Stream and River Classification: Hydrology, Morphology, and Ecology

Channel-forming flow

The flow that shapes channel dimensions over time, typically bankfull discharge (recurs every 1.5-2 years); responsible for forming and maintaining channel morphology.

Lane's Balance Concept

Conceptual model showing sediment-water balance: QsD ∝ QwS. If sediment supply or size increases, slope must steepen or discharge must decrease (aggradation). If discharge or slope increases, erosion (degradation) occurs.

Stream/River Classification Purpose

Categorizes rivers based on morphology, hydrology, or ecology for management and comparison.

Rosgen Classification

Descriptive system using slope, entrenchment, width/depth ratio, sinuosity, and channel pattern; classifies streams as types A-G.

Montgomery & Buffington Classification

Process-based system defining channels as colluvial, cascade, step-pool, plane-bed, or pool-riffle types.

Pros of Classification

Provides standardized comparison, helps predict behavior, aids in restoration and management.

Cons of Classification

Can oversimplify variability, ignore underlying processes, and be descriptive rather than predictive.

EPT Taxa

Ephemeroptera (Mayflies), Plecoptera (Stoneflies), Trichoptera (Caddisflies); groups used to assess water quality.

Ephemeroptera (Mayflies)

Have 3 tails, abdominal gills, and are very sensitive to pollution.

Plecoptera (Stoneflies)

Have 2 tails, thoracic gills, and require cold, well-oxygenated water.

Trichoptera (Caddisflies)

Often make cases from sand/plant materials; moderately pollution sensitive.

% EPT Formula

% EPT = (Number of Ephemeroptera + Plecoptera + Trichoptera) / Total Individuals × 100.

Hilsenhoff Biotic Index (HBI) Formula

HBI = Σ(ni × ai) / N, where ni = # of individuals in taxon i, ai = pollution tolerance (0-10), N = total individuals. Lower HBI = better water quality.

Pacific Salmon Species

Chinook, Coho, Sockeye, Pink, and Chum (genus Oncorhynchus).

Pacific Salmon Traits

Anadromous (spawn in freshwater, mature in ocean), semelparous (die after spawning), depend on cold, clean, connected water systems.

Pacific Salmon Threats

Dams blocking migration, habitat loss, sedimentation, overfishing, and warming/climate change.

Pacific Salmon Management

Fish ladders, dam removal, hatchery reform, habitat restoration, flow and temperature regulation.

River Continuum Concept (RCC)

Model describing predictable changes in energy sources, organisms, and nutrients from headwaters to mouth.

Headwaters (RCC)

Shaded, rely on allochthonous inputs (leaf litter); shredders and collectors dominate.

Mid-order Streams (RCC)

Increased light and autochthonous production (algae); grazers/scrapers dominate.

Lower Reaches (RCC)

Deep, turbid, dominated by fine particulate organic matter (FPOM); collectors dominate.

RCC Pros

Simple framework linking energy and biota longitudinally along rivers.

RCC Cons

Assumes undisturbed systems; ignores floodplain complexity and human influence.

Manning's Equation

V = (1/n) × R^(2/3) × S^(1/2); used to calculate velocity in open channels, where n = roughness, R = hydraulic radius, S = slope.

Manning's Discharge Equation

Q = V × A; discharge equals velocity times cross-sectional area.

Manning's Coefficient Effect

Higher roughness coefficient (n) → lower flow velocity.

Rosgen Classification Levels

Level I-IV: (I) broad type, (II) field measurements, (III) process validation, (IV) monitoring and verification.

Rosgen Example

C-type stream = low gradient, meandering, floodplain connected; B-type = moderate gradient, confined.

Marine-Derived Nutrients (MDN)

Nutrients (mainly N and P) brought from ocean to freshwater via spawning salmon; enhance ecosystem productivity.

Importance of MDNs

Support aquatic insects, juvenile fish, birds, and riparian vegetation via carcass decomposition.

Decline of MDNs

Fewer salmon returns reduce nutrient enrichment and ecosystem fertility.

Flow Regimes

Perennial (year-round), intermittent (seasonal), ephemeral (after storms).

Channel Patterns

Straight (high energy), meandering (moderate slope), braided (high sediment load), anastomosing (multiple stable channels).

Process-Based Stream Types

Colluvial, cascade, step-pool, plane-bed, and pool-riffle streams, classified by sediment and flow dynamics.