Projects & Programs
Hydrological Simulation Program-Fortran Modeling for Port of Seattle Drainage Master Plan (Third Runway), Washington
PNNL staff modified the Hydrological Simulation Program-Fortran (HSPF) model for management of stormwater quantity and quality required as mitigation for the Master Plan Update (MPU) improvements for the Seattle-Tacoma International Airport. This plan is used to identify stormwater management standards that are administered through the Clean Water Act. For three main watersheds encompassing the airport, an existing and a proposed condition model were developed. The difference between these two modeling scenarios quantifies the impact that MPU development has on sub-basin runoff.
HSPF allows continuous simulation of complex drainage networks and is especially appropriate for western Washington, where hydrology is characterized by runoff from sequential storms rather than single storm events. The model calculates runoff from the airport drainage basins to compare the effects of airport runoff downstream of the proposed MPU projects.
The modeling was implemented to identify effectiveness of new and existing stormwater detention facilities for stormwater and water quality control and to test flow regimes in Miler and Des Moines creeks. The facilities were first designed with the King County Runoff Time Series (KCRTS) model; subsequently, an HSPF model was used for more detailed design. The project design at each facility was verified by examining compliance flows to meet the Level 2 King County stormwater discharge standards using log-Pearson Type III analysis by HSPF post-processing software ANNIE and SWSTAT.
Modeling was also used to enhance stream low flows by incorporating infiltration into stormwater facilities. These facilities would supplement low flow with stored stormwater to enhance surrounding wetland habitats and to minimize the maximum duration of open water at detention ponds to 24 hours following the end of the two-year storm event.
Project Highlights:
- PNNL staff modified the HSPF model for management of stormwater quantity and quality required as mitigation for Sea-Tac International Airport Marine Protected Area improvements in compliance with the Clean Water Act
- The HSPF model and post-processing software were applied to examine compliance flows to meet King County Level 2 discharge standards using log-Pearson Type III analysis
- PNNL staff recalibrated the HSPF model using new data and new gages to satisfy Washington State Department of Ecology concerns
- HSPF modeling helped the Port of Seattle in reducing storage volume of several big stormwater detention facilities, resulting in savings of several million dollars
- HSPF modeling significantly helped in legally defending the project before the Washington State Pollution Control Hearings Board during the lawsuit brought by the "Airport Communities Coalition."