Framework

Management Zones

Defining zones such as stream buffers that have specific management rules is a useful policy tool. In conjunctive management, this approach tends to be used to subdivide the catchment based on the likely impact on stream flow or water quality by changes to groundwater discharge. Management zones can be used to address the effect of groundwater extraction. For example, New South Wales takes a zonal approach for managing alluvial aquifers that are highly connected to streams. Buffer zones around these streams have different management rules (Table 1). It should be noted that a zonal approach may not be universally applicable. Numerical modelling scenarios infer that for the case of semi-confined aquifers in narrow (< 5km) valleys, varying the distance from the river of the groundwater pumping had no effect on the rate and magnitude of streamflow depletion (Braaten and Gates, 2004).

Table 1: Zonal approach for managing highly connected alluvial systems in NSW

Distance from High Bank of Stream	Management Rule
<40m	Surface water works approval and surface water rules apply
40-200m	Groundwater works approval and surface water rules apply
>200m	Groundwater works approval and groundwater rules apply

In a general sense, four management zones surrounding the stream and based on the time lag between groundwater extraction and response in stream flow is proposed (Evans et al, 2005), refer Figure 1:

1. Zone 1 Very Short Time Lag, which applies near-stream where there is major interference and the time lag is short (<1 week). All new entitlements should be managed on the basis of surface water extraction rules.
2. Zone 2 Short Time Lag, applying to all groundwater users which could impact stream flow over the critical low flow period of the stream during the planning timeframe. Typically, flow depletion from extraction is detected within three months. Short-term restrictions on groundwater use may be put in place based on triggers such as minimum groundwater levels.
3. Zone 3 Medium to Long Time Lag, applying to groundwater users that have an impact on stream flow over the long term (1-50 years). The focus of management is maintaining groundwater allocation and use within the defined sustainable yield.
4. Zone 4 Very Long Time Lag, where there is no discernable impact on stream flow by groundwater use. No active management relating to streamflow depletion is required.

Figure 2 shows the typical distribution of these zones for a contained alluvial valley. Various methods can be applied to estimate the magnitude of the time lag between groundwater extraction and stream flow depletion. These include field investigations or analytical or numerical modelling.

Figure 1: Proposed zones for managing new water access entitlements (Evans et al, 2005)

Figure 2: Indicative locations of management zones (Evans et al, 2005)

Management zones can also be used to reduce the risk of contamination from industrial spills or septic tank effluent, or manage the salinity impact of rising water tables due to irrigation development. A good example of the latter application is the salinity impact zones (HIZ/LIZ) defined for the Victorian side of the River Murray. There is also the option to subdivide an aquifer (vertically as well as horizontally) as part of managing stream-aquifer connectivity. These zones could then provide a framework for water trade.

Case Studies

NSW time lag models

Relevant Links

References

Braaten R, Gates G, 2004. Lagging behind: exploring the time lag in river-aquifer interaction., 9th Murray-Darling Basin Groundwater Workshop, Bendigo. Murray-Darling Basin Commission.

Evans R, Dudding M, Holland G, 2005. River-groundwater interaction, a practical management approach. Engineers Australia 29^th Hydrology and Water Resources Symposium 21-23 February 2005, Canberra