A STUDY OF IRRIGATION WATER USE FOR 
PADDY CULTIVATION IN THE DRY ZONE OF 
SRI LANKA 
MASTER OF PHILOSOPHY 
BY 
T.N. WICKRAMAARACHCHI 
DEPARTMENT OF CIVIL ENGINEERING 
UNIVERSITY OF MORATUWA 
SRI LANKA 
SEPTEMBER 2002 
LB/VO^/oi/oS 
A STUDY OF IRRIGATION WATER USE FOR 
PADDY CULTIVATION IN THE DRY ZONE OF 
SRI LANKA 
THESIS SUBMITTED TO THE DEPARTMENT OF 
CIVIL ENGINEERING IN FULFILMENT OF THE 
REQUIREMENT FOR THE DEGREE OF 
MASTER OF PHILOSOPHY 
MOVERS IT Y iii-"; 7 ;".;-.T.f>:; ll/if^ o > 
BY 
T.N. Wickramaarachchi 
6 2 " " 
SUPERVISED BY 
Dr. N.T.S. Wijesekera 
CO-SUPERVISED BY 
Prof. D.C.H. Senarath 
Dr. N.P.D. Gamage 
o - -
DEPARTMENT OF CIVIL ENGINEERING 
UNIVERSITY OF MORATUWA ~?C> 8 
SRI LANKA 
ZmSmm September 2002 
76821 76821 
DECLARATION 
I herewith declare that the work included in the thesis in part or whole, has not been 
submitted for any other academic qualification at any institution. 
!. °. .1.'. • . ^ ^ d ^ . ^ y . 
Date T.N. Wickramaarachchi 
Certified by 
^ o . i l ^ T r . ^ ^ J ^ ^ : 
Date Profi D.C.H. Senarath 
Co-Supervisor 
i 
-4 
V 
ABSTRACT 
Water is a scarce resource in the Dry Zone of Sri Lanka and it is a major problem 
faced by the cultivators in the area. Since their cultivations totally depend on 
irrigation water, every possible effort should be put in order to optimize the water 
usage to achieve increased crop production. Recent reports on water management 
activities of several irrigation schemes in the Dry Zone indicates that the water 
distribution is not meeting the demands of farmers in terms of adequacy, reliability & 
timeliness. Further it was said that there is considerable potential to increase paddy 
yield in this system through improved irrigation water management, especially by 
efficient irrigation scheduling. 
Following four study areas in the Dry & Intermediate Zones were selected from 
different irrigation schemes authorized by the different organizations. 
i) Block 404 & 406 of Mahaweli system H 
ii) Track 1 of Rajangana Irrigation scheme 
iii) Ridi Bendi Ela irrigation scheme 
The strengths and weaknesses of the presently adopted water allocations by the above 
schemes were identified. Further, the cultivation practices and present water usage in 
three irrigation schemes were compared. The irrigation requirements according to the 
Irrigation Department guideline recommendations were computed for each scheme 
using a spread sheet model and compared with present water usage in three schemes 
to find out optimum solutions for irrigation water use for paddy cultivation. The 
comparative analysis revealed that the practices adopted in issuing water in each 
scheme differ resulting disparity in water usage, farmers' satisfaction on water issues 
and paddy yield. 
Considering the above comparisons, the recommendations for water issues during 
both land preparation & crop growth in paddy cultivation were presented pertaining to 
the most appropriate date of commencement and duration of the land preparation, the 
variation of depth of water application and frequency of irrigation during different 
growth stages of paddy with possible water saving techniques incorporating farmer 
needs. The optimum quantity of water requirement for the land preparation with 
maximum utilization of rainfall, most favorable quantity of water to meet the crop 
water requirement at different growth stages of paddy and the selection of best canal 
grouping to optimize the water distribution were also presented in the study. 
i- 11 
ACKNOWLEDGEMENT 
The immense credibility of a thesis does not totally lie on the person who carried it 
out. It should go on to all those who guided and supported being at researcher's 
periphery. 
