Goa does not require melting glaciers to produce catastrophic floods; extreme rainfall, sediment mobilisation, unstable slopes, and densely occupied floodplains would be sufficient
The catastrophic Nepal flood of August 26, 2026, carries an important warning for Goa, provided we understand the comparison correctly. Goa has no glaciers, permafrost, or snow-fed Himalayan rivers. Nepal’s disaster originated with the collapse of part of a glacier, generating an enormous ice-and-rock avalanche and a destructive debris-rich flood.
Reports indicate that the affected river rose by approximately 9 meters in some places within half an hour. Goa cannot experience this trigger. However, it can certainly experience the consequences of an exceptional volume of water, sediment, and debris suddenly moving through landscapes where slopes, drainage channels, floodplains, and river margins have been drastically modified. Nepal has given us two warnings. Scientific studies of the devastating September 2024 floods in Kathmandu concluded that extreme rainfall alone did not explain the destruction.
Landslides and debris flows, sediment mobilised from disturbed terrain, riverbank encroachments, rapid urbanisation, and weaknesses in land-use governance magnified the damage. The August 2026 catastrophe again demonstrates what happens when a river temporarily ceases to behave like ordinary flowing water and becomes a fast-moving mass of water, mud, rock, trees, and structural debris. This is the lesson that Goa must take seriously.
For decades, Goa has increasingly treated watersheds as real estate rather than hydrological systems. Outside the relatively protected government forest areas, thousands of constructions have appeared on lateritic plateaus, hillsides, valleys, and riverine lowlands. Hills have been cut, benched, and terraced; natural gradients have been altered; and innumerable seasonal drainage pathways have been narrowed, diverted, or obstructed. Buildings, retaining walls, and roads change the way rainfall moves through a watershed.
Each intervention may appear harmless when considered on a plot-by-plot basis. Their cumulative hydrological impact on an entire catchment can be enormous. Unregulated construction on unstable slopes without adequate geotechnical investigation increases the risk of landslides. This requires greater attention. A lateritic hill is not an indestructible rock block. Deep weathering, fractures, underlying softer horizons, groundwater movement, excavation, and prolonged monsoon saturation can create instability.
When slopes are terraced, cut, and additionally loaded with buildings, retaining structures, and roads, extreme rainfall becomes a severe test of engineering decisions accumulated over decades. Goa has already witnessed sufficient local slope failures to recognise the potential for a much larger Wayanad-like combination of intense rainfall, saturated terrain, and mass movement. The second lesson concerns the floodplains. The disturbing images from Nepal showed how vulnerable buildings and infrastructure are when they are located immediately adjacent to dynamic rivers. A river is not merely a narrow channel carrying water during ordinary weather. Its natural territory includes banks, floodplains, wetlands, abandoned channels, and depositional areas through which exceptional floods spread and dissipate energy.
Goa has permitted extensive development in low-lying landscapes associated with the Mandovi, Zuari, Sal, and Baga rivers, as well as their tributaries and creeks. Coastal regulations cannot substitute scientifically determined floodplain zoning and river setback lines. The third and perhaps the least appreciated danger is sediment. Goa typically discusses floods in terms of millimeters of rainfall and meters of water level rise. However, an extreme rainfall event accompanied by multiple slope failures could mobilise enormous quantities of lateritic soil, weathered material, vegetation, and construction debris.
Sediment can choke drains and culverts, reduce channel capacity, obstruct bridges, temporarily dam streams, and generate destructive surges when such blockages fail. Nepal, therefore, teaches us that future disaster modeling for Goa must consider not simply water but water, sediment, and debris. Goa has another vulnerability that warrants urgent attention: its historic khazan system. Low-lying areas along the Mandovi-Zuari estuarine system, Cumbarjua canal, Sal, and other waterways require bund-breach and inundation modelling. We must also question the comforting assumption that familiar rivers will always remain within their boundaries.
The lower Mandovi, from around Ganjem towards the estuary and Aguada, has followed a recognisable course throughout historical memory. However, rivers are dynamic geomorphological systems. Exceptional floods erode banks, redistribute enormous sediment loads, create bars, and sometimes exploit older or lower pathways. We need scientific modeling of how an extreme, sediment-rich flood could affect the Mandovi, Zuari, and their tributary systems, instead of assuming that tomorrow’s river systems must behave like yesterday’s. Goa’s vulnerability is amplified by its intense urbanisation, with 70 percent of Goa’s population living in urban areas, among India’s highest proportions. Therefore, a major hydrological disaster could simultaneously affect dense settlements, highways, bridges, electricity, telecommunications, drinking-water systems, and sewage infrastructure.
Nepal’s lesson for Goa is ultimately simple: extraordinary natural processes become catastrophes when they encounter accumulated human vulnerability. Goa urgently needs a high-resolution River Corridor, Floodplain, Khazan, and Slope Vulnerability Atlas identifying floodplains, paleochannels, natural drains, unstable slopes, sediment-source areas, vulnerable bridges and culverts, khazan embankments, and probable bund-breach inundation zones.
Vulnerable slopes require geotechnical audits, and future development permissions must consider entire watersheds, not merely individual property boundaries. Goa does not require melting glaciers to produce catastrophic floods. An exceptional monsoon interacting with unstable slopes, massive sediment mobilisation, obstructed drainage, weakened embankments, and densely occupied floodplains would be sufficient. Nepal’s terrible warning is that rivers eventually demand the space that geography gave them. Goa should give that space back voluntarily before a future monsoon takes it back violently.
(Dr Nandkumar M Kamat, who has a doctorate in microbiology, is a scientist and a science writer).
