User:Tibobean113/sandbox/Hydraulic Structures

Hydraulic Structure is any structure that is submerged or partially submerged in any body of water to control the natural flow of water. Hydraulic structure can be used to divert, disrupt or completely stop the water flow. It can be constructed from materials ranging from large rock and concrete to wooden timbers and tree trunks. A few examples of hydraulic structures are dams, weirs, spillway, flumes and breakwater. Typically, hydraulic structures are passive structures, which have little to no moving parts. Despite many of its advantages, there are still ongoing discussions regarding hydraulic structure's effect on the environment.

Significance

Throughout history, most well known civilizations are associated with the construction of storage reservoirs tailored to their irrigation demands from development and expansion of agriculture. In modern days, various types of hydraulic structures are used to benefit national economy and protect the environment in many ways, including hydro power, flood control, water supply, silt mitigation, navigation, irrigation, draining, fish handling and farming.Typically, multiple hydraulic structures with general or special purposes are built in combination to form a single hydraulic project that serves a bigger purpose like irrigation, flood prevention, and hydroelectricity.

History

3000BC- 1800AD

The earliest invention of hydraulic structures like dams, upstream masonry, aqueduct ... marked the dawn period of hydraulic engineering in mankind history. Some of the most notable hydraulic structures in this period was the Ancient Roman's water supply system consisting of dams for drinking or reservoir as well as embankment dams in India and Sri Lanka. These hydraulic structures in India and Sri Lanka were built by placing earthfill across rivers with materials nearby transported using baskets. On the other hand, Ancient Roman builders turned to the most abundant materials available, soils and gravels, to build their water supply system. However, these structures were usually temporary and often failed due to the lack of basic understanding of hydraulic and material mechanics.

Follow the invention of concrete, hydraulic structures' popularity spiked globally due to ease of construction. Islamic states under the rule of a single Islamic Caliphate built many hydraulic structures such as canals, dams, qanats of Persia, the water-lifting system like noria and shaduf in Egypt or the hydraulic driven water supply system from Syria. Unfortunately, these innovative structures were reduced to ruin during the Mongol's invasion. The Renaissance marked another spike in hydraulic structures' construction in Europe. From the period of 1700s, mechanical hydropower started to be used more extensively in milling and pumping. This period also marked the continued development of water turbine.

1800AD- 1940AD

This period marked the fast development in techniques for concrete dams and the sophisticated application of sciences in building hydraulic structures. In 1853, Sazilly, a French engineer, discovered that pressures within gravity dams has to be measured and held to specific limits and the structures themselves should be dimensioned to preclude sliding. This concept was later emphasized and elaborated on by William Rankine, a Scottish mechanical engineer, and named the middle third criterion. The first hydraulic structure to put Sazilly and Rankine's idea into practice was the Furens Dam in France. The Furens Dam was built based on the principle of rational analysis and became the largest dam in the world for about 10 years.

Mining was another reason that leapfrog hydraulic structures into a new era. The need to impound water for mining operations led to the need for more dams and conduits while drill and blast mining techniques provided an endless supply of rock materials for hydraulic structure construction. At the start, most dams were very basic and built using stone-filled log cribs. Later, miners gravitated toward building more intricate dams using dumped rockfill confined by dry rock walls at the faces and lined with two or more layers of wood planking. The highest dumped rockfill dams built in this ear was the Meadow Lake dam of 23 m high.

In 1895, hydraulic structure's design and theory continued to advance. The middle third criterion was questioned by multiple designers following the Bouzey Dam of France's failure in 1895. Many engineers concluded that uplift and sliding heavily influence the longevity of hydraulic structures and must be taken into account when building one. As a result, the Wachussetts Dam in Massachusetts were the first to include a fat section of flat slope to counteract uplift. Following the Wachussetts Dam, the Medina Dam in Texas, the Arrowrock in Idaho and the Elephant Buttle in New Mexico implemented both dam and foundation drainage to better counter uplift and sliding. Since then, drainage holes has become a common practice for large gravity dams.

In 1870, world's first hydroelectric power plant was built in Cragside, Rothbury ( England). This was possible due to a key breakthrough of electric generator being coupled to the turbine which is the core of a hydroelectric power system.

In this period, Embankment dams also started to evolve from simple homogeneous or two-zoned earthfill into complex, highly analyzed, well-instrumented, and multi zoned earthfill and rockfill strucutres. From 1910s to 1940s, rockfill dump dams started to exceed 30m in height. This is due to the "dry rock dump" technique being replaced with placement of multiple rockfill lifts using impervious materials like timber, steel, concrete or asphaltic concrete.

1940AD- End of Twentieth Century

Quickly growing population in major cities increase the demand for large reservoirs for water supply and higher dams for more hydropower. Since the 1950s, both the number and height of dams accelerated around the world. Up to 1939, there were only 11 dams higher than 100 m. By 1960, there were 88 dams higher than 100m throughtout the world. Record for dams' height, volume were set and broken in quick succession. This era also marked the quickest development in hydraulic structure technology.

