Justin Gerardot wrote:
Is the s-curve the elevation profile of the hill upon which the stream is flowing? Is it flattened to calculate the average gradient over a specified distance?
I know this may seem like a small thing to get hung up on because it does not relate to applying patterns to design work, but I keep thinking about it as I try to move on.
Just last week I finished re-reading Chapter 4. I was following it all quite well and then I got to that same point in the chapter about the fish. I moved on cause I was like "huh?" Attached is a picture I drew with three interpretations as to what I think he is trying to say.
A) You are correct in your visualization of the hill profile. He's referring to the general pattern of
water flowing downhill in profile view. It looks like an S that is very flattened out, with changing slopes. Water starts off slowly high up in the landscape at the lowest orders (aka rills and runnels), and it picks up speed as it merges and moves along to the highest gradient (highest slope, that is or "fall over distance" as he explained earlier). This high velocity zone is highly oxygenated as well as erosive, and therefore fish and insects are designed to hold on tight or flatten down or streamline themselves in this region of both turbulent and laminar flow.
B) He's referring to the same location, but is referencing just a slightly different section or profile view, which is the plane normal to (aka perpendicular to) streamflow. It also looks like a flattened S-curve...well two actually, one on either bank.
C) When he says "the flattened S-curve...in profile" referencing the stream bed, he is actually making an analogy to the General Core Model (GCM). The GCM has S-curves going from top to bottom and bottom to top, swirling through the origin. See S1, S2, etc. on the GCM several pages back. At either end of this S curve happens collection (like erosion) and deposits (aggradation). But the flattest part of the S-curves happens at the origin where streams converge. This is the fast part of the GCM, like the center of a black hole. Likewise, streams converging on high slopes are also the fast part of the model, and therefore the ecology adapts to this pattern.
D) All of the above, or something completely else. Something that only "an experienced man" like the one on page 96 would intuitively um...feel.