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1. Metro Colombo Urban Development Project

Environmental Screening Report for Embankment protection of Dehiwela Canal from the Galle Road Bridge to close to the sea outfall and removal of localized rock outcrops from the

canal bed

Final Report

December 2011

Uni‐Consultancy Services University of Moratuwa

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E2886 v10

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Table of Contents

1. Project Identification 3

2. Project Location 3

3. Project Justification 5

4. Project Description 7

5. Description of the Existing Environment 10

6. Public Consultation 21

7. Environmental Effects and Mitigation Measures

7a. Screening for Potential Environmental Impacts 22

7b. Environmental Management Plan 31

8. Conclusion and Screening Decision 42

9. Details of Persons Responsible for the Environmental Screening 49

Annexes

1. Photographs of some of the important locations along project roads

2. Detailed drawings of project components

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Metro Colombo Urban Development Project

Environmental Screening Report

1. Project Identification

Project title Embankment protection and demarcation of canal reservation of Dehiwela Canal from the Gall Road bridge to close to the sea outfall

Project Proponent

Sri Lanka Land Reclamation and Development Corporation

2. Project Location

Location Location of the project is depicted in the Fig. 1.

Definition of Project Area

(The geographical extent of the project & areas affected during construction)

The project area is along the Dehiwala Canal from the Bridge at Galle Road to the sea outfall.

Adjacent land and features

See “Other features” in Section 5.2

URBAN UPGRADING WORK

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Figure 1. Location map showing the Dehiwela Canal and its sea outfall

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3. Project Justification

Need for the project

(What problem is the project going to solve)

The Colombo Drainage System comprises a network of large open drainage canals, smaller tributary canals and low-lying marshes functioning as natural retention basins. It functions to serve the drainage needs of the Greater Colombo area and reduces incidence of flooding and thereby improves the health and sanitation conditions of the urban community, particularly of the urban poor who inhabit low-lying regions of Colombo.

The system could be broadly divided into two, with canals to the north of Sri Jayawardenepura Mawatha as Colombo North system and that to the south as the Colombo South system (see Figure 1. The system has four outlets and three of which Dehiwala and Wellawatte Outfalls and Mutwal Tunnel directly discharging in to the sea, while the North Lock discharges in to the Kelani River. There is a fifth outlet for the spill waters of the Beira Lake, via a circular weir near the old Parliament; the canal system is no longer connected to the lake to prevent highly polluted canal waters entering the lake. When the Kelani River level is high, the gate at the North Lock outlet to Kelani River is closed, so that reverse flow (from the river into the system) cannot take place. This operation is now carried out by the Department of Irrigation. Mutwal Tunnel of diameter 1.8 meters, functions as the outlet of the Main Drain.

The head of the canal system could be considered as Parliament Lake, to the East of Kotte Lake. Under dry weather conditions the North Lock, Wellawatte and Dehiwala outfalls are the major outflow points. In a flood situation, with the North Lock closed due to high water level in the Kelani River, the system has to rely mainly Wellawatte and Dehiwala sea outlets. Also the Mutwal Tunnel helps ease the drainage problems of North Colombo to a great deal at times when the North Lock is closed.

Dehiwala Canal

Dehiwala Canal is one of the main storm water drainage canals discharging storm water directly into the sea from the Colombo Basin. It starts at the branch where the Wellawatta Canal takes off from the Kirillapone Canal.

The length of the Dehiwala Canal is 3.8 km. It has a bottom width of 10 m up to the Bolgoda Canal confluence and it varies up to 24 m thereafter. Both banks of the canal are protected with gabion walls

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and sheet pile walls up to the Galle Road Bridge from the starting point of the canal. The canal stretch from Galle Road Bridge to Railway Bridge is earthen and is unprotected. In several places of the unprotected stretch the canal banks have collapsed and eroded causing severe inconveniences in carrying out maintenance work. The proposed canal stretch between the Galle road and the railway bridge is about 30 m wide and groins have been constructed to prevent formation of sand bar closing the sea outlet.

There are rock outcrops on the canal bed in three locations and flow guidance walls upstream of the railway Bridge causing hindrance to the conveyance capacity of this storm water drainage outlet canal. The project once implemented will facilitate undisturbed flow at the canal section and at the outfall.

Purpose of the project

(what is going to be achieved by carrying out the project)

The purpose of the project is to derive the following benefits and the beneficiaries are listed below:

Benefits

∗ Enhancement of flood control. ∗ Increased land values in adjacent areas. ∗ Improved health conditions & reduction in health

expenditure. ∗ Reduction in annual operation & maintenance cost to the

central government for canal clean-up ∗ Increased use of the canal system for recreational purposes

& waterfront development. Beneficiaries

∗ People residing close to the canal and with the combined effect, the entire Metropolitan area.

∗ The Government and the agencies managing the storm water drainage.

Alternatives considered

(different ways to meet the project need and achieve the project purpose)

No any other alternative is considered for the project as it is envisaged that there are no any other technically feasible and economically viable engineering interventions that could be accommodated in place of the proposed option.

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4. Project Description

Proposed start date The tender documents are expected to be ready by December 2011. Awarding of the tender will take place only after the 16th of March 2011. Construction period is estimated to be one year.

Proposed completion date

It will take minimum 12 – 15 months to finish the project from the date of opening bid documents.

Estimated total cost Estimate: 1.39 US$ million

Present land ownership

Entire project lies in areas belonging to SLLRDC.

Description of the project

(with supporting material such as maps, drawings etc attached as required)

The detailed drawings of the project are given in Annex 2.

1. Dehiwala Canal bank protection from Galle Road Bridge to the outfall.

a. New gabion wall - 671 m b. Provision of flow guidance walls made of gabions at

upstream side of the railway bridge. 2. Reinstatement of storm water drainage connections (hume pipes)

to Dehiwela Canal through gabion walls and introduction of catch pits wherever required.

3. Reinstatement of maintenance road (3 m) and construction of road side drain and cross drainage to the canal.

4. Temporary shifting & relocating of utility posts (electricity & telecom).

5. Removal of localized rock outcrops on canal bed obstructing water flow in three selected locations of the canal bed.

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Project Management Team

Agency: The agency responsible for design and supervision is the SLLRDC and the organization structure for the project is given in Figure 2.

Contact person: Ms.A.H.Thushari

Assistant General Manager (Special Projects) Sri Lanka Land Reclamation & Development Corporation

Nature of the consultation and input received:

Meeting and consultation at design office and site were done. Design drawings, master plans and other relevant information were too gathered.

