Remotely Sensed Trajectory Analysis of Channel Migration in Lower Jingjiang Reach during the Period of 1983–2013

Abstract

Abstract:In China, the Lower Jingjiang Reach (LJR) of the Yangtze River could be one of the most complicated areas in terms of channel migration. The river had undergone many channel changes in the reach since the 18th century. Intensive human activities in recent decades, such as the construction of upstream dams and revetments, had directly affected the channel migration characteristics. The revetment would significantly diminish migration, whereas the reduced sediment caused by dams would increase bank erosion and bank failure risks. Satellite imageries of Landsat Multi Spectral Scanner (MSS), Thematic Mapper (TM), Enhanced Thematic Mapper Plus (ETM+) and Operational Land Imager (OLI) were employed to quantify the planform migration of the reach from 1983 to 2013 and to investigate the possible effect of human activities on the LJR channel evolution. Apart from the commonly used planform morphometric parameters, the migration direction was introduced to predict the future migration trends. Results showed that the LJR was gradually changing to a straighter channel, with sinuosity reducing from 2.09 to 1.9 and river length decreasing from 125.32 km to 113.31 km in the past 30 years. Planform morphometric parameters, such as migration rate of the channel centerline and erosion and deposition areas and rates, also decreased drastically in the past 30 years. The migration rate of the channel centerline decreased from 31.05 m¨year´1 in 1983-1988 to 11.62 m¨year´1 in 2009-2013. The lateral erosion and deposition areas decreased from 21.32 and 25.73 km 2 in 1983-1988 to 4.83 and 5.83 km 2 in 2009-2013. All of these findings indicate that the LJR tended to be in a steady state from 1983 to 2013 and was totally controlled by the bank revetments. However, the undercutting was strengthened because of the restrictive effect of revetments on lateral migration in the LJR. Moreover, the channel migrated to the left bank with a visible tendency as the total migration area to the left bank was approximately two times that of the right bank during the period. Consequently, the left bank of the LJR should be the focus of more attention in future migrations, and bank revetments of the left bank should be kept reinforced and adjusted with the change of water and sediment conditions.

What is the Direction of Land Change? A New Approach to Land-Change Analysis

“…In contrast, in the present study, MCC displacement vectors are characterized by both a length and angle, as noted above, rather than just returning a nominal directional designation. Thus, the explicit directionality of the MCC method fundamentally differs from the river shifting direction of [37] or any other prior similar study, to our knowledge. Furthermore, and importantly, the landscape changes detected by MCC application are not limited to a single entity type (e.g., a river channel) or certain directions (e.g., along river transects), but may demonstrate directional changes of land-covers that do not have complete or well-defined boundaries.…”

“…In contrast, the MCC application proposed in the present study automatically generates directional landscape changes; no manual digitization step is utilized or required, even though manual digitization of river planforms is common practice (e.g., [36]). Yang et al (2015) [37] determined river-channel migration, or shift, direction, based on sequential satellite images; however, this shifting direction focuses on the migration of the centerline and is only comprised of a "left" or "right" designation. That is, the river shifting direction in [37] is based on the migration area of the centerline (i.e., area enclosed by sequential channel centerlines), where that area is divided into left and right portions relative to the river flow direction, employing the old centerline as the reference.…”

“…Yang et al (2015) [37] determined river-channel migration, or shift, direction, based on sequential satellite images; however, this shifting direction focuses on the migration of the centerline and is only comprised of a "left" or "right" designation. That is, the river shifting direction in [37] is based on the migration area of the centerline (i.e., area enclosed by sequential channel centerlines), where that area is divided into left and right portions relative to the river flow direction, employing the old centerline as the reference. The river shifting direction is determined by which migration is larger-the left or right migration.…”

Spatio-Temporal Change Detection of Ningbo Coastline Using Landsat Time-Series Images during 1976–2015

“…The image mosaic was carried out with ENVI 5.1 version software, thereby obtaining a composed image for the entire Ningbo coastal zone. Moreover, image-to-image registration method in ENVI was applied for the geometric correction of the Landsat time-series images [43]. The Landsat OLI image in 2015 was used as the reference for the other images, and the registration errors of all images were within one pixel (less than 30 m).…”

Analysis of Coastline Extraction from Landsat-8 OLI Imagery

“…Image-to-image registration method in ENVI 5.1 was then used to make pixels in the two images precisely coincide to the same points on the ground [27,44]. In the process, Landsat-8 PAN image was chosen as a master and ZY-3 was to be registered.…”