فصلنامه علوم و مهندسی آبیاری
سال سی و ششم شماره 3 (پاییز 1392)

In the present study, monitoring, prediction and zoning of drought in Khuzestan province were investigated using time series provided by Standard Precipitation Index (SPI) and Markov Chain. The obtained results showed that in all stations, based on the SPI index and during a six-month period, the almost normal condition has the highest frequency and is existent in between 33 to 42 percent of all cases. Probability of passing from a specific condition to the same condition in sequential periods is extremely high, and in turn, the probability of passing from the dry condition to wet condition and the other way around is quite low. In average, the possibility of reaching a balance between dry, normal and wet periods in stations of the region are 30.8, 36.5 and 32.7 percent respectively. The average continuity of drought periods predicted on a 6-month scale varied from a minimum of 3 months in Paye- pole station to a maximum of 4.6 months in Shohadaye-Behbahan Dam station. It is predicted that in the next ten years, Khuzestan province will be dealing with 35.5 months of drought.

Density current is one of the most important phenomena that affect sediment processes and water quality in reservoirs and other water resources. Variation of cross sections in natural channels is inevitable and affects hydraulic parameters of density currents. The recent study evaluates the water entrainment of density currents in converging reaches. The experiments were conducted in a flume with 6.0 m length, 60 cm depth and 72.5 cm width by using three converging degrees (8, 16 and 25) and with different discharges and concentrations in hydraulic modeling laboratory of Shahid Chamran University of Ahwaz. Equations were formulated to estimate the water entrainment in converging reaches with different angles and finally an equation was proposed for converging, constant and diverging reaches using experimental data which were gathered from other researchers.

The limitation of fresh water resources in the most parts of the country has necessitated the use of unconventional water resources. Wastewater is one of these unconventional sources, however the environmental impacts of wastewater reuse should be carfully considered. The present study aimed to examine the effect of the rubber powder to absorb the heavy metals of lead, zinc and manganese in laboratory scale. The batch tests to evaluate the absorption equilibrium time were conducted in constant pH of 5.5 and the soluble metal concentration equal to 100 mg per liter. The adsorption kinetic results showed, the removal efficiency of lead, zinc and manganese were 67.2, 74.3 and 39.9 percent, respectively. Time to reach equilibrium for zinc and manganese were 180 and 120 minutes, respectively. But lead does not reach equilibrium during the 180 minutes of testing time. Also, the adsorption isotherms tests were performed for these metals and the data were fitted with the linear, Langmuir and Freundlich models. The results showed that the Freundlich adsorption model with regression coefficient equal to 99 percent was the best compliance with the laboratory results.

The local scour around a bridge pier in recent years has been widely studied by different authors. They proposed different methods to control the scouring depth. Until now, many of authors have studied to find out how to control scouring around a pier along the straight stream. However, it may be required to construct a bridge across a bend of a river due to the some constraints. The objective of this research is to study a scour pattern around such piers on a bend due to the fact that there may be a difference between a flow pattern on a straight stream and the meander. Thus, this study tries to check whether the use of collar and cable together effects on scouring around bridge pier constructed on river meander. The results showed that as cable diameter increases and pitch of helix decrease, scouring depth will be decreased. The reduction of scouring depth by using cable does not exceed from 59% and alone collar reduces scour depth up to 55%. Using collar and cable together is reduced scour depth to 69.7%.

Limited water resources needed for agricultural and non-agricultural water supply has caused major problems. Rain is considered as one of the available water resources. Therefore, to predict and estimate the amount of rainfall in any month or year and for each catchment area as one of the most important atmospheric parameters, of particular importance is the efficient use of water resources. For predict rain can be used of the time series. The aim of this study is the most appropriate model to estimate the rain, so that using the 30-year (1971-2001) monthly rainfall and after determining the model parameters and seasonal and non- seasonal SARIMA model and using the statistical software Minitab end of the period of ten years of monthly rainfall amounts (2002-2011) in the rain stations - located in North Khorasan Province Babaaman survey were estimated. The monthly rainfall amounts predicted by the statistical distribution, was calculated. By comparing the estimated values with actual values corresponding monthly rainfall was result of models with more are parameters the order autoregressive or moving average is more than 1 shows different values for the following years. But these differences are also limited to a few years to exceed the maximum number of model parameters. The correlation coefficients between actual and predicted values at station 0.64 were studied. The regression equation obtained can be used to correct moderate amounts of rainfall stations used in forecasting.