First, I would forward my heartiest gratitude to Dr. N.T.S. Wijesekera for his 
continuous supervision, encouragement and valuable advices throughout the study. 
His contribution to this research is massive even though he was out of the country. 
My sincere gratitude is also forwarded to Prof. D.C.H. Senarath and Dr. N.P.D. 
Gamage for their guidance, supervision and valuable advices, which encouraged the 
research to a success. 
I also convey my gratitude to Prof. S.S.L. Hettiarachchi for his wonderful 
encouragement given throughout the study. 
My special thank goes to the Asian Development Bank Scholarship Programme and 
postgraduate studies division of University of Moratuwa for providing funds and 
facilities for the study. 
The assistance rendered by Mr. S.A.P. Samarasinghe - Director IMD, Department of 
irrigation, Mr. Sellahewa & Miss. L.V.P.N. Jayawardena of MASL, Mr. Lalith de 
Alwis of Department of Irrigation - Rajangana and Mr. W.A.C.K. Weerasekera of 
Ridi Bendi Ela Irrigation Scheme, in collecting data and arranging several field visits 
is invaluable. 
I am grateful to Mr. H.K.W. Kumarasinghe of Hydraulic Engineering laboratory for 
his support in providing computer facilities at short notice. 
I owe much to my parents for paving the path of my education. 
Dishmi, Bhathi and Sriyani are fondly appreciated for their friendship and assistance. 
iii 
Declaration i 
Abstract ii 
Acknowledgement iii 
Table of Contents iv 
List of Tables viii 
List of Figures x 
List of Abbreviations xi 
List of Notations xii 
TABLE OF CONTENTS 
1.0 Introduction 
1.1 General 
1.2 Back ground to the study 
1.2.1 Problems encountered in irrigation water management in the 
Dry Zone 3 
1.2.2 Selection of study areas 3 
1.2.3 Present irrigation water management 
1.2.3.1 Block 404 & 406 in Mahaweli system H 4 
1.2.3.2 Ridi Bendi Ela Irrigation Scheme 8 
1.2.3.3 Rajangana Irrigation Scheme 10 
1.3 Objective of the study 
1.3.1 Overall objective 12 
1.3.2 Specific objectives 12 
1.4 Scope of work & layout of the report 
1.4.1 Scope of work 13 
1.4.2 Layout of the report 14 
2.0 Literature Review 
2.1 Water Scarcity & Irrigation in the Dry Zone 15 
2.2 Water Management Practices for Paddy Cultivation 15 
2.3 LP in Paddy Cultivation 17 
2.4 Water management at Different Growth Stages of Paddy 17 
2.4.1 Water Requirements at Different Growth Stages of Paddy 18 
2.5 Paddy Root Growth 19 
2.6 Rainfall 
2.6.1 Actual rainfall & Probable rainfall 19 
2.6.2 Effective Rainfall 19 
iv 
2.7 Determination of Irrigation Requirement for Paddy Cultivation 20 
2.8 Water Losses 
2.8.1 Evaporation Loss 21 
2.8.2 Percolation & Seepage 21 
2.8.3 Conveyance Loss 22 
2.9 Effect of Water Shortage to Paddy Yield 22 
2.10 Water Efficient Irrigation Techniques suggested for Paddy Cultivation 23 
3.0 Methodology adopted for the study 
3.1 General 24 
3.2 Data Collection 24 
3.2.1 Methods of Data Collection 24 
3.3 Data Analysis 25 
4.0 Data Collection 
4.1 Block 404 & 406 in Mahaweli System H 26 
4.1.1 Climatic Data 
4.1.1.1 Rainfall 26 
4.1.1.2 Evaporation 28 
4.1.1.3 Reference Crop Evapotranspiration 28 
4.1.2 Crop Data 29 
