نشریه پژوهش های آبخیزداری
پیاپی 118 (بهار 1397)

The scarcity of reliable data for the rate of erosion and sedimentation on numerous watersheds all over the country makes the application of empirical models inevitable. One of these models is the Factorial Scoring Model (FMS). The purpose of this research was to evaluate the model's efficiency in the Fars Province This study was conducted on 5 small watersheds where small check dams of the masonry and earth types were constructed at their outlets. These structures did not have spill ways; therefore, all the bed and suspended loads were retained on their upstream for a duration of 10 years. The volume of sediment deposited in reservoirs was obtained, by surveying. The bulk density (BD) of each sediment mass upstream of the check dams was determined at the site and the volume was converted into using the individual BDs. The tonnage of sediment was also determined by the FMS model. The results indicated that the uncalibrated FMS model overestimated the eroded materials. The relative root mean square error (RRMSE) of the model was 0.246, which indicated a low level of the error of the model. Results of the calibrated FMS model indicated a 75% compliance of the model; therefore, we can accept the estimated results of this model as somewhat reliable.

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.

Landslide is one of the most important factors of soil erosion, and is a natural disaster that makes numerous financial and life damages each year. Therefore, identifying this phenomenon, effective agents in landslide occurrence, and determination of susceptible areas is necessary for reducing damages of this phenomenon. The aim of this study is to evaluate landslide hazards in the Kharestan Watershed, Fars Province. Firstly, maps of the main factors affecting landslide occurrence including slope, direction, height, rainfall, distance from fault, distance from the road, distance from the waterway, land use, lithology and landslide were prepared. Each basic layer and landslide map was integrated to compute the rate of each parameter using LNRF and WINF models. Then, with overlapping different data layers, landslide hazard zonation maps were prepared. Finally, three indices including Landslide index (Li), Density ratio (Dr), and Quality summation (Qs) were used in order to choose the premier model. Results showed that in the LNRF model 17.59 and 79.63% of watershed were located in high and very high zone of risk map respectively. The quantity of Qs in the LNRF model is 4.52%. Based on these results it can be concluded that LNRF model shows a better performance for landslide hazard zonation.

This research was carried out to determine the most suitable method of collecting rainwater for Persian oak (Quercus brantii Lindl var persica Zohary) planting in forest regeneration and enrichment projects in Chenarfaryab Kohmareh Sorkhi region of Fars province during three years. In order to provide the moisture necessary for the growth of oak seedlings, four sowing methods were used in the form of a split plot design with the main source of seeding (seed and seedling), and methods for collecting water including hollowing, barley, platform and pothole. Treatments were carried out in four replicates along with control treatment in the field. Results showed that the percentage of seeds and seedlings in the studied years had declining trends. No significant difference was observed between seed and seedling methods. Sowing methods had a statistically significant difference at 1% level, but there was no significant difference in reciprocal effects of seed and seedling sowing and planting methods. In seed planting, rectangular, pitch hole, and furrow showed the highest percentage of survival, while rectangular pitch, pitch hole, and trace method had the highest percentage of survival, respectively in planting of the seedlings. In this way, rectangular and pitch hole planting methods are the most suitable methods for preserving the water available for oak forests, a method commonly used by the owners and contractors.

Participation of beneficiaries in the restoration and protection of watersheds is very important. This research aimed to investigate the factors affecting beneficiaries' participation in the implementation of rangeland management plans on Kiasar Watershed in the of Sari County. This research was a descriptive-survey type based on the simple random sampling method. The surveyed population consisted of 361 beneficiaries of the Kiasar Watershed of which 73 were selected according to the Cochran formula. The required data were collected through filled questionnaires based on the Likert Spectrum Form and analyzed using the SPSS ver.19. analyses provided the Pearson correlation coefficient, the ANOV, and the multivariat regressions. The Results indicated that the level of participation in implementing the plans was moderate. Moreover, there were no significant differences between the participants based on their education level, wealth and degree of cooperation in achieving the objectives of the plans. Results Participation in the range management plans was positively correlated with the education level, wealth and social status. A significant finding of this research is awareness of the successfully implemented range management plans encourages the active participation of the beneficiaries in executing new projects.

Clarification of suspended load (SL) supply variations at different temporal scales is essential to provide a logical management program. In this study, the SL transport variations were investigated at different time scales in the Marboreh River, Darreh-Takht, Lorestan Province, Iran. The four seasonal, seasonal threshold, annual and land use period approaches were analyzed using statistical methods based on the collected data from 1971 to 2016. The seasonal threshold runoff was determined using the best statistical distribution for the return period of 2 years, and the SL concentration-runoff relationships were prepared for large and small events. The land use map was prepared using remote sensing data for the years 1977 and 2016. According to the results, supply and SL transport capacity were high in the large events of spring, when the slope of the sediment rating curve is 1.469. The supply and SL capacity for large events of the autumn was higher than that of the winter. In the study period, although the land use change from rangeland to dry-farming was observed, the impact of other human activities including dam construction on the tributaries has caused a decrease in the mean SL transport, corresponding with the daily runoff in autumn, winter and spring.

Soil erosion is a global problem that seriously threatens soil and water resources. This research was conducted to study the effect of protection of colza straw on runoff and sediment yield from the laboratory plots using the rainfall simulator. Three coverage of 25, 50 and 75% of colza straw mulches and a control treatment (without coverage) were considered with three moisture levels of 15, 20 and 30% in three replications. The results showed that colza straw had a significant effect on runoff and sediment reduction. All moisture levels in three protective coverage levels decreased runoff volume by13.14, 26.29 and 31.52%, respectively, and sediment yield by 41.21, 72.4 and 78.78%, respectively. With increasing of protection coverages from no cover to the higher coverages, the trend of runoff and sediment yield decreased, so that the lowest amount of runoff (1821 ml) and sediment yield (58 g) were measured in the protective coverage of 75% with the moisture of 15%. The highest amount of runoff (5501 ml) and sediment yield (522 g) were observed in the control treatment at a moisture level of 30%. With increasing the moisture levels from the amount of runoff and sediment yield increased. Moreover, by applying the protective cover, runoff and sediment yield decreased at the same moisture levels.