Reliable prediction of boundary shear force distributions in open channel flow is crucial in many critical engineering problems such as channel design, calculation of energy losses and sedimentation. During floods, part of the discharge of a river is carried by the simple main channel and the rest is carried by the floodplains located to its sides. For such compound channels, the flow structure becomes complicated due to the transfer of momentum between the deep main channel and the adjoining floodplains that magnificently affects the shear stress distribution in floodplain and main channel sub sections. In the present study experiments were conducted in a compound rectangular section with different discharges and 3 different aspect ratios. The results showed that in each aspect ratio, shear stress increases by increasing the water level. It is also shown that by increasing the aspect ratio, shear stress is decreased significantly.

Evaporation is one of the important factors in water loss from dam reservoirs. Therefore, the accurate prediction highly helps the reservoir planning and optimum water usage. In this study, using the recorded pan data the evaporation trend is determinded by seasonal Mann-Kendal Test, then the reservoir evaporation is predicted by the time series analysis. After determining the stationary situation of data , the models SARIMA(0,0,1)×(2,0,2)12 , SARIMA(1,0,0)×(1,1,1)12 and SARIMA(1,0,0)×(2,1,2)12 are fund to be suitable for stations Behbahan, Dez and Pay-pol respectively. The results show that due to the data limitation and the predominat assumptions in Time Series method, these models are reliable for the short term prediction.

Prediction of groundwater level fluctuations is an essential step for management, appropriate planning and efficient use in arid and semi-arid regions. According to the existing information, the general trend of groundwater hydrograph represents declining trend and continuous falling of groundwater level during the last years in the Marvast plain. In this study, integrated time series and neural network models was used to predict the fluctuations of groundwater levels in the Marvast plain. For this purpose, the groundwater level data of 1987-2009 time period were provided and different integrated time Series models and artificial neural network were fitted to the data. The efficiency and accuracy of ARIMA model for predicting future values was assessed using the Root Mean Square Errors (RMSE) and Akaike information criterion. The results of different ARIMA states showed the ARIMA (1, 1, 0) is the best-fit time series model. Three train functions of Levenberg-Marquardt, Resilient Back Propagation and Scaled Conjugate Gradient were used for the feed-forward back propagation neural network. The results showed Levenberg-Marquardt function is the best train function to predict groundwater level. Comparing the results of ARIMA (1,1,0) and neural network feed-forward with back propagation algorithm using RMSE, MAE and CE statistics showed neural network model is relatively superior to the Integrated Time Series model.

Variation of intake hydraulic conditions and channel flow discharge cause unsteady flow in irrigation network. To evaluate the performance of the function of the intake structures, study of their hydraulic characteristic is necessary. Therefore in present study a computer model has developed in which the unsteady flow equations (Saint-Venant equation) have been disceretizied using finite difference and Crank-Nicolson method. Water surface elevation at any junction is calculated applying matrix properties and influence line technique implicitly. Different kinds of control structure such as intake and check structures have been introduced to model as internal boundary condition. Combining energy and momentum equations (E-M method) the flow from the gate of check structure at every time steps is calculated. After model verification, the main channel of the Miandarband irrigation network with 27 kilometer length from 15 to end with five radial gates check structures, seventeen turnout structures and five Neyrpic intake was simulated and different kind of optional performance have been studied.

Practices of water table management to reduce the drainage volume and nitrate losses have caused to ensure the sustainability of irrigation and protection of associated ecosystems over the past decade. In this research, two water table management methods including free conventional subsurface drainage and controlled drainage was applied in the 63.41 ha field of the Imam Khomeini's Sugarcane Agro-industry, located in Khuzestan Province. Experimental treatments were a free drainage treatment (FD) and two controlled drainage treatments with water table controls set at 90 centimeter (CD90) and 70 centimeter (CD70) below the soil surface. Drainage outflow, nitrate nitrogen concentration, water table elevation and applied irrigation water amount were measured during study period. With the usage of controlled drainage, the total drain outflow from CD70 and CD90 area was decreased 62.48 and 48.98%, respectively compared with CD. The total of nitrate-nitrogen losses in drain outflow in CD70 and CD90 treatments was 58.43% and 47.25 %, respectively less compared with CD. The total applied water was decreased in CD70 and CD90 treatments 25.64 and 27.67 % compared with CD. The results of this study indicated that large-scale application of controlled drainage systems lead to significant reduction in drainage volumes and nitrate loads as well as increase the potential for economic and environmental benefits compared to unmanaged systems in arid and semi-arid regions of Iran.