4.1.2.1 Area Cultivated 29 
4.1.2.2 Types of Paddy 30 
4.1.2.3 Paddy Yield 31 
4.1.2.4 Crop Coefficients 31 
4.1.3 Water Issue Data 
4.1.3.1 Rotation Intervals & Water Issue Schedules 31 
4.1.3.2 Actual & Planned Water Issues 35 
4.1.4 Canal Details 38 
4.1.5 Soil Types 42 
4.1.6 Field Visits 42' 
4.1.7 Farmer Interviews 43 
4.2 Ridi Bendi Ela Irrigation Scheme 46 
4.2.1 Climatic Data 46 
4.2.2 Crop Data 47 
4.2.3 Water Issue Data 48 
4.2.4 Canal Details 49 
4.2.5 Soil Types 51 
4.2.6 Field Visits 51 
4.2.7 Farmer Interviews 52 
v 
4.3 Rajangana Irrigation Scheme 53 
4.3.1 Climatic Data 53 
4.3.2 Crop Data 54 
4.3.3 Water Issue Data 55 
4.3.4 Canal Details 55 
4.3.5 Soil Types 57 
4.3.6 Field Visits 57 
4.3.7 Farmer Interviews 57 
5.0 Analysis & Results 
5.1 Cultivation & Present Water Distribution System 
5.1.1 Block 404 & 406 in Mahaweli System H 59 
5.1.2 Ridi Bendi Ela Irrigation Scheme 60 
5.1.3 Rajangana Irrigation Scheme 60 
5.2 Determination of Irrigation Requirements using ID Guidelines 61 
5.2.1 Land Preparation water requirement 62 
5.2.2 Crop Water Requirement 62 
5.2.3 Irrigation Duty 62 
5.3 Sensitivity Analysis 64 
5.3.1 Sensitivity Check on Reference Crop Evapotranspiration (ETo) 64 
5.3.2 Sensitivity Check on Application Efficiency (Ea) 65 
5.3.3 Sensitivity Check on Conveyance Efficiency (Ec) 65 
5.3.4 Sensitivity Check on Effective rainfall 66 
5.4 Land Preparation Water Requirement according to Soil Testing 67 
5.5 Frequency of Irrigation 68 
5.6 Comparative analysis of Irrigation Issues 69 
5.7 Rescheduling of Water Issues with Canal Grouping 72 
5.8 Recommendations for Irrigation Water Issues 73 
6.0 Discussion 
6.1 Land Preparation 
6.1.1 Depth of Application 76 
6.1.2 Commencement & Duration of LP 76 
6.2 Crop Growth 
6.2.1 Depth of Application 77 
6.2.2 Duration & Frequency of Irrigation 78 
6.2.3 Termination of Water Issues 78 
6.3 Optimum Water Distribution 79 
vi 
6.4 Efficiencies 
6.5 Sensitivity Analysis 
7.0 Conclusions 
8.0 Future Studies 
List of References 
Annexes 
j -
vii 
List of Tables 
Table 4.1 Monthly Total rainfall in mm - Thambuttegama 
Table 4.2 Monthly Evaporation (mm/month) - Kalawewa 
Table 4.3 Monthly ETo (mm/month) - Anuradhapura 
Table 4.4 Total cultivated areas in Block 404 & 406 (ha) 
Table 4.5 Seasonal Variation of Paddy Varieties - Block 404 & 406 
Table 4.6 Kc values at different growth stages 
Table 4.7 Present Water Distribution Pattern in Block D2/404 During the Growth 
Stages in Maha Season 
Table 4.8 Present Water Distribution Pattern in Block D1/406 During the Growth 
Stages in Maha Season 
Table 4.9 Actual & Planned Irrigation Duty in D1/404, D2/404 & D1/406 
Table 4.10 Results of the Soil Testing - Block 404 & 406 
Table 4.11 Summary of the Questionnaire Survey in Block 404 
Table 4.12 Summary of the Questionnaire Survey in Block 406 
Table 4.13 Monthly total rainfall in mm - Ridi Bendi Ela 
Table 4.14 Monthly Evaporation (mm/month) - Batalagoda 
Table 4.15 Monthly ETo (mm/month) - Batalagoda 
Table 4.16 Seasonal Variation of Paddy Varieties - Ridi Bendi Ela 
Table 4.17 Rotation interval in canals - Ridi Bendi Ela 
