132 temperature criteria (which are well developed for many species) to temperature regimes varying over a diel cycle in rivers (Cawthron 2019). The CRI relies on continuous temperature data being collected at regular intervals (typically every 15 mins) over a period of time (several days or months, most helpfully over the summer period). Continuous temperature data was collected by OGNZL at the regular water quality sampling sites (Table 43) from 20 March 2019 to 30 April 2020. 20.5.4.2 In-river temperatures at Waihi The continuous record from the Ohinemuri River show that CRI temperature ranged from 8.7⁰C to 27.75⁰C. The CRI for the discharge temperatures ranged from 21.93⁰C to 22.48⁰C during the same period. The highest in-river temperature was recorded at site OH5 but sites OH3 to OH6 along the river all showed similar maximum CRI temperatures (27.07⁰C – 27.75⁰C). Mean annual CRI temperatures were all slightly higher at sites OH5, OH1 and OH6 than those upstream. The CRI temperatures during the critical summer period reflected these same patterns (Table 43). In-river CRI temperatures greater than the guideline value of 25⁰C during the critical summer period occurred at all sites but occurred more frequently in the lower reaches of the Ohinemuri River at Waihi (sites below OC2) (Table 44). CRI daily temperature increases above 20⁰C occurred at all sites but reflected the same pattern for annual CRI daily temperature records (Table 44). Differences of >3⁰C between sites for in-river daily CRI temperatures occurred on two occasions (between the two most distant sites OC2 and OH6), but records for >2⁰C occurred between the upper and lower sites at Waihi more frequently (Table 45) Table 43: Summary statistics of discharge and in river water temperature CRI (⁰C) in the Ohinemuri River. Site locations are detailed in Figure vv. OC2A and OC2B are sites located approximately 20 m upstream and 20 m downstream respectively of the HDC potable water take from the Ohinemuri River. Site locations shown in Figure 14. Location Statistic Discharge CRI (°C) OC2A CRI (°C) OC2B CRI (°C) OH3 CRI (°C) OH5 CRI (°C) OH1 CRI (°C) OH6 CRI (°C) Summary for all year temperature record (20 March 2019 – 30 April 2020) Mean 20.85 16.52 16.65 16.86 17.72 17.55 17.16 Median 21.11 15.84 15.88 15.89 16.94 16.74 16.47 Minimum 21.93 8.99 8.85 8.73 9.89 9.70 9.78 Maximum 22.48 25.30 26.05 27.31 27.75 27.51 27.07 n 391 408 408 408 408 408 408 Summary CRI for critical summer temperature period (1 November to 30 April) Mean 25.49 19.83 20.15 20.66 21.32 21.24 20.35 Median 25.61 20.45 20.66 21.05 21.65 21.59 20.46 Minimum 16.72 13.90 13.75 13.27 13.59 13.96 13.78
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