CASE STUDY AND FORENSIC INVESTIGATION OF FAILURE OF DAM

ABOVE KEDARNATH

Leonardo Souza1, Tanvi Prakash Chanekar2 and Grishma Sanjay Pandit3

1
Post-Graduate Student, Foundation Engineering, Civil Engineering Department, Goa College of
Engineering, Farmagudi, Ponda-Goa, India; lrdcs@rediffmail.com
2
Post-Graduate Student, Foundation Engineering, Civil Engineering Department, Goa College of
Engineering, Farmagudi, Ponda-Goa, India; tanvichanekar@gmail.com
3
Post-Graduate Student, Foundation Engineering, Civil Engineering Department, Goa College of
Engineering, Farmagudi, Ponda-Goa, India; grishmapandit0@gmail.com

Keywords: Forensic Investigations, Failure of Earth Dam structures, Slope Failure

ABSTRACT

Many earthen dams are built on hill sides. Failure of such walls can lead to catastrophic
consequences. The effectiveness of a disaster reduction relies on the perception of the disaster
itself and proper analysis of the previous experience. From 14 to 17 June 2013, the Indian state
of Uttarakhand and adjoining areas received heavy rainfall, which was about 375% more than
the benchmark rainfall during a normal monsoon. This caused the melting of Chorabari Glacier
at the height of 3800 metres, and eruption of the Mandakini River which led to heavy floods near
Gobindghat, Kedar Dome, Rudraprayag district, Uttarakhand, Himachal Pradesh and Western
Nepal. Kedarnath, had been obliterated, 608 villages, covering a population of 700,000, in 23
districts of Uttar Pradesh were affected by the flood. Drought in the past year has shown the real
pictures of the basins of many dams in India. There is a dangerous levels of silting up reducing
both the reservoir capacity and factor of safety. The present average rain fall caused massive
flooding all over India. The main result of the Kedernath disaster was a outpouring of silty
sediments from the dams along River Mandakini that swallowed up entire villages. Forensic
analysis of a failure can significantly improve chances of future success. The present paper is a
forensic analysis of failure of dam wall behind Kedarnath temple with respect to danger of silting
up of dams and their potential for failures thus help to prevent future such catastrophes in India

INTRODUCTION
An earth or rock fill dam is a geotechnical structure that forms a “barrier” that obstructs the flow
of a river. Moraine dams are a special category of earth-rockfill dam naturally formed when
glacial debris blocks the path of glacial melt. As they are easily erodible, they need spillways that
are designed to safely pass water to the downstream side of the river. They have to have
sufficient freeboard to absorb sudden rise in water level caused by snowmelts cloudbursts and
floods. Mountain dams tend to get silted up faster as they have greater debris and silt load.
Construction of dams has been known to exist across the Tigris and Euphrates rivers
about 5000 years ago. In Tamil Nadu there is a still serviceable dam 1500 years old. The
damming of streams and rivers has been integral to human population growth and technological
innovation.
 Among other things, dams have reduced flood hazard and allowed humans to settle and
farm productive alluvial soils on river flood-plains; they have harnessed the power of moving
water for commerce and industry; and they have created reservoirs to augment the supply of
water during periods of drought. Recently, the risk of natural disasters has increased in the areas
below dams as a result of increasing anthropogenic activities (Dhobal, 2013). This trend is likely
to increase in the future as human activities will increase. The natural flow paths of the channels
get obstructed due to the construction of man-made structures that results in deviation of the flow
from its natural course. These are the first to be affected in floods and they are usually either
unplanned or illegal in nature.
Dams are categorized generally as earth or concrete dams, depending on the material
used to construct it. This paper, discusses failure of an earth dam. Earth dams have their
embankments constructed of soil and rock. Properly constructed and maintained earth dams
usually have a unending life span. However, improperly constructed and un-maintained dams
usually fail as in the present case. A dam failure is a catastrophic type of failure characterized by
the sudden, rapid and uncontrolled release of impounded water accompanied by the trapped silt
and debris that erode and accumulate additional debris along the way. Major causes of failure of
earth dams worldwide include construction flaws, seepage/ piping, overtopping and
siltation.(Tandeswara, 1992; ASDSO, 2010) This study shows that siltation and overtopping
caused the disaster at Kedarnath.
Sometimes overtopping of a dam could be caused by a poorly designed spillway that is
failing to convey excess water away from the dam. Heavy rains from a single tropical storm can
cause overtopping as the spillway fails to convey excess flood water thus resulting in the
washing away of the dam. The dam above kedarnath did not have a spillway. Excess water
usually used to spill out from the back so the need for spillway was never envisioned. The
plausible causes of such failure in Kedarnath has been researched by Dobhal et al of the Wadia
Institute of Himalayan Geology. (Dobhal, 2013) Dam failure is normally viewed in the context
of the risk that is posed to life and property downstream of dams. This is usually so for large
dams constructed directly above large population centres. These are capable of causing
catastrophic losses. Dam failure can cause loss of life, property damage, cultural and historic
losses, environmental losses as well as causing social impacts (Nyoni, 2013)

