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TUTORIAL
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Online Tutorial
Exercise 3, Steady State Simulations

In this session, we introduce you to the following programs:

_simul - compute a steady state wetness or erosion hazard index
_overlay - ascribe spatially variable catchment properties to an element network
_redflow - redirect flow pathways in an element network

3.1 Let us begin with a simple steady-state wetness index computation; this assumes that evaporative loss is uniform across the catchment.
Perform the following tasks:

run _simul, using basename yahoo.
select option (1) to compute the steady-state drainage index.
use a uniform transmissivity value (T) of 3 m²/d and a uniform drainage flux value (q) of 0.1 mm/d; note results are written to file yahoo_a.ssd.
quit _simul and map results using _display.
in a seaparate window, view the header of file yahoo_a.ssd to see how the input parameters to this simulation were recorded.
run _simul twice more, using q values of 0.2 and 0.3 mm/d; results will be written to files yahoo_b.ssd and yahoo_c.ssd.
map all three .ssd files sequentially in _display.
quit _display.

3.1	Let us begin with a simple steady-state wetness index computation; this assumes that evaporative loss is uniform across the catchment. Perform the following tasks: run _simul, using basename yahoo. select option (1) to compute the steady-state drainage index. use a uniform transmissivity value (T) of 3 m²/d and a uniform drainage flux value (q) of 0.1 mm/d; note results are written to file yahoo_a.ssd. quit _simul and map results using _display. in a seaparate window, view the header of file yahoo_a.ssd to see how the input parameters to this simulation were recorded. run _simul twice more, using q values of 0.2 and 0.3 mm/d; results will be written to files yahoo_b.ssd and yahoo_c.ssd. map all three .ssd files sequentially in _display. quit _display.

3.2 Now let's try running a radiation-weighted wetness index computation; this assumes that evaporative loss is variable across the catchment.
Perform the following tasks:

run _simul, using basename yahoo.
select option (2) to calculate the Radiation-weighted wetness index.
run 3 different simulations using uniform T=3 m²/d and a uniform rainfall rate (R)=3 mm/d.
in the first run, specify a solar declination of 0 degress; this is indicative of equinox conditions.
in the second run, specify a solar declination of 10 degrees; this is indicative of winter conditions.
in the third run, specify a solar declination of -10 degrees; this is indicative of summer conditions.
use default values for all other parameters.
you should end up with three files, called yahoo_a.rwd, yahoo_b.rwd and yahoo_c.rwd.
run _display; sequentially map all three files.
quit _display.

3.2	Now let's try running a radiation-weighted wetness index computation; this assumes that evaporative loss is variable across the catchment. Perform the following tasks: run _simul, using basename yahoo. select option (2) to calculate the Radiation-weighted wetness index. run 3 different simulations using uniform T=3 m²/d and a uniform rainfall rate (R)=3 mm/d. in the first run, specify a solar declination of 0 degress; this is indicative of equinox conditions. in the second run, specify a solar declination of 10 degrees; this is indicative of winter conditions. in the third run, specify a solar declination of -10 degrees; this is indicative of summer conditions. use default values for all other parameters. you should end up with three files, called yahoo_a.rwd, yahoo_b.rwd and yahoo_c.rwd. run _display; sequentially map all three files. quit _display.

3.3 Now, let's see how to handle spatially variable soils and vegetation properties in a steady-state simulation. The first step is to digitise some polygons.
Perform the following tasks:

run _display, using basename yahoo.
map Catchment Boundary and Calculated streams.
digitise three separate polygons (covering roughly the top, middle and bottom regions of the catchment) in one file; the saved file should be written to yahoo.dat.d.
repeat the exercise, digitising 2 different polygons (this time covering the left hand and right hand sides of the catchment) to another file; this time the saved file should be written to yahoo.dat.e.
hide _display; ie. don't quit.

3.3	Now, let's see how to handle spatially variable soils and vegetation properties in a steady-state simulation. The first step is to digitise some polygons. Perform the following tasks: run _display, using basename yahoo. map Catchment Boundary and Calculated streams. digitise three separate polygons (covering roughly the top, middle and bottom regions of the catchment) in one file; the saved file should be written to yahoo.dat.d. repeat the exercise, digitising 2 different polygons (this time covering the left hand and right hand sides of the catchment) to another file; this time the saved file should be written to yahoo.dat.e. hide _display; ie. don't quit.

