GOVERNMENT OF ANDHRA PRADESH

IRRIGATION & CAD (PW) DEPARTMENT

ANDHRA PRADESH WATER SECTOR IMPROVEMENT PROJECT

NAGARJUNA SAGAR DAM

4

th REPORT

OF

DAM SAFETY REVIEW PANEL

Nagarjuna Sagar 2nd

to 6th

November, 2009

2

CONTENTS

SECTION PARTICULARS PAGE NO.

I Introduction. 3

II Hydrology 5

III Construction 8

IV Power House 11

12

V Gates

13

VI Earth Dam

VII Masonry Dam 17

VIII Acknowledgement 21

ANNEXURE

I List of Officers 22

3

Section – I

INTRODUCTION

1. Members of Dam Safety Review Panel (DSRP) assembled in Hyderabad

on November-02, 2009 (FN) and proceeded to Nagarjunasagar Dam,

where on arrival, the DSRP members were presented with the following

documents for study and discussions during the fourth meeting.

(i) Comprehensive and detailed technical history of Nagarjunasagar

Project (Head works only) volume-I and Volume-II, July 1998.

(ii) Inspection Reports of Technical Expert Committees and Special Dam

Safety Inspection Committees.

(iii) Estimation of PMF: Progress report by IIT Kharagpur.

(iv) Dam break analysis and EAP: Proposals submitted by NIH and

Engineering staff College of India.

(v) Paper on PVC Geomembrane for water proofing the upstream face of

Kadamparai Dam.

(vi) Action Taken on 1st and 2

nd Reports of DSRP.

(vii) Action Taken on 3rd

Report of DSRP

(viii) TM on seepage through porous hole No.3 in Block No.24 in Gallery

at El.420.00 Feet

4

(ix) TM on Damages to Glacis of spillway and Bucket Portion.

(x) TM on seepage at CH.15.00 of left Earth Dam

(xi) Month wise record of observations of seepage in porous drain 3 of

Block 24 and deflections in Blocks 14 and 54 for the years 2007,2008

and 2009.

2. On November 03,2009 (FN) DSRP discussed the Action Taken on

its 3rd

report with project officers. Later in the after noon, the

galleries were inspected with reference to the reported high seepage

from porous drains.

3. The Right and Left earth dams, the left bank saddle dam, Spillway

Glacis, Bucket and down stream area were inspected and the left bank

power house visited on November 04, 2009.The DSRP had further

discussions with project authorities on November 05,2009 before

preparing its report.

4. The DSRP met with Dr.G.Malsur on Nov.05,2009 and discussed the

progress of rehabilitation measures.

5. The sections that follow give detailed review of Hydrology,

Construction, Power House, Gates, Earth Dam and Masonry Dam

including recommendations.

6. DSRP proposes to schedule its next meeting when the Reservoir

Water level is at the lowest.

7. The list of Officers who participated in discussion and site visits

and assisted in preparation of this report is appended.

8. DSRP presented its report to Chief Engineer, Nagarjunasagar

Project before dispersing on November 06,2009.

5

Section - II

HYDROLOGY

1.0 Probable Maximum Flood :

1.1 The information available shows that the dam has been designed for an

inflow design flood of 42,476 cumecs (15 lakhs cusecs). Subsequently

after the construction of the dam, 1000 year return flood was estimated as

58,340 cumecs (20.60 lakhs cusecs). The latest information indicates that

the PMF at Srisailam Dam is of the order of about 73,853 cumecs

( 26 lakhs cusecs). The catchment area of the Kirhsna basin at Srisaliam is

2.06 lakhs sq.km where as at the Nagarjunasagar Dam site it is 2.15 lakhs

Sq. Km. The PMF at the latter, therefore, is expected to be more than 26

lakhs cusecs.

1.2 At the time of second review, DSRP was informed that an interim report on

PMF would be available by February28, 2009. At the time of the 3rd

review, it was informed that IIT, Kharagpur will furnish a interim report by

12.09.2009.

