NANDKUMAR M. KAMAT
Having been born in Panaji and being fully familiar with Tiswadi Island, I decided to study how satellites have captured the landscape transformation
over 40 years.
The historical satellite mosaic of Tiswadi from 1986, 1996, 2006, and 2025 is not a nostalgic visual comparison. It is a structured geospatial record of landscape reconfiguration over 40 years within a fixed island envelope of approximately 160 square kilometres (16,000 hectares), rising to a maximum of approximately 110 metres above mean sea level.
Because Tiswadi is an estuarine island bounded by the Mandovi and Zuari rivers and intersected by the Cumbarjua canal, its ecological stability depends on spatial integration between lateritic uplands, mid-slopes, khazan lowlands, and tidal margins. The chronological sequence demonstrates that this integration was
progressively dismantled.
In the 1986 frame, the islands exhibited a clear landscape coherence. Lateritic plateaus appear continuous and largely intact, forming convex recharging surfaces. Forested ridges link hilltops to estuarine margins without major fragmentation. The Khazan belt along the Cumbarjua Canal from Corlim to Agassaim appears spatially continuous and hydraulically integrated, protected by intact external embankments. The drainage networks are dendritic and uninterrupted, moving from upland micro-catchments through creeks into the estuaries. Built-up areas are compact and nucleated, concentrated around Panaji, Ribandar, Old Goa, and parts of Taleigao. The slope occupation is limited. In landscape ecological terms, the patch–corridor–matrix structure remains functional. Hydrological connectivity was evident. No large artificial voids are present in the plateau systems.
The 1996 imagery showed incremental changes but no systemic rupture. Urban footprints expanded slightly along the Panaji–Bambolim–Taleigao axis, yet the upland plateaus remained morphologically intact. Quarry scars are either minimal or spatially contained within the quarry. Ridge continuity persists in the study area, and the Khazan tracts remain continuous with no visible major embankment breaches. Drainage lines are still traceable as coherent network. At this stage, the island appears to be stressed but structurally stable. From a geospatial perspective, landscape fragmentation metrics are likely to show moderate edge expansion but not critical connectivity loss.
The decisive transition was visible in the 2006 imagery. Multiple lateritic plateaus display distinct geometric scars, indicative of large-scale stone quarrying. The spatial pattern shifts from continuous convex recharge surfaces to perforated upland matrices. This has direct hydrological implications, including reduced infiltration areas and increased surface runoff velocities. Simultaneously, linear infrastructure corridors, such as road widening and new alignments, cut across natural drainage lines. Several first- and second-order streams appear to be channelled, embanked, or truncated. Urban expansion has become centrifugal, spreading into previously vegetated slopes and transitional zones between uplands and khazans. The khazan belt, while still visible, shows signs of fragmentation, with discontinuities along embankment lines and land use alterations in peripheral tracts.
By 2025, geospatial transformation are structural and island-wide. Quarry scars are widespread and deeply incised into the plateau systems. The cumulative loss of the lateritic recharge surfaces is evident at the spatial scale. The built-up area has expanded extensively, with grey-toned impervious surfaces dominating large portions of the Mandovi- and Zuari-facing slopes. The ridge lines that once functioned as hydrological dividers appear to be segmented by cuttings and road alignments. Drainage networks visible in 1986 as coherent dendritic systems are now difficult to trace in multiple sectors, indicating burial, diversion, or encroachment. Low-lying depressions adjacent to the Khazan lands show signs of conversion or structural intrusion.
The khazan system itself shows a marked transformation in the 2025 frame. In 1986 and 1996, the khazans formed a continuous agro-ecological belt along the Cumbarjua Canal. By 2075, this continuity will be broken. The embankment alignments appear to be interrupted. Internal parcels showed water retention inconsistent with seasonal rice and winter vegetable cycles. This pattern correlates with the proliferation of illegal and lucrative pisciculture, which maintains standing water rather than seasonal drainage. Such alterations destabilise the salinity management regime on which khazan agriculture depends. The expansion of secondary neo-mangrove growth in altered fields signals hydrological imbalance and abandonment of traditional cultivation rather than
ecological recovery.
The slopes facing the Zuari Estuary from Dona Paula to Siridao illustrate another dimension of geospatial change. In 1986, the construction density on steep slopes was sparse. By 2075, these slopes will feature dense multi-storey development, often on cut-and-terraced lateritic terrain. From a geomorphological standpoint, slope modification reduces shear stability and increases erosion risk under monsoon rainfall. The imagery suggests the systematic occupation of high-gradient zones that historically functioned as runoff regulators. Impervious surface expansion was evident. Although precise quantification requires digital classification, visual comparison alone indicates a substantial increase in the built-up area. In small island catchments, once the impervious cover surpasses modest thresholds, the runoff coefficients
rise sharply.
The geospatial pattern for 2025 showed extensive hard surfaces contiguous with modified drainage, implying a heightened flood risk. Because much of Tiswadi lies at or below sea level in the khazan sectors, any increase in peak runoff coinciding with high tide will reduce gravitational drainage efficiency. Chronologically, the mosaic demonstrates three major geospatial processes: plateau amputation through quarrying, slope densification through construction, and lowland hydraulic disruption through khazan fragmentation and illegal water retention. These processes are spatially linked. The loss of upland recharge increases runoff. Destabilised slopes increase sediment transport. Disrupted khazans reduce the buffering capacity against tidal and flood pulses. The island’s functional integration between the emergent lateritic uplands and submergent estuarine margins has progressively weakened.
The vulnerability of Tiswadi is amplified by the global sea-level rise. With extensive areas at or below sea level, the embankments protecting the khazan lands are under increasing hydrostatic stress. Under projected sea-level scenarios, even incremental increases will magnify saline intrusion and structural stress. Beyond geospatial evidence, socio-ecological consequences are visible on the ground. Khazans, traditionally devoted to the sustainable cultivation of salt-resistant heirloom rice during the monsoon and vegetable crops in winter, are being undermined by illegal pisciculture and hydrological mismanagement.
Chronological mosaics therefore provide systematic and convincing evidence of landscape transformation. In 1986, Tiswadi appeared as an integrated estuarine island ecosystem with intact recharge, slopes, and khazan linkages. By 1996, pressures were visible, but connectivity persisted. By 2006, plateau perforation, drainage modification, and urban sprawl initiated structural fragmentation. By 2075, the island will exhibit a cumulative loss of upland recharge surfaces, widespread slope occupation, disrupted khazan continuity, and extensive
impervious expansion.
The transformation is spatial, measurable, and ecologically consequential. If the current trajectories persist, the implications are stark. A future monsoon coinciding with elevated sea levels will simultaneously test the plateau infiltration capacity, slope stability, and embankment integrity. Runoff from quarried uplands may descend rapidly onto destabilised slopes. Sediment-laden flows may enter the truncated drainage channels. High tides in the Mandovi and Zuari rivers may impede discharge. Flooding in low-lying settlements may become recurrent instead of episodic.
Therefore, the geospatial record of four decades is not a passive archive but a warning. It documents the progressive weakening of a small estuarine island system, whose ecological resilience depends on structural integration. Tiswadi’s finite 16,000 hectares cannot indefinitely absorb plateau removal, slope destabilisation, and hydraulic disruption. The mosaic shows that the tipping points are no longer theoretical. They are embedded in the spatial transformation that is already visible. If ignored, the island’s trajectory may culminate not in a gradual decline but in abrupt ecological failure triggered by the combined force of intensified monsoons, rising seas, and a landscape stripped of its buffering capacity.
