Culverts are essential hydraulic structures designed to convey water beneath obstructions such as roads, railways, levees, or embankments. Culverts play a critical role in flood risk management, infrastructure resilience, and roadway drainage systems. Accurately modeling culverts is essential for estimating flow capacity, assessing backwater effects, predicting upstream inundations, and evaluating the risk of overtopping or structural failure.
In GeoHECRAS, culverts can be modeled in both 1D and 2D hydraulic models:
- 1D Models: Culverts are incorporated as part of a roadway or bridge crossing.
- 2D Models: Culverts are represented using connection structures that link two adjacent 2D flow areas or a 2D flow area and a storage area. These structures allow for embedded culverts, where users input geometric and hydraulic data to simulate interactions with surface flow and surrounding terrain.
Design Considerations for Culverts
The structural choice of a culvert and corresponding inlet depends on various factors such as environmental considerations, risk to property, cost of construction and maintenance, etc. The capacity of an existing culvert can be increased with an improved inlet. Refer to this article in our knowledge base to learn more about culvert design considerations.
Types of Culverts
In GeoHECRAS, the user can model a variety of standard culvert types. The most commonly used culvert shapes include circular, box (rectangular), arch, pipe arch, low-profile arch, high-profile arch, elliptical (horizontal and vertical), semi-circular, and Con/Span. Each culvert type can be modeled with up to 25 identical barrels. Refer to this article in our knowledge base to learn more about culvert types.
Cross Section Location for Culverts
In GeoHECRAS, culverts are defined within a cross section that represents the roadway embankment. This cross section acts as the control section where the culvert conveys flow from upstream to downstream. To accurately represent this flow, the software uses computational routines that account for how water enters, moves through, and exits the culvert. The culvert computational routines for a HEC-RAS project require the same four cross sections as the bridge computational routines. These cross sections include:
- Cross section sufficiently downstream from the culvert such that the flow is unaffected by the culvert
- Cross section at the downstream end of the culvert
- Cross section at the upstream end of the culvert
- Cross section located far enough upstream so that the culvert again has no effect on the flow
The following figure illustrates the cross section locations at a culvert roadway crossing. Refer to this article in our knowledge base to learn more about cross section location for culverts.
Expansion and Contraction Coefficient for Culverts
Expansion and contraction coefficients are used to account for energy losses due to changes in flow area as water enters and exits a culvert. These coefficients are applied to the velocity head when computing head losses through the culvert system. If the velocity head increases in the downstream direction, a contraction coefficient is applied. When the velocity head decreases in the downstream direction, an expansion coefficient is used. Refer to this article in our knowledge base to learn more about cross section location for culverts.
Culvert Hydraulics
Culvert hydraulics refers to the simulation of how water flows through a culvert structure, typically located at a roadway crossing over a channel or stream. This involves computing water surface elevations, flow rates, and energy losses associated with the movement of water as it enters, moves through, and exits the culvert structure. Refer to this article in our knowledge base to learn more about culvert hydraulics.
Entering and Editing Culvert Data
After defining the necessary cross-section data, the user can define culverts using the Culverts data panel of the Bridge & Culvert Data dialog box. This dialog box allows the user to define the culverts at a roadway crossing. Refer to this article in our knowledge base to learn more about the Bridge & Culvert Data command.