Final EMP Report of Bursar Project

Chapter 9
DAM BREAK ANALYSIS AND
DISASTER MANAGEMENT PLAN

9.1 Introduction

A hydropower project is laid in river valleys possessing virgin landscape of the natural
environment. These projects involve construction of various civil structures like dam,
diversion tunnels, headrace tunnel, open channels, shafts, underground/surface
powerhouses etc, of all the structures dams are the most critical one which creates a
barrier and impounds huge reservoir of water behind and are thus vulnerable to failure
because of natural hazards if ill designed. To ensure long and economic life of the
project, it requires to be appropriately designed based on the inputs gathered from
topographical, hydrological, geological, geotechnical and seismological
surveys/investigations of the site selected. The impact of project components on the
environment need to be critically and scientifically analyzed, evaluated and a detailed
account of disaster be incorporated as a “Disaster Management Plan” (DMP) forming
part of EMP. The disaster would occur either because of technical flaw in dam design
or because of some natural calamity/catastrophe like earthquakes, incessant rainfall,
cloudburst and glacial outburst etc. The principal objective of the Disaster Management
Plan is to identify the disaster potential scenario, suggest advance planning and
measures to combat any eventuality that the project may experience during the project
operation and its life. Thus it is very important to have the dam disaster management
plan prepared in advance so that prompt action is taken for rescue operations in case of
any eventuality to minimize the damage to nearby settlements, loss of life and property
and environment.

9.2. Model for Dam Break Analysis

A number of dam break models are followed to assess failure of dam. However, the
choice of a model depends upon the ground prevailing situations. All dam break models
are categorized into two groups i.e; the simple empirical models and the sophisticated
ones requiring high-level computer skills. Among these National Weather Services
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(NWS) dam break (DAMBRK) model has been widely used over and has also been
followed in the present study with the help of an empirical method. For purpose of
making a decision about as to what exact magnitude of inflow to be adopted for design,
a comparison needs to be made between computed synthetic values and record of
floods that have occurred in the general area of interest. In the present investigation,
such a comparison has been made following the methods outlined here. The input
parameters used in these models include reservoir details, failure time interval, terminal
size, shape of breach, downstream river cross sections, hydraulic parameters of stream,
catchment characteristics, etc.

9.3. Principles of the Dam Break Model

The DAMBRK model simulates the failure of a dam, computes the resultant outflow
hydrograph and also simulates movement of the dam break flood wave through the
downstream river valley. The model is built around three major capabilities- reservoir
routing, breach simulation and river routing. The reservoir routing may be carried out
using hydrological routing techniques. DAMBRK model is capable of adopting storage
routing or dynamic routing methods for routing floods through reservoirs depending on
the nature of flood wave movement in reservoirs at the time of failure. After computing
the hydrograph of the reservoir outflow, the time of occurrence of flood in the
downstream valley is determined by routing the outflow hydrograph through the valley.

The dynamic wave method based on the complete equations of unsteady flow is the
appropriate technique to route the dam break flood hydrograph through the downstream
valley. The method is derived from the original equation developed by St. Venant.
DAMBRK model uses St. Venant‟s equations for routing dam break floods in channels.

i) Reservoir Routing:

In this model the reservoir routing may be performed either by using storage routing or
dynamic routing.

ii) Storage Routing:

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The storage routing is based on the law of conservation given as:

I-Q=ds/dt (a)

Where,

I: Inflow into the reservoir

Q: Outflow from the reservoir

ds/dt: Rate of change of reservoir storage volume with time

The above equation (a) can be expressed in finite difference from as given
below:

(I+I')/2-(Q+Q')/2= ∆s/ ∆t (b)

In which the superscript (') denotes values at the time t-∆t. The term ∆s may

be expressed as below:

∆s = (As+A's) (h-h')/2 (c)

Where,

As: Reservoir Surface Area w. r. t. Reservoir Elevation (h)

A's: Reservoir Surface Area w. r. t. Reservoir Elevation (h')

The discharge „Q‟ in the equation (b) is a function of reservoir storage and

is evaluated using Newton-Raphson technique.

iii) Dynamic Routing:

The hydrologic storage routing technique, expressed by equation (b) implies that the
water surface elevation within the reservoir is horizontal. The routing principle is same

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as dynamic routing in river reaches and it is calculated by using St. Venant‟s equation.
The movement of the dam break flood wave through the downstream river channel is
simulated using the complete unsteady flow equations for one dimensional open
channel flow, alternatively known as St. Venant‟s equations. These equations consist of
the continuity equation and the conservation of momentum equation:

∂Q/∂t+∂ (A+A0)/∂t=q (d)

And the conservation of momentum equation is

∂Q/∂t +∂ (Q2/A) ∂x+g*A(∂h/∂x+Sr+Sc+Lc)=0 (e)

Where,

A= Active cross-sectional flow area

A0= Inactive (off-channel storage) cross-sectional area

X = Distance along the channel

q=Lateral inflow or outflow per unit distance along the channel

g=Acceleration due to gravity

Q=Discharge

h=Water surface elevation

Sf= Friction Slope

SC= Expansion-contraction loss slope

Lc= Lateral inflow/outflow momentum effect due to assumed flow, path

of inflow being perpendicular to the main flow.

