Effects of tanks on peak flow rate of runoff

Leeuwe, G.W. van (2015) Effects of tanks on peak flow rate of runoff.

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Abstract:The increasing infill in the suburbs of Adelaide results in higher peak flow rates of runoff. This may lead to flow rates of runoff that are beyond the capacity of the drainage system. One way of preventing this from happening might be the use of detention or retention tanks. This report has investigated what the hydrological effects of detention and retention tanks are on the peak flow rates of runoff. Two types of storm simulation techniques are used for this. One type was applying a 19 year continuous series of rainfall data to the models and the other type was applying design events with a duration of 5,10,15 and 20 minutes. A single allotment and a street with 19 allotments have been modelled in this report. To see what the effect are of infill the models are both made in two variations. One is the pre-developed variant and the other is the redeveloped variant. This last variant is after infill and has a much higher impervious area. The redeveloped allotment has been equipped with detention or retention tanks of varying sizes. Also the street has been equipped with single detention or retention tanks of varying sizes and the allotments on the street have been equipped with the detention or retention tanks of varying sizes. The flow rates of runoff with an average recurrence interval (ARI) of two years have been calculated for the continuous series and the peak flow rates of runoff generated by the design storm events. On the allotment scale detention tanks have a much higher impact on the flow rate of runoff with a two year ARI than the retention tanks. This is just for the continuous series, when applying the design events the detention and retention tanks turn out to have almost the same impact on the peak flow rates of runoff. The detention tank reduces the flow rate of runoff for both storm simulation techniques back to the level of the pre-developed allotment. For the design events the retention tanks do this too but during the continuous series none of the retention tanks can lower the two year ARI flow rate of runoff to the level of the pre-developed allotment. On the street scale the detention tanks per allotment and the single lump sized tank work very well for both storm simulation techniques as well. The two year ARI flow rate of runoff from a pre-developed street is almost the same as from a redeveloped street equipped with a single lump sized detention tank or where the allotments in the street are equipped with detention tanks. Lump sized retention tanks perform much worse and have almost no effect on the two year ARI flow rate of runoff. The street where all allotments are equipped with retention tanks still has a higher two year ARI flow rate of runoff than the pre-developed street. The lump sized retention and detention tanks perform very well during a design event, better than the distributed tanks. This is because the volume of rainfall is lower than the volume of the tanks, except for the 38 kL variant. The method of calculating the two year ARI flow rate of runoff turned out to be not ideal. The few highest flow rates of runoff occurring during the 19 years’ time series had an impact on the two year ARI flow rate of runoff that was higher than it should be. As a result of this the calculated the flow rate of runoff with a two year ARI was higher than it should be. By ignoring the highest few results the two year ARI flow rate of runoff became much more realistic. To calculate an accurate two year ARI flow rate of runoff more research has to be done.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering BSc (56952)
Link to this item:http://purl.utwente.nl/essays/68745
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