Flood Analysis Model

Development of the flood analysis computer model was among the 45 recommendations identified by the Delaware River Basin Interstate Flood Mitigation Task Force, formed at the request of the four governors, in its July 2007 action agenda.

The interagency team that developed the flood analysis model included staff from the U.S. Army Corps of Engineers (USACE) Hydrologic Engineering Center, National Weather Service (NWS), U.S. Geological Survey (USGS), and DRBC. Work on the flood analysis model began in August 2007 with $500,000 provided by the four basin state governors. Additional funds and in-kind services from USACE, NWS, and USGS totaled $285,000.

Intended Model Capabilities & Uses:

  • For the September 2004, April 2005, and June 2006 storm events, the model will be capable of evaluating effects of initial reservoir voids on downstream flood crests.
  • It will provide a tool to inform decision makers on the potential development of discharge mitigation plans for 15 basin reservoirs (13 upstream of Trenton, N.J).
  • It will enhance understanding of the impacts or benefits of reservoirs on basin hydrology.
  • Under different work efforts, the model and data sets will be capable of modification and improvement as new information and technology become available.

The Model WILL NOT:

  • be run in a real-time mode to direct operational changes during flood events. The model is intended to be used as a planning tool to inform decision makers.
  • be used for real-time flood forecasting. Real-time flood forecasting is already provided by the NWS.
  • determine policy regarding the use of reservoir storage for flood mitigation. Model results will be among the considerations that inform reservoir management for multiple objectives and policy decisions.
DRBC Releases Results of Flood Analysis Model

The commission’s review of the 2004, 2005, and 2006 storm events utilizing the new Delaware River Basin Flood Analysis Model demonstrated that widespread river flooding would have occurred in each instance regardless of the preevent storage condition in the upper basin reservoirs. These findings were presented in December 2009 to the DRB Interstate Flood Mitigation Task Force at a public meeting held in Flemington, N.J.

“The results of the flood analysis computer model developed by a federal interagency team for the commission, as well as a review of inundation mapping and structural surveys prepared by the U.S. Army Corps of Engineers, indicate that operational changes to reservoirs alone will not substantially reduce flooding if we experience storms similar to the three major events in September 2004, April 2005, and June 2006,” DRBC Executive Director Carol R. Collier said. “We believe the results support the earlier conclusion of the Interstate Flood Mitigation Task Force that no single approach will eliminate flooding along the Delaware River and that we must continue to focus efforts on implementing a combination of flood loss reduction strategies.”

The integrated flood analysis model was used to evaluate the effects of various reservoir pre-event storage conditions for downstream flood mitigation. Simulations indicated that the amount of additional flood mitigation that can be achieved with changes to operations of existing reservoirs is highly variable and dependent upon the storm event (timing, intensity, path), local topography and channel configuration, local runoff contributions and antecedent conditions.

DRBC will continue to work with basin reservoir operators to evolve spill mitigation programs that shift spilled water to managed water without diminishing the security of regional water supplies. Eleven million people in New York, New Jersey, and Pennsylvania depend upon New York City’s three Delaware Basin reservoirs for drinking water — either directly via an out-of-basin diversion or through releases to augment river flows downstream.