User's guide of Proceessing Modflow 5.0

Processing Modflow 91
For the case that h is greater than H , Q is negative. It means that water flows from the
RIV RIV
aquifer into the river and is removed from the groundwater model. When h has fallen below the
bottom of the riverbed, the rate of leakage through the riverbed is given by eq. 3.20.
Q RIV ' C RIV @(H RIV & R BOT ) h#R BOT
The value C of a river-cell is often given by
RIV
C RIV ' K·L·W
M
(3.20)
(3.21)
where K is the hydraulic conductivity of the riverbed material, L is the length of the river within
a cell, W is the width of the river and M is the thickness of the riverbed. If C is unknown, it
RIV
must be adjusted during a model calibration.
MODFLOW < Streamflow-Routing
The Streamflow-Routing package (Prudic, 1989) is designed to account for the amount of flow
in streams and to simulate the interaction between surface streams and groundwater. Streams are
divided into segments and reaches. Each reach corresponds to individual cells in the finite-
difference grid. A segment consists of a group of reaches connected in downstream order.
Streamflow is accounted for by specifying flow for the first reach in each segment, and then
computing streamflow to adjacent downstream reaches in each segment as inflow in the upstream
reach plus or minus leakage from or to the aquifer in the upstream reach. The accounting scheme
used in this package assumes that streamflow entering the modelled reach is instantly available
to downstream reaches. This assumption is generally reasonable because of the relatively slow
rates of groundwater flow.
Streamflow into a segment that is formed from tributary streams is computed by adding the
outflows from the last reach in each of the specified tributary segments. If a segment is a
diversion, then the specified flow into the first reach of the segment is subtracted from flow in
the main stream. However, if the specified flow of the diversion is greater than the flow out of
the segment from which flow is to be diverted, then no flow is diverted from that segment.
In the Data Editor, you can press the right mouse button and specify the following required
cell values in the Streamflow-Routine Package dialog box (Fig. 3.23). The specified cell values
will be shown from left to right on the status bar.
< Segment is a number assigned to a group of reaches. Segments must be numbered in
downstream order. The maximum number allowed in PMWIN is 25.
3.6.1 MODFLOW