Journal of Water Resources Engineering
Year:2017 | Volume:10 | Issue:32|Papers Count:8

Bridge is the most important structure in road building where the route crosses a river. Local scour around bridge piers built over a curve in a river is an important reason for its failure. Correct placement of ripraps around the base of piers protects the streambed from scouring by the turbulent flow, which could undermine the pier, resulting in the settlement that terminates in the bridge collapse. Roughening the smooth surface of the pier base and using rough-hewn stones for the riprap is a logical method for their protection. Controlled laboratories experiments were conducted in a 180 degree bent Plexiglas flume where two cylindrical piers had been installed in the bend, one with smooth and the other with the roughened surface. Treatments consisted of two bulk densities and four diameters for the riprap with only one flow rate of freshwater. Results indicated that stability of the riprap depended on the Froude number at the failure threshold, and the relative diameter of the riprap. Furthermore, the presence of roughness on the pier base surface enhanced its stability.

The water demand is rapidly increasing due to economic and social development and population growth. In keeping with the freshwater restrictions, the allocation of water needs to take a comprehensive view and integrated management approaches are vital in different sectors. This study was implemented in the Gamasyab Watershed, which is the main sub-watershed of the Karkheh River. Much of the watershed is located in the Province of Kermanshah, while its headwaters are in the Province of Hamadan. In this study, the WEAP Software was used as a powerful tool to assess an integrated water resources management for investigating an applied management in the Gamasyab Watershed, and evaluating the effect of upstream dams on the performance of the Bistoon reservoir. Long term hydrological data were used to model the water resources and demands in the watershed. The water demands were obtained using the data of population, agriculture, and industries, and the environmental flow requirements determined using the Montana Method. Different management scenarios were defined in accordance with the current conditions and watershed development perspective. The results indicated that the demands maybe fully met under the present conditions; however, the demands will exceed the available water in the Bistoon Reservoir if the planned dams come in to operation. Its regards to the importance of considering the principles of integrated water resources management, the results of this study may be used with certainty by the researchers and decision-makers in the water sector in Iran.

Many algorithms and methods have been applied, so far, in order to operate reservoirs, optimally. Recently, the Cuckoo Optimization Algorithm (COA) as a new Evolutionary Algorithm (EA) has been utilized for solving a number of bench mark functions and real problems, and high performance and efficiency has been reported for solving difficult optimization problems. The main objective of the current study was an assessment of the COA efficiency in water resource systems in order to extract optimal operation policy for a reservoir with hydropower application. An application of this algorithm in a thirty-year operation of the Karun4 Reservoir was evaluated. The results were compared with those results of Genetic Algorithm (GA) outcomes. The results showed that the COA has a greater ability to reach optimal solution in comparison with the GA. The mean values of the objective functions were 6.34 and 9.28 for the COA and GA algorithms, respectively. Furthermore, the obtained results by the COA showed less difference to the global optimum.

Water contaminants concentration is important based on water usage in different sections such as domestic, agriculture, and industry, and etc. QzlOuzanRiver has a wide range of potentialities in a variety of economic fields including water transmission, agro-industry, development of organic farming, tourism, and etc. The river reaches the Sefidrood Reservoir after crossing 8 provinces. Recently, an increasing trend in water salinity has been observed in tributaries. In this regard, the water quality in the river and four of its tributaries has been monitored. In order to determine contribution of each pollutant sources, a mathematical model, the Qual2K, has been applied. Results indicated that the contribution of flow in four tributaries, which four of its tributaries are located in the Province of Zanjan, to water salinity of the QzlOuzan River, is significant. The Goorani River with 28.6 percent and the Chesb River with 0.3 percent of pollution load contributed the highest and the least salt load of the QzlOuzan River, respectively.