One of the most notable invention of this time period is the RCC dams (roller compacted concrete dam). RCC dams is defined as a composite construction material composed primarily of aggregates, cement and water. This method of constructing dam is more economical competitive with other construction method while maintaining the same quality. The RCC dams were a major factor in helping hydraulic structure construction to keep up with the forever increasing demand of the population.

As electricity demand grows, hydropower plants' popularity also rose quickly. Early hydropower plants were small to medium sized and built wherever there was an strong supply of flowing water. Today, hydropower plants is built in various sizes from a few watts to tens of GW. The largest hydropower plants project is the Three Gorges in China with 22,400 MW installed generator and produce 100 TWh/year. The variety in size of hydropower plants enable hydroelectricity to meet both large centralized urban energy needs and decentralized rural demands.

Types of Hydraulic Structures

Embankment dam

Embankment dams are defined as dam constructed from natural materials excavated close by. These materials are utilized by engineers to build dams in designated are without the need to transport additional material. The material are placed and compacted without the use of any binding agent using high-capacity mechanical plant. The two most popular types of Embankment dam are earthfill and rockfill dam. Embankments are classified as earthfill or rockfill if its content is made up of more than 50% of soil or rock respectively. There are multiple advantages to building Embankment Dam:

1. adaptability to almost any foundation conditions ranging from competent rock to soft and compressible soil
2. minimizing the need to import or transport large amount of processed materials or cement by using natural materials
3. extremely flexible in its ability to accommodate different fill material
4. the construction process is highly mechanized and only require little human labor
5. embankment Dams tend to be cheaper than any other type of dam
6. embankment Dams are less susceptible to cranking and failure if properly designed

However, embankment dam also has it disadvantages. Some of embankment dam's shortcoming are being more susceptible to damage due to overtoping, vulnerability to concealed leakage and internal erosion in dam or foundation.

Concrete dam

Concrete dam are defined as dam constructed entirely or mostly using concrete. As demand for bigger and taller dam increase, concrete dam replaced masonry dam for large non-embankment dam due to economic benefits and ease of construction for more complex dam system. Some of the most popular type of concrete dam are: Gravity dam, Buttress dam, and Arch dams. Gravity dams are concrete dams with triangular gravity profile to ensure stability and distribute its weight equally at the foundation. Buttress dams are any concrete dam with continuous upstream face supported at regular time interval by down stream buttresses. Arch dams are concrete dams with considerable upstream curvature. The arch helps transmit the major portion of the water load to valley sides rather than to the floor. Arch dam is more efficient than gravity dam and buttress dam in term of concrete usage. As a whole, Concrete Dam offers several benefits:

1. suitable to the site topography of wide or narrow valleys alike, given that a competent rock foundation is accessible at moderate depth.
2. not susceptible for overtopping under extreme flood condition
3. Outlet pipework, valves and other ancillary works are readily and safe housed within the dam
4. Being able to withstand seismic disturbance without catastrophic collapse

Yet, Concrete Dam also has some disadvantages like: demanding foundation conditions, require processed material, relatively labor intensive, higher cost than embankment fills.

Spillways and outlets

Spillways are hydraulic structure designed to pass flood water safely downstream when the reservoir is overflowing. Spillways are usually uncontrolled and function automatically when the water level passes maximum water level for the reservoir, but some are still controlled by flood gates.

Outlets are hydraulic structures that are designed to direct water to pipe lines, to irrigation areas or to the main river. Outlets also serve the purpose of emptying reservoir for emergency or maintenance reason. In order to accomplish both tasks, Outlets' intake must locate at a relatively high elevation to store potential energy while its outtake must be at the lowest elevation to to empty reservoir. Outlets are usually build in conjunction with dams to create a more functional hydraulic system.

Pros and Cons

Pros

There are various benefits that different types of hydraulic structures can offer. One of the most beneficial and well known aspect of hydraulic structures is hydroelectric power. Hydroelectric power is created by letting water passes through a turbine within the dam. Hydroelectricity is one of the best form of alternative energy due to its low cost, reliability, and abundance. Another benefit of hydraulic structure is to control waterways. Flooding is one of the most dangerous natural disaster for many communities. To prevent flooding, many hydraulic structures are built to re-divert waterways and impound floodwater and then safely divert it to other places. On the other hand, hydraulic structures can also act as water reservoir for irrigation to prevent harsh droughts. Hydraulic structures also help protect the environment by traaping hazardous materials in water and capturing sediment that contain toxic substances.

Cons

Despite various benefits of hydraulic structures, there are still some drawbacks to consider. When water rushes through a hydraulic structures, it can create a spot for sediment layers to build up and congregate, which then can pollute the water and disrupt the ecology of the water system. As a side effect of stopping floodwater, hydraulic structures also prevent the replenishment of nutrients in the soil in water, which can disrupt the delicate natural ecosystem. Fish ladders have been built to aid fish migrate, but many are not able to use the fish ladders properly, especially if they are used to fast moving water. Erosion of river banks have also been noticed near hydraulic structures, which can lead to landslide along the side of the river. Hydraulic structures also come with an inherent risk for disaster. A dam collapse or break would be a catastrophe many time worse than natural flooding.