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The friction slope and expansion-contraction loss slope are evaluated by the following
equation:

Sf =N2*Q2/2.21* A2* R ¾ and

SC = K*∆ (Q/A)2/2* g* ∆x

Where,

N= Manning‟s roughness coefficient

R=A/T where T is the top width of the active portion of the channel

K= Expansion-Contraction Coefficient

∆ (Q/A)2 = Difference in (Q/A)2 for cross sections at their reach end.

* is used to denote multiplication

The non-linear partial differential equations (d) and (e) are represented by a
corresponding set of non-linear finite difference algebraic equations and they are solved
by the Newton-Raphson method using weighted four point implicit scheme to evaluate
„Q‟ and „h‟. The initial conditions are given by known steady discharge at the dam, for
which steady state non-uniform flow equations are used. The outflow hydrograph from
the reservoir is the upstream boundary condition for the channel routing. The model is
capable of dealing with fully supercritical or fully sub critical flow or the upstream
reach supercritical flow. There is a choice of downstream boundary conditions such as
internally calculated loop rating curve, user provided single value rating curve, user
provided time dependent water surface elevation, critical depth and the dam which may
pass flow via spillways, overtopping and/or breach.

9.4 Methodology

The computation of flood wave resulting from a dam breach basically involves two
problems, which can be considered jointly or separately, they are:

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i) Outflow hydrograph from the reservoir, and

ii) Routing of the flood wave downstream from the breached dam along the
river channel and flow plain.

If breach outflow is independent of downstream conditions, or if their effect can be

neglected, the reservoir outflow hydrograph is referred to as free outflow hydrograph.
In this case, the computation of the flood characteristics is divided into the following
two distinct phases:

i) Determination of outflow hydrograph with or without the routing of the

negative wave along the reservoir, and
ii) Routing of flood wave downstream from the dam breach.

The problem of simulating the failure of a dam is done by computing the free outflow
hydrograph from the breached dam using storage routing technique. The routing of this
outflow hydrograph along the downstream channel is done by using dynamic routing
technique with the aim of reproducing the maximum water level marks reached during
the passage of flood wave. The information regarding inflow hydrograph into the
reservoir due to the Probable Maximum Flood (PMF) at the time of failure, the
structural and the hydraulic characteristic details of the dam, the time of failure, the
channel cross sectional details, the maximum water level marks reached in the reservoir
at the time of failure and those observed in the downstream reach of the dam due to the
passage of flood wave, etc have been considered in this study.

9.5 Project Salient Features and Details

The summary of the project salient features are given in Table 9.1 and the details are
described in the following paras.

iv) The Bursar Project is proposed on River Marusudar which involves construction
of straight gravity concrete dam near village Pakal, about 25km downstream of
the confluence of Wadwan and Rin rivers. It is proposed to divert a designed
discharge of 209.95 cumecs (at Pakal having invert level of the intake structure
at EL 2014.69m) through 6.7Km long tunnel of 8.5m diameter to surface
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powerhouse (at Lopara). A dam toe powerhouse is also planned to utilize 22.90
cumecs of water for power generation as well.
v) Bursar Project is envisaged as a storage project. Based on the Reservoir
Elevation-Area-Capacity studies, by utilizing 35 cross sections (at interval
varying from 100m to 500m) from the dam axis covering the upstream distance
of 22.80km up to tail of the proposed reservoir. Reservoir parameters computed
are: surface area 12.48 sq km at FRL (EL 2134m) and the gross storage of
reservoir at proposed FRL (EL 2134m) is as 726.30 Mcum. At MDDL (EL
2030m), capacity of reservoir has been as 107.86 Mcum and therefore live
storage works out to 618.44 Mcum (0.501MAF). At FRL the reservoir surface
area would be of elongated shape.
vi) The proposed dam would be 265m high from river bed level (EL 1872) the dam
top would correspond to EL 2137m. The dam top ( EL 2137m) shall have a
length of 737m, of which non-overflow portion 677m in length and overflow
portion 60m in length. The overflow section constitutes spillway portion (total
60m length), to cater the designed flood discharge, which comprises four blocks
(each 15m) which has its crest elevation at 2114.50m. Each spillway shall be
provided with hydraulically operated radial gates.
vii) Marusudar is a mighty right bank tributary of the river Chenab. The catchment
area of the Marusudar River at Dam site is 3060 km2, comprising 1676 km2
snow-fed and 1384 km2 rain-fed.
viii) Design flood analysis has been carried out for the project. The flood/peak
discharge in Marusudar River is generally observed during the monsoon period
due to heavy rains and snowmelt in its catchment. As the reservoir storage is
726.30 MCUM, the height of the dam being higher than 30m, therefore, as per
Central Water Commission criteria and IS-1223-1985, the spillway of the dam
is required to negotiate maximum probable flood.

