مجله هیدرولیک
سال نهم شماره 2 (تابستان 1393)

Many investigations have been performed in order to increase the efficiency of energy dissipation over the spillways. In this study, the chute was roughened by means of the dentate blocks that were made of Teflon with new geometric shape and configurations. The experiments were carried out at three slopes, under six discharges and five dentate blocks configurations. Based on the laboratory results, it was concluded that the roughness geometry influences the relative energy loss. It was also found that using mix arrangements and selecting different sizes among roughness elements can increase the value of relative energy loss. Finally, it was observed that the dentate blocks spillway caused an extra 21% reduction in energy dissipation compared to the stepped spillway which is widely utilized to dissipate the energy.

Bridge pier scour occur due to down-flow and flow redirecting after it impinges the pier. Any increase or decrease of the strength of such flow can result in the decrease or increase of the scour depth. The present study showed that roughness can decrease the down flow strength and thereby the scour depth. This result was concluded through laboratory experiments. The results of experiments under different roughness dimensions and flow conditions are also

Fuse gate is one of the spillway types that according to the plan view have two models of straight and labyrinth crest. Labyrinth crest fuse gates with increasing crest length, discharge capacity and storage of water in reservoir, can prevent flooding of upstream land by reducing water level above the structure. They have three different types: Narrow Low Head (NLH), Wide Low Head (WLH), and Wide High Head (WHH). In this study, the effect of increasing canal slope on discharge coefficient in 3 models of fuse gate: WLH, Straight, and Straight with Inclined Side view was investigated. These models were made of Plexiglas with a bucket height of 16.7 cm. Tests were made in a sloping experimental canal with a length of 12 m, width of 0.5 m, and height of 0.8 m. The results showed that the discharge coefficient of fuse gate spillway depends on h/H. In WLH model of fuse gate, the discharge coefficient reduces as parabolic with increasing discharge and in Straight Fuse gates, the discharge coefficient in the form of linear has increasing, constant and decreasing depending on the slopes. In all 3 models with increasing slope, the downstream water depth of spillway reduces and discharge coefficient value increases. Model comparison showed that in a constant h/H, the Straight spillway with Inclined Side view has higher discharge coefficient and stores the maximum volume of water in the reservoir. It was also found that at a constant discharge, the WLH model has lower upstream water level. Finally, the discharge coefficient equation for straight and labyrinth fuse gates were obtained in the form of linear and power functions. The statistical analysis indicated high accuracy of the equations.

A baffle sluice gate was proposed for delivering a relatively constant discharge within a specific variation range of water surface elevation. Its design criteria were based on baffle’s discharge coefficient and the water surface elevations in which the subsequent baffle takes over the flow controls. The structure, which could play effective role in delivering accurate volume of water, should be used in parallel (dual) modules, while published design criteria deal with the application of an individual module. In this research, the discharge coefficient of each baffle was determined considering the impact of the presence of other baffles. Also, the water surface in which the flow control is given to the next baffle was more accurately defined based on the actual performance of the module. Then, the new design method for parallel modules was accordingly proposed. The proposed design method decreased the deviation in water delivery, within the predefined flow depth variation range, to about 1%, while it was about 8% for previous design methods. In addition to the mentioned significant improvement in water delivery, parallel installation of the modules facilitates the application of the structure in higher levels of an irrigation network, than the one originally was considered by its capability of delivering larger discharges.

In this paper a new method for mitigation of dam reservoirs sedimentation is introduced and its performance is evaluated. This method includes a self-cleaning and permanent function structure resembling a short dam built across the rivers discharging into the dam reservoir. This structure, called Dam-Type Sediment Excluder (DTSE), extracts suspended sediment from flows upstream of reservoir through a middle opening (gate) and prevents entrance of sediments into the reservoir. In this study, using laboratory experiments, the efficiency of the proposed DTSE method was examined under three ratios input discharges, three middle opening relative heights and the output (bypass) to input flow rates of 0.1, 0.2 and 0.3. The results showed that: 1) the efficiency of the DTSE increased with increase of middle opening height, 2) increase of bypass flow ratio affects the model efficiency and sediment concentration of bypass flow in a positive and negative manner, respectively. Therefore, between three flow ratios, bypass flow ratio of 0.2 is the optimum one, due to the water loss of 20% and proper efficiency, 3) the maximum extraction efficiency of the model was found to be about 40% while the average optimal efficiency, for bypass flow ratio of 0.2, was about 26%. Therefore, the new DTSE method could be introduced as an effective method for sediment mitigation, in comparison to other reservoirs sedimentation mitigation methods such as density current venting with only 20% efficiency.

Development of irrigation network and overuse of water is the main cause of desiccation of the internationally recognized Urmia Lake, Iran, in the last decades. In the restoration planning of the Urmia Lake, the allocation of environmental flows for the main rivers and security of water flows along these rivers are essential. The main aim of the present study was to determine the monthly distribution of the rivers environmental flows. This paper presents the ecological requirements of a typical river, the Nazloo River in the west coast of the Urmia Lake, using eco-hydrology-hydraulics methods. An ecological integrated method (Habitat Similitudes) was used for sustaining targeting species in the river system (i.e. Siah, SiahKoli and Zardak fishes). The Water Quality method (Q- relationship) was considered for species tolerance to pollutants. The flow predictions from most of the hydrological methods are higher than the river's natural flow capacity during low-flow period (July to February). The results from the hydraulic method (Maximum Curvature) have limited flexibilities to present reasonable flows during different months of the year. The concentrations of phosphate are also found to be critical to the targeting fish species. In this study, the integration of "Habitat Similitude" and "Water Quality" methods, considering the potential of the natural flows and the hydraulic requirements of the riverine species, would offer the monthly environmental flows of the river in a more realistic way. The results indicate that in order to maintain the Nazloo River at acceptable environmental condition, water flows ranging from 0.8 m3/s (in September) to 8.0 m3/s (in April) are to be provided along the river towards the Urmia Lake, in Iran.