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

Last updated:
6 December 2018
Thumbnail of the Namoi subregion

Product Finalisation date

2018
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