Abdulvahed Khaledi Darvishan

Experimental comparison of some techniques for estimating natural raindrop size distribution on the south coast of the Caspian Sea, Iran

Abstract Knowledge of the relationship between rainfall intensity and kinetic energy and its variations in time and space is important for the prediction of erosion hazard. Kinetic energy and erosivity are also strongly controlled by raindrop size. However, studies on raindrop measurement and different practical techniques have been rarely documented. The current study therefore aimed to apply existing raindrop-size measurement techniques—the photographic, flour-pellet and stain methods, as well as an innovative flour-stain method—and to evaluate their applicability at several intensities in Mazandaran Province, Iran. The distribution of raindrop size obtained by the different methods was recorded and compared with those obtained through applying a high-speed imaging technique. All the analyses were made with the help of a SPSS software package. The results showed that the raindrop diameters ranged from 0.2 to 5.16 mm at different rainfall intensities. Statistical comparison of the methods using the Duncan test showed that the flour-pellet method presented similar results to the photographic technique; it was concluded that this can be used as a practical and inexpensive method to estimate a wide range of raindrop sizes. Editor Z.W. Kundzewicz Citation Sadeghi, S.H., Abdollahi, Z., and Khaledi Darvishan, A., 2013. Experimental comparison of some techniques for estimating natural raindrop size distribution on the south coast of the Caspian Sea, Iran. Hydrological Sciences Journal, 58 (6), 1374–1382.

Effectiveness of Straw Mulch on Infiltration, Splash Erosion, Runoff and Sediment in Laboratory Conditions

Abstract Mulches have extraordinary potential in reducing surface runoff, increasing infiltration of water into the soil and decreasing soil erosion. The straw mulches as a biological material, has the ability to be a significant physical barrier against the impact of raindrops and reduce the detachment of soil aggregates. The present study is an attempt to determine the efficiency of straw mulch as conservation treatment in changes in the splash erosion, time-to-runoff, runoff coefficient, infiltration coefficient, time-to-drainage, drainage coefficient, sediment concentration and soil loss. The laboratory experiments have been conducted for sandy-loam soil taken from deforested area, about 15 km of Warsaw west, Poland under lab conditions with simulated rainfall intensities of 60 and 120 mmh–1, in 4 soil moistures of 12, 25, 33 and 40% and the slope of 9%. Compared with bare treatments, results of straw mulch application showed the significant conservation effects on splash erosion, runoff coefficient, sediment concentration and soil loss and significant enhancement effects on infiltration and drainage. The results of Spearman-Rho correlation showed the significant (p < 0.05) correlation with r = –0.873, 0.873, 0.878 and 0.764 between rainfall intensity and drainage coefficient, downstream splash, sediment concentration and soil loss and with r = –0.976, 0.927 and –0.927 between initial soil moisture content and time-to-runoff, runoff coefficient and infiltration coefficient, respectively.

EFFECT OF EXCLOSURE ON RUNOFF, SEDIMENT CONCENTRATION AND SOIL LOSS IN EROSION PLOTS

Nowadays watershed and rangeland management projects play the important role in water resources and soil management worldwide. Although watershed and rangeland management projects have the considerable importance as approaches to rural areas development and natural resources management, more studies have been focused on their effects on sediment and their effects on soil erosion have rarely been considered. The present study was conducted in two treated and control sub-watersheds with exclosure treatment and under grazing respectively, in Khamsan representative watershed with an area of 4337.27 ha in south of Kurdistan Province, Iran. Three plots were installed in each western, northern and eastern slopes for the runoff volume and coefficient, sediment concentration and soil loss measurement. The exclosure treatment was operated for installed plots in treated sub-watershed from 2007. Then, all the data of runoff volume and coefficient, sediment concentration and soil loss from USLE standard plots in both control and treated sub-watersheds for 52 events over the years 2009 to 2014 were compared and evaluated. Therefore, in order to the number of plots and subwatersheds, 18 USLE standard plot data were finally recorded and analysed for each storm event. The results showed the significant (p≤0.05) decreasing effect of exclosure treatment on runoff volume, sediment concentration and soil loss at plot scale. Finally, decreasing rates of 15.68, 6.13, 16.67, 24.37 and 21.43% due to exclosure respectively for runoff volume and coefficient, sediment concentration, soil loss and sediment yield were obtained. The variables of runoff volume, soil loss and sediment yield had statistically significant differences (p≤0.05) in treated and control sub-watersheds. The sediment concentration variable had p value of 0.058 and therefore the effect of exclosure treatment on sediment concentration was also significant (p≤0.06).