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Nilwala River flood bunds: salt-water extrusion gate hydrodynamics during southern storms?

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C
Clara Croc•940 rep

How do automated tidal flap gates and flood protection dikes in Matara prevent ocean surge backflow into agricultural paddy lowlands during monsoonal storm tides?

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3 Answers from travellers

✓Accepted Answer

The lower Nilwala River basin in Matara is prone to severe monsoonal flooding paired with coastal storm surge inundation. To protect surrounding agricultural lowlands, the Irrigation Department operates the Nilwala Flood Protection Scheme. The system utilizes continuous clay-core earthen flood embankments (bunds) paired with one-way tidal extrusion flap gates (salinity exclusion structures) at canal mouths. During high ocean tides, hydraulic pressure pushes flap gates shut against concrete headwalls, blocking seawater from invading low-lying paddy tracts. At low tide, hydrostatic pressure from upstream drainage pushes flap gates open, discharging interior storm runoff into the main river.

37
E
Eng Chathura Water•1860 rep

Large axial-flow diesel pumping stations at Bandaththara pump trapped interior storm runoff over high flood embankments when river spates exceed gate gravity discharge.

20
C
Clara Croc•940 rep

Heavy river dredging near the river mouth helps maintain sediment discharge, preventing sand spits from damming river spates during monsoon cloudbursts.

16
C
Capt Roshan Sea•1720 rep

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