DIVERSION OF DIYAWINI OYA INTO THE 
SURGE CHAMBER OF 
SAMANALA WEWA POWER STATION 
 
 
 
By 
A.R.M.M.S. Karunasena 
 
 
 
This thesis was submitted to the Department of Electrical Engineering 
in partial fulfillment of the requirements for the 
Degree of Master of Engineering 
 
 
Supervised By: Prof. Priyantha D.C. Wijayatunga 
 
 
Department of Electrical Engineering 
University of Moratuwa 
Sri Lanka 
 
 
2004 
 
82486 
 
 
  
Abstract 
 
Investigations of the development of hydro power in the upper Walawe river basin 
using the head difference of about 350 m between the two pineplaines of the south 
eastern part of the central high lands of Sri Lanka had commenced in mid 1950's. 
 
Several studies have been conducted since then on the possible ways of developing 
this potential .These studies lead to the finalization of Samanalawewa hydro power 
project in 1985.  
 
The scheme envisaged the development of the potential in two stages .Under the 
stage I major components such as main dam, low pressure tunnel ,surge chamber ,a 
single penstock add power plant of 120MW capacity housing two generating units 
were to be developed. Work under stage I was completed and plant was 
commissioned in 1992. 
 
Stage II of the scheme envisaged the construction of Diyawini Oya reservoir, a 
second penstock and an extension to the stage I power house to install two additional 
generating units to bring the total installed capacity of Samanalawewa hydro power 
project to 240MW. 
 
According to the studies the installation of additional 120MW capacity in the second 
stage of the project was aimed at providing the needs of additional peaking capacity 
in the CEB generating system at a future date .The studies conducted in 1985 
expected such requirement to be in the CEB system in early 21st century. 
 
After completion of the wet blanketing of the reservoir to arrest the leakage which 
developed on the right abutment of the dam Ceylon Electricity Board wished to 
evaluate the feasibility of the development of stage II of the scheme in the early years 
of 21" century as envisaged ill 1985. 
 
  
In 1999, CEB requested Central Engineering Consultancy Bureau to review the 
feasibility of implementing the stage II of Samanalawewa hydro power project. 
During this review the capacity of the existing system to cater for the conditions after 
the installation of additional units the feasibility of construction of Diyawini Oya 
reservoir and the installed capacity to be developed in the near future were evaluated. 
Most of components of the existing project are found to have sufficient capacity to 
cater for the increased flows after stage II . Some modifications are required in the 
surge chamber in order to connect the Intake from the Diyawini oya reservoir. A 
provision has already been made available for this purpose in the surge chamber. 
 
Review of the feasibility of the development of Diyawini reservoir by CECB 
indicated that the water tightness of the reservoir is uncertain in the light of the latest 
geological information available .It was also noted that any treatment of reservoir to 
improve the water tightness will be prohibitively costly. Accordingly CEB 
apparently had given up the proceeding of stage II studies. 
 
