Bengalla Mine Environmental Impact Statement (1993) - Part 1 of 3

2:7
The main characteristics of the catchments are given in Table 2.2. The discharge for each catchment has been
calculated using the Rational Method (Institute of Engineers, Australia 1987).
TABLE 2.2
CATCHMENT CHARACTERISTICS
Catchment Area in km 2 tc in hours Q 10 m 3 /s Q 100 m 3 /s
1
25.1
2.59
17.9
43.3
2
7.8
1.66
7.6
18.5
3
8.0
1.68
7.8
18.9
tc
Q 10
Q 100
= time of concentration, time taken for all areas of the catchment to contribute to the discharge
= discharge for 1 in 10 year event, for a storm of tc duration
= discharge for 1 in 100 year event, for a storm of tc duration
All development in the project area will be carried out in accordance with the Joint Venture Policy on water,
presented in Appendix 7.
2.6.2 Flood Levels
The area of inundation caused by the February 1955 flood of the Hunter River is taken as the 1 in 100 year
flood level (Water Resources Commission New South Wales, 1985). In the northeastern part of the Bengalla
Authorisation, this level occurs at approximately 145 m AHD, about 200 m east of the intersection of Bengalla
and Wybong roads. In the southern part of the Bengalla area, the 1 in 100 year flood level lies at approximately
135 m AHD, on the northern side of the Muswellbrook - Ulan Railway (Figure 2.7).
The proposed opencut mining area does not encroach onto the floodplain nor the 1 in 100 year flood level. The
proposed surface facilities in the southwestern corner of the project area are also above the 1 in 100 year flood
level. Part of the rail loop will be located below 1 in 100 year flood level and hence may be inundated in an
extreme flood event.
2.6.3 Surface Water Quality
Criteria for Assessing Water Quality
Criteria for interpreting the quality of water from physical and chemical analyses are given in Croft &
Associates Pty Limited (1983) and in Berkman (1989). Some important water quality criteria relevant to this
BENGALLA EIS. F156
NOVEMBER 1993