1.3 The current status of studies, as reported, is that Agriculture and Food

Engineering Department, IIT Kharagpur has started PMF studies in

September’2009. They have collected some data and have approached

various organizations and departments such as CWC, IMD, Indian Institute

of Tropical Meteorology ( IITM) for some more vital data as input in

studies. The IIT Kharagpur has informed the Project authorities that they

will produce an interim report in two months time after they obtain all the

data from different organizations and departments

6

1.4 It is advised that the IIT Kharagpur may be pursued to provide the interim

report with out further delay and the final report based on the detailed

studies for estimation of the PMF at the earliest.

2.0 Dam Break Analysis and EAP

2.1 The project authorities reported that two agencies, namely National

Institute of Hydrology, Roorkee and Engineering Staff College of India,

Hyderabad have submitted their proposals. The DSRP has following

observations to make on these proposals.

2.2 The NIH Proposal is restricted to dam break analysis only. Details of

technical personnel to be involved in the studies have not been included in

the proposal. The proposal is very sketchy.

The proposal submitted by the Engineering Staff College of India,

Hyderabad includes both the dam break analysis and the preparation of

emergency action plan (EAP). The time schedule proposed by them

includes two years for preparation and submission of the EAP from the

date of signing the agreement and for finalization of the plan at various

levels one more year . The above points may be kept in view while

finalizing the agency.

2.3 The agency should also keep the following points in view while giving their

proposals.

i) “Guidelines for Development and Implementation of Emergency

Action Plan (EAP) for Dams” , 2006 may be followed strictly

while preparing the report .The guidelines are approved by the

National Committee of Dam Safety in their meeting convened in

2006.

7

ii) The EAP is supposed to be covered from the Nagarjuna Sagar dam

to the Pulichintala dam site located on the river Krishna.

iii) The credentials of the experts involved in the studies may be

verified.

iv) The time for completing the studies could be shortened.

v) The EAP may be subject to review after it is reviewed to

the DSRP.

3.0 In view of the huge unprecedented flood occurred in September –

October 2009, in the Krishna basin and actual discharge measured at

Srisailam dam, the hydrological and meteorological data of this period

must be taken into account while carrying out the PMF and Dam Break

Studies and preparation of the EAP.

4.0 It was suggested by the panel that pending the estimation of the

PMF, the dam break analysis and preparation of emergency action plan

could be initiated assuming an average value of PMFs computed for the

Srisaliam and the Pulichintala Project as the Nagarjunasagar Dam is

located in between Srisailam and Pulichintala dams.

5.0 Keeping in view the importance of PMF for Dam Safety evaluation,

the Project is advised to get the studies done on priority basis. Dam

break analysis and EAP should also be expedited.

8

Section-III

CONSTRUCTION

1.0 Spillway

It is reported that during October 2009, the spillway was operated for a short

period of 11 days to allow a maximum outflow of 10.22 lac cusecs against the

previous maximum of 8.58 lac cusecs in 1998. The max. water level attained

was R.L.589.40 Feet .The DSRP inspected the Spillway glacis on 03.11.09 and

04.11.09 to note the extent of damages.

1.1 Glacis

Spillway became fully operational after erection of Radial Gates in the year

1974 and since then damages due to scouring/erosion were a recurring feature

whenever the spillway was put into operation. Remedial measures have been

carried out from time to time to restore the damaged surface by back filling with

concrete using epoxy mortar as bond between old and new concrete. DSRP has

opined earlier that the damage to glacis concrete is a typical cavitation induced

erosion which can be remedied only through aeration .The extent and method of

aeration can be decided only through physical model studies.

1.2 Stop Logs

Piers have to be extended for accommodating stoplog gates and this will also

require a physical hydraulic model study for evaluation of Cd. These model

studies have , therefore, to be expedited . Meanwhile, details of proposed civil

structure arrangement for stoplog gates may be furnished to DSRP for review .

9

1.0 Foundation Drainage holes

The progress of reaming of drainage holes in foundation gallery and the results

there, of may be presented to DSRP for review .

