Report No FR0318
TESTING OF THE STOCHASTIC RAINFALL GENERATOR (SRG)
The testing programme reported here, and earlier testing, show that the Stochastic Rainfall Generator (SRG) model can provide long series of hourly rainfall data representative of any site in the UK. These data can be used to drive sewer flow quality, quantity and river impact models for investigation and planning purposes.
To assess the characteristics of SRG rainfall and compare them to equivalent historical series.
To report on the accuracy of spill/storage predictions when SRG rainfall is used in simplified sewer flow models.
To test the accuracy of a disaggregation routine that converts hourly rainfall data to 5 minutely data which are suitable for models such as WALLRUS.
Rainfall time series provide the user with a means of assessing the hydraulic performance and pollution impact of sewer systems. They allow the frequency, rates, volumes and durations of discharges to be quantified.
The methods currently available for creating suitable rainfall input to models are inadequate. The SRG model is the result of a research programme designed to develop a model for the synthesis of rainfall time series (to a resolution of 5 minutes) for urban areas in the UK. The efficacy of this product needs to be tested in practical terms.
The recommended interim procedures for using the SRG are:
The disaggregation model provides an accurate method of producing 5 minutely values from either SRG or historical hourly rainfall data.
The SRG and disaggregation models should be packaged in a form which is applicable to users in the water industry.
One important aspect which has not been fully addressed is the most suitable technique for sampling from the rainfall record. Further guidance on this, and on how to use the SRG and disaggregation models, will have to be completed before the practising engineer can adopt the technique.
The SRG model is amenable to further development should practical application experience suggest it to be necessary. Such work should focus on the simulation capabilities in respect of rainfall events of return periods in excess of two years. The accuracy of the simulation parameters could be improved, to reduce the existing error band, with further development. In addition, an effort should be made to improve knowledge of the spatial variation in rainfall to the point where it can be incorporated into a practical design methodology.
VI RESUME OF CONTENTS
This report describes the testing undertaken on the SRG and disaggregation models.
Copies of the report are available from FWR, price £25.00, less 20% to FWR Members.