A permaculture enthusiast may want to inquire: how do the structures of both the Great Wall of China and Water Harvesting System relate
A Brief history of the Great Wall
Designated as a UNESCO World Heritage site in 1987, the Great Wall of China has always been the most visible symbol of power and influence of the past Chinese Empires. Initially built by Emperor Qin Shi Huang (c.259-210 B.C.) in the third century as a deterrent to prevent nomadic barbarians from finding their way into the Chinese Empire. Since then, from Qin, Sui to Tang dynasty, the Great Wall had undergone several transformations, the prominent one being its reconstruction under the powerful Ming dynasty (1363-1644), which considered the defense of China as its main priority and extended the Great Wall from East to West to cover places we know today as Beijing, Inner Mongolia, Shanxi, Gansu, Shaanxi, Ningxia, Hebei, Liaoning and Tianjin. Fortresses and gates (three inner and three outer passes) were constructed along the Wall to facilitate limited and monitored entry and exit into the Chinese Empire.
The Great Wall’s Contour Structure
Of utmost interest to structural engineers or anyone who cares about structural strength is all the intricacies that went into the construction of the Great Wall. The Great Wall is a more than 10,000 li (a li is a third of a mile) strong, mammoth fortification that extends across Chinese states, from the China Sea port of Shanhaiguan to Gansu Province. The Wall was made from stone and earth, and a huge number of soldiers, commoners and convicts were used as construction workers. In certain areas, some parts of the Wall overlapped to provide the much-needed strength for the structure, and a long, undulating contours could be seen all along the Wall. With a base width of 15 to 50 feet and a height of 15 to 30 feet, China’s Great Wall towered high into the sky with 12-feet ramparts mounted on its top. Guard towers were scattered at intervals on top of the Wall. The Wall’s design takes after the contours of the land and mountains it meanders through. This is an interesting perspective in the overall structural aesthetics of this World Heritage treasure, because these contours may have been responsible for its enduring strength and, surprisingly enough, help it withstand hundreds of years of all manners of climatic and circumstantial pressures without falling into a state of disrepair.
Water Harvesting System
There are probably some strategic comparisons between the structure of the Great Wall of China and that of Water Harvesting System as shown in vivid explanations provided later in this article. A water (rainwater) harvesting system has become a viable tool of environmental sustainability in cities, towns and small villages as people consciously embrace the process of water conservation. The good thing about rainwater harvesting system is that once installed, it could last for many years. This characteristic strength is attributable to the design of its features (or components), and their relative arrangement in contours or spiral configuration.
Typically, there are two forms of water harvesting systems:
(i) Rooftop rainwater harvesting and
(ii) surface runoff harvesting. For its complexity and being the more applicable rainwater harvesting process used by many cities, municipalities and residential estates, we will be concentrating on rooftop rainwater harvesting in this article.
The best way to understand how rooftop rainwater works is to explore the functions of its components.
Here are the detailed overview of the components of the rooftop water harvesting system:
(i) Catchments: They are an essential part of the rainwater harvesting system: they are actually the first surface to capture the rainwater that will later be transported to the reservoirs or storage facilities. Catchments can be a terrace, unpaved or paved open ground or a courtyard. If they are a terrace, they could be a sloping, convoluted roof or flat RCC/stone roof. Without a firm and strong catchment, it may be difficult to harvest adequate rainwater that would be utilized for several domestic purposes. While setting up a water harvesting process, builders or construction experts must pay serious attention to the strength of these catchments.
(ii) Transportation: It is one thing to capture enough rainwater and it is another to install a functional transportation network that would convey the water down the system. A good rule of the thumb is to connect pipes (some pipes are ringed with internal contours) or drains (brick drains have contours, too!) between the catchments and the storage facilities or reservoirs. It is advisable that these water pipes be resistant to Ultra Violet rays, like ISI HDPE/PVC pipes, and they should also be of required capacity. It would be a gross miscalculation to use small pipes to collect mass of water that gush from a large catchment facility. Setting up appropriate transportation mechanism will help transport rainwater down from the sloping roofs through gutters or terrace. The mouth of the terrace should have wire mesh that will be useful in removing debris and other particles from the water that is to be transported to the storage tanks.
(iii) First flush: If your goal is to harvest clean and uncontaminated water, you must be ready to set up first flush system. This is a device that will help you flush off the very first water collected after it started to rain. No doubt, the first mass of water harvested will be dirty because of some particles, contaminants, silt and sandy wastes that may have been deposited on the roofs during the dry season. So, if you are aiming at gathering nothing but the cleanest water, your first flush system should be immediately installed as you put up your rainwater harvesting system.
(iv) Filter: To achieve your goal of collecting clean, microbe-free water, it is imperative that you have an efficient filtration mechanism in place. It is possible to assume that your first flush system may not effectively remove all contaminants, turbidity, microorganisms, colorful materials and so on that the rainwater may have contained, but filters are intricately designed to remove all contaminants including leaves, debris, stones, silt, stones, and other unwanted items that could pollute the water and make it unusable. There are different kinds of filters that you could utilize, highlighted below are some commonest filter types:
Sand gravel filters:-Everyone knows this kind of filter, and it is built by brick masonry. The inside is filled with pebbles, sand and gravel. You need to use wire mesh to separate each layer of the filter.
