In a hydrological model, bank stations are used to define the geometry of a river channel and specify the locations of hydraulic structures and other features.
A bank station divides a river channel into three distinct conveyance zones: the left overbank, the main channel, and the right overbank. This segregation simplifies the calculation of energy loss in the system using Manning’s equations. Therefore, the importance of bank station placement cannot be overstated. This article outlines the best practices that a user can follow for optimal bank station placement in CivilGEO software.
Common Mistakes to Avoid
The following mistakes should be avoided when placing bank stations:
Placing Bank Stations at Grade Break
Bank stations are typically placed at the grade break between the physical channel and the flatter overbanks, as shown below.
The placement of a bank station should always be determined based on the location of the change in conveyance. For instance, excessive roughness pushes the boundary between conveyance zones down closer to the toe of the banks. This is often the case where thick vegetation occurs down the banks of the channel, as shown below.
Placing Bank Stations at Lower Depth
For a cross section with two channels of varying depths, it may seem logical to place the bank stations in the deeper channel.
However, before making this decision it is important to check the upstream and downstream sections of the river of the specific cross section. It is possible that the smaller channel may carry most of the flow, while the other side is primarily a low-lying area.
Parameters to Consider
The above mistakes can be avoided by considering the below parameters when placing bank stations at a cross section:
- Having aerial imagery behind the geometry schematic makes bank station placement easier. The user can study the reach above and below a cross section to correctly determine the location at which the bank station is to be placed.
- When moving through a reach, the placement of bank stations should be consistent from cross section to cross section. Changes in main channel width should generally be gradual from one cross section to the next.
- An essential step to constructing a model is the deliberate and methodical consideration of each cross section and the proper placement of each bank station.
- If importing cross sections from GIS, make sure that the bank line delineation places the bank stations properly.
- After importing cross sections, make sure to fine tune the bank station placement.
There are always exceptions, but the key thing to remember is that bank stations capture the change in conveyance between the main channel and the overbanks. In addition, make sure that the resulting channel width does not change too drastically from one cross section to another.