Hi All,
I am trying to justify the use of spreadsheet calculation instead of hydraulic model(Info Works or similar) for hydraulic analysis of a small exisiting catchment of sewer diameter 150mm. This query is in relation to a project in the United Kingdom.
The project involved hydraulic assessment of existing sewer network to understand the cause of internal flooding of a residential property, confirming the flood volume for a 30 year return period, which is a design standard as per the client and finding solution-most likely to be upsize or offline storage tank.
There was no hydraulic sewer model available or provided by the client for the cacthment. Due to the size of the catchment and the diameter of the sewer-150Ø, a good level of flow verification was not anticipated. As a result it was decided that a spreadsheet calculation would suffice to confirm the carrying capacity of the existing sewer without the need for the higher costs of generating a computer model.
A Flow survey was carried out for a period of 6 weeks. Two rain gauges were also installed to estimate the rainfall within the catchment during the survey.
I prepared a spreadsheet based on Rational Formula(for run off calculation) and Manning Equation(for pipe carrying capacity).
Using the flow survey data, i.e. litres per second,'Qobserved', for a particular rainfall intensity,'I', observed during the survey, I tried to play with the contributing area,A, and the co-efficient of run-off, C, to match the flow observed during the survey against the flow predicted by the spreadsheet,using Rational formula. I selected three rainfall events, short, long and medium duration. Once a good level of verification was achieved for all the three events which ensured that the model will predict reasonable run off data for the various storm duration, then I used design rainfall intensity, for a storm return period of 30 year to predict the flow expected in the system. Comparing the Qactual versus Qfull, I identified the undercapacity sewers and found solution accodringly. Qactual is the verified flow based on the rational formula for a 30 year return period and Qfull is based on manning equation.
I followed the above mentioned steps using a spreadsheet model without the need of generating a hydraulic model.
I am going to apprear for my professional review and I am expecting some difficult questions to be raised since my method may not be considered as traditional way of undertaking flood investigation.
I would like your view in this regard. Please ask me some difficult question so that I can prepare myself for the worst case scenario.
Regards
I am trying to justify the use of spreadsheet calculation instead of hydraulic model(Info Works or similar) for hydraulic analysis of a small exisiting catchment of sewer diameter 150mm. This query is in relation to a project in the United Kingdom.
The project involved hydraulic assessment of existing sewer network to understand the cause of internal flooding of a residential property, confirming the flood volume for a 30 year return period, which is a design standard as per the client and finding solution-most likely to be upsize or offline storage tank.
There was no hydraulic sewer model available or provided by the client for the cacthment. Due to the size of the catchment and the diameter of the sewer-150Ø, a good level of flow verification was not anticipated. As a result it was decided that a spreadsheet calculation would suffice to confirm the carrying capacity of the existing sewer without the need for the higher costs of generating a computer model.
A Flow survey was carried out for a period of 6 weeks. Two rain gauges were also installed to estimate the rainfall within the catchment during the survey.
I prepared a spreadsheet based on Rational Formula(for run off calculation) and Manning Equation(for pipe carrying capacity).
Using the flow survey data, i.e. litres per second,'Qobserved', for a particular rainfall intensity,'I', observed during the survey, I tried to play with the contributing area,A, and the co-efficient of run-off, C, to match the flow observed during the survey against the flow predicted by the spreadsheet,using Rational formula. I selected three rainfall events, short, long and medium duration. Once a good level of verification was achieved for all the three events which ensured that the model will predict reasonable run off data for the various storm duration, then I used design rainfall intensity, for a storm return period of 30 year to predict the flow expected in the system. Comparing the Qactual versus Qfull, I identified the undercapacity sewers and found solution accodringly. Qactual is the verified flow based on the rational formula for a 30 year return period and Qfull is based on manning equation.
I followed the above mentioned steps using a spreadsheet model without the need of generating a hydraulic model.
I am going to apprear for my professional review and I am expecting some difficult questions to be raised since my method may not be considered as traditional way of undertaking flood investigation.
I would like your view in this regard. Please ask me some difficult question so that I can prepare myself for the worst case scenario.
Regards