فصلنامه مهندسی منابع آب
پیاپی 11 (زمستان 1390)

Scour a very complicated process, is one of the main factors in abutment destruction. Complication of stream pattern around abutments, and the variation of effective factors on scour,have lead to the develop of innumerous empirical equations, which have many restrictions due to the limited experimental conditions. Applicability of multilayer pereceptron(MLD)networks to prediction of the maximum scour depth was evaluated for abutments having vertical, winged and semi-circural walls. The ANN results were compared with the calculated values by an empirical equation suggested by Barbhuya and Dey (2004). Eight scenarios were defined using effective parameters and several networks with different important parameters to predict scour depth. Comparison of the results of different scenarios showed that the one, which used only two parameters and to predict scour depth around abutments was the most efficient indoing so. Results of sensitivity analysis indicated that the two parameters, and, had the most effect on the scour depth prediction around abutments. A comparison of the obtained results using the ANN model, and the empirical equation with the experimental data revealed that the ANN model presented more precise results than the empirical equation for scour depth prediction around abutments. Moreover, the ANN model is more applicable to the scour depth prediction around the obutments wilk vertical walls than the other 2 types of walls.

Evapotranspiration (ET) is one of the key elements in both energy and water balance studies. The satellite-assisted data acquisition method is instrumental in collecting the temporal and spatial ET variations at the regional scale. Evaporative fraction (EF) has been used by Roerink to simplify a procedure of ET derivation, S-SEBI, from the satellite acquired data. The EF data in this study were obtained using the reflectance and temperature colleted by the MODIS satellite over the Province of Isfahan in an 8-day time steps during the 2000-01 (dry year) and 2004-05 (wet year) periods based on the application of a triangle space concept between the land surface temperature and the surface albedo data. A simplified procedure to obtain the surface albedo has been mentioned. Spatial distribution of the EF has shown that during the 2004-05 period the EF values of the province, particularly in the western and central parts were significantly higher (at the 0.01 level) than those of the dry period. Furthermore, a linear relationship (r2=90%) was obtained the EF and soil water index, which may be considered as a water stress indicator.

The geotextile materials, initially used for soil conservation practices, have found a new application as ready-made filters in subsurface drainage projects. As clogging decreases the efficiency of filters, this phenomenon has to be investigated in detail before the widespread utilization of such materials take place. Necessary instruments were designed and manufactured to apply the modified ASTM-5101 standards to investigate the clogging potential of 300 and 500 gm-1 polyester fabric. Soil samples were placed on these fabrics underlain with gravel, concrete blocks, a supporting steel screen, uniform-sized steel beads, and a steel plate uniformly perforated. Infiltration tests were conducted under 1 and 4 hydraulic gradients. It was observed that the type and magnitude of contact between the geotextile and the substrata affects the drainage system. The direct contact between the granular particles or concrete blocks and the geotextile influences the cross-sectional area through which drainage takes place, and the clogging potential increases with the reduction in this area. Of these substrata only the steel beads and the perforated plate were used to simulate drainage under laboratory conditions.

Forecasting the probable maximum flood in a watershed is of vital importance in designing the spillways of the dams and estimating the volume of the reservoirs to be constructed on its respective river. As numerous watersheds are unguaged or lack reliable long-time data, many hydrologists have tried to develop theories based on the geomorphology of such basins. We simulated the direct surface run-off (DSRO) hydrographs for 4 rainfall events for the Shoor Indica Catchment (SIC) in the Khuzestan Province, I.R.Iran using the GIUH-based Clark-Nash models and compared them statistically with the instantaneous unit hydrograph (IUH) model option of the HEC-HMS package and the Nash IUH model using some commonly used objective functions. The geomorphological parameters of the SIC were evaluated as the Horton’s ratio from the topographic and hydrographic maps using the GIS package. Individual dynamic velocity parameter was estimated for each event using the regional relationships developed between the flow velocity and the excess mean rainfall intensity based on the river cross sectional geometry. Statistical comparison of the developed and the recorded hydrographs indicated that the GIUH-based estimations more precisely predicted the events than the IUH routine.

Water scarcity and the need to obtain the highest water use efficiency have encouraged installation of subsurface drip irrigation systems in the pistachio orchards in the hyper-arid southeastern I.R. Iran. As the economics dictate system design optimization, the water distribution pattern around drippers should be determined accurately. We used the highly regarded HYDRRUS-2D software, which simulates water, salt and heat transport under both saturated and under saturated conditions both during and after termination of irrigation, to estimate water distribution pattern around drippers installed at a depth of 30 cm in a sandy soil. Plastic mulching was also included in the treatments. The discharge rates were 2 and 4 liters per hour. The model satisfactorily simulated water redistribution in the soil profile 24 hours after irrigation termination (R2=0.92, RMSE=0.0192). Increasing the discharge to 6 liters per hour resulted in the reduction of the wetted bulb diameter. This will entail a reduction in the lateral spacing, thus an increase in the cost of the irrigation system. Covering the area above the drippers with plastic mulch reduced potential evaporative losses due to maintaining a higher relative humidity under the cover.

Occurrence of recurrent and prolonged meteorological droughts is the rule rather than the exception in the Land of Iran. These events, which are usually followed by hydrological and agricultural droughts, are the most disastrous natural phenomenon that may happen to any dryland. Associated food shortages that may end in famine have been repeatedly experienced in Africa during the past 50 years. Exponential population growth entails a higher demand for the limited water resources; therefore, the prudent management of these resources urges the water-related authorities to collect reliable data and analyze them thoroughly to plan and implement hydraulic structures and distribution systems. I (we?) used the threshold method (truncation level) to analyze the flow of 4 gauged rivers at the GharehGuni, Duab-e-Nowsood, Panbeh Daneh, and Pol-e- Adinan hydrometry Stations. Qά in the application of the threshold method signifies the minimum flow where ά percentiles of the data exceed that level. The interior criterion method was also used to eliminate the minor droughts and pool (cluster?) the same magnitude (dependence?) droughts. The results of frequency analysis indicated that the mean deficit volume was 17.7 million cubic meters, and the mean drought duration was 76 days. The best distribution models for the drought-related deficit volume were those of Johnson and Pearson, and for the drought duration were Johnson and exponential. The mean return period for the hydrological drought was 4 years based on these distribution models.

The application of statistical science, is developing increasingly in scientific researches. The aim of many research activities is to distinguish similar and different members in an assemblage. One of the useful tools to approach this goal is statistical methods. The Evan plain is located in southwest of Andimeshk City in Khuzestan province. Groundwater is one of the main water resources for agriculture, drinking and industry in this area. In this investigation, the statistical computations have been done on the basis of 18 ground water and 3 surface water sampels. For quality zoning of groundwater of the studied area, cluster analysis method has been used. On the basis of the acquired outcome,the aquifer has been divided into three zones. Hydrochemical study shows that sampels in the first group, have the best quality and in the third group, have the worst quality. The important impacting factors on groundwater chemical quality is identified as the interaction between water and geologic formations(the Lahbari member dissolution) and reversion exchange processes.

Removal of the basic fuchsin dye from the fabric manufacturing wastewater was studied using the batch method. The adsorbent was the rice husk, which is an inexpensive agricultural residue. Effects of pH, temperature, solution volume and duration of the reactions in the dye removal were investigated. The adsorbent, which was treated with a 3M sulphuric acid for 60 minutes, gave the best results. The best fitted isotherm of the process resembled that of Longmuir. The maximum adsorbent efficiency was 100 mg of fuchsin per 1 g of the acid- treated rice husk.