Journal of Water Resources Engineering
Year:2009 | Volume:2 | Issue:3|Papers Count:8

In geophysics, especially river engineering, any processes may be considered occurring in several time scales. For example, while sediment or contaminant transport is studied, it is preferred to follow the problem in each second. On the other hand, the unstable morphology of a river is a problem of decades and centuries. Identification of the presence of scaling in the river flow processes has been a challenging problem in hydrology. While large number of unidentified dominant variables affect river flow, it is common to consider it as a stochastic process. However, recent studies indicate that by employing nonlinear deterministic and chaotic dynamic concepts, the river flow process could easily become an outcome of a deterministic system with only a few dominant variables. This paper attempts to investigate river flow in four time scales (15 minute, hourly, daily and weekly) utilizing the flow data recorded for the Uncompahgre River in Colorado, USA. The correlation dimension was used as an indicator to distinguish between chaotic and stochastic behavior. It is concluded that the flow was completely chaotic in small time scales (15 min), while it tended to be more stochastic in large time scales.

Erosion and transport of suspended and bed loads are of the most complex and important problems of hydrodynamics inherent in the study of water supply projects. As the artificial neural networks (ANRs) are endowed with two fundamental characteristics of learning based on empirical data (the potential and ability to generalize) and parallel structuralism, they are one of the most important versions of artificial intelligence in which, by drawing inspiration from human brain, the desired data are saved in the networks. In this study we not only designed the ANRs applying the error back scattering method and stability analysis, and the convergence of control parameters of its ring systems, but also implemented it to assess its performance in predicting the rate and distribution of sediments in the Ekbatan Reservoir. Moreover, we employed the linear and multiple regression techniques for the same purpose and compared the results with those of the ANRs. The regression coefficients RSME and R2 indicated that the ANRs are the most accurate method to predict the rate and distribution of sedimentation in a reservoir. Furthermore, the linear regression is preferred over the multiple regression due to the mechanism of error distribution in non-linear calculations.

Qanats of Arsenjan City, 130 km northeast of Shiraz, I.R. Iran, are the most important source of supplying water for its vast irrigated farm fields. Of these, the Katak Qanat, with the base flow of 20 l/s, situated 7.5 km west of the city, was singled out for our study. The physical characteristics of this qanat, namely its geology, discharge, bed slope, water surface slope, the length of wet (tareh–kar in Farsi) and dry (khoshkeh–kar in Farsi) galleries were measured using the field survey techniques. The collected data were analyzed to assess the possibility of damming its base flow during the off season when it is wasted. The preliminary results confirm our hypothesis that this is a practicable technique in water resources management in a large expanse of Iran where water is the country’s economic mainstay.

Drought is one of the most important natural hazards that affects many countries all over the world and causes socio-economic, political and cultural problems. Awareness of and ability to forecast drought may help to reduce its consequences. In this research some geostatistical methods including simple kriging (SK), ordinary kriging, inverse distance weighing (IDW) of 1 to 5 degrees for drought severity mapping in the Province of Fars in 2007 using the percentage of normal index. Comparison of results based on RMSE and MAE showed that Using the SK method resulted in the lowest values (RMSE=11.44 and MAE=6.94), the refores it was selected as the most appropriate method for drought severity mapping in the mentioned year. Based on the prepared map, the province of Fars suffered showed two classes of drought, severe and very severe, drought which covered 21.58 and 78.42, respectively, of the Province area.

The Karkheh River, which originates in the Zagros Mountain Ranges, is the third largest river in western I.R. Iran, flows through the Khusistan Plain and drains into the Persian Gulf. The Karkeh Earth Dam, which is 3030 m long and 128 m high with an initial capacity of 7 billion m3, was constructed during the 1992-2001 period. The conglomerate and mudstone strata outcrops at the dam site provide the needed strength and water tightness for the foundation and abutments. The stability analyses under both static and dynamic conditions have been performed employing appropriate software programs, and slope displacement of the up-and downstream shells has been verified. The great value of water in dry lands dictates that impoundage should start as soon as the construction stages permit. The development of pore water pressure (PWP) in the clay core due to the seepage of the impounding water, which is supplemented by the loading of the fill material, enhances the probability of hydraulic fracturing of the core. PWP development in the core during impoundage was simulated using the CA2 Software. The output data were agreeably similar to the instrument readings. We conclude that both the PWP and fill loading significantly impact the stability of the Karkheh Earth Dam core.  

The hydraulics of bottom rack intakes was 3D numerical simulate and some of its important specifications like the wetted rack length were studied. The bottom rack intake is a hydraulic structure designed for achieving robust function of water intakes in mountain regions. Computational abilities of CFD techniques were employed to simulate the flow hydraulics on this structure. To achieve this, the software Fluent 6.3.26 and finite volume method are used. The water intake and the bottom rack were simulated according to the physical model built Vienna University of Technology by Dorbir et al. in 2003. Analytical computations performed by former researchers were also compared to the numerical results in addition to the physical ones. This comparison shows outstanding adaptation and relevant relationships between the numerical CFD results and the analytical and physical model findings. The optimum wetted rack length is studied according to the bottom rack bar sections and spacing.

In this research, from data of 26 hydrometric station records and l-moment approach, regional and stational flood frequency of Dez basin was analyzed. For identifying homogeneous regions, Ward hierarchical cluster method was used. The appropriate number of homogeneous regions was determinate from nonhomogeneity test and discordancy measure. The Dez Basin was divided into three homogeneous regions. In these regions parameters of the regional frequency distribution were evaluated by the L-moment ratios. The L-moment diagram, goodness of fit test, and plotting position methods were used for the selection of appropriate distribution and plotting position formula. Generalized Extreme-Value distribution and Chegodieve plotting position formula is appropriate for region A, generalized logistic distribution and Greengurten plotting position formula for region B and Generalized Extreme-Value distribution and Greengurten plotting position formula for region C were selected. The relative root mean square error (rRMSE) between observed and estimated data, in all stations, in high return periods is small and in small return periods is vicversa. Regional models evaluated for determination of flood discharge magnitude in different frequency by linear and multiple regression method. 

Fuse-plug is a very important appurtenance to irrigation and other water supply systems; therefore, many theoretical and experimental investigations have been performed to design and construct a better structure. However, employing the numerical modeling in the design of this structure has been relatively neglected. The BREACH numerical model along with the finite difference method was used to solve the hydraulic and sediment transfer equations, particularly for calculating the time required for the complete wash out of a fuse-plug containing a vertical or an oblique argillaceous core. Construction of nomograms facilitated calculation of the wash out time of the plugs with vertical or oblique argillaceous cores. It was observed that the fuse-plug with the core slope of 120o and the m/H ratio of 0.4 (m: thickness of core, H: high of dyke) offers the best design. Employing the numerical models (BREACH, SEEPW, and STABL) revealed that the optimum compaction percentage for the fuse–plug was 84%. Results also confirmed that ripraps better protect the downstream shell of the fuse plugs against erosion than vegetative covers.