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Explore the critical flow regime features essential for sustaining instream values, including water quality, habitat, and amenity values. Learn about the impact of flow variability on habitat quality and quantity, particularly for salmon and trout fisheries. Discover the importance of balancing flow allocation for irrigation and hydropower generation with environmental and recreational needs. Dive into the mechanisms for managing environmental flow requirements and maintaining flow variability to support diverse aquatic ecosystems.
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Environmental & Recreational Impacts of Irrigation John 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.
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
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 Wairau River
Mid range flow variability – everyone wants a share of it: salmon angling
Mid range flow variability – everyone wants a share of it: salmon angling
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
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