Dam Breach Analysis And
Flood Mapping of Idukki Dam Project Report 2017
1. INTRODUCTION
1.1 General
In the heart of Idukki district in Kerala lies the Idukki dam- Asia’s biggest arch dam of
169.164m height proudly standing between two mountains- Kuruvanmala (839m) and
Kurathimala(925m). This prestigious project is situated in Idukki district and its underground
power house is located at Moolamattom which is 43 kilometer away from Idukki. Fig 1.1 and
fig 1.2 shows the upstream and downstream side of dam
When the Idukki dam was commissioned in 1976, a new landmark was created in Indian
construction. In many ways the project was unique and is regarded as a hallmark of
construction quality. This is India’s first arch dam. This is also the second highest concrete
dam in India.
The shape and quality of rock at the deep gorge where this dam was built was immensely
suitable to adopt the arch shape of dam. The double curvature arch shape has resulted in a
saving in concrete volume by 60% as compared to a gravity dam of this height.
The Idukki dam has been constructed across Periyar river in a narrow gorge between two giant
hills. It is 169.164m height and at the base its thickness is 19.81m. This is a double curvature
arch dam and in regard to height it comes second in the country. The water impounded by these
three dams has formed a single reservoir spread over 36 miles on a height of 2300 feet. Fig 1.3
and fig 1.4 shows Cherothoni and Kulamavu dam. In the power house, there are huge
generators of total capacity 780M. After the generation of electricity, water flows through a
4000 feet long tunnel to a tributary of Thodupuzha river. The Idukki project was completed
with the economic and technological assistance of Canada in accordance with the Colombo
plan of Commonwealth Countries.
1.2 History
The possibility of Hydroelectric development at Idukki was first conceived in 1919. According
to history, Sri Karuvellayan Kolumban, the Head of ‘Araya’ tribe, during 1922 showed the
way, to the Malankara estate Superintendent and his friend Thomas, the spot of present arch
dam while the two were hunting in the forest. Thomas was inspired by the site of the water
Department of Civil Engineering 1 KMPCE
Dam Breach Analysis And
Flood Mapping of Idukki Dam Project Report 2017
flow between the mountains and his idea made the dream come true of Idukki arch dam. Sri
W.J.John of Malankara estate submitted a report to the Government of Travancore in 1932 on
the possibility of constructing a Hydroelectric dam at Idukki.
In 1947, Sri P Joseph John, the Chief Electrical Engineer of the Government of Travancore
made a preliminary investigation report. On the request of the Government, the Central Water
and Power Commission took up detailed investigation in 1956. The project report was prepared
in 1961 and Planning Commission accorded sanction for the scheme in 1963.
The construction of this dam commenced on 30 April 1969. Storage of water in Idukki
reservoir commenced in February 1973. The inauguration of trail run of the first machine was
celebrated on 4th October 1975. Commercial operation of the power station was commissioned
on 12th February 1976 by the Prime Minister Smt. Indira Gandhi.
Construction of this arch dam and two other dams at Cheruthoni and Kulamavu has created an
artificial lake of 60 sq.km and the water stored is utilizes for the production of electricity at the
Moolamattom power house which is located inside the rocky caves.
The Canadian Government gave financial aid to the project and well known firms of
Construction Engineers were advising and assisstig the Project Engineers
Fig 1.1 Upstream Side of Idukki Dam Fig 1.2 Downstream side of Idukki Dam
Department of Civil Engineering 2 KMPCE
Dam Breach Analysis And
Flood Mapping of Idukki Dam Project Report 2017
Fig 1.3 Cheruthoni Dam
Fig 1.4 Kulamavu Dam
Department of Civil Engineering 3 KMPCE
Dam Breach Analysis And
Flood Mapping of Idukki Dam Project Report 2017
2. LITERATURE REVIEW
2.1 General
Investigators have carried out studies about the breach down analysis of different dams
including Idukki dam. They used different softwares including FLDWAV,HEC 1 etc. HEC
RAS is one of the simplest software used for breach down analysis of dams. No literature is
available for the breach analysis of Idukki dam using HECRAS software.
2.2 Review of Previous Works
Sanjay and Ravindra(2012) performed Dynamic Flood Routing and Unsteady flow
Modelling of Upper Krishna River. The Krishna River reach of length about 233 Km from the
downstream of Dhom Dam to Sangli city was considered for the flood routing studies. They
concluded that the model set up can be reliably used to get the flood flow profiles at Sangli.
Studies were also conducted to estimate the changes in the hydrographs under the estimated
worst scenarios. The analysis of available flood data was done to identify the flood sensitivity
of Sangli, due to Koyna and Dhom dam flood water release.
Adewale et.al.(2010) performed Flood Routing in Ogunpa river in Nigeria using HEC-RAS.
