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 1.5 - 2 years Range 1-10 years, depending on channel type Applies best to gravel-cobble rivers with floodplains

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?)

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

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

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

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

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

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

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

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

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

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.

Mineral vs. Organic substrates Table 3.4 -- 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

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)

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. 4.10 – Moss on stones ? ? A rolling stone gathers no moss … the proof!

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

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)

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