- Asked 2/30
- 2078 Kartik · 3+3 marks
- 2080 Baisakh · 2+2 marks
Major sources and selection factors
Short answer
Major sources are rain, rivers, lakes, reservoirs, springs, wells, and infiltration galleries; surface sources are plentiful but need treatment, ground sources have limited yield but better quality. Selection depends on dry-season quantity, quality, distance and elevation for gravity flow, cost, reliability, protection, water rights, social acceptance, and environmental effects.
Discuss/list the major sources of water with respect to quantity and quality, briefly describing them with examples. What are the key factors to be considered while selecting a water source?
Major sources of water
| Source | Quantity | Quality | Example |
|---|---|---|---|
| Rain water | Limited; seasonal | Fairly pure and soft but slightly acidic; picks up dust from roofs | Roof catchment tanks |
| Rivers and streams | Large, fluctuating | Turbid, soft, polluted downstream | Bagmati, Trishuli, Seti |
| Lakes and ponds | Moderate to large | Clear but may have algae | Phewa Lake (Pokhara) |
| Impounded reservoirs | Large and controlled | Good after settling | Kulekhani reservoir (Indra Sarovar) |
| Springs | Small to moderate | Clear, bacteriologically safe | Hill springs, dhunge dhara |
| Wells (shallow/deep) | Small to large | Hard, clear; shallow wells may be polluted | Tube wells in the Terai |
| Infiltration gallery | Small to moderate | Naturally filtered | River banks in the Kathmandu valley |
Surface sources are plentiful but need treatment; ground sources give better quality but their yield is limited.
Factors for selection of a source
- Quantity: the yield in the dry season must satisfy the demand at the end of the design period.
- Quality: wholesome, or easily treatable at low cost.
- Distance and elevation: a short pipeline and a higher level for gravity flow, avoiding pumping.
- Cost: construction, operation and maintenance.
- Reliability and protection: perennial, and safe from pollution, floods and landslides.
- Water rights and social acceptance: no conflict with existing users.
- Environmental effect: minimum effect on downstream flow and ecology.
✓ Answer checked by Claude Opus 5.5 (high effort)
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