  We report preliminary results of the complementary experimental and numerical
studies on spatiotemporal tangle development and streamwise vortex line density
(VLD) distribution in counterflowing $^4$He. The experiment is set up in a long
square channel with VLD and local temperature measured in three streamwise
locations. In the steady state we observe nearly streamwise-homogeneous VLD.
Experimental second sound data as well as numerical data (vortex filament
method in a long planar channel starting with seeding vortices localized in
multiple locations) show that the initial build up pattern of VLD displays
complex features depending on the position in the channel, but the some tangle
properties appear uniform along its length.
