The cultivation of rice in the semi-arid and dry-sub humid zone of Sri Lanka is based since 2,000 years on traditional water harvesting techniques: During two monsoonal periods rainfall and surface-runoff are stored in man-made reservoirs, so called tanks or wewas, and are used for irrigation throughout the year. In the hinterland of the ancient capital of Anuradhapura (377 BCE – 1017 CE) these tanks were aligned predominantly along shallow valleys forming so called tank-cascade systems. In contrast, in the surrounding of Polonnaruwa, which was the successional capital between 1055 and 1215 CE, water storage systems are characterised by single large scale tanks. In both regions water harvesting and water storage systems are still in use and are adapted to specific environmental and socio-economic conditions.
In the next decades urbanisation processes will lead to a transition from a present-day mainly rural to a more urban society, which will be, beyond that, affected by climate change. In an interdisciplinary project incorporating expertise from physical geography, archaeology and sociology this study aims to analyse the interdependencies between the cultural and natural system referring to the introduction of the different water harvesting strategies in a diachronic and comparative approach.
This is done by coupling the following methods:
a) modelling of water balance of selected catchments in the hinterland of Anuradhapura and Polonnaruwa, prior and after the implementation of the ancient water harvesting measures,
b) simulation of the water balance for future land use and climate scenarios,
c) analysis of present day resilience of the landscape by determining soil erosion rates and survey of recent land use practises,
d) conduction of qualitative interviews to catalogue traditional knowledge related to the water harvesting measures and
e) reconstruction of (pre)historic social-economic conditions related to the implementation and development of the water harvesting systems on the base of epigraphic sources, literature analysis and archaeological findings.
Workshops and interviews with smallholders and stakeholders serve to discuss traditional knowledge and management practices as well as to balance this knowledge against modern requirements. Project results will be provided on an online platform for smallholders and stakeholders in the wider study areas.
The overall project outcome will contribute to the documentation of the ancient water harvesting systems in Sri Lanka and its further sustainable development and will facilitate planning criteria to cope future challenges of change.