HY8:Outlet Control Computations
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 due to outlet control is shown below:
This flowchart uses the following terms:
HJ = Check for Hydraulic Jumps
Full flow = Check if the culvert is flowing full
TWH =
twOutletDepth =
IH =
OH =
RISE =
Inlet Depth =
D1 =
Critical =
Normal =
The following table describes the various flow types defined in the above flow chart:
Flow Type | Flow Control | Submerged Inlet | Submerged Outlet | Length Full | Loss Calc | Outlet Depth |
---|---|---|---|---|---|---|
1 |
Inlet |
No |
No |
NONE |
S2n |
Normal |
1 |
Inlet |
No |
No |
NONE |
S1t |
Tailwater |
1 |
Inlet |
No |
Yes |
Part |
S1f |
Full |
1 |
Inlet |
No |
No |
NONE |
JS1t |
Jump to Tailwater |
1 |
Inlet |
No |
Yes |
Most |
JS1f |
Jump to Full |
5 |
Inlet |
Yes |
No |
NONE |
S2n |
Normal |
5 |
Inlet |
Yes |
No |
NONE |
S1t |
Tailwater |
5 |
Inlet |
Yes |
Yes |
Part |
S1f |
Full |
5 |
Inlet |
Yes |
No |
NONE |
JS1t |
Jump to Tailwater |
5 |
Inlet |
Yes |
Yes |
Part |
JS1f |
Jump to Full |
2 |
Outlet |
No |
No |
NONE |
M2c |
Critical |
3 |
Outlet |
No |
No |
NONE |
M1t |
Tailwater |
3 |
Outlet |
No |
No |
NONE |
M2t |
Tailwater |
3 |
Outlet |
No |
Yes |
Part |
M1f |
Full |
4 |
Outlet |
Yes |
Yes |
All |
FFf |
Full |
6 |
Outlet |
Yes |
No |
Most |
FFt |
Tailwater |
6 |
Outlet |
Yes |
No |
Most |
FFc |
Critical |
7 |
Outlet |
Yes |
No |
Part |
M1t |
Tailwater |
7 |
Outlet |
Yes |
No |
Part |
M2t |
Tailwater |
7 |
Outlet |
Yes |
No |
Part |
M2c |
Critical |