unpredictable, rare and random nature of natural rainfall. The rainfall simulator, as an alternate effective approach, facilitates quick measurements of different hydrologic components. However, calibrated suitable conditions and optimization of governing situation have been rarely taken in to account. Therefore, the Nozzle Type rainfall Simulator Laboratory was established at Tarbiat Modares University to simulate rainfall similar to storm events happened in Mazandaran Province climate. In the current study, the potency of creating different rainfall intensities by permuting intake discharge, water pressure and nozzle decoration and also their effects on Simulated rainfall characteristics were investigated. The results indicated that in different water pressure, the Simulated rainfall characteristics were significantly different. The results also showed that drop size distribution and their velocities produced by manufactured nozzle coded as Apd4, in optimum pressure (10 to 50 kpa), were 0. 5 to 4. 7 mm and 4. 8 to 9 m s-1 respectively. Besides, The results also indicated that a rainfall with intensity of 30 to 120 mm h-1 with coefficient of uniformity ranged from 80 to 95% by 27 nozzle spacing 0. 85 m could be properly Simulated under intake optimum pressure.

Rill erosion is the detachment and transport of soil particles by concentrated flow of runoff. It is the most common form of water erosion in the hill slopes. Rill erodibility is the rate at which soil particle is detached and transported by shear force of the concentrated flow. The study was conducted to determine the rill erodibility in different soil textures in Zanjan province using a rainfall simulator. To this end, samples of eight soil textures consisting of clay, clay loam, silty loam, sandy clay loam, sandy loam, loamy sand, and sandy were collected from land surface and transported to small plots (120 cm - 100 cm) on a sloped uniform land (10%). The plots were exposed to five Simulated rainfalls with a constant intensity of 60 mm h-1 for one hour. Based on the results, there was a significant difference among the soil textures in the rill erodibility (p< 0.01). Rill erodibility of the soils significantly correlated with mineral fraction (sand, clay, gravel) and exchangeable sodium percentage (ESP). With an increase in sand and gravel percentage, soil infiltration rate strongly increased and consequently production of the concentrated flow steadily decreased. Multiple regression analysis indicated that the rill erodibility in the soils was remarkably related to ESP (R2= 0.85, P< 0.01). Clay soil showed to have the highest rill erodibility among the soil textures due to higher exchangeable sodium percentage (ESP=13).

Antecedent soil moisture is one of runoff and sedimentation crucial factors affected by parameters such as soil properties, topographic-, climatic-, and coverage circumstances etc. The work aimed at determining effects of soil properties and rainfall on runoff and sediment load at various antecedent moisture levels. Heavy, medium and light textured field soils were selected, exposed to a constantly intensified 80mm/hr rainfall under air-dried, air-dried to field capacity point, field capacity point and nearly saturated conditions, and two slopes of 5 and 15%.Recording runoff and sedimentation values every 2-5 min; populated values were calculated within 10, 20 and 30 min. intervals. All experiments were carried out with Simulated rainfall technique in a 1×1×0.1m flume. Treatments showed most significant differences within first 10min. decreased with increasing rainfall duration. Maximum runoff coefficients increased as 2- 5 folds as minimum ones with all durations. When moisture increased to field capacity point, light, medium and heavy textured soils had the lowest to the highest values of runoff coefficient, respectively. Under nearly saturated condition, increasing runoff trend decelerated with heavy textured soils and decreased to a lesser extent as compared to medium textured samples. Also, sedimentation process was consistent with runoff fluctuations. Medium textured soils showed a significant level of sedimentation under nearly saturated conditions. Runoff coefficients were unnoticeably different with 5 and 15% slopes; however, a more significant sedimentation increase occurred with 15% slope.

