The Technology of Ancient Irrigation
- With the increase in population, irrigation engineering witnessed significant advancements and ambitious projects.
- Historical records indicate that construction of giant-sized reservoirs began as early as the 1st century B.C.
- The development of irrigation systems led to the evolution of highly sophisticated engineering skills, including the implementation of large-scale sluice gates and near zero-gradient irrigation canals.
- Maintaining these systems necessitates a profound understanding of hydrology and hydraulics, particularly when dealing with large-scale irrigation networks.
Sri Lankan Hydraulic Civilization
- The hydraulic civilization in Sri Lanka successfully connected small village reservoirs to massive reservoirs, forming intricate hydraulic systems.
- Brohier (1934, 1937a) identified a chain-like structure in the organization of small tanks and their relationship with large ancient reservoirs and waterways.
- The term "cascades" was coined by Madduma Bandara (1994) to describe the pattern where water from upstream tanks was successively stored and released downstream.
- These small cascades are interconnected with large reservoirs and giant feeder canals, creating highly complex and extensive irrigation systems.
- The ingenious Sinhala irrigation engineers invented the "biso kotuwa," a sluice that functions as a valve-pit to regulate the outward flow of water.
- The "biso kotuwa," dating back over 2100 years, allowed water distribution from large reservoirs through a single sluice gate, enabling watering of crops at any time.
Tank Cascades
- Irrigation system comprises a series of cascades of interconnected villages, reservoirs, paddy fields and trees that act as a wind breaking barrier. Small tank cascades are linked to large reservoirs and giant feeder canals to form extremely complex large irrigation systems.
- Analysis of tank distribution by each province shows that it is a function of rainfall and population density. Only 104 cascaded out of 240 cascades had adequate catchment area to supply adequate runoff.
