- Asked 2/34
- 2070 Magh · 8 marks
- 2062 Jestha (old course) · 4 marks
Surface versus sub-surface drainage
Short answer
Surface drainage removes rainfall runoff from pavement and ground surface via camber, side drains, culverts using open-channel gravity flow. Sub-surface drainage controls groundwater, seepage, capillary water via trench drains, drainage blankets using Darcy flow. Surface is visible, cheaper; sub-surface is buried, costlier, needed where water table is high.
Describe the main differences between surface drainage and sub surface drainage.
Surface drainage removes water that falls on or flows over the ground surface and the carriageway. Sub-surface drainage controls water in the soil beneath the surface: the water table, seepage and capillary water.
| Basis | Surface drainage | Sub-surface drainage |
|---|---|---|
| Water handled | Rainfall runoff on pavement, shoulders, slopes and catchment | Ground water, seepage flow, capillary and vapour water |
| Purpose | Prevent ponding and erosion; keep the surface dry | Keep subgrade moisture low, protect strength |
| Flow type | Open-channel flow by gravity | Flow through soil pores (Darcy flow) |
| Structures | Camber, shoulder, side drains, catch drains, culverts, bridges | Trench drains with perforated pipe, interceptor drains, drainage blankets, cut-off layers |
| Design basis | Rainfall intensity, runoff, Manning's equation | Permeability, depth of water table, seepage quantity |
| Visibility | Visible, easily inspected and cleaned | Buried, difficult to inspect and repair |
| Cost and time | Lower, quicker | Higher, needs skilled work and filters |
| Need | Needed on every road | Needed where water table is high or seepage is present (cuttings, hill roads) |
Both are needed together: surface drainage stops water entering the road structure, and sub-surface drainage removes the water that has already entered or comes from below.
✓ Answer checked by Claude Opus 5.5 (high effort)
Related questions
- Control of sub-surface water and seepage · Transportation Engineering I, chapter 4 · asked 15×
- Design steps of surface drainage · Transportation Engineering I, chapter 4 · asked 3×
- Surface water drainage in hill roads · Transportation Engineering I, chapter 5 · asked 2×
- Surface drainage system · Transportation Engineering I, chapter 4
- Hill road drainage structures · Transportation Engineering I, chapter 5 · asked 4×
- Subsurface drainage and its importance · Transportation Engineering I, chapter 4
- Surface versus sub-surface investigation · Engineering Geology II, chapter 4 · asked 3×
- Surface and sub-surface irrigation methods · Irrigation and Drainage Engineering, chapter 1 · asked 11×
- Speed-time curves: urban, sub-urban, main line · Utilization of Electrical Energy, chapter 4
- Short note: Sub-surface irrigation · Irrigation and Drainage Engineering, chapter 1