The site must be such that a dam can form a large reservoir. The bed under the site should be impervious to ensure water tightness, with cracks filled by pumping cement grout into boreholes. Dams may be of masonry, concrete, or earthwork faced with stone and clay puddle walls. Provision for flood overflow is essential, often through wing walls or channels. Before use, all timber and vegetation must be removed and houses relocated from the catchment area. Hawksley’s formula determines reservoir capacity based on days’ supply needed. Compensation and settling reservoirs are also discussed, along with service reservoirs that store water near delivery points to compensate for varying demand. Water pressure is explained in terms of head (height) and its effects on tanks and pipes. Distribution methods include open channels, covered channels/tunnels, cast-iron or steel pipes, and reinforced concrete pipes. Pipes can be laid at various levels but must avoid air-locking by managing rises and falls properly.
<Callout type="important" title="Critical for Water Tightness">Ensuring the dam’s foundation is carried well into an impervious stratum is crucial to prevent water leakage.</Callout>
Water mains can be made of cast-iron, steel, lined iron, or asbestos cement. Each material has its advantages and disadvantages in terms of cost, weight, durability, and resistance to corrosion.
<Callout type="risk" title="Beware of Corrosion">Steel pipes are more prone to corrosion than cast iron but can be protected with coatings like asphalt or Hessian cloth impregnated with bitumen.</Callout>
Key Takeaways
- Select a site for the dam that allows for large reservoir capacity and an impervious bed.
- Use appropriate materials like masonry, concrete, or earthwork with clay puddle walls to ensure water tightness.
- Calculate reservoir capacity using Hawksley’s formula based on days’ supply needed.
Practical Tips
- Ensure the dam foundation is carried well into an impervious stratum for maximum water tightness.
- Use flexible joints in pipes to reduce the risk of fractures from traffic vibration or ground subsidence.
Warnings & Risks
- Do not ignore potential leaks due to cracks near the site; they must be filled with cement grout under pressure.
- Steel pipes are more prone to corrosion than cast iron and require protective coatings for longevity.
Modern Application
While this chapter focuses on historical methods of reservoir construction, many principles remain relevant today. Understanding water tightness, proper dam foundation placement, and material selection is crucial in modern survival scenarios where access to clean water is critical. The knowledge of how to construct effective dams and manage water supply systems can be invaluable for both emergency preparedness and long-term sustainability.
Frequently Asked Questions
Q: What materials are recommended for constructing a dam?
The chapter recommends masonry, concrete, or reinforced concrete for the body of the dam. Alternatively, an earthwork dam faced with stone setts and clay puddle walls can be used.
Q: How is reservoir capacity determined according to Hawksley’s formula?
Hawksley’s formula determines the number of days’ supply (D) needed for a normal capacity, which is usually about 180 days. The formula is: D = 1000 / F, where F represents the average annual rainfall in inches.
Q: What are some advantages and disadvantages of steel pipes over cast iron?
Steel pipes can be thinner and lighter than cast-iron pipes, making them less expensive. However, they are more prone to corrosion and require protective coatings like asphalt or Hessian cloth impregnated with bitumen.