IRAN-WATER RESOURCES RESEARCH
Year:2007 | Volume:3 | Issue:1 (7)|Papers Count:11

The development of water delivery schedules in irrigation canals is mostly performed on the basis of hueristic methods and personal judgment. However, the great impact of water delivery schedules on the performance of systems has recently called for analytical methods to be considered. Analythical methods used so far are mostly single objective. Only one study has considered a multi-objective approach using simulated annealing optimization techniques. In this research the genetic algorithm is used and a model has been developed accordingly. In this model an optimal water delivery schedule for lateral intakes is developed such that different objectives of canal capacity and/or delivery periods are optimized. In this model the number of lateral intakes, their delivery flow limits, and coverage areas are given and a optimal water delivery schedule for the distributary canal is determined. The model is applied on one of the secondary canals of Fomanat Irrigation Network in west Gilan Province, Iran. For this purpose, two objective functions and two options for irrigation blocks including 6 and 7 groups of lateral intakes, totally 4 variants, are tested. The model has derived the optimal water delivery schedule for each variant.Considering the management strategies, the best option could be selected. The results show the ability of the developed model as an efficient tool for water management in irrigation canals.

Reliable prediction of dry and wet periods is an essential component in competent management of water resources. A more reliable prediction of the climate, pushes the public approach to these predictions further and lowers the disaster costs. Since the (ENSO)1 has recently been introduced as an important predictor for the anticipation of seasonal wet and dry conditions in Iran, the present study evaluates the significance level of such prediction for autumal and sixmonthly (October-march) precipitation using Fisher Exact test. Using the summer time (SOI)3 as the predictor, the significance of the occurrence of meteorological dry and wet conditions during following autumn is investigated. It has been shown that after a strong El, Nifio event in summer (SOI<-5), wet conditions are anticipated for most parts of the country at a 95% significance level. On the other hand, the prediction of dry conditions is not significant for such an event. It has found that the occurrence of normal rather than wet or dry conditions is significant for the eastern coasts of the Caspian Sea as the El Nifio is prevalence. During strong vigorous cold ENSO periods (SOI>5), the occurrence of autumnal dry conditions are significant for most of the studied stations at the 95% level. During such periods the prediction of wet conditions were found to be statistically meaningless for all parts of the country. It is shown that the occurrence of summer EI Nifio leads to the dominance of wet conditions in about half of the studied stations. The prevalence of summer La Nina does not however lead to the wide spread six-monthly drought.

Drought is an insidious environmental phenomenon which is more pronounced in arid and semi arid regions. Central eastern, and southern regions of Iran are characterized as arid, and semi arid climate. Precipitation variability in the Sistar and Balouchestan Province is very high. This is due to remoteness from Mediterranean cyclonic trajectory and the predominance of a subtropical high pressure system Accordingly, the Sistan and Balouchestan is more prone to drought than other provinces in Iran. In this paper, the probability of drought occurrence and extent in this province is investigated applying lag-1 Markov chain on SPI time series in 3- and 6-month time scales. The results showed that the probability of drought persistence; based on 6-month SP time series, is higher than 70 percent in central portion of the province and decreases to 50 percent moving east Considering the drought equilibrium probability, the result: also indicated that the central district of the province an affected by drought events 30% of the time and therefore is more vulnerable to drought conditions compared to other regions in the province.

Like many other hydro-climatological data, runoff has seasonal variability incorporated with random processes. Previous research has shown that stochastic models are the most suitable simulation tool for random variables with seasonal variability. In this study, a time series analysis approach was utilized to obtain monthly, bimonthly, and seasonal runoff stochastic models in a few sub-basins in Dez and Karun Basin, in southwestern Iran. These sub-basins vary widely in area (from 37 to 9900 square kilometers) in order to study the models with respect to the different spatial scale. The results have shown that the kind of stochastic model in longer temporal scales is not correlated with the area of the basin. Therefore, this result could be generalized to other similar basins. On the other hand, the Monthly Autoregressive Integrated Moving Average model has different patterns regarding the spatial scale of the basin. It is shown that the autoregressive order of small basins could be greater than one. Extracted stochastic models in this research can be used for runoff forecasting in future studies and research.