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PROJECT

DEPUTY PROJECT

Consultant

Engineer (Contract

Planning

Design Engineer

Accountan

Quantity Surveyors

Draughtsma

AO/Cler

Computer

Office

Drive

Consultant (Land

Land

Project Engineer

(B)

Project

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Project Engineer

(A)

Project

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Project

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Project

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Environmentalist

Social Planne

Figure 2.Imeplemntation arrangements for MCUDP under SLLRDC

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5. Description of the existing environment

5.1 Physical features – Ecosystem components

Topography and terrain

The topography of Sri Lanka is marked by great diversity caused by long years of faulting and erosion of the landscape. The central mountainous region with the highest elevations covered by virgin forests and grasslands rises up to about 2,500 m above mean sea level. The surrounding plains, which rise to about 50 to 100 m above sea level, are largely used for agriculture and homesteads, but still have virgin scrubland where the population distribution is lower. This general topography of the country can be divided into three distinct geographical areas or well marked peneplains featuring the coastal belt, the plains, and the central highlands. The Colombo district which incorporates the project area falls into the so called lowest peneplain of Sri Lanka (after P.G. Cooray – Geology of Sri Lanka, 1984). The elevation variation of Colombo district situated in this coastal peneplain ranges to a maximum elevation of 150 m from sea coast. The terrain in Colombo largely consists of gently undulating plains and low-lying flatlands with a high density of drainage paths formulating a geography consisting of a mix of land and water. The city has many canals and the 65-hectare (160-acre) Beira Lake situated in the heart of the city is one of the most distinctive landmarks of Colombo. Dehiwala City is part of the Colombo Core Area and lies about 8 km to the south of Colombo City. Dehiwala Canal considered under the proposed drainage improvement and embankment strengthening is connected to Kirillapone Canal, Diyawanna Ela (canal) and Kolonnawa Ela in the upstream and drains a large area consisting of low-lying marshes and other local water bodies, eventually entering the sea at the sea outfall located about 1.2 km north to Dehiwala main city area. The canal which is 3.836 km in length is located within a mere 2.0 km inland from the coastal line and the elevation varies from 0 m above mean sea level (MSL) at the coast line up to a maximum of 15 m MSL only. Therefore, the slopes encountered in the project area are flat to mild (<1.0 %) and gently slope in seaward direction while the contour lines are aligned approximately parallel to the shoreline. The surface drainage in the area is largely determined by the trellis-patterned storm water drainage system consisting of both concrete-lined open canals and underground ducts connected to Dehiwala Canal in the downstream, diverting accumulated surface flows directly into

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the sea through its outfall with a maximum capacity of 30 m3/s which runs across a short strip of bare sandy beach devoid of beach vegetation. Patchy sandstone reefs occur in the sea at about 1 km distance away from the shore, but presumably have no any direct impact on the discharge capacity of the outfall.

Soil (type and quality)

The geology of Colombo is representative of the geology of the western coast of Sri Lanka and has existed for much of the Quaternary era. Bore holes drilled in central Colombo City show that this area once formed an estuary of the Kelani River and the Kalu Ganga River, the two main rivers that drain into the sea on the western coast. A few kilometers upstream in the inland valleys, there is a high-level gravel formation consisting of quartz pebbles embedded in a matrix of laterite separated with pebble-free layers of laterite. The floodplains along the rivers consist mainly of alluvial deposits. The floodplains of Kelani River also provide thick alluvial profiles for unconfined aquifers, in addition to the productive overburden along tributary banks. Vast area (over 90%) of Sri Lanka is underlain by metamorphic crystalline rocks of Precambrian age, which includes the project area, which cover a variety of Gneisses. The geology of Colombo is representative of the geology of the western coast of Sri Lanka and has existed for much of the Quaternary era. This is shown in the 1:10,000 and 1:50,000 geological maps of Colombo region produced by the Geological Survey and Mines Bureau. The typical rock types of this basement include Biotite gneiss, Hornblende Biotite gneiss, Charnockites, Charnockitic gneisses, Quartzite and undifferentiated Meta sediments. The floodplains along Kelani River and the Kalu Ganga rivers consist mainly of alluvial deposits. The floodplains of Kelani River also provide thick alluvial profiles for unconfined aquifers, in addition to the productive overburden along tributary banks. According to Survey Department soil maps (Figure 3) the main soil types in the project area are as follows.

• Red Yellow Podzolic soils with soft or hard laterite and undulating terrain • Bog and Half bog soils: flat terrain • Alluvial soils of variable texture and drainage: flat terrain • Regosols on recent beach sands: flat terrain

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Field surveys and observations carried out using trial pit holes have indicated that the local geology in the proposed project area is characterized by organic clays with sand and deep bedrock while the soil peaty clays with clayey laterite types are intermittently distributed in patches. It is presumed that these site-specific features are the most important ones as the environmental impact is considered.

Figure 3. Soil Maps of the Study Area (Source: Greentech, 2011)

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Surface water (sources, distance from the site, local uses and quality)

Sources

The most prominent source of surface water in the vicinity is the Dehiwala Canal and surface water drainage canal network that are connected with the main canal:

Distance from the site: Project area is the banks of the canal and the outfall.

Local uses: The canal plays an important role in conveying surface drainage and flood waters. Although the local people do not derive other benefits than diverting their surface drainage into these canals, the intrinsic function is vital and most important in draining the flood waters of the area. There are numerous illegal discharge points of grey water from residences, commercial establishments and warehouses located adjoining the canal, and due to the appalling level of water pollution, no other local uses can be derived from the water body.

Quality

Table 1. Water quality fluctuations of Dehiwala Canal

Parameter Water Quality (during 1997-2009)

pH 6.4 – 7.9 Conductivity (dS/m) 0.47-12.3 Turbidity (NTU) 13-37 Ammonia (mg/l) 0.84-6.2 Nitrates (mg/l) 0.3-16.1 Phosphates (mg/l) 0.4-3.4 DO (mg/l) 1.2-3.5 BOD (mg/l) 13-48 COD (mg/l) 17-134

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The water quality measured at two locations of the Dehiwala Canal is given in Table 1.

COD, BOD, turbidity and total suspended solid content are very high in the water. Dissolved oxygen, and pH are within the normal range. Phosphate concentrations are relatively high which indicate nutrient enrichment due to disposal of domestic and industrial wastewater into the canal over time.

Ground water (sources, distance from the site, local uses and quality)

Sources

According to the Land Use Division of the Irrigation Department, the project area falls within the local or discontinuous moderate to low aquifer in fractured rock. Only available source of ground water in the project site is shallow wells. However, ground water as a source of water is only been used for bathing at present. There are two bathing wells located in the banks of the canal: one is been used and the other is abandoned due to bad water quality. This is due to two reasons: availability of ample water supplies by NWS&DB and ground water being polluted.

Distance from the site

The ground water table is very shallow and is about 0.4 - 0.5 m on average close to the Canal, and can be at a level from almost at surface up to 1.5 - 3.0 m.

Local uses

Only a handful of households use shallow wells to abstract water. Even those who have shallow wells do not use water for daily consumption; they use the wells only occasionally for bathing and washing of clothes.

Quality

There are no data available for quality of ground water. However, it can be assumed that dissolved solid levels including salinity to be high as the project area is located very close to the coastal belt. The ground water can get contaminated due to dilapidated state of sewer connections and leakages.

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Flooding The downstream catchment area has suffered from frequent flooding up to around two to three times per year, before the previous canal widening/dredging and drainage improvement works were carried out (2004/2005). The canal stretch and all road segments in the proposed project area appear to have adequate drainage capacity and systems in place at present. The terrain is either flat in most areas or consists of mild slopes, therefore, no historical records of recent flooding are available in the area under consideration. However, after extremely heavy storm events and especially due to temporary blockage of existing storm water drainage system, the water movement concentrates in the low-lying areas causing temporary ponding or minor flooding in the adjacent localities, as has occurred in the recent past. Another factor, besides clogged drains and lack of proper maintenance that contributes to the flash flood problem is that excessive and unplanned land filling especially in the upstream marshes, leading to devoid of retention and detention capacity in the basin. Nevertheless, these effects are yet not significant in the project area and can easily be avoided by ensuring that the existing drains are well maintained and routine checks are carried out, particularly after major storm events. Tidal effects (on main drainage lines and sea outfall) The tidal effects should be considered in determining design levels for the downstream drainage structures including sea outfall. Due consideration should be given to maximum tidal variations and maximum wave heights when establishing drainage line and sea outfall design capacities. Tidal Levels and Periods The tide around Sri Lankan coast is mixed semi-diurnal type with two high waters and two low waters occurring approximately every 24 hours. First high water is almost twice high than the second high water. Amplitude of the tide in the west coast sea where the proposed project is located ranges from 35 cm at neap tide to 75 cm at spring tide. Wave Heights, Periods, Dominant Directions and other Ancillary Offshore and Nearshore Wave Parameters Directional wave measurements near the project area are not available. However the wave conditions in the area have been established by a wave transformation study. According to Directional Wave Climate Study of Southwest Coast of Sri Lanka, dominant wave characteristics of the project area can be summarized as follows.

