POSSIBILITY OF

DAM FAILURES

Submitted to: Submitted By:Dr. Ankit Sahai AMOL AGARWAL Asst. Prof 144122

Mechanical

DAMS A dam is a barrier across flowing water

that obstructs, directs or slows down the flow, often creating a reservoir, lake or impoundments.

Most dams have a section called a spillway or weir over which, or through which, water flows, either intermittently or continuously, and some have hydroelectric power generation systems installed.

SPILLWAY A spillway is a structure used to provide

the controlled release of flows from a dam or levee into a downstream area, typically being the river that was dammed.

Spillways release floods so that the water does not overtop and damage or even destroy the dam.

Except during flood periods, water does not normally flow over a spillway.

DAM FAILURE Dams are generally an expensive

structure that directly affect the economy of the area through power generation, flood control and water supply (reservoirs). As the population of an area grows, structural failure of a large dam due to an earthquake poses an increasingly great danger for residents exposed to sudden flooding.

Failure of dam across the Kern River following the 1952 Kern County Earthquake

MAIN CAUSES

OVERTOPPING

Overtopping of a dam, as shown, is often a precursor of dam failure. National statistics show that overtopping due to inadequate spillway design, debris blockage of spillways, or settlement of the dam crest account for approximately 34% of all U.S. dam failures.

PIPING

Another 20% of U.S. dam failures have been caused by piping (internal erosion caused by seepage). Seepage often occurs around hydraulic structures, such as pipes and spillways; through animal burrows; around roots of woody vegetation; and through cracks in dams, dam appurtenances, and dam foundations.

LOCATION AND GEOLOGY

Poor dam siting (ex: Teton 1976) and poor engineering (ex: Banqiao 1975) can be key contributing factors in failures.

Geological events like landslides (ex: Vajont 1963) and earthquakes (ex: Fujinuma  2011) are in rare instances associated with dam failure, but the historic record is dominated dams successfully weathering earthquakes, landslides, and reservoir tsunamis.

Vajont Dam after the Landslide

FOUNDATION FAILURE The foundations of any dam can be

compromised, and this is one of the most feared and dangerous types of dam failure.

Concrete arches have in some cases ruptured suddenly. Notably, Malpasset arch dam in France suddenly broke from its foundations in 1959 during a heavy rainstorm, killing 421 people.

Foundation failure is believed to have caused the dam to collapse, but no witnesses survived the event.

OTHER CAUSES Structural failure of materials

used in dam construction Earthquakes Sliding of a mountain into

the reservoir 

HIDDEN CAUSES

CHANGES IN LAND USE

The most important factor in whether a dam will fail is the amount of water that it has to hold back,  Dams are designed and built based on the state of the watershed at the time.

So when the landscape is changed, it can have a big impact on how quickly water is absorbed into the ground or runs off, toward the dam.

A dam near homes in Columbia is overtopped by flooding on October 6.

CHANGES IN WEATHER PATTERNS

Shifting weather patterns can also put more strain on dams, as some areas get wetter while others get drier.

The engineering community is working on this problem, but right now we don’t have good models that tell us how much to adjust our plans based on changing climate,” says France.

OUTDATED DESIGNS

Dam design has also improved over the past century, although many communities can’t afford to replace their old dams with the latest technology.

Newer earthen dams, for instance, are built with the filter design, which puts progressively coarser material toward the interior of the walls.

That allows a small amount of water to seep into the dam but prevents the smaller grains from moving with it, locking them in place.

 LACK OF MAINTENANCE AND FUNDING

Unlike roads, which are largely paid for with a regular excise tax on gasoline, dams have historically had more haphazard funding.

Another problem is the rising number of orphan dams, which no longer serve a useful purpose and often end up in a state of disrepair.

DAM FAILURES IN INDIA

KADDAM PROJECT DAM, ANDHRA PRADESH

The dam was overtopped by 46 cm of water above the crest, inspite of a free board allowance of 2.4 m that was provided, causing a major breach of 137.2 m wide that occurred on the left bank.

Two more breaches developed on the right section of the dam. The dam failed in August 1958.

MACHHU II (IRRIGATION SCHEME) DAM, GUJARAT

The dam failed on August 1, 1979, because of abnormal floods and inadequate spillway capacity.

The spillway capacity provided for 5663 m³/s. The actual observed flow following the intense rainfall reached 16307 m³/s, thrice what the dam was designed for, resulting in its collapse.

THANK YOU FOR YOUR

PATIENCE !!