Are there any open source or inexpensive tools to detect and fill sinks on a DEM? ArcGIS Spatial Analyst is just out of my price range.
SAGA has several fill methods
Sink Drainage Route Detection
Fill Sinks (Planchon/Darboux, 2001)
Fill Sinks (Wang & Liu)
Fill Sinks XXL (Wang & Liu)
This is actually an area of active research for me.
You can use the Priority-Flood algorithm as described by this journal article, which is also available on arXiv. This allows you to fill depressions in O(n log n) time for floating-point data and O(n) time for integer data. Source code is available here.
The foregoing algorithm is serial and works well up to a hundred million cells or so. Sometimes, though, your datasets are larger.
(Disclaimer: I wrote the articles and code mentioned above.)
Yeap, there is. I haven't tested yet, but I ran my eyes trough the source code. It seems a good program.
Landserf (free to use) - Click to Goto Homepage
I have used it, and love it.
I also think the algorithms are much more accurate in Landserf than in Arc, very very solid maths used and Jo Wood lists the maths used for his analysis.