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Wave Frequency Wave frequency has not been measured but seasonal variations need to be taken care of. Such data are given below. Waves, tides and ocean current regimes Much of the swell that affects Sri Lanka originates in the South Indian Ocean under the influence of westerly depressions and storms. This moves northwards and is felt most along the coasts of the Southern half of the island. Most large waves have a southerly component, but they rarely reach a height of over two metres. The highest waves are during the SW monsoon season, but the effective fetch is only about 800 km between the Maldives Island chain and Sri Lanka. During the SE monsoon, the northerly winds blow over short stretches of water from the North, and even when blowing across the bay of Bengal, are not steady enough to generate large waves. The period between tides is approximately 12 hours and is thus semidiurnal.

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Air quality (any pollution issues)

Heavy vehicle movements along Galle Road (A2 Motorway) and other bye-roads in the project area lead to high levels of air pollutant emissions, such as dust including particulate matter, smoke including CO, CO2, NOx, SOx etc. Such air pollution episodes can aggravate during peak hours when traffic movements are impeded. Fugitive dust particles could escape into the atmosphere during construction activities and during transportation and subsequent storage and handling. Emanation of foul odors from the canal, especially during dry weather when water levels are low, could take place from rotting solid wastes thrown in the water and sewage discharges.

Noise level and vibration (Any anticipated issues)

Existing ambient noise and vibration levels in the area correspond to highly urban and light industrial, businesses, hotel and restaurants. There is also heavy traffic noise from Galle Road, a road which carries heavy traffic during peak hours as well as during the night time. Intermittent high levels of noise and vibration levels are observed due to train operations, which is also one of the busiest railway sections of the country. All these urban activities contribute to high noise levels in the project area.

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5.2 Ecological features – Eco-system components

Vegetation

(trees, ground cover, aquatic vegetation)

Since the canal's embankment (one side) was encroached, there is neither ground cover nor natural vegetation in the project area. The other side of the canal is bordered by a road. Therefore, the canal embankment is dominated by man-made environment and no ecological sensitivity has been found. However, there are some common domestic tree species such as Mangifera indica (Amba), Cocos nucifera (Pol), Terminalia catappa (Kottan), Leucaena leucocephala (Ipil Ipil), Musa x paradisiaca (Kesel), Tabernaemontana divaricata (Watu Sudda), Filicium decipiens (Pehimbiya), Carica papaya (papol) etc. that are found in the site. No aquatic vegetation was found in the canal. No endemic or threatened plant species were recorded in this rapid screening survey.

Presence of wetlands No wetland habitats within or in the vicinity of proposed project area are recorded.

Fish and fish habitats

The canal water has entirely been converted into black colour and appeared to be a dead water body during site inspection, unless there are fish species adapted to extremely low dissolved oxygen levels. However, fish sampling was not carried out.

Birds (waterfowl, migratory birds, others)

Acridotheres tristis (Common Myna), Columba livia (Rock Pigeon), Copsychus saularis (Oriental Magpie Robin), Turdoides affinis (Yellow-billed Babbler), Corvus splendens (House Crow), Streptopelia chinensis (Spotted Dove) are common birds observed during the rapid screening survey and no endemic or threatened animal species were recorded.

Presence of special habitat areas (special designations & identified sensitive zones)

Neither special designations nor sensitive zones have been identified within and immediate surroundings of the proposed project area

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Other features

Residential/Sensitive Areas (Eg, Hospitals, Schools)

The land use on the left bank includes a wide road and middle income housing while the right bank is occupied by underserved settlements, known as Ranjan Wijerathne pura. The access road is 3 – 4 m wide and this settlement has been developed along the canal bank. At several places encroachments to the canal to create some gardening space was visible. A small Buddhist worship place was located behind the settlement and the main Buddhist temple Anandaramaya is located on Galle road adjacent to the canal. A well has been established near to the canal for bathing purpose. No sensitive land uses such as hospitals, schools are located within the project area.

Traditional economic and cultural activities

No any traditional economic or cultural activities are located within the project area

Archeological resources

No archeological resources are located within the project area.

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6. Public Consultation

Public consulted Consultation method

Date Details/Issues raised

Ms. Chandani – Resident at the beginning of the underserved settlement from the bridge

Informal Interviews

19.12.2011 This housing scheme to the present status was developed in early 1990s by reclaiming the canal bank area and over 100 families are living. Wastewater is connected to the Municipal system and therefore no wastewater is discharged into the canal. The canal pollution is mainly due to the upstream activities due to which people of this settlement are affected. If heavy vehicles are used on this road during the construction of the proposed Gabion wall, it would create a danger particularly to children who are always playing on the road.

Mr. G.D. Wiggin – resident living at the centre of the settlement

It is good to have the bank protection gabion wall similar to the opposite of the canal so that people will not encroach. It is good if the strip of land between the gabion wall and the road is permitted for people to plant. It is necessary to take care during construction as the access road is always full of people.

Mr. Careem – Resident living at the end of the settlement

The bathing well located on the strip between the road and the canal is heavily used by the people for bathing and washing. During the construction activities care must be taken to protect the well and reserve that land for the public well.

Mr. Ranjith – Resident living at the end of the settlement

It is good to pave the road so that people can use it without any problem during rainy period. Further it is requested that he strip between canal and road be given to people for cultivation of different crops.

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7. Environmental Effects and Mitigation Measures

7a. Screening for Potential Environmental Impacts

Screening question Yes No Significance of the effect

(Low, moderate, high)

Remarks

1 Will construction and operation of the Project involve actions which will cause physical changes in the locality

Yes Moderate – Positive impact

Most of the interventions are carried out along the canal hence no physical changes in topography and landform is anticipated other than strengthening of the canal banks with gabion structures, landscaping, paving of foot walks and road surfaces.

2 Will the Project involve use, storage, transport, handling or production of substances or materials which could be harmful to human health or the environment or raise concerns about actual or perceived risks to human health?

Yes Low

Transport of material and construction activities, including excavation, demolition of existing structure and material piles will emit dust and fugitive particles which may pose a health hazard to vulnerable persons on temporary basis. The winds will be the triggering factor for such impacts though it is sporadic in nature.

3 Will the Project produce solid wastes during construction or operation?

Yes Moderate

During construction:

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There will be general spoilage (construction debris) produced during the wall construction.

In addition, constructing gabions along the canal banks is expected to generate a moderate quantity of excavated material mixed with bottom sediment which will need to be disposed so as not to pollute the environment. Therefore, the sediment quality at the site (the proposed stretch of the canal) needs to be established prior to preparing the canal banks for gabion placing in order to determine the disposal method.

During operations

There will be material excavated along the canal, solid waste collected along canal banks etc which need regular collection and disposal appropriately. In addition, debris and sediments, floating matter and other solid waste carried by surface drainage can get collected along the canal that needs proper disposal methods. Regular cleaning of side drains and road will too generate such material. Culverts will also generate spoil material.

