Ditch network extraction and hydrogeomorphological characterization using LiDAR-derived DTM in wetlands

While much emphasis has been placed on the importance of hydrology as a driving force for wetlands, few small stream drainage networks have been mapped. Light Detection and Ranging (LiDAR) data can provide very high-precision topographic maps over large areas, and have been used to extract drainage networks in forested areas, vineyards, and high mountain pastures. The study objective is to reconstruct the ditch network from LiDAR data in wetlands estimating the required accuracy for assessing their functions. Several Digital Terrain Models (DTMs) have been derived from LiDAR data with different point densities, ranging from 4 to point/m(2) with four interpolation methods. Then, the drainage network has been extracted from each DIM using an object-based image analysis. This approach has been applied in wetlands located near the Mont-Saint-Michel, France. Results have been validated with field data. They show that the quality of the drainage network map significantly depends primarily on the LIDAR data precision (point-density) and, to a lesser extent, on the interpolation method used. A minimum precision of 2 points per m(2) is required to properly represent the ditch network. The Nearest Neighbor interpolation method provides the best results and in the shortest computation time.