In civil engineering hydrology, which statements about infiltration capacity and the actual infiltration rate are correct?

Introduction:
Infiltration is the entry of water from the ground surface into soil. Designers must distinguish the soil’s maximum ability to absorb water (infiltration capacity) from the instantaneous absorption that actually occurs (infiltration rate). This distinction controls runoff generation, detention sizing, and irrigation scheduling.

Given Data / Assumptions:

• Statements compare rainfall intensity with soil infiltration capacity.
• Soil properties and antecedent moisture influence capacity.
• No ponding or overland‐flow routing is explicitly modeled here.

Concept / Approach:
Infiltration capacity is the upper limit (maximum possible rate) at which soil can accept water under current conditions. The actual infiltration rate cannot exceed this limit; it is supply-limited when rainfall intensity is low and soil-limited when rainfall intensity is high.

Step-by-Step Solution:
If rainfall intensity > capacity ⇒ actual rate = capacity (excess becomes surface storage/runoff).If rainfall intensity < capacity ⇒ actual rate = rainfall intensity (soil could accept more, but supply is limiting).By definition, infiltration rate is the instantaneous prevailing entry rate at the surface.

Verification / Alternative check:
Standard hydrology texts (Horton concept) state f_actual ≤ f_capacity at all times; equality holds when rainfall supply is not limiting.

Why Other Options Are Wrong:

• Each individual statement is true, but choosing only one ignores the full relationship.

Common Pitfalls:

• Equating infiltration rate with capacity in light rain (supply-limited cases).
• Assuming infiltration can exceed capacity (it cannot).

Final Answer:
All the above.