Determination of the drainage structure of a watershed using a digital elevation model and a digital river and lake network

Distributed hydrological models require a detailed definition of a watershe d's internal drainage structure. The conventional approach to obtain this d rainage structure is to use an eight flow direction matrix (D8) which is de rived from a raster digital elevation model (DEM). However, this approach l eads to a rather coarse drainage structure when monitoring or gauging stati ons need to be accurately located within a watershed. This is largely due t o limitations of the D8 approach and the lack of information over flat area s and pits. The D8 approach alone is also unable to differentiate lakes fro m plain areas. To avoid these problems a new approach, using a digital river and lake netw ork (DRLN) as input in addition to the DEM, has been developed. This new ap proach allows for an accurate fit between the DRLN and the modelled drainag e structure, which is represented by a flow direction matrix and a modelled watercourse network. More importantly, the identification of lakes within the modelled network is now possible. The proposed approach, which is large ly rooted in the D8 approach, uses the DRLN to correct modelled flow direct ions and network calculations. For DEM cells overlapped by the DRLN, flow d irections are determined using DRLN connections only. The flow directions o f the other DEM cells are evaluated with the Dg approach which uses a DEM t hat has been modified as a function of distance to the DRLN. The proposed approach has been tested on the Chaudiere River watershed in s outhern Quebec, Canada. The modelled watershed drainage structure showed a high level of coherence with the DRLN. A comparison between the results obt ained with the D8 approach and those obtained by the proposed approach clea rly demonstrated an improvement over the conventionally modelled drainage s tructure. The proposed approach will benefit hydrological models which requ ire data such as a flow direction matrix, a river and lake network and sub- watersheds for drainage structure information. (C) 2001 Elsevier Science B. V. All rights reserved.