About river structures

River structures:

• weirs
• bridges
• culverts
• other structures that influence the hydraulics of the river

Most ancillary structures found along a river are modelled in the same way as a sewer network.

Connect ancillary structures to an upstream and downstream river reach via a break node. Exception: bridges built from section data (river reaches).

If building an integrated model containing interaction between the sewer and river network:

• Flap valve representation is extremely important.
• Other items such as (clean) screens, may be unlikely to significantly impact the hydraulic performance.
• Consider whether headloss objects at points of interaction are necessary.

Culverts:

Historically three links were used to define a culvert:

• Culvert inlet, used to define inlet losses
• Conduit, represents the culvert - allows the user to specify all the data within a single conduit link
• Culvert outlet, used to define outlet losses

Culvert code coefficients from Hydraulic Design of Highway Culverts, third edition by FHWA, can be populated from the drop-down menu.

The culvert inlet and outlet replace the usual headloss calculations.

Both the upstream and downstream headlosses in the conduit should be set to NONE.

Culverts with multiple barrels should ideally be modelled as a single link.

Bridges:

In ICM, a bridge object is represented as a single object comprised of:

• a link between two nodes (defining the center line of the bridge)
• an associated polygon

Five cross sections are defined at the link, representing:

• Upstream end of the link, located at the upstream end of the contraction zone
• Upstream face of the bridge, at the toe of the embankment
• Downstream face of the bridge, at the toe of the embankment
• Downstream end of the link, located at the downstream end of the expansion zone
• The Bridge deck

Bridge opening objects, and inlet and outlet objects, may also be associated with the bridge link.

A bridge can contain multiple openings and irregular shapes. In the simulation engine, the bridge object is modelled as a set of objects, as described in the schematic.

Contraction and Expansion Reaches:

Contraction reach - consists of two sections and user-supplied loss coefficients with ineffective flow areas blocking the conveyance parts of the downstream section.

In parallel:

• A conduit link for each bridge opening
• An irregular weir for overtop flow
• An entry, an exit, and a conduit for each defined culvert

Expansion reach - consists of two sections and user-supplied loss coefficients, with ineffective flow areas blocking the conveyance parts of the upstream section

The contraction reach and expansion reach are modelled in a similar way to river reaches, with additional support for ineffective flow areas and contraction and expansion losses.

Ineffective flow areas:

Represent the areas outside of openings, where no flow occurs until overtopping of the road deck occurs.

ICM determines the ineffective flow areas from bridge opening geometry:

EXAMPLE: a single opening bridge has 2 ineffective flow areas

1. One from the left bank to the left of the bridge opening
2. One from the right of the bridge opening to the right bank

Contraction and expansion losses are energy losses associated with the change in the shape of river sections, or effective flow area.

Calculated by multiplying loss coefficient by the absolute value of the change in velocity head.

Bridge Deck Profile:

Defined in the Bridge deck data of the bridge object.

ICM models flow over the bridge deck as flow over an irregular weir.

Location of bridge section openings are specified in the Bridge property sheet.

Geometry of openings defined as Bridge Opening objects. Geometry and location of piers within each opening can also be defined in the Bridge Opening object.

Bridge openings can be associated with bridge sections manually by entering details in the Bridge property sheet, or by using the Build bridge openings tool.

Bridge Section Data:

Bridge section data can be built from cross section lines from the Model menu. Data from the first five cross sections intersected by the bridge link are copied to the section data fields of the selected bridge.

Cross sections are reversed if necessary, so that they are always displayed from left to right, facing downstream.

Additional tool options allow for openings to be built into the bridge and the bridge boundary.

Floodplain:

If building a 1D-only river model, represent the floodplain or flood storage areas using Storage area polygons, and storage or pond nodes.

Storage areas associated with a storage or pond node allow you to interrogate the ground model data and populate the level-area table for the node.

If the storage area intersects or runs parallel to the bank line, it is connected to your river reach when the Build bank connections tool is used.

You can also manually populate the fields of the river reach.