In this research, the effects of irregular wave action on rundown on the slope of reshaping rubble-mound breakwaters have been investigated. Reshaping breakwater is a new kind of breakwater in which the initial profile is changed to an S-shaped profile, once affected by waves. Therefore, the relations related to run-down levels on conventional breakwaters cannot be used for this type of structure. This research is conducted based on Experimental Modeling. Experiments were performed in the Soil Conservation and Watershed Management Research Institute (SCWMRI) for multiple cross sections of reshaping breakwaters with three different slopes in years 2003 and 2004. The wave flume was equipped with a modern Dill wave generation system, which contains paddle, power pack, hardware and software divisions. The hydraulic responses mentioned above, were investigated by changing the wave parameters such as significant wave height, mean and peak wave period and storm duration on the three structure's seaward slopes, equal to 1:1.25, 1:2.0, 1:2.5. JONSWAP wave spectrum was used in all experiments. The Armored layer materials were included in three grading classes (Dn85A/Dn15A=1.14, 1.44, 1.82) and a Range of structural index permeability, Pe (1£Dn50A/Dn50C£ 2). In order to investigate the effects of changing structural geometry, wave properties, and the comparison between two scales (l=50, 30), 120 tests were performed with 1000 to 6000 waves. Finally the results of different scale factors were compared. The experimental results were plotted as graphs showing the run-down levels versus the surf similarity parameter and deepwater wave steepness. Because the Iribarren number does not accurately describe the combined effects of slope and wave steepness, an improved and new formula was fitted to data using multiple linear regression and nonlinear regression, which results in some new empirical equations presented in this paper.

Velocity and Entrainment of density current in the expansion reach where a river enters into a dam reservoir, a lake, or open sea is of utmost importance. The present study investigates the head velocity and entrainment of density currents in an Expansion Reach. The effects of discharge and bed slope on the head velocity and entrainment of the density current were evaluated by a physical and 3D mathematical model. Experiments were conducted in a flume, 6.0 meters long, 0.72 meters wide, and 0.6 meters in height. Head velocity was measured for an expansion degree of 8 in slopes of 0.0009 and 0.0016 for various discharges. Important parameters were normalized and a two dimensional laser Doupler was used to develop the flow body velocity profile. The measurements showed that mixing values were higher in a divergent cross-section compared to a fixed cross-section. During some experiments a hydraulic jump was also detected depending upon the levels of the density current and slope of the bed in the divergent cross-section, which was investigated and the results are presented accordingly.

Sedimentation in reservoirs is one of the most serious problems of most dams. Sustainable reservoir management necessitates the deposited sediment most be removed to reduce the inactive storage of the reservoir. Different methods can be used accordingly to control sedimentation and maintenance of the dam reservoir. Dredging, sluicing, and flushing are among these methods. In flushing methods, the previously deposited sediment would- be flushed from the reservoir by opening the bottom outlets. In the pressure flushing method, the amount of the flushed sediments depends on many parameters such as the water depth over the bottom outlets, the discharge through bottom outlets, the size of the outlets, the geometry of the reservoir, and the size and type of the sediments. In this study laboratory experiments were performed to investigate the flushing processes during pressure flushing. The effects of the discharge through bottom outlets and the water depth over the bottom outlets were investigated using 3 sizing of non-cohesive sediments (fine, medium, and coarse sediments). The physical model was constructed in the Hydraulic Laboratory at the Water and Science Collage of the University of Shahid Chamran, Ahwaz, Iran. The results indicated that the amount of sediment flushed increases as the depth of water in reservoir decreases and the discharge from outlets increases. Under the same conditions the flushed sediment volume is increased moving from coarse sediments to fine sediments.

In this paper effects of constructing detention ponds for flood control in basins immediately upstream an urban area, are studied. Comparisons are made between this practice and conventional localized river engineering countermeasures regarding socio-economical aspects. The study is conducted in Abkharvar urban basin in Behbahan city in the Khouzestan Province, in southwestern Iran. Based on the design flood routing, the effects of detention ponds on the dimensions of the conveyance canal are studied. Total costs of flood control alternatives are then compared. Results show that regarding socio-economical issues, detention ponds are superior to conventional localized river engineering and flood control countermeasures for flood control purposes in urban basins.

Studying the role of drops as one of the important hydraulic structures for flood control is essential. In the present study, the effects of drops on inundation depth and extension have been investigated in a reach of the Kan River with 7 Km in length. The hydraulic characteristics of flow were computed for floods with 5 to 700 year return periods using the HECRAS computer model for both upstream and downstream sections of the structures. The results of this study verified a different role of drops as well as an incremental and reductive impact on inundation depth and extension in upstream and downstream, respectively.