4 Will the Project release pollutants or any hazardous, toxic or noxious substances to air?

Yes Low

Rock breaking of boulders in the canal bed with chemicals might potentially release hazardous

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substances. However, this can be carefully planned and carried out using rock breaking technologies specifically designed to operate in inner city area with written clearance and supervision of the competent authority (the Geological Surveys and Mines Bureau) to minimize the risk.

5 Will the Project cause noise and vibration or release of light, heat energy or electromagnetic radiation?

Yes Low

Removal of rock outcrops will cause some level of vibration during drilling.

The project activities will cause noise and vibration during demolition of temporary structure along the canal (not houses), excavation of trenches, compaction, and during transport of material etc. These impacts are temporary in nature and cause only inconvenience to the neighboring people only.

6 Will the Project lead to risks of contamination of land or water from releases of pollutants onto the ground or into surface waters, groundwater or coastal wasters?

Yes Low

The canal bank/bed at the base of the gabions will need to be excavated to build a consistent base layer for the structure. Such excavated material should be disposed of safely. Stock piling of excavated matter mixed with soft sediments, soil, debris and other material may release pollutants back into surface waters, groundwater or coastal waters. If the excavated material would contain sediments

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contaminated with heavy metals, it would have to be appropriately handled and disposed in order to avoid any potential environmental and health risks to the residents and downstream marine ecosystems. It is anticipated that additional canal bank clearing, levelling and other preparatory activities may be needed prior to and during the proposed improvement of storm water drainage and embankment strengthening works in the canal. The surface soil and the topmost layers of subsoil in the proximity of proposed site areas are either Red Yellow Podzolic soils with laterite or sandy clay in subsurface layers. Laterite soils consist of reasonable grade distribution and are relatively more stable than typical clayey soils while clayey and sandy soils with their smaller grain sizes are less resistant to erosion and washout. Therefore, in those cases where the preparation of the canal banks would intersect sandy clayey sub-surface layers once exposed due to removal of land cover, loosened due to excavation and harrowing or heaped and left uncovered, these soil layers may pose a threat to the environment by causing washout of fine material degrading water quality, removing soil fertility, silting of the canal, degrading soil stability and risking slope and bank failures.

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On the other hand, proper construction practices like soil compaction and stabilization, turfing, maintaining naturally stable slopes, vegetation replanting, etc. will improve soil stability, reducing erosion risk and siltation effects during the construction phase and in the aftermath of project completion. Proper treatment and disposal of excavated material will help control the aforementioned associated adverse effects to a minimal and acceptable level.

7 Will the project cause localized flooding and poor drainage during construction

Is the project area located in a flooding location?

Low

Raised embankments and raised finish levels, stock piling of construction debris and other materials may block existing drainage flow paths, causing flow stagnation and localized flooding effects.

However, the proposed project area is not a flood prone area and the ensuring of proper construction practices like provision of improved drainage network, maintaining naturally stable slopes, vegetation replanting/turfing, etc. will improve drainage conditions, reducing flood risk during the construction phase and in the aftermath of project completion.

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8 Will there be any risks and vulnerabilities to public safety due to physical hazards during construction or operation of the Project?

Yes Low Safety issue in terms of injuries caused by construction material, machinery and falling into excavated trenches by neighbors and commuters could be anticipated.

9 Are there any transport routes on or around the location which are susceptible to congestion or which cause environmental problems, which could be affected by the project?

Yes Low

The road on the left bank is wide enough to allow for construction equipment and machinery to be moved and hence impacts on residents and commuters on the left side of the canal from restriction to access will be minimum. The road that goes through the underserved settlement on the right canal bank is narrow and hence residents will be temporarily impacted by access restriction during right bank construction works. However, there are many connecting roads so that impact would be mitigated.

10 Are there any routes or facilities on or around the location which are used by the public for access to recreation or other facilities, which could be affected by the project?

Yes Low

Use of road to access for residential areas and the restaurants down the lane may be temporary affected but not completely cut off.

11 Are there any areas or features of high landscape or scenic value on or around the location which could be affected by the

No Since project mainly deals with work along canals and roads, no impact is anticipated.

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project?

12 Are there any other areas on or around the location which are important or sensitive for reasons of their ecology e.g. wetlands, watercourses or other water bodies, the coastal zone, mountains, forests which could be affected by the project?

Yes Low

No such sensitive areas are found in the project area other than the coastal area.

13 Are there any areas on or around the location which are used by protected, important or sensitive species of fauna or flora e.g. for breeding, nesting, foraging, resting, migration, which could be affected by the project?

No No such areas are found.

Since the area has already been interfered by human activities, neither important nor sensitive species of fauna or flora were found.

14 Is the project located in a previously undeveloped area where there will be loss of green-field land

No No such green-field is encountered.

15 Will the project cause the removal of trees in the locality?

Yes Low

Some of the trees along the canal will be removed during construction of the gabion wall. Most of these trees are coconut or fruit bearing trees, which have been planted by residents in the canal demarcated bank reservation.

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16 Are there any areas or features of historic or cultural importance on or around the location which could be affected by the project?

No Low

There are several religious places located along the canal but not be affected during construction.

17 Are there existing land uses on or around the location e.g. homes, gardens, other private property, industry, commerce, recreation, public open space, community facilities, agriculture, forestry, tourism, mining or quarrying which could be affected by the project?

Yes Low

The strip of land between the canal and the access road is used by the community as an open space and home garden area.(This space is the canal reservation and has been demarcated by the SLLRDC) During the construction of the Gabion wall this area will be affected. However after canal bank fixing with the Gabion wall, a much organized strip of land would be available to create a linear park along the canal for the use of the community.

18 Are there any areas on or around the location which are densely populated or built-up, which could be affected by the project?

Yes Low

The project area is densely populated. However the project will not create major impacts as the construction activities of the project is in the canal only the access road of the settlement would be impacted during transportation of building materials and construction equipment.

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19 Are there any areas on or around the location which are occupied by sensitive land uses e.g. hospitals, schools, places of worship, community facilities, which could be affected by the project

Yes Low

There is a temple located along the Galle Road bordering the canal, which can be slightly affected due to noise generated during project activities.

20 Are there any areas on or around the location which contain important, high quality or scarce resources e.g. groundwater, surface waters, forestry, agriculture, fisheries, tourism, minerals, which could be affected by the project?

Yes Low

The canal is the only freshwater resources that exists (being closed to the sea the water quality in this stretch would make it moiré brackish) in the immediate project area. However, water in the canal is polluted due to a high concentration of urbanization with poor waste disposal practices. No significant additional impacts are expected due to proposed project components and intended construction activities.

21 Are there any areas on or around the location which are already subject to pollution or environmental damage e.g. where existing legal environmental standards are exceeded, which could be affected by the project?

Yes Dehiwala Canal and connected canals are highly or moderately polluted depending on the seasonal effects. However, the addition from the project seems to be very marginal or perhaps negligible.

31

7b. Environmental Management Plan

Key project activities Potential Environmental Effects

Mitigation Measures

Site preparation including provision of access roads, material storage yards

Emission of dust

Generation of noise

Disturbance to pedestrian movement and children who play on the road.

Cutting off of mainly coconut trees along the canal reservation during site preparation

Clearing of the canal bank for on-site material storage and access has to be carried out with the minimum use of machinery and sprinkling of water should be done appropriately.

Using the existing access and storage yards maintained and used by the State Engineering Cooperation for the present bridge construction site should be used as much as possible, which will mitigate most of the impacts.

Not to use heavy vehicles for transportation of building materials, especially along the narrow access road on the right canal bank.

Cutting of the coconut trees should be avoided as much as possible.

