The State of Chesapeake Bay Watershed Modeling

The Chesapeake Bay Total Maximum Daily Load (TMDL) is a “pollution diet” for the Chesapeake Bay, which has long been impaired by excessive levels of nitrogen, phosphorus and sediment. The ongoing effort to restore the Chesapeake Bay reached its midpoint in 2017, halfway between the beginning of the current cleanup process (in 2009) and the target date of 2025 for implementing all of the strategies necessary to restore the health of the Bay. Also in 2017, Bay states started using a new model to assess pollution loads from the watershed.

This paper is intended to provide a very broad-brush assessment of how our understanding of TMDL progress might have been affected by the transition from one model to another. It does not delve into the technical differences between the two models, but instead focuses on model outputs.