For the estimation of the design flood for the Bursar project the annual flood peaks for
the period 1975-2013 have been used in the flood frequency analysis. Thus the series
developed in this manner for the period 1975-2013 has been used to perform analysis at
the dam site. Since the peak flow can pass at any time other than the observed time of

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the discharge flow, the annual flood peaks were enhanced by 36% to make it
instantaneous flood peaks, as the hourly gauges are not available for the flood period.
The data on flood peaks at the dam site for the period from 1975-2013 are given in
Table 9.2 and Fig 9.1.

On the basis of the results of the flood frequency analysis Probable Maximum Flood of
4577 cumecs has been recommended and adopted for the Bursar Project. Unit
hydrograph studies, for computation of flood inflow to a full reservoir, reveal peak
flood discharge of 4419 cumecs which is nearly comparable with the value of 4577
cumecs computed by frequency analysis method. 2-day SPF has been worked out as
2792 cumecs. 100 year return flood value of 2126 cumecs has been adopted. The
diversion flood value of 1650 cumecs, based on the available data base, has been
recommended for 25 year return period.

HEC-RAS model was run to develop the rating curves at Dam site and at TRT outlet
locations on the Marusudar River, and the curves indicate that the discharge of 4750
cumecs correspond to the water level of 1887.66m for the dam axis location while as at
the TRT outlet location the discharge of 4750 cumecs correspond to the water level of
1737.65m.

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Table 9.1 Salient Features of Bursar Project

S. No Description Features
1 River Marusudar
2 Catchment Area Up to Dam Site 3060 Sq Km
3 Elevation (Origin) of River 5175m
Average Annual Rainfall 757.00mm
4
Average Annual Snowfall 467.10mm
5 Design of the Project Storage
6 River Length Up to Dam Site 133 Km
7 Type of the Dam Concrete Gravity
8 Dam Top EL 2137m
9 Bed Elevation at the Dam site 1872m
10 Height of the Dam (from river bed level) 265m
11 Full Reservoir Level (FRL) 2134m
12 Maximum Water Level 2134m
13 Minimum Draw Down Level 2030m
Gross Storage
At FRL 726.30 MCUM
At MDDL 107.90 MCUM
14
Live Storage 618.40 MCUM
(0.5 MAF)
Reservoir Surface Area at FRL 12.48 Sq Km
18 Manning‟s “n” 0.040
Design Flood Value (PMF) Adopted 4577 Cumecs
19
GLOF 371 Cumecs
20 Diversion Flood Adopted 1650 Cumecs
21 Annual Peaks Discharges Enhanced by 36%
22 Average Annual Sediment Load (computed) 253.20 Ham
23 Bed Load Sediment (Assumed) 20%
24 Annual Sediment Load (Adopted) 306 Ham
25 Rate of Sediment Inflow 0.1 ham/sq.km/year

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Table 9.2 Annual Peak Discharge (cumecs) of the Marusudar River at the Dam
Site
S. Peak Discharge Instantaneous Peak Discharge
Year
No (Cumecs) (Cumecs)
1 1975 1010.1 1373.73
2 1976 1062.6 1445.13
3 1977 1003.2 1364.35
4 1978 1257.4 1710
5 1979 1099.8 1495.72
6 1980 1169.9 1591.06
7 1981 970 1319.2
8 1982 898.9 1222.5
9 1983 1097.7 1492.87
10 1984 1184.1 1610.37
11 1985 936.2 1273.23
12 1986 1417.7 1928.07
13 1987 1407.4 1914.06
14 1988 1476.3 2007.76
15 1989 961.1 1307.09
16 1990 1196.5 1627.24
17 1991 1324.1 1800.77
18 1992 1189.4 1617.58
19 1993 1345.1 1829.33
20 1994 1212.7 1649.27
21 1995 1081 1470.16
22 1996 1162.4 1582.66
23 1997 699.5 951.32
24 1998 1060 1441.6
25 1999 761.1 1035.09
26 2000 571 776.56
27 2001 575.2 782.27
28 2002 735.6 1000.41
29 2003 961.3 1307.36
30 2004 388.7 528.63
31 2005 882.9 1200.74
32 2006 952.1 1294.85
33 2007 1005.4 1367.84
34 2008 1036.9 1410.18
35 2009 854.9 1162.66
36 2010 1031.1 1402.29
37 2011 1021.81 1389.66
38 2012 937.7 1275.27
39 2013 1104.2 1501.71

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2500

2000
Peak Discharge (Cumecs)

1500

1000

500

0
1 6 11 16 21 26 31 36

Time in Year (1975-2013)

Fig.9.1 Annual Flood Peak Discharge Curve of Marusudar River at the Dam Site

9.6 Data Requirement

The analysis of the dam failure involves the generation of database on catchment which
includes soil, drainage, precipitation and topographic characteristics; and hydraulic
characteristics, etc. to prepare the following:

i) Inflow hydrograph to the reservoir at the time of failure,

ii) Routing through the reservoir at the time of failure,
iii) Outflow hydrograph at various desired downstream locations, and
iv) Finding the movement of the flood wave downstream to determine travel
time, maximum water level reached, inundated areas, etc.

