The Impact of Watershed Rehabilitation Measures on the Flow and Sediment Characteristics of the Fashand Catchment, Hashtgerd

Watershed management measures are ways and means to restore, enhance and maintain vegetative cover in order to reduce runoff, control flood and reduce erosion and sediment concentration in the watershed. Soil and water conservation structures (SWCS) were installed on the Fashand Catchment, Hashtgerd during the 1996–1998 period with the aim of delaying the onset of flooding, increasing the time of concentration, decreasing the runoff discharge, recharging groundwater and reducing damage on the sub-basins. The study was designed to evaluate the effects of those structures not only on the outflow of the basin, but also on the water quality. To this end the double mass analysis was performed. The results indicated the positive impact of the SWCS. The ratio of calcium to magnesium had increased, and the sediment concentration of the basin discharge had dramatically decreased. The slope of the double-mass curve of rainfall-runoff had decreased from 0.3336 to 0.2033, i.e. by 60 percent; the mean annual suspended load had decreased from 1480 tons to 317 tons, a 4.66 fold reduction. The SWCS had effectively trapped the bed and suspended loads up to 2003, when their upstream reservoirs were overflowed with sediment.