As a part. of the study of dissolved oxygen (DO) dynamics in Holland Lake, the
underlying flow, temperature and material.transport were simulated. In this report the
simulation results are being presented. The simulation was two-dimensional to capture
the interactions between the shallow and deep subbasins of the lake in addition to the
water/air heat and momentum exchange. The vertical cross section in which flow
veloCities, water temperatures and· material concelltrations were simulated extended from
the westerly shallow ~ubbasin through Jhe deep basin to the northeasterly shallow
subbasin. Flow velocities were induced by wind shear on the lake surface and· by
buoyancy forces due to temperature differences. Temperatures were in response to heat
exchange through the water surface by radiation, convection and evaporation.
The two-dimensional model developed for Holland Lake.computed velocities and
water temperatures at 5 minutes intervals. Weather conditions (data) observed during the
period from July 1 to August 1, 1999 were imposed as boundary conditions. The flow
field calculated for the month of July 1999 was then used to investigate. how a material
such as dissolved oxygen or dissolved organic carbon is transported from the shallow
subbasin to the deep subbasin. These simulations show the intrusion of bottom waters
from the shallow subbasins to the metalimnion of the deep basin. This mechanism can
explain the rapid DO. depletion of metalimnetic waters in the summer because the bottom
waters in the shallow subbasins are known to be low in DO and rich in detrital carbon.
The simulation results also show that the low water temperatures associated with
groundwater intrusion are largely responsible for the movement of oxygen-poor water
from the shallow subbasins into the deep subbasin.
The selection of alternative supplemental aeration techniques will benefit from the
simulations results. The depth at which aeration systems should be placed, and their
location will be guided by the model results.
Metro Region Fisheries, Minnesota Department of Natural Resources
Stefanovic, Dragoslav L.; Stefan, Heinz G..
Simulation of Water Temperature, Flow and· Dissolved Oxygen Exchange Processes in Holland Lake.
St. Anthony Falls Laboratory.
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