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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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

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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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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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Mid range flow variability – everyone wants a share of it: trout angling

Figure 8: Wairau River at Goulter - Angling opportunity

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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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Effect of 40 m3/s abstraction on jet boating opportunity