Structure Check: Bridges, Culverts, and Inline Weirs

The Structure Check validates hydraulic structures including bridges, culverts, and inline weirs.

Overview

This check examines:

1. Section Distance (SD) - Cross section spacing around structures
2. Type Flow (TF) - Flow classification (low flow classes, pressure, weir)
3. Pressure Flow (PF) - Pressure flow conditions and coefficients
4. Loss Coefficients (LF) - Entrance, exit, and friction losses
5. Pressure/Weir (PW) - Combined pressure and weir flow
6. Lateral Weir (LW) - Weir overflow characteristics
7. Geometry (GE) - Structure geometry alignment

Bridge Checks (BR_*)

Bridge Section Distance Messages (BR_SD_*)

BR_SD_01 - Upstream Distance Too Short

Field	Value
Severity	WARNING
Message	Distance from upstream XS to bridge ({dist} ft) is less than recommended
Cause	Upstream cross section is too close to bridge
Resolution	Move upstream XS to allow approach velocity to stabilize. Typical minimum is 1-2x opening width

BR_SD_02 - Deck Width Inconsistency

Field	Value
Severity	WARNING
Message	Deck width inconsistent with section distances
Cause	Roadway/deck width doesn't match section geometry
Resolution	Verify deck/roadway width matches structure geometry data

BR_SD_03 - Downstream Distance Too Short

Field	Value
Severity	WARNING
Message	Distance from bridge to downstream XS ({dist} ft) is less than recommended
Cause	Downstream cross section too close to bridge
Resolution	Move downstream XS to capture flow expansion. Typical minimum is 1-2x opening width

Bridge Type Flow Messages (BR_TF_*)

Bridge flow is classified into low flow (Classes A, B, C) and high flow (pressure, weir, combined):

BR_TF_01 - Low Flow Class A

Field	Value
Severity	INFO
Message	Low flow Class A (free surface) computed at bridge for
Cause	Free surface flow through bridge opening. WSE below low chord on both faces
Resolution	Normal operating condition. No action required

BR_TF_02 - Low Flow Class B

Field	Value
Severity	WARNING
Message	Low flow Class B (free surface with hydraulic jump DS) computed at bridge for
Cause	WSE above low chord upstream, below downstream. Hydraulic jump occurs
Resolution	Transitional flow condition. May indicate capacity limitations

BR_TF_03 - Low Flow Class C

Field	Value
Severity	WARNING
Message	Low flow Class C (supercritical) computed at bridge for
Cause	Supercritical flow through opening
Resolution	Relatively rare. Verify geometry and flow conditions. Typically occurs with steep slopes

BR_TF_04 - High Flow (Pressure Only)

Field	Value
Severity	WARNING
Message	High flow (pressure only) computed at bridge for
Cause	Bridge opening is fully submerged (pressure flow)
Resolution	Verify deck elevations. Consider scour potential under pressure conditions

BR_TF_05 - High Flow (Weir Only)

Field	Value
Severity	WARNING
Message	High flow (weir only) computed at bridge for
Cause	Water overtops roadway but opening not pressurized
Resolution	Verify roadway profile elevations and weir coefficient

BR_TF_06 - High Flow (Pressure and Weir)

Field	Value
Severity	ERROR
Message	High flow (pressure and weir combined) computed at bridge for
Cause	Opening pressurized AND water overtops roadway
Resolution	Severe condition - structure significantly undersized. Review design adequacy

Bridge Pressure Flow Messages (BR_PF_*)

BR_PF_01 - Pressure Flow Detected

Field	Value
Severity	WARNING
Message	Pressure flow detected at bridge for
Cause	Bridge opening is submerged
Resolution	Verify deck and low chord elevations are correct

BR_PF_02 - Weir Flow Detected

Field	Value
Severity	WARNING
Message	Weir flow detected over bridge deck for
Cause	Water flows over roadway
Resolution	Verify roadway profile elevations