Data on the dam parameters, inflow hydrograph into the reservoir and outflow
hydrograph include information on:

v) Reservoir elevation-area-capacity relationship,

vi) Spillway details,
vii) Elevation of top and bottom of the dam,

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viii) Elevation of water surface in the reservoir at the beginning of analysis and
the time of failure,
ix) Breach description data, and
x) Cross-sections of the river at different locations downstream of the dam site

The data considered for conducting the dam break analysis included data pertaining to
dam and river characteristics as given in Table 9.1. The breach parameters included
time of failure of breach (T), bottom width of breach (b), side slope of breach (z), final
elevation of the bottom of breach (hbm), initial elevation of water level in the reservoir
(hi), final elevation of water level when breach (hf) begins to form and top of dam (hs)

Concrete gravity dams tend to have partial breach as one or more monolith sections
formed during the construction of the dam are forced apart and over turned by the
escaping water. The time for breach formation is a matter of a few minutes. It is
difficult to predict the number of monoliths, which may be displaced. In the present
study, the concrete dam (top 2137m and FRL at 2134m) is having 46 blocks (25 on left
bank, 17 on the right bank and 04 spillway blocks). It has been assumed that the four
spillway blocks are most critical. Since spillway is in four blocks (each of 15m width),
therefore breach widths have been taken 15m, 30m, 45m and 60m. The breach time
assumed for all the breach widths are 15 minutes. Since the dam is of concrete type
therefore side slope breach has been taken as zero. Bottom breach is at 1872m
elevation.

31 cross sections of the river Marusudar downstream of the proposed dam axis, were
used 18 of which were furnished by the project authority whereas data of 13 were
generated from the available Survey of India Topo Sheets (1: 50,000 Scale and 25,000
Scale). The contraction and expansion coefficients between cross-sections were
estimated for all other parameters such as initial size of time step and downstream
boundary parameter. The weighting factor the convergence criterion was kept at zero.
The routing of the outflow hydrograph through the reservoir to downstream valley was
carried out.

The data pertaining to the 31 locations, downstream from the dam, is given in Table

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9.3. This data includes that of bed levels, water columns in the river channels, flood
levels after the dam breach and the lag time.

Table 9.3 Bed Level versus Flood Wave Level at Different Locations Downstream
of Dam
Location Flood Wave Bed Pre-Flood Time
(D/s from Dam Level Level Water Lag
site) (m) (m) Level (m) (m)
0 km 1982.50 1872.00 1876.42 0
1 km 1962.78 1847.78 1854.54 5.90
2 km 1943.23 1825.73 1828.23 11.80
3 km 1921.00 1803.60 1806.10 17.70
4 km 1885.00 1783.30 1788.08 23.60
5 km 1870.00 1743.90 1750.42 29.50
6 km 1795.00 1717.20 1721.04 35.40
7 km 1740.00 1704.23 1705.73 41.30
8 km 1770.00 1679.66 1680.16 47.20
9 km 1734.50 1669.25 1669.50 53.10
10 km 1732.80 1647.55 1647.80 59.00
11 km 1727.50 1637.62 1637.87 64.90
12 km 1718.50 1622.64 1625.64 70.80
13 km 1736.25 1612.13 1615.13 76.70
14 km 1743.00 1605.75 1608.75 82.60
15 km 1695.00 1597.66 1601.66 88.50
16 km 1673.07 1575.48 1578.48 94.40
17 km 1691.84 1540.90 1542.59 100.30
18 km 1706.40 1520.00 1521.50 106.20
19km 1617.33 1480.00 1482.00 112.10
20km 1624.62 1440.00 1441.48 118.00
21km 1588.75 1400.00 1402.49 123.90
22km 1567.98 1399.00 1401.38 129.80
23km 1482.91 1263.33 1265.83 135.70
24km 1469.69 1185.82 1187.32 141.60
25km 1326.12 1156.05 1158.55 147.50
26km 1401.42 1154.28 1155.78 153.40
27km 1313.35 1154.10 1155.40 159.30
28km 1299.29 1153.50 1154.80 165.20
29km 1213.69 1152.90 1153.90 171.10
30km 1294.32 1152.10 1153.20 177.00
31km 1293.53 1145.25 1146.75 182.90

