Investigation into sub five minute time of concentration in urban drainage design

Blyth, Mitchell (2014) Investigation into sub five minute time of concentration in urban drainage design. [USQ Project]


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Professional civil engineers hold an important responsibility to consider the impact of surface runoff in the design of developments of any type. Surface runoff from rainfall can produce large amounts of discharge through overland and flow corridors including creeks, rivers and can damage property, life and the natural environment. Effective management of surface runoff is necessary to reduce risk of potential damages. This research aims to investigate the impact of sub five minute time of concentration (Tc) in high density urban developments to determine if the current minimum Tc (as used Australia wide as part of hydrological calculations) is promoting inaccurate design solutions. The findings will allow conclusions to be drawn on realistic minimum Tc s for small urban design cases and recommendations for reducing the minimum Tc in the current Queensland Urban Drainage Manual (QUDM). This project looks to confirm that urban drainage guidelines in Australia are in touch with current urban site characteristics and that responsible design solutions are promoted in order to reduce risk to property and life. A mixed method research approach was used to investigate the project topic. Primary data was collected in the form of physically test Tc in residential sub catchments which was then compared against comparative modelling results replicating the same design scenarios Additionally, secondary data was collected in the form of a content analysis on the opinions and views of industry professionals and relevant authority representatives. Early results indicate that Tc of between two and five minutes is a very realistic Tc for urban sub catchments. Preliminary modelling has confirmed that a reduced Tc can equate to a higher catchment discharge. It is clear that because of the current findings catchment discharges have the potential to be underestimated because of assuming a minimum 5 minute Tc. This study should be considered during the consideration of urban water quality design principles and devices, which is an important aspect of development engineering responsibility. Additionally, as roofed catchments utilise use of downpipes for directing flow to the outlet point, it should be investigated whether current Australia Standard plumbing guidelines (Standards Australia,2003) recognize the feasibility of sub five minute catchment Tc. Investigation has confirmed that sub five minute Tcs are realistic and produce a higher flow
from catchments. For this reason it is suggested that drainage guidelines consider minimum Tc of less than five minutes (down to the shortest duration of available IFD data that is available for that particular area).

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Item Type: USQ Project
Item Status: Live Archive
Additional Information: Bachelor of Engineering (Civil) project.
Faculty/School / Institute/Centre: Historic - Faculty of Health, Engineering and Sciences - School of Civil Engineering and Surveying (1 Jul 2013 - 31 Dec 2021)
Supervisors: Brodie, Ian
Date Deposited: 08 Sep 2015 02:13
Last Modified: 08 Sep 2015 02:25
Uncontrolled Keywords: time of concentration, urban drainage
Fields of Research (2008): 09 Engineering > 0905 Civil Engineering > 090509 Water Resources Engineering
Fields of Research (2020): 40 ENGINEERING > 4005 Civil engineering > 400513 Water resources engineering

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