جستجوی مقالات مرتبط با کلیدواژه « Physico » در نشریات گروه « آبخیزداری، بیابان، محیط زیست، مرتع »

In water quality modeling، erosion and deposition of cohesive sediments are processes of paramount importance. Existing classic and processed based models can not predict the erosion flux and its trend properly. In order to evaluate the ability of the existing models، the Partheniades model as the most frequently used and Govindaraju and Winterwerp-Vankesteren Models as the most recent ones are evaluated by a set of laboratorial experiments. The sediment and water samples have been extracted from Sefidrud Dam reservoir bed. The test results have shown that despite the Partheniades model prediction، the results strictly depend on consolidation period and the erosion flux has decreasing exponential behavior with respect to time. Moreover، it has been found that the flux values are 2-7 times less than the model results. Govindaraju model is sensitive to consolidation but the temporal behavior and the quantity of the erosion flux is almost similar to Partheniades model. Winterwerp-Vankesteren model results show much less values than the latter two models but the curve behavior is the same as the latter models. It seems that these models are not able to simulate the variation of flux with time both in short term and long term. The laboratory results have shown that erosion flux has an exponential decreasing behavior with respect to time and consolidation. So if one can correlate the erosion flux with physico-mechanical parameters of bed sediments، such as Shear strength، dry density، cohesion، Gelling concentration and entrainment rate which are time and depth dependent، it will be possible to derive the more sophisticated physically and process based models.

The healthy condition of the Taleghan River in upstream of the Taleghan dam was studied in order to better understanding the role of benthic invertebrate bio-purification faced to waste water inflows to the river in several parts. Sampling was started from the fall of 2005 and continued to the winter of 2006. In this way, five stations were selected using a pre-sampling strategy based on similarity and dissimilarity coefficients among stations, consisted of 10 sampling points along the river was carried out. The stations 1 and 2 are situated before station 3, where the waste water of Shahrak town enters directly to the river flow. Stations 4 and 5 are located after the entrance of the waste water. Distance between stations remaining constant of 1 Km. All of 13 families belonging to 6 orders were then determined consisted of insect larvae among them Ephemeroptera, Trichoptera and Diptera were dominant and omnipresent. The results showed significant fluctuations of nitrogen compounds from fall to spring passing by winter. Nitrogen pollutant compounds decreased from 1.9 to 1.5 mg.L-1. Chironomids worms as indicators of high trophic current water decreased significantly (P<0.05) from station 3 to 5. Parallel to this reduction of polluted indicators, the healthy state of the river increased in Hilsenhoff Family Biotic Index (FBI). The index was ameliorated from the entrance of Shahrak town waste water from 4.3 to 3.85. Both of these values indicate high qualities but smooth amelioration of the quality. This work consider that the healthy state of the Taleghan river is not in high risks of quality in the moment, but could be easily balanced to poor qualities, if human activities around this basin do not take in account purification plants before rejection to the river.