Design of Rainwater Storage Basins

Different types of storage basins can be built, if enough space is available near the greenhouse:

• Simple basins, dug in the soil, if the soil at the bottom of the basin is sufficiently watertight.

Month

Pre l/m2 month

CV l/m2 month

dim

ET0 l/m2 day

CWRm l/m2 month

STPm l/m2 month

STPm

accumulated

Jan

259

233

31

0.86

27.7

+205.3

+495.8

Feb

175

157.5

28

1.55

45.1

+ 112.4

+608.2

Mar

79

71

31

2.24

72.2

-1.2

+607

Apr

38

34

30

3.5

109.2

-75.2

+531.8

May

33

30

31

4.75

153.1

-283.1

+248.7

Jun

13

12

30

5.9

184.1

-172.1

+76.6

Jul

3

2.7

31

6.4

206.3

-203.6

-127

Aug

3

2.7

31

5.6

180.5

-177.8

-304.8

Sep

15

13.5

30

3.82

119.2

-105.7

-410.5

Oct

53

48

31

2.25

72.5

-24.5

-435

Nov

119

107

30

1.11

34.6

+72.4

+72.4

Dec

267

240

31

0.68

21.9

+218.1

+290.5

Table 14.2 Data for the calculation of the storage volume in Antalya (Turkey)

• Earth basin lined with plastic film.

• Concrete basins; durable, need less maintenance, but are very expensive.

All storage basins should be covered at the surface by swimming plastic film, for example, to avoid too high evaporation.

Figure 14.1 shows the arrangement of a plastic-film water basin with water tubes from the gutters to the basin (von Zabeltitz and Baudoin 1999). To collect heavier rainfall, the gutters and tubes leading to the storage basin must have an adequate diameter. The tubes leading the water to the basin should have a slope of about 1:50-1:100. The following diameters are recommended:

Greenhouse floor area (m2)

Tube diameter (mm)

<400

100

400-700

125

700-1,200

150

If the level of the storage basin is deep enough, the rainwater can be led via open gutter lined with plastic film.

The basin has to be situated at the deepest point of the site. If this is not the case and the greenhouses are placed deeper than the basin, the rainwater can be con­ducted into the basin by a siphon system (Fig. 14.2). Watertight tubes are installed

sloping downward to a deepest point near the basin, and from there into the basin. The gutters have to be above the water level of the basin. When rainwater in the tubes rises above the water of the basin, positive pressure develops, and the water flows from the tube into the basin.

When digging out the basin, the soil is thrown up around the basin as an embankment (Fig. 14.3).The angle of the embankment is about 34°, or it has a ratio of 1:1.5. Thus it is within the range of frictional angles of most types of soil.

In the case of a 2 m-deep square basin, the measurements a, b, c and d have the following values (m) for different quantities of water:

Water quantity(m3)

a(m)

b(m)

c(m)

d(m)

200

7.25

13.03

12.8

0.75

400

11.7

17.5

17.25

09

600

15.05

20.8

20.6

1.0

Updated: June 30, 2015 — 5:23 pm