r r 1 DEMOCRATIC SOCIALIST REPUBLIC OF r SRI LANKA MINISTRY OF TRANSPORT AND fflGHWAYS MINISTRY OF FINANCE AND PLANING COLOMBO-KATUNAYAKE EXPRESSWAY PROJECT '.r^ DESIGN BUILD & TURNKEY CONTRACT NO. RDA/CKE/01 VOLUME V- ANNEX 16 Engineering Consultants Limited - May 1999 (Interim Report replaced by Final Report, refer Addendum No. 04) BETWEEN ROAD DEVELOPMENT AUTHORITY OF SRI LANKA AND DAEWOO - KEANGNAM JOINT VENTURE L REPUBLIC OF SOUTH KOREA L I ROA:) r»EVE!.0PM3!NTAUTH0Rm' . w. F)NAL REPORI Siii\ml!ieJ fly Etigiiu'tirltg Cl »sultan!!Lbttiti-ä No. JOSS. SriJcvctfür<ien.i^iiaMa-<vaiha, 'H'etikada. May 19^^^ •m'.-' '..••'t •.. iv-«*:" «fe -.^. •^ 1 ROA!> DKVE:.OFM?NTAUrHOR:rV I l: FINAL ïtEFORr L ,u\ }09S. Sri,'cvci^cire'i:r..ij7iii-aÄ4a-i-aihü. Ü'elikada. L F.ajasSriw. L. May l'») 1 . "•.:.'•.'•.••.• •'• L :: •.*•> p • L .:••;-•;•:•••' . 'i.'«11 ••- ';- .-•..:;•;:::•:•.-1.:, . -i- '•- i \ p-'afci.>; DETAILED IIYDROLOGICAL STUDY FOR PROPOSED COLOMBO - KATUNAYAKE EXPRESSWAY PROJECT FINAL REPORT CONTENTS Page EXECUTIVE SUMMARY Es-1 L Objectives of Study 1-J M Preamble M 1.2 Terms of Reference 1-2 1.3 Reports Submitted to date 1-3 1.4 Special Comments M 2. IdeDtification of Catcbmeots aad Sub-cafcfameats 2-] 2.1 Drainage Patterns 2-1 2.2 Major Catchments 2-1 2.2.1 AttanagaluOya J-1 2.2.2 Kalu Oya 2-2 2.3 Minor Catchments 2-2 2.3.1 MudunEIa ' 2-2 2.3.2 Micro Catchments 2-3 3. Rainfall Analysis 3-1 3.1 Available Run-ofTData 3-1 3.2 Available Rainfall Data 3-2 3.3 Rainfall Intensity Studies 3-2 3.4 Catchment Rainfall 3-3 3.5 Flood Experienced in Colombo City in June 1992 3-3 4. Catchment Parameters 4-1 r Page r 5. Development of Flood Hydrographs 5-1 5.1 Available Data 5-1 5.2 Alternatives for Development of Flood Hydrographs 5-1 5.2.1 Model I -SCS Model 5-1 5.2.2 Model 2-HECl Model 5-1 5.3 Model Selected for the Study ' 5-2 5.4 Flood Hydrographs Developed for Pre-project Conditions 5-2 5.4.1 Model Parameters Used 5-2 5.4.2 Flood Routing - Dandugam Oya, Ja Ela and Kaiu Oya 5-3 5.4.3 Flood Routing - Minor Catchments 5-4 6. Hydraulic Conditions Downstream of A3 and CKE 6-1 6-1 General 6-1 6.2 Mudun Ela Catchment 6-1 6.3 Kalu Oya Catchment 6-1 6.4 Micro Catchments 6-1 6.5 Ja Ela Catchment 6-2' 6.6 Dandui^am Oya Catchment 6-2 6.7 Section of CKE Traversing along and through a part of the Lagoon 6-2 7. Hydraulic Design of Drainage Crossings under Proposed CKE 7-1 7.1 Methodology 7-1 7.2 Estimation of Flood Levels 7-1 7.2.1 Description of the Model 7-2 7.2.2 Results obtained from the Model 7-3 L 7.2.3 Estimation of Flood Levels along CKE Trace 7-3 7.3 Design of Major Drainage Crossings & other Watenvay Openings 7A L 7.4 Impact of CKE on Flood Levels upstream of A3 7-4 7.4.1 General 7-4 7.4:2 Mudun Ela Catchment 7-5 7.4.3 Kalu Oya Catchment 7-5 7.4.4 Micro Catchments between Mabole and Ja Ela 7-5 L- 74.5 Ja Ela Catchment 7-5 7.4.6 Dandugam Oya Catchment 7-5 L L 11 L •rj;..."