Evaluating dynamic mechanisms and formation process of freshwater lenses on reclaimed atoll islands in the South China Sea

Sheng, Chong; Han, Dongmei; Xu, Hengchao; Li, Fucheng; Zhang, Yunfan; Shen, Yongqiang

doi:10.1016/j.jhydrol.2020.124641

Cited by 14 publications

(17 citation statements)

References 48 publications

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“…This assumption is reasonable for the rainfall intensity in a small area, but it is not realistic for the recharge of aquifers, because the process of infiltration is affected by geological characteristics such as topography, soil type and evapotranspiration, land use type, and human activities (Park et al., 2014; Werner et al., 2017). Field investigations have showed that the groundwater lens shape and thickness can be affected by spatially variable recharge rates induced by ridge topography (Ruppel et al., 2000), terrain and vegetation patterns (Schneider & Kruse, 2003, 2006), distribution of different soil types (Park et al., 2014) and heterogeneous hydrogeological properties including hydraulic conductivity, impermeable layer, and boundary conditions (Cellone et al., 2018; Holt et al., 2019; Rathore et al., 2018; Rathore, Lu & Luo, 2020; Sheng et al., 2020). In addition, the knowledge and insights on how the volume and shape of a groundwater lens change in response to spatially variable recharge rates can provide very useful information for determining the location and recharge rate of artificial recharge to control seawater intrusion (Bouwer, 2002; Rajasekhar et al., 2019; Senanayake et al., 2016).…”

Section: Introductionmentioning

confidence: 99%

Analytical Solutions for Fresh Groundwater Lenses in Small Strip Islands With Spatially Variable Recharge

Tang

Yan

Wang

et al. 2021

Water Resources Research

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Groundwater lens may provide the primary freshwater supply for the inhabitants of small islands. The lens profile and volume are sensitive to spatially variable recharge caused by topography, soil type, land cover, evapotranspiration and human activities. We derive analytical solutions based on the sharp‐interface approximation to describe transient and steady‐state lens profiles for spatially variable recharge rates in small strip islands. The derived solutions are validated by a steady‐state solution for simple spatial recharge patterns and numerical simulations. Numerical investigations show that the spatial recharge pattern has a significant impact on the lens profile. For a given constant total recharge, smaller recharge areas or a more concentrated recharge rate can result in a larger lens volume. The volume increase can be over 20% compared with the lens volume of a uniform recharge. For the steady‐state lens profile corresponding to a point recharge, the squared lens thickness peaks at the recharge location and linearly decreases to the boundary, resulting in a triangle shape for the profile of squared lens thickness. Moreover, compared with recharges in other locations, recharge in a small area at the domain center has the greatest impact. Uncertainty analysis can be conveniently implemented based on the derived analytical solution to investigate the lens behavior under spatially variable recharge with uncertainties. Results show that the lens volume tends to have a larger variance for a recharge rate with a higher variance and longer correlation length.

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Section: Introductionmentioning

confidence: 99%

Analytical Solutions for Fresh Groundwater Lenses in Small Strip Islands With Spatially Variable Recharge

Tang

Yan

Wang

et al. 2021

Water Resources Research

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“…Previous studies indicated that the hydraulic properties of coral sand or fill materials exhibit highly spatial heterogeneity (Sheng et al., 2020; Werner et al., 2017). For example, Bailey et al.…”

Section: Discussionmentioning

confidence: 99%

Influence of Land Reclamation on Fresh Groundwater Lenses in Oceanic Islands: Laboratory and Numerical Validation

Sheng

Jiao

et al. 2021

Water Resources Research

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There are approximately 425 atolls in the world (Falkland, 1992) and most of them belong to Small Island Developing States (SIDS) in the Indian and Pacific Oceans. About 65 million people live in these SIDS (UN-OHRLLS, 2015). When precipitation recharge across an oceanic island is sufficient, a fresh groundwater lens (or freshwater lens) develops above the denser saline groundwater derived from the sea, which is a