BR_PF_05 - Orifice Flow Submergence

Field	Value
Severity	INFO
Message	Submergence ratio ({submergence}) indicates orifice flow
Cause	High submergence ratio (TW/HW > 0.8) indicates orifice conditions
Resolution	Verify model correctly computes orifice flow conditions

BR_PF_06 - Tailwater Controls

Field	Value
Severity	WARNING
Message	Tailwater controls pressure flow: TW elev near deck
Cause	Tailwater elevation near or above deck controls flow
Resolution	Verify downstream boundary conditions and channel geometry

BR_PF_08 - Pressure Flow Coefficient

Field	Value
Severity	WARNING
Message	Pressure flow coefficient ({coef}) outside typical range (0.8-1.0)
Cause	Coefficient below 0.8 indicates high losses; above 1.0 is unrealistic
Resolution	Review coefficient setting in bridge data

Bridge Loss Coefficient Messages (BR_LF_*)

BR_LF_01 - Contraction Coefficient

Field	Value
Severity	WARNING
Message	Bridge contraction coefficient ({coef}) outside typical range (0.1-0.6)
Cause	Coefficient outside typical range for abutment types
Resolution	Review coefficient based on abutment geometry (vertical wall, wing wall, spill-through)

BR_LF_02 - Expansion Coefficient

Field	Value
Severity	WARNING
Message	Bridge expansion coefficient ({coef}) outside typical range (0.3-0.8)
Cause	Coefficient outside typical expansion range
Resolution	Review coefficient based on downstream conditions

Bridge Lateral Weir Messages (BR_LW_*)

BR_LW_01 - Weir Length Mismatch

Field	Value
Severity	WARNING
Message	Bridge lateral weir length differs significantly from roadway width
Cause	Weir length should correspond to roadway width
Resolution	Verify weir length in structure data

BR_LW_02 - Weir Coefficient

Field	Value
Severity	WARNING
Message	Bridge weir coefficient ({coef}) outside typical range (2.5-3.1)
Cause	Coefficient outside typical range
Resolution	Typical value is 2.6 for roadway overtopping. Sharp-crested maximum is ~3.1

Culvert Checks (CU_/CV_)

Culvert Section Distance Messages (CU_SD_*)

CU_SD_01 - Upstream Distance

Field	Value
Severity	WARNING
Message	Distance from upstream XS to culvert is less than recommended
Cause	Upstream section too close to culvert inlet
Resolution	Move upstream XS to capture approach conditions

CU_SD_02 - Downstream Distance

Field	Value
Severity	WARNING
Message	Distance from culvert to downstream XS is less than recommended
Cause	Downstream section too close to culvert outlet
Resolution	Move downstream XS to capture outlet conditions

Culvert Type Flow Messages (CV_TF_*)

Message ID	Flow Type	Description
CV_TF_01	Type 1	Outlet control, unsubmerged
CV_TF_02	Type 2	Outlet control, submerged outlet
CV_TF_03	Type 3	Inlet control, unsubmerged
CV_TF_04	Type 4	Inlet control, submerged
CV_TF_05	Type 5	Full flow
CV_TF_06	Type 6	Pressure flow
CV_TF_07	Type 7	Overtopping

Culvert Loss Coefficient Messages (CV_LF_*)

CV_LF_01 - Entrance Loss Coefficient

Field	Value
Severity	WARNING
Message	Entrance loss coefficient ({Ke}) outside typical range (0.2-0.9)
Cause	Coefficient doesn't match typical inlet types
Resolution	Typical: 0.2 (well-rounded), 0.5 (square-edged), 0.9 (projecting)

CV_LF_02 - Exit Loss Coefficient

Field	Value
Severity	WARNING
Message	Exit loss coefficient ({Kx}) outside typical range (0.5-1.0)
Cause	Standard exit coefficient is 1.0 for sudden expansion
Resolution	Values <1.0 may be used for gradual transitions

Culvert Pressure Flow Messages (CV_PF_*)

