Oceanography 200, Spring 2008 Estuary Study Sheet
V. In-class activity (5 pts.)
1. [1 pt.] Using the map at left, select from the
locations labeled A-E to identify the 4 major basins
in Puget Sound using the map below.
Main Basin _____D_______
Whidbey Basin ___C_______
South Sound _____E______
Hood Canal _____A_______
2. [4 pts.] For each of the 4 categories of estuary listed
below, match the most suitable location on the map
(A–E), and explain what about the basin shape and
circulation at that location in Puget Sound make it
fit into that category.
Type of estuary
Letter on map
Explanation
Salt wedge
C
(To be a salt wedge, a basin must have a high input of fresh
water and weak tidal mixing.) 2/3 of the freshwater entering
Puget Sound enters the Whidbey Basin. Tidal mixing is
weakened because the incoming tide must turn 180˚ to enter
the basin.
Fjord
A
(A fjord is essentially a salt wedge with a sill at its mouth that
reduces tidal intrusion of deep water.) Hood Canal is long,
narrow, and deep, with several rivers and a sill at its mouth.
This results in strong vertical stratification, and very weak
tidal exchange and low oxygen in deep water.
Partially mixed
D
(For a basin to be partially mixed, it must have roughly equal
influences of fresh water input and tidal mixing.) The Main
Basin is fed by several rivers and is open to tidal currents
from Admiralty Inlet, so the two drivers have roughly
equivalent influence.
Well mixed
B
(To be well mixed, a basin must have a low input of fresh
water and strong tidal mixing.) Admiralty Inlet has no
significant river input. It is narrow and directly exposed to
incoming tides from the ocean and is underlain by a series of
shallow sills. This combination of factors creates strong
mixing.
