Bamboos are an extremely versatile and renewable resource with multipurpose usage. Given its high compressive strength and low weight, it has been mostly used as a building material in construction. Bamboo is traditionally associated as construction material in South American, Asian and South Pacific cultures. It can be used to build entire homes, earthquake resistant structures and other many types of construction that can withstand strong winds and storms. Bamboo is durable, sustainable and environmentally friendly. It is as strong as steel in terms of tensile strength and because of its hollow body, it is stronger than concrete in terms of compressive strength. Bamboo weighs much less than wood, concrete and steel and can also be cut and laminated into sheets and planks. It is flexible and can be curved or flattened into desirable building structures by the application of heat and pressure and because of its water-resistant properties, it does not warp due to heat or dampness as wood does.
Farmers in the North-eastern state of Meghalaya, India have used bamboo in the construction of an indigenous technique of drip irrigation to irrigate their plants for over 200 years. The farmers of the Jaintia and Khasi hill regions developed this system of tapping into springs and stream water to grow betel leaves, black pepper and ‘Arcea nut’ or tobacco. The topology of the hilly areas of Meghalaya is defined by steep slopes and rocky boulders and while the area gets plenty of rainfall during the rainy monsoon season, irrigation becomes a necessity during the dry season because of poor water retention capacity as a result of the low soil depth of the hills. The steep terrain of the hills makes it a challenge to divert groundwater or bring water from distant water sources to the plantations. Faced with these challenges, tribal farmers of Meghalaya came up with a unique irrigation system, commonly known today as the “bamboo drip irrigation system”.
Mechanism of Drip Irrigation Network
The bamboo drip irrigation system is based on gravity and the steep topography of the Meghalayan hills helps to facilitate the flow of water through the network. Bamboo culms are cut longitudinally in half along their length and these portions act as the channels and diversions through which the water flows.
Water from an uphill source is tapped and led into the main bamboo channel. The main bamboo channel runs for hundreds of meters and in some cases even for a few kilometres. Water diversion devices are made from bamboos of lesser diameter than the main channel and are used to divert the water to secondary and tertiary bamboo networks.
These networks have 4 or 5 diversion stages themselves called sub-channels that lead the water to lower elevation to the base of the plants.
At lower elevation, the bamboo channels that deliver water at the base of the plants have holes cut in them through which water drips through. 18-20 litres of water flowing through the entire network, eventually gets reduced to 18 to 20 drops per minute at the end of the network.
Cost and Maintenance of the Bamboo Drip Irrigation System
The cost of building a bamboo drip irrigation system is minimal since it requires no fuel or power and bamboo itself is free or available at low cost. The system can be built by a single person or at most three people and a single installation lasts for about three years because bamboo begins to rot after this period. After a rainy season, the ground needs to be cleared and the supports must be reinforced or substituted for new supports.
An Example of the Bamboo Drip Irrigation System
In Blake Garden in Kensington California, water is collected from the rooftop and stored in a 200- gallon cistern. Water flows from the cistern through a network of bamboo channels and irrigates plants in a greenhouse. This is a well-known example of an urban setup of the bamboo drip irrigation system.
Properties of Bamboo as a Building Material
Tensile Strength: Bamboo is able to resist more tension than compression. The fibres of bamboo run axially and the tensile strength of these fibres is higher than that of steel. The vascular bundles beneath the outer skin have a tensile strength of up to 400 newtons per millimetre squared. Strong wood fibres have a tensile strength of only about 50 newtons per millimetre squared.
Slimmer tubes of bamboo have a higher compressive strength value than bigger and broader tubes. The portion of lignin inside bamboo culms affects compressive strength. Broader bamboo tubes have a minor part of outer skin along with high portions of cellulose in the bamboo fibres which influence buckling and tensile strength in bamboo.
A high number of strong fibres in the outer wall of the bamboo tube provide the tube with elasticity as well in addition to tensile and compressive strength. A high elastic modulus defines a good quality bamboo tube and this high elasticity of bamboo makes them ideal as construction material in areas prone to earthquakes.
Bamboo shrinks more than wood when it loses water and bamboo canes can tear apart at the nodes. Bamboo shrinks in its cross-section by 10-16% and in its wall thickness by about 15-17%. Therefore, it is important to prevent water loss when using bamboo as a construction material.
Bamboo fibres have a high content of silicate acid which provide it with high fire resistance. A bamboo tube filled up with water can withstand temperatures up to 400 degrees Celsius.
Advantages of Bamboo for the Construction of Drip Irrigation System
- Bamboo is light, strong, versatile and durable
- It is environment-friendly
- It is easily accessible to the poor
- Bamboo is a self-renewing source of nature
- It is fast-growing and abundant
- It is highly productive
- Bamboo is a low-cost material
- Construction of Bamboo Drip Irrigation System
The construction of a bamboo drip irrigation network is based on a simple rule of thumb – the ratio of the diameter of the primary channel to the diameter of tertiary channel determines the quantity of water that will reach the plantation. A single network can be constructed by two labourers and one network can cover one hectare of land in 15 days.
- Bamboos of varying diameters are used to build the channels, support structures, diversion pipes and strips.
- The channels are held above ground level by Y-shaped sticks
- One stretch of the channel is lashed to another by a thin cord or bamboo strips
Indigenous tools like the ‘Dao’ which is a type of local axe and chisels of various shapes and design are used to build the bamboo network. A bamboo drip irrigation system network is built with such subtle skill that water wastage by leakage is minimum. It is a skill that can be mastered with only years of observation and experience.