A NEWLY DESIGNED RECTANGULAR WEIR FOR FLOW REGULATION AT RIVER FORK THROUGH A PHYSICAL MODEL (CASE STUDIES OF KARKHEH/HUFEL/NISSAN STREAMS)

摘要

Specific hydraulic conditions prevail river forks, where streams need to be examined through physical and analytical methods. Given the numerous parameters effective in triple streams, it is impossible to establish a mathematical equation in which all parameters have been included. For this reason, previous studies in this regard mostly led to laboratory research with a newly developed physical-hydraulic model. After Hamidieh Diversion Dam near the city of Hamidieh, Karkheh River is divided into two streams known as Hufel and Nissan. At lower flow rates, Nissan makes up a greater share than Hufel due to steeper slope of the former. This study attempted to construct a hydraulic structure to appropriately divide water flow in Hufel. In the laboratory experiment, a flume with a 90-degree bend was used at Islamic Azad University of Ahvaz. Various experiments were conducted at different widths and heights. Furthermore, this model was simulated through CCHE2D, the results of which were compared against those of HEC-RAS physical and mathematical models. The results indicated that the weir height increases the deviation flow percentage to Hufel stream due to rising water level. Moreover, the deviation flow percentage to Hufel declined as the weir width increased due to falling water level. At Hufel, the installation of rectangular weir in different dimensions yielded minimum 34.3 and maximum 61.5c increase in flow rate. Moreover, the deviation flow percentage to Hufel increased by changing the deviation angle from 60° to 30° in both control modes as well as the weir. In normal mode without any weirs installed, however, there will be an increase in flow rate compared to the mode where a weir has been installed. This can be associated with the ^ow controlled by the weir. On average, the deviation flow rate increased by 2.8 in weir mode and 7.7 in weir-less mode. An increase in the Froude number from 0.21 to 0.38 led to lower average deviation flow rate by 19.3. Moreover, the results of simulation through CCHE2D demonstrated to be largely similar to those of physical model experiments. The results of simulation through HEC-RAS were also similar to those of the physical model. However, an increase in Froude number did not lead to a decline in deviation flow rate (i.e. it remained constant). This trend was inconsistent with the results of the physical model. Finally, the nearest structure for 60 flow rate deviation into Hufel had dimensions of (h/H=0.17 and b/B) =0.9.