Categories

Archives

A sample text widget

Etiam pulvinar consectetur dolor sed malesuada. Ut convallis euismod dolor nec pretium. Nunc ut tristique massa.

Nam sodales mi vitae dolor ullamcorper et vulputate enim accumsan. Morbi orci magna, tincidunt vitae molestie nec, molestie at mi. Nulla nulla lorem, suscipit in posuere in, interdum non magna.

Renewable resource models & groundwater management

I once worked on renewable resource modeling (fisheries, forests) but could see that – conceptually at least – the same types of models could be adapted to groundwater problems. One such problem was examined at the recent PhD conference I attended by QUT’s Wasantha Athukorala.  The main difference with respect to ‘renewability’ in these latter problems is that the growth function of an aquifer is very distinctive.  The change of water stock in an aquifer is the natural recharge rate less the rate at which the aquifer is depleted.  If the recharge rate is fixed then so too is the steady state rate of use of the aquifer whenever the aquifer is to be sustainably used. If the aquifer is should be optimally ‘mined’ then exhaustible rather than renewable resource models needs to guide optimal extraction rates.

For simplicity I will ignore issues of artificially recharging aquifers from surplus surface water.

With long-run rates of water usage then fixed by the environment then the main issue is the amount of water than should be kept long-term in the aquifer.  For one thing the more water in the aquifer the lower will be the pumping costs of extracting it.  Some have also suggested that water quality might be lower with smaller aquifer stock size but I really don’t know about this.  Water quality will be also damaged by excessive flow rates of usage – these sorts of costs will act to slow down the pace of approach to the sustainable steady state.

Thinking about the pumping costs it might be thought that an optimal management regime applied to an initially under-utilized aquifer would involve keeping the aquifer at close to its unexploited optimum size. This isn’t optimal since it might pay to get a large delivery of water initially provided that longer-term pumping costs are not driven too high. The size of the initially optimal unsustainable usage depends on production smoothing issues, flow effects of the water gorging on salinity and on discount rates.

Of course almost all aquifers are currently over-utilized so that some sort of more-or-less strict moratorium on use would make sense prior to switching to a regime where sustainability use was sought.   Again the period of reduced use would depend on production smoothing issues and discount rates.

Turning optimal control models of aquifer use into empirically useful frameworks is challenging. The transitional dynamics of use are complex to assess in terms of water quality usage dynamics.  If the focus is on the steady state then the analysis needs to be cast in terms of the effects of marginal increments to the stock of water as it effects pumping and salinity costs not on flow rates of use which are, as I say, predetermined.

1 comment to Renewable resource models & groundwater management

Leave a Reply