The runoff generation and soil erosion in the Kechik Watershed, Golestan Province, was assessed, using a designed and constructed portable rainfall simulator. Treatments were applied on different land-uses, slopes and aspects as the most influential factors. Results showed that land-use significantly affected runoff generation (13.35 l, 6.9 l, and 4.12 l, respectively for agriculture, forest and rangeland uses), however slope (7.7 l for Class I; 9.23 l for Class II) and aspect (8.52 l for the northern aspects; 8.32 l for the southern aspects) did not have significant influence. All factors, significantly altered sediment concentration (Agriculture 9.6 g l-1, forest 8.24 g l-1, and rangeland 5.26 g l-1; slope class I 6.6 g l-1 and slope class II 8.7 g l-1; northern aspect 8.7 g l-1, and southern aspect 6.9 g l-1). Agricultural fields generated the highest runoff and sediment under Simulated rainfalls. Rangeland and forest did not have significant runoff generation and sediment concentration. Results showed that land-use management, especially in terms of agriculture, could not only hamper current erosion, but reduced further advancement of this encroaching phenomenon.

Aggregate breakdown and splash particles are the most important results of raindrops impact on soil surface. The study was conducted to investigate the temporal variations of breakdown and splash processes in a virgin marl soil in Zanjan Province. The experiment was carried out as a completely randomized design with eight rainfall duration treatments and three replications, in 2010. Twenty four flat boxes with dimensions of 30 cm×40 cm were filled with soil aggregates (6-8 mm). The aggregates boxes were placed under a rainfall simulator with a constant intensity of 40 mm h-1.The aggregate breakdown values was obtained based on comparison of the mean weight diameter of the aggregates before and after rainfall events. The splash values were determined from the dry weight of soil particles that had splashed out around the boxes during each rainfall event. Based on the results, there were significant relationships between the rainfall duration and both the aggregate breakdown (R2=0.99, p<0.01) and the particles splash (R2=0.95, p<0.05). The aggregate breakdown value was low at the beginning of rainfall (7.5 min), but it increased with increasing rainfall duration and, subsequently, soil surface was crusted in 45 min. At this time, aggregate breakdown and particles splash values were almost maximized. After 45 min, aggregate breakdown and particles splash values were negligibly increased due to crust formation at soil surface. There was a significant relationship between the particles splash and the aggregate breakdown (R2=0.98, p<0.05).

The set covering problem (SCP) is one of the location -allocation models. It s objective is to minimize the cost of facilities location-allocation in an optimal structure in such a way that each customer or zone has been covered by at least one facility. The above problem is a class of NP-Hard problems that cannot be solved by exact algorithms in a reasonable amount of computational time. Thus in this paper, a Simulated annealing (SA) algorithm is proposed to solve the SCP. This algorithm is one of the efficient metaheuristics based on a neighbourhood search within solution space, acceptance of probability, and inferior solutions to scape from trap (i.e., local optimal solution). Ten test problems are solved in which associated results show the efficiency and validity: of the SA algorithm for solving the SCP. The validity comparisions of the results obtained the proposed algorithm are compared with the results reported by three methods named as Lingo 8 Software, Heragu's heuristic, and Genetic Algorithms (GAs).

This study was conducted to study the effect of zeolite and slope on sediment concentration, nutrient loss, and some hydraulic flow parameters in a loess soil of Northwest of Iran. The loess soil used for the experiments is collected from the surface layer (0-30 cm depth) and experiments were done using a rainfall simulator with three zeolite treatments (0%, 10% and 20%) and three slopes (15%, 30% and 45%). All experiments were conducted as a factorial with three replications at the rainfall intensity of 80 mm.h-1. Data analysis, variance analysis, and mean comparison (through Duncan's test at p<0.05) were performed. The results of statistical analysis showed that the zeolite and slope had a significant effect on the sediment discharge, runoff discharge and sediment concentration (p<0.01). Sediment discharge in the control and in the slopes of 15, 30 and 45% was in order 7.22, 50.61 and 77.09 gr.m-1.s-1 and in 10% and 20% zeolite was 6.31, 43.60 and 54.96 gr.m-1.s-1 and 6.81, 42.06 and 52.27 gr.m-1.s-1 respectively. The amount of nitrogen in the sediment varied between 0.3 and 0.41 percent. Phosphorus content in sediments was between 13 and 22 ppm and potassium evaluated 300 to 470 ppm. The highest content of nitrogen, phosphorus, and potassium in the sediment was observed at the 0% zeolite and 45% slope. Our results suggest that zeolite can be considered as an effective modifier of soil physicochemical properties and lead to better protection of soil in the loess regions.

