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- Namoi subregion
- 2.6.2 Groundwater numerical modelling for the Namoi subregion
- 2.6.2.6 Parameterisation
- 2.6.2.6.2 Summary of parameters in the groundwater model
Eighty-one parameters were used in the groundwater model. After the stress test described in Section 2.6.2.7.3.1 some of the parameters were identified to have an insignificant influence on the model predictions. These parameters were then either fixed or tied to the independent parameters leaving a total of 37 parameters that varied in the sensitivity and uncertainty analyses. These parameters can be broadly grouped by model function into parameters relating to:
- land-surface fluxes: three fixed parameters for defining evapotranspiration processes (see Section 2.6.2.4.2); one parameter each for the diffuse, irrigation and flood recharge used as multipliers vary the recharge input to explore uncertainty in these components of recharge
- general-head boundary behaviour: two fixed parameters to explore variability in the head and conductance of all lateral boundaries
- surface water – groundwater fluxes: five parameters that define the boundary conditions for the movement of water between groundwater and the river. River-stage height varies with riverbed depth. Two parameters that limit the minimum and maximum hydraulic conductivity of the riverbed and two parameters that define the slope of the riverbed in any model cell are used to compute the conductance of the riverbed in all river cells (see Section 2.6.2.4.3)
- hydraulic properties: parameters to define horizontal and vertical hydraulic conductivities and storage that varies with depth for each model layer (Section 2.6.2.6.1)
- hydraulic enhancement: two parameters to characterise the magnitude of and depth over which hydraulic conductivity changes occur due to longwall mining (see Section 2.6.2.5.3)
- drains: three parameters control the conductance of the open-cut mines, longwall mines and coal seam gas wells.
Table 10 summarises the groundwater model parameters, including the minimum and maximum values of the range over which parameters are varied in the uncertainty analysis (see Section 2.6.2.8) and salient points. As identified above, a number of these parameters are dealt with in other sections of this product.
The range of conductivity and storage values explored in the sensitivity analysis and its comparison with measured data is shown in Figure 19 (which is Figure 21 in companion product 2.1-2.2 for the Namoi subregion (Aryal et al., 2018)). As mentioned above, an upscaling analysis may be performed to yield a probability distribution for hydraulic conductivity, and the result of such an analysis is shown in Figure 19, which motivates the uncertainty bounds in Table 10.
Conductivity enhancement above and below mines is discussed in Section 2.6.2.5.3, and the wide range of variation (four orders of magnitude, and heights ranging between 100 m and 500 m above longwall workings) reflects the wide variation that may be experienced in different mining scenarios (Adhikary and Wilkins, 2012; Guo et al., 2014).
Table 10 Groundwater model parameters: minimum and maximum values used in the uncertainty analysis
Number |
Package |
Name |
Description |
Note |
Unit |
Minimum |
Maximum |
---|---|---|---|---|---|---|---|
1 |
RCH |
Scale_r_fl |
scaler on flood recharge |
log |
- |
0.01 |
0.1 |
2 |
RCH |
Scale_r_ir |
scaler on irrigation recharge |
log |
- |
0.01 |
1 |
3 |
RCH |
Scale_r_dr |
scaler on diffuse recharge |
linear |
- |
0.5 |
2 |
4 |
RIV |
k_min |
minimum conductivity of river bed |
fixed |
m/d |
1 |
1 |
5 |
RIV |
k_max |
maximum conductivity of river bed |
fixed |
m/d |
3 |
3 |
6 |
RIV |
m_min |
minimum depth of river bed |
fixed |
m |
0.5 |
0.5 |
7 |
RIV |
m_max |