^^^.'"-" "•' •-'«F^ . 1-1.' ' Jrf »W^» Page 7.5 Validation of Road Embankment Levels 7-5 75,1 General 7-5 7.5.2 Mudun Ela Catchment 7-6 7.5.3 KaluOya Catchment 7-6 7.5.4 Micro Catchments from Maboie to Ja Ela 7-6 7.5.5 Ja Ela Catchment 7-7 7.5.6 Dandugam Ova Calchmenl 7-7 7.5.7 Area Draining into Negombo Lagoon 7-8 7.6 Inventory of Drainage Crossings across A3 7-8 8. Improvements to DowDstream Drainage System to Mitigate the Impact of High Floods 8-1 8.1 The Concept 8-1 8.2 Mudun Ela Catchment 8-1 8.3 Kalu Oya Catchment 8-1 8-4 Micro Catchments from Maboie to Ja Eia 8-1 8.5 Ja Ela Catchment 8-2 8.6 Dandugam Oya Catchment 8-2 9. Floods Mapped Out 9-1 9.1 Dandugam Oya Catchment 9-1 9.2 Ja Ela Catchment , 9-1 9.3 Kalu Oya Calchmeni 9-2 9.4 Mudun Ela Catchment 9-2 9^ Field Surveys Done 9-3 10. Mapping of Flood Inundation Areas Corresponding to High Return Periods lO-I 10.1 Methodology 10-1 10.2 Estimation of Flood Levels for Different Return Periods lO-I 10.3 Duration of Flooding . 10-2 Hi r Page 11. Additional Flood Deteation Areas to Mitigate the r Impact of High Floods 11-1 1 1 11.1 The Concept ll-l * 11.2 Mudun Ela Catchmenl ll-l 11,3 Kalu Oya Catchmenl 11-1 11.4 Micro Catchmenis 11-2 11.5 Ja Ela Catchmenl 11-2 [ ' 11.6 Dandugam Oya Catchment 11-2 12. Monitoring System Recommended during Construction 12-1 13. Identifying Areas on Verges of Negorabo Lagoon for Expanding its area 13-1 13 1 The Problem 13-1 13.2 Selection of Areas for Investigations I3-I 13.3 Augur Hole Survey Carried Out 13-1 13.4 Report on Soil Survey 13-1 13.5 Identification of Areas 13,2 13.6 Recommendations 13-2 14. Baseline Survey of Ground Watei Levels and Water Quality' in Project Area 14-1 14.1 Objective 14-1 14.2 Selection of Wells 14-1 14.3 Ground Water Survey Done 14-1 14.4 Location of Wells 14-1 14.5 Water Level Observations 14-1 14,6 Chemical & Physical Parameters 14-1 14,7 Microbiological Tests 14-1 L 14.8 Comments on Water Quality of Samples Tested based on Standards for Potable Water 14-2 L 14,8.1 Colour 14-2 14.8.2 Turbidity 14-2 14,8.3 PH 14-2 14,8.4 Eleclrical Conductivity 14-2 14,8.5 Chloride 14-2 14.8.6 Total Alkalinity 14-2 L 14,8.7 Nitrate 14-2 14,8.8 Nitrite 14-3 L L iv L •--;;ÏX' i4.8.9TotaI Phosphates 14-3 14.8.1 OTolal Hardness 14-3 MS.IlTotallron 14-3 14.8.12Free Ammonia 14-3 14.8,13AIbuminoid Ammonia 14-3 14.8. MBacteriological Examination Reports 14-3 IS. Concluding Remarks IS-1 r LIST OF TABLES r. Tabic 3.1 List of Raiafall Stations Table 3.2 Rainfall Intensities Table 4.1 Catclimcot Parameters Tabic 5.1 Ordinales of Outflow Flood Hydrographs Table 7.1 Ncgombo Lagoon Flood Routing Table 7.2 Drainage Crossing and other Waterway Openings Table 