Given that, a lot of soil lost from watershed area by erosion factors. The application of management methods is necessary for soil loss control. Therefore, the use of the available, economical and environmentally friendly conditioners can be the suitable approach in soil loss and runoff control. On the other hand, the soil and water conservation need to the suitable amount determination of soil conditioners to be in addition to reducing costs, from water contaminants prevented with application of chemical fertilizers. However, the optimum amount determination of soil various conditioners with quantifying aim of this effect less attended on runoff and soil loss components. Accordingly, in this study, the effect of various amounts of manure compost with rates of 2. 25, 4. 5, 9. 0 and 18. 0 t ha-1 on amount of runoff and soil loss from experimental plot with area of 0. 5 m 2, slope of 20 percent, was conducted using rainfall intensity of 50 mm -1 ha for duration of 10 min in agricultural soil that it collected from Sari province in year 2018. The results of statistical analysis indicated on the significant effect of various amounts of manure compost on changes of increasing time to runoff and decreasing runoff volume and coefficient, soil loss and sediment concentration in level of 99 percent. Also, the study of conservation effect and grouping various amount of manure compost showed that the compost with rate of 9. 0 t ha-1 for the same effect with amount of 18. 0 t ha-1 on changing sediment concentration can suggest as the optimum and practical amount in natural conditions.

The surface soil moisture content has an important and effective role in runoff generation and soil loss, especially in the arid and semiarid regions. For this purpose, an experiment to determine the effect of initial moisture on runoff and soil loss in two soil texture of loamy, sandy clay loam in intact land in the vicinity of the University of Zanjan was performed with four initial moisture levels (one, four, seven and 10 days). Field experiment as factorial in randomized block design was carried out in plot scale (60*80cm) using a rainfall simulator. Twelve plots for each soil were installed on a uniform slope of seven percent and accordingly exposed to Simulated rainfall with intensity of 55 mmh-1 for 30 min. The results showed that, significant difference was found in runoff generation (p<0. 01) among initial soil moisture levels in each soil, that this issue was affected by the initial moisture content in the soils. No significant difference was observed in soil loss between the initial moisture levels in loamy soil (p>0. 05), high initial moisture aggregates in this soil resisted versus detachment by raindrops, while these changes were significant among the soil moisture levels of the sandy clay loam soil (p<0. 05), which was associated with a small amount of organic matter and more clay. Contrary to expectation, there was no significant relationship (p>0. 05) between soil loss and runoff generation under moisture levels in soils.

Many factors affect soil erosion and runoff generation. However, the role of some factors such as freeze-thaw (FT) processes has not been well considered yet. The present study therefore aimed to simulate and explain the effect of FT cycle on runoff generation and sediment yield under rainfall simulation condition. Towards this attempt, air and different soil depth temperatures were analyzed in natural condition and 10 cm soil depth was targeted for the soil laboratory experiments. A FT cycle with three and two days for freezing and thawing was taken place. The rainfall storm with 1.2 mm/min and 30 min duration was Simulated and conducted for three treatments in soil erosion and rainfall simulation laboratory of Tarbiat Modares University. The results showed that the induced FT cycle soil had a distinct and significant behavior and different from that seen for the control plot. So that, the times of runoff generation in freezed and FT cycle treatments were 2.74 and 3.25 times less, respectively, compared to that reported for the control plots. The runoff volume and sediment yield were also respectively reported in turn of 1.46 and 1.16 and, 11.92 and 2.65 times more for freezed and FT cycle induced treatments compared to those recorded for control plots. Ice lenses and frost heaves plus creating situations close to soil saturation after FT cycle were the most effective factors in distinct behavior of soil induced by Freezing and FT cycle.