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Troubleshooting of Lateral Structures Modeling

In HEC-RAS, lateral structures are used to model flow being transferred between a river and adjacent elements, such as another river, storage area, or 2D flow area. A lateral structure can physically represent a wide range of geometric features, including a levee, a flow diversion structure, a spillway, or natural ground. Lateral structures are also used to simulate flow transfer from the river to a tributary during a flood event.

Often, you may encounter certain error warnings in the GeoHECRAS software while modeling lateral structures using the HEC-RAS analysis engine. This article describes how to fix these modeling errors in the GeoHECRAS software.

The following are some of the error warnings you may have come across while modeling lateral structures:

Question: “Lateral structure data specifies a weir line plus upstream distance that equals or exceeds the length of the reach.” How do I fix this error while modeling lateral structure?
Lateral structure data specifies a weir line
Answer: The lateral structure cannot be geo-referenced in the 4.1.0 HEC-RAS analysis engine, and it must be done manually. However, in the 5.0.7 HEC-RAS analysis engine and higher versions, the lateral structure is geo-referenced, so it can read the length of lateral structures automatically. Therefore, it is recommended that you use HEC-RAS analysis engine versions 5.0.7 and higher. Note that the lateral structures in GeoHECRAS are geo-referenced by default.

Note that in the GeoHECRAS software, the user can change the HEC-RAS analysis engine version from the Options backstage page. To learn more about how to change the HEC-RAS analysis engine, refer to this article in our knowledge base.

Question: “Lateral structure data spans an internal boundary (bridge, culvert, or inline structure). Lateral structure… around the internal boundaries.” How do I fix this error while modeling lateral structure?
Lateral structure data spans an internal boundary
Answer: This error will be displayed while modeling lateral structures near hydraulic structures (i.e., bridges, culverts, inline structures, etc.) in the 4.1.0 HEC-RAS analysis engine and previous versions. Therefore, it is recommended that you use HEC-RAS analysis engine versions 5.0.7 and higher.

Note that in the GeoHECRAS software, the user can change the HEC-RAS analysis engine version from the Options backstage page. To learn more about how to change the HEC-RAS analysis engine, refer to this article in our knowledge base.

Question: I have drawn a lateral structure to make the flow from one river reach to overflow to the adjacent river reach. I am getting this error messageWeir profile length is: 300 and the GIS centerline length is: 364.860. These lengths need to be within 0.3(m) (or 0.5% whichever is smaller). Adjust the weir profile stationing or the centerline GIS data. How do I fix this error?
Weir profile length is: 300 and the GIS centerline length is: 364.860
Answer: The lengths of the Weir profile and GIS centerlines must always be within 0.3 m (or 0.5%, whichever is less). It is recommended that you either change the stationing of the weir or update the GIS centerline of the weir to be the same. You can enter the weir elevations and adjust the stationing so that it matches the length of the GIS centerline.

Question:The Lateral Structure at BM 1 10643 has a weir elevation lower than the cells they are connected to for 2D Area SA_2D-Mid_2. This is not allowed in HEC-RAS:How do I fix this error?
The Lateral Structure at BM 1 10643 has a weir elevation
Answer: This error warning will be displayed if the weir elevations are lower than the cell elevations. Therefore, for given cell locations, make sure that you adjust the weir elevations on those stations so that the weir elevations are not lower than the cell elevations. By checking these elevations, you can eliminate this error warning.

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