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yanglong09

Setup detention basin in GSSHA

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I have three questions regarding detention basins in GSSHA:

1) Does anyone know how to determine min/max and init water surface elevation for detention basins in GSSHA? Should we just assign min elevation based on the background elevation of the points?

2) While developing rating curves for the detention basins, is GSSHA still using elevation instead of water depth?

3) If we assign the same elevation for the detention basin as the channel, probably water would back up instead of filling the detention basin. How to deal with this.

I'm using WMS 10.0

Thanks,

Long

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Long,

A person normally knows or has an idea of the min/max water surface elevations for a detention basin. The max would be close to the maximum elevation of the top of your embankment; the min would be the elevation of the bottom of the detention basin. You would have to approximate an initial water surface elevation.

Yes, GSSHA is still using elevation instead of water depth for the static rating curve for a detention basin.

You would normally want a detention basin elevation that is lower than the main channel, and if not, then yes, the water backs up. This should be fine.

Chris

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Hi Chris,

I noticed on the GSSHA wikipage: it says" it is recommended to define lakes as point attributes in a GSSHA coverage."

I guess I could just define a node as a detention basin hydraulic structure without creating polygons as the embankments. However, this seems not working. An error message pops up while progressing to "number of coords for lake #1's search order". Is the polygon feature necessary here?

Thanks,

Long

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Long,

I edited the following xmswiki page (first topic) to describe the process of creating lakes (or detention basins) in GSSHA:

http://www.xmswiki.com/wiki/WMS:GSSHA_Lakes_and_Wetlands

You no longer need to define a polygon representing the lake. Just add a node at the outlet point of your lake on your stream network and assign a Detention basin attribute to this node. You can also add any other outlet attributes you need, such as a rule curve. Then create an embankment arc downstream from the lake following the rules described above. That's all you need to do.

You might refer to the WMS tutorial that describes how to add a detention basin in WMS. The tutorial is located on our WMS Learning Center at the following web page and is called "Analyzing the Effects of Land Use Change (Part II)":

http://aquaveo.com/software/wms-learning-tutorials

Chris

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