Beach profile behaviour: which statements correctly relate sediment characteristics to beach slope and profile evolution under waves and wind?

Introduction / Context:
Beach morphology is governed by sediment size, sorting, and hydrodynamic forcing. Understanding how grain size and angle of repose influence the equilibrium slope helps coastal engineers predict shoreline response and design stabilization measures.

Given Data / Assumptions:

• Coarser sand and shingle typically possess higher angles of repose than fine sand.
• Finer, uniformly sorted particles are more easily mobilized by swash and wind.
• We consider qualitative tendencies, not a specific storm case history.

Concept / Approach:
Steeper slopes are associated with coarser materials due to higher percolation rates and greater resistance to motion, reflected in a larger angle of repose. Conversely, finer, uniform sediments transport more readily, migrating leeward and flattening the beach. These relationships are widely observed in berm-bar systems.

Step-by-Step Solution:
Evaluate (a): claims coarser with smaller angle gives steeper slope — contradictory, hence incorrect.Evaluate (b): coarser with greater angle leads to steeper slope — consistent with theory and observations.Evaluate (c): small uniform particles moving leeward flatten the profile — also consistent.Therefore, the correct combined choice is “Both (b) and (c).”

Verification / Alternative check:
Empirical beach profiles and Dean-type equilibria reflect the trend of coarser sediments forming steeper foreshore slopes.

Why Other Options Are Wrong:

• (a) reverses the angle-of-repose relationship.
• Single-statement options omit the complementary mechanism of leeward fine-sediment transport.

Common Pitfalls:
Assuming all beaches behave identically regardless of wave climate; ignoring permeability effects that enhance backwash infiltration on coarse beaches.

Final Answer:
Both (b) and (c).