Temporal and Spatial Variation of Suspended Sediment Concentration at Downstream of a Sand Mine

The growing population led to greater human need to use natural resources such as sand and gravel mines. Direct removal of sands from the bed river leads to increase suspended sediment concentrations in downstream of harvested area and creates other problems viz. filling reservoirs، change in hydraulic characteristics of the channel and environmental damages. However، the range of temporal and spatial effectibility of such human interferes has been rarely considered. The present study، therefore، aimed to investigate the spatial and temporal variation of suspended sediment concentration in the Kojour River in Educational and Research Forest Watershed of Tarbiat Modares University in Mazandaran Province، Iran. Towards this attempt، the effect of a conventional sand and gravel mining on suspended sediment concentrations was studied in a range of 0 to some 4 h and 0 to some 200m from the beginning and location of mining، respectively. The results showed that the exploitation from a local small sand and gravel mines had remarkable impact on suspended sediment concentration at a distance of approximately 100m and 2 h after mine exploitation. The statistical results by General Linear Model in Repeated Measure factor verified the increasing trend in suspended sediment in range of 50m after about 30 min of mining (P=0. 05)، while the effect of mining on increasing suspended sediment concentration could be recognized up to 200 m from the location of study up to about 10 min (P=0. 01) of time of sand mining.