Chapter 5 ....continued
Dynamic Water Balance Modelling

Sections 5.9 to 5.12

5.9

Solute data inputs
The solute transport module can only be invoked when using the Newton-Raphson (NR) soil moisture accounting scheme. It is activated in the .par file, built using Topog_simgen.

As mentioned earlier, when the solute transport option is invoked, the soil depth nodes (.nodes) file must include a column specifying the initial solute concentration at each node (see section 5.7.1). These values are ignored when initial values are read from a restart .fin file.

5.10

Overland flow data inputs
The kinematic wave overland flow option is only invoked when running Topog_dynamic on a sub-daily timestep. It is activated in the .par file, built using Topog_simgen.

The only additional input required to run this model is a value for the surface roughness parameter (n); see eq. 5.18. This can be a single value, applied to the whole catchment, or a spatially distributed one, allocated to various catchment elements using Topog_overlay. The value, or filename of values, is listed in the .par file.

5.11

Sediment data inputs
The sediment transport option can only be invoked when running Topog_dynamic on a sub-daily timestep, in association with the kinematic wave overland flow option. It is activated in the .par file, built using Topog_simgen.

Data supporting the sediment transport option must be provided in the .veg file (see section 5.8.1) and the .soil file (see section 5.6.2).

5.11.1 Input data associated with vegetation type

In the .veg file, three parameters must be set. These are as follows:

Variable Units Typical values Description
C1
or
fmgu 		(0-1) 0-1 fraction of exposed soil, where 1 denotes soil is completely exposed and 0 denotes soil is completely covered; only needed when sediment transport option is invoked; see eq. 5.23
c
or
canopa 		(0-1) 0-1 fraction of canopy cover, where 1 denotes full canopy cover and 0 denotes no canopy cover; only needed when sediment transport option is invoked; see eq. 5.24
H
or
canoph 		m 0-30 distance from ground to gravity centre of plant canopy; only needed when sediment transport option is invoked; see eq. 5.26

Note that these three parameters can be spatially variable across the catchment, with unique values being ascribed to each vegetation type represented.

5.11.2 Input data associated with soil type

In the .soil file, eight parameters must be set, though not all of these are necssarily used by the model. The eight parameters which must be set are:

Variable Units Typical values Description
rs kg/m3 1800 - 2650 specific weight of sediment; see eq. 5.30
d50 mm 0.002 - 0.02 median sediment diameter; see eq. 5.30
h (0-1) 0-1 sediment entrainment ratio; see eq. 5.29; parameter not used if using Yang's unit stream power theory
rw kg/m3 1 specific weight of water; see eq. 5.32;
wi mm/s 0.003 - 30.0 fall velocity of median diameter sediment; see eq. 5.28; parameter not used if using Yang's unit stream power theory
Ae 1/N.m 1000 - 5000 soil erodibility factor; see eq. 5.21; parameter not used if using Yang's unit stream power theory
g . . gamma factor; see eq. 5.32; parameter only used if using Yang's unit stream power theory
b . . beta factor; see eq. 5.32; parameter only used if using Yang's unit stream power theory

Note that these eight parameters can be spatially variable across the catchment, with unique values being acsribed to each soil type represented.

5.12

Spatial variation inputs
Several types of landscape properties can be made spatially variable in a Topog_dynamic catchment analysis. These include:

To spatially distribute such values across a catchment, you must provide an overlay file, generated using program Topog_overlay . Input to this program is a polygon map, usually obtained by digitising a series of polygons in Topog_display. Topog_overlay co-registers the element network and the polygon map, so that each element is assigned the value of the polygon in which it lies.

Overlay files have three columns of data. The first column contains the element number. The second contains the polygon number that the element is associated with, and the third column contains the attribute ascribed to that element. This can be an index or a value.

In the case of vegetation type or soil profile type the attribute ascribed to each element an index (integer value). The integer value is a file number index, where a value of 1 means refer to the first relevant file in the .par file, built using Topog_simgen.

In the case of LAI and Manning's n roughness values, this is a discrete value (say 1.7 or 0.1).

5.12.1 A typical vegetation type polygon file

Part of a typical vegetation type overlay file is shown below. In this instance, elements 1 and 2 lie within polygon number 3 and are assigned an integer value of 1, corresponding to the first .veg file listed in the .par file. Similarly, element 3 lies within polygon number 2, which corresponds to the second .veg file listed in the .par file. 

 1	3	1.0000
 2	3	1.0000
 3	2	2.0000

5.12.2 A typical soil type polygon file

Part of a typical soil type overlay file is shown below. In this instance, element 1 lies within polygon number 1 and is assigned an integer value of 1, corresponding to the first .nodes file listed in the .par file. On the other hand, elements 2 and 3 lie within polygon number 2, which corresponds to the second .nodes file listed in the .par file. 

 1	1	1.0000
 2	2	1.0000
 3	2	2.0000

5.12.3 A typical LAI values file

Part of a typical LAI values overlay file is shown below. In this instance, element 1 lies within polygon number 3 and is assigned an LAI value of 2.5. Elements 2 and 3 are associated with polygons 2 and 1, respectively, and are ascribed values of 2.2 and 1.8, respectively. 

 1	3	2.5
 2	2	2.2
 3	1	1.8

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last modified on 24 June 1997