On hill roads, intermediate catch-water drains (in addition to the main catch-water drain) are provided under which circumstances?
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AWhen the catchment area of the hillside above the road is large
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BWhen rainfall intensity is heavy
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CWhen a single catch-water drain is inadequate to intercept surface runoff
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DAll the above
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E
Answer
Correct Answer: All the above
Explanation
Introduction / Context:Catch-water drains run along the uphill side of hill roads to intercept runoff before it reaches the carriageway and slopes. In severe conditions, a single drain may be insufficient.
Given Data / Assumptions:
- Steep hillside with significant contributing catchment.
- Events of high-intensity rainfall are possible.
- Objective is to prevent erosion, scouring, and flooding of the roadway.
Concept / Approach:Where inflows are large or concentrated, intermediate drains at different bench levels divide and safely convey runoff, reducing peak flow into any single channel and improving stability.
Step-by-Step Solution:
Assess contributing area and rainfall intensity → estimate peak hillside runoff.Check capacity of single catch-water drain.If inadequate, add intermediate drains to share the load and protect the roadway.Verification / Alternative check:Hydraulic sizing shows that multiple drains lower flow depth/velocity, preventing overtopping and erosion.
Why Other Options Are Wrong:Any single listed condition can justify extra drains; restricting to only one factor ignores combined hydrologic needs.
Common Pitfalls:Underestimating peak intensities; neglecting sediment/debris which further reduces capacity of a single drain.
Final Answer:All the above