مجله هیدرولیک
سال ششم شماره 2 (تابستان 1390)

Berm breakwaters are structures that reshape under waves action and reach to a stable profile. In thistype of breakwaters the units of the armor layer are allowed to move in order to take a final formwithout changing the serviceability performance of the structure. The remaining berm width - afterrescission - is the main criterion for stability of these structures. If the rescission become more than theinitial berm width, the breakwater will be unstable and failure will occur.In this paper the effect of nominal diameter on stability of reshaping berm breakwaters is investigatedby experimental studies. In order to consider the effect of this parameter in comparison with otherparameters, 120 tests have been carried out in the wave flume of Tarbiat Modares UniversityHydraulic Laboratory. The waves in all tests are irregular waves conforming JONSWAP spectralenergy. The amount of is assumed for graining.Results indicate that water depth has a considerable effect on berm rescission comparing to nominaldiameter. However, the initial berm width has the same effect as nominal diameter. The results alsoshow that by raising the position of berm to water level, rescission effect is reduced. On the other handby decreasing nominal diameter and increasing the initial berm width the same percentage ofrescission could be expected.

Flood plain is the preferred place for agricultural and other socio-economic activities. High densityflood plain’s residential region shows this fact. These advantages encourage societies to invade river’sbed and right-of-way. Lots of changes occur due to this invasion and cause some morphological andecological damages. On the other hand, rivers are subject to floods. Therefore, determination of risk ofriver’s bed and right-of-way directly relate to flooding damages and flood management plans.In this paper, a new method for hazard and risk determination of river bed and right-of-way isproposed. The approach is Integrated Flood Management (IFM). IFM not only concerns to riverhydraulics and technical issues, but it considers other issues like legal, environment and socioeconomicconditions. This study tries to create a new method for determination of flood risk in thefloodplain. We have composed ordinary flood zone mapping (technically using numeric hydraulicmodels) for Fordo River in Qom province in IRAN. We have also used a Multi Criteria DecisionMaking (MCDM) approach, which represents IFM aspects to produce another set of flood zoning mapby IFM approach. In this procedure, we have benefited from an Analytically Hierarchy Process (AHP)to define land use flood risks. Final map was produced by merging technical map and IFM map.To sum up, new proposed method shows moderate and reasonable zoning instead of hydraulic floodhazard and risk mapping because it uses more criteria for determining the level of flood`s risk infloodplain. Furthermore, this method is more reliable for flood insurance and early flood warningsystems or flood damage mitigation, particularly in metropolitan areas.

One of the structural methods for flood control is construction of levees on the banks of rivers. Intraditional design method, the height of floodwall is computed for a fixed design discharge anduncertainties in design flood determination, river hydraulic conveyance and economic analysis areignored whereas in the risk analysis method effects of these uncertainties are included. In this paper,details of this method were firstly described and then the heights of floodwalls in Qeshlaq River, as acase study, were calculated by application of the risk analysis method. For this purpose, parameters ofthe load function were calculated by fitting statistical distributions on maximum daily flows andparameters of the wall resistance function were estimated by consideration of uncertainties associatedwith Manning coefficient, slope of energy line and geometric characteristics of the sections.Furthermore, in economical analysis effects of hydraulic and hydrologic uncertainties wereconsidered. Results showed that application of the traditional method provided underestimated designvalues and were less reliable compared with the risk-based design method for the floodwalls ofQeshlaq River. In conclusion, application of risk analysis method for design of floodwalls wasrecommended taking all technical and economical aspects into consideration.

The groundwater system in many small islands consists of a freshwater lens surrounded by seawater.A transition zone exists between the freshwater and the seawater in which relative salinity graduallychanges from zero to 100 percent. Saltwater intrusion is the most important hazard to groundwaterquality in small islands. Kish Island is one of the few islands in the Persian Gulf with extractable freshgroundwater resources. This paper presents details of a comprehensive study conducted to modelseawater intrusion in Kish Island. Three dimensional numerical simulations were carried out usingSUTRA a density dependent flow and transport numerical model. Model calibration was performed byInverse modeling. For this purpose the PEST inverse code was combined with SUTRA. Finally modelsensitivity was evaluated for aquifer recharge and permeability. This study shows that SUTRA can beregarded as a valuable tool in saltwater intrusion modeling. This is mainly due to the model`s ability tosimultaneously solve flow and solute transport equations, as well as other key features of the modelsuch as its ability to simulate the transition zone and the unsaturated layer above the main aquifer andto model the groundwater system in three dimensions.

