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Title: Cobbins Brook : Onda model - investigation of flood flows and levels, full report
Author: National Rivers Authority Thames Region
Document Type: Monograph
Flood alleviation channel improvements were carried out along the Cobbins brook in the urbanised area of Waltham Abbey in 1979. Serious flooding occurred in 1987 and there have been two bankfull events since then. It was decided to use the mathematical model, ONDA, to evaluate the existing channel capacity and assess the increase in channel capacity obtained by raising banks, constructing a by pass pipe and widening the channel. The ONDA model would evaluate the maximum discharge of all structures, investigate the afflux of the flume, evaluate the capacity of the Honey brook tributary and reestimate the peak flow for the 1987 event. There was no in bank flow level calibration data available at the start of the study. Water level recorders were installed during the study and hopefully useful proving data will be forthcoming in the near future to confirm the results and conclusions. During the study it emerged that the flume appeared to drown at high in bank flows. The main results of the study were that existing channel capacity is 17 cumecs along Broomstick Hall Road. With a very large by pass pipe the capacity can be increased to 21 cumecs. By widening the channel by 2m the capacity can be increased to 26 cumecs. The maximum discharges under the road bridges were found to be 26 cumecs at Parklands, 26 cumecs at Broomstick Hall Road and 24 cumecs at Honey Lane. It would appear therefore that in order to contain the 50 year return period target level of protection of 28.9 cumecs in an environmentally and economically acceptable way a combination of measures will be needed including upstream storage and raising bank heights.
Publisher: National Rivers Authority
Publication Date: 1990
Publication Place: Reading
Subject Keywords: Flood controlRiver levelHydraulic engineeringMathematical modelsBrooks
Geographic Keywords: LondonLondon catchment
Extent: 97
Total file downloads: 265

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