Page 347 - Proceedings book

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approach provides a precise method for reconstructing long-term human-environment

dynamics.

Results
1. Spatial Extent and Organization
GIS analysis revealed a highly organized and interconnected hydraulic landscape

within the Kala Oya Basin. The study identified over 180 tanks and 60 kilometers of
canals, demonstrating clear patterns of cascading tank systems where upper tanks

efficiently fed into lower reservoirs. The strategic placement of large reservoirs, such

as Kala Wewa, at higher elevations was observed. This strategic placement aimed to
maximize gravity-fed irrigation, thereby reducing the need for mechanical water

lifting and efficiently distributing water to lower areas. Additionally, minor tanks
were distributed across lower catchments, functioning effectively as sediment traps

and systems for moisture retention. Dense clusters of tanks were also identified in
zones with high agricultural potential. Hydrological modeling further confirmed that

many of these systems were strategically positioned to maximize gravity-fed

irrigation, which minimized the need for mechanical lifting of water.

2. Sediment and Environmental Analysis
Analysis of sediment cores revealed multiple episodes of alluvial deposition, which

corresponded to past flood events and periods of erosion. A key finding was the

increased siltation observed in the lower tanks starting around 800 CE. This increase
in siltation coincided with evidence of deforestation, indicated by high charcoal

concentrations in the sediment layers. Furthermore, a reduction in organic content in
sediments from post-1100 CE suggested agricultural abandonment and potential

climatic desiccation during that period. While the specific types of pollens found were

not detailed, pollen analysis generally revealed transitions from forest to scrub
vegetation, supporting the narrative of intensive land clearance in the area. The study

did not highlights a specific type of invasive vegetation, but it did note that canal
obstructions due to invasive vegetation and siltation were observed.

3. Land-Use Change and Ecological Stress
Land-cover analysis using satellite imagery from 1985 to 2023 demonstrated a

significant 44% reduction in forest cover within critical upper catchment areas. This
deforestation directly correlated with increased sedimentation in the tanks and a

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