Explaining the ‘Dam’ Family

A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. The earliest known dams were built by Ancient Egyptian and Mesopotamian civilizations, and since then dams have become common infrastructure worldwide, with over 58,000 large dams. Dams are constructed for a variety of purposes, including water supply, irrigation, power generation, flood prevention, navigation, recreation, and fish farming. The most common types of dams include embankment dams, gravity dams, arch dams, and buttress dams. Embankment dams are the most widespread, accounting for about two thirds of dams worldwide. They are constructed from compacted earth or rock and use their weight and mass to resist the force of water. The content will also cover other less common dam types, considerations around dam safety and environmental impacts, and some notable historic and modern dam projects worldwide. The goal is to provide a comprehensive overview of dam engineering and the role of dams in water management infrastructure.

Embankment Dams

Embankment dams are constructed from earth, rock or both. They are the most common type of dam in use today. Material used for embankment dams include natural soil or rock, or waste material obtained from mining or excavation. The material is compacted and shaped to create the dam structure. The most common method of construction is the rolled-fill method. Soil, rocks or other fill material is placed in thin layers and then compacted by heavy machinery. This process is repeated until the embankment reaches the designed height. Other methods include dumping, hydraulic filling and upstream construction. Proper compaction of materials and construction of suitable spillways and drains are critical in creating a stable embankment dam. When designed and built correctly, they are a cost-effective dam option.

Gravity Dams

Gravity dams are solid concrete structures that rely on their own weight and geometry to resist the tremendous pressure exerted by the reservoir water behind them. They are well-suited for narrow gorges or canyons with a solid rock foundation. Gravity dams have a triangular cross-section, resembling an inverted pyramid. The wide base and sloped upstream face help stabilize the dam against the reservoir water pressure. The downstream side is commonly vertical to minimize the amount of concrete required in construction. These dams use mass and gravity to counter the overturning forces caused by the water pressure. The low and wide structural profile accomplishes that by lowering the center of gravity. Gravity dams come in a variety of designs, including constant angles, variable angles, or curved faces.

Arch Dams

Arch dams are curved concrete structures that rely on strength from the shape of the arch to resist the large pressures from the reservoir. They provide economical designs for narrow canyons as they require much less concrete than a gravity dam. Arch dams are typically double-curvature structures built from concrete that span the full width of a canyon or gorge. The curve of the dam allows it to transfer the water load principally into the canyon or gorge walls. This makes an arch dam well suited for narrow canyons where there is good foundation rock on each side. The basic design uses a larger radius curve on the upstream face and a tighter curve on the downstream face. This shape allows the reservoir forces to be transferred to and resisted by the canyon. The concrete arch structure is often very thin compared to its height, just thick enough to support its own weight and transfer the loads to the abutments.

Buttress Dams

Buttress dams are a type of dam built using several triangular shaped buttresses to support the dam against the force of the water. They are a relatively uncommon type of dam compared to arch or gravity dams. Buttress dams contain thick, angled vertical walls called buttresses that support the upstream face of the dam. The buttresses connect to the dam core wall and help resist the water pressure. The triangular shaped buttresses transfer the water load to the dam foundation. The spaces between the buttresses are usually left open but can be filled in with concrete or rockfill materials. Buttress dams are often used for sites where the foundation could potentially cause issues for a gravity dam. The buttresses and core wall work together to divert stresses safely downward into the foundation. Buttress dams require less concrete and materials than gravity dams, but they are more structurally complex to design and build.

Dams are an incredible feat of engineering and construction that provide many benefits like hydropower, water storage, and flood control. However, they also come with drawbacks like environmental impacts and safety risks that must be carefully managed. Over the decades, dam design and construction has vastly improved to enhance safety and reduce harmful effects. Arch and gravity dams in particular exemplify the amazing progress in dam engineering. Moving forward, the focus will likely remain on limiting ecological disruption and making dams as structurally sound as possible. This overview of major dam types and considerations shows the complexity of these projects. When designed well, dams serve crucial purposes for society. But we must also acknowledge their consequences and pursue new solutions. With responsible dam development, communities can enjoy their benefits while safeguarding nature and public safety.

Source: Tata & Howaard