Rainwater Utilization of Quake Disaster Area Rebuilding Programs in Taiwan

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1 Rainwater Utilization of Quake Disaster Area Rebuilding Programs in Taiwan Shih-Chi Lee, Min-Chaur Lin, Wen-Hong Chou, Jen-Chung Chen Researcher, Energy & Resources Laboratories, Industrial Research Institute, Hsin-Chu, Taiwan, Introduction Utilizing rainwater harvesting in schools brings two major benefits. The most direct and substantial benefit is the saving in water and electricity bills. The educational benefit is that students learn to appreciate water resources and make water saving a habit and contribute to its spreading. School reconstruction works in the disaster areas must be planned as a whole and it is compulsory to include a rainwater catchment system. This is in fact much easier than a reconstruction design of an existing building. All data must be accurately calculated and all measurements must be estimated by professionals in order for every rainwater catchment system to achieve its ultimate economic effect. Principles for Planning and Economic Evaluation of Hope Engineering Project Considerations and analysis for the planning of rainwater catchment systems in the Hope Engineering Project are: Water Consumption Population and Purposes: Setting the water consumption, population and purposes. System Capacity Analysis: Continuity equations, as shown below, can be applied to calculate the capacity of each water storage tank. K t+1 = K t +V t -R t if K t +V t -R t >0 OR K t+1 = 0 if K t +V t -R t <0 where K t : Volume of water stored in the tank at the end of time period (day) t V t : Volume of collected rainwater during the time period, R t : Volume of water used during the time period. This method uses the actual daily rainfall data to calculate the maximum required capacity in order to avoid any possible overflow, i.e. water resource wastage. By means of the long-term rainfall data in the area, K t during different time periods can be simulated and capacity of the water storage tank can be set as: K max =max (K t ) Then, after the capacity is set, project selection can be carried out based on a water supply rate of between 30% and 50%. 1

2 Equipment Type and Selection: Equipment should be selected based on factors, such as school building designs and number of students. Construction Cost Analysis: Cost analysis for the rainwater catchment system should be performed based on factors, such as construction capacity, rainfall condition and water consumption; costs for building constructions, such as excavation, spoil, and water repelling works; and expenses for water, electricity, maintenance, and others. Items included in equipment benefit analysis are: (a) Equipment service time, (b)annual interest rate of investment, (c)catchment area and the annual public water volume can be substituted, (d) Costs of rainwater processing equipment, (e) Annual investments on equipment, (f) Operation and maintenance costs. In Taiwan, the current water rate is approximately US$ 0.32/ton, while the average development costs of water supplied from the existing reservoirs and from the newly planned reservoirs are approximately US$ 0.73/ton and more than US$ 1.52/ton respectively. For the water rate in Taiwan to rationally reflect supply costs, it is only sensible to use the average development cost of water supplied from the existing reservoirs (at US $0.73/ton) for P/E calculation and use P/E>1 as the basis for the determination of construction necessity. Selection principles used for the Hope Engineering Project After completing the said economic evaluation at each school to be reconstructed, selection should be made based on the following principles: 1. For schools whose construction costs of all rainwater processing equipment are lower than the average development cost of water supplied from the existing reservoirs, a standard rainwater catchment system should be installed. 2. For schools whose construction costs of all rainwater processing equipment are higher than the average development cost of water supplied from the existing reservoirs, rainwater education facilities may be installed after evaluating the conditions of respective school based on the following principles: For schools with more than 1,000 students, underground piggy banks for rainwater should be installed. For schools with less than 1,000 students, above-ground piggy banks for rainwater should be installed. Case Studies Chung-Yuan Primary School Geographical Features: It is located at Chao-Tun, Nan-Tou County in the central part 2

