Overcoming Spatial-Temporial Rainfall Variation using Rainfall RADAR

It is nearly impossible to accurately quantify rainfall variability across a stormwater or sewer catchment using discrete point rainfall measurements. The variability across the catchment can be significant depending on the catchment location and surrounding terrain and the nature of the meteorological processes producing the rain. For many hydrological applications, such as sewer inflow and infiltration modelling, extrapolation and interpolation of point rainfall measurements is standard practice and is one of largest unknowns in the model. Decisions about the techniques used for extrapolation, as well as the adequacy of the conclusions drawn from the modelling results, depend heavily on the magnitude and the nature of the uncertainty involved. 

In this paper we will outline our recent investigation using accurate short range radar in an attempt to quantify how standard point rainfall measurement and extrapolation techniques effect sewer model calibration and eventually options resulting from the model. In the highlighted case study we completed a detailed sewer model calibration using current industry best practice. As a second work stream we obtained radar data from the University of Auckland’s short range mobile radar unit for the entire monitoring period. We then tested the model calibration using the “true” rainfall distribution over each sewer-catchment as identified from the radar and commented on the variation in model calibration parameters and how the different rainfall distribution effects the perceived system performance and potential options analysis.