This study was focused on modeling of steady flow water surface profiles. Flood routing is
used to simulate flood wave movement through river reaches and reservoirs. Routing can be
applied using either hydrologic or hydraulic approaches. In a hydrologic approach, the spatially
lumped form of the continuity equation is applied, a water budget (or water balance) is
determined, and the flux relation of inflow, and outflow is evaluated. Hydraulic approaches
require both continuity and dynamic equations, which requires mass and momentum
conservation, channel geometry (cross section shape, bed slope, etc.), and resistance
characteristics such as river bed, banks, and floodplains. They concluded that the HEC-RAS
model has been able to identify those particular sections of the Ogunpa river course that are
susceptible to high water elevation levels and head, both of which are significant
indicators/precursors to flooding events.
Department of Civil Engineering 4 KMPCE
Dam Breach Analysis And
Flood Mapping of Idukki Dam Project Report 2017
Sunil Kute et.al.(2014) performed a case study of Godavari river flood modeling using HEC-
RAS software. The flood released for Gangapur dam, which is constructed on upstream of
Nashik city at 14 km distance is considered for the modeling. The HEC-RAS provides the
flood profile for the worst flood intensity. This profile will facilitate to adopt appropriate flood
disaster mitigation measures. Flood modeling using HEC-RAS is effective tool for hydraulic
study, handling of disaster management measures.
Yi Xiong(2011) carried out Dam break analysis using HEC-RAS. He considered Foster Joseph
Sayers Dam for the analysis. For better understanding the Foster Joseph Sayers Dam Break
mechanisms and impacts, some dam breach parameters were adjusted to simulate the dam
break and analyze the sensitivities. In addition, only piping break mode was analyzed because
the spillway has adequate capacity to prevent the dam failure due to overtopping. Five
scenarios of break simulation were compared: break with adjusted full formulation time, break
with adjusted breach width, break with adjusted breach depth, break with adjusted side slope
factor under PMF, and break without adjustment under PMF. He concluded that Dam break is
a complicated and comprehensive process and the actual failure mechanics are not well
understood. The dam break due to piping elongates the time period of high water surface level,
which increases the duration of risk. Foster Joseph Sayer dam break has greater impact on the
downstream location where is nearer the dam in accordance with the comparison of the
hydrographs at different locations.
Dam failure analysis models developed by National Weather Service (NWS) such as
DAMBRK, SMPDBK and FLDWAV are widely used. Gee and Brunner(2005) compared
USACE Hydrologic Engineering Center’s River Analysis System (HEC-RAS) model with
FLDWAV in the aspect of dam break flood routing. They concluded that the differences in the
interpretation and approximation of river geometry are the primary source of the differences
in the model simulations, although the numerical algorithms for solution of the St. Venant
Equations are similar.
Sunit Deo and Muchard compared common techniques and assumptions for Dam Break
Modelling with HEC-RAS. Unsteady flow modeling is often used in dam breach analysis due
to regulatory requirements or the need to obtain more detailed or accurate results for inundation
Department of Civil Engineering 5 KMPCE
Dam Breach Analysis And
Flood Mapping of Idukki Dam Project Report 2017
mapping than a simplified steady-state model can provide. Unsteady modeling of various
aspects of the dam failure and downstream flood wave propagation with HEC-RAS can be
performed using differing techniques and assumptions. The simplified breach method relies on
conservative assumptions to compute the breach discharge and the downstream reach length
over which the flood wave is attenuated. They identified that the reservoir routing method,
breach parameters, model used to develop the breach hydrograph, inclusion or exclusion of
bridges, method of modeling storage in tributaries, and flow level in the receiving stream are
just some of the factors that must be considered in the analysis. Each of these affects the results
to varying degrees and the impact on one model may be different than on another.
2.3 Need for Study
The need for conducting this study includes:
When the Mullaperiyar dam collapses, the water to be stored in the Idukki reservoir.
the capacity of Idukki dam for holding that much amount of water and the possibility
of break down has to be identified.
Idukki dam is one of the oldest dams in Kerala.
No breach analysis is done for the Idukki dam yet.
Proper rescue operations can be coordinated.
2.4 Scopes
Only HES RAS software is used.
Mainly Idukki related dams are considered.
Chances of inaccuracy in input datas may occur.
2.5 Objectives
To assess the breach down analysis of Idukki dam.
To assess the breach down analysis of Cheruthoni and Kulamavu dam.
To study the river analysis software.
To assess flood mapping using HEC RAS program – GEO HEC RAS.
Department of Civil Engineering 6 KMPCE
Dam Breach Analysis And
Flood Mapping of Idukki Dam Project Report 2017
2.6 Methodology
Site investigation.
Study of the software.