2.0 Porous drains

These are also being cleaned but in the slant portion only. It is well known that

it is difficult to maintain these drains in original condition. It is understood that

Maharastra had initiated development of a machine named RF-03 and modified

as ZR –04 to clean the porous drains. This machine is said to be working

successfully at Bhatsa Dam near Mumbai. Project authorities may obtain

details and literature along with performance reports of the said machine from

Bhatsa Dam project. If found suitable, the same can be tried at NS Dam to make

Porous Drains functional.

4.0 Up stream face of Dam

Panel had earlier opined that the following measures may be undertaken to

minimize seepage of water in to the dam body .

(a) Block joints on upstream face to be treated with epoxy.

(b) Upstream face of Dam to be shotcreted, from top of Dam to minimum

possible MDDL ( 510 feet).Block No.24 may be taken up on priority

basis.

The DSRP does not consider installation of a Geo-membrane on the

upstream face as a solution as the same cannot be taken down below MDDL

and anchored to foundation rock. Shotcreting / Guniting is considered as the

best available option. A detailed proposal may be presented for review by

DSRP.

5.0 Area down stream of Right NOF Blocks

Regular leakage is being observed from Right bank canal Power House area

with water flowing into the depression downstream of NOF Blocks 50 to 60.

10

This needs to be regulated and the area developed as a park. An infrastructure in

the form of tanks etc appears to be in place but in deplorable condition. The

area may be restored and maintained for safety as well as aesthetic reasons.

This area can also be utilised for housing machinery required for immediate

repairs and regular maintenance of spillway and EDA.

The alignment of proposed road to connect area down stream of spillway

may be further examined in light of unprecedented floods in October 2009.

11

Section –IV

POWER HOUSE

No specific problem relating to the power houses, especially having any

bearing on dam safety, were brought to the notice of DSRP. Fine clearances of

the mechanical equipment of power plant, normally closely monitored during

maintenance, form good indicators for development of any distress to the dam.

12

Section - V

GATES

From the Action taken report, it is seen that action is initiated by

Project Authorities for taking up repairs/replacement of equipments as

suggested by DSRP during the previous visits. Further progress may be reported

for review by DSRP.

13

Section - VI

EARTH DAM

1.0 Left Earth Dam

1.1. A Technical Memo on seepage at Ch. 15.00 was presented by the project

authorities. The problem of seepage through left earth dam is continuing

since 1978. TIMS Book mentions that there was not much seepage after

remedial measures were taken. The book, however, does not mention any

details about the measures and the year of their implementation. The

subject matter was also not refered to any committee since 1978. The

seepage is reported to start when reservoir water level reaches El 545 ft.

During last 5 years, the maximum seepage observed was 1285 GPM in

2005 when water level reached El. 589.90 ft. On 13.10.09, with water level

at El. 588.60 ft, the seepage observed was 1035 GPM. As reported by

Project authorities, some bubbling was also noticed at the toe at Ch.

15.00.It is necessary to keep a continuous record of the leakage

measurements through out the year, both for rising and receding reservoirs

water levels.

1.2. DSRP, during its visit in November 2008 (2nd meeting) (Reservoir Water

level 577.10 Feet) had discussed this issue and suggested certain measures.

On 04 -November’2009 i.e., one year later the site inspection again under

similar conditions, did not reveal much change in the scenario which was

observed during November’08 visit. The bubbling phenomenon, as was

reported during discussion is not considered a major problem. The seepage

water was clear. It is not practical to prevent the seepage entirely. The

only way is to allow this water to pass safely without causing any damage

to the dam toe. Keeping this in view, remedial measures were suggested in

the 2nd

report of DSRP (6th to 10th

Nov.2008).

14

1.3. The suggested measures are reiterated below.

• On the left bank, in most of the length, two parallel longitudinal

drains carry the seepage discharge. The drains are separated by a

high ground. Cross drains joining the above drains are provided at

twenty two locations.

