Assessment of hydrologic connectivity in an ungauged wetland with InSAR observations

Abstract

The Ciénaga Grande de Santa Marta (CGSM) is one of the world's most productive tropical wetlands and one that has witnessed some of the greatest recorded dieback of mangroves. Human-driven loss of hydrologic connectivity by roads, artificial channels and water flow regulation appears to be the reason behind mangrove mortality in this ungauged wetland. In this study, we determined the CGSM's current state of hydrologic connectivity by combining a remote sensing technique, termed as Wetland Interferometric Synthetic Aperture Radar (InSAR), with a hydrologic study of river water discharge. For this research, we processed 29 ALOS-PALSAR acquisitions taken during the period 2007-2011 and generated 66 interferograms that provide information on relative surface water level changes. We found that change in water discharge upstream on the main tributary of the CGSM could explain at most 17% of the variance of the change in water level in the CGSM. Fresh water inputs into the wetland were identified only when the mean daily water discharge in the river exceeded 700 m 3 s −1 , which corresponds to only 30% of the days during the period. The interferogram analysis also revealed that artificial channels within the wetland serve as barriers to water flow and contribute to the overall loss in hydrologic connectivity. We recommend increasing fresh water inputs from the Magdalena River by reducing water regulation of fresh water from the river and improving connectivity on either side of the artificial channels crossing the CGSM. This study emphasizes the potential of the application of wetland InSAR to determine hydrologic connectivity in wetlands that are completely or poorly ungauged and to define the necessary guidelines for wetland hydrologic restoration.

Towards monitoring groundwater‐dependent ecosystems using synthetic aperture radar imagery

“…The first generation of synthetic aperture radar (SAR) data became available in the 1990s and since then, it was applied in found applications in land cover mapping (e.g., Waske & Braun, ), wetland characterisation (Floyd et al, ; Touzi et al, ), fire hazard monitoring (e.g., Rykhus & Lu, ), sediment transport monitoring (e.g., Roering et al, ), landslide hazard monitoring (Scaioni et al, ), earthquake characterisation (e.g., Fujiwara et al, ), volcano monitoring (e.g., Brothelande et al, ), mangrove monitoring (e.g., Jaramillo et al, ), glacier displacement sensing (e.g., Euillades et al, ), groundwater extraction (e.g., Castellazzi et al, , , ), or oil‐spill detection (e.g., Fiscella et al, ). Most of these applications are now deployable operationally, thanks to the maturity of processing strategies, the development of freely available processing tools, the availability of archive datasets to establish baseline observations and infer change‐detection thresholds, and finally, the guarantee of frequent and regular future SAR acquisitions.…”

Effects of Hydroclimatic Change and Rehabilitation Activities on Salinity and Mangroves in the Ciénaga Grande de Santa Marta, Colombia

“…It is only during extreme La Nina wet event years such as 1999-2001 and 2008 that the salinity gradient of this channel behaves as a common estuary, with salinity increasing in the downstream direction. These data point to a lack of functionality of the channel possibly due to lack of hydrologic connectivity and heavy siltation (Jaramillo et al 2017).…”

Peer Review #1 of "Investigating the potential use of Sentinel-1 data for monitoring wetland water level changes in China’s Momoge National Nature Reserve (v0.1)"

“…RADARSAT-1/2 (Brisco et al 2017;Gondwe et al 2010;Kim et al 2017;Kim et al 2009;Lu & Kwoun 2008;Mohammadimanesh et al 2018a;Siles et al 2020), ENVISAT (Wdowinski et al 2006), ALOS PALSAR-1/2 (Cao et al 2018;Jaramillo et al 2018;Kim et al 2017;Kim et al 2014;Kim et al 2009;Mohammadimanesh et al 2018a;Palomino-Ángel et al 2019;Yuan et al 2017) and TerraSAR-X (Hong et al 2010b;Mohammadimanesh et al 2017) to detect water level changes in different types of wetlands. However, most SAR satellites that provide data for previous wetland InSAR studies have a relatively short life span and have been out of operation for years or even two decades.…”

“…Wetland InSAR technique can be an excellent complementary tool for in-situ ground observations to better understand and monitor a wide area with high spatial resolution (Hong & Wdowinski 2017). Since the first time Alsdorf et al (2000) and Alsdorf et al (2001) mapped a spatial detailed image of centimeter-scale variations in the Amazon floodplain water level response to changing river discharge through InSAR, innovative applications of InSAR to monitoring hydrologic changes in wetlands have also been successful in different regions of the world (Kim et al 2014), including but not limited to the Everglades (Hong et al 2010a;Kim et al 2014;Liao & Wdowinski 2018;Wdowinski et al 2004;Wdowinski et al 2008), the Louisiana wetlands (Kim et al 2009;Kwoun & Lu 2009;Lu et al 2005), the Amazon floodplain (Cao et al 2018), the Sian Ka'an in Yucatan (Gondwe et al 2010), the Yellow River Delta (Xie et al 2013;Xie et al 2015;Yuan et al 2016), the Liaohe River (Zhang et al 2016), the Great Dismal Swamp (Kim et al 2017), the Ciénaga Grande de Santa Marta (Jaramillo et al 2018), the Yukon Flats Basin (Pitcher et al 2019) and, most recently, the Peace-Athabasca Delta (Siles et al 2020). Today, wetland InSAR technique has evolved from monitoring relative water level changes to monitoring absolute water level time series.…”