Case Study cum Forensic Investigation Procedure

Many Earthen Dams are built as part of infrastructure projects in India. They lie mostly on the
hillsides and are a potential cause of future danger unless properly constructed and maintained.
Failures of one such dam lead to devastating consequences. A disaster reduction plan is essential
and its effectiveness relies on the expectation of the disaster itself, previous experience and state
of preparedness.
The present case study aims to present the data available in a new light. From the review
of the studies carried out by multiple agencies in the area, it is seen that the reasons given for the
disaster are inadequate. As a forensic procedure the data was collected from various sources and
assimilated and a conclusion was reached that the disaster occurred due to reduced reservoir
capacity due to siltation, improper compaction as it was a natural blockage and increase in height
without spillway provisions.
 We will first study the data available from the source at closest proximity to the site- the
Wadia Institute of Himalayan Geology, Dehradun which operate monitoring stations in that area.
We will also study the impact of the siltation on the reservoir. From these studies we will draw
reasonable conclusion as to the possible plausible cause of the Earthen Dam Failure.

Study area
The Kedarnath temple town (see Fig. 1) is located in Uttrakhand state of India in the western
extremity of the Central Himalaya (30 44 6.7 N; 79 04 1 E) in the Mandakini River valley which
has a total catchment area of ~67 km2 (up to Rambara), out of which 23% area is covered by
glaciers. The Primary deity of Kedarnath is the 'Lord of Kedar Khand' (Shiva) (Wikepedia,
2016). The catchment area is situated in the glacier modified U-shaped valley; the altitude ranges
from 2740 to 6578 m asl (above sea level). Such a variation in the altitude provides diverse
landscape.
Mandakini River originates from the Chorabari Glacier (3895 m) near Chorabari Lake
and joins Saraswati River which originates from Companion glacier at Kedarnath, passing
through Rambara and Gaurikund. The Madhu Ganga and Dudh Ganga are the main tributaries
that merge into the Mandakini River at Kedarnath town.
The Chorabari Lake (3960 m asl) also known as Gandhi Sarovar Lake is a snow melt and
rain fed lake, located about 2 km upstream of Kedarnath town which is approximately 400 m
long, 200 m wide having a depth of 15–20 m. The bursting of this lake led to its complete
draining within 5–10 min as reported by the watch and ward staff of the Wadia Institute of
Himalayan Geology (WIHG) who were present in WIHG camp at Chorabari Glacier on 16 June
and early morning of 17 June 2013(Dobhal 2013).

