Automated channel ordering and node indexing for raster channel networks

Abstract

A numerical algorithm is proposed for automated interpretation of channel networks from raster images, indexing of network nodes, and ordering of channels by the Strahler method. Channel ordering and node indexing is fundamental to the automation of flow-routing management in distributed hydrologic models and morphometric evaluation of channel-network structure. The node index numbers can also serve to link network nodes to corresponding tabulated attributes of network channels. The proposed algorithm uses a two-step approach: first, the raster image of the network is interpreted and a channel attribute table is created; second, the network nodes are indexed based only on the network connectivity information contained in the channel attribute table. The use of attribute information in the second step eliminates a repeat of the time consuming cell-by-cell interpretations of the network raster image. In addition to the general case of nodes with two upstream inflows, the algorithm also handles complex nodes (nodes with more than two upstream inflows) which are rare under natural conditions, but more frequent in raster networks. The final product of the presented algorithm is a table of channel orders and node indices derived from raster images of channel networks.