• The longitudinal toe drain adjacent to the rock toe may be filled up

by pervious materials comprising of graded filter laid under the

rock - fill. The filling is required to be done to the same level as

the high ground between the two longitudinal drains. Wherever the

drain is silted up, the same shall be removed before being back

filled to the required level with pervious material. The

arrangement will provide a loading berm on the existing toe of the

dam. The material being permeable, the seepage discharge is not

obstructed. The loading will provide safety to the toe against any

bubbling or excessive pressure. The provision of filter will take

care of any possibility of particle migration from dam body.

• The cross drains shall be filled with rock-fill laid over the

appropriate filter upto the raised ground level. This provides a

continuous path way near the dam toe. The cross drains filled with

pervious material will release the seepage discharge into the outer

longitudinal drain. Thus the entire seepage discharge will get

released away from the dam toe.

The sketches showing the arrangement were appended with report

of 2nd

DSRP meeting.

1.4. The instrumentation proposed in the 2nd

Report was meant to know the

phreatic surface in the dam body. The same may be augmented as given

below .

15

• Instruments may be provided in sections at Ch. 15.00 and

Ch. 35.00 at the following locations

- At the dam axis

-Downstream edge of top road

-Inner edge of the berm on Downstream slope at

El.575.0 ft.

There is no objection for vibrating wire type instruments as suggested

by CWPRS so long as phreatic surface can be delineated.

1.5 In order to review the seepage problem further, the following shall be

prepared.

i. Contour map of upstream area along with cross sections at

representative locations.

ii. Detailed Geological map of the area upstream of dam.

iii. Data on Drilling and Grouting done earlier.

2.0 Right Earth Dam

2.1. The seepage in the dam body was of the order of 130 GPM when the

water level reached El. 588.60 in October 2009.On 04.11.2009, during

DSRP’s inspection, the water level and discharge reported were El. 573.0

ft. and 40 GPM respectively. Out of total length of dam from Ch. 133 to

Ch. 158.5, only the reach from Ch. 150 to Ch. 155 is contributing to this

seepage, which is being carried to the natural drain. To prevent water

logging of the Downstream Zone, measures were suggested during 2nd

DSRP meeting of November’08.

2.2. Similar instruments, as proposed for left earth dam, are recommended for

right earth dam also at Ch. 152.0 at following three locations to establish

the phreatic surface.

• Axis of Dam

• D/s edge of top road

• At El. 590. D/s slope.

16

3.0 Saddle dam.

3.1 The data regarding rock fill dam in the saddle dam could not be traced by

the project authorities. DSRP, could therefore, only review the safety of the

saddle dam by visual inspection.

3.2. Settlement was noticed on the top of dam at the junction with head

regulator structure. Bulging in upstream and downstream slopes at higher

elevations in this reach was also noticed .Survey may be carried out to

establish the dam profile and sections in all reaches of the dam.

The section at the junction with head regulator may be made up to match

with the profile in the in the rest of the dam by filling or removing the

bulges.

3.3. As reported the dam behaved satisfactorily during the monsoon and no

distress was noticed. However, the seepage discharge needs to be

channelised properly. The existing water pools may be filled up to bring

low-lying areas to an uniform level. The vegetation has to be removed

and the large quantity of quarry spoil available around can be used for

back filling.

17

Section – VII

MASONARY DAM

1.0 Third Report of DSRP

1.1. The fourth review is in continuation of the earlier review. This section

shall, therefore, be read along with section-VII of the 3rd

Report.

2.0 Review of Documents

The Project authorities made a power- point presentation of the following

documents.

- Action taken on 3rd

Report

- Technical Memorandum on seepage through porous hole No. 3 in

Block No. 24, in top gallery.

- Technical Memorandum on damages to Glacis of spillway and Bucket

Portion.

3.0. Stability Analysis

It was reported that Stability Analyses have been completed by

CDO through a consultant. The results have to be presented through a

proper Technical Memo for further review by DSRP.

4.0. Spillway Glacis

It is abundantly clear that restoration of the damaged surface with

concrete backfill is not a lasting solution. Such concrete backfill cannot

resist cavitation induced damages. A proper aeration arrangement

together with the use of high strength concrete and epoxy mortar bonding

should be able to substantially reduce the degree of damage.

