1. Bankfull discharge (Qbkf), an important concept
Fills the channel and does work on boundaries
"Dominant discharge”
Greatest total volume of sediment moved
Frequency-Magnitude Concept (Fig. 3.10, text)
Magnitude sediment load
Freq. of Q
The highest flows are not the “dominant discharge”!
Suspended
Bedload
For suspended: Qd is ~Qbkf a “channel forming flow”
Peak discharge that occurs on average once in years
Range 1-10 years, depending on channel type
Applies best to gravel-cobble rivers with floodplains

2. MORPHOLOGIC CLASSIFICATIONS OF STREAMS Based solely upon physical features and processes
1) Reach scale (Rosgen 1994)
based on physical appearance (hydrogeomorphic processes implicit)
41 channel types based on sinuosity, width to depth ratio, confinement, slope
repeatable and widely-applicable (but "cook-book”)
used by agencies for channel (physical) restoration
Easily misapplied (and often fails?)

3. 2) Reach scale (Montgomery and Buffington 1997)
focus on processes that form and maintain channels
5 types of channels (for mountain streams)
cascade
step-pool
plane-bed
pool-riffle
sand-bed
Increasing stream gradient

4. 3) Hierarchical, multi-scale
Processes acting at LARGE scales influence/constrain patterns at small scales
For example:
basin geology constrains the kind of channel reach morphology and habitat sediment types
Climate determines flood frequency and stability of riffle gravels over an annual cycle
Hierarchical classification systems allow choice of the level of habitat resolution that is required to meet specific objectives

5. Frissel et al. 1986
Watershed  Segment  Reach  Pool/riffle  Microhabitat
Spatial and Temporal Scale Relationships

6. Other Hierarchical Classifications
Hawkins et al. (1993)
Classify “channel geomorphic units”

7. Substrate-Organism Relationships
Substrate = Substratum (Substrata)
Fundamental Roles
1) Habitat
2) Food
3) Protection

8. Ways to Characterize Substrate
1) type
2) size (area) and shape
3) heterogeneity
4) texture
5) stability

9. Substrate Type & Size Inorganic -- mineral Organic Exposed Bedrock
Particles (from weathered bedrock)
Wentworth Scale: B > C > G > Sa > Si > C
Organic
Fine Particulate OM (FPOM, < 1mm)
Course Particulate OM (e.g., whole leaves) (CPOM, > 1mm)
Wood
Living plant surfaces / Moss

10. Mineral particles SIZE [Table 12.3 b (Minshall)] SHAPE [Table 12.3a]
Richness (# spp.)
increases
Species density (#spp./m2)
declines
Abundance (#individuals)
Density (# ind./m2)
declines … a bit
Same pattern in Table 12.3a
SHAPE [Table 12.3a]
Irregular shape more microhabitats

11. Mineral Particle Mixtures
Table 12.1 (Minshall)
Density and biomass of invertebrates
Sand supports low abundance and biomass
Rubble (pebble + cobble) and gravel support more
Interstitial spaces between substrate particles influence many aspects of habitat quality
Habitat space
Flow (Fig.8-12, Ward)
Oxygen
Stability
Sand
Gravel-Cobble
Cobble-Boulder

12. Fish spawning
Salmonids can create redds in gravel having median size up to 10% of their body length
Particles < 1 mm reduce gravel permeability and impair egg development (reduced flow and oxygen)
Particles 1-10 mm block intergravel pores and impede “swim-up” of newly-hatched fish.

13. Mineral vs. Organic substrates
Table classic study
sand supports fewest numbers and species
organic substrates support more (but they are seasonal)
Wood
Steep channels: creates habitat (pools) and increases CPOM retention.
Low gradient channels with silt/sand bottoms: stable habitat
Table 3.5
Satilla River, GA

14. Surface Texture Scale relative to the organism
Field observation - more “pits”, more algae or invertebrates
Experimental approaches:
Example 1: Algae (Fig. 2, Bergey)
4 surfaces with different “pittedness”
Experimental sand abrasion
Interpret graph
Effect of abrasion level on diatom density?
Effect of surface ”pittedness” on density? (panel A vs. B)

15. Stability ? ? Particle resistance to movement by high flows
Critical erosion velocity (Fig. 1.7)
Hydro-Geomorphic setting
Slope, channel confinement
difference in Q regime among streams
Fig – Moss on stones ? ?
A rolling stone gathers no moss …
the proof!

16. Heterogeneity
Generally, RIFFLES > POOLS for both benthic Diversity and Production. WHY?
More substrate diversity
Cob
Boul
Pbl
Gvl

17. Heterogeneity
a) Particle sorting by flowing not perfect. Many “patches” (range) of particle sizes.
b) Scales of heterogeneity
Local patch : some terms
Embeddeness - excess fines (draw picture)
Channel
Armoring - loss of fines (draw picture)
mid-channel (thalweg) to edges
Reach scale
riffles vs. pools
Whole river system
uplands channels more heterogeneous than lowland (excluding floodplains)

18. Organism-substrate relationships?
Many loose patterns -- interacting factors, due to correlations among important variables:
Current
Oxygen
Food
Stability
Riffles: coarse substrate mixtures with high interstitial flows, high O2, trapped CPOM, and relatively high stability
Pools: fine substrates, low interstitial flows, low O2; lots of organic matter, low stability