Statistical Trend Analysis of Suspended Sediment Load in Association with Watershed Management Practices (Case Study: Bar Watershed, Neyshabur, Iran)

Erosion, sediment transport, sedimentation and water quality are considered as very important controversial issues in watershed management. Since many watersheds in countries including Iran don’t have any sediment gauging station, using statistical techniques to analyze erosion/sediment process is one of the important strategies for evaluating the trend of sediment yield. According the purpose of this study was to statistically evaluate the trend of suspended sediment load by using time series analysis in the Bar watershed, Neyshabur. In this work, the sediment load statistical records of the Bar hydrometric station during the period 1967-2012 were analyzed through the Mann-Kendall and Pettit tests. Results showed that the gradual change of sediment load was decreasing and significant at the level of 5%. Abrupt change of sediment load time series was also significant at the level of 5%. The change point was matched with the year 2003 in which the average sediment load of 317.62 tonnes per day declined by 17.25 tonnes per day after that. The statistical trend analysis of daily rainfall at the representative stations “Karkhane Ghand”, “Marusk” and “Bar” and water discharge time series at the Bar hydrometric station for the period 1967- 2012 showed no significant trend at the level of 0.05. As a result, it can be stated that at least in the last three decades, there was no marked changes in rainfall and water yield and consequently meteorological and hydrological drought in the watershed. Therefore, we cannot attribute the decreasing trend of sediment load of the Bar watershed to metorological drought conditions in the period leading up to the change point. Investigations revealed that watershed management operations in the Bar basin started in 2005 (corresponding with the change point in time series of suspended sediment load) and officially continued until 2010. Therefore, the downward trend in the time series of suspended sediment load can be associated with structural operations (Gabion, rock and soil chack dams) from the late 90's until now which trap a considerable part of sediments.