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