Proposed Conjunctive Management Framework Brydon Hughes Outline - - PowerPoint PPT Presentation
Form and Content of The Proposed Conjunctive Management Framework Brydon Hughes Outline Background to groundwater / surface water interaction Outline of the proposed management framework Specific provisions relating to the
Brydon Hughes
management of stream depletion effects (Appendix P / Table 4.1)
Significant interaction between groundwater and surface water is observed throughout the Wellington Region
to groundwater
low rainfall (including springs)
range of groundwater dependant ecosystems
Darcy’s Law
Groundwater flow (including flow exchange between groundwater and surface water) is proportional to permeability and hydraulic gradient
Gaining Stream
Losing Stream
Disconnected (perched) Stream
water table
Describes the nature and extent of interaction between groundwater and surface water.
groundwater and surface water (e.g. shallow, highly permeable riparian aquifers)
(e.g. stream separated from an underlying aquifer by a layer of low permeability material)
Groundwater abstraction has the potential to:
rivers/streams
and springs Typically expressed in terms of stream depletion ratio (q/Q)
Is not a 1:1 ratio The potential for stream depletion depends on:
10 20 30 40 50 60 70 80 90 100 50 100 150 200 250 300 Stream Depletion (% of pumping rate) Time (days)
100 m 250 m 500 m 1000 m 1500 m 2000 m
surface water (high q/Q)
extended period
surface water (low q/Q)
Stream depletion from individual groundwater takes occur along a continuum
Managing stream depletion effects at a catchment scale requires an approach that:
abstractions with a high degree of hydraulic connection
with a moderate to low hydraulic connection on catchment baseflow
Category A Category B (high connection) Category B (moderate connection) Category C
High hydraulic connection Low hydraulic connection
allocation
apply
by groundwater allocation volume
Areas which exhibit a high connectivity to surface water
develop/dissipate rapidly
volume pumped derived from surface water Analogous to surface water abstraction
allocation
Areas where groundwater abstraction can have a significant impact on surface water but where minimum flow cut-offs may/may not provide mitigation during low flows
Areas where groundwater abstraction may contribute to a cumulative reduction in baseflow at a catchment scale but where minimum flow controls provide limited mitigation
Why map hydraulic connectivity categories?
management controls)
Hydraulic connectivity categories delineated (spatially and with regard to depth) on the basis of:
Approach utilised detailed in Hughes and Gyopari (2011)
250 500 750 1000 1250 60.5 61.0 61.5 62.0 62.5 63.0 63.5 64.0 Waiohine River at Gorge Stage (mm) Groundwater Level at S26/0490 (m asl) S26/0490 Waiohine River at Gorge
Physical Observations Groundwater Modelling Hydraulic connectivity zone maps
Category A
Significant and direct effect on surface water
average pumping rate)
reduction)
by hydrogeological assessment
Category B Represents ‘transition’ areas where nature and magnitude of stream depletion is influenced by local factors Assessment criteria defined to establish if an individual take is better managed in terms of:
Minimum rate of take 5 L/s (takes <5 L/s default to Category C)
connection) from Category B (moderate connection).
Time since pumping stopped q/Q 10 Days 20 days 30 days 40 days 0.8 54% 71% 79% 83% 0.7 31% 53% 64% 71% 0.6 13% 34% 48% 57% 0.5 2% 18% 32% 43% 0.4
2% 13% 24%
10 20 30 40 50 60 70 80 90 100 50 100 150 200 250 300 Stream Depletion (% of pumping rate) Time (days) 100 m 250 m 500 m 1000 m 1500 m 2000 m
(high connection) takes included in surface water allocation and take may be subject to minimum flow cut-
terms of groundwater allocation (no minimum flow)
Takes with a calculated effect >10 L/s default to Category B (high connection) even if stream depletion ratio <0.6.
2 4 6 8 10 12 14 16 20 40 60 80 100 Stream Depletion (L/s) Duration of Pumping (days) 10 L/s, Q/q = 0.7 20 L/s Q/q = 0.6 30 L/s Q/q = 0.5
large effect included in surface water allocation
size
The assumed pumping rate and duration of pumping significantly influence the calculated rate of stream depletion. Proposed assessment based on:
maximum demand occurring 1 in 10 years (90% reliability)
the Wairarapa Valley
Category C groundwater takes:
into account cumulative effects on baseflow at a catchment scale)
Application of regional-scale mapping at a local-scale, particularly in complex geological environments, always involves uncertainty. Such uncertainty is addressed by proposed framework in two ways:
uncertainty regarding the potential magnitude and nature of stream depletion effects
specified set of criteria
“Any abstraction from an aquifer has an effect that eventually propagates throughout the whole aquifer. This effect may be a lowering of piezometric levels or induced additional recharge from a river. The effect from any one well may be infinitesimal in terms of practical measurement, but the cumulative long-term effects of many wells can be very significant. The result is that every user of groundwater from an aquifer is a contributor to environmental effects such as reduction of low flows in streams or salt water intrusion which are determined by natural
Dr Vince Bidwell, 2003