Temporary shifting & relocating of utility posts (electricity & telecom).

Community will lose the services for short periods.

Disturbance to pedestrian movement of the road and children who play on the road.

Take minimum possible time for shifting of such services, not using heavy machinery on the road and keeping the community adequately informed of the project activities and possible cutting off of utilities until the temporary relocation is completed.

32


Mitigation Measures

Canal bank/bottom excavation,, dewatering and disposal of bottom sediments

Excavation of the canal bank and bottom will be necessary where the gabions are to be placed. This will generate a mixed spoilage consisting of soil from the bank, solid waste and sediments from the canal bed. Stock piling of such excavated material, soil, debris and other material may block surface drainage paths causing localized flooding during constructional and operational periods.

If not properly stored and adequately covered, fine material washout may significantly contribute to the further degradation of surface water quality in the canal, inland reservoirs and sea outfalls, while increasing risk of slope failures, siltation and

Sediment quality in the proposed section of the canal should be established to understand the potential risk of contamination and to determine the most suitable disposal method for the excavated debris and sediments. If contamination is established according to accepted reference criteria, the following mitigation measures are proposed to be implemented.

(a) given the small volume of excavated matter (mixed with sediments, solid and solid waste) that will be generated from this stretch of the canal (300 m) the project should explore the possibility of using the two existing (and only) small semi engineered landfills in Sri Lanka at Mawanella and Nuwara Eliya. Since the anticipated volume of excavated matter in this case would be small, the project should be able to obtain the necessary clearances from the Central Environmental Authority and the relevant Pradheshiya Sabhas to use their facilities, or (b) dispose to Holcim industrial incinerator as alternative fuel. There will, however, be a cost involved in incinerating the material at Holcim which is presumably not significant given the small quantities.

If contamination is ruled out, the excavated matter along with other construction debris can be disposed to a landfill operated by the Dehiwela/Mt Lavinia Urban Council.

As the excavated matter, when it includes debris/sediments from the canal bed, would be watery/slurry, drying is

33


Mitigation Measures

blockage of structures.

If not properly disposed, the excavated material will pollute water sources at locations where it is disposed.

The low water table in the project area may cause dewatering a crucial issue to reduce pore pressure build up, slope instability and transport of fines. Dewatering may also be needed to carry out construction activities without interruption in canal embankments especially for gabion wall construction and for other excavations during the periods of high groundwater table.

Dewatering may cause surface ponding of removed water if proper drainage is not allowed, especially when the

necessary prior to transport to the disposal site, which will prevent leachate from leaking out during material handling and transportation. Drying can be done at the banks of the canal where the leachate will flow back to the canal.

If the sediment analysis confirms the canal to contain contaminated sediments, the SLLRDC should carry out excavation in such a way that bottom sediments/debris is isolated (to the extent possible) from the rest of soil/spoilage, so that quantities needing special disposal would be minimal. Also, separating excavated soil from the bank from the rest of the debris should be pursued if the soil is considered suitable as a backfill for the gabions. Proper and adequate dewatering should be ensured either using a proper monitoring schedule or using an automated submersible pipe with float device to ensure site activities are uninterrupted due to seepage water.

Proper surface drainage and retention-detention capacity should be provided to safely remove pumped-up water from the site to a natural drainage to avoid in site ponding effects.

Construction activities can be planned during the periods of low water table to avoid excessive dewatering requirements and

34


Mitigation Measures

upper soil layers are saturated due to recent storm events.

Possibility exists for changing the water quality of the public well that is used by the community for bathing and washing.

Smothering of benthic fauna

save costs while reducing risks of slope failures, increased erosion, etc.

Suitably arranged barge may be used where access through existing roads is not available.

Make sure that the bathing well would be re-instated after dredging of that part of the project is over.

Due to the changes in the debris or sediments, particularly morphology temporary smothering effect for benthic fauna may be possible but the impact is marginal.

Removal of temporary structures, debris, demolition waste, trees and other solid waste along the banks

Emission of dust

Generation of noise

Disturbances to local traffic, residents and other road-users during storage of material and debris.

Loss of flower and fruit bearing trees planted by people along the canal reservation strip. People will

The demolished materials and debris intended for temporarily storage should be properly stockpiled in most appropriate areas in the site to avoid disturbance to site mobility, local traffic and stored away from drainage paths and suitably covered to avoid washout.

Demolition has to be carried out with the minimum use of machinery and sprinkling of water should be done appropriately.


35


Mitigation Measures

lose such home gardens.

Develop a landscape plan to maintain this strip a linear park and mobilize the community to look after the areas in front of their properties. The landscape plan should include a line of trees similar to the existing one along the protected canal bank.

Excavation for the gabion wall construction and coffer damming

The construction of gabion walls along the canal embankment for bank strengthening and stabilization would require substantial excavation close to the existing earth embankments. Such deep excavations in saturated weak soil could result in collapsible vertical soil faces and increased susceptibility to erosion and liquefaction leading to bank failures.

Coffer damming is required to contain and divert movement of canal water and to provide a reasonably dry construction area for the


Proper dewatering plan must be made and stability of coffer dams during rainy period must be ensured. Excavated material must be carefully managed as highlighted earlier due to the potential risks involved.

Cracks that are likely due to vibration should be monitored in the immediate neighborhood and if appear either rectification or compensation should be made. Hence a background crack survey in the immediate vicinity must be done prior to commencement of the rock removal

36


Mitigation Measures

laying of screed concrete base (if required by design) and interlocking rubble work arrangement during gabion wall construction. The excavations in saturated soil may lead to failure if collapsible soil faces and excavated material will pose health and environmental risks if not properly handled and disposed.

Excessive vibration during hydraulic driving of sheet piles for coffer damming may weaken adjacent soil layers while it may also affect nearby foundations and other structures.

Removal of rock outcrops on canal bed.

Noise and vibration issues Approval from Geological Survey and Mines Bureau for removal of the rock outcrops should be obtained. Rock removal should be planned and calculated not to impact the nearby structures from vibration. In any case if there is damage to

37


Mitigation Measures

structures they will be rectified to the original level or compensation should be paid, as per the contract of the executing agent.

Material transport and storage

Emission of dust due to transport of material

Disturbance to pedestrian movement and the children playing on the road

The construction materials intended for temporary storage should be properly stockpiled in most appropriate areas in the site to avoid disturbance to site mobility, traffic and stored away from drainage paths and suitably covered to avoid washout.

Dust emissions should be controlled by wet spraying of construction sites and roads which are used for transportation of construction materials at regular intervals. Dust barriers if there are nearby houses and tarpaulin covering are mandatory on trucks / lorries which are used for transporting materials.

Vehicles should be maintained in good condition and regular maintenance needs to be done.


No heavy vehicles for transportation of building materials are encouraged. Building materials should be stored in places that will not disturb the accessibility to the community.

38


Mitigation Measures

Construction of flow guidance walls made of gabions at upstream side of the Railway bridge (length of the new gabion wall is 671 m)

Excavations beyond root depth may affect existing trees and deep excavations may pose risk of soil slope failures, disturbances to structures, etc.

Improper alignment of gabion wall and inadequate bottom support, as well as erosion of soil loosening bank support will lead to weakening of the interlocking of rubble used causing immature failure of gabion structure before its intended design life.

Pedestrian movement and the children playing on the road will be disturbed, when the building materials are handled using the road. However this impact is very short time as this impact will not exists through out the

Adequate measures should be taken to minimize damages to existing structures due to vibration by applying minimum driving power. Adequate support should be provided to nearby trees when excavation depth exceeds root depth.

