Remote Sensing of Narrowing Barrier Islands along the Coast of Pakistan over Past 30 Years

Abstract

Barrier islands (BIs) are the first line of defense against the sea/wave actions in coastal areas, and assessing their stability is crucial in the context of effective coastal planning. Therefore, this study evaluates the spatial–temporal shoreline changes of the BIs in Pakistan over the past three decades (1989–2018). Satellite data from Landsat missions are used to delineate the shorelines of 19 BIs in Pakistan. After delineating the shorelines from satellite observations, two well-known statistical methods (i.e., end point rate (EPR) and linear regression rate (LRR)) are used to capture the localized changes in the BIs. The results ascertain that nearly all of the BIs have experienced noteworthy erosion during the past three decades. While the mean erosion over all the BIs during the study period is estimated to be >6 m/y, significant spatial heterogeneities among the individual BIs exist. The interdecadal comparison indicates that the highest mean erosion of the BIs occurred during the period 1989–1999 (13.03 ± 0.62 m/y), which gradually reduced over the preceding decades (i.e., 7.76 ± 0.62 m/y during the period 1999–2009 and 3.8 ± 0.7 m/y during the period 2009–2018). Nevertheless, ~65% of the total BIs experienced high erosion (>2 m/y), ~15% experienced moderate (<2 m/y), and ~20% experienced low erosion (<1 m/y) during the period 1989-2018. This situation implies that while ~65% of these BIs need immediate interventions from the concerned authorities, the 15% BIs with moderate erosion might experience high erosion in the wake of rising sea levels and decreasing sediment influx in the near future without proper measures. This depletion of the BIs might not only affect Pakistan but also have regional consequences due to their various services.

Vertical Ground Displacements and Its Impact on Erosion along the Karachi Coastline, Pakistan

“…Erosion in the East Karachi sub-zone suggests that these natural barriers gaurding against the erosional effects coming from the Arabian Sea have already been badly impacted. This finding is broadly in accord with the earlier work of Kanwal, et al [13], which also found that the islands were undergoing very high erosion (~8.9 m/yr). However, more assessment in this regard is required-this is left for future work.…”

“…This reduction in the sediment supply has escalated the erosional effects of tides and waves, resulting in seawater intrusion (SWI) into coastal plains. The results from these studies agreed well with those of Kanwal, et al [13], who investigated the evolution of the barrier islands (BIs) along Sindh coastal regions in Pakistan and concluded that ~65% of these BIs underwent high erosion (i.e., >2 m/yr), during 1989-2018. Their study implies that the ~15% of these BIs experiencing moderate erosion (i.e., <2 m/yr), are likely to be subjected to high erosion (i.e., >2 m/yr) in the wake of SLR and reduced sediment influx received by the IDR plains in the near future, without proper measures.…”

“…A closer inspection of the coastline's change shows that the coastline of the study area oscillates between accretion and erosion (Figure 7). Annual coastal erosion is increasing along the west-east axis (same as the littoral drift), reaching its maximum of ~2.4 m/yr in East Karachi, located next to the Buddo and Bundal barrier islands, which have been eroding at an even higher rate (i.e., ~14.33 m/yr) [13]. In contrast, the displacement patterns are variable across the city over the 2004-2016 timeframe and along the coastline, precluding the probability of a relationship between coastline erosion and ground subsidence in general.…”

Mangrove Health: A Review of Functions, Threats, and Challenges Associated with Mangrove Management Practices

“…Fluctuations in freshwater currents coming down from inland dams and irrigation also affect mangroves by altering their salinity and resulting in mangrove loss [262]. For instance, in Pakistan, the Indus Delta freshwater incurrent has been reduced by up to 90% due to diversion [263]. This affected the bed load composition and reduced the uniform sediment deposition in those mangrove areas [264].…”

Monitoring Wetland Landscape Evolution Using Landsat Time-Series Data: A Case Study of the Nantong Coast, China

“…Traditional field surveys have certain limitations in terms of their monitoring scope, frequency, and intensity [16]. Combining remote sensing (RS) with geographic information system (GIS) technology, coastal landforms have been effectively monitored in near real time at different spatial scales and resolutions [17][18][19][20][21][22][23]. Murray et al (2019) mapped the global tidal flats during 1984-2016 using Landsat images [11].…”