Environmental and Recreational Impacts of Irrigation: Flow Regimes for Sustaining Instream Values

1. Environmental & Recreational Impacts of Irrigation John Hayes

2. 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.

3. Flood flows = Channel maintenance Ecologically important components of flow regimes Example flow regime, Lower Waiau River, Tuatapere, Southland High flows = Habitat quality Low/min. flow = Habitat quantity

4. 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.

5. 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)

6. 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

7. 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

8. Mid range flow variability – everyone wants a share of it: flushing and benthic production Wairau River

9. Mid range flow variability – everyone wants a share of it: salmon angling

10. Mid range flow variability – everyone wants a share of it: salmon angling

11. Optimal flow range Mid range flow variability – everyone wants a share of it: trout angling Effect of 40 m3/s abstraction on trout angling opportunity

12. Optimal flow range Mid range flow variability – everyone wants a share of it: jet boating Effect of 40 m3/s abstraction on jet boating opportunity