Around 90% of the water consumed in the agricultural sector is constituted of groundwater. This means, in the state of groundwater depletion crisis, the major setback is faced by farmers and cultivators and with this, the entire dependent population will have to suffer. Under this threat, the gutter-connected greenhouse rainwater harvesting solution is bringing the required relief.
Constructing a greenhouse for the cultivation of vegetables and flora is a sustainable method of farming. It is a transparent structure of walls and roof, made chiefly with materials like glass and are used to grow plants which require regulated climatic conditions. The crops are exposed to an optimal amount of sunlight for required warmth and protection against excessive warm or cold conditions. The modern greenhouses are equipped with screening installations, heating, cooling, lighting, computer to provide optimal conditions for plant growth and managing micro-climate (air, temperature, relative humidity, and vapor pressure deficit).
Like other farming, irrigation is also a hefty requirement for greenhouses. The greenhouse crops may need as much as 0.4 gallons of water, per square foot of growing area, per day. The volume, of course, depends on the type of the crop, time of year and location. Setting up a rainwater harvesting system, in conjunction with greenhouse, helps in meeting this demand of greenhouses, especially in the groundwater scarce and arid regions of the world.
Expected Harvest through greenhouse RWH systems
The estimated harvest of rain, from a greenhouse rainwater harvesting system, can be made by using a simple calculation; divide the total catchment area measured in square feet by 1000 and then, multiply the resultant by 550. This will determine gallons of water to be collected, per one inch of rain. Further, multiply the result by the average annual rainfall in your area, to get the amount of water you could collect. An approximate 20% of water loss is observed due to evaporation, leaks, plugged gutter, etc. On an average, a 1-inch rainfall on an acre of greenhouse amounts to 550 gallons per 1000 sq. ft. of the catchment area. The amount is enough to make a huge difference.
Types of Greenhouses
The basic construction of greenhouses depends upon many aspects, which includes the type of material used, construction method, facilities, and equipment rendered. Hence, there is more than one way of categorizing the type of greenhouse. Few common ones are as under:
- Based on location
The colder regions such as central and northern Europe have glass greenhouses while the warmer and Mediterranean regions use plastic films to cover their greenhouses for extra protection against the rough environment. These regions have Venlo-type, wide-span, plastic, and arched greenhouses.
- Based on the shape
Most common shapes found in greenhouses are
- Gable roof or pitched roof,
- Sawtooth or shed roof,
- Round-arched tunnel,
- Round arch with a vertical sidewall,
- Pointed arch with a sloping sidewall,
- Pointed arch with a vertical sidewall.
- Based on the construction materials
The greenhouse can be constructed with wood, steel, aluminium or their combination. Each of these has its own pros and cons. For cladding, glass, synthetic panes or rigid plastics and plastic films are commonly used.
- Based on the facilities and equipment
- Low technology greenhouses
They use simple technology, with few or no automation equipment. The structure is low lying (may be less than 3 meters in total height), made up of wood or bamboo sticks or steel and do not have vertical walls. The ventilation is majorly passive, and the internal climate strongly depends on external conditions. This type supports low yielding crops and requires high maintenance against pests and crop diseases.
- Medium technology greenhouses
They are more steady structure since they use galvanized iron and aluminium in their construction. The vertical walls are 2 to 4 meters tall and the total height is kept less than 5.5 meters. They are covered by either single or double skin plastic film or glass. They use varying degrees of automation for internal climate control.
- High technology greenhouses
They are modern and the most sophisticated structures build with galvanized iron support structures, aluminium glass supports, glass as a covering material. The vertical wall’s standing is at least 4 meters, with the roof peak being up to 8 meters above ground level. They are equipped with high-end computer-based technologies and facilities to provide optimal ventilation, temperature, and incident light, to provide a favourable growth environment through climate control.
Structure of a Gutter-connected Greenhouse
Any type of greenhouse can be combined with a rainwater harvesting system. The roof of the greenhouse is taken as a catchment surface with gutters installed and have a series of the downspouts, which are connected to a 4-inch or 6-inch PVC pipe. With the increase in the number of gutters, the downspouts are connected to larger pipes (the length of the end pipes can go up to 18 inches or larger, for big greenhouses). The pipes must be installed with a minimum slope of a 1/16th inch per foot, with cleanouts at every 100 ft.
The structure uses filtration methods with the use of first flush systems and filters, to restrict debris and contaminated substances from entering the pipes and storage units.
The storage tank of common materials (concrete, steel, wood, plastic) are used to collect filtered water. For large acres of greenhouses, the construction of the pond is usually preferred to retain the harvested rainwater. The size of the pond is recommended by the licensed engineer, after considering the capacity of the RWH system and the legally allowed limits. A vinyl liner is placed at the bottom of the pond to prevent seepage, for the areas where the soil has the porous characteristic. This is a suitable option, but the water collected in the pond is exposed to contamination by algae growth.
Finally, the water from the storage area is distributed to the greenhouse with the help of the normal irrigation system.
The overflow is managed by redirecting the excess flow to a wetland or drainage area, to avoid flooding one’s own property, as well as that of its neighbours.
Benefits of using greenhouse rainwater harvesting
Along with the usual benefits of rainwater harvesting, there are following unique benefits of greenhouse RWH systems.
- Rainwater is generally soft with very few chemicals. It provides a soothing effect on the quality of the crop yield.
- The gutter-connected greenhouse structure can harvest large quantities of water at a reasonably low cost.
- It promotes convenient irrigation by reducing the stress of physically watering the cultivation.
- The jamming of micro-irrigation pipes is a big concern. The chemical composition of rainwater helps in reducing this problem, to a great extent.
- The cost of running and maintaining the greenhouse is reduced due to savings on the cost of labour, pesticides and electricity for pumping water.
Greenhouse rainwater harvesting is now a worldwide phenomenon. It is even supported by the government of many states, to promote environment-friendly cultivation of crops.
Rooftop filters available at Chaitanya, for your Greenhouse RWH initiatives
Keeping a pace with advanced technologies, Chaitanya rain harvest products and systems offers the most modern filtration systems for your rainwater harvesting systems. Be in touch with our engineers and hydrogeological survey team to prepare customized reports for your greenhouse rainwater harvesting project.