7884

• UCREFRP Catalog Number: 7884
• Author: Hydrosphere Resource Consultants.
• Title: Reconnaissance Evaluation of Yampa River Diversion Structures.
• USFW Year: 1995.
• USFW - Doc Type: Boulder, CO.
• Copyright Material: NO

Evaluation of Diversion Structures I
GENERAL OBSERVATIONS ON DIVERSION STRUCTURES
The evaluation of diversion structures initially focused on structure height, size, and the
degree to which structures entirely or partially block fish passage. However, during the second
field reconnaissance it became clear that other passage factors should also be considered.
These included navigability of the approach channel (from a downstream direction), seepage of
baseflow through permeable sections of berm, and positioning of berms that might direct
migrating fish to false passages.
The primary biological focus of the evaluation effort was to determine which structures t
were possible impediments to migrating Colorado squawfish. The critical periods for migrating
Colorado squawfish are downstream migrations in the spring and early summer (rising limb of the '
hydrograph) and upstream migrations in the late summer (summer base flow); the latter period
coincides with the time that temporary diversion structures are placed in the river each year. A
secondary biological focus was on the extent to which the construction and maintenance of
diversion structures caused significant disturbance of riverine and riparian habitat.
It is safe to say that most of the diversions from the Yampa River do not impede fish
migration. The majority of the diversions use pumps or minor structures to divert water into the '
ditches. The minor structures include such features as small berms or rock wing dams to get
water to the pump or head gate. These type of structures do not present migration barriers.
The structures that have the highest potential for blocking passage are those that have major
structural components that extend partially or fully across the main river channel. There are
approximately six or seven such structures in the river. Several of these structures are only fully
in place during summer low flow (August) and remain until eroded by river flows; this can be as
short as a few weeks or up to several months. High flows remove the structures that are
constructed of gravel/cobble material. The structures constructed of rock can remain in the river '
for several years. These more permanent structures potentially pose the highest risk to migrating
fish.
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In general, structures that have a well defined overflow channel constructed o
cobble, such as structures at the Williams and Deep Cut ditches, should be more easily passable
than the rock overflows. The rock overflow structures, except for the Maybell Canal, do allow

fish passage although the fish may not be able to find a route through the rock as easily as through '
the cobble overflows. Only one diversion structure (Maybell Canal) evaluated causes greater
than a two-foot drop in water level. The significance of that finding is that a constructed
instream lowflow channel (versus a fish ladder) should be adequate as a swimmable fish
passage at most structures and this same passage feature could also provide watercraft
navigation. ,
Diversion structures with a well defined approach channel (coming up from the
downstream side) are more easily passed by fish than those with a broad shallow approach. The
latter condition exists at structures that require the most gravel disturbance for construction. The
Marshall-Roberts structure would be an example of a broad shallow approach channel. A well-
defined approach channel such as at the City of Craig structure facilitates fish migration as well as
downstream navigation by watercraft. i

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