CV_PF_01 - Pressure Flow

Field	Value
Severity	WARNING
Message	Pressure flow detected at culvert for
Cause	Culvert operating under pressure conditions
Resolution	Review culvert sizing. May indicate undersized structure

CV_PF_02 - Deep Submergence

Field	Value
Severity	WARNING
Message	Inlet submerged by more than 1.2D (HW/D = {hw_ratio})
Cause	Headwater depth exceeds 1.2x culvert diameter
Resolution	Consider increasing culvert size or adding barrels

Inline Weir Checks (IW_*)

Inline Weir Section Distance Messages (IW_SD_*)

IW_SD_01 - Upstream Distance

Field	Value
Severity	WARNING
Message	Distance from upstream XS to inline weir is less than recommended
Cause	Upstream section too close to weir
Resolution	Move upstream XS for approach conditions

IW_SD_02 - Downstream Distance

Field	Value
Severity	WARNING
Message	Distance from inline weir to downstream XS is less than recommended
Cause	Downstream section too close to weir
Resolution	Move downstream XS for tailwater conditions

Inline Weir Type Flow Messages (IW_TF_*)

IW_TF_01 - Weir Flow Only

Field	Value
Severity	INFO
Message	Inline weir has weir flow only (no gate flow) for
Cause	Water flowing over crest, gates not contributing
Resolution	Normal when headwater above crest and gates closed/absent

IW_TF_02 - Gate Flow Only

Field	Value
Severity	INFO
Message	Inline weir has gate flow only (no weir flow) for
Cause	Flow through gates, headwater below crest
Resolution	Normal condition when gates are open

IW_TF_03 - Combined Weir and Gate Flow

Field	Value
Severity	INFO
Message	Inline weir has combined weir and gate flow for
Cause	Both weir overflow and gate flow occurring
Resolution	Verify gate operations and weir coefficient

IW_TF_04 - Submerged Weir

Field	Value
Severity	WARNING
Message	Inline weir is submerged: tailwater approaches crest for
Cause	Tailwater elevation near or above weir crest
Resolution	Submergence reduces capacity. Verify downstream conditions

Inline Weir Coefficient Messages (IW_*)

IW_03 - Weir Coefficient

Field	Value
Severity	WARNING
Message	Weir coefficient ({c}) outside typical range
Cause	Coefficient outside 2.5-3.1 range
Resolution	Typical broad-crested: 2.6-2.8. Sharp-crested: up to 3.1

Structure Geometry Messages (ST_GE_*)

ST_GE_01L / ST_GE_01R - Section 2 Alignment

Field	Value
Severity	WARNING
Message	Left/Right effective station at Section 2 doesn't align with roadway
Cause	Effective flow limits don't match roadway geometry
Resolution	Verify ineffective flow limits correspond to bridge opening

ST_GE_02L / ST_GE_02R - Section 3 Alignment

Field	Value
Severity	WARNING
Message	Left/Right effective station at Section 3 doesn't align with roadway
Cause	Effective flow limits don't match downstream roadway geometry
Resolution	Verify ineffective flow limits at downstream face

Structure Distance Messages (ST_DT_*)

ST_DT_01 - Upstream Distance for Expansion

Field	Value
Severity	WARNING
Message	Upstream distance too short for flow expansion at
Cause	Cross section too close to structure
Resolution	Typical minimum is 1-2x structure opening width

ST_DT_02 - Downstream Distance for Recovery

Field	Value
Severity	WARNING
Message	Downstream distance too short for contraction recovery at
Cause	Cross section doesn't capture flow re-expansion
Resolution	Move downstream section further from structure

References

• HEC-RAS Hydraulic Reference Manual, Chapter 5: Modeling Bridges
• HEC-RAS Hydraulic Reference Manual, Chapter 6: Modeling Culverts
• FHWA Hydraulic Design of Highway Culverts (HDS-5)
• FHWA Hydraulics of Bridge Waterways (HDS-1)