In catchment hydrology, which definition best describes surface runoff?
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AWater absorbed by soil
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BWater intercepted by buildings and vegetative cover
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CWater filling surface depressions only
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DWater that reaches and flows through stream channels
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EWater that evaporates back to the atmosphere
Answer
Correct Answer: Water that reaches and flows through stream channels
Explanation
Introduction / Context:Surface runoff links precipitation to streamflow and is a critical input to flood routing, reservoir design, and watershed management. It is important to distinguish runoff from other precipitation losses.
Given Data / Assumptions:
- Runoff represents the liquid water contribution to streams and rivers originating from precipitation (and snowmelt) after losses.
- Losses include interception, infiltration, and depression storage plus evapotranspiration.
Concept / Approach:After rainfall reaches the ground, part is intercepted or infiltrates. Some fills micro-depressions (depression storage). Once these losses are satisfied and rainfall intensity exceeds infiltration plus storage, the excess flows overland to channels; this overland flow, together with direct channel precipitation and interflow contributions, becomes surface runoff reaching and moving through stream channels.
Step-by-Step Solution:
1) Identify hydrologic components: interception, infiltration, storage, evaporation, runoff.2) Define surface runoff as the part of precipitation that becomes streamflow via overland or near-surface pathways.3) Choose the option that states 'water that reaches the stream channels'.Verification / Alternative check:Standard hydrology texts define surface runoff (direct runoff) as the portion of water that appears in the channel during or immediately after a storm event, consistent with option (d).
Why Other Options Are Wrong:
- Absorbed by soil / intercepted / evaporated: These are loss components, not runoff.
- Filling surface depressions only: This is storage before runoff initiation.
Common Pitfalls:
- Confusing interflow/throughflow with deep groundwater baseflow.
- Ignoring the threshold behavior when depression storage is satisfied.
Final Answer:Water that reaches and flows through stream channels