The most important advantage of applying the combined weir and gate is to maximize its performanceunder sedimentation conditions. In this paper, a new mathematical model is presented to determine therelationship between stage and discharge for structures consisting of the weirs and gates by differentgeometries in different flow conditions. Since the geometry of these structures has lateralcompression, velocity distribution in transverse section is not uniform. Therefore, the energy andmomentum correction coefficients should be used, and in this research, these coefficients arecalculated using optimization approach. One great important advantage of this procedure is the use ofrelatively simple hydraulic principles. To verify the given method, different combinations of weir andgate as a physical model are tested in the laboratory. From the laboratory data it is concluded that theproposed method is capable of calculating stage-discharge relationship by reasonable accuracy.

During a critical river flood event, a bridge deck may become partially or completely submerged bythe flow. The deck submergence may be a critical condition for structural stability of river bridges. Inthis paper, the mean flow fields around a submerged bridge deck and the time averaged dragcoefficient on it have been simulated by using FLUENT software. The turbulence models consideredare the standard k 
, renormalization group (RNG) k 
and Realizable k 
. In these simulations,the VOF and rigid lid methods have been used for free surface simulation. Reconstruction and Finitevolume schemes have been used to determine the position of the free surface in VOF method and theresults have been compared. Simulation results of time averaged drag coefficient show that in the caseof partially submerged deck, Geometric Reconstruction Scheme in VOF method with standardturbulence model is in better agreement with the experimental results. In the case of fully submergeddeck, RNG k 
and Realizable k 
turbulence models provide better accuracy than standardturbulence model. Also, simulation results show that Reconstruction based schemes in VOFmethod are not capable to simulate mixing of water and air and finite volume schemes have to be usedfor mixing of water and air simulation.

Aeration is one of the most practical and economical methods for prevention of cavitation attack inhigh speed flows. Many research works are conducted on aerators. Although a general method is notavailable for aerator design, many aerators are designed and constructed all over the world. Cavitationdanger in tunnels also makes the designers to consider aerators for tunnels. Since tunnel sections areusually circular or horse shoe, a specific type of aerator is required for tunnels. Lack of information onapplication of aerators in tunnels makes some of designers to change the tunnel section to rectangularby subsequent concrete operation and then design the same type of aerators used in spillways. Thismethod is expensive and time consuming. In the present work, annular aerators are studied in aphysical model of a tunnel with horse shoe section. The effect of aerator geometry on jet length andspray formation is studied. Experimental results showed that to reduce spray formation, the aeratorgeometry should follow the tunnel section. It was also concluded that to reduce spray formation in therange of Froude numbers tested, it is better to keep the ramp angle less than 5 degrees. To increase thejet length and efficiency of the aerator, the ramp height should also be increased.

Although water and soil conservation activities reduce reservoir sedimentation, it is inevitable thatreservoirs fed by rivers transporting high amounts of sediment will experience sedimentation. TheGhezel-Ozan and Shahroud rivers, which flow into the Sefidroud reservoir dam, are both highlysediment-laden and transport significant amounts of sediment in both forms of bed and suspended loadto the reservoir. Hence, it seems that the only practical way to remove the sediment from the reservoiris to flush it out using the chasse method. But it consists of a highly-concentrated water flow of thesoil mass move through the bottom outlet that is called a density current. The flow causes significantdamages to the boundaries of the conduit by soil erosion and corrosion. In this paper, density currentin bottom outlets and its related problems are evaluated and the effects of concentration on wall shearstress are studied. To obtain the requirements for numerical modeling of three phase air-watersedimentflow pattern, the model was first calibrated with the experimental measurements of twophase air-water flow taken at Water Research Institute of Iran. Therefore, a numerical model based onmulti-phases systems and available theories of numerical models for sediment transport was developedwithout applying empirical coefficients. Two different concentrations of suspended sediment havebeen used and the results are compared. The results showed that wall shear stress increases bysediment concentration. For both cases, the shear stress increases up to a maxima after a short distancefrom the gate. The quantity of these maxims is higher than those measured by flow of pure water.Thus, it is concluded that the sediment flow causes intense shear stress, which is a major threat to thetunnel walls. These damages stimulate the pressure field, which also may trigger cavitations.