THREE DIMENSIONAL MODELING OF FECAL COLIFORM IN THE TIDAL BASIN AND WASHINGTON SHIPPING CHANNEL, WASHINGTON D.C.

摘要

Fecal coliform is a widely used bacterial indicator in the US and around the world. Fecal coliform impaired water has high possibility to be polluted by pathogenic bacteria. The Tidal Basin and Washington Shipping Channel in Washington DC are on the Total Maximum Daily Load (TMDL) list due to the high fecal coliform level. To support TMDL development, a three-dimensional numerical model of fecal coliform was developed using the EFDC framework. The model calculates the transport of fecal coliform under the influences of flap gate operations and tidal elevation. The original EFDC code was modified to calculate the die-off of fecal coliform under the impact of temperature and layer averaged solar radiation intensity. The watershed contribution is expressed as stormwater inflow and the load carried by the runoff. Model results show that fecal coliform vary strongly in space in both the Tidal Basin and Washington Shipping Channel. The stormwater only impacts a small area around the stormwater outfall in the Tidal Basin and the impact is negligible in the Washington Shipping Channel due to dilution. The water from the Potomac River may affect the fecal coliform level in the area close to the flap gate in the Tidal Basin. The fecal coliform level in the Washington Shipping Channel is mainly controlled by the fecal coliform level in the Anacostia River, which is located at the open boundary of the Washington Shipping Channel. The potential sediment layer storage of fecal coliform was analyzed and it was found that the sediment layer fecal coliform level could be much higher than the water column fecal coliform level and becomes a secondary source under high bottom shear stress condition. The developed model built solid connection of fecal coliform source and concentration in the water column and can be used to develop and evaluate TMDL.