Introduction of aeration arrangement on the existing glacis will

necessarily take a long time, especially because of the length and the

number of bays. APERL should expedite their studies. Meanwhile

18

action should also be taken to finalise design mix for silica fume based

concrete with or without steel fibre reinforcement to be used for repair if

aeration arrangement cannot be executed before next reservoir filling.

Aeration may also have to consider for execution in phases.

The Technical Memo may also be upgraded to demarcate more

precisely the damaged areas and extent of damage in each block.

5.0. Porous Drains

5.1 Porous Drain No. 3 in Block 24

During October 2009 when the reservoir level reached EL.587.60

Feet, leakage of the order of 106 GPM was observed in the above drain

outlet into gallery at EL.420. It was apprehended that this drain is

connected to the reservoir through some channels formed in the dam body

as the colour of leakage water was the same as that of reservoir water.

Other five holes in the blocks were discharging insignificant quantity. The

graphs showing RWL Vs the leakage quantity presented in the current TM

are completely at variance with those presented in TM submitted during 3rd

DSRP meeting. The data needs to be checked. It is also necessary to

continue the plot as the RWL recedes to complete the cycle. Plots with

RWL on Y-axis and discharge along X-axis will help to have a better

visual appreciation. On 03.11.2009, the RWL was EL. 574 feet and the

seepage quantity was 79 GPM. Though a ‘V’ notch is fixed in block No.25,

the measurement of leakage quantity is done by collecting the water in a

drum and recording the time. It was emphasized by the panel that ‘V’

notches, wherever installed, should be got calibrated by APERL and future

measurements done by using the same . More ‘V’ notches be installed to

compartmentalize the gallery to precisely measure the reach wise

leakage/seepage.

19

5.2 Porous Drain No.4 in Block No.77

The leakage from the above drain into EL.420 gallery which is also the

foundation gallery, of the order of 6 GPM with reservoir water level at

EL.574 feet is not significant. However, the other five drains in the block

carry no water. The leakage, per se, through this hole may not be of

immediate concern.

5.3 Porous Drain No.5 in Block. No.44

The out let of the above drain into foundation gallery at EL.250 is

fitted with a 3” pipe and a valve, which is not functional. The leakage was

reported to be 5.30 GPM at the time of the visit. The TM for the 3rd

review

showed a decreasing trend in leakage. The plotting of RWL Vs leakage

should be continued. The valve may be replaced. The closure of the valve

temporarily may help in studying the behavior of other porous drains in the

block.

6.0 Drainage Holes

6.1 In block No.79 the drainage hole in the gallery is fitted with a pressure

guage and a valve. The guage is not functional. However, significant flow

of water can be noticed by opening the valve. Reaming of all other

drainage holes in the block in the vicinity of the above drainage hole may

mitigate the problem.

6.2. Drainage holes in the foundation gallery at EL. 250 were being reamed.

As reported, the cleaned holes are getting operative.

7.0 Down Stream face seepage

On the downstream slope of the NOF blocks on either side of

spillway, seepage is being observed since long. Seepage is also observed

on the down stream face at contraction joints between block No.67,68 as

well as block No.35.The likely reasons for these seepages have been

discussed in the 3rd

review report.

20

8.0 Remedial Measures

The reasons for dam body leakages and seepage have been discussed in

the earlier reports. Visual inspection of the upstream face of dam above EL 510

has not revealed any areas of direct access of water from the face. Various

measures of re-pointing and sealing of contraction joints in the upstream have

not proved successful. In view of this and considering the service of the dam for

more than 30 years, DSRP is of the view that the entire upstream face of dam,

which can be exposed by lowering the water level to the extent possible, may be

treated by shotcreting / Guniting. Project authorities should prepare a TM on

this subject for review by DSRP.

