Short note: Local materials in design

Using local materials lowers cost and construction time, especially in the hills and Terai of Nepal where hauling cement, steel and stone is expensive. Considerations in design:

1. Availability and quantity. Survey nearby borrow areas for sand, gravel, boulders, clay and stone; the haul distance should be small, and the supply sufficient for the entire work.
2. Quality. Test strength, durability and gradation (e.g. aggregate crushing value, soundness, clay content in sand, plasticity of clay). Boulders should be hard and not weather quickly; river sand should be free from silt.
3. Suitability of the structure. Gabion, boulder or stone masonry weirs, drop structures, canal lining with stone pitching or clay lining, brick lining where bricks are made locally, and earth embankments from selected compacted soil.
4. Design adjustments. Use factors of safety suited to the lower or variable strength; thicker sections for masonry; flatter side slopes; use mortar mixes (1:4, 1:6) as tested; avoid very thin RCC sections.
5. Skilled labour and method. Design should match the skills of local workers; simple shapes, standard dimensions and labour-intensive techniques that can be carried out with community participation.
6. Cost. Compare unit rates including transport with imported materials; prefer the cheaper option that gives the required service life.
7. Maintenance. Local materials should be easy to repair by users' groups (Water Users' Associations); also consider the environmental effect of extraction (avoid river-bed over-mining).
8. Standards. Specifications and sampling must still follow Nepal standards (NS) / relevant IS codes.