Ordering Discontinuous Digital Stream Networks in a Watershed by Developing an Object-oriented Model in the GIS Environment

Document Type : Original Articles


1 Ph.D. Candidate, Faculty of Natural Resources, Sari University and Research Instructor in the Soil Conservation & Watershed Management Research Institute.

2 Member of Scientific Board of the Soil Conservation & Watershed Management Research Institute.


A watershed stream network consists of a collection of rivers and streams that drain surface water flows within a watershed. These spatial data are key in calculating various aspects of a watershed, such as physiography, hydrology, soil erosion, sediment, etc. One of physical parameters in a watershed is the “bifurcation ratio”, which shows the level of roundness or elongation of a watershed related to a stream network. The bifurcation ratio is calculated on the basis of an ordered stream network and it is one of the main criteria used to evaluate watershed flood hydrograph patterns. The main problems in ordering watershed stream networks are the discontinuity in stream networks of topography maps and differences with water flow model maps. These deficiencies create problems in calculating other watershed parameters such as length, ordering, and density of streams. As current GIS software is not able to compensate for these shortcomings, the present research used a previously designed GIS model (ArcGIS environment, using ESRI ArcObjects), applying a new approach for ordering watershed stream networks. The results of this study showed that this methodology could be applied to conduct a more accurate ordering of stream network (based on Strahler’s Algorithm) where there is no discontinuity between streams in a network, and to gain better harmony with water flow model of a watershed.