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9.7 Results and Conclusions

The dam is apparently safe for various upstream and downstream water level cases but
a drag force would be exerted on remaining blocks due to assumed breach cases.
However, in case of dam break, the maximum water levels of the outflow downstream
of dam axis up to 31 km are given in Table 9.3 and Fig. 9.2. The study was conducted
on 60m breach width and 15-minute breach period. As per the UK Dam break
Guidelines and U.S. Federal Energy Regulatory Commission (FERC) Guidelines the
short beach time of 15-minute has been taken because the concrete dam failure is
instantaneous. The results of modelling reveal a time lag of about 182.90minutes (about
3h and 04m) to reach 31 km downstream of the dam site. The distribution of time lag
v/s flood wave downstream from the dam for 31 km distance is given in Table 9.3 and
the resulting curve is given as Fig. 9.3 (a & b). Flood Wave Level versus Different
Downstream Locations is shown in Fig. 9.3 (a); while as Time Lag Curve of Flood
Wave is shown in Fig. 9.3 (b).

However, it is seen that the flood wave would terminate near about RD 24875 & EL
1326.12m of the river course i.e; near Simanhine and Kurur located along right and left
banks respectively after a time lag of 2h and 45m.

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2100 Flood Level (m)

Series1
2000

1900 Bed Level (m)

Series2

1800

1700

1600

1500

1400

1300

1200

1100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Distance Downstream of Dam Axis (Km)
Fig.9.2: Maximum Flood Wave v/s Bed Level at Downstream Locations of Dam

2100
2000
1900
1800
1700
1600
1500
1400
1300
1200
1100
0 1 2 3 4 5 6 7 8 9 10111213141516171819202122232425262728293031

Distance Downstream of Dam Axis

(Km)
Fig. 9.3 (a) Flood Wave Level versus Different Downstream Locations

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200
180
160
140
Lag Time (minutes)

120
100
80
60
40
20
0
1 5 9 13 17 21 25 29

Fig. 9.3 (b) Time Lag Curve of Flood Wave

From the profiles of flood wave crests and flood map downstream of the dam, it seen
that the flood wave would inundate the lower portions/fringes of the villages:

 Along right bank- Kaspal Had, Hirar, Tarungai, Bhardu, Lopora, Batpora,
Thonsar, Prangas & Tundar, Kraipokhun, Gwan, Bazdiun, Cherabhatson and
Simanhine. Amongst all the settlements located in these villages only five (05)
houses: one (01) at Bhatpora and three to four (04) at Cherabhatson and
Simanhine would get affected.
 Along left bank- Chhichha, Sirshi, Tragbal, Panjdhar, Loharna, Sondar, Tandar,
Swarbhati, Drungdhuran, Pinj and Kurur. Amongst all these settlements located
in these villages only twenty nine (29) houses: one (01) at Chhichha, three (03) at
Chirazbal, one (01) at Loharna, two (02) at Sonder, one (01) at Drangdhuran, six
(06) at Pinj, seven (07) at Ikhala and six (06) of Kurur would get affected.
 From the above it is also seen that in all 32 (thirty two) households besides some
ropeways, mills and wooden bridges may also get affected.

Based on this likely anticipated disaster that may occur at the time of dam breach a
comprehensive Disaster Management Plan with tentative costs has been formulated to
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deal with the situation and is discussed in the paras that follow.

9.8 Disaster Management Plan

Preparation of “Disaster Management Plan” for any hydroelectric project is a

prerequisite, as catastrophic situation, which is highly unpredictable, may occur any
time in the life span of project. To tackle the catastrophic situation development of an
effective “DMP” is imperative to establish co-ordination between District
Administration and Project Authority. Line/Assisting agencies from district
administration side are Fire Services, Police Department, Medical Services, Consumer
Affairs and Public Distribution Department, Transport Department, Communication
Department, Meterology Department, Irrigation and Flood Control Department, Civil
Defence Forces and Voluntary Organizations. Coordination and close cooperation
among all the agencies involved is essential for the timely and successful
implementation of “DMP” to provide relief to the affected at the time of need.

Well defined role and responsibilities of assisting agencies in “DMP” is required, so

that proper planning, according to the intensity of disaster could be made by agencies.
Identification of the event and its intensity in the affected area is assessed by the Chief
Co-ordinator. He should be authorized to declare “disastrous situation” based on
detailed information available, so that assisting agencies swing in action to mobilize
their resources in affected area. Based on the intensity of disaster in project a proper
relief programme may be implemented by District Administration with the help of
assisting/line agencies.

9.8.1. Preparation of Inundation Map

The downstream areas vulnerable to inundation by dam break flood are shown in the
inundation map prepared for the area is placed as Fig.9.4. In the dam break models
maximum flood elevation at each original or interpolated cross section is computed.
The selected dam break flood for this purpose corresponds to the extreme conditions
that yield maximum possible flow storage at the downstream locations. The extreme
condition is estimated from various parameters like breach width, minimum time of

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Fig. 9.4 Inundation map of Bursar Project

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failure and Manning‟s coefficient. The inundation map has been prepared with the help
of water surface elevation profile, which has been computed for maximum flood
discharge elevation and at various downstream locations.

