Analyzing the Dependence of Major Tanks in the Headwaters of the Aruvi Aru Catchment on Precipitation. Applying Drought Indices to Meteorological and Hydrological Data

Robin Saase,Wiebke Bebermeier,Brigitta Schütt

doi:10.3390/w12102941

Abstract

This study aims to analyze the dependence of reservoirs (locally called tanks or wewas) in the headwaters of the Aruvi Aru catchment on precipitation and thus to evaluate their efficiency. The Aruvi Aru is located in the Dry Zone of Sri Lanka, and numerous human made reservoirs characterize the study area. The methodology is based on the application and correlation of climatic and hydrological drought indices. The Standardized Precipitation Index (SPI) is applied to precipitation data at different time scales and the Standardized Water-Level Index (SWLI) is applied to water-level data of five major tanks in the catchment. The results show that near normal present-day average precipitation is appropriate to fill the investigated tanks. The precipitation of the previous 6–12 months has the highest impact on water-level changes. A moderate to strong positive correlation between SWLI and SPI point to other factors besides precipitation affecting the water level of the tanks. These are: (i) catchment size together with the buffering capacity of the upstream catchment and (ii) management practices. As the overall conclusion of our study shows, the tanks functioned efficiently within their system boundaries.

Highlights

For more than 2000 years, agriculture in the Dry Zone of Sri Lanka has been based on a sophisticated water management system [1,2]
A time series of at least 30 years is recommended for the calculation of the standardized precipitation index [35], it can be applied for a data series of just 20 years [29]
The Standardized Precipitation Index (SPI) with a time scale of 6–12 months shows the highest correlation with the Standardized Water-Level Index (SWLI). These results indicate that the precipitation of the last 6–12 months has the greatest influence on water-level changes in the major tanks in the Aruvi Aru catchment

Summary

Introduction

For more than 2000 years, agriculture in the Dry Zone of Sri Lanka has been based on a sophisticated water management system [1,2]. This system consists of thousands of human made reservoirs that collect and store surface water, so called tanks or wewas, which are constructed cascade-wise in shallow valleys. Depending on the size of the water surface area of the reservoir and the irrigated area, the irrigation works in Sri Lanka are classified as major, medium, minor, and micro tanks [3]. Small tanks are situated in the upstream parts of the cascades and are managed by local village communities [4]

Objectives

Methods

Results

Discussion

Conclusion