Rouhangiz Akhtari; mohammad Rostami; Bahram Saghafian; Mohammad Elmi
Abstract
Introduction
The construction of check dams in the branches is one of the common methods of watershed management to control sedimentation, watercourse stability and reduce the flood hydrograph from the time of concentration and peak flow. In Iran, despite being 50 years old, in the wide implementation ...
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Introduction
The construction of check dams in the branches is one of the common methods of watershed management to control sedimentation, watercourse stability and reduce the flood hydrograph from the time of concentration and peak flow. In Iran, despite being 50 years old, in the wide implementation of this small-scale structure by the bodies affiliated to the country's Natural Resources and Watershed Management Organization as an executive body, a suitable quantitative and qualitative evaluation method has not been provided. In expressing the effectiveness of this structure, it is inevitable to simulate natural conditions in the presence and absence of this structure in hydrological and hydraulic models. Of course, field visits and measurement of the relevant parameters in the field are also considered to be primary measures in the verification of the simulation and the approximate expression of the effectiveness. The investigations showed that in many researches, the effect of correction dams on the runoff hydrograph has been considered. Simulation of the dams has been done hydrologically with changes in the slope of the waterway and basin time concentration or by using the method of routing in the reservoir that according to simplified hypotheses, estimates more than reality. Hydraulic simulation is more precise but has its own complexity and obstacles. Therefore, in this study, we tried to apply the effectiveness of improving check dams in runoff hydrograph by using both the accuracy of hydraulic simulation and the lack of complexity of hydrological relations. The effectiveness of check dams is computed by determining and applying coefficients in the waterway output hydrograph without improving check dams to obtain the waterway output hydrograph with check dams.
Material and methods
In this research, the effectiveness of successive check dams in reducing the output hydrograph of a triangular channel with three lengths of 1000, 2000 and 3000 meters in three longitudinal slopes of five, 10 and 15%, using the MIKE 11 hydrodynamic model, is considered. In this study, it is assumed that series check dams with a height of 2.5 meters will be constructed in each triangular canal, therefore, the number of check dams will vary from 20 to 180 based on their length and slope. In this study, the output hydrograph of the triangular channel was considered as the dependent variable, and the input hydrograph, channel length, and channel slope were considered as independent variables. Variations of outflow hydrograph peak discharge were investigated under two scenarios. The first scenario for the condition where the channel is without improving check dams and the second scenario for the case where the channel was studied with full of sediment series check dams in order to simulate the effectiveness of the dams in a waterway with hydrological parameters. Two criteria were defined to express effectiveness: the percentage of the intensity of hydrograph routing and the percentage of flow discharge change. The percentage of changes in peak discharge of the hydrograph is determined in relation to the peak discharge of the inlet hydrograph. In other words, "attenuation coefficient" was named based on the difference between inlet and outlet discharge for the scenario and for changes in length of waterway, slope and different amounts of inlet hydrograph. The percentage of change in peak flow discharge from the second scenario compared to the first scenario was also considered as the percentage of flow discharge change.
Results and discussion
Evaluation of the model results for hydrograph routing along the channel in exchange for changing independent variables in the form of two scenarios resulted in decreasing peak flow, increasing the base time of output hydrograph, and delayed time due to trending. The existence of check dams has doubled the change in the mentioned parameters. As the longitudinal slope of the waterway increases, the amount of storage in the canal decreases, and the output discharge and therefore the intensity of the routing (decrease in peak outflow relative to the inlet). Increasing the volume of inflow decreases the intensity of the routing. Routing intensity has an inverse relationship with longitudinal slope and has a direct relationship with channel length. Increasing the number of check dams increases the amount of storage in the canal and as a result, slope reduction occurs and the changes in output discharge are greater than inlet flow. Therefore, the intensity of routing increases. The main purpose of this study was to determine the effectiveness of improving check dams in reducing peak discharge of ouflow hydrograph from a triangular channel based on different conditions using a mathematical model. After performing various simulations and investigating different methods, it was observed that the effects of improving check dams on a outflow hydrougraph can be modeled as the effect of a linear reservoir with a lag time at the end of the channel. In other words, two linear reservoir function and a lag time function are applied to independent variables to obtain the dependent variable. For both output hydrographs obtained in the channel without and with improving dams, K values were estimated as linear reservoir function and TL as lag time function. The average storage coefficient (K) of the linear reservoir was estimated 500, 1100 and 1400 seconds respectively for lengths of 1000, 2000, and 3000 m and for three slopes. The mean lag time for the three mentioned lengths was 540, 1750, and 3700 seconds, respectively. As the length of the channel increases, the slope of the canal, as well as the inflow to the canal, as well as the inflow to the canal decreases, and the amount of the above parameters and therefore the attenuation coefficient increases.
Conclusion
If a stream is selected for the construction of improving check dams and the output hydrograph is available using empirical, hydraulic, and hydrological models in the absence of check dams, the outflow hydrograph from the stream will be simulated and modified for the existence of small-scale structures by applying the linear reservoir storage coefficients and the lag time obtained from this research. In this way, the effectiveness of the construction of improving check dams in flood control will be achieved in the mentioned waterway.
pedram esmaeli; siamak Boudaghpour; mehdi Mirzaee
Abstract
The spur dike has been known as one of the most common organizing constructs of the river to reduce the erosion of coasts and river banks. These structures are developed with the right lengths and angles towards the flow of the natural walls of the river that cause flow deviation from the sides and lead ...
