Preliminary assessment of the radial extent of the cone of depression and pumping rates and times for all dewatering operations is critical for assessing the risk of disturbing acid sulfate soils in potential acid sulfate soil areas.
Broad-scale acid sulfate soil risk maps for several coastal regions of WA are accessible via Data WA.
Empirical methods to calculate the radial extent of the groundwater cone of depression and pumping rates and times for dewatering operations are outlined in National Acid Sulfate Soils Guidance: Guidance for the dewatering of acid sulfate soils in shallow groundwater environments.
Calculator
Input |
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| Length of excavation: | metres | |
| Width of excavation: | metres | |
| Drawdown required: | metres | |
| Aquifer thickness(1): | metres | |
| Hydraulic conductivity: | metres/second | |
Results |
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| Effective pumping radius, Re : | metres | |
| Cone of depression radius, Ro : | metres | |
| Total pumping rate: | litres/second | |
| Pumping time required: | hours | |
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 (2).
| Lithology | Hydraulic conductivity (metres/day) | Hydraulic conductivity (metres/second) |
|---|---|---|
| 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(3) | ||
| 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.) |
Notes
- In the absence of site-specific information, the saturated thickness of superficial aquifers may be obtained from Perth Groundwater Map for sites in the Perth metropolitan region.
- Adapted from Davidson, W.A., 1995, Bulletin 142: Hydrogeology and Groundwater Resources Of The Perth Region, Western Australia, Geological Survey Of Western Australia.
- Hemond,H.F. and Goldman, J.C., 1985, On non-Darcian water flow in peat. Journal of Ecology, 73, 578-584.
