Holocene dynamics of the salt-fresh groundwater interface under a sand island, Inhaca, Mozambique

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• 作者：Lars Væ ; ret^a ; ^{lars.varet@gmail.com} ; Anton Leijnse^b ; ^{toonleijnse@gmail.com} ; Fortunato Cuamba^c ; Sylvi Haldorsen^a ; ^{sylvi.haldorsen@umb.no}
• 刊名：Quaternary International
• 出版年：2012
• 期刊代码：77_10406182
• 类别：ear
• 出版时间：20 April, 2012
• 卷：257
• 期：Complete
• 页码：74-82
• 文件大小：1441 K

摘要

The configuration of coastal groundwater systems in southeast Africa was strongly controlled by the Holocene sea-level changes, with an Early Holocene transgression 鈭?5聽m (10,000-5000聽cal BP), and two assumed high-stand events in the Middle and Late Holocene with levels higher than the present. The fluctuation of the salt-fresh groundwater interface under Inhaca Island in Mozambique during the Holocene has been studied using an adapted version of the numerical code SUTRA (Saturated-Unsaturated Transport). In this study, small-scale variations such as tidal effects have not been considered. A number of transient simulations were run with constant boundary conditions until the steady state condition was reached in order to study the sensitivity of response time, salt-fresh interface position, and thickness of the transition zone to different parameters such as hydraulic conductivity, porosity, recharge, and dispersivity. A 50%increase in horizontal hydraulic conductivity yields a rise in the location of the interface of >15聽m, while an increase in recharge from 8%to 20%of mean annual precipitation (MAP) causes a downward shift in the interface position of >40聽m. A full transient simulation of the Holocene dynamics of the salt-fresh groundwater interface showed a response time of several hundred years, with a duration sensitive to porosity, hydraulic conductivity and recharge and a position determined by the recharge rate and the hydraulic conductivity. Dispersivity controls the thickness of the transition zone in this non-tidal model. Physical processes, such as changes in recharge and/or the sea level, may cause rapid shifts in the interface position and affect the thickness of the transition zone.