Collection of input datas from related Government official.
Hydrograph Generation.
Breach down analysis and Flood mapping.
3.SOFTWARE STUDY
Several softwares are available for the dam breach analysis i.e., FLDWAV, HEC 1, HEC
RAS etc. We have choosed HECRAS for the dam breach analysis of Idukki dam due to its
simplicity.
3.1 HEC RAS
HEC-RAS is a computer program that models the hydraulics of water flow through natural
rivers and other channels. The program was one dimensional, meaning that there is no
direct modelling of the hydraulic effect of cross section shape changes, bends, and other
two and three dimensional aspects of flow. The release of version 5.0 introduced two
dimensional modelling of flow as well as sediment transfer modelling capabilities. The
program was developed by the US Department of Defence, Army Corps of Engineers
inorder to manage the rivers, harbours, and the public work under their jurisdiction.
The Hydrologic Engineering Center (HEC) in Davis, Clifornia developed the River
Analysis System (RAS) to aid hydraulic engineers in channel flow analysis and flood plain
determination. It includes numerous data entry capabilities, hydraulic analysis components,
data storage and management capabilities, and graphing and reporting capabilities.
Department of Civil Engineering 7 KMPCE
Dam Breach Analysis And
Flood Mapping of Idukki Dam Project Report 2017
3.2 Working
The basic computational procedure of HEC-RAS for steady flow is based on the solution
of the one dimensional energy equation. Energy lossess are evaluated by friction and
contraction/ expansion. The momentum equation may be used in situations where the water
surface profile is rapidly varies. These situations include hydraulic jumps, hydraulics of
bridges, and evaluating profiles at river confluences.
HEC-RAS is equipped to model a network of channels. It is capable of modeling
subcritical, supercritical, and mixed flow regime floe along with the effects of bridges,
culverts,weirs and structures
3.3 Uses
HEC-RAS is a computer program for modeling water flowing through systems of open
channels and computing water surface profiles. HEC-RAS finds particular commercial
application in flood plain management and flood insurance studies to evaluate flood way
encroachment. Some of the additional uses are : bridge and culvert design and analysis,
levee studies, and channel modification studies. It can be used for dam breach analysis,
though other modeling methods are presently more widely accepted for this purpose.
3.4 Advantages
HEC-RAS has merits, notably its support by the US Army Corps of Engineers, the future
enhancements in progress, and its acceptance by many government agencies and private
firms. It is in public domain and peer-reviewed and available to download free of charge
from HEC’s website.
Department of Civil Engineering 8 KMPCE
Dam Breach Analysis And
Flood Mapping of Idukki Dam Project Report 2017
3.5 Disadvantages
Users may find numerical instability problems during unsteady analysis,especially in steep
and highly dynamic rivers and streams. It is often possible to use HEC-RAS to overcome
instability issues on river problems.
3.6 HEC-RAS Programs
Aquaterra : Professional software for canals and river engineering works design.
ArcView : Can read in AutoCad drawings for backgrounds and can create DTM.
GeoHECRAS : 2 D/3D visualization program in HEC-RAS
Fig 3.1 3 D view of River Channel
Department of Civil Engineering 9 KMPCE
Dam Breach Analysis And
Flood Mapping of Idukki Dam Project Report 2017
4.INPUT DATAS
4.1 Dam Features – Idukki dam
Latitude at Dam Site : Degree 9 Minute 50 Second 33 North
Longitude at Dam Site : Degree 76 Minute 58 Second 36 East
Type: Concrete (Double curvature thin parabolic arch dam)
Length of dam at Top (m): 365.85
Width of Dam at Top (m): 7.62
Height above deepest foundation level (m): 168.91
Volume Content of Dam (103 m3): 0.465
4.2 Reservoir Features
Catchment Area at Dam site (km2): 526.29
Maximum Water Level (m): 734.30
Full Reservoir Level (m): 732.62
Minimum Draw Down Level (m): 694.94
Dead Storage Level (m): 695.12
Live Storage Capacity (Mm3): 1545
Gross Storage Capacity (Mm3) at FRL: 1996.30
Reservoir Spread Area (km2) at FRL: 59.83
Department of Civil Engineering 10 KMPCE
Dam Breach Analysis And
Flood Mapping of Idukki Dam Project Report 2017
Table 4.1 Instruments Installed in the Dam
Sl No. Name of Instruments Total Functioning % Reliability
Instrument
1 Stress Meter 52 22 42
2 Strain Meter 83 49 59
3 Rock Target 30 - -
4 Pendulum 6 6 100
5 Clinometer 1 - -
6 Base Meter 4 - -
7 Instrumented Cylinders 7 - -
8 Water Thermometer 8 - -
Department of Civil Engineering 11 KMPCE
