So
    b. Calculate S1 curve "1-S1f".
    If oh >= rise, inlet submerged "5-S1f".
    c. If oh is < twh, tailwater drowns out jump.
    Calculate M1 curve "3-M1f".
    If oh >= rise, inlet submerged "5-M1f".
    C. If twh is < rise, outlet is unsubmerged, inlet can be either.
    i. Headwater (oh) = fullflow headwater
    Calculate S2 curve "1-S2n" for outlet depth.
    If oh >= rise, inlet submerged "5-S2n"
    ii. If twh > headwater, tailwater drowns out jump.
    Calculate M1 curve "3-M1t".
    If culvert flows part full, "7-Mit".




OUTLET CONTROL 'FIXES' FOLLOWING HY-8 6.1

KE = KE(IC)
A7 = 64.4: A8 = 29: A1 = 1: A2 = .25: A3 = 2: A4 = 4 / 3: A5 = 3.14159: A6 = 4
SELECT CASE PSHAPE 'CRITICAL DEPTH
CASE 2
GOSUB 6210
CASE 1, 3 TO 10
GOSUB 6220
END SELECT
GOSUB 6280 'NORMAL DEPTH

SELECT CASE WSP$ '***added 3.1, 4.4 changed wsp CASE "F"

GOSUB fullflow

CASE ELSE

SELECT CASE DCO 'changed to DCO from DNO 4.5
CASE IS >= RISE'If Yn = to RISE, assume full. ***added >.95 3.3, revised 4.5
WSPTYPE$ = "FFc"
GOSUB fullflow
IF (IH + I1E) > (OH + I1E) THEN
WSPTYPE$ = "S2n": GOSUB S2CURVE
IF IH > RISE THEN FLTYPE = 5 ELSE FLTYPE = 1 'added 3/05 to correct FLTYPE=6
END IF
CASE IS < DNO 'Mild slope
SELECT CASE TWH
CASE IS >= S0 * L + RISE 'Pipe flows full
GOSUB fullflow
CASE IS >= RISE 'Outlet submerged, Inlet unsubmerged
'Pipe flows partially full, M1 Curve
D0 = RISE
LCURVE = L - (TWH - RISE) / S0: LADJ = LCURVE
GOSUB M1CURVE 'M1 Profile
DL = RISE: GOSUB SectionProp: VOUT = Q / AC: DOUT = RISE '***added 3.3
FLTYPE = 3: WSPTYPE$ = "M1f"
'Inlet unsubmerged, outlet unsubmerged
'If Inlet is submerged FLTYPE = 7 is returned
CASE IS >= DCO
SELECT CASE TWH
CASE IS >= DNO
FLTYPE = 3: WSPTYPE$ = "M1t"
D0 = TWH: LADJ = L
GOSUB M1CURVE: DL = TWH: GOSUB SectionProp: VOUT = Q / AC: DOUT = TWH
CASE IS < DNO
FLTYPE = 3: WSPTYPE$ = "M2t"
D0 = TWH '**3.3 changed from DO=DCO
GOSUB M2CURVE: DL = TWH: GOSUB SectionProp: VOUT = Q / AC: DOUT = TWH
END SELECT
CASE IS < DCO
FLTYPE = 2: WSPTYPE$ = "M2c"
D0 = DCO: GOSUB M2CURVE: DL = DCO: GOSUB SectionProp: VOUT = Q / AC: DOUT = DCO
END SELECT 'TWH for mild slope
CASE IS >= DNO 'Steep slope
SELECT CASE TWH
CASE IS >= S0 * L + RISE
GOSUB fullflow
CASE IS >= RISE 'Outlet submerged, Inlet unsubmerged
'STEEP CHANNEL-HYDRAULIC JUMP FORMS
IF TWH < DNO THEN TWH = DNO '***3.3 moved
GOSUB fullflow
IF OH < RISE THEN
LFULL = (TWH - RISE) / S0
D0 = RISE: LCURVE = L - LFULL
GOSUB S1CURVE
IF OH + I1E > TWH + I2E THEN
FLTYPE = 1: WSPTYPE$ = "S1f"
ELSE
FLTYPE = 3: WSPTYPE$ = "M1t"
D0 = RISE: LADJ = L 'Tailwater drowns out jump
GOSUB M1CURVE
END IF
END IF
CASE IS < RISE 'Outlet unsubmerged, Inlet unsubmerged & submerged
'OH = IH deleted 12/05 (should check OH from M1 with IH
'IF OH + I1E > TWH + I2E THEN
' 'GOSUB fullflow 'added 45 to revise plot, deleted 61
' FLTYPE = 1: WSPTYPE$ = "S2n"
' GOSUB S2CURVE
'ELSE 'Tailwater drowns out jump
' FLTYPE = 3: WSPTYPE$ = "M1t" 'M1 profile
' D0 = TWH: LADJ = L
' GOSUB M1CURVE: DL = TWH: GOSUB SectionProp
' VOUT = Q / AC: DOUT = TWH
' 'If culvert flows part full FLTYPE = 7 is returned
'END IF
IF TWH <= DNO THEN
FLTYPE = 1: WSPTYPE$ = "S2n"
GOSUB S2CURVE
ELSE 'assume Tailwater forces jump calculate M1
FLTYPE = 3: WSPTYPE$ = "M1t" 'M1 profile
D0 = TWH: LADJ = L
GOSUB M1CURVE: DL = TWH: GOSUB SectionProp
VOUT = Q / AC: DOUT = TWH
'If culvert flows part full FLTYPE = 7 is returned
IF IH > OH THEN 'M1 does not control calculate S2
FLTYPE = 1: WSPTYPE$ = "S2n"
GOSUB S2CURVE
END IF
END IF
IF OH >= RISE THEN FLTYPE = 5
END SELECT 'TW for steep
END SELECT 'DNO

END SELECT 'HDS5

WSPTYPE$(0, 0) = WSPTYPE$
RETURN