Proper alignment of rock wall and adequate bottom support should be maintained by following appropriate design guidelines and correct construction methodologies to ensure precise interlocking of the rubble work. Lined concrete flow guide walls should be used where necessary to control bottom and side erosion when the gabions walls are exposed to through flow.

Take adequate care in handling building materials so that no accidents happen harming the people.

39


Mitigation Measures

canal at once. At a given time a small section will be affected.

Reinstatement of storm water drainage connections (Hume pipes) to Dehiwela Canal through gabion walls and introduction of catch pits wherever required

Erosion of soil adjacent to structures will lead to loosening of bank support. This will weaken the interlocking of rubble used causing immature failure of gabion structure before its intended design life. Blockage due to accumulation of fines due to cross drainage flows will lead to pore pressure build-up behind the gabion structure, leading to unbalanced pressure forces, making the structure susceptible to failure by toppling.

Storm water connections across the gabion walls should be provided using hume pipes or box culverts of adequate size according to pre-determined design storm events and return periods.

Catch pits should be provided at suitable spacing to remove excessive fines through settlement. Catch pits should be regularly cleaned and maintained in proper order. Fines removed should be properly disposed to avoid them joining flow paths again.

Backfilling of banks behind the gabions, turfing and replanting of trees

Selection of below grade fill materials will not attain required soil strengths after

Backfill materials should be selected after proper analyses of soil characteristics. Adequate compaction should be applied to

40


Mitigation Measures

compaction and will lead to differential settlements causing the gabion walls to misalign and fail.

Lose of vegetation (flowery plants, vegetables, coconut trees etc)

attain required soil strengths in banks and embankments.

The construction materials intended for temporarily storage should be properly stockpiled in most appropriate areas in the site to avoid disturbance to site mobility, traffic and stored away from drainage paths and suitably covered to avoid washout.


Make such spaces available for development of a linear park for public use and get the community involved in voluntary maintenance.

Reinstatement of maintenance road (width: 3 m) and construction of road side drain and cross drainage to the canal.

Lack of side drains and toe drains of adequate sizes alongside of the maintenance roads will lead to localized ponding in road pavements and weakening of soil sub-base underneath.

Pedestrian movement and the children playing on the road will be disturbed. Especially

Side drains and toe drains of adequate design sizes should be provided alongside of the maintenance roads and proper cross drainage structure should be provided where necessary to divert accumulated flows to the main drains.

The construction materials intended for temporarily storage should be properly stockpiled in most appropriate areas in the site to avoid disturbance to site mobility, traffic and stored away from drainage paths and suitably covered to avoid washout.

41


Mitigation Measures

children will be subjected to accidents if construction equipment are not handled taking extreme care.


Make the community adequately educated about the project activity. Exhibit sign boards in both Sinhala and Tamil languages at appropriate locations. Organize the re-statement activities in such a way so that alternate ways of accessibility to houses are made sure.

42

8. Conclusion and Screening Decision

Summary of environmental effects: Assuming that all mitigation measures are implemented as proposed, the following effects can be predicted

Key project activities Potential Environmental Effects Significance of the environmental effect with mitigation in place

NS- Effect not significant, or can be rendered insignificant with mitigation SP - Significant positive effect SN - Significant negative effect U - Outcome unknown or cannot be predicted, even with mitigation NA – Not applicable

Site preparation including provision of access roads, material storage yards

Emission of dust

Generation of noise

Disturbance to pedestrian movement and children who play on the road.

During site preparation domestic trees will be cut-off.

NS

NS

NS

NS

Temporary shifting & relocating of utility posts (electricity & telecom).

Community will lose the services for short periods.

NS

43

Disturbance to pedestrian movement of the road and children who play on the road.

NS

Canal bank/bottom excavation, dewatering and disposal of bottom sediments

Excavation of the canal bank and bottom will be necessary where the gabions are to be placed. This will generate a mixed spoilage consisting of soil from the bank, solid waste and sediments from the canal bed. Stock piling of such excavated material, soil, debris and other material may block surface drainage paths causing localized flooding during constructional and operational periods.

If not properly stored and adequately covered, fine material washout may significantly degrade surface water quality in canals and the sea outfalls, while increasing risk of slope failures, siltation and blockage of structures.

If not properly disposed, the material excavated from the canal banks and bottom will pollute water sources at locations where it is disposed.

The low water table in the area may cause dewatering a crucial issue to reduce pore pressure build up, slope instability and transport of fines. Dewatering may also be needed to carry out construction activities without

SN

SN

SN

NS

44

interruption in canal embankments especially for gabion wall construction and widening, and for other excavated areas during the periods of high groundwater table.

Dewatering may cause surface ponding of removed water if proper drainage is not allowed, especially when the upper soil layers are saturated due to recent storm events.

Possibility exists for changing the water quality of the public well that is used by the community for bathing and washing.

Smothering of benthic fauna

NS

NS

NS

Removal of temporary structures, debris, demolition waste and other solid waste along the banks

Emission of dust

Generation of noise

Disturbances to local traffic and pedestrians during storage of material and debris.

Many people have planted flowery plants, vegetables, banana and coconut trees on the strip between the road and the canal. People will lose such home gardens.

NS

NS

NS

NS

45

Excavation for the gabion wall construction and coffer damming

The construction of gabion walls along the canal embankment for bank strengthening and stabilization would require substantial excavation close to the existing earth embankments. Such deep excavations in saturated weak soil would result in collapsible vertical soil faces and increased susceptibility to erosion and liquefaction leading to bank failures.

Coffer damming is required to contain and divert movement of canal water and to provide a reasonably dry construction area for the laying of screed concrete base (if required by design) and interlocking rubble work arrangement during gabion wall construction. The excavations in saturated soil may lead to failure if collapsible soil faces and excavated material will pose health and environmental risks if not properly handled and disposed.

Excessive vibration during hydraulic driving of sheet piles for coffer damming may weaken adjacent soil layers while it may also affect nearby foundations and other structures.

NS NS NS

46

Removal of rock outcrops on canal bed using chemical blasting.

Noise and vibration issues may occur due to chemical blasting.

NS

Material transport and storage

Emission of dust due to transport of material

Pedestrian movement and the children playing on the road will be disturbed.

NS

NS

Construction of flow guidance walls made of gabions at upstream side of the Railway bridge (length of the new gabion wall is 671 m)

Excavations beyond root depth may affect existing trees and deep excavations may pose risk of soil slope failures, disturbances to structures, etc.

Improper alignment of gabion wall and inadequate bottom support, as well as erosion of soil loosening bank support will lead to weakening of the interlocking of rubble used causing immature failure of gabion structure before its intended design life.

Pedestrian movement and the children playing on the road will be disturbed, when the building materials are handled using the road. However this impact is very short time as this impact will not exists though out the canal at once. At a given time small section will be affected.

NS

NS

NS

47

Reinstatement of storm water drainage connections (Hume pipes) to Main Drain through gabion walls and introduction of catch pits wherever required

Erosion of soil adjacent to structures will lead to loosening of bank support. This will lead to weakening of the interlocking of rubble used causing immature failure of gabion structure before its intended design life. Blockage due to accumulation of fines due to cross drainage flows will lead to pore pressure build-up behind the gabion structure, leading to unbalanced pressure forces, making the structure susceptible to failure by toppling.

NS

Backfilling of banks behind the gabions, turfing and replanting of trees

Selection of below grade fill materials will not attain required soil strengths after compaction and will lead to differential settlements causing the gabion walls to misalign and fail.

Loss of planted species (flowery plants, vegetables, coconut trees etc.)