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“…It was reclaimed from August 2014 to September 2015, with the land area increased from less than 0.2 km 2 to 2.23 km 2 . The length is 3.71 km, and the maximum width is 0.99 km [26]. The topography is flat, with an elevation normally 3 to 4 m above the mean sea level.…”

Section: Study Areamentioning

confidence: 99%

“…PRP, the only source of fresh water on the coral islands, is mainly consumed by ET a , infiltration, and rainwater collection or water flowing into the sea. Storage changes within the unsaturated zone and surface runoff can be neglected [1,5] on coral islands due to the low water-binding capacity of gravelly and sandy soil texture, both for natural and for reclaimed islands [26,50]. In this study, the water budget analysis could be written as ∆V = PRP − Eta, where PRP is rainfall (mm); ET a is the actual evapotranspiration (mm), which contains E c , E s , and E i ; and ∆V is the total amount of infiltration, rainwater collection, and water flowing into the sea.…”

Section: Evapotranspiration Distribution On the Three Islandsmentioning

confidence: 99%

“…The most important freshwater problem on natural islands is water contamination and sustainable exploitation of water resources [1]. However, for newly reclaimed coral islands that have no fresh groundwater, it will take 20 years to form a stable freshwater lens [26]. The most important thing is to evaluate the spatial and temporal distribution of the fresh water of coral islands and the available water resources [51].…”

Section: Evapotranspiration Differences In Natural and Reclaimed Areamentioning

confidence: 99%

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Evapotranspiration on Natural and Reclaimed Coral Islands in the South China Sea

Han

Liu

et al. 2021

Remote Sensing

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Studies of evapotranspiration on remote tropical coral islands are important to explore and sustain scarce freshwater resources. However, there is a significant knowledge gap between research to evaluate evapotranspiration based on remote sensing methods and the influences of different land use types on water dynamics on reclaimed coral islands. This study applied the remote-sensing-based Vegetation Interfaces Processes (VIP-RS) model to estimate actual evapotranspiration (ETa) on Zhaoshu Island, Yongxing Island, and Yongshu Island in the South China Sea from 2016 to 2019. The results showed that the average annual ETa of Zhaoshu Island, Yongxing Island, and Yongshu Island was 685 mm, 530 mm, and 210 mm, respectively. Annual transpiration (Ec) and soil evaporation (Es) exhibited similar patterns on the natural islands; however, Es controlled the water consumption on the reclaimed islands. Water dynamics exhibited seasonal fluctuations due to the uneven distribution of precipitation (PRP). However, ETa of the natural islands was higher than PRP in the dry season, indicating vegetation has to absorb water from the groundwater to sustain growth. The results also agreed with the analysis of dominant driving factors based on partial correlation analysis, which demonstrated that the Normalized Difference Vegetation Index (NDVI) is the most important factor that influences ETa, while relative humidity (RH) controlled the bare land or sparsely vegetated areas on the reclaimed islands. The setting of different land use types showed that vegetation and built-up or hardened roads took control of evapotranspiration and rainwater collection, respectively, which play important roles in water dynamics on corals islands. The evaluation of ETa based on a remote-sensing-based model overcame the difficulty in fieldwork observation, which improves the certainty and accuracy at a spatial scale. In addition, it gave us a new reference to protect and manage scarce freshwater resources properly.

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Evaluating dynamic mechanisms and formation process of freshwater lenses on reclaimed atoll islands in the South China Sea

Cited by 14 publications

References 48 publications

Analytical Solutions for Fresh Groundwater Lenses in Small Strip Islands With Spatially Variable Recharge

Analytical Solutions for Fresh Groundwater Lenses in Small Strip Islands With Spatially Variable Recharge

Influence of Land Reclamation on Fresh Groundwater Lenses in Oceanic Islands: Laboratory and Numerical Validation

Evapotranspiration on Natural and Reclaimed Coral Islands in the South China Sea

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