Sri Lanka’s annual flooding has become a recurring nightmare, leaving thousands displaced and livelihoods destroyed. While heavy rainfall is often blamed, experts argue that the country’s river mouth maintenance program is a significant contributing factor.
The Problem: Inadequate Maintenance
Sri Lanka’s river mouths and canals are often clogged with debris and sediment, reducing their capacity to drain floodwaters. The lack of regular maintenance and dredging has led to narrowed river channels, exacerbating flood risk. For instance, the Kelani River, which flows through Colombo, has experienced regular annual flooding due to heavy rainfall and inadequate drainage.
Consequences: Devastating Floods
The consequences are stark. In 2024, over 76,000 people were affected by floods, with the Gampaha district reporting the highest number of affected residents. The Disaster Management Centre (DMC) allocated Rs. 50 million for relief operations, but the damage was already done. Crops were submerged, homes destroyed, and livelihoods ruined. The best of Finance personnel would be challenged to place a final tally.
Cyclone Fengal: A Wake-Up Call
The recent Cyclone Fengal, which hit Sri Lanka in November 2024, highlighted the country’s vulnerability to extreme weather events. The cyclone brought heavy rainfall, powerful winds, and devastating floods, affecting over 441,000 individuals. The response was swift, with the government and aid agencies providing relief efforts, but the question remains: what’s being done to prevent future disasters ²?
The Root Cause: Mismanagement and Lack of Planning
Experts point to inadequate planning, encroachment, and lack of coordination among authorities as key factors contributing to Sri Lanka’s flood woes. The country’s river basins are not being managed holistically, leading to environmental degradation and increased flood risk.
Solutions: Integrated Water Resources Management
To mitigate flooding, Sri Lanka needs to adopt an integrated approach to water resources management. This includes:
Regular Dredging and Maintenance: Clear River mouths and canals to ensure efficient drainage.
River Basin Management: Develop and enforce comprehensive plans to balance water use, conservation, and flood control.
Flood Mitigation Infrastructure: Upgrade and maintain flood control structures, such as dams and levees.
Community Engagement: Educate and involve local communities in flood risk management and planning.
By addressing these issues, Sri Lanka can reduce its vulnerability to flooding and ensure a safer, more resilient future for its citizens.
Meanwhile in Malaysia, there appears to be a workable River Mouth Management process:
This is a clear, technical, engineering-level explanation of how Malaysia carries out temporary river-mouth dredging and temporary refilling (sand-plugging) as part of its annual river-mouth management strategy, especially on the east coast (Terengganu, Pahang, Kelantan).
This method is used because monsoon (rainy season) and non-monsoon (dry season) drastically change the behaviour of the river mouth.
Malaysia’s Annual Temporary River-Mouth Dredging + Refilling Strategy — 10 Technical Points
1. Seasonal hydraulic modelling
Malaysia’s DID (Jabatan Pengairan & Saliran) uses two seasonal models:
Monsoon (Nov–Feb): high flow, dangerous waves, heavy sediment discharge.
Non-monsoon (Mar–Oct): low flow, sand accumulates at the mouth.
This tells them how much dredging is needed and where the sand plug must be opened or rebuilt.
2. Pre-monsoon dredging (“opening the mouth”)
Before heavy rains arrive, JPS orders temporary dredging to create a deepened navigation + flood-release channel at the mouth.
Purpose:
Prevent river water from backing up.
Reduce flood level inside towns.
Allow fishing vessels safe crossing.
3. Emergency dredging during monsoon
When unexpected sandbars reform, JPS uses maintenance dredging to re-open the river mouth:
Cutter-suction dredgers
Long-reach excavators (from shore)
Amphibious excavators
Goal: maintain minimum hydraulic cross-section for flood discharge.
4. Post-monsoon refilling / temporary sand-plugging
After monsoon, when waves are calmer and river flow drops, the dredged mouth may allow excessive saltwater intrusion or destabilize nearby beaches.
So temporary refilling is done:
Bulldozers push sand back into the old channel
Excavators reshape the bar
Natural coastal drift completes the fill
This stabilizes salinity balance, fish-nursery areas, and prevents shoreline erosion.
5. Continuous monitoring by drone + tidal stations
Malaysia uses:
Drones to capture weekly imagery
RTK-GPS surveys to measure mouth depth
Tidal gauges to monitor saline intrusion
Flow sensors upstream
The data shows when the mouth is too shallow or too deep and triggers action.
6. Bathymetric surveys every 1–3 months
Specialized survey boats run bathymetry (seabed mapping) across the channel:
Depth
Channel width
Sandbar direction
Volumetric siltation rate
This identifies “critical points” that need dredging or refilling.
7. Sediment-transport analysis (monsoon vs non-monsoon)
The east-coast rivers have very high littoral drift.
JPS uses sediment modelling to predict:
How quickly sand will return after dredging
Where the new bar will form
Whether temporary refilling will create or prevent beach erosion
This guides exactly where the temporary bar must be placed.
8. Using temporary channel markers for fishing boats
During temporary dredging or refilling:
JPS installs PVC/steel markers, sometimes with solar lights
These show fishermen the safe route across the mouth
Markers are moved when dredged channels shift (every few weeks).
9. Community reporting + on-site inspection
Fishermen and local communities report:
Boats getting stuck
Very shallow crossings
Strong wave crashes at the entrance
JPS uses this feedback to adjust the temporary channel alignment.
10. Environmental monitoring & thresholds
Before dredging/refilling, JPS checks:
Turbidity limits
Impact on fish-breeding zones
Saltwater intrusion levels
When thresholds exceed acceptable limits, dredging or refilling is approved immediately.
This ensures that the temporary river-mouth management protects both flood safety and ecosystem stability.