Studies on groundwater recharge characteristics at a reclaimed land site with an equatorial climate using time‐series and spectral analyses

Tan, Stephen Boon Kean; Shuy, Eng Ban; Chua, Leok Poh; Yee, Woon Kang

doi:10.1002/hyp.6289

Cited by 5 publications

(9 citation statements)

References 24 publications

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“…The theory of residence time t R established in the present study provides physical proof for the theory of stress transfer velocity (Tan et al, 2007) developed from time-series and spectral analyses. This previous study observed that net recharge percentages and stress filtering characteristics at the Changi Reclaimed Land depend strongly on the stress transfer velocity, which was a combined function of rainfall pattern and vadose zone thickness.…”

Section: Physical Explanations To Rainfall-recharge Relationshipsupporting

confidence: 57%

Effects of meteorological and hydrogeological factors on gross recharge percentage at unconfined sandy aquifers with an equatorial climate

Tan

Shuy

Chua

2007

Hydrological Processes

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A thorough understanding of rainfall recharge processes and their controlling factors is essential for management of groundwater systems. This study investigates the effects of various meteorological and hydrogeological factors on the gross recharge percentages, the rainfall-recharge relationships and the recharge threshold values for unconfined sandy aquifers under an equatorial climate. Among the meteorological factors investigated, rainfall intensity was found to have the most significant impact on the gross recharge rate. The effects of potential evaporation rate, relative humidity and air temperature on the gross recharge percentage were significant when the vadose zone thickness is larger than 2Ð5 m. The recharge threshold values were found to depend strongly on the vadose zone thickness. The rainfall-recharge relationships could generally be well defined by a normal-log relationship. The rainfall-recharge relationships derived here are applicable to yield estimates of gross recharge percentages for unconfined sandy aquifers under an equatorial climate, using rainfall intensity and vadose zone thickness as input variables. In this study, a theory was developed and validated to provide physical explanations for the observations, based on the residence time of the percolated rainwater within the vadose zone. Among the soil hydraulic parameters tested, porosity and saturated hydraulic conductivity were found to have the most pronounced effects on the gross recharge percentage. Utilizing the sensitivity results and the theory derived, an approach was developed for extending the application of the derived rainfall-recharge relationships to other sand textures. The approach was found to be capable of producing rough and fast estimations of gross recharge percentage for other sand textures.

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Section: Physical Explanations To Rainfall-recharge Relationshipsupporting

confidence: 57%

Effects of meteorological and hydrogeological factors on gross recharge percentage at unconfined sandy aquifers with an equatorial climate

Tan

Shuy

Chua

2007

Hydrological Processes

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“…Nevertheless, rainfall recharge characteristics at unconfined sandy aquifers were found to be significantly different between isolated rainfall events and rainfall clusters. Compared to isolated rainfall events, rainwater from intense rainfall clusters was found to propagate more rapidly from the soil surface to the water table, leading to a significantly higher groundwater recharge percentage at the unconfined sandy aquifer (Tan et al, 2007c). In order to apply the developed equations on rainfall clusters, additional guidelines were established to integrate the effects of rainfall clusters into the estimation.…”

Section: Recharge Estimation Methodsmentioning

confidence: 99%

“…To obtain the rainfall-induced water level fluctuations, the time series of daily water-level fluctuations were filtered using low pass filter, as the wave component contributed by rainfall recharge was found to have a frequency band between 0 and 0Ð0938 cycle/day (Tan et al, 2007c). On the basis of the Equation (8), the monthly net groundwater recharge percentages R(%) at the study site were computed using:…”

Section: Other Estimation Methodsmentioning

confidence: 99%

“…With an overestimation of about 20-30% ( Figure 7) and the low 'Ratio' value (Table III) of about 3-15%, the overall overestimation in the annual recharge percentage was generally restricted to about 0Ð9-4Ð5%, which is insignificant. As groundwater discharge was found to be insignificant at the Changi reclaimed land, except for those areas adjacent to the open sea and the unlined drain (Tan et al, 2007c), Equation (8) could be reduced to:…”