Given the topographic characteristics the flood will be confined generally within the
narrow valley sections barring low lying areas of Kaspal Had, Hirar, Tarungai, Bhardu,
Lopora, Batpora, Thonsar, Prangas & Tundar, Kraipokhun, Gwan, Bazdiun,
Cherabhatson and Simanhine along the right bank; and Chhichha, Sirshi, Tragbal,
Panjdhar, Loharna, Sondar, Tandar & Swarbhati, Drungdhuran, Pinj and Kurur.
However, thirty two household owners of these villages shall get affected. The details
of these are: Five (05) houses: one (01) at Bhatpora and three to four (04) at
Cherabhatson and Simanhine along the right bank would get affected; and Twenty
nine (29) houses: one (01) at Chhichha, three (03) at Chirazbal, one (01) at Loharna,
two (02) at Sonder, one (01) at Drangdhuran, six (06) at Pinj, seven (07) at Ikhala and
six (06) of Kurur along left bank would get affected. Besides some ropeways, mills and
wooden bridges may also get affected.

The map thus prepared, would serve as a guide for working out details of these
vulnerable areas. The inundation map would be displayed at all the downstream flood
prone locations depicting maximum water level that would be attained. The elevations
together with other geographical details could be marked on ground of the downstream
areas (fig. 9.5).

On the basis of the dam break analysis the flood wave is expected to inundate some low
lying areas in the first twenty five km downstream of the dam site approximately in 02
hour and 45 minutes. This means that very little time would be available for execution
of any rescue and/or evacuation plan. Therefore, the Disaster Management Plan has
been devised mostly for preventive measures. As a first measure of the management
plan it is suggested that surveillance and monitoring schemes be implemented
simultaneously with the design and detailed engineering stage of the project. It should
continue during the construction phase through impoundment of reservoir, early
operation period, and operation and maintenance phases during the life of the dam. On

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Fig. 9.5 Elevation contours of Bursar project area

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the onset of high discharge period on all dates the electricity, public announcement
system, power generator backups etc; should be thoroughly checked.

In the event of dam break the following flood conditions have been considered for
different levels of alertness.

Table 9.4 Flood conditions for different levels of alertness

Sl. No. Water Level Status

1 Below FRL (2134m) (20% of the PMF) Normal Flood

Level-1
2 Rises above FRL Emergency

3 Top of Dam (2137) and keeps on rising Level-2 Emergency

Top of dam and continues to rise and breach Disastrous Level

4
start

The following precautionary and preventive measures need to be taken up at the

different levels of emergency:

Level-1 Emergency: At the Level-1 Emergency all gates should be kept fully
operational. All concerned officials should reach at the dam site to take suitable
preventive measures. All warning systems should be kept on alert. The local
monitoring officials should be kept abreast of the situation. A flood warning should be
issued to the people at risk for taking up of life saving measures.

Level-2 Emergency: At this point only a few minutes would be available for taking
any action. All the staff from the dam site would be alerted and advised to move to a
safe place. The District Administration and NHPC authorities should be informed about
the possibility of dam failure. All the communication systems and safety measures
should be put into operation immediately. Public announcement system and/or

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centralized siren system should be used.

Disastrous Level: Under the disastrous conditions only life saving measures should be
given priority and the administration and project authorities should be intimated
immediately.

9.8.2. Mitigation Measures/ Dam Safety Measures

The following measures should be taken to avoid loss of lives and property.

a. Monitoring

As the dam safety plan is most important, the project authorities (NHPC) should
prepare detailed effective dam safety surveillance and monitoring scheme, which
should include rapid analysis and interpretation of instrumentation and different
observation data along with periodic inspection, safety reviews and their evaluation.

The Dam Safety Plan is implemented during the following the following five phases
covering the life of the dam.

(i) Design and investigation phase

(ii) Construction Phase
(iii) First reservoir impoundment
(iv) Early operation period, and
(v) Operation and maintenance phase

b. Strengthening of river banks downstream of dam

The slopes of the low lying areas of the Kaspal Had, Hirar, Tarungai, Bhardu, Lopora,
Batpora, Thonsar, Prangas & Tundar, Cherabhatson and Simanhine along the right
bank; and Chhichha, Sirshi, Tragbal, Panjdhar, Loharna, Sondar, Tandar & Swarbhati,
Chirazbal, Drangdhuran, Pinj, and Kurur along the left bank shall get inundated thus be
provided with protection measures viz; construction of gabions/wire mesh crates. These
structures may be raised up to the level of danger mark.

