Routing:Links and nodes
Channel flow is simulated as a 1-D finite volume system of links and nodes. Four types of links are available to represent different stream and flow structure. These are channel links, lake and detention basin links, and in-stream flow structure links. Each of these will be discussed in turn.
Channel Links
Channels in GSSHA are represented as linear series of nodes that form links, which in turn can be connected in a network fashion. A node is the basic computational element in channel routing and represents a volumetric portion of a channel. The possible channel link types are presented in Table 2. Currently WMS does not support a fluvial link with dual side slope trapezoidal cross section.
| Description | Num. Parameters per cross section |
|---|---|
| Fluvial link, trapezoidal cross section | 5 |
| Fluvial link, trapezoidal cross section, subsurface parameters | 7 |
| Fluvial link, dual side slopes trapezoidal cross section | 6 |
| Look-up table (break point) cross sections | 2 |
| Look-up table (break point) cross sections, subsurface parameters | 4 |
Table 2. Different channel link types that can be used in GSSHA. WMS supports all but the fluvial, dual-sided trapezoidal cross section link.
Information on the links and nodes is contained in two text files: the channel input file and the grid stream file. The channel input file conveys the cross-section and hydraulic properties of the channels to GSSHA, while the grid stream file is used to relate the position of channel links and nodes to overland flow and saturated groundwater cells. WMS creates these two files from the information entered as the feature arc attributes. Some general features of the channel networks are:
- Looped reaches cannot be simulated.
- Link types cannot be mixed within a link.
Lake Links and Detention Basin Links
Lakes and detention basins are defined similarly in GSSHA. They are represented as a set of cells that are ordered according to elevation. Both the lakes and detention basins must have an outlet structure and a set of embankment arcs that detain the water in the natural relief next to the outlet structure. Lakes and detention basins are stored as part of the channel input file. Three parameters must be specified for each lake or detention basin - the minimum, initial, and maximum water surfaces; lakes and detention basins must have an outlet structure. A lake outlet may be the simulation outlet as well.
Structure Links
Structures links are represented as sets of in-stream locations that reference both upstream and downstream water surface elevations in order to compute flow across or through the defined structure. Structure links are stored in the channel input file. The rating curve and rule curve types allow an implicit representation of the flow mechanics of any structure not explicitly defined. Multiple structures may exist at a single location. The possible structure links are presented in the following table.
| Description | Num. Parameters per structure |
|---|---|
| Weir, horizontal broad crested | 4 |
| Weir, infinite sag vertical curve | 5 |
| Culvert, Round | 8 |
| Culvert, Oval | 9 |
| Culvert, Rectangular | 9 |
| Rating Curve | <curve data> |
| Rule Curve | <curve data> |
| Scheduled Discharge | <curve data> |
Related Topics
GSSHA Wiki Main Page
Primer Main Page
