Land uplift linked to managed aquifer recharge in the Perth Basin, Australia

While the link between groundwater extraction and land subsidence is well documented, observations of land uplift associated with groundwater replenishment are less so. In the Perth Basin, Western Australia, a programme of managed aquifer recharge (MAR) commenced in August 2017 and is designed to sustain levels of hydraulic head in aquifers valuable for extraction. Space-based TerraSAR-X satellite radar measurements were used to capture the first 3.5 years of MAR, providing an insight into the evolution of ground uplift in the Perth Basin that is spatially and temporally related to the MAR injection volumes and the injection-induced changes in hydraulic head. Significantly, the X-band InSAR has spatial coverage around the single injection point, and the time series begins prior to the start of the injection, rather than a generalised study of ground surface and aquifer change from multiple groundwater recharge contributions. This enables the observed ground uplift to be correlated with the time of initial injection, pause, then resumption with increased volumes. The X-band InSAR identified maximum displacements of up to 20±3 mm in the vicinity of the injection bores, but which subside when injection is paused. The spread of displacements from the injection site extends over 14 km southwards with the dispersion pattern identifying linear boundaries that sharply delineate displacements in the north-west and north-east. The extent of the region impacted by ground uplift is likely linked to the distribution of extraction bores and heterogeneities in the subsurface geology, including a persistent linear feature that has not yet been considered in hydrogeological models of the region. This article focusses on the immediate surface response to the MAR injection, and identifying the constraining physical features for the injected recharge, thus providing an additional insight into the challenging and complex Perth Basin. It also demonstrates the millimetric accuracy possible from X-band radar satellites that permits MAR volumes to be managed to avoid infrastructure damage that may undermine public confidence in the MAR program

Water surface height determination with a GPS wave glider: a demonstration in Loch Ness, Scotland

A geodetic GPS receiver has been installed on a Wave Glider, an unmanned water surface vehicle. Using kinematic precise point positioning (PPP) GPS, which operates globally without directly requiring reference stations, surface heights are measured with ~0.05-m precision. The GPS Wave Glider was tested in Loch Ness, Scotland, by measuring the gradient of the loch’s surface height. The experiment took place under mild weather, with virtually no wind setup along the loch and a wave field made mostly of ripples and wavelets. Under these conditions, the loch’s surface height gradient should be approximately equal to the geoid slope. The PPP surface height gradient and that of the Earth Gravitational Model 2008 geoid heights do indeed agree on average along the loch (0.03 m km−1). Also detected are 1) ~0.05-m-sized height changes due to daily water pumping for hydroelectricity generation and 2) high-frequency (0.25–0.5 Hz) oscillations caused by surface waves. The PPP heights compare favorably (~0.02-m standard deviation) with relative carrier phase–based GPS processing. This suggests that GPS Wave Gliders have the potential to autonomously determine centimeter-precise water surface heights globally for lake modeling, and also for applications such as ocean modeling and geoid/mean dynamic topography determination, at least for benign surface states such as those encountered during the reported experiment

Widespread low rates of Antarctic glacial isostatic adjustment revealed by GPS observations.

Bedrock uplift in Antarctica is dominated by a combination of glacial isostatic adjustment (GIA) and elastic response to contemporary mass change. Here, we present spatially extensive GPS observations of Antarctic bedrock uplift, using 52% more stations than previous studies, giving enhanced coverage, and with improved precision. We observe rapid elastic uplift in the northern Antarctic Peninsula. After considering elastic rebound, the GPS data suggests that modeled or empirical GIA uplift signals are often over?estimated, par t icularly the magnitudes of the signal maxima. Our observation that GIA uplift is misrepresented by modeling (weighted root?meansquares of observation?model differences: 4.9–5.0 mm/yr) suggests that, apart from a few regions where large ice mass loss is occurring, the spatial pattern of secular ice mass change derived from Gravity Recovery and Climate Experiment (GRACE) data and GIA models may be unreliable, and that several recent secular Antarctic ice mass loss estimates are systematically biased, mainly too high.Remote SensingAerospace Engineerin