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c. Emergency action plan

The formulation of an emergency action plan would depend upon the expected levels of
emergency. The specific safety plans for different levels of emergency would have to
be prepared for tackling the dam break situation and chalk out appropriate warning
procedures to be followed in case of failure and/or potential failure of the dam. The
main emphasis should be an issuing timely warning to the people at risk and alert the
officials responsible for taking action in case of an emergency.

d. Administrative setup

The administrative and procedural aspects of an Emergency Action Plan consist of a

flow chart depicting the names and addresses of the designated officials appointed for
the purpose. In case the failure is imminent or the failure has occurred or a potential
emergency condition is developing, the observer at the site should report to the
Engineer-in-Charge through a wireless system or by any fastest available
communication system. The Engineer-in-Charge would in turn be responsible for
informing the Civil Administration, viz; District Magistrate about the developing
situation.

For implementation of “Disaster Management Plan” at the time of emergency, setting

of a control room as nodal point to monitor the ground situation is essential. Control
room should be located in close vicinity of the project and equipped with the following:

i. Copy of Disaster Management Plan

ii. Resource Plan prepared by the District Administration
iii. Map indicating evacuation points for affected population at the time of
emergency and their shelter areas etc
iv. Area map showing topographic, demographic and infrastructure details, i.e;
hospitals, roads, helipads, school etc.
v. Telephone directory to contact various assisting agencies and communication
system such as telephones, VHF sets etc.

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Each person should be made aware of his/her responsibilities/duties and the importance
of work assigned under the Emergency Action Plan. All villages falling under the flood
prone zone or on margins should be connected through wireless communication system
with a back-up of standby telephone lines. A centralized siren alert system should be
installed at all the village “Panchayat Ghars” so that in the event of a warning all
villagers can be alerted through sirens.

e. Maintenance measures

The personnel responsible for preventive measures would identify equipments that
need repairs and the materials needed for the purpose, labour and expertise for use
during an emergency. The amount and type of material required for emergency. The
amount and type of material required for emergency repairs should be determined for
the dam, depending upon its characteristics and design. Sufficient and suitable
construction materials should be stockpiled near the dam site. The anticipated need of
equipment should be evaluated and if these were not available at the dam site, the exact
location and availability of this equipment should be determined and specified. The
sources/agencies be provided with necessary information/instruction or assistance in
case of emergency situations.

Dry mock runs, drills and exercises should be conducted from time to time simulating
the emergency situations in order to evaluate and assess the effectiveness of various
preventive actions that should be framed to tackle emergency situations. A plan for
regular inspection of the dam should be drawn. The overflow and non-overflow
sections be properly illuminated. Whenever sinkholes, boils increase in leakage,
movement of soil, gate failure, rapid rise or fall of the level in the reservoir or wave
overrun of the dam crest are observed, the personnel on patrol should immediately
inform the Engineer-in-Charge. He should inform local administration authority about
the situation. The downstream population should be warned about the imminent danger
using siren or other warning systems available.

f. Communication system

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An efficient downstream warning and communication system is essential for the

success of Emergency Preparedness Plan. The population living downstream should be
educated about the difference between a high flood and dam break situation. In case of
emergency situations telecommunication plays a critical and crucial role in mitigating
the problems faced by people during and after calamity. Any efficient communication
system in disaster management should have the following characteristics:

i. Reliability
ii. Ease of maintenance
iii. Quick deployment
iv. High tolerance to extreme adverse conditions
v. Compatibility on alternative power sources, and
vi. Fast transportability and easy deployment

The traditional communication facilities such as telephones, microwave links, telex

services, mobile phones, etc. should be installed simultaneous with project initiation.
Besides, the project authority should install a modern suitable communication system
in the project impact area.

g. Communication Components

The communication system, in general consists: (a) Strong Mobile network with
dedicated towers for efficient network availability in the entire project earlier, (b) a
Transmitter; (c) a Receiver, and (d) a network management system. A single
communication unit may have both transmitter and a receiver on a single platform. In
addition, there has to be a medium for messages and data to travel. Keeping various
factors in mind, the basic medium would be radio waves as other mediums such as
copper or fibre optic cable are likely to be distorted during disaster. In the far flung
areas such terrestrial links are either not existing or are extremely expensive and time
consuming. The foremost requirement of a communication system is to support voice,
fax and data services so as to enable transmission of any type of data from one site to
other.

