Determine Flow Accumulation GRID: Using Python; Map Algebra and NumPy

Question

I'm currently busy with a hydrology study where I'm determining the location and structure requirements (culverts & bridges) for a proposed Railway Alignment. My initial assessment is based on the STRM 90m DEM and the size of my DEM is 34 651 X 24 934 cells = 863 988 034 cells. I can't afford to split my DEM or to increase the cells size as its already a coarse cell size. I've used the Flow Accumulation tool within Arc Hydro, the Flow Accumulation tool within the Spatial Analyst Extension; Hydrology Toolbox as well as tried running it from Python hoping for better processing time. The Flow Accumulation algorithm that is being used seems to be hard coded in that it doesn't use any more than 2 GB memory when processing the Flow Direction GRID to generate the Flow Accumulation GRID.

Is there a way to use Python; Map Algebra and Numpy to improve my processing time in generating the Flow Accumulation GRID for large DEM's.

The current Flow Accumulation GRID runs for almost 72 hrs.

Regards

PaulHedlund · Answer

Peter,

I compared processing times between the Arcpy Flow Accumulation and Arc Hydro Flow Accumulation.  They appear to be almost identical.

The multi-processing algorithm sounds interesting.

PeterWilson · Answer

Hi Paul

I've not been able to improve the Arc Hydro Flow Accumulation processing, but I must give credit to the Arc Hydro Team. I'm using one of the latest versions of Arc Hydro and the processing time has drastically improved. I've processed a 500 000 000 million cells DEM study area within 2hrs.

I'm currently busy with my Masters Thesis and busy developing a Multi Flow Direction algorithm that will divide the study area into smaller tiles and process them simultaneously, improving the overall processing time and accuracy of the derive flow accumulation grid and derived river network.

Regards

PaulHedlund · Answer

Any luck with using NumPy for Flow Accumulation?