Radar Rain or Rain Gage Data? Utilizing Multiple Sources of Rainfall Data in Collection System Modeling

Wastewater collection system models, developed by Philadelphia Water in EPA SWMM (Environmental Protection Agency Storm Water Management Model), represent the collection systems that convey combined and sanitary flow to the water pollution control plants. These models are the foundation of Green City, Clean Waters, Philadelphia’s plan to reduce stormwater entering the combined sewer system through the implementation of green infrastructure, and thus reduce wet weather overflows. The collection system models are driven by rainfall, and hydrologic parameters have been validated with data from a flow monitoring program. Historically, rainfall data from a network of rain gages throughout the City of Philadelphia has been used to drive the models. However, radar rainfall data has been acquired to cover the extent of the model domain, and has been used in recent model validation exercises. This paper will present how model validation with radar rain data compares with the validation results using data from the rain gage network. Accurate and reliable rainfall data is important because it is the primary data input to the models. The modeled runoff results will only be as reliable as the input data. The paper will also discuss how these datasets can be analyzed and the value of utilizing multiple sources of rainfall data to improve model prediction.