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Estimating the Time of Concentration in Small Urban Watersheds (Case Study: Tehran)

Ghazizadeh Hashemi, Sedigheh Alsadat | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 46450 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Tajrishy, Masoud
  7. Abstract:
  8. Hydrologic analysis in order to design the collection and transmission structures of urban runoff require some time parameters as input that the accuracy of these analysis is directly sensitive to the accuracy of these parameters. Among these parameters, the time of concentration is the most frequently utilized time parameter and numerous equations for estimating the time of concentration in urban watersheds have been proposed. The purpose of this study is to propose some equations to estimate the time of concentration of overland flow in small urban watersheds with pattern similar to arid and semiarid regions and investigate the effect of using LIDs on reducing the surface runoff. Experiments using rainfall simulator was conducted on a rectangular
    shaped test watershed(6m×1m)at the sharif university of technology. slope ranging is 0.5%-8% and rainfall intensity ranging is 22-40 (mm/hr). Surface types tested include nylon, permeable asphalt, concrete pavers with cement and permeable interlocking concrete pavers. A regression analysis was conducted to construct models for predicting time of concentration. Results where compared with 30 empirical equations in the literature. Among these equations Morgali (1965)-Linsely(1965) and Wong(2005)-Chen(1993)can predict the time of concentration acceptably well for nylon surface, Izzard and NAASRA (1986)are the best empirical equations respectively for permeable Asphalt and concrete pavers with cement. Based on results, the slope variable is the most important parameter in estimation of time of concentration for nylon surface and concrete pavers with cement and rainfall intensity is the most important parameter for asphalt surface. With using permeable interlocking concrete pavers as the best management practice it is found that for rainfall intensity ranging 22-40 (mm/hr) runoff coefficient is equal to zero and by making permeable 10-15 percent of surfaces in a watershed, significant reduction in runoff amount will occur in that watershed
  9. Keywords:
  10. Concentration Time ; Small Urbon Watershed Hydrology ; Overland Flow ; Rainfall Simulator ; Peak Discharge

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