3.4 We must now co-register the digitised polygons on top of the catchment element network. This is done using program _overlay.
Perform the following tasks:

run _overlay, using basename yahoo; here we will ascribe spatially variable values of T to the catchment.
use yahoo.dat.d as the overlay file; three polygons should be detected.
ascribe (T) values of 3, 4 and 2 (m/d) to polygons 1, 2 and 3 respectively. use a default value of 4 (m/d); this is ascribed to catchment elements not covered by a polygon.
save results to file yahoo.tvals.
note that a file called yahoo_y.dat is also produced; this is a map of the various T values you have allocated to different parts of the catchment.
map file yahoo_y.dat using _display, using the Simulation button.
hide _display and view contents of file yahoo.tvals; note how the header records what input values were used for which polygons and how much catchment area is covered by each polygon.
run _overlay again, using basename yahoo; this time we will ascribe spatially variable values of q to the catchment.
use yahoo.dat.e as the overlay file; two polygons should be detected.
ascribe (q) values of 0.3 and 0.2 (mm/d) to polygons 1 and 2, respectively.
use a default value of 0.25 (mm/d).
save results to file yahoo.qvals.
map file yahoo_y.dat using _display.
note that this file has been overwritten; if you want to save these map files you must rename them before re-running _overlay.

3.4	We must now co-register the digitised polygons on top of the catchment element network. This is done using program _overlay. Perform the following tasks: run _overlay, using basename yahoo; here we will ascribe spatially variable values of T to the catchment. use yahoo.dat.d as the overlay file; three polygons should be detected. ascribe (T) values of 3, 4 and 2 (m/d) to polygons 1, 2 and 3 respectively. use a default value of 4 (m/d); this is ascribed to catchment elements not covered by a polygon. save results to file yahoo.tvals. note that a file called yahoo_y.dat is also produced; this is a map of the various T values you have allocated to different parts of the catchment. map file yahoo_y.dat using _display, using the Simulation button. hide _display and view contents of file yahoo.tvals; note how the header records what input values were used for which polygons and how much catchment area is covered by each polygon. run _overlay again, using basename yahoo; this time we will ascribe spatially variable values of q to the catchment. use yahoo.dat.e as the overlay file; two polygons should be detected. ascribe (q) values of 0.3 and 0.2 (mm/d) to polygons 1 and 2, respectively. use a default value of 0.25 (mm/d). save results to file yahoo.qvals. map file yahoo_y.dat using _display. note that this file has been overwritten; if you want to save these map files you must rename them before re-running _overlay.

3.5 Now let's run _simul again using spatially variable T and q values we have created.
Perform the following tasks:

run _simul, using basename yahoo.
select option (1).
enter yahoo.tvals for FILENAME OF TRANSMISSIVITY.
enter yahoo.qvals for FILENAME OF DRAINAGE FLUX.
save results; these should be written to yahoo_d.ssd.
view results using _display.
in a separate window, view the header of file yahoo_d.ssd to see how the input parameters to this simulation were recorded.

3.5	Now let's run _simul again using spatially variable T and q values we have created. Perform the following tasks: run _simul, using basename yahoo. select option (1). enter yahoo.tvals for FILENAME OF TRANSMISSIVITY. enter yahoo.qvals for FILENAME OF DRAINAGE FLUX. save results; these should be written to yahoo_d.ssd. view results using _display. in a separate window, view the header of file yahoo_d.ssd to see how the input parameters to this simulation were recorded.

3.6 It's time to return to _simul and run the routines relevant to erosion processes. Let's begin with the stream power computations.
Perform the following tasks:

run _simul, using basename yahoo.
select option (3), uniform excess stream power.
specify a uniform rainfall excess of 240 mm/d.
results should be written to file yahoo_a.usp.
view yahoo_a.usp using _display; use colour table power.ctb.
run _simul again, using basename yahoo.
select option (4), variable excess stream power.
base the simulation on steady-state wetness.
use a uniform transmissivity value (T) of 3 m²/d and a uniform drainage flux value (q) of 0.3 mm/d.
specify a uniform rainfall excess of 240 mm/d.
results should be written to file yahoo_a.vsp.
view yahoo_a.usp using _display; use colour table power.ctb.

3.6	It's time to return to _simul and run the routines relevant to erosion processes. Let's begin with the stream power computations. Perform the following tasks: run _simul, using basename yahoo. select option (3), uniform excess stream power. specify a uniform rainfall excess of 240 mm/d. results should be written to file yahoo_a.usp. view yahoo_a.usp using _display; use colour table power.ctb. run _simul again, using basename yahoo. select option (4), variable excess stream power. base the simulation on steady-state wetness. use a uniform transmissivity value (T) of 3 m²/d and a uniform drainage flux value (q) of 0.3 mm/d. specify a uniform rainfall excess of 240 mm/d. results should be written to file yahoo_a.vsp. view yahoo_a.usp using _display; use colour table power.ctb.