maximum depth of river bed |
fixed |
m |
5 |
5 |
8 |
RIV |
dh |
depth of river incision below topography |
linear |
m |
2 |
15 |
9 |
GHB |
Scale_ghb_h |
scaler on general head bounday head |
fixed |
- |
1 |
1 |
10 |
GHB |
Scale_ghb_cond |
scaler on general head boundary conductance |
fixed |
- |
1 |
1 |
11 |
EVT |
sc_PET |
scaler on PET |
fixed |
- |
1 |
1 |
12 |
EVT |
minrd |
minimum rooting depth |
fixed |
m |
1 |
1 |
13 |
EVT |
rd_vh |
fraction of vegetation height added to minimum rooting depth |
fixed |
- |
0.2 |
0.2 |
14 |
LPF |
al1_kh |
alluvium layer 1 horizontal conductivity |
log |
m/d |
0.1 |
3 |
15 |
LPF |
al1_ka |
alluvium layer 1 horizontal conductivity decay constant |
fixed |
/m |
0 |
0 |
16 |
LPF |
al1_we |
alluvium weathered zone parameter |
fixed |
- |
0 |
0 |
17 |
LPF |
al1_kv |
alluvium layer 1 vertical conductivity scaler |
linear |
- |
0.5 |
1.5 |
18 |
LPF |
al1_S0 |
alluvium layer 1 Storage |
log |
- |
0.0001 |
0.01 |
19 |
LPF |
al1_Sa |
alluvium layer 1 storage decay |
fixed |
/m |
0 |
0 |
20 |
LPF |
al1_SY |
alluvium specific yield |
log |
- |
0.05 |
0.3 |
21 |
LPF |
al2_kh |
alluvium layer 2 horizontal conductivity |
log |
m/d |
1 |
10 |
22 |
LPF |
al2_ka |
alluvium 2 horizontal conductivity decay constant |
fixed |
/m |
0 |
0 |
23 |
LPF |
al2_we |
alluvium 2 weathered zone paramter |
fixed |
- |
0 |
0 |
24 |
LPF |
al2_kv |
alluvium layer 2 vertical conductivity |
log |
- |
0.001 |
0.1 |
25 |
LPF |
al2_S0 |
alluvium layer 2 storage |
log |
- |
0.0001 |
0.01 |
26 |
LPF |
al2_Sa |
alluvium 2 storage decay constant |
fixed |
/m |
0 |
0 |
27 |
LPF |
al2_SY |
alluvium layer 2 specific yield |
log |
- |
0.05 |
0.3 |
28 |
LPF |
IB1_k0 |
interburden 1 horizontal conductivity at surface |
log |
m/d |
0.0001 |
0.01 |
29 |
LPF |
IB1_ka |
interburden 1 horizontal conductivity decay constant |
linear |
/m |
0.003 |
0.01 |
30 |
LPF |
IB1_we |
interburden 1 weathered zone |
linear |
- |
1 |
3 |
31 |
LPF |
IB1_kv |
interburden 1 ratio of kv to kh |
log |
- |
0.001 |
0.1 |
32 |
LPF |
IB1_S0 |
interburden 1 storage at surface |
log |
- |
0.000001 |
0.0001 |
33 |
LPF |
IB1_sa |
interburden 1 storage decay constant |
linear |
/m |
0 |
0.03 |
34 |
LPF |
IB1_SY |
interburden 1 specific yield |
log |
- |
0.0005 |
0.05 |
35 |
LPF |
pil_k0 |
Pilliga horizontal conductivity at surface |
log |
m/d |
0.001 |
1 |
36 |
LPF |
pil_ka |
Pilliga horizontal conductivity decay constant |
linear |
/m |
0.003 |
0.01 |
37 |
LPF |
pil_we |
Pilliga 1 weathered zone |
linear |
- |
1 |
3 |
38 |
LPF |
pil_kv |
Pilliga ratio of kv to kh |
log |
- |
0.001 |
0.1 |
39 |
LPF |
pil_S0 |
Pilliga storage at surface |
log |
- |
0.000001 |
0.0001 |
40 |
LPF |
pil_sa |
Pilliga storage decay constant |
fixed |
/m |
0 |
0 |
41 |
LPF |
pil_SY |
Pilliga specific yield |
log |
- |
0.001 |
0.1 |
42 |
LPF |
IB2_k0 |
interburden 2 horizontal conductivity at surface |
tied IB1_k0 |
m/d |
0.0001 |
0.01 |
43 |
LPF |
IB2_ka |
interburden 2 horizontal conductivity decay constant |
tied IB1_ka |
/m |
0.003 |
0.01 |
44 |
LPF |
IB2_we |
interburden 2 weathered zone parameter |
tied IB1_we |
- |
1 |
3 |
45 |
LPF |
IB2_kv |
interburden 2 ratio of kv to kh |
tied IB1_kv |
- |
0.001 |
0.1 |
46 |
LPF |
IB2_S0 |
interburden 2 storage at surface |
tied IB1_S0 |
- |
0.000001 |
0.0001 |
47 |
LPF |
IB2_sa |
interburden 2 storage decay constant |
tied IB1_sa |
/m |
0 |
0.03 |
48 |
LPF |
IB2_SY |
interburden 2 specific yield |
tied IB1_SY |
- |
0.0005 |
0.05 |
49 |
LPF |
hos_k0 |
Hoskissons horizontal conductivity at surface |
log |
m/d |
0.001 |
0.1 |
50 |
LPF |
hos_ka |
Hoskissons horizontal conductivity decay constant |
linear |
/m |
0.003 |
0.01 |
51 |
LPF |
hos_we |
Hoskissons weathered zone parameter |
linear |
- |
1 |
3 |
52 |
LPF |
hos_kv |
Hoskissons ratio of kv to kh |
log |
- |
0.01 |
1 |
