GENERAL42732

• Permit No: M1976032
• IBM Index Class Name: General Documents
• Doc Date: 6/5/1996
• From: USFS
• Media Type: D
• Archive: No

drawings attached to this document. This channel configuration is more
consistent with an alluvial fan and will result in a more stable situation.
A new channel will be created for both the San Miguel and the South Fork Rivers
above their confluence and for a short distance below. These will be created
using design criteria based upon sediment load, discharge and valley gradient.
The objective is to make them look as natural as possible. However, placement
of rock wiers and revetment will look somewhat artificial to those familar with
natural channel features, but over the long-term, these structures should
accomplish the stabilization in as short a period as possible and provide a
stable system and create suitable instream habitat for fish and benthic
organisms.
Material that would be eroded out of the banks over time under Alternative 1
would be excavated and moved to build a new channel and floodplain, under this
alternative. This would significantly reduce the bedload supply into the
channel that is now contributing to the braided condition downstream. Due to
the nature of the work, use of large earthmoving equipment will result in
sediment introduction to the stream and increased turbidity. However, the net
input of sediment over time is significantly less for this alternative than for
Alternative 1 because bank erosion under Alternative 1 will occur during high
flow periods, when the stream carries the majority of its natural sediment
load, while any increase in sediment during the short term, for this
alternative, will occur during low water periods when the expectation ie to
find the streams running clear. Mitigation measures such as the use of
settling ponds will minimize the effects associated with excavation,
transportation and placement of material, to the extent possible.
Creation of ponds adjacent to the river would create an opportunity to
diversify the recreational fishery, as well as provide materials for
restoration of floodplains and streambanks.
Given the natural inclination towards channel adjustments across the alluvial
fan this alternative provides the best chance for long term stability, and
would eliminate the need for significant excavation, as well as the
construction of a gabion spillway leading to an overflow channel, required in
Alternative 3.
The over-all affects of Alternative 2 would be: 1) to allow the riparian
vegetation to become reestablished, and increase that community type over what
currently exists; 2) to provide a more stable stream channel end increase
habitat diversity and recreational fishing opportunities; 3) to arrest the
on-going erosion and sedimentation; 4) improve the visual and aesthetic values;
and 5) restore the total system back to a more stable situation.
Alternative 3. RESTORE AQUATIC/RIPARIAN SYSTEM TO A STABLE CONDITION.
MAINSTEM RECONSTRUCTED TO A 'C' CHANNEL TYPE.
The affects of this alternative are similar to Alternative 2, except that under
this alternative the mainstem channel above the confluence would be
reconstructed to form a meandering "C" channel type, as shown in the attached
drawings.
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