Reporting Mapping Errors

[k-bob]

tb, yes the article's example 16 notes "More than 100% widening along Big Bear Creek, tributary to Loyalsock Creek" and has a wild picture.

interesting that some channeling berms that may have existed since the logging days (and can be seen in the 2006-2007 lidar images) were eroded away in the 2011 flood.

 

[troutbert]

k-bob wrote:
tb, yes the article's example 16 notes "More than 100% widening along Big Bear Creek, tributary to Loyalsock Creek" and has a wild picture.

interesting that some channeling berms that may have existed since the logging days (and can be seen in the 2006-2007 lidar images) were eroded away in the 2011 flood.

What is shown in the video is that Big Bear Creek "jumped," i.e. made a channel avulsion from the south side of the floodplain to the north, right into the road grade of Dunwoody Road.

So Dunwoody Road became the new main channel of the stream.

I had been up that road some years before the flood, and the road grade was obviously at a significantly lower elevation than the stream channel. Not a good situation.

I haven't been up there since the flood. Very likely the stream has since been put "back where it belongs," until the next big flood.

 

[albud1962]

Most of the GIS mapping of streams poorly follows the actual
stream course. Starting in 2006 Pennsylvania aerially mapped the state's terrain using LIDAR. Very rarely do the streams digitized from the older maps hit the defined channels indicated in the LIDAR mapping.
Proper map rectification and synchronization is challenging given the map sources and the methods used that converted hardcopy maps to digital format. Also streams are simplified in order to reduce storage space in the various mapping apps. Looking at the LIDAR is one of the better ways of determining a streams actual course.

The LIDAR is available at the PASDA website. If you have a viewer or mapping APP that can display shape files its worth the time to download to topography of your favorite trout stream.