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# Calculating lake depth from DEM

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11-19-2013 12:26 PM
New Contributor
Hi

I was looking for help related to finding the depth of a lake with a DEM. The only data sets I have are a DEM and a lake polygon. I am not sure if my DEM includes bathymetry. So, I was wondering how I can tell if my DEM has bathymetry and if not how can I calculate the depth of the lake. My DEM has negative numbers for ocean areas but not for lakes, if that helps determining if it has bathymerty I am not sure.
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5 Replies
MVP Emeritus
did you try clipping out the DEM using the lake file?  A lake won't have a negative elevation unless it is below sea level
Regular Contributor III
If you build a hillshade for the DEM in the area of the lake, does it appear to have "topographic relief"? Otherwise if it appears flat (as a lake surface would), the DEM probably represents the surface elevation.

Probably unlikely that the DEM includes bathymetry... For example, if it's a USGS 10m DEM or something I guarantee it doesn't.

A lake won't have a negative elevation unless it is below sea level

Sort of... A lake may have a surface elevation of 314ft > MSL, but the depth of it may be 350ft deep, so that would leave the bottom of the lake at 36ft < MSL. For example: http://en.wikipedia.org/wiki/Lake_Whatcom
New Contributor
You are right the DEM does not have bathymetry, the lakes just show up flat. Ist there I way to calculate the depth by using the elevation of the surrounding areas? Thank you so much for the help
Frequent Contributor III
You should not be able to determine a lake depth based on surrounding topology.

Lakes are formed in different ways and that is a significant factor in how deep it is.

Typically very round lakes are often meteor impacts.  They will be very shallow and have raised edges.  This is not always true.  We have a large lake near where I live that is very round and has raised edges but is exceptionally deep and is fed by a spring at 106 feet.

Thin very deep lakes are often formed by glaciers or erosion etc...

what state are you in?  Some states DNR's provide bathymetric

A DEM will typically show the elevation of the lake surface at the time it was made.

Bathymetrics used to be made by throwing a weighted rope into the water and marking how deep it goes.  modern technology uses sonar.  The technology used to generate modern DEM cannot penetrate water surface.

You are right the DEM does not have bathymetry, the lakes just show up flat. Ist there I way to calculate the depth by using the elevation of the surrounding areas? Thank you so much for the help
MVP Notable Contributor
If you did obtain some sort of bathymetry data for your lake then have a look at this thread on how to use it.