Eng. L. S. Sooriyabandara Divisional Irrigation Engineer Irrigation - - PowerPoint PPT Presentation

• Eng. L. S. Sooriyabandara

Divisional Irrigation Engineer Irrigation Department Matara

River Basin Map

MATARA KOTAPOLA AKURESSA PITABEDDARA

River Basin Information

 Catchment Area

: 970 km2

 Length of the river

: 70 km

 Average Annual Rainfall

: 1650 -4000 mm

 Average Annual Discharge : 1500 MCM

50 100 150 200 250 300 350 Oct Nov Dec Jan Feb Mar Apr May June Jul Aug Sept Rainfall in mm Month Long term Average

Average Rainfall

Nilwala Flood Prone Area

1960 Feasibility study

Engineering Consultants, Inc. (ECI), Denver Colorado, USA Irrigation Department, Sri Lanka

 Three Basin Study

 Gin Ganga  Nilwala Ganga  Kalu Ganga

 Objectives

 Flood Protection  Power Generation  Irrigation  Water Supply  Transbasin Diversion

Proposal in Nillwala under Three basin Study

Large scale reservoir in upper catchment

Nilwala Ganga Flood Protection Scheme

 Period of construction

: 1980 s

 Financial & technical Support

: French Government

 Original Proposals

 Developing low lands at RB for paddy cultivation (Stg. I)  Protection of LB paddy cultivation area from flooding (Stg. II)  Construction of multipurpose reservoirs in the upper catchment.

(Stg. III)

 Protection of Matara city and suburbs from flooding

(Stg. III)

General Map of Project

HULANDAWA DIGILI OYA

Strategy Applied

Embanking (Flood Bunds) Channelization (Drainage System) Storm water evacuation by pumping

What was implemented by French in 1980s

 Stage I & II

• To develop low lands in the lower basin

(Kiralakele & Kadawedduwa) for paddy cultivation (2000 ha in each).

 Additional works

• Minor protection for Kadduwa sector &

Akuressa lift irrigation scheme

• Bypass canal at Panadugama

Sea outfall Indian Ocean Kadduwa Sector Kadawedduwa Sector Kiralakele Sector Unprotected zone

Flood Bunds

Panadugama Bypass canal

Panadugama spill

Bypass canal Akuressa town

 Paddy Cultivation in Kiralakele was not successful

due to poor soil conditions and shortage of water. (only about 500 ha out of 2000 is cultivated)

 Stage II (LB side) is successful, but the operation

cost of pumps is extremely high.

 Extent of unprotected area is very high

General View on Stage I & II of the Project

Lapses of the Nilwala Ganga Flood Protection Scheme

 Higher flood levels in unprotected area of

3000 ha

 Formation of acidity in 800 ha of paddy lands

in Kiralakele area

 High Costs of Operation and Maintenance

Crucial Environmental Issues

Causes

 Natural  Unplanned

developments

 Urbanization  Sand mining  De-forestation  Plantations, Industries  Increase of population

Effects



Flooding



Saline water intrusion



Water pollution



Soil erosion



Siltation



Water Scarcity



Soil Salinity



Acidity

Present Requirements

(1) Implementing stage 3 with necessary changes to suit present conditions (i) Digilioya Reservoir , Aparekka Ara & Batuwita reservoir (ii) Enlarging river channel with removing

• bstacles to flood way.

(2) Rehabilitation of stage II (LB area) & Pumps of

Akuressa Lift Irrigation sch.

(3) Find alternative solution for Kiralakele (RB side)

• Stage 3

(1) Construction of reservoirs in the upper

catchment

 Objectives - Providing Irrigation facilities

Developing Hydro power Mitigation of floods (Upper basin & the unprotected area, either side

• f river)

Stage 3 (continued)

(2a) Construction of bypass canal for the river. Objectives - To protect the city of Matara & suburbs from flooding

• Lowering the flood levels of

unprotected area

(2b) Alternative proposal – Enlarge the river channel from Bandaththara to sea out fall

Proposed Reservoir Location

PROPOSED RESERVOIRS

Matara Akuressa Kamburupitiya Aparekka Tank Kotapola Tank Urawa Tank Kirama Tank KadukannaTank Digili Oya Tank Batuwita Ara Tank

BANDATHTHARA SEA OUTFALL THUDAWA PUMP STATION

Proposed River Enlargement

Nilwala Transbasin Diversion

Objectives

 Diversion of Gin -

Nilwala surplus water to Hambantota

 Power Generation  Gin – Nilwala Flood

Mitigation

Locations of Proposed Tank

Pitadeniya Kotapola Ampanagala

CASCADE ROUTE OF GIN – NILWALA DIVERSION PROJECT

Kotapol apola Ampanagal gala Kirama ama Muruth thawe awela Chandr drika ika Wewa wa

POWER PLANT NT

Pitade deniya niya

Project Lay Out Map cont……

Project Lay Out Map

Kiralakele Sector

• Most affected area after project

Kiralakale Drainage

Bund Nilwala River Thudawa pump house

Solution to eradicate drainage problem of Kiralakale….

• Kirala kele is in the right bank of the basin, which is

boggy and marshy and the land is in the same level with the sea.

• In 1988 the area was isolated by flood bunds and a

pump house was provided to evacuate drainage water in to the river at Thudawa.

Kiralkale

Scheme Data

 In Matara District  Area of the scheme = 2000Ha  Farmer organization of the scheme = 33  Total number of Regulators = 70

Canal Network

• Primary canal system

Canal Name Canal length km S 7.0 T 8.0 U 8.0

Length of secondary -48 48 km.

Drainage Methods

 Two methods used

 Gravity outlet  Pumping

Gravity

• utlet

Pump House

Draining

Draining …

Gravity

• utlet

Pump House

Drainage Canal Sea Level

PH 5.0 – 5.5

0.3m Paddy Fields upto 0.3m above Sea Level Paddy Fields – below Sea Level Paddy Fields above 0.3m from Sea Level

PH 4.0 – 5.0 PH 2.5 – 3.5

Land Elevation Effect

Land Degradation

Water logging Vegetation

Marshy low land with mangroves Rich with Iron Pyrites (Fe2S) When water table is decreasing… Oxidization taken place Form Acidity Displacement of Iron & Aluminium ion Toxic soil

Critical & Limitative condition in paddy cultivation

Soil Acidity & Salinity

Also……

• Salts creep to the top soil due to

evaporation & capillary action

• Harmful salinity

Distribute this soil problem to adjoining areas due to the variation of water table In dry season

Challengers …

Maintenance of canal network

Challengers …

Water Management structures

Potential

Nature Parks

Future of farming

Change of Land use

Detention Reservoirs as a Flood Control Measure

Detention ponds Temporary detention area Permanent pool River Sea Inlet & Outlet canals Multi purpose reservoirs

“Water is the planet's

essential resource, the primary control on health and crucial to the security of food, energy and biodiversity. Despite this, water's role is not well understood and this precious resource remains undervalued ”

Thank you