9.0 Toe Gallery

It was earlier expected that the cross wall in block 48/49 was a temporary

structure and could, therefore, be dismantled easily. The reasons for its

construction now need to be ascertained since the wall is reported

to have been constructed in RCC. TIMS report may throw some light. Now

that the gallery is dewatered, its layout and longitudinal profile may be prepared

and TIMS report studied to find out the objectives of the gallery as also the

extent of foundation grouting from and drainage holes in the gallery. The

gallery will have to be inspected from both ends before taking any further action

on the cross wall.

10.0 Other Actions

Progress on other actions being taken may be reported for review by

DSRP.

21

Section – VIII

ACKNOWLEDGEMENT

The DSRP acknowledges with thanks the participation of the officers (list

enclosed) in the field visit and in discussions and their help and co-operation in

preparation of the Report.

The DSRP would like to compliment the efforts in preparation of the

TMs and other documentation presented during the visit.

The DSRP appreciates very much the participation and assistance of Sri

I.S.N. Raju, Chief Engineer, CDO in the field visit and in review discussions.

The DSRP would like to specially thank Dr.G.Malsur, Project Director

and Sri M. Ramachandraiah, Chief Engineer, N.S. Project for their support.

Special thanks are due to Sri G.V. Appa Rao, Assistant Engineer for the logistic

and pre and post review assistance.

Dr M.S. Reddy

Chairman

Sri A.N. Singh Sri M.K.V. Sharma

Member Member

Sri G.S. Choudhary Sri B.M. Upadhyay

Member Member

Sri S.R. Toley Sri S.R. Pradhan

Member Member

22

ANNEXURE

List of Officers Present

1. Sri M. Ramachandraiah : Chief Engineer, N.S.Project, Hill Colony.

2. Sri I.S.N.Raju : Chief Engineer, Central Designs

Organisation, I & CAD Department ,

Hyderabad.

3. Dr. G.Malsur : Project Director, PPMU, APWSIP,

Hyderabad.

4. Sri B. Lakshman Reddy : Superintending Engineer, N.S.Dam Circle,

Hill Colony.

5. Sri M.A. Saleem, : Executive Engineer, Dam Maintenance

Division, Hill Colony.( A/c)

6. Sri A.Vijaya paul : Dy. Chief Engineer, N.S.Project, Guntur.

7. Sri.S.M. Subrahmaneswera

Rao

: Dy . Superintending Engineer,

NSLBC O& M Circle, Tekulapally.

8. Sri A. Solomon : Dy. Executive Engineer, Earth Dam

Sub- Division, Hill Colony.

9. Sri G.V.V. Madhusudhana

Rao

: Dy. Executive Engineer, O/o Chief

Engineer , N.S.Project, Hill Colony.

10 Sri .M.N.V. Chandrashekar : Dy. Executive Engineer, Central Designs

Organization, I & CAD Department ,

Hyderabad.

11 Sri K. Vijay Kumar Asst. Executive Engineer, N.S .Dam Circle

12 Smt B. Ananda kumari : Asst. Executive Engineer, Dam Mtc

Division

13 Sri B. Adiseshu : Asst. Executive Engineer, Spillway Section

14 Sri. K Krishnaiah : Asst. Executive Engineer, Gates Section

23

15 Sri BH. Subrahmanyam : Asst. Engineer, Gates Section

16 Sri T. J. Narasimhamurthy : Asst. Engineer, D & G Section

17 Sri K. Manohar : Asst. Executive Engineer, Earth Dam

Section

18 Sri A Kesava Rao : Asst. Executive Engineer, D & G Section

19 Sri .V.S. R. Prabhu Asst. Executive Engineer, Earth Dam

20 Sri B..Satyanarayana

Murthy.

: Asst Engineer , O/o Chief Engineer ,

N.S.Project,

21 Sri. B. Srinivasa Rao : Asst Engineer , B& R Section

20 Sri G. V. Appa Rao : Asst Engineer , O/o Chief Engineer ,

N.S.Project,

21 Sri M.Vinod Babu : Asst.Executive Engineer , O/o Chief

Engineer , N.S.Project, Camp office,

Hyderabad.