Figure 1(a)Location of Kedarnath in Utrakhand (Wikipedia);(b) Kedarnath Temple

Legend of the Chorabari Lake
The Chorabari lake is a moraine dammed reservoir. It is caused by the natural blockage of a
glacial valley by glacial moraine. It causes the resulting sediments to pile up behind the blockage
thus creating a reservoir for molten snow, ice and rain. The unstable temple is not directly
accessible by road and has to be reached by a 14 kilometers (8.7 mi) uphill trek from Gaurikund.
Pony and manchan (porter-carried) service is available to reach the structure. The temple was
allegedly built by Pandavas during their journey to heaven and revived by Adi Sankaracharya (
the great Hindu reformer ) and is one of the twelve Jyotirlingas, the holiest Hindu shrines of
Shiva. (Wikepedia, 2016) Kedarnath is an in accessible place even today accessible with great
difficulty only six months in a year. With modernization of India‟s transport system the rush of
pilgrims grew from a trickle in 1900‟s to a torrent today. There was an acute shortage of water
for consumption. As the area developed, the water from the Snowmelt Rivers was insufficient.
The people prayed for divine intervention. It is said that one day as the parched people of
Kedarnath prayed to Lord Shiva, and he sent his „ling‟ down to dam the valley above Kedarnath
and created a lake. Over the years the dammed portion was raised and used for consumption.
When disaster struck it is claimed that that very giant stone (Ling) that had dammed the valley,
tumbled down and came and stood between the temple and the mud flow thus protecting the
shrine. A huge rock got stuck behind Kedarnath Temple and protected it from the ravages of the
flood. The waters gushed on both the sides of the temple destroying everything in their path.
Even eyewitness observed that one large rock got carried to the rear side of Kedarnath Temple,
thus causing obstruction to the debris, diverting the flow of river and debris to the sides of the
temple avoiding damage. (Wikipedia, 2016) It still stands there today a mute spectator to the
destruction caused by mans greed and negligence. Deforestation and denudation of vegetation on
the slope to feed the firewood-fuel-needs of the ever growing pilgrim population, hap-hazard
development, unsustainable augmentation of reservoir height without provision of proper
spillway and design freeboard, (see Fig. 2) and no effort to de-silt the reservoir caused and
compounded this disaster.

Plausible Causes of Failure

The standard cause of failure was the cloud burst followed by snowmelt and overtopping. The
real reason for over topping was the silted up reservoir. We will discuss both the scenarios here.
Recent climate changes have had significant impact on high-mountain glacial
environment. Rapid melting of snow/ice and heavy rainfall has resulted in the formation and
expansion of moraine dammed lakes, creating a potential danger from dammed lake outburst
floods. The Indian Summer Monsoon is the major source of precipitation (rainfall) in the study
area with partial contribution from western disturbances during winter. On 16 and 17 June 2013,
heavy rains together with moraine dammed lake (Chorabari Lake) burst caused flooding of
Saraswati and Mandakini Rivers in Rudraprayag district of Uttarakhand.

Figure 2 the photo shows the raised part of the dam, the breech at the abutment and
the silt accumulated in the dam (WIHG).

Figure 3 Rain fall and pressure at Ghuttu observatory 38 km from Kedarnath

 Prolonged heavy down pour (Figure 3) on 16 and 17 June 2013 resembled „cloud burst‟
(except for amount of precipitation of 100 mm/h) type event in the Kedarnath valley and
surrounding areas that damaged the banks of River Mandakini for 18 km between Kedarnath and
Sonprayag, and completely washed away Gaurikund (1990 m asl), Rambara (2740 m asl) and
Kedarnath (3546 m asl) towns. The preliminary results suggest that the following two events
caused devastation in the Kedarnath area of the Mandakini River basin.(Dobhal et al 2013). This
was widely accepted as the official version as it exonerated all responsibility from any one
especially the powers that be. Subsequent Analysis of the disaster was only limited to the
overtopping and breech. The actual cause of the rapid overtopping was never discussed. This
paper suggests that the silting up of the reservoir by glacial deposits combined with the silt
pressure to enhance the impact of the disaster.

Preliminary Devastation Event

On 16 June 2013, at 5:15 p.m., the unprecedented heavy rains fell on the Saraswati River and
Dudh Ganga catchment area. This resulted in excessive flooding as the flow across all the
channels increased beyond safety limits. The slopes were denuded of vegetation due to active
deforestation in that area.

Figure 4: (a) Denuded Slope (Dobhal; May 2012 (b)Devastation of the valley See small
house in middle left edge for comparison of size. (Gupta 2013)
There was very active erosion creating deep gulleys and causing excessive water and
sediment accumulation in the rivers leading from that area (Fig 4). Subsequently, large volumes
of water struck the towns down river which as a result of erosion simultaneously picked huge
amount of loose sediment en route. The voluminous muddy water studded with debris from the
surrounding regions and glacial moraines moved towards Kedarnath town, washing off all newly
constructed structures that lay on and blocked the direct path of the flow - Sankaracharya
samadhi, Jalnigam guest house, Bharat Seva Sangh Ashram, etc. the whole upper part of
Kedarnath was buried and torn apart and leading to the biggest ever devastation ever witnessed
in the region. The WIHG meteorological stations near Chorabari glacier recorded 325 mm
rainfall at the base of the glaciers in two days on 15 and 16 June 2013. Due to heavy downpour,
the town of Rambara was completely washed away on 16 June evening.

