Using Gage-Adjusted Next Generation Weather Radar to Improve Wastewater Conveyance System Condition Assessments and Modeling

The use of computer models to estimate the response of a wastewater conveyance system to probabilistic design rainfall events (e.g. 25 year 24 hour storm) is common practice. It is also common to implement a program of wastewater flow and rain monitoring to calibrate these computer models. The purpose of this paper is to demonstrate how weather radar can be used to improve these processes.The typical result of a flow monitoring program is an approximation of the relationship between rainfall and wastewater flow. The two components, wastewater flow and rainfall volume, are equally important.Modern flow, when operating properly, can provide accurate flow measurement. Modern rain gages are also reasonably accurate. However, they only provide data from an extremely small area, the area of the gage opening. Typical flow monitoring programs incorporate several rain gages to estimate the total rainfall across the study area. Historically, standard techniques such as Theissan Polygons or Inverse Squared Distance methods must be used to approximate the rainfall distribution between the rain gages over the study area.Gage-adjusted NEXRAD data provides an alternative to these historical methods. NEXRAD weather radar provides an excellent representation of the spatial distribution of rain in given storm. However, this representation is only qualitative. Radar alone cannot accurately predict actual rainfall intensity.Gage-adjusted radar combines the spatial distribution information of NEXRAD radar with the intensity information of rain gages. This combination of radar and rain gage data should provide an improved approximation of the spatial distribution of rainfall when compared to standard gage-only techniques. Using this rainfall data in conjunction with flow monitoring data should provide improved approximations of the relationship between rainfall and inflow to wastewater collection and conveyance systems.Gage adjusted radar also offers the benefit of estimating rainfall volumes occurring between rain gages. In some cases this rainfall may be much more intense than the rain falling on the rain gages, this fact would be missed by gage-only rain fall measurement strategies.