Monitoring of subsidence with UAVSAR on Sherman Island in California's Sacramento–San Joaquin Delta

Abstract

Sherman Island, the westernmost island in the Sacramento-San Joaquin Delta in California, plays a crucial role in maintaining the water flux between saline ocean water from the San Francisco Bay to its west and the rest of the Delta to its east. Land elevation below mean sea level and continuous subsidence over the past century has made this island a high priority area for investigations of subsidence and restoration in the Delta. This study reports the results of successful application of Interferometric Synthetic Aperture Radar (InSAR) data and technique to measure subsidence in the Delta, which is a coherence-challenged non-urban area. We carried out a time-series interferometric analysis of Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) L-band (23.8 cm) data, collected from July 2009-August 2014, to assess both the spatial and temporal variation of subsidence on Sherman Island. We report both large-scale (island-wide) subsidence trends and small-scale (levee/farm scale) subsidence features in Sherman Island. Assuming the subsidence is linear during the five years of UAVSAR data acquisition, subsidence rates across the island range from 0-5 cm/yr, with an average of 1.3 + 0.2 cm/yr. We estimate our systematic uncertainty to be 0.3 cm/yr. Overall, the central region in the island has subsided at a faster rate than the rest of the island. We find our results to be consistent with previous measurements of subsidence rates at electric transmission line towers scattered throughout the island. The results of this study provide insights into several factors influencing subsidence, including soil type, water table depth, land use, land elevation and the location and time of levee repairs. Subsidence monitoring on Sherman Island is essential for maintaining a reliable water supply for the state of California and for protecting the Delta ecosystem.

A New Method for Isolating Elastic From Inelastic Deformation in Aquifer Systems: Application to the San Joaquin Valley, CA

“…This thick aquifer layer, which is confined by the Corcoran clay, has experienced groundwater extraction for agricultural irrigation since the 1920s. Prolonged pumping has resulted in several meters of accumulated lowering of the ground surface, with localized subsidence rates larger than 20 cm/year in areas with the highest volumes of pumping (e.g., Farr, 2016;Farr et al, 2017;Galloway et al, 1998;Jones et al, 2011;Sharma et al, 2016;Sneed, 1999;Sneed et al, 2013;Sneed & Brandt, 2015;Wisely et al, 2010). Measurements from extensometers, leveling, GPS, and InSAR have recorded phases of acceleration, such as the 2012-2015 California drought .…”

Factors and Processes Affecting Levee System Vulnerability

“…Measurements simultaneously cover large areas at one time in imaged swaths that are tens to hundreds of kilometers wide. It is possible to achieve measurement accuracies of aproximately 5-to 10-mm surface deformation when earthen levees are imaged in a single pair of measurements, and significantly higher accuracy, as fine as 1-2 mm yr -1 , when using a time-series of multiple images (e.g., Sharma et al 2016). InSAR also differs from traditional survey methods and LiDAR because it can see through clouds, smoke, haze, and image surfaces without solar illumination.…”

“…Earthen levee and farm field monitoring is particularly challenging because surface disturbance (temporal de-correlation) caused by grazing and agricultural (e.g., cultivation) activities corrupts the deformation signal. Nonetheless, single pairs of images, and a time-series of images collected at intervals of roughly 2 months, have successfully been used to identify deformation on or near levees (Jones et al 2012Sharma et al 2016).…”

“…This could be supplied by continuous GPS stations and extensometers (Deverel and Rojstaczer 1996). Extensometer data on Sherman Island ) was useful to validate the Sharma et al (2016) estimates. Bawden et al (2014) reported the use of terrestrial LiDAR (T-LiDAR) to topographically map 3-D surface elevation displacements with exceptionally high resolution.…”

How Groundwater Level Fluctuations and Geotechnical Properties Lead to Asymmetric Subsidence: A PSInSAR Analysis of Land Deformation over a Transit Corridor in the Los Angeles Metropolitan Area

“…A number of studies have been carried out to measure surface deformation along the transit corridors and their near infrastructures such as aqueducts and levees in California [55,56] and Rome (Italy) [57]. For instance, land subsidence rate of Hampton Roads in Virginia, USA, was estimated [58] using GPS observation and InSAR applied to ALOS-1 radar data.…”