The dams one of the greatest and largest civil constructions built by man Absolutely. During the rings of history, large dams have been built to prevent the dangers of flooding, irrigate agricultural land, and generate enormous amounts of energy by exploiting the potential nature of trapped water Thus, dams have long ago changed clear landmarks in human civilization. the dams were very old engineering structures, building dams in the world more than 5000 years ago. The ancient Egyptians were the first to build the first and largest dams known to humankind, but they also invented many different models of dams to resist the strong river water
Various kinds of dams:
The design of dams is always related to the geology of the area and the nature of soil and terrain.
The arched dams are considered the simplest form of dams and the least expensive in terms of materials and design of any form Other dams.
This type of dam is used in narrow and rocky places, where the dam is in the form of a curved arch, which holds behind it the vast amounts of river water
The arched geometrical shape of the arc during the process of compressing the water reserved behind the dam, where the water applied a large pressure on the back surface of the convex wall, causing the compression of the wall arch towards the cohesion and convergence of the wall material from each other because of their geometric shape as shown in the previous figure
Where & why we design it:
1- Appropriate when “Width / Height of valley” (B/H) < 6
2- Rocks at the base and hillsides should be strong enough with high bearing capacity.
3- To save in the volume of concrete.
4- Stresses are allowed to be as high as allowable stress of concrete.
5- Connection to the slope of hillsides should be 45o at least.
These dams may be slightly flat or a lot or curved, but there are always design principles that distinguish them from others. They are a series of pillars (used to transfer the Influential forces on the wall to another area that is more powerful and hold like the ground or foundations). These structural pillars reinforce and support the building of the dam from the outside side downstream.
According to the engineering design of these types of dams, the water generates large pressure forces resulting from its weight towards the wall of the dam, causing it to be pushed or reversed while the pillars on the opposite side react completely in an attempt to install the building in place, while the weight of the pillars is fully applied to the ground
Where & why we design it:
The design of butters dams is based on:
Knowledge and judgment that comes from long experience in this field
They are huge dams made up of rocks and dust, similar to the pattern of gravity dams, where these dams depend on their enormous weights to resist the enormous forces resulting from the reserved water, and what distinguishes these dams are the density of the material inside. The internal insulator prevents filtration or leakage through the construction of the dam
The forces of water pressure push along the wall towards the coup, while the massive weight of the dam or wall works to stabilize the wall in place because of the gravity that drives it towards the earth permanently and along the wall of the dam
A Gravity dam has been defined as a structure Which is designed in such a way that its own Weight resist the external forces.
\"This type of a Structure is most durable and solid and requires Very less maintenance.
Such dams are constructed of masonry or concrete.
however, concrete gravity dams are favored nowadays and for the most part built
Rock - Fill Dams
Rock fill dams are embankments of compacted granular soil in combination with impervious areas. Rock fill dams must contain an impervious zone, usually selected aggregates with filter zones, comprising a substantial volume of the dam. These structures are effective because the force of the river or reservoir hits the core of the embankment, in a downward direction, and transferred to the solid foundation of the dam.
Type of dams according to material used for dam constructions:
We have talked about it before like (arch dams, gravity dams, ……)
Type of dams according to their uses:
They are built to store water during the flood period for later use during periods of water shortage. the Water stored can be used in different seasons for different uses such as navigation, recreation and electricity generation.
These dams are used to raise the water level of the river in order to supply the suspended canal, which is useful for the development of irrigation works
The detention dams:
These dams detain water during floods temporarily and thus reduce the bad effects of sudden flooding
Type of dams according to hydraulic design:
It is designed to reflect excess water of its crest and must be made of non-corroding materials due to these behaviors
They are those are which not designed to be overtopped.
This type of design gives us a wider choice of materials including earthfall and rockfill dams.
Many times, the overflow dam and non-overflow dam are combined to form a composite single structure.
Rigid dams and non-rigid dams:
factors governing of a particular type of dam
As everybody know dams have a lot of benefit like electricity, Irrigation of agricultural crops, and Flood prevention. But the disadvantages also a lot:
1- Fish problem
Many type of fishes move from downstream to upstream to lay their fertilized eggs at the end of summer season like Salmon and Hilsa. These are commercially valuable fish and important industries are dependent on them. These fishes can\'t go upstream because the dam barrier is constructed on the river. These fishes don\'t return back to the downstream. It starts jumping trying to get over the dam. At the end, these fishes get exhausted and die after some time.
In the beginning, nobody interests in this phenomenon. But after some time, the number of died fishes is start increasing. People start finding some solution. They invite a giant steel and plastic nets called Fish ladder. The fish entering the lowest rung of the ladder in the down of the dam. Then it starts jumping from pool to other until it reaches the top of the dam. And the new born fishes can use this way again when it back to downstream.
There several problems started appearing when they are trying the fish ladder for first time. Fishes seemed to prefer to mill ground in splashing water under spillway and the slow water stream it sound strange for fishes. But after a lot of researches people improve the fish ladder to became more attractive for fishes. There are researches trying to make fishes spawn in other places better than upstream. There a lot of researches to help anadromous fishes.
2- submergence problem
Dams usually constructed on rivers to store water in the upstream side. When the level of water increases the area behind the dam will submergence. So, we have to calculate this area before we construct the dam and compensated the owners of the land. And it\'s very important to know the total damage of submergence.
3- failure problem
There a lot of reasons make dam failure. The most three reasons are bad workmanship, faulty design and the occurrence of unanticipated floods. So, we try to build dam can live hundreds of years without any problem. Most of problems come from high pressure of water that make disaster. But due to modern engineering advancement these disasters have been reduced. To ensure our dam can support the various forces which going to face. we must have rational and proper design, good supervision and Periodic maintenance that will make us fairly confident.
Dams can fail unexpected excessive earthquakes. Like what happen in Spain in January 1959 the Vega de tera dam failed and 123villages were drowned. Also, the maltase dams its arch dam 200 feet height. the dam also failed in 1956 and the floods kill 421 persons. That mean these dams hadn\'t been built strong enough to bear the full weight of its intended reservoir. So, must blamed the faulty design and bad engineering. And we must learn from our mistakes.
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