8249

• UCREFRP Catalog Number: 8249
• Author: Modde, T., W. J. Miller and R. Anderson.
• Title: Determination of Habitat Availability, Habitat Use, and Flow Needs of Endangered Fished in the Yampa River Between August and October.
• USFW Year: 1999.
• USFW - Doc Type: Project #CAP-9,
• Copyright Material: NO

CHAPTER 3: HABITAT AVAILABILITY AND HYDRAULIC
SIMULATION

Introduction

In riverine ecosystems the physical habitat and biotic communities are inextricably linked. Peak flows
form and maintain channel morphology, which significantly affects the quality and quantity of aquatic
habitats during the baseflow period. The integrity ofthe aquatic community is afunction of habitat
quality and availability. By identifying relationships between channel characteristics and flow we can
estimate the influence of flow reduction on habitat quality and quantity. Many instream flow
methodologies are based on relationships between flow and channel configuration. These methods rely
on the assumption that reliable and stable riffle habitats maintain biological integrity. The approach taken
by this study was to determine curve breaks in the relationship between flow and channel variables and to
use them as indicators of the point at which flow reduction most impacts habitat availability and
production in the Yampa River.

While there is some lower flow that; maintains a healthy, functioning river community, methods to identify
this flow are controversial. Instream Flow Incremental Methodology (IFIM) (Bovee 1982) generates'a
prediction of the amount of usable habitat for fish as a function of discharge by combining habitat
suitability curves with a hydraulic model. The habitat component of the model has received much criticism
because of assumptions concerning positive relationships between habitat availability and fish abundance.
When habitat availability is not limiting, biological interactions primarily determine community structure
and carrying capacity (Allan 1995). Even when environmental factors are stressful, the correlation between
habitat availability and fish abundance may not be readily apparent. However, at some reduced flow, lack
of habitat can become a limiting factor and maintenance of normally stable habitats is necessary for
maintaining community structure. IFIM is a useful tool for identifying habitat stability over a range of low
flows.

Even though IFIM is capable of integrating two to three variables, the weighted useable area (WUA)/flow
relationship only applies to individual life stages of a single species, in this study adult Colorado
pikeminnow and humpback chub. Flows that appear to be adequate for maintaining Colorado
pikeminnow and humpback chub habitat may not necessarily be adequate for other members of the
aquatic community. Conversely, flows adequate to protect the aquatic community should be inclusive for

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