Add GraphFlood example

[wkearn]

This adds a Jupyter notebook that runs GraphFlood on the Green River DEM as in Gailleton et al. (2024). This generates the figure that is planned for the TT3 manuscript.

@bgailleton: Any ideas for improving this example?

[bgailleton]

@wkearn I have two main suggestions. First it can be interesting to have a bit more outputs than just the flow depth, for example flow velocity or discharge or eventually other component that would demonstrate the advantage of using both graphflood integrated into topotoolbox.
Q and u are not directly calculable with the run_graphflood method. I am thinking of completing the interface of graphflood on pytopotoolbox with a Object Oriented interface to facilitate the use, for example

gfo = GraphFloodObject(...)
gfo.run(N_iterations)
gfo.get_Qin()
gfo.run(N_more_iterations)
gfo.get_u()
...

Second suggestion, I do not mind using green_river, but as it has already been used in the 2024 paper, maybe another field site would bring more demo?

let me know your thoughts.

[bgailleton]

#344 added the graphflood Object and paves the way to the example (sorry for the delay)

I hope to get time to do this, but at least for now you can get a bunch of new metrics.

here is a minimal example:

import numpy as np
import topotoolbox as ttb
import matplotlib.pyplot as plt

# dem =ttb.read_tif('exampleDEM.txt')
dem = ttb.load_dem('bigtujunga')
dem = dem.fillsinks()
gfo = ttb.GFObject(dem, p=1e-4, manning=0.033)
gfo.run_n_iterations(dt=1e-1, n_iterations=200)

# Plot relevant flow depth
fig,ax = plt.subplots()
ax.imshow(dem.hillshade(), cmap = 'gray')
thw = gfo.hw.z
thw[thw < 1e-2] = np.nan

ax.imshow(thw, cmap = 'Blues')

# Getter to other metrics:
gfo.qvol_i # Discharge accumulated via drainage area (non local)
gfo.qvol_o # Local discharge calculated from manning's
gfo.sw # Hydraulic slope 
gfo.u # flow velocity
gfo.compute_tau() # Computes river basal shear stress