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DER requires a preliminary assessment of the radial extent of the cone of depression and pumping rates and times for all dewatering operations in ASS areas.

Empirical methods to calculate the radial extent of the groundwater cone of depression and pumping rates and times for dewatering operations are outlined in Appendix 5 of pdfTreatment and management of soils and water in acid sulfate soil landscapes5.45 MB (Published July, 2011)

Calculator

Input

Length of excavation (metres): m
Width of excavation (metres): m
Required groundwater drawdown (metres): m
Saturated thickness of the unconfined aquifer(A) (metres): m
Hydraulic conductivity of the aquifer (K) (metres per second): m/sec

 

Results

Effective radius of pumping well , Re (metres): m
Radius of influence of dewatering, Ro (metres):
(i.e. radius of the cone of depression)
m
Total pumping rate (litres per second): l/sec
Time taken to establish the cone of depression (hours): hrs
 

Tools for Calculating the Radius of Influence and Pumping Rates and Times for Dewatered Excavations
In the absence of site-specific hydraulic data, default hydraulic conductivity values (K) listed below for a variety of Western Australian soil types may be used(B).

Lithology Hydraulic conductivity (m/d) Hydraulic conductivity (m/s)
Sand
Very coarse to gravel 246 0.002847
Very coarse 204 0.002361
Coarse 73 0.000845
Medium to coarse (moderately sorted) 50 0.000579
Fine to gravel (poorly sorted) 10 0.000116
Medium 16.5 0.000191
Fine to medium 8.2 0.0000949
Fine 4.1 0.0000475
Fine to very fine 1.7 0.0000197
Very fine 0.8 0.00000926
Silty 4 0.0000463
Clayey 1 0.0000116
Clay 0.4 0.00000463
Sand and limestone: Ascot Formation 8 0.0000926
Limestone and calcarenite:
Tamala Limestone
100-1000 0.001157 to 0.011574
Peat(C)      
Sapric peat (highly decomposed, few visible fibres) 0.00864 (approx.) 0.0000001 (approx.)
Fibric peat (least decomposed, lots of visible fibres) 1.728 (approx.) 0.00002 (approx.)

 

  1. In the absence of site-specific information, the saturated thickness of superficial aquifers may be obtained from: Perth Groundwater Atlas, Second Edition (Department of Environment, 2004) for sites in the Perth metropolitan region; and from information held by the Department of Water (for sites elsewhere in the State). www.water.wa.gov.au/idelve/gwa/
  2. Adapted from Davidson, W.A., 1995, Bulletin 142: Hydrogeology and Groundwater Resources Of The Perth Region, Western Australia, Geological Survey Of Western Australia.
  3. Hemond,H.F. and Goldman, J.C., 1985, On non-Darcian water flow in peat. Journal of Ecology, 73, 578-584