3.7 Next, we turn to the erosion hazard index; this can be based on either uniform or excess stream power, underpinned by either the regular wetness index or the radiation weighted wetness index.
Perform the following tasks:

run _simul, using basename yahoo.
select option (5), erosion hazard index.
base the simulation on variable excess.
base the simulation on steady-state wetness.
use the same T, q and rainfall excess values as in the last simulation.
specify a b1 value of 0.1 and a b2 value of 10.0.
specify a surface cover (Cr) of 0.1; results should be written to file yahoo_a.ehi.
repeat the above, specifying a Cr value of 0.9; results should be written to file yahoo_b.ehi.

3.7	Next, we turn to the erosion hazard index; this can be based on either uniform or excess stream power, underpinned by either the regular wetness index or the radiation weighted wetness index. Perform the following tasks: run _simul, using basename yahoo. select option (5), erosion hazard index. base the simulation on variable excess. base the simulation on steady-state wetness. use the same T, q and rainfall excess values as in the last simulation. specify a b1 value of 0.1 and a b2 value of 10.0. specify a surface cover (Cr) of 0.1; results should be written to file yahoo_a.ehi. repeat the above, specifying a Cr value of 0.9; results should be written to file yahoo_b.ehi.

3.8 Now, let's return to _stripgen for a moment. Let's create a simple grid of elements that we can use to simulate the effects of line sources and sinks
Perform the following tasks:

run _stripgen, using option (0) and basename mesh.
create a 50 x 50 element network with a 1 x 1 m element size.
allocate a slope of 0.4 to all elements.
specify aspect 180 degrees, latitude -30 and lowest contour 50 m.
run _display, using basename mesh.
plot the element network.
using the Search button, detect the location of contours 13 and 42, just to get a feel for where these lie.
quit _display.
using the editor, create a line source/sink file called mesh.lines.
specify a line source of 1 m³/d between elements 25 and 35 on contour 42.
specify a 100% efficient line sink between elements 5 and 15 on contour 13.
run _simul twice, using basename mesh, and option (1).
in each case, assume uniform values of T=1 m/d and q=5 mm/d.
do one run without and one run with the line source/sink file specified; the two results files should be called mesh_a.ssd and mesh_b.ssd.
compare the two results files using _display.

3.8	Now, let's return to _stripgen for a moment. Let's create a simple grid of elements that we can use to simulate the effects of line sources and sinks Perform the following tasks: run _stripgen, using option (0) and basename mesh. create a 50 x 50 element network with a 1 x 1 m element size. allocate a slope of 0.4 to all elements. specify aspect 180 degrees, latitude -30 and lowest contour 50 m. run _display, using basename mesh. plot the element network. using the Search button, detect the location of contours 13 and 42, just to get a feel for where these lie. quit _display. using the editor, create a line source/sink file called mesh.lines. specify a line source of 1 m³/d between elements 25 and 35 on contour 42. specify a 100% efficient line sink between elements 5 and 15 on contour 13. run _simul twice, using basename mesh, and option (1). in each case, assume uniform values of T=1 m/d and q=5 mm/d. do one run without and one run with the line source/sink file specified; the two results files should be called mesh_a.ssd and mesh_b.ssd. compare the two results files using _display.

3.9 Next we turn to flow diversions; these can be imposed in a _simul run if we first run program _redflow. But first we must digitise the diversions using _display.
Perform the following tasks:

run _display, using basename mesh
map the element network.
digitise three diagonal lines (ie. polygons of two points each) in a single file.
using the editor, check that the resulting file, mesh.dat.a, contains 3 'polygons'.
run _redflow, using mesh.dat.a as the polygon file; a message should appear indicating that 3 polygons of two points each.
note that _redflow produces a file called mesh.red.
run _simul again using uniform values of T=1 m/d and q=5 mm/d but also supplying mesh.red as the redirection of flow file.
check that results are written to mesh_c.ssd.
compare mesh_a.ssd and mesh_c.ssd using _display.
for clarity, overlay the file mesh.dat.a to see where the flow diversions were placed; use thick black lines.

3.9	Next we turn to flow diversions; these can be imposed in a _simul run if we first run program _redflow. But first we must digitise the diversions using _display. Perform the following tasks: run _display, using basename mesh map the element network. digitise three diagonal lines (ie. polygons of two points each) in a single file. using the editor, check that the resulting file, mesh.dat.a, contains 3 'polygons'. run _redflow, using mesh.dat.a as the polygon file; a message should appear indicating that 3 polygons of two points each. note that _redflow produces a file called mesh.red. run _simul again using uniform values of T=1 m/d and q=5 mm/d but also supplying mesh.red as the redirection of flow file. check that results are written to mesh_c.ssd. compare mesh_a.ssd and mesh_c.ssd using _display. for clarity, overlay the file mesh.dat.a to see where the flow diversions were placed; use thick black lines.

TUTORIAL
Exercise 1 | Exercise 2 | Exercise 3 | Exercise 4 | Exercise 5

last modified on 16 August 1997