53 |
LPF |
hos_S0 |
Hoskissons storage at surface |
log |
- |
0.000001 |
0.0001 |
54 |
LPF |
hos_sa |
Hoskissons storage decay constant |
linear |
/m |
0 |
0.03 |
55 |
LPF |
hos_SY |
Hoskissons specific yield |
log |
- |
0.001 |
0.1 |
56 |
LPF |
IB3_k0 |
interburden 3 horizontal conductivity at surface |
tied IB1_k0 |
m/d |
0.0001 |
0.01 |
57 |
LPF |
IB3_ka |
interburden 3 horizontal conductivity decay constant |
tied IB1_ka |
/m |
0.003 |
0.01 |
58 |
LPF |
IB3_we |
interburden 3 weathered zone parameter |
tied IB1_we |
- |
1 |
3 |
59 |
LPF |
IB3_kv |
interburden 3 ratio of kv to kh |
tied IB1_kv |
- |
0.001 |
0.1 |
60 |
LPF |
IB3_S0 |
interburden 3 storage at surface |
tied IB1_S0 |
- |
0.000001 |
0.0001 |
61 |
LPF |
IB3_sa |
interburden 3 storage decay constant |
tied IB1_sa |
/m |
0 |
0.03 |
62 |
LPF |
IB3_SY |
interburden 3 specific yield |
tied IB1_SY |
- |
0.0005 |
0.05 |
63 |
LPF |
mau_k0 |
Maules ck horizontal conductivity at surface |
tied hos_k0 |
m/d |
0.001 |
0.1 |
64 |
LPF |
mau_ka |
Maules ck horizontal conductivity decay constant |
tied hos_ka |
/m |
0.003 |
0.01 |
65 |
LPF |
mau_we |
Maules creek weathered zone parameter |
tied hos_we |
- |
1 |
3 |
66 |
LPF |
mau_kv |
Maules ck ratio of kv to kh |
tied hos_kv |
- |
0.01 |
1 |
67 |
LPF |
mau_S0 |
Maules ck storage at surface |
tied hos_S0 |
- |
0.000001 |
0.0001 |
68 |
LPF |
mau_sa |
Maules ck storage decay constant |
tied hos_sa |
/m |
0 |
0.03 |
69 |
LPF |
mau_SY |
Maules creek specific yield |
tied hos_SY |
- |
0.001 |
0.1 |
70 |
LPF |
base_k0 |
basement horizontal conductivity at surface |
tied IB1_k0 |
m/d |
0.0001 |
0.01 |
71 |
LPF |
base_ka |
basement horizontal conductivity decay constant |
tied IB1_ka |
/m |
0.003 |
0.01 |
72 |
LPF |
base_we |
basement weathered zone parameter |
tied IB1_we |
- |
1 |
3 |
73 |
LPF |
base_kv |
basement ratio of kv to kh |
tied IB1_kv |
- |
0.001 |
0.1 |
74 |
LPF |
base_S0 |
basement storage at surface |
tied IB1_S0 |
- |
0.000001 |
0.0001 |
75 |
LPF |
base_sa |
basement storage decay constant |
tied IB1_sa |
/m |
0 |
0.03 |
76 |
LPF |
base_SY |
basement specific yield |
tied IB1_SY |
- |
0.0005 |
0.05 |
77 |
TVM |
K_ramp_up |
ramp function maximum impacted distance up |
linear |
m |
100 |
500 |
78 |
TVM |
max_dk_up |
ramp function maximum change in k in up direction (orders of magnitude) |
linear |
- |
0 |
4 |
79 |
DRN |
Cond_mine_OC |
scaler for open cut drain conductance |
log |
- |
6,000 |
100,000 |
80 |
DRN |
Cond_mine_LW |
scaler for longwall mine conductance |
log |
- |
2,000 |
25,000 |
81 |
DRN |
Cond_CSG |
scaler for CSG drain conductance |
log |
- |
1,000 |
15,000 |
Package refers to the MODFLOW package that the parameter belongs to, these are: recharge (RCH), river (RIV), general-head boundary (GHB), evapotranspiration (EVT), layer properties flow (LPF), time varying materials (TVM) and drain (DRN). Note refers to the treatment of the parameter, linear is uniformly distributed between minimum and maximum, log is log transformed and then fitted uniformly between minimum and maximum, fixed means the parameter does not vary between model runs and tied means that the parameter is made equal to another parameter in the list.
PET = potential evapotranspiration; ET = evapotranspiration; GHB = general-head boundary; SW = surface water; GW = groundwater; CSG = coal seam gas
Product Finalisation date
- 2.6.2.1 Methods
- 2.6.2.2 Review of existing models
- 2.6.2.3 Model development
- 2.6.2.4 Boundary and initial conditions
- 2.6.2.5 Implementation of the coal resource development pathway
- 2.6.2.6 Parameterisation
- 2.6.2.7 Observations and predictions
- 2.6.2.8 Uncertainty analysis
- 2.6.2.9 Limitations
- Citation
- Currency of scientific results
- Acknowledgements
- Contributors to the Technical Programme
- About this technical product