Section: Estimation Of Mean Annual Net Recharge Percentagementioning

confidence: 99%

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Regression method for estimating rainfall recharge at unconfined sandy aquifers with an equatorial climate

Tan

Shuy

Chua

2007

Hydrological Processes

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A reliable estimate of rainfall recharge is essential for groundwater system managements. This study develops a method based on regression equations for estimating rainfall recharge at unconfined sandy aquifers with an equatorial climate. The developed method (GR-I method) is generally efficient for estimating long-term regional recharge, as the computational procedures could be formulated and executed easily using Microsoft's Excel spreadsheet. More importantly, its application could be extended to sand textures different from the sand texture used in developing the regression equations. To evaluate its reliability, the method was applied to estimate monthly gross recharge percentages at the Changi reclaimed land. When ignoring the effect of rainfall clusters, the GR-I method was found to underestimate the monthly gross recharge percentages for those months with high monthly rainfall depths. By integrating the effect of rainfall clusters, the GR-I method yields reliable estimates of monthly gross recharge percentages. By including daily potential evaporation as an additional input variable, the Extended GR-I method was found to be not superior to the GR-I method, implying that soil moisture availability is the major governing factor for actual soil evaporation in the highly porous sand medium, instead of atmospheric demand represented by the potential evaporation rate. Using the GR-I method, the mean annual net recharge percentage of the study site was found to fall between 56Ð9 and 69Ð9%, which corresponds to a net recharge depth of 1073Ð8-1745Ð8 mm. Although the developed method provides a good alternative to other widely used methods, its recharge estimates still needs to be collaborated with estimates from other methods, as multiple techniques are highly recommended in any groundwater recharge estimations.

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“…Water from these drains is routed directly to the Singapore Strait. This study is one of several carried out at this site exploring the feasibility of using the area for groundwater storage and in situ treatment (Chua et al, 2007;Ngonidzashe, 2004;Tan et al, 2007c…”

Section: Study Sitementioning

confidence: 99%

Precipitation patterns and moisture fluxes in a sandy, tropical environment with a shallow water table

Minihane

Freyberg

2011

Preprint

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Identifying the dominant mechanisms controlling recharge in shallow sandy soils in tropical climates has received relatively little attention. Given the expansion of coastal fill using marine sands and the growth of coastal populations throughout the tropics, there is a need to better understand the nature of water balances in these settings. We use time series of field observations at a coastal landfill in Singapore coupled with numerical modeling using the Richards' equation to examine the impact of precipitation patterns on soil moisture dynamics, including percolation past the root zone and recharge, in such an environment. A threshold in total precipitation event depth, much more so than peak precipitation intensity, is the strongest event control on recharge. However, shallow antecedent moisture, and therefore the timing between events along with the seasonal depth to water table, also play significant roles in determining recharge amounts. For example, at our field site, precipitation events of less than 3 mm per event yield little to no direct recharge, but for larger events, moisture content changes below the root zone are linearly correlated to the product of the average antecedent moisture content and the total event precipitation. Therefore, water resources planners need to consider identifying threshold precipitation volumes, along with the multiple time scales that capture variability in event antecedent conditions and storm frequency in assessing the role of recharge in coastal water balances in tropical settings

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Studies on groundwater recharge characteristics at a reclaimed land site with an equatorial climate using time‐series and spectral analyses

Cited by 5 publications

References 24 publications

Effects of meteorological and hydrogeological factors on gross recharge percentage at unconfined sandy aquifers with an equatorial climate

Effects of meteorological and hydrogeological factors on gross recharge percentage at unconfined sandy aquifers with an equatorial climate

Regression method for estimating rainfall recharge at unconfined sandy aquifers with an equatorial climate

Precipitation patterns and moisture fluxes in a sandy, tropical environment with a shallow water table

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