3 of Taiwan where 87.5% of rainfall occurs during the rainy season (from April to October), the local average annual rainfall is at approximately 1,730mm and, over the years, the maximum daily rainfall depth is 405mm. Water Consumption Conditions: There are approximately 800 students in this school and each year vacations are between July and September and between January and February. Operating in connection with the installed water saving equipment, the daily toilet water consumption is approximately 8.3 tons and the weekly gardening water consumption is approximately 256 tons. Application Purposes: Rainwater collected may be used for garden watering, toilet flushing and floor mopping at school. Design, Planning, and Effects of Rainwater Catchment System: By using the raft foundation Drain Pipe To Gardening Water System Buffer Tank Rainwater Supply Tank Over Flow to the Deep Drain Well Filter System Rooftop Catchment Area F.L.4 F.L.3 F.L.2 F.L.1 R.F.1 Raft Foundation Storage Space (700Tons) Ground Water Public Water Supply Tank Buffer Tank (having a capacity of 700 tons) of the newly built school building as a rainwater storage space (a rainwater supply tank having a capacity of approximately 11.5 tons is also installed on the roof) in combination with the public water and the ground water supply system, the water supply volume of the rainwater catchment system is estimated to be approximately 3,200 tons/year. This should be able to replace 100% of toilet water consumption and 15% of gardening water consumption. Related designs and plans are shown in the attached drawings. Chu-Shan Primary School Geographical Features: It is located at Chu-Shan, Nan-Tou County in the central part of Taiwan where 92% of rainfall occurs during the rainy season (from April to October), the local average annual rainfall is at approximately 2,240mm and, over the years, the maximum daily rainfall depth is 713mm. Water Consumption Conditions: There are approximately 1,350 students in this school and vacations are between July and September and between January and February each year. Operating in connection with the installed water saving equipment, the daily toilet water consumption is approximately 15 tons and the weekly gardening water consumption is approximately 514 tons. Design, Planning, and Effects of Rainwater Catchment System: Since there is no raft G.L. 3

4 foundation, the aim is to install rainwater education facilities, i.e. embedded piggy banks for rainwater (non-power consumption underground rainwater storage tanks), in the school mainly for rainwater catchment education and garden watering. Related designs plans are shown in the attached drawings. Application Purposes: Rainwater collected may be used for garden watering and floor mopping at school. Non-power pump Rainwater storage tank Drain pipe Screen tank Catchment area(roof) and Conclusion Overflow pipe 100 Tons 10holes/inch 50holes/inch 100holes/inch Rainwater collection pipe valve In Taiwan, in terms of rainwater utilization, the main issue is not technology but changes of thoughts and habits. In the past, most private promotions of rainwater catchment system in Taiwan could only proceed in combination with government funded resources. In this case, the promotion and installation of rainwater catchment systems in schools, the Hope Engineering Project is sponsored by the Tzu-Chi Foundation. It provides important tools for dealing with any future water shortage in the areas affected by one of the most severe earthquakes of the last century. The project will become the largest local rainwater catchment project in the history of Taiwan. After the project is fully completed, it is estimated that the disaster areas will benefit by the supply of approximately 250,000 tons of rainwater every year (approximately equivalent to the total daily water consumption of Nan-Tou Area). In terms of future rainwater utilization, the educational benefits that the project provides to students are also substantial. As many schools to be reconstructed in this Hope Engineering Project are located either at a town center or on a hillside where the local maximum daily rainfall is more than 300mm (some even go over 600mm), the rainwater storage tanks installed should be able to effectively reduce the peak flow during rainstorms and provide important contributions to local disaster prevention. To include rainwater catchment system design in reconstruction or new construction work should not significantly increase their overall cost. For instance, in the Hope Engineering Project some schools use their raft foundation or underground storage space to install the rainwater catchment system, the average construction cost of water supplied from the rainwater catchment system is US$ 0.58 per ton. As the average development cost of water supplied from new reservoirs in Taiwan is estimated at 4

5 more than US$ 1.52 per ton, investment on the installation of rainwater catchment system is apparently more economic. References S.C.Lee, M.C. Lin, W.H. Chou, (2000) Rainwater Catchment System Planning and Design in Hope Engineering Project, East Asia 2000 Regional Symposium on Rainwater utilization, Nov, 2000, Taipei, Taiwan. S.C.Lee, M.C. Lin, W.H. Chou, W.L. Tsai, (1999) Design of the Hualien Tzu-Chi Medical and Cultural Park s Rainwater Catchment System, Buddhist Compassion Relief Tzu-Chi Foundation, Energy & Resources Laboratories(I.T.R.I.), Hsu s Associates of Architects and Engineering, Apr 1999, Taipei, Taiwan. 5