Secondary Devastation Event

The second event occurred on 17 June 2013 at 6:45 a.m., after overflow and collapse of the
moraine dammed Chorabari Lake which released large volume of water that caused another flash
flood in the Kedarnath town leading to heavy devastation downstream (Gaurikund, Sonprayag,
Phata, etc.). Our study shows that the main cause of the Chorabari Lake collapse was torrential
rains that the area received between 15 and 17 June 2013.
 After the heavy rainfall the right lateral basin of the glacier, which is thickly covered by
snow more than 2 meters thick near the upper part of lake during June 2013, rapidly melted due
to rainwater allowing large amount of water accumulation in the Gandhi Sarovar lake. There
were no outlets in the lake, the water was simply released through narrow passages at the bottom
of the lake which were already partly blocked by silt. The sudden water accumulation blocked
these passages too. Suddenly millions of gallons of water accumulated in the moraine dammed
lake within 3 days, which increased their potential energy and reduced the shear strength of the
dam. Ultimately the loose-moraine dam breached causing an enormous devastation in the
Kedarnath valley (Figures 5 a,b,c,d & 6)

Figure 5: Shows the Devastation at Kedarnath

Figure 6: Showing devastation due to silt (Gupta ,2013)

Alternative methods available to prevent dam failure
Many retaining walls are built as part of housing projects on hill sides. Failure of such walls can
lead to catastrophic consequences. The effectiveness of a disaster reduction relies on the
perception of the disaster itself and previous experience

Analysis by other agencies

Various experts from all over the world studied this disaster; ASI, TERI, IITM, WIHR and many
others international and national agencies. There was just too much devastation and too much
data floating around. Each analyzed the failure in their own unique way and reached the same
conclusion. The danger was caused by excessive runoff, no runoff control (adequate dan storage)
and runoff diversion mechanisms and overtopping of the reservoir. But none dared to dwell into
why the reservoir overtop. The real reason was simple reduction of capacity due to siltation.
The experts, who were asked by the Archaeological Survey of India (ASI) to examine the
condition of the foundation in wake of the floods have arrived at the conclusion that there was no
danger to the temple. The IIT Madras experts visited the temple thrice for the purpose. Non-
destructive testing instruments that do not disturb the structure of the temple were used by the
IIT-team for assessing the health of the structure, foundation and walls. They have submitted
their interim report that the temple is stable and there was no major danger (Wikipedia, 2016).
Geologic Study
Geologically, the area north of the Pindari Thrust comprises calc silicate, biotite gneisses, schist
and granite pegmatite apatite veins belonging to the Pindari Formation3. Above 3800 m asl
altitudes, glacial processes dominate and between 3800-2800 m asl glacio-fluvial processes are
dominant; below 2800 m asl mainly the fluvial processes are active.
Geomorphologically Mandakini valley (Figure 7) was formed by the erosional and
deposional processes of glacio-fluvial origin. The Kedarnath town is situated on the outwash
plane of Chorabari and Companion glaciers. The channels of Mandakini and Saraswati Rivers
encircles this outwash plane and meet near the Kedarnath town where the outwash plane ends.

Figure 7: geomorphology of Kedarnath (Gupta ,2013)

These streams cut their banks every year. Overcrowding of the people near the temple led
to an artificial change in the course of Sarswati River which now flows just behind the Kedarnath
town. This was the major reason for the scale of the disaster.

