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Environmental & Recreational Environmental & Recreational Impacts of IrrigationImpacts of Irrigation
John HayesJohn Hayes
Environmental flow regimes: - critical flow regime features for sustaining instream values
• Flow variability at a range of scales,
• Minimum flow - for: water quality, instream habitat, amenity values.
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1/07/2001 31/07/200130/08/200129/09/200129/10/200128/11/200128/12/200127/01/200226/02/200228/03/200227/04/200227/05/200226/06/2002
Flo
w (
m3/
s)
Ecologically important components of flow regimes
Example flow regime, Lower Waiau River, Tuatapere, Southland
Low/min. flow =Habitat quantity
High flows =Habitat quality
Flood flows =Channel maintenance
Critical values
• The most flow sensitive and important instream value(s) often salmon or trout (habitat)
- trout and salmon have higher flow & water quality requirements than most native fishes
or angling sometimes birds sometimes boating (e.g. jet boating)
• Assumption that if flow needs of critical value are met then less flow sensitive values will be also be OK.
Those pesky trout and salmon
• Why should the instream needs of introduced fishes be allowed to constrain flow allocation to irrigation and hydropower generation? they are the nation’s most important freshwater fisheries –
economically (incl. to tourism) & socially (and contribute to recreational and cultural diversity)
they substitute for otherwise limited native freshwater fisheries they belong to all New Zealanders and all have the opportunity
to participate in the fisheries (c.f. recreational and subsistence marine fisheries).
• These values have been recognised in statute in the responsibility invested by Gov’t in Fish & Game and DOC for protection & management of these fisheries on behalf of public of NZ (Conservation & Fisheries Acts) - and hence too in environmental law (e.g. RMA)
Flow management mechanisms to provide for environmental flow requirements
• Annual or seasonal minimum flow for maintaining instream habitat
• A flow allocation limit, or flow sharing rule, for maintaining flow variability over a range of scales and avoiding prolonged flat-lining at the minimum flow
size and frequency of channel forming and flushing flows may be prescribed
Flow variability – why is it so important?
• Large floods frequency - multiyear for channel maintenance
• Medium floods (freshes) frequency - months flushing periphyton flood recessions contribute to aquatic invertebrate production?
• Minor variation frequency – weeks-months maintenance of fine sediment and periphyton (refreshing
channel margins)?
? needs research
Mid range flow variability – everyone wants a share of it: flushing and benthic production
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Notes: 1) Trustpower regime includes minimum flow only as follows;Jan-Jul 10m3/s, Aug 12, Sep & Dec 15 and Oct-Nov 20 m3/s.2) Preferred regime includes above listed minimum flows plus a 1:1 sharing of flow in excess of those mimima.
Natural
preferred
Trustpower
Wairau River
Mid range flow variability – everyone wants a share of it: salmon angling
Angler diarists fishing in the river between the RDR intake and the top of the lagoon between Jan and Apr 1991and flow in this river reach at the time.
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Actual Flow
Mid range flow variability – everyone wants a share of it: salmon angling
Figure 4: Angler flow frequency distribution for various water management scenarios - Rangitata River
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Flow class (m3/s)
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ay
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No abstraction
Draft WCO (33 cap)
Draft WCO (36cap)
Ecan #8/03 (40 cap)
Mosley (40 cap)
46.5 angler days
Mid range flow variability – everyone wants a share of it: trout angling
Figure 8: Wairau River at Goulter - Angling opportunity
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Flow class (m3/s)
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e cl
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post WES
post TP
Optimal flow range
Effect of 40 m3/s abstraction on trout angling opportunity
Mid range flow variability – everyone wants a share of it: jet boating
Figure 9: Wairau River at Goulter - Jet boating opportunity pre and post development
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naturalpost WES
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Optimal flow range
Effect of 40 m3/s abstraction on jet boating opportunity
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