RAINWATER HARVESTING FOR SLOPE AND DESERT AREA IN VIETNAM

By Vu Dinh Xiem

VIETNAM INSTITUTE FOR WATER AND INVIRONMENT (IWE)

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

The research areas

Mountainous area

in the Northern

Desert area at North

and South of the Middle VN

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 for household 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.

Methodology

1. 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 cultivationAgricultural

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

With Physical work:

Brick masonry pond, tank

Pond lined by clay

Pond lined by composit layer for

infiltration block

...

Z: Chiều sâu hiệu quả tầng rễ

Methodology 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

Methodology for design calculation for RWH system (cont.)

With physical work:

- Determination of water storage volume V:

V = (W0.*M- Wa) + Wt (m3)

where:

+ W0 (m3/ha): water demand of specific tree;

+ M (ha): cultivated area;

+ Wa (m3): volume of water from other sources

+ Wt (m3): safety storage volume

- Determination of catchment A:

A = V/(C x R) (m2)

where:

V: water storage volume (m3);

R: design annual rainfall (m);

C: RWH effective coefficient.

A

V

M

Basic data for RWH system design

Rainfall

Water resources

Temperature, huminity, evaporation, wind

Topography

Soil

Type of tree and its cultivation measure

Economic efficiency

Harvesting Storing Irrigating

1. Gutters2. Ditch take water

from gutters3 Deposition and

filtration pool4 Pipe5 Storage

1

3

Slope

2

4

5

Rainwater harvesting for slope area (in the mountainous area, north Viet Nam

Cross section

Plan

Rainwater harvesting for desert area (in south-middle Viet Nam with annual rainfall is 500-700mm)

HDPE 0.3mm for RWH catchment

Pipe system

Pond

Fruit - tree crop

Neem tree for wind barricade

Fruit tree

Neem tree for wind barricade

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

0

1

23

4

5

6

7

T (ngµy)

BÓ g¹ch x©y BÓ BT ®Êt BÓ BT vámáng

BÓ HDPE

(So s nh cï ng mét dung tÝch 30m3)

BiÓu ®å so s¸ nh thêi gian thi c«ng

Basic design for tank by materials

a1H

1

H2

a3

H

a2 a1L

L1 L1

c¾t däc bÓ x i m¨ ng ®Êt

H2

H

L1

L2

L

H1

C¾t däc bÓ x i m¨ ng vá mángC¾t däc bÓ HDPE

Basic design for pond and catchment

B

b

d

m = 1-

1,

5

m = 1m = 1

h

i

Catchment and pond Gutter

Basic design for inlet

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

Planning for 1000ha

DiÖn tÝch hiÖn t¹ i tr ång cam : 12,56 ha

DiÖn tÝch hiÖn t¹ i tr ång mÝa: 11,6 ha

DiÖn tÝch ®Êt canh t¸c : 24,16 ha

Tæng diÖn tÝch khu quy ho¹ch: 25,4 ha

Sè hé d©n canh t¸c : 24 hé

Sè hÖ thèng thu tr ÷ n í c theo quy ho¹ch: 220

DiÖn tÝch quy ho¹ch tr ång cam : 24,16ha

Tæng dung tÝch n í c cÇn thu tr ÷:8480 m3

S¬ ®å ph©n v ï ng t í i

1100 m2

750 m2

BÓ XM ®Êt 24 m3

BÓ XM ®Êt 24 m3

BÓ g¹ c h 35m3

1400 m2

BÓ HDPE 54 m3

Result of model

Efficiency coefficient of RWH system vs 10days rainfall

C = 0,1571R+ 7,9329

r2 = 0,6271

0

5

10

15

20

25

30

35

40

45

50

55

60

65

10 40 70 100 130 160 190 220 250 280 310 340

Lượng mưa R (mm)

Hiệ

u q

uả

thu

trữ

C (

%)

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

Result of model

- Local people can build and easy for operation and maintenance

- Meet water demand of tree during the year

Result of model

- Orange in the project area is taller than outside by 20 - 30%.

- Economic analysis:

Cost is 10 -14 USD/1m3 storage decreased by 4-5 times comparison with reinforce concrete and rock masonry

B/C (12%)= 3,25

EIRR= 33,2%

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

Planning for 4 haNeem tree

Trôm tree

RWH system

Result

- High efficiency of harvesting (>70%);

- Efficiency of storage is high with good coverage water lost by <10%.

Result

- Plant is growing well;

- Economic analysis: EIRR= 22,8%;

- New project has been implementing with 100 ha;

Some other projects applying this technology in VN

- Environmental project for desertification declining in southern of Middle Viet Nam funded by government

- Project for desertification declining funded by GEF (UNDP) in Thanh Hoa, Nghe An provinces;

- Rural development project in mountainous area in Binh Thuan province.

Thank you for attention!