Hi.

I am doing hydrological analysis for a river catchment in a DTM.

I have produced a graph like (b). This shows the elevation of the study river in the catchment with respect to distance upstream.

Aim: I want to take it one step further and plot a log slope-area graph like graph (a).

In order to do this, I assume I must find two things. First, the slope. Second, the area of the catchment (upstream).

I am working with the chi transform function in Matlab.

However, I am not sure what slope I must find. Is it the slope of the study river, or the the slope of all the rivers in the catchment? I assume the (+) on the graph in figure (a) shows the slope of different rivers? If so, how do I replicate this approach in my DTM?

I am working with topotoolbox in Matlab using this code:

DTM = GRIDobj(A);

FD = FLOWobj(DTM, 'preprocess', 'carve');

Sr = STREAMobj(FD, 'minarea', 1000);

A = flowacc(FD);

c = chitransform(S, A, 'mn', 0.494);

Note: flowacc calculates the number of upstream cells based on a flow% direction object (FLOWobj). To obtain upslope or contributing area in% metric units, multiply A by the square of the cellsize, e.g. A = flowacc(FD).*(FD.cellsize^2)

https://github.com/wschwanghart/topotoolbox/blob/master/%40FLOWobj/flowacc.m

I assume the A variable is most useful here. How would you plot this to produce the graph in (a)?

How would you plot this?

Help appreciated. Thank you.