A model has been developed for estimation of groundwater inflow to a stream reach from
observations of stream temperature, groundwater temperature, stream flow rate, and
standard weather parameters. The purpose of this model is to provide an estimate of
groundwater inflow rate for stream reaches where groundwater inflow is significant. This
information is useful for management of fisheries and urban development in watersheds
where stream temperature is a concern. In particular, the model was developed for use in
the Vermillion River, which has designated trout stream reaches that may be impacted by
development in the watershed.
The model estimates groundwater inflow rate from a stream reach heat budget, which
takes into account atmospheric heat flux, sediment-water heat exchange, and groundwater
inflow. The model requires the following data as input: stream temperature at the
upstream and downstream ends of the stream reach, stream flow at either end of the
reach, standard weather data, and no significant tributaries or inflows between the ends of
the reach. The model was applied to six reaches in the Vermillion River watershed.
Estimated groundwater inflow rates showed considerable spatial and temporal variability,
both seasonally and between the two years simulated (2006 and 2007). In North Creek,
groundwater inflow rate was 0.45 to 1.30 cfs/mile in 2007; in the upper Vermillion River
main stem for the same period estimated inflow rates ranged from 0.15 to 3.87 cfs/mile.
In the middle Vermillion River main stem, estimated inflow rates were unnaturally large
and more variable (0.39 to 11.1 cfs/mile); these estimates include significant tributary
inflow, which is lumped with groundwater inflow in the model. This, along with the
failure of the model for reaches or periods involving high stream flows, is the likely
source of the over-predicted groundwater inflow values. Simulations for lower South
Creek showed negligible groundwater inflow for 2006; results for lower South Branch
were very typical of a groundwater-fed stream, with relatively constant groundwater
inflow (around 1.0 cfs/mile) that fluctuated only slightly during periods of heavy rainfall.
A comparison of predicted groundwater inflow rates throughout the watershed for both
dry (baseflow) and high-flow conditions suggest the presence of shallow groundwater,
particularly in the lower reaches of the watershed.
The significant variability in groundwater inflow rate predicted by the model can be
traced to a number of factors, including data quality and sensitivity of the model to
groundwater temperatures, stream shading/sheltering, and especially to stream flow. An
extensive sensitivity analysis of the model is presented in this report, as well as an
analysis of available data, in particular, groundwater temperature. Limitations of the heat
budget approach to modeling groundwater inflow rate are also discussed and criteria for
application of the model are developed from the results of sensitivity analysis.
Janke, Ben; Herb, William R.; Mohseni, Omid; Stefan, Heinz G..
Estimation of Groundwater Inflow to the Vermillion River from Observations of Stream Flow and Stream Temperature.
St. Anthony Falls Laboratory.
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