About building a river reach

A river reach in ICM is modeled as a link, since links—and not lines—are used in the simulation engine. Once the river reach link has been defined, reach geometry can be built from line data. All of the cross section and bank section data are stored as subtables within the river reach link. Importing the line data into a river reach link is a simple process using the toolbars. The timesaving Build all functionality performs all of the river reach build options—Build sections from lines, Build banks from selected lines, Create bank lines from section ends, Build boundary from banks and section ends, and Build bank connections—in a single operation.

ICM allows for viewing the calculated conveyance in the river reach conveyance table once sections have been built. It is important to check this data to ensure that the conveyance curve is monotonic—that is, always positively increasing. The conveyance calculation is performed based on the Mannings equation for open channel flow. Where the channel bed flattens, the wetted perimeter can increase with little or no change in area. This leads to a decrease in conveyance if the calculation is done as a whole for the section. In these cases, panel markers can be used to break up the calculations into sensible chunks, to prevent this anomaly.

Each river bank may be connected to a single object into which flow from the river reach can spill: a river reach, a storage area, or a 2D zone. Flow over the bank is calculated as a flow over a jagged or irregular weir. The flow over the bank is calculated by splitting the calculation into determining flows over segments using an integrated form of the weir equation for dry, free, and drowned, in the forward and reverse modes. These flow and associated matrix coefficients are then summed together, subject to stability constraints, to give values over the entire bank.

The geometry of the bank, discharge coefficient Cd, and modular limit are all defined in the River Sections Editor, which is accessed via the river reach property sheet.

The levels used to determine spill flow come from the river reach section points, from mesh element points along the bank, and from any computational nodes. Updating all banks individually would be time-consuming, so this task is perfect for SQL.

The Build boundary from banks and section ends tool creates a bounding polygon for a selected river reach from upstream and downstream river sections, as well as right- and left-bank profiles, where possible. This is necessary to later use the flood mapping theme, or if undertaking 2D simulations.