Surface Flow Routing using Kinematic Wave and Time – Area Methods for Upstream Watershed of the Bustan Dam in Golestan Province, Iran

This study aims to evaluate two methods of surface water routing including kinematic wave and time-area in upstream of the Bustan dam. To this end, first considering the features and application prerequisites of both methods and describing the hydraulic and hydrologic conditions within the Tamer watershed, algorithms and scripts of kinematic wave and time-area methods were developed. Then the scripts were run to simulate flow hydrograph at outlet of the watershed. The results of performance evaluation showed that Nash-Sutcliffe coefficient for kinematic wave method is 0.882 and 0.745, respectively for the calibration and validation data sets, while for the time – area method it is 0.903 and 0.748, respectively. These results showed a difference in timing of simulated and observed hydrographs especially in time to peak of hydrographs. One of the reasons for this non-compliance in hydrograph timing can be attributed to the lack of enough rain gauge stations across the watershed and errors associated with spatial distribution of rainfall on rain input maps. According to rainfall zoning map using GIS, two rainfall polygons were specified across the watershed and rainfall in each polygon was considered as uniform, but there might be a significant difference in rainfall pattern within each polygons which can be a main source of errors in timing of simulated hydrographs. In general, according to the assumptions and limitations of both models and also likely errors in rain input maps of events, performance of these surface runoff routing methods are considered suitable for simulation of outflow hydrographs. A main limitation of kinematic wave is assumption that the hydraulic gradient is equal to the bed slope which limits its application only for small watersheds with higher slopes. In the distributed time-area method, the storage effect of pixels is very small and negligible, whereas the storage effects of whole watershed is remarkably high depending on drainage density and watershed shape factor.