Charcoal filter:-You can make a charcoal filter by just adding some charcoal between gravel and sand layers in the sand gravel filter described above.
PVC-Pipe filter:-It is possible make a filter of this kind by using a PVC pipe of 1 to 1.20 m length. The desirable diameters should be commensurable with the area of the roof. Take for instance, a 1500 sq. ft. roof will be fine with 6 inches diameter pipe, while 8 inches diameter pipe should be used for more than 1500 sq. ft. roof. Wire mesh is used to divide the pipe into different separate compartments, and it is advisable that each compartment be filled alternately with gravel and sand. Insert a layer of charcoal between the two layers. The tube-like ends of the pipe filter should be small enough so as to be able to connect them with the inlet and outlet structures of the water harvesting system. You can choose to have your pipe filter lay horizontally on the ground or have it stand up vertically.
Sponge filter:-If you are looking for the cheapest and easiest filter to use, sponge filter comes in handy. Its structure is very simple: all you need to do is to set up a layer of sponge in the middle of drum and it is ready for use!
Contour Accuracy and Tensile Strength of Ceramic and Metal Joints
In their studies published in the journal of Advanced Engineering Materials, Li et al. (2012) proved that there is a certain correlation between contour accuracy and tensile strength of ceramic and metal joints. Without meaning to replicate their complex research findings in this article, it is quite clear from their work that when a particular structure that is composed of ceramic or concrete and metal joints has accurate and recurring contours, it tends to enjoy some tensile strength that could make it withstand pressures of any kind.
A permaculture enthusiast may want to inquire: how do the structures of both the Great Wall of China and Water Harvesting System relate to Li et al. interesting finding? It is true to acknowledge that the two structures are not absolutely similar, but there are some similarities and differences that could be explored and applied in the design of stronger and enduring rainwater harvesting systems. So, outlined below are some useful comparisons we can conclude from examining the two structures discussed about in this article.
(i) Continuous contours: Recurring contours creates a condition of higher contour accuracy. A structure with higher contour accuracy tends to become stronger than the one with lower contour accuracy. Considering the examples in this article, the Great Wall of China has more regular contours than the Water Harvesting System, hence it is stronger. And a good thing about a very strong structure is that it is very sustainable and can survive any unexpected pressure. Here are some questions to be considered: Will it be possible to make the Water Harvesting System stronger by increasing its contour accuracy? How can this contour accuracy be achieved in order to increase the tensile strength of the water harvesting system components? In as much as there is little research done in this respect, one can only conjecture some possibilities: First, designing the components of water harvesting system in a cyclical contours may add more strength to each of them. Second, the overall strength of the system can depend on the sum of the strength of individual components. In the light of this, anyone thinking of durability and sustainability of their water harvesting system should concentrate mainly on the ability of increasing the contour accuracy or regularity of each component of their system.
(ii) Sustainable design: It is undeniable to aver that the Great Wall of China’s design provides the much-needed strength and durability that each Emperor had had in mind when constructing the fortification. If the design wasn’t done properly, the Wall could have suffered serious damage through the invasion of the nomadic barbarians, and Chinese people may have been attacked from every corner. Similarly, to make an enduring water harvesting system, emphasis must be laid on the design. It must be a design that gives room for the strengthening of the individual components of the system. It must consider the significance of contour accuracy. According to Li et al. (2012), a system’s tensile strength can be improved through the process of increasing its contour accuracy. This can be done at the beginning of the construction of the water harvesting system or during a routine reconstruction. Just as every new Chinese Emperor made it a duty to rebuild the Great Wall in their days, so also regular reconstruction must be carried out on the water harvesting system to guarantee its continued strength and sustainability.
In conclusion, the desire of every owner of a water harvesting system is to use it for as long as possible. The bulk of information revealed in this article indicates that such an expectation can be met only if efforts are made to pay attention to the design of the system and consider the probability of meeting a very important requirement: which is making sure that the contour accuracy or the rate of contours recurring along the system is constant.
Li, C., Kuhn, B., Brandenberg, J., Beck, T., Singheiser, L., Bobzin, K., Bagcivan, N., & Kopp, N. (2012). Improving Contour Accuracy and Strength of Reactive Air Brazed (RAB) Ceramic/Metal Joints by Controlling Interface Microstructure. Advanced Engineering Materials, Volume 14, Issue 6, pages 394-399. https://onlinelibrary.wiley.com/doi/10.1002/adem.201100274/full
The History Channel, 2015. ‘Great Wall of China’. https://www.history.com/topics/great-wall-of-china
The Constructor, 2015. ‘Methods of rainwater harvesting’. https://theconstructor.org/water-resources/methods-of-rainwater-harvesting/5420/