Desiccation Cracking
The phenomenon of cracking is present in most geotechnical structures and has been of
particular interest to civil and mining engineers. Cracks increase by progression as drying
increases as shown in the (fig 8). Cracks pose a threat to the integrity of geotechnical structures
such as slopes, embankments, dams, tunnels, pavements, foundations, etc. Cracks adversely
influence the stability of slopes by:
1. Providing a preferential path to water flow, thereby inducing high pore-water pressures
2. Cracks can form part of the slip surface providing little or no shear strength.
3. Surface cracks formed due to silt deposition on the dam surface have a tendency to
progress inwards thus reducing the critical section of the dam.
4. Cracks provide initial route for piping failure
5. Cracks aid in washout during overtopping failure

Figure 8: shows Progression of desiccation or shrinkage cracks

Therefore, a clear understanding of the effect of cracks is vital for safe and economical
designs of levees, dams and slopes. Traditional design of earth embankments is based on the
hypothesis of intact fill, i.e., the presence and occurrence of cracks is disregarded. But under
actual conditions, it is unavoidable to prevent cracks formation. Desiccation cracks are formed
due to shrinkage of the soil mass as a result of evaporation of water during summer seasons. In
the hot summer seasons of India cracking is natural. The phenomenon of desiccation cracking is
presumed to increase in future due to global warming, when the range of the extreme
temperatures will increase. The total flow increases dramatically with increases in crack size
(Figure. 9a)

Figure 9: (a) flow v/s cracks (b) Dessication cracks (Khandelwal 2011)
The presence of cracks (fig 9b) makes the soil slopes susceptible to water seepage,
erosion, loss of shear strength and consequent failures (Khandelwal 2011)
Loss of storage Capacity of dam: The observed annual percentage loss in gross storage is given
in Tables below. The annual percentage loss in gross storage has been worked out as the average
based on the data of 239 reservoirs (CWC, 2015). Earlier it was believed that sediment in a
reservoir always deposited in the bottom elevations of a reservoir rather than depositing
throughout the full range of reservoir depth. It has now fully been established that sediment
deposits throughout the depth of reservoir and reduces the capacity of reservoirs at all elevations.
The maximum silting takes place at the interface of dam and water.

Figure 10: shows transport of sediments in dams

There is an up-wash of bottom sediments against the wall due to back pressure build up
and continuity of motion (Figure 10). This causes a bowl shaped bottom that can be seen in
various photographs of dried up dams elsewhere in India and internationally too.
In the reservoirs which have small sluicing capacity with respect to normal floods and
which have no reservoirs above them, the siltation rate is comparatively high in the first 15-20
years and thereafter it decreases. This is because the obstruction by the dam causes the dips and
flanks of the storage basin to fill up with silt in the early years. Besides, the progressive
development of deltas above reservoirs helps in trapping some of the silt load (Table 1a & 1b).
These tables show that the reservoir capacity is steadily decreasing. The impact is more
on the Himalayan region dams. The silt arrives as a suspension and different particle sizes settle
at different rates. The turbidity currents and eddies caused by heat cycle keep much of the silt in
suspension. The various sizes and turbulence cause a sub-zones in the reservoir storage zone as
shown in the figure below (Figure 11). There is a clear water zone of about one third height, a
turbid water zone of one sixth height, a sludge zone of one third height maintained by turbidity
currents and the settled sedimentation zone of the balance height. These values are not absolute
but vary from dam to dam depending on the properties of the catchment area. They are as seen
the tables above (CWC, 2015) the highest for Himalayan region. The values of siltation often
record only the bottom zone and ignore the other zones.
Additional Silt Pressures: Normally dams are designed for water pressure on the upstream side.
The silt load creates an additional pressure on the water face of the dam. As mentioned earlier
the various sizes cause a zonation of the reservoir storage zone. The IS code (IS:6515-1984)
gives the following provisions for Consideration of Silt Load. Gravity dams are subjected to
earth pressures on the downstream and upstream faces where the foundation trench is to be
backfilled. Except in the abutment sections in specific casts and in the junctions of the dam with
an earth or rock-fill embankment, earth pressures have usually a minor effect on the stability of
the structure and may be ignored. The present procedure is to treat silt as a saturated cohesionless
soil having full uplift and whose value of internal friction is not materially changed on account of
submergence. Experiments indicate that silt pressure and water pressure exist together in a
submerged fill and that the silt pressure on the dam is in proportion of the fill by submergence.
Criteria for Design - Horizontal „ silt pressure ‟ is assumed to be equivalent to that of a fluid
with a mass of density of 1360 kg/m2, and Vertical „ silt pressure ‟ is determined as if silt
equivalent to that of a fluid of mass density of 1 925 kg/m2. Thus we see that the factors of
safety will get considerably reduced due to siltation.
Stability calculation: Himalayan dams as mentioned earlier have a huge silt load almost 3.5 to 5
times that of dams in the rest of India. We will compare the factor of safety for normal dams with
no silt load and dams with silt load.
The silt is assumed to be uniformly distributed throughout the height of the water storage
during peak rainy season. The following values were adopted for the purpose of calculation.
Height of dam = 15 m; Density of moraine dam =2 Mg/m3 ; Density of water = 1
3
Mg/m
Density of silty water = 1.75 Mg/m3
 Figure 11: shows different zones in a Dam Storage

