Category: Hydraulic Structure

Oroville Dam – Tallest Dam in the USA

Oroville Dam

The United States is home to many large and amazing dams. One such dam is the Oroville Dam. Moreover, it is the tallest dam in America with a height of 770 feet. The construction of the Oroville Dam started in 1961, and it was opened on May 4, 1968. It is an earth-fill embankment dam constructed in the Feather River in the Oroville City of California. The dam has created the Oroville Lake which is the second-largest water reservoir in the state of California. The lake can hold about 3.5 million acre-feet of water.

The dam was constructed by the California Department of Water Resources under the California State Water Project. The Oroville Dam is used for hydroelectricity, flood control, water supply, and Feather River fish hatchery.

The Edward Hyatt Power Plant was constructed underground and completed shortly after the Oroville Dam was completed. This hydroelectric power plant generated 819 megawatts of electricity which made it the largest underground power plant at that time. This along with the Thermalito reservoir produces about 2,200 gigawatt hours of electricity per year.

Another reason for which the Oroville Dam was constructed was to supply fresh drinking water in the semi-arid California state. After the Feather River joins the Sacramento River before it goes into the delta a California aqueduct diverts fresh water. This aqueduct is used to supply fresh drinking water to San Joaquin Valley and South California. The water from his dam is used for irrigation of 755,000 acres of land.

The Oroville Dam, like other dams, also helps in flood control. During the early winter when storms are very frequent the dam makes one-fifth of its capacity available for flood control. During such times the dam releases 150,000 cubic feet per second to control any major flooding. During the 1997 flood, it was the dam because of which a large area of the Sacramento Valley was saved from flooding.

The Feather River was a migration route for Chinook salmon and steelhead trout. However, the construction of the dam disrupted this route. So, in 1967, the DWR and the California Department of Fish and Games built the Feather River fish hatchery. When the fishes reach the Thermalito diversion dam they are made to move upward to the hatchery. Every year this hatchery produces 10 million salmon and 450,000 trout.

The Oroville Dam has been a very safe and reliable dam however it also has a fair share of up and down as well. In 2009, there was a river valve accident which almost took the lives of 3 workers. This happened when they were deep below the operating flow control.

In 2020, a safety assessment was done by the DWR which concluded that the Oroville Dam was safe and safe for operations.

What is the Double-walled Cofferdam? Learn about it

What is the Double-walled Cofferdam?

A double-walled cofferdam is the same as a single-walled cofferdam, except for the construction of a double wall in place of a single wall.

A double-walled cofferdam is provided where the area is to be enclosed is large and also the depth of water is large. It is very important to choose the perfect cofferdam for a particular situation. A double-walled cofferdam is very essential in case of large depth of water say about 10 to 11 m.

In the case of a double-walled cofferdam, a pair of walls is constructed along the length of the cofferdam, and a suitable gap is kept between the two walls. The space between the two walls is generally filled with a thick mixture of sand or clay and gravel

The filling is to be done in thin layers and it should be well consolidated when it is in a damp state

Sometimes, a clay berm is provided on the outside of the cofferdam in order to provide an additional safeguard against leakage.

The width of the cofferdam depends on various factors such as structural stability, degree of imperviousness desired, etc. So, the width of the cofferdam should be decided after considering all the influencing factors. The following thumb rule should be followed in this respect.
If,
B = The width of the cofferdam
h = Depth of river water
Then,

Up to depth of river water 3 m ———— B = h

For depth more than 3 m ———— B = 3 + ¹/₃(h-3)

Weir and Barrage – MCQ || Hydraulic Structure

Weir and Barrage – MCQ

1. To lengthen the path of seepage flow _ are provided on the cut-off walls of the weir or barrage

View Answer

Sheet piles

2. On every streamline there may be a point of equal residual head. If all these points are joined, then the line is known as

View Answer

Equipotential line.

3. To allow the seepage water to escape without dislocating the soil particles on the downside of the weir the _ is provided

View Answer

Invert filter.