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The spur dike has been known as one of the most common organizing constructs of the river to reduce the erosion of coasts and river banks. These structures are developed with the right lengths and angles towards the flow of the natural walls of the river that cause flow deviation from the sides and lead it toward the central river axis. In this experimental study, the flow pattern around the simple series spur dike in the meandering channel with a sloped erodible wall consisting of three consecutive arches with angles of 45, 90 and 45 degrees, has been studied for 40, 35 and 30 liter/sec rates. The results indicate that the collision position of the first line of flow in the near bed to the inner wall of bend no. 2 in discharge 40 liters per second earlier than discharge 35 liters per second and in discharge 35 liters per second earlier than the discharge 30 liter per second. So that the collision position of the first line of flow in the near bed to the inner wall of bend no. 2 in discharge, 40, 35 and 30 liters per second, respectively, in the -18, -15 and -10 degree sections compared to the central arc of the mentioned bend. In conditions of the presence of spur dikes, the vortex dimensions change with the depth of movement, so that moving towards the surface of the water in a fixed discharge, due to the tendency of flow to the outer wall, the slope of the bend wall and increasing the level of contact surface of the spur dike length, the vortex dimensions are increased.
shahab nayyer; saeed farzin; hojat karami; mohammad rostami
Abstract
Erosion is one of the most worrisome issues associated with the river and coastal sides. The use of spur dikes is one of the newest methods for controlling and reducing erosion. The spur dikes are in various forms, such as simple, l-shaped and t-shaped. In this experimental study, the effect of different ...
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Erosion is one of the most worrisome issues associated with the river and coastal sides. The use of spur dikes is one of the newest methods for controlling and reducing erosion. The spur dikes are in various forms, such as simple, l-shaped and t-shaped. In this experimental study, the effect of different geometry of upstream and downstream spur dikes on the scouring of middle t-shaped spur dike was study for a series of spur dike combinations. Experiments have been analyzed for movable bed in the threshold of motion condition. The results of this study showed that the average scour depth around the mid-t-shaped spur dike is about 0.8 times the flow depth. The best performance of the t-shaped spur dike occurs when the upstream spur dike is l-shaped and downstream is t-shaped (L T T). In fact, the lowest volume and average scour depth due to the all situations is related to this combination. The erosion volume was calculated using the Surfer software. The average scouring volume of this combination is 0.063 m3 and the average scour depth is about 1.21 times the flow depth. At the site of the first spur dike, the entire amount of erosion on the side of spur dikes but by crossing the spur dikes, erosion is directed toward the opposite.
Yaser Mehri; Jaber Soltani; Mojtaba Saneie; Mohammad Rostami
Abstract
A side weir is a structure which is set in a side of main channel and used for discharge of additional flow, diverting excess water and water level control of channels and in irrigation and drainage systems. Due to difficulties presented in mountainous regions, lateral ‘piano key weirs’ could ...
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A side weir is a structure which is set in a side of main channel and used for discharge of additional flow, diverting excess water and water level control of channels and in irrigation and drainage systems. Due to difficulties presented in mountainous regions, lateral ‘piano key weirs’ could be used in arc-shaped channels. In addition, curved channels, which are commonly used in mountainous areas, are places that can be used to locate the side piano key weirs. In this research, experimental investigation was performed on side piano key weirs type B, type c and sharp crest side weir on flow in the 30 degree curved channel. Among the findings of the above survey, one could point out to the equality of the specific energy on the two edges of piano key lateral weirs, the changes of which equal 0.277% for type C piano key lateral weir and 1.98% for type B weir. Also, focusing on the empirical analyses, it becomes evident that the coefficient of discharge for piano key weir bears a higher quantity considering the more effective length corresponding to rectangular weir. Comparing the coefficient of discharge of the two weir types C and B, it becomes evident that type B weir has a better functioning in relation to type C.
Mohammad Rostami; Nima Rohani; Hamdi Reza Sheybani
Abstract
Login driftwoods into the river flow and their accumulation in the upstream of the bridge will decrease the flow carrying capacity of the bridge. Blockage may cause a strong reduction in the flow rate through the bridge and therefore a strong increase in upstream water level which may lead to flooding ...
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Login driftwoods into the river flow and their accumulation in the upstream of the bridge will decrease the flow carrying capacity of the bridge. Blockage may cause a strong reduction in the flow rate through the bridge and therefore a strong increase in upstream water level which may lead to flooding or nearby urbanized areas. Drift woods either accumulates at a single pier, or it spans between two or more piers or it gets blocked at the bridge deck. Since the evaluation of such a mechanism in nature and in flood time is very difficult and limited knowledge is currently available on the likelihood of bridge blocking by the driftwoods, therefore, it is necessary to evaluate experimentally the movement of the driftwoods through the river flow and the effect of bridge characteristics on driftwood accumulation and blockage. The main purpose of this experimental study is to analyze the driftwood blocking probability at bridge depending on drift dimensions, driftwood shape (single log and log with branches), flow characteristics, method of driftwood entry into the flow and bridge characteristics. Tests were carried out in an inclinable rectangular flume and a bridge with guard rails was installed into the flume. The tests were performed by different length of driftwood, smooth and with branches, the number of entering driftwood to the channel flow (individual or aggregate), in the presence and absence of bridge pier and with three levels of water flow in the upstream face of the bridge. Entering each case of driftwoods has been repeated 10 times and then bridge clogging probability has been determined. The results showed that in case of water level come to low cord of the bride's deck , the clogging probability a bridge with and without pier changed from 13% to 93% and 33% to 100 respectively. The results showed that lengthening and increasing the number of driftwood and trunk with branches, the presence of the pier, and finally the rising water flow will increases the clogging possibility.