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h. Evacuation Plan

The Emergency Action Plan also includes evacuation of people at risk and procedures
for implementation are based on the local needs. Generally the following procedure
forms the basis of the plan:

i) Demarcation and prioritization of areas to be evacuated

ii) Notification procedures and evacuation instructions
iii) Safe routes, transport and traffic control
iv) Safe areas and shelters, and
v) Functions and responsibilities of members of the evacuation team

The flood prone zone identified from the dam break studies should be delineated and
the entire zone should be assigned adequate factor of safety. As the flood wave would
take about two hours and forty five minutes up to 25 Km, the people living in
downstream areas namely Kaspal Had, Hirar, Tarungai, Bhardu, Lopora, Batpora,
Thonsar, Prangas & Tundar, Cherabhatson and Simanhine along the right bank; and
Chhichha, Sirshi, Tragbal, Panjdhar, Loharna, Sondar, Tandar & Swarbhati, Chirazbal,
Drangdhuran, Pinj, and Kurur along the left bank should be informed well in time
through wireless, alerted through sirens, etc. The flood zone should be marked at all the
inhabitated areas downstream.

i. Notification

Notification procedure forms an integral part of any Emergency Action Plan. Different
procedures are suggested to establish for different situations in the process of dam
break. Two types of notifications should be issued. The first one should include
communication of an alert situation indicating that although failure or flooding is not
imminent, a more serious situation could occur unless conditions improve. The second
type of notification should include an alert situation followed by a warning situation. A
warning situation should indicate that flooding is imminent due to expected dam
failure. It should normally include an order for evacuation of delineated inundation
areas.

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The copies of the Emergency Action Plan also include the above described inundation
map. This map should be made available to the persons responsible for execution of the
plan. Besides, the copies of the map should be displayed at prominent locations and in
the offices of the authorities concerned. Inundation maps should be displayed in the
Village Panchayat Ghars in the project impact area. For a regular watch on the flood
level situation, two or more people should man the flood cells so that an alternative
person is available for notification round the clock.

For speedy and efficient communication, a wireless system would be a preferable mode
of communication. Telephones and mobile phones should also be used as and when
required. All the critical points in the project impact area including dam component
should be provided with the wireless/cordless communication systems.

The guidelines to be observed by the inhabitants in the event of dam break, formulated
under the public awareness for disaster mitigation in the Disaster Management Plan
are:

i) Listen to the radio/TV for advance information and advice,

ii) Disconnect all electrical appliances and move all valuable personal and
household belongings out of reach of flood impact area,
iii) Move vehicles, farm animals and movable goods to the nearby safer places,
iv) Prevent dangerous pollution by moving all insecticides out of reach of water,
v) Turn off electricity and gas,
vi) Lock all outside doors and windows in case of evacuation, and
vii) Do not enter floodwater

9.9. Public Awareness Programme

The people living around the project area can play a vital role in the event of disaster
due to dam break. For this purpose Public Awareness Programs should be conducted
regularly to make the general public aware about potential hazards likely to occur in the
project area. Emphasis may be given to the following aspects:

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 Pamphlets and booklets containing details about the hazards associated with
hydropower project may be prepared and distributed among general public,
 Permanent notice boards may be fixed at all the suitable places in the area
displaying information related to assisting agencies, their telephone numbers,
etc;
 Help from local youth organizations, voluntary organizations, educational
institutions may be sought to conduct educational sessions to make people
aware about the safety measures and rescue operations in the event of the
disaster, and
 Teachers in these areas can educate the students about the preparedness in the
event of any eventuality in case of dam break.

A monitoring committee should be constituted in consultation with the District

Administration to ensure preparedness for implementation of the “Disaster
Management Plan”. The committee shall review the effectiveness of plan at regular
intervals and call for mock-rill as per requirement in the project area. The committee
may also suggest improvement in the action plan as may be deemed fit by it on the
basis of its observations through time.

9.10. Setting up of the Seismic Observatory

The area fall in the seismic Zone –IV, as per the Seismic Zonation Map of India
prepared by India Meteorological Department (IMD), all the characteristics related to
seismicity, tectonics, seismotectonics and associated aspects have been dealt in detail in
the Geology Chapter of the EIA Report. Therefore, a plan of seismic surveillance of the
area by establishing a seismic monitoring station is recommended. Setting of seismic
observatory and installation of the equipment should coincide with the commencement
of project execution in order to gather micro details and refine the already collected
data: (i) with regard to neo-tectonic activity prevailing if any in the area, and (ii) to
judge the effect of reservoir impoundment on the seismic status of the area.

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9.11. Cost Estimates

The disaster management plan and related activities would incur some expenditure on
construction of gabions/wiremesh crates, rehabilitation costs of affected household
owners etc; and setting up of the seismological and communication networks,
preparation of different plans related to the warning system, administrative jobs,
training programmes, public awareness programmes, setting of seismic observatory etc.
For this purpose budgetary provision of Rs. 750.00 Lakhs has been kept in the Disaster
Management Plan the details of which are given in Table 9.5.

Table 9.5 Cost Estimates for Implementation of Disaster Management Plan

S. No Particulars (Item of Work) Amount (Rs in Lakhs)

1 Construction of Gabbions/Wire mesh Crates, etc 200.00

Rehabilitation and relief measures of the affected 224.00

2
household owners
Installation of alert systems, setting up of control 50.00
3
room etc

5 Setting of Communication System 30.00

Notification and publication procedures, 10.00

5
miscellaneous, etc

6 Setting Up of Seismological Observatories 200.00

7 Costs on account of future detailed studies 36.00

Total 750.00

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