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LISEM 2.50 Baseflow 

Baseflow setup

In LISEM 2.50 baseflow can be added to the channel flow. Baseflow is mutually

exclusive with channel infiltration. If water enters the channel through groundwater, it

is assumed there is no infiltration at the same time. Baseflow can be selected in themain window:

Baseflow is calculated with 3 maps:1.  chanbaseflux.map: flux into the channel from wet perimeter in m3 /s 

2.  chanvini.map: Initial channel volume in m3: a map with the volume of water

that is in the channel for the event

3.  chanincrease.map: factor (0-1) of increase in chanbaseflux.map from the start

of the event to the end of the run. The increase in baseflux is triggered by the

fcat of channel inflow from overland flow to the chnnel. If this happens in any

channel cell, the baseflux is increased gradually with this factor. For instance

if the baseflux into the channel s 0.1 m3 /s and chanincrease has a value of 

0.01, the influx in LISEM is calculated as: 

channel volume = chan volume + baseflux * (1+increase) 

Baseflow simulation: step 1Because of the channel network length, dimensions, gradient and Manning's n, it

cannot be calculated before hand what the baseflow in m3 /s at the outlet will be from a

given "chanbaseflux". In each cell this amount of water is added and starts to flow

with the kinematic wave until an equilibrium is reached between inflow along the

network and outflow at the outlet. The 3 variables above are therefore totally

empirical.

As an example we take the Ganspoel catchment and assume a baseflow of 200 l/s is

measured at an outlet. On top of that a peak flow is measured. The two are separated

through some peakflow separation procedure. First we have to simulate a baseflow of 

200 l/s. LISEM. To do that we have to run he model without rain, but with a

"baseinflux". To run the model without rain, an rainfall input file is made with zero

rainfall for 1000 minutes:RUU CSF TIMESERIE INTENSITY NORMAL 1

station_1

0 0

100 0

1000 0 

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The three baseflow input files made are made from the channel mask map and given

constant values: chanbaseflux.map is 0.002 m3 /s, the initial volume chanvini.map is

2 m3

and the chanincrease.map is 0.001.

On the "output maps" page of lisem the channel volume has been added as map series

that can be reported. Select this series:

LISEM now simulates the following hydrograph:

A value of 198.0 l/s is reached after approximately 120 minutes. It takes about 100

minutes to reach an equilibrium situation.

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Baseflow simulation: step 2

We can now use the output channel volume as initial volume for he run. Copy in this

case map "chanvol0.150" from he results directory to he map directory and rename it

to chanvini.map. This will cause LISEM to start at the equilibrium situation so you

do not loose time to establish an equilibrium. Several trials show that the timestep has

very little influence on the equilibrium baseflow discharge value. It does however

have an influence on the overland flow and peak value.

With these maps we can now run LISEM with a rainstorm. The result looks as

follows: an increase in baseflow from 198 to 280 l/s is caused by the value 0.001 inchanincrease.map. The following graphs show the difference with and without

baseflow.

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