Semi-Automatic Extraction and Morphometric Characterization of Paleochannels using LiDAR Data: A Case Study in the fens of Lincolnshire, England

Paleochannels are natural features in floodplains, and their identification and geometric characterization can guide river restoration and natural flood management interventions. This study focuses on identifying the network of dendritic drainage patterns in a portion of the Lincolnshire fens near Billinghay. A semi-automatic approach was developed for identifying paleochannels and performing a morphometric analysis of these features.

A high-resolution LiDAR data survey from 2022 was downloaded from the UK environment portal. The LiDAR digital terrain model has a resolution of 2 m and vertical accuracy of +/- 15 cm. The raw LiDAR point cloud was pre-processes using CloudCompare. An initial ground-level extraction was performed with automatic filters and further refined by identifying and removing additional anthropogenic features such as roads, buildings, and artificial levees along canals, using a vector data analysis. The dendritic drainage channels of the particular study site (6.78 km²) were isolated using a semi-automatic selection with specific elevation filters. The differences in elevation between the paleochannel surface and the surrounding flat areas were used to define distinct elevation ranges for different altimetric bands. Points within these ranges were selected and reclassified to create a preliminary morphological model of the paleochannels. Discontinuous segments were interpolated, and areas with missing values were resampled, resulting in a consistent and detailed representation of the paleochannels.

The dendritic drainage network was characterized in terms of Strahler order, sinuosity, length, and location of connection nodes. Additionally, several cross-sectional profiles were generated and a Python script was developed to quantify the width, depth, and area between the crest of the paleosurface and the ground level. Reaches of paleochannels of higher Strahler order were found to be deeper and wider. The sinuosity is lower for the reaches in the upper part of the dendritic network. Interestingly, the channels are located in areas that are highly convex compared to the surrounding flat areas. The total surface area occupied by the identified paleochannels in the study site is approximately 1.8 km², which represents a significant portion of the floodplain.

The geometry of the identified enclosed basin and of the dendritic network are being used to test a morphodynamic model in order to identify the sea level and tidal ranges responsible for the formation of the paleochannels.