مهندسی آبیاری و آب ایران
سال:1394 | دوره:6 | شماره:21 |تعداد مقالات:13

The accuracy of the classical methods to calculate evapotranspiration of plants for use in large areas may not be sufficient and therefore less useful. Thus, the choice of high-precision approaches, despite of restrictions ahead seems necessary. The purpose of this study is calculation of sugarcane evapotranspiration in Ahvaz, Khuzestan province using two methods. In method one, soil evaporation and crop transpiration were separately calculated using NDVI index extracted from MODIS images in. In the second approach, evapotranspiration was estimated using single crop coefficient approach known as FAO 56 method using available coefficients. Besides, crop coefficient values were calculated using SimDualKc software during entire growing season and FAO Penman-Monteith equation was worked out accordingly. The results were also compared to a lysimetric dataset. Correlation coefficient of ET estimations using single and dual crop coefficient approaches with lysimetric measurements were 0.954 and 0.885, respectively. A. On the other hand, the standard error for single coefficient approach was 67.29 and 29.34 dual approach. The results showed that the remote sensing-based dual coefficient approach provides acceptable estimations of sugar cane in the region. More studies are recommended for further scrutiny.

Morphology of rivers constantly changes due to their dynamic features, and these changes can negatively affect the structures in riversides, agricultural lands, etc. Meanders are considered as important indicators of environmental change. This study examines the changes of the sealing degree and meander shapes of the Kashafroud river using 1966 aerial photography, 1987 Landsat TM sensing images, and 2013 Google Earth images. In this study, morphological parameters of 16 meanders in a range of 11 kilometers along the Kashafroud river was determined for each period. The results of the paired t mean comparison showed that changes in the sealing degree ranging from 1966 to 2013 have a significant difference at level of one percent. To determine the effects of changes in some meanders parameters on sealing degree, multivariate linear regression model was used. The results showed that in case of change in the sealing degree, meanders reduce along the river. In addition, Spearman correlation analysis showed that changes in the parameters of sealing level and meander shape are strongly interdependent, so that there is a significant correlation between changes in sealing degree and meander shape at level of one percent. With increasing degree of sealing, meander shapes convert into U and  W shapes, and meanders tend to close. In meanders with reduced sealing degree, such as meanders number 2, 3, 11, and 12, the path will mainly change into a strait one, and a part of the river will be separated as bovine horn ponds.

Currently, agriculture is a crucial support for the national food security as well as economic sustainability. Among all factors, water is the most important and limited production factor. The simulation models of yield response to the water and irrigation water salinity are expected to play an increasingly important role in the optimization of water productivity (WP) in agriculture. AquaCrop model is a powerful and valuable tool for improvement of water management in the field and calculating water productivity. In this study, canopy cover, yield, biomass and evapotranspiration of cotton were simulated by using AquaCrop model under different levels of water salinity and deficit irrigation condition. The treatments included three levels of irrigation water salinity and three levels of irrigation depth. The experiment design was laid out with split-split plot in a factorial design with three replications. Results showed that the model can simulate different parameters with high accuracy (d>0.95). By reducing the amount of irrigation water and increasing of irrigation water salinity, simulation error was increased, but simulation results were in the acceptable range. For low levels of water and salinity stress, there was no very difference in the simulation results. AquaCrop model can be valuable tool in water and salinity management.