However it was interesting to investigate the possibility of using Diyawini Oya 
waters diverted in the direction of the surge chamber and released in to the surge 
chamber at a feasible point. This way additional water quantity from the stream can 
be pumped in to the surge chamber and it is added to generate electricity at the power 
station. It is very important to check the electrical energy loss when pumping such a 
quantity of water and then compared with the energy gain at the end. All relevant 
calculations were done and it indicates that the project is well profitable and impacts 
on Environmental and social aspects are in favor of the project. 
l>ECLARATIO~ 
T~ the best of my knowledge and belief , the work mcluded in this thesis in part or in 
whole has not been submitted fot any other academic qualification at any institution. 
Signed by: 
df:;;~ . 0 
AR.~t.:\1.S . Kanmascna 
Certified by : 
~ 
Prof P'iiynrrth~ WtJayafunga ' 
• 
Director General - Publtc Uttltltes Commtsston 
Sn Lanka. 
i 
... 
--
II 
• Preface 
This is a thesis on a specific project called "Diversion of Diyawini oya in to the surge 
chamber of Samanalawcwa Power Station'' carried out by me for partial fu lfilment of 
Master of Engineering Degree (Electrical) at University of Moratuwa. 
Review of the feasibility study of the development of Diyawini reservoir carried out 
by Central Engineering Consultancy Bureau in the year 2000, indicated that the \\atc.::r 
tightness of the reservoir is uncertain in the light of the latest geological information 
a'ailable. It was also noted that an; treatment of reservoir to improve the water 
tightness will be prohibitivcl) cost!;. Beside this .energy gains of about 23 G" h due 
to the addition of Diyawini rcsen oir is not economical compared to the ... n-..t ,,1 
de\elopment . 
Hence it '"'as the intention of me to further stud) about the above mentioned 
Oi) awini oya stream and construct a pump intake and divert a?s.much flow as possihle 
to the surge chamber while fulfilling do,,n stream rcquiremen of the people li' ing. 
Also to ascertain the Jinancial and social henefits that could be gained b) Cc) lun 
Electricity Board as well as the farmer community at the down stream and to evaluate 
any impacts in terms of social and cnviromnental issues. 
A.R.M.M.S. Karunasena 
Samanalawewa Power Station. 
December 2004. 
--
1\ 
• Acknowledgement 
Prof. R.Lucas, Dr. Thilak Siyabalapitiya and Dr. Thusitha Sugathapala for 
giving me lot of valued inputs to improve this thesis during 1inal evaluation. 
Professor Priyantba D.C. Wijayatunga deserves a very special word of thank who 
has guided me through out this exercise as my supervisor and for giving lot of inputs 
to me with the knowledge of his vast experience carrier. 
H.S. Somathilaka the Chief Engineer of the Samanalawewa Power Station , where r 
am presently working and this project site is located , has given his attention and 
fullest corporation to carry out my studies on this project . 
\1r. Kamal Laksiri is one of the Chief Ci\ il Engineers attached to Cr B and 
presently working in the Kukule llydro Power Station to whom. all critical ci\ il 
design matters were referred and spending his precious time t~help me in making 
this thesis a successful one . 
Mr. W.H. Wickramaratna is the Mechanical Engineer of Samanalawev•a Power 
Station who had always been discussed with me the Mechanical aspect or this 
project and very keen in giving a lot of valued information. 
Mr. K.L.R. Perera an Engineer attached to Samanalawewa Power Station who \\as 
very helpful to me especiall y in computer related work. 
'\1r. Jayantba de Silva of M/s Lanka Development Network (Pvt) Ltd for prompt 
reply made to find out all pump data at present Sri Lankan market. 
1\1/s ACL Cables (Pvt) Ltd for helping me with prm iding price-; etc for l".thk 
products. 
The International Centre for Hydro Power - Nonvay for selecting my paper on 
this project and inviting me to the international seminar held in Aruza in Tanzania in 
