"Nature Guide
Journal"
15 November
2001
We were fortunate to fly out of the North Bend
airport under sunny, mid-day skies last week. As
we gained altitude, the red-and-yellow vine maples
became small flecks of brilliant color in the deep
velvet green of the conifer forests.
Flying inland, another feature commanded my
attention: The shapes of the valleys etched into
the hills by eons of rain.
Slightly curved, each watershed fit between it's
neighbors like pieces in a child's puzzle. Each
watershed divided into sub-drainages, with steep, narrow
valleys drawing down to the stream tracing the
bottom. High ridges separated the watersheds;
lower ridges separated each drainage within the
watersheds. The overall visual effect was one of
nested paisleys.
It seems to me that the size and shape of each
drainage and sub-drainage, as well as the steepness of
land drained, are functions of the amount and timing of
precipitation, the kind of soil and the formations of
bedrock, the plants living on the surface, and the
length of time the land area was exposed to such
erosion.
Whatever the effect of the various elements and
processes, the resulting pattern is a
"fractal." Fractals are patterns that
repeat on a descending scale. The classic example
is the branching on a head of cauliflower. As you
break apart a cauliflower head, you can clearly see how
large branches divide into smaller ones; smaller
branches break down into branches that are still
smaller. The characteristic that makes it a
fractal is that the angle and relative arrangement of
the branches is similar at each level.
The nested, recurring patterns of fractals are very
common in nature. Examples include: the
tight spiral of a coiled fern head, cracks in dried mud,
lacy frost on a window pane, the rhythm of dunes and the
ripples on their surfaces, spiral arrangement of
galaxies.
Material from those watersheds followed the path of
another fractal. Looking like sinuous twigs and
branches on a tree, tiny rivulets collected into creeks
that gathered into streams. The streams formed
narrow winding valleys, joining with others to widen the
river. Sediment eroded from the steep hillsides
settled in the more level areas where watersheds met,
creating narrow ribbons of flat-bottomed
floodplains. The sediment-built floodplain
broadened where the river's path was slowed by
obstructions and as it neared sea level.
It was clear that different species of trees lined
the edges of the rivers than grew on the hillsides—plant
communities dictated by the water and the sediment it
relocated.
I had flown over these hills many times before, but
not when the sun was so low in the southern sky.
The low angle of the November sunlight cast deep shadows
that starkly accentuated the shape of the forested
hills, dramatically detailing the complex patterns of
drainage that are lost in the high sun of summer's
midday.