NS NS

Reinstatement of maintenance road (width: 3 m) and construction of road side drain and cross drainage to the canal.

Lack of side drains and toe drains of adequate sizes alongside of the maintenance roads will lead to localized ponding in road pavements and weakening of soil sub-base underneath.

Pedestrian movement and children playing on the road will be disturbed. Especially children will be subjected to accidents if construction equipment are not handled taking extreme care.

NS

NS

48

9. Screening Decision Recommendation:

Final recommendation

Majority of the potentially adverse effects can be classified as general construction related impacts and are mitigatable with known technology. Public concern does not warrant further assessment. Therefore, a stand alone Environmental Assessment is not required and, the Environmental Management Plan provided with this report would be sufficient to mitigate the identified impact. The following specific recommendations given in the EMP are of utmost importance to be implemented.

A sediment quality testing and the quantification of the excavated material that will be removal must be undertaken by the SLLRDC. Depending on the results of the sediment quality disposal method should be determined as specific in the EMP. If not the excavated matter can be stored in a suitable site and subsequently disposed to a municipal waste dump. Some parts of the excavated material such as soil from canal banks could be used by the SLLRDC for backfilling. But the suitability of the material for such a purpose needs to be confirmed.

Safe handling of material excavated from the canal including transport must be implemented.

Construction debris management plan must be worked out and implemented. Vibration monitoring survey must be undertaken prior to breaking the rock outcrops.

Heavy vehicles i.e., large trucks, should not be allowed for material transport. Only small vehicles such as tractors, carts will be promoted.

Construction activities should be encouraged during dry season so that impacts due to water levels will be minimal.

49

10. EMP implementation responsibilities and costs The overall responsibility of ensuring compliance with safeguard requirements for the sub-project lies with the SLLRDC. Specifically, it will be responsible for undertaking sediment quality testing in the proposed section of the canal, estimation of excavated material quantities generated and guiding the contractor on suitable disposal methods. The contractor will be responsible for implementing all other provisions in the EMP that relate mostly to good construction planning, site management and public safety practices. The additional cost involved in implementing the EMP relate to (a) undertaking sediment quality tests and (2) disposal of excavated material if contamination is established. Environmental monitoring will be carried out largely through compliance monitoring using the checklist provided in the EMF by the Environmental Officer of the SLLRDC and the contractor jointly. As such, the only additional costs envisaged are explained below:

Item Cost (Rs) Implementation Responsibility

Sediment quality testing – 2 samples

For following physical and chemical parameters

Particle size distribution, pH, Sulphate, Chloride, Total Organic Carbon, Fe, Cd, Ni, Zn, Cu, Cr, Al, Pb, Mn, Ca, Mg, Hg, As and leachability test for heavy metals

The testing will be done in early January 2012

120,000 SLLRDC

Disposal of excavated material The cost of mitigation is hard to estimate at this stage as the quantities of material, quality of pollutants/substances, detailed methodologies, and sites for disposal etc. are undecided. The consultant will work with the SLLRDC for estimating the mitigation cost once results of the sediment quality test

Contractor

50

Screening report completed by Dr. Mahesh Jayaweera, Team Leader

University of Moratuwa

Tel: 0777320590

email: [email protected]

Name/Designation/Contact information

Date Signature

Screening report reviewed by Name/Designation/Contact information

Date Signature

Approved by Name/Designation/Contact information

Date Signature

51

9. Details of Persons Responsible for the Environmental Screening (1) Dr. Mahesh Jayaweera, PhD, BSc in Civil Eng (Hons.), MIE (SL), CEng. – Team Leader (Overall coordination and planning) Experience: Team Leader/Consultant/Expert for more than 60 EIA and IEE studies during the past 15 years (2) Professor Mrs. Niranjanie Ratnayake, BSc in Civil Eng (Hons.), MSc, FIE (SL), CEng. – Environmental assessment specialist Experience: Team Leader/Consultant/Expert for more than 40 EIA and IEE studies during the past 20 years (3) Dr. Jagath Manatunge, PhD, MSc, DIC, BSc in Civil Eng (Hons.), MIE (SL), CEng. – Environmental Engineer (Noise, Water, Wastewater, Vibration, Air) Experience: Team Leader/Consultant/Expert for more than 40 EIA and IEE studies during the past 12 years (4) Dr. Lalith Rajapakse, PhD, MEng, BSc in Civil Eng (Hons.), MIE (SL), CEng. – Civil Engineer (Hydrology, Geology, other civil engineering aspects) Experience: Consultant/Expert for more than 20 EIA and IEE studies and assignments mainly related to hydrological during the past 6 years (5) Mr. Hemantha Jayasundara, BA (Hons.), MSc (Town and Country Planning), PG Dip in Urban Development, PD Dip in Environmental Sci. –Urban Planner Experience: More than 20 years as a Consultant/Expert on Urban and Regional Planning, Urban Design, Disaster Management, Environmental Management, Projects Management etc. (6) Dr. Anusha Kasige, PhD, MSc, BSc in Zoology – Ecologist (Flora, Fauna, Ecosystems) Experience: more than 15 EIA and IEE studies and ecological studies during the past 5 years

52

References

Cooray, P.G.(1984). An introduction to the geology of Sri Lanka (Ceylon), with a foreword by John Sutton, National Museums of Sri Lanka Publication, Colombo, Sri Lanka.

Greentech (2011). Environmental Assessment Final Report for Metro Colombo Urban Development Project, Vol. 1, Greentech Consultants (Pvt) Ltd., Colombo 5, Sri Lanka.

54

Annex 1:

Photographs of some of the important locations

Photographs of Dehiwala Canal

Fig.A‐ 1. Lat‐6.862810 Lon‐79.860130 Fig.A‐ 2. Lat‐6.862930 Lon‐79.862950

Fig.A‐ 4. Lat‐6.862620 Lon‐79.861670Fig.A‐ 3. Lat‐6.862610 Lon‐79.861660

Fig.A‐7. Lat‐6.862650 Lon‐79.860020 Fig.A‐ 8. Lat‐6.862680 Lon‐79.860040

Fig.A‐ 6. Lat‐6.863040 Lon‐79.863080Fig.A‐ 5. Lat‐6.862720 Lon‐79.860700

Fig.A‐ 11. Lat‐6.862940 Lon‐79.862970

Fig.A‐ 9. Lat‐6.862680 Lon‐79.861370 Fig.A‐ 10. Lat‐6.862750 Lon‐79.860930

Figure A-1. A location at the canal where wastewater is discharged from a vehicle service station

Figure A-2. A general view of the canal

Figure A-3. Coconut trees along the bank of the canal, which needs removal

Figure A-4. A pave section of the road that runs along the canal bank

Figure A-5. Debris collected along the canal banks

Figure A-6. Garbage and debris collected at the banks of the canal

Figure A-7. The railway line that crosses the canal and the location of the sea outfall

