PUB00118

• Year: 2000
• Title: Arkansas River Water Needs Assessment
• CWCB Section: Interstate & Federal
• Author: Smith and Hill
• Description: Information and findings associated with the Arkansas River Water Needs Assessment study
• Publications - Doc Type: Historical

Arkansas River Water Needs Assessment - Section 1. Executive Summary

November-Mid-ApriI - Boating and angling use is
low during this period and the riparian community
is largely dormant. While it is best for the
warmwater fishery to have the water level as high as
possible during this period, the fishety can survive
if there is a sufficient pool of water during the fall
and if the reservoir is filled during the winter. The
WWSP, as currently operated, benefits the fishety
in Pueblo Reservoir.

Mid-April-October (Growing Season) - Water
level needs are in conflict during this period. To
support boating, optimal water levels would be to
have a full reservoir all season, but this conflicts
with operational demands on the reservoir.
Wildlife and riparian needs are best supported by a
full reservoir on May 15, with slight drawdown
starting anytime between May 15 and July 15. A
slight drawdown allows the rooting zones of
riparian plants to remain in contact with ground-
water levels, but allows exposure of some reservoit
substrate to grow annual vegetation species. The
warmwater fish population is best supported by a
full reservoir through July 15, followed by a rapid
drawdown between July 15 and August 15. The
rapid drawdown allows colonization of the exposed
substrate by annual species during the growing
season, which contributes to reservoir food
supplies when reservoit levels rise again. Given
these conflicting demands, the overall resource
preference is to prevent drawdown as long as
possible in the spring, within the confines of oper-
ational demands.

Summary of Natural Resource
Water Preferences by Individual
Resource Values

Water Preferences for Fish Populations

Arkansas River

The Arkansas River is noted for its exceptional
brown trout fishery and for its developing rainbow
trout fishery. Brown trout were the focus of this

study because they are prevalent in the river, the
population is self-sustaining, and any given opera-
tional program will influence rainbow trout in a
similar manner. There are a number of nongame
fish species present in the Arkansas River drainage,
primarily found between Canon City and Pueblo
Reservoir. This area was not extensively studied,
but flows that protect and maintain game species
should also protect nongame species. Rare species,
such as greenback cutthroat trout, Arkansas River
darter, and redbelly dace, are all found in the
upper Arkansas River Basin but have not been
collected in the main stem river or reservoirs.
Habitat needs for brown trout and rainbow trout
were analyzed using the Instream Flow Incremental
Methodology (IFIM).

The two most important physical variables
affecting fish habitat on the Arkansas River are
velocity and depth. The further these variables are
from the optimum value, the less likely that
position is going to be occupied by a trout,
because brown trout occupy positions in a stream
that maximize net energy gain during foraging.
The carrying capacity of a stream may be deter-
mined by available habitat and number of foraging
sites. Increasing flows frequently produce unfavor-
able habitat conditions in the Arkansas River, as
illustrated in Figure 1-7 and Appendix D.

Increasing velocity accounts for large drops in
suitable habitat, particularly for small fish. For
example, adult brown trout prefer a velocity of 1.3
feet per second for spawning, and velocities
ranging from 0.9 to 1.3 feet per second for other
activities, such as foraging. However, fry and
juveniles prefer velocities of 0.3 to 0.7 feet per
second. For all life stages, increased velocities not
only increase the metabolic cost associated with
foraging, but also create conditions that reduce the
capture of drifting insects.

As with velocity, increasing depth accounts for drops
in suitable habitat, especially for small fish. Depths
of 2.0 to 3.0 feet are optimum for adult brown
trout spawning, while the suitable range of depth
for spawning is 4.8 to 36.0 inches. Redds
(spawning locations) are generally found at depths

1-20 - Water Needed to Protect or Promote Critical Resource Values