Worldwide, soil erosion by water is one of the most important factors in land degradation, and is a critical environmental hazard of modern times. The present study aims to estimate the average annual specific production of sediments and the intensity erosion map at two sub-basins of the DEZ Watershed, south-west of the Lorestan Provine, Iran, namely Absorkh and Keshvar using the Erosion Potential Method (EPM), the Geographical Information System (GIS) and the Remote Sensing (RS) techniques. The total area of these sub-basins is 19920 hectares. Nearly 60 percent of the area has negligible vegetation cover or bare land. The study area can be categorized into slight, moderate, high and very high erosion zones. The amount of soil erosion and sediment yield predicted by the EPM model were 3203.718 and 2204.844 m3.km-2.y-1, respectively. The areas located at the middle and southern parts of the watershed were subjected to significant erosion due to the geology formation and vegetation cover and probably competent geological formations, while the area at the northern part was relatively less eroded because of verdant land cover. The measured sediment yield of the watershed at the Keshvar Hydrometric Station was approximately 2223.178 m3.km-2.y-1, which confirmed the satisfactory performance of the EPM Model.

Turbidity currents are the main process for the transport and deposit of sediments in reservoir, especially in the deepest part near the dam, where vital structures such as power intakes and bottom outlets are located. The existence of an obstacle in such current can cause a decrease in the velocity and thickness of the second turbidity current which, occurs after the obstacle. In this study that was carried out as a two-dimensional experimental study, the effect of a solid obstacle, its height on the vertical distribution profiles of the velocity, when there is an abrupt decreasing in the bottom slope, was investigated. Separate non-dimensional equations for the vertical distribution of velocity in different cases were developed. The coefficient of the non-dimensional equations were compared with each other. Results indicated that the existence of an obstacle can reduce the velocity of the turbidity current, which passes the obstacle, about 20%-50%, and also can reduce the discharge of the current by increasing the relative height of the obstacle from 0.0091 to 0.273 by about 20% -60%, respectively. This effect on turbidity current’s velocity and discharge would be increased by the increasing the height of the obstacle. The results also indicate that the highest change in the current discharge occurred in the jet region of the velocity profile.

The latest investigations have demonstrated the climate change is definitely happening. As the climate change strongly impacts the global temperature and rainfall, and their variabilities, it highly affects water resources, thus the environment, as well as agricultural and industrial activities. In this study, the climate change impacts on the Gavehrud basin runoff during the 2016-2099 periods was investigated using the outputs of the HadCM3 GCM model under the A2 scenario. The SDSM (statistical downscaling model) was used for the statistical downscaling of temperature and rainfall. For simulation of the future runoff using the downscaled data, HYMOD model was used. The HYMOD was calibrated using the DREAM model for considering its parameters uncertainty. The SDSM results indicated a considerable change in temperature and rainfall, in the future as compared with the historical time horizon of 1989-2000. The mean temperature increase in the future would be about 5% to 8.5%, while the mean rainfall decrease would be about 3% to 5%. The results of this study indicated that a 5% to 23% decrease in the future average runoff in comparison to the historical values.

Time of concentration is one of the main topics of physiographic and hydrology studies in watersheds, and it has relatively large impact in calculation of other hydrology parameters, especially flood peak discharge. Moreover, it is used to derive the unit hydrograph of watershed. Fractal geometry can be used as a qualitative tool in order to examine the geomorphology of rivers and also modeling of complex natural phenomena. The most important feature which is analyzed about the phenomena is the fractal dimension that has a great importance to understand and predict the behavior of river changes. This article is aimed to find relationships for time of concentration based on fractal dimension using the production of fractal triangular unit hydrograph of Walnut Gulch watershed. Accordingly, all sub-watersheds and waterways of Walnut Gulch watershed were separated using the GIS software, image of sub-watersheds were digital image processed and the fractal dimension of waterways were calculated using box counting method. Then, by fitting the curve of watershed fractal dimension with the concentration time, which had been calculated by the Kirpich method, a new time of concentration relation was obtained based on the fractal dimension. Finally, fractal triangular unit hydrograph was developed using the new time of concentration. Results showed that the developed triangular unit hydrographs had a relatively appropriate match with NRCS triangular unit hydrograph.