You are here:
DEVELOPMENT OF THE VIRTUAL BEACH MODEL, PHASE 1: AN EMPIRICAL MODEL
Citation:
GE, Z. AND W. E. FRICK. DEVELOPMENT OF THE VIRTUAL BEACH MODEL, PHASE 1: AN EMPIRICAL MODEL. Presented at EPA Science Forum, Washington, DC, May 16 - 18, 2006.
Impact/Purpose:
A main objective of this task is to combine empirical and physical mechanisms in a model, known as Visual Beach, that
- is user-friendly
- includes point and non-point sources of contamination
- includes the latest bacterial decay mechanisms
- incorporates real-time and web-based ambient and atmospheric and aquatic conditions
- and has a predictive capability of up to three days to help avert potential beach closures.
Description:
With increasing attention focused on the use of multiple linear regression (MLR) modeling of beach fecal bacteria concentration, the validity of the entire statistical process should be carefully evaluated to assure satisfactory predictions. This work aims to identify pitfalls and misunderstandings of the statistical aspect of modeling. The importance of preliminary inspection of raw data, useful transformations, development of interaction terms, adjustment for time-series effects, identification of outliers, correlation studies, and model selection criteria are stressed. It is recommended the model selection process should be conducted using R2 and Cp statistic as joint criteria. The methodology is illustrated with real data of Huntington Beach, OH, in 2001. Dynamic modeling, as a new concept, is advanced for prediction purpose, as beach bacteria MLR models are in fact beach specific and time varying. This work also serves as a statistical basis for US EPA's public domain pathogen assessment software, Virtual Beach.