7.3 Impact of 100 year Return Period Floods Table 7.4 Inxentory of Drainage Crossings Across A3 Table I O.I Flood Levels for Different Return Periods Table 12.1 Tentative Sampling Program for Lagoon Turbidity Table 14.1 Baseline Survey of Ground Water-Ground water Surface Elevations Table 14.2 Results of Ground Water Ana I) sis-Sam pled in November 1998 Table 14.3 Results of Ground Water Analysis-Sampled in February 1999 vi .'«.^ LIST OF FIGURES Figurcl.1 - CKE Trace (in the docket) Figure 2.1 - Schematic Sketch showing Ilydrologicaf and Hydraulic characlerisfics Affecfing Proposed CK£ during storm conditions Figure 3.1 - Location of Rainfall Stations Figure 3.2 - Depth - Duration Cune for Vincit Estate Flgffre 3.3 - Depth - Duration Cune for Katunayaka . Figure 3.4 - Depth - Duration Cur^'e for Colombo Figures.! - Schematic diagram for development of Inflow Ilydrographs by SCS Model Method Figure 5,2 - Schematic diagram for development of Inflow Hydrographs by HECl Model Method Figure 5.3 - Flood Hydographs -50 year return period- Dandugam Ova Catchment Figure 5.4 - Flood Hydographs -100 year return period- Dandugam Oya Catchment I' Figure 5.5 - Flood Hydographs -200 year return period- Dandugam Oya C Catchment Figure 5.6 - Flood Hydographs -50 year return period- Ja-EIa Catchment Figure 5.7 - Flood Hydographs -100 year return period- Ja-EIa Catchment Figure 5.8 - Flood Hydographs -200 year return period- Ja-EIa Catchment Figure 5.9 - Flood Hydographs -50 year return period- Kalu Oya Catchment Figure 3:10 - Flood Hydographs -100 year return period- Kalu Oya Catchment Figure 5.U - Flood Hydographs-200 year return period-Kalu Oya Catchment Figure 6.1 - Schematic of Simplified Drainage System. vn ^_..-.^' •->i,':'^ -V . ! I Figure 7.1 - Schematic of Negombo Lagoon Hydraulic Characteristics-under r Storm Conditions Figure 7.2 - Methodology For Estimation Of Flood Levels at Ja Ela r Dandugam Oya Road Crossings Figure 7.3 - Schematic High Flood Water Surface Profile Dandugam Oya Figure 7.4 - Schematic High Flood Water Surface Profile Ja-EIa Figure 7.5 - Schematic High Flood Water Surface Profile Kalu Oya Figure 12.1 - Location of Monitoring Points Figure 14.1 - Location of Areas Selected for Auger Hole Survey Figure 14,2 - Location of Auger holes I L L- L- L L viii • 'J -i s^ LIST OF ANNEXES Annex 1 - Monthly Rainfall Data - 7 no Rainfall Stations Annex 2 - Bacteriological Examination Reports L be :-•- •w.-yrjiBM'ï ...... -, ^ -l^p EXECUTIVE SrM.\ÏAR\ DESCRIPTION OF CKE TR\CE AND CATCHMENTS INTERCEPTED The proposed trace commencing from the left bank of Kelani Ganea, crosses Kelani Ganga and runs in a northerly direction intercepting the catchments of Mudun Ela, Kalu Oya, Lfruwal Oya (Ja-EIa), Dadugam Oya and the micro catchments intervening these basins.