Waterflow routing algorithm

[boriskaus]

This adds a water flow routing algorithm to a topographic dataset imported with import_topo, and retrieves catchment areas and upstream area. We use the package WhereTheWaterFlows.jl by Mauro Werner for this:

Usage:

julia> using GeophysicalModelGenerator, GMT, GLMakie
julia> Topo = import_topo([6.5,7.3,50.2,50.6], file="@earth_relief_03s");

# Flow the water through the area:
julia> Topo_water, sinks, pits, bnds  = waterflows(Topo)
julia> Topo_water
GeoData 
  size      : (961, 481, 1)
  lon       ϵ [ 6.5 : 7.3]
  lat       ϵ [ 50.2 : 50.59999999999999]
  depth     ϵ [ 0.045 : 0.724]
  fields    : (:Topography, :area, :slen, :dir, :nout, :nin, :c, :cellarea_m2, :catchment_large, :log10_area, :largest_catchment, :largest_area)

julia> log10_area_largest_catchment = log10.(Topo_water.fields.largest_area);
julia> fig, ax, hm = heatmap(Topo_water, log10_area_largest_catchment)
julia> ax.title="Ahr catchment area"
julia> Colorbar(fig[1,2], hm, label="log10(upsteam area)")
julia> fig

[aelligp]

Looks good. Thanks for implementing this

[albert-de-montserrat]

Looks good to me! Just a random dot that could be removed