Figure A-8. A general view of the canal towards upstream from railway line

Figure A-9. A smaller drainage canal connected to Dehiwala Canal

Figure A-10. Debris collected at the banks of the canal

Figure A-11. The bridge across the Galle Road

55

Annex 2: Detailed drawings of project components

DC-CS 72

at 3+

324

6

0

0

Ï

H

P

H

WAL

L

CONC. POST &

FENCE

TEMPLE

H

DRAIN

GABIONS

TP

TP

EP

EP

B

Gabion Wall

Gabion

Wall

W

MDN

MDN

MDN

W

W

W

W

PP P

W

P

P

Bo Tree

W W

MDN

Road

TP

Road

Drain

Drain

Road

Dra

in

Road

Road

DP

DP

DP

DP

EP

EPEP

TP

TP

EP

TPEP

EP TP

TPEP

Gal

le R

aod

Dehiwala Bridge

From

Col

ombo

To D

ehiw

ala

Well

Drain

HP

HP

HP

Reservation

P

P

P PP

PWell

P

PP

P

UP

P

P

PP

P

P

Road

Road

RoadIP

IPIP

HP

HP

To Galle Road

BM -D3/GPS

ELV. 8.437M

U

W

P

Dia. 0.3mIL 0.395m

Dia. 0.3mIL 0.472m

Dia. 0.4mIL 0.900m

HP

Dia. 0.4m

IL 1.526m

Dia. 1.0m

IL 0.920m

Dia. 0.6mIL 0.702m

3993

90.0

0E

CB

DC

- C

S 73

at 3

+349

DC -

CS 7

4 at

3+3

74

DC - CS 75

at 3+

418

DC

- C

S 76

at 3

+480

DC

- C

S 7

7 at

3+5

27

484830.00N

3994

40.0

0E

484780.00N

3993

90.0

0E

3992

40.0

0E39

9240

.00E

484730.00N

484880.00N

PROPOSED GABION WALL TYPE - I

PLAN

484930.00N

3992

90.0

0E

484930.00N

600Ï

1

2

0

0

Ï

4

5

0

Ï

20405


& 3m WIDE WALKWAY & SIDE DRAIN


I

& 3m WIDE W

ALKWAY & SIDE DRAIN

AUTHORITY

CHKD

MINISTRY OF DEFENCESRI LANKA LAND RECLAMATION AND DEVELOPMENT CORPORATION.

RECOMMD :SUBD :

SCALE : 1:500

DESI :

APPROV :

CHKD :

DATE :

DATEREVISION

PROJECT :

TITLE :

NO: 03, SRI JAYAWARDENAPURA MAWATHA , WELIKADA , RAJAGIRIYA.

GOVERNMENT OF THE DEMOCRATICSOCIALIST REPUBLIC OF SRI LANKA

BY DATE AUTHO

{Funded by World Bank}

METRO COLOMBO URBAN DEVELOPMENT PROJECTCOMPONENT 1 ( STAGE - 1 ) FLOOD MITIGATION AND WATER FRONT MANAGEMENT

PLATE NO: 100

EP Electric Post

DP Dranaige Pit

TP Telephone Post

HP Hume Pipe

IP Iron Post

CB Cement Bank

REFERENCE

W Wall

P Permanent Building

B Bank

U Indifinite Boundary

PE Pipe Edge

MDN Masonary Drain

Proposed Bank

Existing Bank

Existing storm water drainage hume pipes - not to be touched.

Existing storm water drainage hume pipes - to be replaced by a new pipe.

New storm water drainage connection.

Catch Pit (CP)

LEGEND

DWG.No : E - DC / P / 9.109

DEHIWALA CANALPLAN SHEET - SHEET 9/10

NOTES :

1. This drawing is based on survey made by Hydrodynamics & Geophysical Survey (PVT) ltd in September 2011.

2. All dimenstions are in metres and all the levels are based on MSL unless otherwise stated .

3. Only canal banks and main features closely associated with the canal banks are indicated.

4. All details shall be verified by the contractor on site as required for his correct pricing , planning and execution of the work.

5. This drawing should be read in conjunction with Dwg. Nos. E - DC / P / 9.101 - 9.108 , E - DC / P / 9.110 , E - DC / CS / 9.201 - 9.202 , E - DC / LS / 9.301 - 9.304

DRAWN : Nadeesha

TP

TP

TPTP

TPTP

EP

EPEP

EP

W

CB

CB

B

B

B

B

B

MDN

MDN

MDN

MDN

Road

Road

Roa

d

Roa

d

Roa

d

Roa

dD

rain

EPEP

EP EP TPTPEP

EP

EPBridge

HP

HP

Road

P P P P P P P P P P P P P P P P P P P P PP P

PP

P PP

PP

P P P P P P P P P P P P P P P P

DEHIWALA ELA

U U

W

W

B

HPHP

HP

PE

PE HP

From

Hou

ses From HousesBM-D2/GPS

ELV. 2.835M

UU

BM-D1/GPS

ELV. 2.818M

Sea Outfall

Breakwater

Breakwater

Beac

h

Bea

ch

Dia. 0.4mIL 0.807m

Dia. 0.8mIL 0.983m

Dia. 1.2mIL 1.038m Dia. 1.0m

IL 1.070m

Dia. 0.8mIL 1.282m

Dia. 0.6mIL 0.793m

DC

- C

S 7

8 at

3+5

76

DC

- C

S 7

9 at

3+6

26

DC

- C

S 8

0 at

3+6

77

DC

- C

S 81

at 3

+727

DC

- C

S 82

at 3

+777

DC

- C

S 8

3 at

3+7

87

DC

- C

S 8

4 at

3+8

27

484730.00N

3991

40.0

0E

3990

90.0

0E

3989

40.0

0E

3989

90.0

0E

484730.00N

484880.00N 484880.00N


PLAN

3991

90.0

0E

484880.00N

3988

90.0

0E

484730.00N

900Ï

600Ï

BRIDGE OVER DEHIWALACANAL AT DEHIWALA FORMARINE DRIVE EXTENSION( 32.18m x 11.7m )

PROPOSED GABION WALL TYPE - II& 3m WIDE WALKWAY & SIDE DRAIN


& 3m WIDE WALKWAY & SIDE DRAIN

AUTHORITY

CHKD

MINISTRY OF DEFENCESRI LANKA LAND RECLAMATION AND DEVELOPMENT CORPORATION.

RECOMMD :SUBD :

SCALE : 1:500

DESI :

APPROV :

CHKD :

DATE :

DATEREVISION

PROJECT :

TITLE :

NO: 03, SRI JAYAWARDENAPURA MAWATHA , WELIKADA , RAJAGIRIYA.

GOVERNMENT OF THE DEMOCRATICSOCIALIST REPUBLIC OF SRI LANKA

BY DATE AUTHO

{Funded by World Bank}

METRO COLOMBO URBAN DEVELOPMENT PROJECTCOMPONENT 1 ( STAGE - 1 ) FLOOD MITIGATION AND WATER FRONT MANAGEMENT

PLATE NO: 101

EP Electric Post

DP Dranaige Pit

TP Telephone Post

HP Hume Pipe

IP Iron Post

CB Cement Bank

REFERENCE

W Wall

P Permanent Building

B Bank

U Indifinite Boundary

PE Pipe Edge

MDN Masonary Drain

Proposed Bank

Existing Bank

Existing storm water drainage hume pipes - not to be touched.

Existing storm water drainage hume pipes - to be replaced by a new pipe.

New storm water drainage connection.

Catch Pit (CP)

LEGEND

DWG.No : E - DC / P / 9.110

DEHIWALA CANALPLAN SHEET - SHEET 10/10

NOTES :

1. This drawing is based on survey made by Hydrodynamics & Geophysical Survey (PVT) ltd in September 2011.

2. All dimenstions are in metres and all the levels are based on MSL unless otherwise stated .

3. Only canal banks and main features closely associated with the canal banks are indicated.

4. All details shall be verified by the contractor on site as required for his correct pricing , planning and execution of the work.

5. This drawing should be read in conjunction with Dwg. Nos. E - DC / P / 9.101 - 9.109 , E - DC / CS / 9.201 - 9.202 , E - DC / LS / 9.301 - 9.304

DRAWN : Nadeesha

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