2. “Low Flow”
“Water is taken out of the stream for a variety of uses, such as irrigated agriculture, municipal and industrial. Low flow means that amount of water that must be left in the stream for the fish. With anything less than the low flow, the fish will die.”
Only differentiated between two relative events:
Disastrously low
Everything else
Used Instream Flow Incremental Methodology to negotiate acceptable flow levels from multiple possibilities

3. Instream Flow Incremental Methodology
Interdisciplinary Problem Solving Tool
Determine benefits or consequences of management
Solves water resource allocation problems including riverine habitat
Modular Decision Support System
Library of linked analytical procedures
Three macrohabitat-level stratifications
Drainage basins, networks, segments

4. Instream Flow Incremental Methodology
Interdisciplinary Problem Solving Tool
Determine benefits or consequences of management
Solves water resource allocation problems including riverine habitat
Modular Decision Support System
Library of linked analytical procedures
Three macrohabitat-level stratifications
Drainage basins, networks, segments

5. Physical Habitat Simulation (PHABSIM)
USGS Fort Collins Science Center
used Version 2 (DOS)
Developed a Windows interface so that results could be displayed graphically
Domain/Objective
The basic objective is to obtain a representation of the physical stream so that the stream may be linked biologically to the social, political, and economic world.
Combines empirical descriptions of channels to gain a relationship between streamflow and area of habitat available.

6. Top Uses Instream flow requirements Water delivery schedules
Area planning
Water rights
Water delivery schedules
Minimum release
Hourly, seasonal and yearly flow regime (wet vs. dry)
Impact analysis
Flow depletion
Flow augmentation
Channel alterations

7. Temporal/Spatial Scale
Key Assumptions
Assumes benefits for fish limited by availability of habitat
Uses empirical formulas to solve hydraulic models
Organisms will use less favorable areas as the stream becomes more crowded
WUA in each cell is indicative of total habitat at a given discharge
Temporal/Spatial Scale
Reach scale (20-30 widths), divided into sub-segments based on slope
Results for a point in time, or on a monthly time-step

8. Input Drivers Channel morphology; bed elevation (m)
Channel substrate (grain size, cm)
Mean column velocity (m/s)
Water surface elevations (m)
Discharge (m3/s)
Habitat Suitability criteria (what depths/qualities are best for a species)

9. Habitat Suitability Criteria
Category I, II, III
I – derived from a consensus of experts’ accumulated knowledge of habitat use
II – derived directly from observations of habitat use
III – derived from observation data corrected for habitat availability

10. Habitat Suitability Curves

11. Key Outputs
Weighted Usable Area (WUA) – measure of microhabitat quantity and quality (habitat area/stream distance)
Competition analysis between species

12. PHABSIM

13. Urban Streams
Physical modification to the channel has reduced instream habitat availability
Urban restoration schemes should consider habitat in concert with water quality

14. Salmon Spawning Sensitive to habitat suitability index
Ex-situ curves are often used for practicality
Must consider transferability from one site to another