Journal of Water Sciences Research
Volume:5 Issue: 1, 2013

Block ramps are hydraulic structures which are commonly used in river restoration projects. Especially in the last few decades, the use of this type of structures have become more and more popular. They furnish a correct balance between the hydraulic functioning and the environmental care, as they minimize the impact on the environment in which they are located. In addition, they can be considered flexible structures, i.e. they can easily adapt to the in situ conditions and they can be easily built to re-convert traditional concrete structures. They can be built either by loose or fixed blocks, arranged on a sloped bed. However, a correct design of this structural typology has to take into consideration several aspects. In particular, the hydraulic functioning of a block ramp is assured when the structure remains stable, i.e. when the blocks are not removed from their original position. Thus, the first step in designing block ramps has to be the structural stability. Furthermore, the analysis has to focus also on the dissipative process occurring on them, in particular it has to consider the different flow regimes that can take place and the effect of the bed roughness on the energy dissipation. Another important aspect is the stilling basin design. In fact, a block ramp has not to be considered as an isolated element in the contest in which it is located. It is part of that contest and it contributes to modify it. Thus, it is extremely important to consider the scour process occurring downstream of the structure. In particular, the maximum scour depth and length have to be carefully estimated in order to avoid structural collapse of the ramp. The scour process occurring downstream of the structure is also extremely important in terms of energy dissipation. In fact, the global dissipative process is the result of two distinct processes: one occurring on the ramp and the other in the downstream stilling basin.

Sloshing is a well-known phenomenon in liquid storage tanks subjected to base or body motions. In recent years the use of multiple vertical baffles for reducing the sloshing effects in tanks subjected to earthquake has not been taken into consideration so much. On the other hand, although some of the existing computer programs are capable to model sloshing phenomenon with acceptable accuracy, the full dynamic analysis subjected to random excitations, such as earthquake induced motions, is very time consuming. In this paper a method is presented for this purpose based on conducting several dynamic analysis cases, by using ANSYS-CFX for rectangular tanks with various dimensions, subjected to seismic excitations, and then using neural network to create simple relationships between the dominant frequency and amplitude of the base excitations and the maximum level of liquid in the tank during the sloshing. At first, the numerical modeling has been verified by using some existing experimental data. Then, several cases of time history analysis have been conducted to obtain the required numerical results for teaching the neural network. Finally, the predicted results of the neural network have been compared with those obtained by some other cases of analyses as control values.

Grade control structures are used to control bed erosion in steep small rivers mostly in the mountains. Scour downstream of this structure can lead to failure. Over the past years, the effect of different variables on this phenomena have been studied, however the effect of upward seepage which is common due to head difference of the banks water table or water surface level between the upstream and downstream reaches of a grade control structure has not been studied. In this paper, results of an experimental investigation on the maximum scour depth downstream of a grade control structure with and without upward seepage through bed sediments are presented. Experiments were run for the conditions of free falling jets, over sedimentary beds (median sizes = 1.5, 2.4 and 3.15 mm). Our data for the case of existing upward seepage shows that D'' Agostino and Ferro (2004) expression significantly overestimates the scour depth. New finding of this study indicates that with the presence of upward seepage the scour depth decreases significantly which confirms the results of Sarker and Dey (2006) on scour downstream of horizontal jet with no horizontal apron.

Groundwater drought is a natural hazard that develops when groundwater systems are affected by climatical drought, when climatical drought occures, first groundwater recharge, later groundwater levels and groundwater discharge decrease. The origin of drought is a deficit in precipitation and that takes place in all the elements that comprise the hydrological cycle (flow in the rivers, soil moisture and groundwater). Hydrological drought is concerned with the effects of periods of precipitation (including snowfall) shortfalls on surface or subsurface water supply (such as streamflow, reservoir and lake levels, and groundwater). The frequency and severity of hydrological droughts are often defined on a watershed or river basin scale. Although all droughts originate with a deficiency of precipitation, Hydrological droughts are usually out of phase with or lag the occurrence of meteorological and agricultural droughts. It takes longer for precipitation deficiencies to show up in components of the hydrological system such as soil moisture, streamflow, and groundwater. In fact the present research has focused on forecasting the effects of drought on water budget and groundwater table using MODFLOW mathematical model in Garbaygan plain, located in the southeastern of Iran. In this study four scenarios including wet year, normal, moderate and severe drought have been considered. using an agreement with relationship between precipitation and recharge (natural and artificial) in transient calibration, the best estimators have been fitted for forecasting of recharge. Also the forecasting of water budget illustrates that under different precipitation conditions (from wet year to severe drought). Moreover groundwater level will fluctuate in different conditions and it will decline more in the locations with high densities of wells.

Water obtained from any source may contain impurities induced by erosion, dissolved minerals, dissolved gases and material produced from organic matter decomposing. If the amount of these substances exceed a certain limit, not only the water would not be potable, but the water containing the material will not be suitable to be used in most applications, or at least before treatment cannot be applied in everyday use. Sediment particles separation from flow via gravity in settling tanks and basins is one of the effective solutions in water treatment, urban water delivery projects and prevention of sediment entrance into irrigation networks. Construction cost of a settling basin is about one third of the total expenditure involved in constructing a water treatment plant. So a great economy may be achieved by increasing settling efficiency. Herein this paper by applying CCHE2D numerical model, the effect of geometric parameters such as inlet and outlet locations on flow field and sedimentation pattern in a rectangular settling basin is investigated. Results show that some variations in flow field and eddies formation and hence, sedimentation pattern takes place in the basin. Results also confirm that the model could appropriately simulate flow field and sedimentation pattern with a reasonable error percentage.

Analysis of non-laminar flows in coarse alluvial beds has a wide range of applications in various civil engineering, oil and gas, and geology problems. Darcy equation is not valid to analyze transient and turbulent flows, so non-linear equations should be applied. Non-linear equations are classified into power and binomial equations. Binomial equation is more accurate in a wide range of velocity changes in comparison to power equation and its validity has been verified by dimensional analysis and Navier–Stokes equations. But since velocity changes are rather limited in engineering problems, power equation would be accurate enough. Non-Darcy flow analysis for the cases in which streamlines are almost parallel has been investigated by numerous investigators in pressured and free surface conditions. Radial flows are accompanied by streamlines contraction. Contracted streamlines in free-surface radial flows result in flow inflation, i.e. flow depth through the path increases significantly in comparison to parallel flows. This phenomenon makes free surface radial flows behave completely different from other types of flows. To investigate the behavior of free-surface radial flows in coarse porous media, power and binomial equations are analyzed in this paper. Furthermore, several experiments have been conducted by setting up a semi-cylindrical experimental device with a diameter and height of 6 and 3 meters, respectively. Results indicate that free-surface radial flows behave different from pressured radial flows and Non-Darcy flows in which streamlines are relatively parallel.