The factor of safety against over topping is reservoir volume (reach and depth)
dependent. The Chorbari dam was neither designed nor maintained hence there was no safe
balance storage volume. We have not calculated the factor of safety against over topping as there
was insufficient data available. But as seen in these deliberations siltation reduces the balance
storage to zero thus it also reduces the Factor of safety from 1 to nearly zero.

Figure 12: showing schematic silt pressure diagram and table used for stability check for
dam

The available commercial software do not adequately provide for silting load on
reservoir. The calculations of the factors of safety were hence performed on excel sheets
prepared by us. The results are shown below for comparison.

Table 3: of comparison between normal and silt load

Case Fs (Sliding) Fs (Over turning) Fs (Over topping)
normal load 1.5 4.8 0
silt load 1.26 4.39 0

Conclusion
Moraine dams are basically temporary natural earth dams. When these dams are augmented for
height without the proper precautions they are in danger of failure. The melting of Chorabari
Glacier combined with the cloud burst and the reduced capacity of the dam due to silting up
caused a major disaster that was avoidable. The results have shown that there is critical loss of
soil when an earth dam fails. The accumulated silt load cascades down the slope carrying with it
loose boulders and rock that obliterate everything in their path. Also the bigger the dam, the
greater the soil loss and resulting damage. The Government has to take care of these issues in
future zoning of such areas.(Dobhal et al 2013) Failure of such dams can lead to catastrophic
consequences. The data collected from various sources indicates that the disaster occurred due to
reduced reservoir capacity due to siltation, improper compaction as it was a natural blockage and
increase in height without spillway provisions. Due to natural formation of the lake there was no
proper bondage at the abutment of the moraine with the mountain. This was the weakest spot and
was saturated due to the ongoing monsoon season. It was the first to give way during the
overtopping caused by reduced reservoir flood absorption capacity due to silting up of the
reservoir. The effectiveness of a disaster reduction plans rely on the perception of the disaster
itself and what is learnt from such an experience.

References
ASDSO-Association of State Dam Safety Officials(2010) Dam Failures, Dam Incidents (Near
Failures) www.damsafety.org
CWC-Central Water Commission APRIL 2015 COMPENDIUM ON SILTING OF
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facts and plausible causes-Wadia Institute of Himalayan Geology, Dehradun 248 001,
India -CURRENT SCIENCE, VOL. 105, NO. 2pg 171-174
Gupta A. K et al (2013) - A Report On Kedarnath Devastation- Wadia Institute of Himalayan
Geology, Dehradun
IS:6512(1984) Indian Standard- Criteria For Design Of Solid Gravity Dams- Bureau Of Indian
Standard-„Smanak Biiava-N. 9 Bahadur Sliah Zafar Hlarg New Delhi 110003-section 5
Kaniraj. S. R IIT Delhi – 1995 – Design Aids in Soil Mechanics and Foundation Engineering. –
Tata McGraw Hill, New Delhi
Khandelwal S (2011) Effect Of Desiccation Cracks On Earth Embankments A Thesis Texas
A&M University
Nyoni K. -August 2013-Environmental Impacts of Earth Dam Failures and Spillway
Malfunctions-Greener Journal of Physical Sciences Vol. 3 (5), pp. 177-186, ISSN: 2276-
7851
Thandaveswar B.S. (1992) History of Dam Failures – ppt Lecture Notes- Indian Institute of
Technology Madras
Wikipedia,(2016) Kedarnath Temple www.wikipedia.com