Rainwater Harvesting Xiem Vn

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Regional Conference for Southeast Asia on Rainwater Harvesting in IWRM: An ExChange of Policies and Learnings November 25-26, 2008 Davao City

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  • 1. RAINWATER HARVESTING FORSLOPE AND DESERT AREA IN VIETNAM By Vu Dinh Xiem VIETNAM INSTITUTE FOR WATER AND INVIRONMENT (IWE)

2. General view and purpose

  • General view
  • Rainfall is distributed differently by seasons and regions
  • About 70% of slope and desertification area are not irrigated
  • More than 50 ethnic minority communities living in mountainous area
  • Water quality is big issue due to hydro-power building, urbanization and industrialization
  • Purpose of RWH technology studied
  • Cheap,
  • Easy (making, operation and management)
  • Using local materials

3. The research areas

  • Mountainous area
  • in the Northern
  • Desert area at North
  • and South of the Middle VN

4. Traditional method of rainwater harvesting (RWH) in VN

  • In the past
    • Using roof and tree to harvest rainwater and store to the jar and tank forhousehold water demand for rural areas
    • Terraced field in slope areas
  • In present
    • Plastic, composite, brick, rock masonry, and reinforce concrete tank to store harvesting rainwater in rainy for dry season for household demand;
    • Small storage lined by plastic for irrigation,
    • Reinforce concrete storage built in high rocky mountain for water supply and irrigation.

5. 6. Methodology

  • Classification of RWH:
  • (by FAO and WB)

WATER HARVESTING Surface WH (from stream) RWH At the surface of ground With physical work (run in to tank, pond, reservoir) With physical work W/O physical work Agricultural cultivation Agricultural cultivation At the roof and tree Drinking water W/O physical work (run in to the ground) Agricultural cultivation Drinking water Drinking water With physical work Source for harvesting By kind storage By purpose of use 7. With Physical work:

  • Brick masonry pond, tank
  • Pond lined by clay
  • Pond lined by composit layer for
  • infiltration block
  • ...

8. Method ology for design calculation for RWH system

  • Without physical work:
  • Water balance equation:
  • SWi + R + U E T D = SWi+1
  • Where:
    • SWi, SWi+1: the depth of aquifer at root-depth for time (i) and (i+1)
    • R: rainfall
    • U: runoff created by area A
    • E: evaporation at the cultivated area a
    • T: tree evaporation
    • D: infiltration
    • Z: effective root depth

Z: Chiu su hiu qu tng r Aquifer with root depth 9. Method ology for design calculation for RWH system (cont.)

  • With physical work:
  • - Determination of water storage volume V:
  • V= (W 0 .* M - Wa) + Wt (m 3 )
  • where :
    • W 0(m 3 /ha):water demand of specific tree;
    • M(ha):cultivated area;
    • Wa (m 3 ) : volume of water from other sources
    • Wt ( m 3 ): safety storage volume
  • - Determination of catchment A:
  • A = V/(C x R)(m 2 )
  • where:
    • V:water storage volume(m 3 );
    • R: design annual rainfall (m);
    • C: RWH effective coefficient.

A V M 10. Basic data for RWH system design

  • Rainfall
  • Water resources
  • Temperature, huminity, evaporation, wind
  • Topography
  • Soil
  • Type oftree and its cultivation measure
  • Economic efficiency

11. Rainwater harvesting for slope area (in the mountainous area, north Viet Nam Harvesting StoringIrrigating Cross section Plan

  • Gutters
  • Ditch take water from gutters
  • Deposition and filtrationpool
  • Pipe
  • Storage

1 3 Slope 2 4 5 12. Rainwater harvesting for desert area (in south-middle Viet Nam with annual rainfall is 500-700mm) HDPE 0.3mm for RWH catchment Pipe system PondFruit - tree crop Neem tree for wind barricade Fruit tree Neem tree for wind barricade 13. Material selection and structural calculation

  • Experiment in the Lab and field to identify suitable materials:
  • HDPE film,
  • Concrete mixed by soil and cement
  • Thin reinforce concrete
  • Brick masonry
  • Structural calculation based on selected material and shape for storage optimization with cost and stable

14. Basic design for tank by materials 15. Basic design for pond and catchment Catchment and pond Gutter B b d m=1-1,5 m=1 m=1 h i 16. Basic design for inlet 17. Pilot project:

  • 1. In Cao Phong Hoa Binh province
  • -Slope: 10% - 20%.
  • Average annual rainfall: 2114 mm, rainy season (May - Nov) = 80% annual rainfall
  • Other water resources: no
  • Tree: orange and sugar-cane
  • Cultivated area: 1000 ha

18. Planning for 1000ha 19. 20. 21. Result of model Efficiency coefficient of RWH system vs 10days rainfall 22. Result of model

  • - High efficiency of storage: 93%;
  • 90% sediment have been blocked by deposition and filtration system;
  • 85% cultivated area irrigated by gravity;
  • -High declining of soil erosion

23. Result of model

  • Local people canbuild and easy for operation and maintenance
  • Meet water demand of tree during the year

24. Result of model

  • - Orange in the project area is taller than outside by 20 - 30%.
  • - Economic analysis:
    • Cost is 10 -14 USD/1m 3storage decreased by 4-5 times comparison with reinforce concrete and rock masonry
    • B/C (12%)= 3,25
    • EIRR= 33,2%

25. Pilot project (cont.)

  • 2. In Bac Binh Binh Thuan province
  • -Slope: 5% - 10%.
  • Average annual rainfall: 700 mm, rainy season (Jun - Oct) = 85% annual rainfall
  • Baking sun, high evaporation, high wind speech;
  • Other water resources: no;
  • Soil: sand dune, desetification;
  • Tree: medical tree (local called neem)
  • Project area: 4ha

26. Planning for 4 ha Neem tree Trm tree RWH system 27. Result

  • High efficiency of harvesting (>70%);
  • Efficiency of storage is high with good coverage water lost by