Find the 'start points' of a stream and buffer a certain distance upstream

The solution listed here is a shell indicating one method to get the results desired. The concept of stream ordering is used to help locate the start points.

Code:

/* General operations preparing original data

/* Calculate flow direction.
FDIR = flowdirection (ELEV)

/* Calculate flow accumulation
FACC = flowaccumulation (FDIR)

/* Generate stream network.  value of 45 to be in/decreased
/* according to dataset.
STREAMS = con (FACC > 45, 1)

/* Gives unique value to each section of the stream.
SLINK = streamlink (STREAMS, FDIR)

/* Assign each link its minimum elevation.
ZMIN = zonalmin (SLINK, ELEV)
**************************************
THIS STEP ASSUMES A LINEAR NETWORK THAT
IS ONE CELL WIDE, WHICH MAY NOT BE THE
CASE. IF THE NETWORK IS 2 CELLS WIDE THE
REST OF THE SOLUTION FALLS APART. MORE
RESEARCH NEEDS TO BE DONE TO DETERMINE A
WAY TO DETERMINE THE START CELL.
/* Finds "start" cells for each stream segment.
START_CELL = con ( ELEV eq ZMIN, ZMIN, 0)
**************************************

/* Assigns all start cells value 1.
START_CELL1 = con (START_CELL > 0, 1)
/* Determine the stream ordering

/* Stream network of elevation values.
STR_ELEV = setnull (STREAMS eq 0, ELEV)

/* Calculate flow direcion along stream network.
STR_FLOWDIR = flowdirection( STR_ELEV)

/* Calculate the stream ordering.  Use Shreve order. 
STR_ORDER = (STREAMS, STR_FLOWDIR, shreve)
/* Measure upstream from the start cells and buffer out.
/* Note that this has been done only for the first order streams.  
/* The process will need to be looped to evaluate remaining orders. 
/* Set the first order streams to value 1.
SO1_ORDER = setnull (STR_ORDER ne 1, 1)

/* Find the start cells for order 1 streams.
SO1_SOURCE = con ( START_CELL1 eq 1 and SO1_ORDER eq 1, 1)

/* Measure the distance upstream.
SO1_COSTDIS = costdistance (SO1_SOURCE, SO1_ORDER, #, #, 100)

/* Set the upstream distance to single value.
SO1_LENGTH = con (SO1_COSTDIS ge 0, 1)

/* Generate buffers.
SO1_BUFF = eucdistance (SO1_LENGTH, #, #, 20)

/* Final buffers as single value.
SO1_FINAL =  con (SO1_BUFF ge 0, 1)

/* For the next stream order,  update the SOx_ORDER line accordingly:
/*   ie: SO2_ORDER = setnull (STR_ORDER ne 2, 1)

/* In this example, the upstream distance was 100 units, and
/* the buffer was 20.  Set these as appropriate.