Assessment of Road Network Connectivity using Graph Theory in the Chehel-Chai Watershed, Golestan Province

Planning, construction and assessment of road network are among the investigations for infrastructure development at watershed scales. The main aim of this study is assessing the road network connectivity in the Chehel-Chay Watershed, located in Golestan Province using Alpha (α), Beta (β), Gamma (γ), Eta (η), network density and detour indices in graph theory. The available road network map was extracted on 1:25,000 scale, satellite imagery and mapping by GPS. Then the values of indices were calculated for road network that located in forest and non-forest land uses as well as for the whole of the study area. Then, the calculated indices were compared with each other and also with standard index values correspondingly. In forest land use, non-forest land use and whole of the study area the value of calculated indices are: for Alpha index 0.79, 0.14, -.021, for Beta index 0.4, 0.78, 0.56, for Eta index 1.2, 0.64, 1.32, for Gamma index 0.37, 0.23, 0.19, for network density index 6.12, 27.53, 13.12, and for detour index 0.61, 0.81, 0.77, respectively. The results showed that the network connectivity in forest area is suitable but in non- forest area despite of an increase in network density, the network connectivity is inappropriate and for the whole of the study area the network connectivity is considered to be too weak. The network density in forest area is inadequate and in non-forest area network connectivity has been decreased despite of an increase in network density. However, for the whole of the study area the amount t network speed is low due to topographic status and inadequate level of network development. The analysis indicates that the available road network despite of high length of roads constructed in the area and the associated high costs and environmental impacts has not have essential efficiency to connect various land uses in the study area. It is necessary to improve road network based on principles of network connectivity, economic, social and environmental considerations as well as inhabitant's needs in future researches.