August 2003. 
The Institution Of Engineers - Sri Lanka for giving me an opportunity to mal--e a 
presentation on this project for 9ih Annual session of Young members section on 
241h October 2003. 
All the farmers in the Surge Chamber Area for providing me their information 
during the interviews in all possible ways. 
..... 
Figure 1.2(a): 
Figure 1.2(b ): 
Figure 2(a): 
Figure 2(b ): 
Figure 4.3 (a): 
Figure 5(a): 
Figure 7.l(a): 
figure 7.1(b): 
hgurc 7.1(c): 
Figure 7.2(a): 
Figure 7.2(b): 
Figure 7.3(a): 
Figure 7.3(b): 
Figure 7.3(c): 
Figure 7.4(a): 
Figure 7 .4(b ): 
Figure 9.1 (a) . 
Figure 9.3(a) : 
Figure 9.3 (b) : 
figure 9.3 (c): 
Figure lO.l(a): 
Figure lO.l(b): 
figure IO.l(c): 
Figure 10.2(a): 
Figure 10.2 (b): 
figure II (a) : 
figure ll (b): 
I·igure 11 (c): 
Figure II (d) : 
APPENDIX H 
Figure 8(a): 
APPENDIX K 
Figure 9 (a) 
Figure 9 (b) 
APPENDIXM 
Figure 10 
\ 
List of Figures 
Map of Samanala Wewa Reservoir 
Schematic representation of Samanala Wewa Reservoir 
Location Map ~ 
Cross section of surge chamber and Diyawini oya 5 
Observed stream flo~ s (2002/2003) I 0 
Location Map 12 
Schematic top view of the location of the project 16 
Schematic side 'it:\\ of the location of the project 17 
GPS measuring points 17 
Shortest way between Intake and surge chamber I X 
Shortest wa) up the hill 18 
Pipe connection under the ground level of surge chamber I X 
Pipe connection just above the ground level of surge chamber 19 
Pipe connection over the surge chamber j I 9 
Variation of surge level with reservoir ,,;ater leYel 21 
Variation of reservoir water levels from 1992-2002 22 
A centrifugal pump (left) and an axial pump (right). 26 
Net energy gain and saving for different flow rates 2X 
Combined performance curves \0 
Performance curves for difkrent speed~ 3.2 
Dimensions of existing weir. 36 
Front. side elevation and plan of proposed structure. 3 7 
Side elevation and plan of Proposed pump Intake Building 38 
Sectional view of weir 3~ 
Weir calibration cun c 
Schematic diagram of control panel 
Pump control circuit no I 
Pump control circuit no 2 
Existing supervisory control system 
Moody diagram 
Pump performance curves for 200 1/s pump 
Pump pcrl"ormancc curves lor 680 1/s pump 
Flood hydrograph 
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~I 
-t2 
~3 
44 
66 
(ll) 
70 
79 
Table 4.1 (a): 
Table 4.3(a): 
fable 4.4(a) : 
Table 6(a): 
Table 7. l (a): 
Table 7.2(a): 
Table 8(a): 
Table 9.3(a): 
Table 9.3(b): 
Table 9.3(c): 
fable 9.3(d): 
Table 9.3(e): 
fable II (a): 
Table ll(b): 
Table 12(a): 
1able 12(b): 
Table 12(c): 
Table 13.1 (a): 
Table 13.2(a): 
Table 13.3(a): 
Table 13.4(a): 
APPENDIXB 
Table 4 (a): 
APPENDIX C 
Table 4 (a): 
APPENDIX D 
Table 4 (b): 
APPENDIX E 
fable 5 (a): 
rable 5 (b): 
Table 5 (c): 
APPENDIXG 
Table 7 (a): 
APPENDIX 
Table 7{a): 
APPENDIX I 
Table 7 (a): 
APPENDIXJ 
Table 7 (a): 
List of Tables 
Mean values of rain fall and temperature 
Observed stream flows in 1/s 
Comparison of previous stream flow studies 
Flow available for pumping in m1/s 
GPS measurements 
Length of the routes 
Absolute roughness values of selected pipe materials 
Pump capacities 
Performance curves and load curve data 
Combinations of pumps 
Performance cun·e data for different speeds 
l:.nerg} required for single pump" ith \·sn 
Pump combinations 
Floater fixing levels 
Flow available for pumping ./ 
Total energy gain with pump operated in parallel 
Total energy gain with single pump with a VSD 
Total cost for the project (case 1) 
Cost analysis for the project (case I) 
Total cost for the project (case 2) 
Cost analysis for the project (case 2) 
Average monthly rain fall figures 
Temperature recorded in the area 
Hydrological calculations 
J nterview results area S2-S3 (left bank) 
lntervic\\ results area S2-S3 (right bank) 
Interview results area S3-S4 
Variations of surge levels 
Monthly average rcsen oir water level 
Friction calculations 
Pump data 
--
7 
9 
II 
15 
7 
lR 
2-l 
29 
29 
30 
31 
.., .., 
' ' 