4. Which of the following reasons for the failure of the weir and barrage on the permeable foundation

a) By scouring
b) By piping
c) By uplift pressure
d) All of these

View Answer

d) All of these

5. Which of the following precautions can be taken to prevent weir and barrage failure on permeable foundation

a) Shallow foundation should be provided for the barrage piers
b) Sheet piles should be provided only on the upstream side
c) Sheet piles should be provided on the upstream and downstream side
d) Loose talus should be provided as possible as small in size.

View Answer

c) Sheet piles should be provided on the upstream and downstream side

6. The loss of head per unit creep length is known as

a) Hydraulic gradient
b) Creep coefficient
c) Potential drop
d) Lane’s coefficient

View Answer

a) Hydraulic gradient or percolation coefficient

7. If ‘H’ is the depth of water on the upstream side of the weir and ‘L’ is the creep length, then the Bligh’s creep coefficient will be

a) H/L
b) L/H
c) HL
d) None

View Answer

b) L/H

8. According to Bligh’s theory, which of the following relation indicates that there will be no danger of piping

a) [latex] \frac{H}{L}\leq \frac{1}{C} [/latex]
b) [latex] \frac{H}{L}\geq \frac{1}{C} [/latex]
c) [latex] \frac{H}{L} > \frac{1}{C} [/latex].
d) None

View Answer

a) [latex] \frac{H}{L}\leq \frac{1}{C} [/latex]

Read More:

Bridge and Culvert – MCQ

Definition of Weir and their Advantages and Disadvantages

5 Component Parts Of A Bridge

Dam – MCQ

What are the Uses of Cofferdams?

Uses of Cofferdams

Following are the 8 uses of cofferdams:

1. The cofferdams are used to enclose the workplace for preventing the entry of water into it.

2. To provide a safe water-enclosed platform for the workers while working on laying the foundation in water.

3. To provide a space for foundation work without affecting the safe conditions of adjoining structures.

4. To facilitate pile-driving operations.

5. To place the raft foundation.

6. To provide space for carrying out the foundation work and superstructure work of concrete dams.`

7. To facilitate the construction of foundations for piers and abutments of bridges, locks, etc.

8. To lay the grillage foundation.

Read More:

Box Caissons

Gravity Dam – Hydraulic Structure

Gravity Dam

It is constructed with masonry or concrete it resists the force acting on it by its own weight.

Where Gravity Dam Are Constructed?

Good soil area
For large spillway
In granite basalt area
For large height and small length dam
For long time

Forces Acting On Gravity Dam

Following are the 6 major forces which acting on the dam

1. Weight of Dam

The total weight of the dam acts at the C.G. of its section.

2. Water Pressure

The horizontal water pressure P = wh²/2, this acts at height h/3 from the base of the dam.

3. Pressure Due to Earth Quak

In this case two types of pressure acts

Horizontal acceleration force FH = W.α
Vertical acceleration force Fv = W(1- α)

(Where W = weight of dam and α = acceleration)

4. Uplift Pressure

The uplift pressure is an upward pressure of water as it flows through the body of the dam or its foundation.

Uplift pressure at the heel, A = wh
Uplift pressure at the toe, F = wh՛
Uplift pressure at gallery = w[h + 1/3(h-h՛)]

Mode of Failure of Gravity Dam

By overturning
By rupture from tension
By sliding
For crushing by compressing
By uplift of floatation

The Force That Gives Stability To The Dam

Self-weight of the dam
Trust of the tail water

Read Also:

Types of Dam

Factors affecting For Selection of Type of Bridge

Choice Of Types Of Dam According To Topography, Height, Stability, Earthquake Areas, Spillway

Spillway – || Purpose || Types || Spillway Gates

A spillway is the outlet portion of the dam, over which surplus discharge flow from the reservoir to the downstream. Hence, a spillway is known as surplusing work.

Purpose of Spillway

It resists water pressure at the mid reservoir level.
It can be able to control excessive flood water.
It can be able to save free-board and crest of the dam.
It’s shape and size so constructed that it should be able to resist excessive water pressure.
It should be able to protect the downstream side portion of the dam water-fall into the downstream.