Estimation of Freshwater Runoff into Glacier Bay, Alaska and Incorporation into a Tidal Circulation Model

Freshwater discharge is one of the most critical parameters driving water properties within fjord estuarine
environments. To date, however, little attention has been paid to the issue of freshwater runoff into
Glacier Bay, a recently deglaciated fjord in southeastern Alaska. Estimates of discharge into Glacier Bay
and the outlying waters of Icy Strait and Cross Sound are therefore presented. Existing regression
equations for southcentral and southeastern coastal Alaska are applied to Glacier Bay to arrive at the
estimates. A limited set of acoustic Doppler current profiler (ADCP) measurements generally support the
predictions of the regression equations. The results suggest that discharge into the bay ranges from a few
hundred to a few thousand m3 s�1 during a typical year. Peak discharges can be much higher, approximately
10,000 m3 s�1 for the 10-year flow event. Estimates of the seasonal variation of discharge are also
obtained and reveal a broad peak during the summer months.
The hydrologic estimates are then coupled with a barotropic tidal circulation model (ADCIRC – ADvanced
CIRCulation model) of Glacier Bay waters. This coupling is achieved by treating the entire coastline
boundary as a non-zero normal-flux boundary. Numerical simulations with the inclusion of runoff allow
for the estimation of parameters such as the estuarine Richardson number, which is an indicator of
estuary mixing. Simulations also allow for the comparison of Lagrangian trajectories in the presence and
absence of runoff.
The results of the present paper are intended to complement a comprehensive and recently-published
dataset on the oceanographic conditions of Glacier Bay. The results will also guide continuing efforts to
model three-dimensional circulations in the bay.