Fusion of Time‐Lapse Gravity Survey and Hydraulic Tomography for Estimating Spatially Varying Hydraulic Conductivity and Specific Yield Fields

Abstract

Hydraulic conductivity (K) and specific yield ( Sy) are important aquifer parameters, pertinent to groundwater resources management and protection. These parameters are commonly estimated through a traditional cross‐well pumping test. Employing the traditional approach to obtain detailed spatial distributions of the parameters over a large area is generally formidable. For this reason, this study proposes a stochastic method that integrates hydraulic head and time‐lapse gravity based on hydraulic tomography (HT) to efficiently derive the spatial distribution of K and Sy over a large area. This method is demonstrated using several synthetic experiments. Results of these experiments show that the K and Sy fields estimated by joint inversion of the gravity and head data set from sequential injection tests in unconfined aquifers are superior to those from the HT based on head data alone. We attribute this advantage to the mass constraint imposed on HT by gravity measurements. Besides, we find that gravity measurement can detect the change of aquifer's groundwater storage at kilometer scale, as such they can extend HT's effectiveness over greater volumes of the aquifer. Furthermore, we find that the accuracy of the estimated fields is improved as the number of the gravity stations is increased. The gravity station's location, however, has minor effects on the estimates if its effective gravity integration radius covers the well field.

Measuring Aquifer Specific Yields With Absolute Gravimetry: Result in the Choushui River Alluvial Fan and Mingchu Basin, Central Taiwan

“…It can be challenging to map the three‐dimensional function of S y ( x , y , z ) in Equation considering aquifer heterogeneity and the high cost of conducting pumping tests over different depths, despite some successes reported in the literature (Tsai et al, 2017; Yeh & Liu, 2000; Zhu & Yeh, 2005). Furthermore, the groundwater level surfaces at T 1 and T 2 are functions of ( x , y ), which may be inferred using the electrical resistivity imaging method (Chang et al, 2017; Rayner et al, 2007).…”

“…where dv ¼ dxdydz : differential volume change G : gravitational constant (6.67 × 10 −11 m 3 kg −1 s −2 ) ρ w : the water density (¼ 1,000 kg/m 3 ) r : the distance between the gravimeter and the center of the differential volume x, y, z : the three coordinate components of the differential volume x 0 , y 0 , z 0 : the coordinate components of the gravimeter S y (x, y, z) : specific yield It can be challenging to map the three-dimensional function of S y (x, y, z) in Equation 3 considering aquifer heterogeneity and the high cost of conducting pumping tests over different depths, despite some successes reported in the literature (Tsai et al, 2017;Yeh & Liu, 2000;Zhu & Yeh, 2005). Furthermore, the groundwater level surfaces at T 1 and T 2 are functions of (x, y), which may be inferred using the electrical resistivity imaging method (Chang et al, 2017;Rayner et al, 2007).…”

“…Because of a large number of evenly distributed wells and the stable recharge by Choushui River, CRAF and MB are two ideal places for experimenting with the methods of impulse flow and hydraulic tomography (Kennedy et al, 2017; Tsai et al, 2017). Furthermore, the shallow groundwater levels, large seasonal groundwater level variations, and abundant cross‐well pumping test sites make CRAF and MB two ideal places for experimenting with the gravity‐based S y determination.…”

Short‐Time Geodetic Determination of Aquifer Storage Coefficient in Taiwan

“…Recent studies (Fernández‐Álvarez et al, ; Kennedy et al, , ; Maina & Guadagnini, ; Tsai et al, ) showed that gravity observations in pumping tests, pulse flows, and artificial recharges can provide additional information for estimating hydrogeological parameters such as S s , S y , and transmissivity ( T ) that are related to storage and groundwater flow rate. The geodetic method of S y estimation over small areas or at selected points has been used in several studies.…”

“…After a heavy rain stops, the aquifer level can rapidly decline to lower gravity values. We measure such gravity changes and surface deformations to determine hydrogeological parameters critical to understanding aquifer storage capacity and managing groundwater resource.Recent studies (Fernández-Álvarez et al, 2016;Kennedy et al, 2016Kennedy et al, , 2017Maina & Guadagnini, 2018;Tsai et al, 2017) showed that gravity observations in pumping tests, pulse flows, and artificial recharges can provide additional information for estimating hydrogeological parameters such as S s , S y , and transmissivity (T) that are related to storage and groundwater flow rate. The geodetic method of S y estimation over small areas or at selected points has been used in several studies.…”