Infiltration Rate of Groundwater in Vadose Zone of Uplifted Carbonate Island

Yutaka Tashiro

doi:10.11648/j.ajwse.20170305.12

Abstract

Solute contents in the vadose zone of limestone strata on Miyako Island of the Ryukyu Archipelago in Japan were measured by means of electrical conductivities (EC) of the extracted solutions of limestone core samples. A vertically nonuniform distribution of solute content was observed, which should lead to temporal variations of solute concentration in the groundwater under the water table. On the other hand, the data of chloride concentration in groundwater from 13 wells on the island was analyzed to see their long time variations. Both of these two approaches resulted in recharge rates of around 10<sup>-7</sup> m s<sup>-1</sup> for the vadose zone in the limestone strata of this typical uplifted carbonate island of the western Pacific Ocean.

Highlights

Cenozoic limestone strata constitute karstic aquifers covering much of the small islands in the tropics and the subtropics
They are the resource of groundwater which is indispensable for the inhabitants, a range of industries, and the ecosystem on the islands
The sample beneath the water table had high electrical conductivities (EC), which should be attributed to a high content of water with the solutes in the saturated zone

Summary

Introduction

Cenozoic limestone strata constitute karstic aquifers covering much of the small islands in the tropics and the subtropics. They are the resource of groundwater which is indispensable for the inhabitants, a range of industries, and the ecosystem on the islands. When the rainfall rate exceeds the infiltration rate, surface water moves into closed depressions and descends rapidly through relatively open pathways to the water table, bypassing the matrices [5]. Such difference in water pathways affects the concentration of solutes, as geometry and residence time determine the degree and characteristics of water/sediment and water/rock interaction [6]. Taborosi et al [8] reported the hydrology of the island of Guam according to this context, and emphasized the importance of ‘slow flow’ in water infiltration of carbonate island karst because of the high porosity of the young host limestones

Methods

Results

Conclusion