Difference between revisions of "Routing:Node spacing"
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Latest revision as of 19:35, 18 June 2008
Correct node spacing is important for successful simulations. The stream routing algorithms use a finite volume solution. In the volumetric equations both the channel shape and the channel length are important factors. GSSHA uses a constant node spacing in order to help mitigate numerical instability problems from having too large or too small of nodes next to each other. Since GSSHA is expecting a constant node length then the stream network must be set up to have a constant node length. The node length is the length between verticies on the stream arcs. Small differences in stream node length are acceptable but not desirable. If the actual node length is very different from the specified node length the calculated depth of water in the channel will be off and thus throw off the hydraulic gradient which drives the flow. The flow in the channel could be significantly altered from what it should be if the actual node spacing is very different from the specified node spacing.
The actual node lengths are set by redistributing the vertices along all of the stream arcs. Node lengths may vary slightly from arc to arc. The minimum permissible node length will vary depending on the velocity of the water in the channels, but a good rule of thumb would be to make them no shorter than 1/2 the cell size. In WMS the redistribute vertices option is available in the Feature Objects | Redistribute... menu command or the Smooth GSSHA Streams dialog.
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