Journal of Irrigation and Water Engineering
Year:2011 | Volume:1 | Issue:3|Papers Count:7

Rainfall simulation is frequently employed in soil erosion and related processes studies. A rainfall simulator was constructed in Soil Conservation and Watershed Management Research Institute (SCWMRI), which is superior to other existing simulators in country. This simulator consists of some parts such as; water supply, rainfall boom, tilting flume, runoff collection and storage system, control keyboard and laboratory. Rainfall boom has 6 nozzles which introduce a distribution of drop sizes from height of 7.75 m. Tilting flume consists of flow generation section, drainage part, slope control facility adjusting to 60%, and runoff collection system. Rain Intensity can be controlled by water pressure, number of active nozzles, their distance and pattern, so different intensities ranges 35 to 125 mm h-1 are simulated with coefficient of uniformity more than 90%. Depending on rain intensity, mean drops diameter varies from 1.64 to 2.15 mm and terminal velocity ranges 5.70 to 6.78 m s-1. Besides, the kinetic energy of falling drops varies from 16.24 to 22.97 J m-2 s-1. This simulator can generate rainfall and or runoff separately or simultaneously. So, it is possible to study raindriven and or flow- driven processes under laboratory conditions.

Potential Evapotranspiration (PET) is one of the important elements in hydrologic cycle which is required to be estimated in many fields such as irrigation, drainage and hydrological studies. This element represents potential losses from moist soil layer and vegetation cover. In this research different methods (Blaney-Criddle, Thorenthwaite, Penman and Hargreaves- Samani) are applied and then their results were compared with Fao Penman-Montieth method (as reference) and the best one is selected and suggested to estimate PET in Mazandaran province. The results show that the Blaney-Criddle has the lowest standard error and the highest correlation with the Fao Penman-Montieth method in the province. The results also show that the Blaney-Criddle method estimated PET about 5% lower than the reference method. Furthermore the results indicate that PET decreases from east to west of the province.

In recent years Neyshabur’s plain has faced increasing slump in water table. Thus, the role of management and administrative factors is important. This article evaluates the effects of rainfall and climate on the fluctuations in groundwater level. We used 22 Pluviometry and Evapometry station data during 1352-1385. The average amount of rainfall and evaporation calculated with IDW method on Plain. According to man-Kendal, Valdvlfovitz and least squares tests was found the slope of groundwater level has negative trend and in 5 percent level is statistically significant. Therefore to find correlating rainfall on groundwater levels trend of groundwater level measurement was omitted with and the difference curve and extrapolation method, at first. Results of correlation between rainfall and groundwater level showed that rainfall with a 10 monthly lag (R=0.539) has greatest impact in groundwater level. Besides, SPI index used for considering dryness and wetness effects on groundwater.SPI consecutive time series analysis showed long-term timescale of 42 monthly has greatest correlation with the groundwater level (R2=0.519). Also, analyzing seasonal groundwater level and SPI index in different delays and time steps pointed out that winter rainfalls with 30 monthly SPI and with four lagged seasons have the most effect on the surface of groundwater (R2=0.62).

Passing of debris floods over spillways and stilling basins of the diversion dams in steep channel of the mountainous rivers causes abrasion of spillways and stilling basins. This type of spillways and stilling basins abrasion has been reported in different countries including Iran. The purpose of this research provides a method for analyzing the destructive effects of debris floods passing over concrete diversion dams’ weirs. Thus, in this research the proposed empirical equations by the authors are evaluated using field data and an algorithm is provided for estimation of the abrasion of diversion dams’ stilling basins. Roozbahan Diversion Dam in Fars Province is selected as case study to evaluate the ability of proposed algorithm for estimation of abrasion of a real case. Then, abrasion of Roozbahan Diversion Dam by floods 1995 to 1999 is calculated and compared with real abrasion percentage. For this propose, debris flood is simulated and velocity, sediment size, and impact energy of passing sediment over Roozbahan Diversion Dam are estimated. Then, the abrasion of the concrete slab of stilling basin of the dam is provided by using the empirical equations. This research shows that the estimated abrasion percentage by proposed algorithm has acceptable agreement with real case.

abstract In this study, climatic factors statistical trend analysis of rainfall, temperature and drought on seasonal and yearly scales at 15 stations of the Hamadan region, was performed. For this purpose, initially at the level of drought each station standardized precipitation index (SPI) and then calculate the variation factors studied using Kendall nonparametric test was. Average annual rainfall trend analysis showed that 60 percent of stations, the process of reducing precipitation was noticed that the further reduction of spring, winter and summer. Seasonal scale, both in summer and autumn, temperature increase and decrease in spring and winter temperature showed. Trend of increasing droughts similar trend was raining, so that 67 percent of the annual drought of stations increased to 33 percent increase on the station level 0.05 significant. The most significant trends in mean climatic factors studied were observed in summer. The trend in the two stations Ghahavand and Amr Abad for all factors studied in both time scales was significant. These two station receiving values of the, maximum and minimum of rainfall are that significant all climatic factors studied is justifiable.

The accumulation and movement of salts in the soil and its modeling have been considered significantly in recent years. In this article, the simulation of movement of salts in soil using HYDRUS-2D Model for various leaching times has been performed and profiles of advancing salt movement on the dry and wet basins has been drawn and also the effect of initial moisture has been investigated. This model has a strong ability for simulation. Results of the above model show that the leaching repetition causes a quick movement of salts to bottom of the root zone. this movement had more speed on the dry basin in comparison with the wet.The applied conclusion of this article is that if the soil is dry before the irrigation; salts would be influenced by prefrential flows by Joint gaps resulting from contraction and expansion and therefore will smoothly transported. After a week of leaching, results show a faster salts movement on the dry basin causing by capillary forces and therefore the accumulation on the topsoil.

Flow measurement is very important in sewers and water transmission systems. Many types of instruments such as weir, gate and parshall flume…. is use to measuring discharge in free surfaces flow. If there are sediment or crash in water the work of measuring system were done trouble. Using two control system flow “gate-weir” increases the accurate of flow measurement. Weir and gate system is a plate that seated at end of canal and the flow current from over and under it. Sediment through out under and buoyancy material current over the weir-gate system. The aim of this research is study the characteristics of flow hydraulic and cross section geometry on coefficient discharge in two control system weir -gate. A rectangular plate fixed at the end of a pipe with 240 mm diameter and 8000 mm length and flow was measured for each part (weir and gate). The results show that the new system can modify the flow pattern upstream and the characteristic flow nearer to theory condition, that increases the accurate of estimation coefficient discharge and flow measurement relate to common weirs.