Flow Accumulation (upslope area)

Flow accumulation algorithm that routes through flats

Description

How much water flows where? Use this algorithm to calculate the upslope area of each cell in a digital elevation model.

Algorithm specifications:
- multiple flow direction
- single flow direction
- routes across flats
- calculates deterministic, randomized and random flow
- allows you to specify a weighting exponent that governs the relation flow direction - slope
- handles edge effects

• Acknowledgements: This submission has inspired the following:; Strahler Stream Order
• MATLAB release: MATLAB 7.0.1 (R14SP1)

[looks good]

looks good

[Salvatore Manfreda]

Good, but do not have a fill sinks option that would be very useful.

[Wolfgang Schwanghart]

I did not include a fill sinks option as it requires the image processing toolbox. If you have this toolbox use

demfs = imfill(dem,'holes')

Best regards,
Wolfgang

[Jorge Santos Santos]

Does not work for large rivers

[Wolfgang Schwanghart]

Hi Jorge,

you are right. The algorithm is quite memory demanding and grids exceeding 600x600 cells may cause problems. I am currently working on an improved version that allows for huge grids. Please be a bit patient...

Best regards,
Wolfgang

[Liam Reinhardt]

A good user friendly piece of code. Unfortunately it does not seem to generate single thread 'rivers' 1 cell wide. Instead cells of high accumulation are often adjacent to each other (i.e. perpendicular to the primary flow direction) producing messy flow paths.

[Wolfgang Schwanghart]

Hi Liam,

thanks for your feedback. The code is it stands right now is a multiple flow direction algorithm, and yes, it can be very "dissipative". There is a way to avoid this behavior by element-wise exponentiate the flow direction matrix (M), so that steep gradients gain a larger weight than smaller ones.

I'll work on an update of this version and include it as an additional option.

Thanks a lot again for the feedback.

Wolfgang

[Wolfgang Schwanghart]

To all: TopoToolbox is now available here: http://physiogeo.unibas.ch/topotoolbox/

TopoToolbox can handle larger grids than wflowacc can and has many more utilities related to digital elevation model analysis.