Chesapeake Bay Program Watershed Model Scenario Output Database

The Watershed model is an application of HSPF (Hydrologic Simulation Program -
Fortran ) run on a unix workstation. The model divides the 64,000 square mile
Chesapeake Bay drainage basin into 87 model segments. Each segment contains
information generated by a hydrologic submodel, a nonpoint source submodel, and
a river submodel. The hydrologic submodel uses rainfall, evaporation, and
meteorological data to calculate runoff and subsurface flow for all the basin
land uses including forest, agricultural lands, and urban lands. The surface
and sub surface flows ultimately drive the nonpoint source submodel, which
simulates soil erosion and the pollutant loads from the land to the rivers. The
river submodel simulates flow and associated pollutant loads from the land
through the lakes, rivers, and reservoirs to the Bay.

Model Output, stored in the online database, includes a ten year annual average
of both edge-of-stream and delivered nutrient and sediment loads to the bay.
Nitrogen, phosphorous, and sediment (NH3, NO3, ORGN, TN, PO4, ORGP, TP, TSS)
loads are estimated from agricultural, urban, and forested lands, as well as
from point sources, septic, and air deposition.

The database provides modeled nutrient and sediment load data under different
management scenarios for the purpose of developing tributary strategies.