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LiDAR-defined Dikes

Started by jmkassak, November 11, 2010, 09:02:41 AM

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jmkassak

I am modeling in an area that has been significantly altered by mosquito impoundments.  We have high quality LiDAR data for the region, so I'm wondering if there is any reason to use a separate dike file.  Based on our results, it appears that the dike is simply being overtopped after a sufficient sea level rise has occurred (I'm a bit confused, however, because the area behind the dike is becoming inundated but the dike itself, dry land which is not assumed to be protect in my run, remains as such).  It is not the intent to protect these diked areas from inundation, but rather to just let inundation occur naturally, and efforts are being made to re-establish connectivity.  Would the connectivity model allow water to simply flow into these diked areas, rather than inundation only occurring after the dike itself has been overtopped?

Thanks!
Jen

Evan Larson

As far as I know, dry land is the only land category that can block inundation in the connectivity algorithm.  If the high elevations surrounding the mosquito impoundments are anything but dry land the impoundments will be flooded.

I recommend using a separate dike file and filling in the mosquito impoundments manually with Set Map Attributes.

Hope this helps,
Evan

Evan Larson

The Connectivity section in the technical documentation (page 31) will give you a more in depth explanation of connectivity than I did.

Evan

Jonathan S. Clough

The connectivity algorithm can be useful in these cases but note that overtopping of a single dry-land cell will cause the whole area behind the dike to overflow.  Given the fact that an individual LiDAR cell elevation can be 20 cm off, this means error in a single cell's elevation could have significant effects.  I'm guessing that there is some sort of pathway in your simulation in which water is able to flow into the mosquito impoundments but it may not be visible in model results because it is such a small pathway.  Or it could be a roundabout pathway around the dikes somehow.

We've run into issues when there are canals with pump houses.  This is because the pump houses don't show up in the LiDAR coverages and the water simply moves through the canal unobstructed and floods the protected region behind the dikes.

-- J

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