River Load: The Three Ways Rivers Carry Their Burden

River load = total solid material transported by a river. It moves in three distinct modes, each governed by particle size and flow hydraulics:

1. Bed Load (Traction Load)

• Mechanism: Rolling, sliding, saltating (bouncing) along bed.
• Particles: Gravel, cobbles, boulders (>2 mm).
• Fraction: ~5–15% of total load (by weight), but does the heavy geomorphic work (channel shaping).
• Formulas: Meyer-Peter & Müller, Einstein-Brown, Wilcock-Crowe.

2. Suspended Load

• Mechanism: Held in water column by turbulence (u* > wₛ).
• Particles: Sand, silt, clay (0.002–2 mm).
• Fraction: ~80–95% of total load (most visible — muddy water).
• Measurement: Depth-integrated samplers (US DH-48, D-96).

3. Dissolved Load

• Mechanism: Ions in true solution.
• Particles: Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃⁻, SO₄²⁻, Cl⁻, SiO₂(aq).
• Fraction: ~5–15% (higher in limestone basins).
• Source: Chemical weathering (carbonation, hydrolysis).

Controls on Load

• Discharge (Q): Load ∝ Q^b (b ~1.5–3 for suspended).
• Velocity / Slope: Higher stream power → more transport.
• Bed/Bank Material: Alluvial (supply-unlimited) vs. bedrock (supply-limited).
• Vegetation / Land Use: Deforestation → 10–100× sediment yield.

Why It Matters

• Channel morphology (braided vs. meandering).
• Reservoir sedimentation (lifespan).
• Water quality (turbidity, nutrients, contaminants).
• Coastal sediment budgets (delta survival).

A river's load is its geological resume — written in mud, sand, and dissolved ions.