Determination of the Catchment’s Time-Area Diagram by Using Nash Instantaneous Unit Hydrograph Technique

Subject Areas : Article frome a thesis

T. سبزواری ¹ , SH. نوروزپور ² , M. جامیشی ³

1 - دانشگاه آزاد اسلامی، واحد استهبان، گروه مهندسی عمران، استهبان، ایران
2 - دانشگاه آزاد اسلامی، واحد استهبان، گروه مهندسی عمران، استهبان، ایران
3 - دانشگاه آزاد اسلامی، واحد استهبان، گروه مهندسی عمران، استهبان، ایران

Received: 2014-10-01 Accepted : 2014-10-01 Published : 2014-11-22

Keywords: Iran, Nash model, time-area, instantaneous unit hydrograph, Kasilian and Jafarabad, Ajay and Godawri, India,

Abstract :

Runoff prediction in un-gauged catchments is of importance for designing hydraulic structures. Some rainfall runoff models such as Clark requires time-area diagram of catchments. In this study, a novel method to derive time-area diagram using Nash’s instantaneous unit hydrograph model is presented. This method was compared to time-area equation already introduced by USACE (1999). The values of parameters n and k were obtained as n=4.7 and k=t_e/7.4. The results were validated using the existing time-area diagrams in Kasilian and Jafarabad, Iran and Ajay and Godawri, India. Moreover, the time-area diagrams derived from the new method were converted to direct runoff hydrographs using Clark model. The hydrographs were compared with observed ones. The average efficiency coefficients for Ajay and Godawri are 0.96 and 0.78, respectively. The errors in peak discharge estimation vary between 14 to 22 percent and 4 to 17.5 percent for Kasilian and Ajay, respectively.