Table 4.18 Total Irrigation Duty at each FO area - Ridi Bendi Ela 
Table 4.19 Summary of the questionnaire survey at Ridi Bendi Ela scheme 
Table 4.20 Monthly total rainfall in mm - Rajangana 
Table 4.21 Monthly Evaporation (mm/month) - Nachchaduwa 
Table 4.22 Seasonal Variation of Paddy Varieties - Rajangana 
Table 4.23 Total Irrigation Duty at each season - Rajangana 
Table 4.24 Summary of the questionnaire survey at Rajangana scheme 
Table 5.1 Summary of the Total Irrigation Duty 
Table 5.2 FIR at Different Growth Stages of Paddy (in mm) 
Table 5.3 Summary of the Total Irrigation Duty according to ID Guide lines 
Table 5.4 Evaluated sensitivity of ETo 
Table 5.5 Evaluated sensitivity of Ea 
via 
4 
Table 5.6 
Table 5.7 
Table 5.8 
Table 5.9 
Table 5.10 
V 
Evaluated sensitivity of Ec 
Evaluated sensitivity of Effective Rainfall 
Depth of water required for saturation 
Total LPWR for Block 404 & 406 (in mm) 
Depth of Applications for Block 404 & 406 
List of Figures 
Figure 1.1 Locations of Mahaweli Systems 
Figure 1.2 Mahaweli System H 
Figure 1.3 Sub Systems of Mahaweli System H 
Figure 1.4 Ridi Bendi Ela Scheme 
Figure 1.5 Rajangana Irrigation Scheme 
Figure 4.1 Monthly total rainfall in mm - Thambuttegama 
Figure 4.2 Annual rainfall in mm - Thambuttegama 
Figure 4.3 Monthly Evaporation (mm/month) - Kalawewa 
Figure 4.4 Monthly ETo (mm/month) - Anuradhapura 
Figure 4.5 Actual & Planned Irrigation Duty in Dl/404 
Figure 4.6 Actual & Planned Irrigation Duty in D2/404 
Figure 4.7 Actual & Planned Irrigation Duty in D1/406 
Figure 4.8 Canal Network Diagram for Dl/404 
Figure 4.9 Canal Network Diagram for D2/404 
Figure 4.10 Canal Network Diagram for D1 /406 
Figure 4.11 Average Monthly Rainfall, Evaporation & ETo (mm/month) - Ridi Bendi 
Ela 
Figure 4.12 Distribution Net Work of Ridi Bendi Ela Scheme 
Figure 4.13 Average Monthly Rainfall, Evaporation & ETo (mm/month) - Rajangana 
Figure 4.14 Canal Net Work System in RB Track 1 of Rajangana scheme 
Figure 5.1 Variation of Crop Water Requirement during the Growth Stages 
x 
List of Abbreviations 
AO - Agricultural Officer 
BIE - Block Irrigation Engineer 
D canal - Distributary canal 
DRPM - Deputy Resident Project Manager 
D1/406 - Dl Distributary canal in Block 406 
D1/404 - Dl Distributary canal in Block 404 
D2/404 - D2 Distributary canal in Block 404 
Ea - Application Efficiency 
Ec - Conveyance Efficiency 
ET C - Crop Water Requirement 
ETo - Reference Crop Evapotranspiration 
FAO - Food & Agricultural Organization 
FC canal - Field canal 
FIR - Field Irrigation Requirement 
FO - Farmer Organization 
ID - Irrigation Duty 
ID Guideline - Irrigation Department Guideline 
IE - Irrigation Engineer 
IMD - Irrigation Management Division 
IWMI - International Water Management Institute 
LB - Left Bank 
LHG - Low Humic Gley 
LP - Land Preparation 
L P S T - Land Preparation Water Requirement 
LPIR - Land Preparation Irrigation Requirement 
LPWR - Land Preparation Water Requirement 
MASL - Mahaweli Authority of Sri Lanka 
RB - Right Bank 
RBE - Reddish Brown Earth 
RPM - Resident Project Manager 
xi 
List of Notations 
MCM = million cubic meters 
1 cusec = 28.3 1/s 
xn