WMS:GSSHA Embankment Arcs

Embankment Arcs in WMS

In WMS, man-made embankments are represented as embankment arcs. These embankment arcs are placed along the centerline of the actual embankment. Often these embankment arcs represent roads that cross a drainage. The embankment arc can intersect a stream arc and an in-stream hydraulic structure (a culvert) placed at the intersection to allow water to pass through. For the embankment arc to function correctly in GSSHA, the elevations along the top of the arc must be defined. This is done through the Embankment Arc Profile Editor.

In the Embankment Arc Profile Editor the arc elevations can be generated by entering the parameters for a vertical curve. WMS will then take the given parameters and compute the correct elevation values for each vertex of the arc. The parameters needed for the vertical curve are the elevation of the point of vertical intercept, the left (back) tangent slope, the right (forward) tangent slope, and the curve length. Note that the arc need not be a straight line in plan view for the vertical curve to be computed.

The arc elevations can also be set by using the Conform Arc to Grid option, which sets the elevations of the arc to the corresponding grid elevations. The Offset Arc option will change all arc elevations by a user specified constant.

The Embankment Arc Profile Editor, shown in the image below, is accessible from the Feature Arc Attributes dialog in the GSSHA coverage. The feature arc type in order to access the dialog.

Embankment Arc Profile Editor dialog

The Embankment Arc Profile Editor allows the embankment profile to be manually adjusted or set as a computed vertical curve.

Embankment Arcs in GSSHA

In WMS, the embankments are represented as feature arcs and are given profile elevations that define the top of the embankment. These feature arcs are then mapped to the nearest cell edge. The embankment acts as a wall all along the edge, interrupting flow between the two adjacent cells.

The wall elevation at each cell is determined by interpolation along the embankment arc. Once the water elevation has risen to this elevation, water will commence flowing over the embankment in a horizontal broad-crested weir fashion.