.\ l) 
40 
45 
46 
47 
..fR 
49 
50 
51 
60 
(>I 
62 
63 
() ) 
6} 
64 
\ I 
65 
67 
6S 
APPENDIX L 
Tablcl2 (a): 
Table 12 (b): 
Table 12 (c): 
Table 12 (d): 
Table 12 (e): 
APPENDIX 1'1 
Table 7 (a): 
APPENDIX P 
Photo!:,rraph I : 
Photograph 2 : 
Photograph 3 : 
Photograph 4 : 
Photograph 5 : 
Photograph 6: 
Photograph 7 : 
Flow data 
Energy 
Pump capacities 
Energy for pumps 
Cost saving 
Weir calibration data 
Cylinders for measuring flO\\S 
lntervie\\ ing of farmers 
Proposed site for the pump intake 
Dov. n stream fiow 
Existing structure 
Surge chamber 
Access road to the pump intake 
I 
·" 
~ 
71 
71 
72 
72 
7".. 
74 
75 
75 
76 
76 
77 
77 
n 
\II 
\Il l 
List or Symbols 
\p pressure difference [Pal or [har] 
D diameter [m] or [mm] 
f friction factor 
() 
e gravitation l m/s:c] 
h head [ml 
l length fmj 
Q now rate [m3/s] 
Rc Reynolds number 
\ , ·elocity [m/s] 
~l viscosit) [Ns/rn~] 
1t 3.1415 ;f 
p density fkg/m
3] 
u Evapotranspiration fmmj 
k Coefficient of monthly consumption by vegetation 
p Monthly percentage of day time hours of the year 
c Coefficient of runoff 
Intensity of rain fall lmm/hr] 
A Catchment area [sqkm] 
L l'psurge level fm 1 
B Width ofthe ''eir [m] 
-. 
Declaration 
Preface 
Abstract 
Acknowledgement 
List of figures 
List of Tables 
List of s~mbols 
Chapter 1-lntroduction 
Table of Contents 
1.1 Samanala,,c,, a Power Station 
1.2 Samanala'' e'' a Rc::;cn nir 
1.3 Samanala\\c\\a lntal--c 
1.4 Samanalawcwa P(m cr runnel 
1.5 Samanalawcwa Surge Chamber 
I .6 Development of second stage proposals I 
1.7 Review of previous studies 
Chapter 2-Description of Di~awini Oya and its surroundings 
Chapter 3-Rcsearch Questions 
Chapter 5-Flow Calculations 
4.1 Calculation of now using past data 
4.2 Calculation to find maximum flow 
4.3 Calculation of flov .. "ith obser\ed data 
II 
Ill 
1\' 
\' 
\I 
\ Ill 
~ 
., 
1 
3 
1 
-l 
6 
7 
7 
l{ 
9 
1:--
4.4 Compari-.on \\ ith data obtained from previous studic... 11 
Chapter 5-Down Stream \\'at~r R~quir~m~m 1.2 
5.1 Location map 12 
5.2 Results of lnten iews 12 
5.3 Water use 13 
Chapter 6-Calculation of a\ ailablc nov. for pumping 15 
Chapter 7-Design of pipe route and connection at the surge chamber 16 
7. I G PS Measurements 16 
7.2 Route Options 18 
7.3 Options of pipe connections at the surge chamber 18 
7.4 13cst design for connection at the surge chamber 19 
Chapter 8-Design of pipe line 
Chapter 9-Selections of pumps 
9 .I T) pes of pump-. 
9.2 Pump combination 
9.3 Requirement for the pumps 
Chapter 10-Design of Weir and Pump Intake 
---
10.1 Design of\\eir ~ 
I 0.2 Calibration of ''ater height O\ er the "eir 1\ ' ~ 
" 
l 
,.., 
--' 
26 
26 
2<> 
27 
3-l 
3-1 
)) 
Chapter ll-Dcsign of pump control center 
Chapter 1 2-Energy calculations 
Chapter 1 3-Cost and Benefit calculations 
13. I T ota I cost for the project (case I ) 
13.2 Operational i\nal) '>is (case I) 
13.3 ·r otal cost for the project( case 2) 
13.4 20perational Analysis (case 2) 
Chapter 14-Requirement of other facilities 
14.1 Electricity Suppl) 
14.2 Control cable for data transmission 
14.3 Construction ot' access road 
14.4 Construction of pump intaJ..c building 
14.5 Surge chamber modification 
Chapter IS-Environment and Sociallmpacts 
15.1 Environmental Impacts 
15.2 Social Impacts 
Chapter 16-Conclusion 
Chapter 17-Rccommendations 
Refer ences 
Appendices 
A-Project Layout 
B-Rain fall Data ( 1918-1998) 
C-Temperatures recorded in the Area 
D-Hydrological calculations 
E-Details of Interviews 
F-Variation or Surge le' cis 
G-Reservoir water level ( 1992-2002) 
H-Moody Diagram 
I Friction calculations 
1 -Pump data 
K- Performance curves of pumps 
j 
L- Calculation or energy gain \\ ith di rkrent tlO\\ s 
M-Fiood Hydrograph 
N-Weir calibration Data 
P- Photographs 
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~9 
45 
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50 
51 
-.., )_ 
52 
-..., )_ 
" ') )_ 
52 
52 
5-l 
5~ 
55 
56 
57 
58 
\. 
59 
60 
61 
62 
()~ 
(l-l 
65 
66 
67 
68 
69 
71 
79 
75 
76