130 20.5.3 In-river and discharge temperatures Weekly (and often irregular) water temperature data has been collected from the Ohinemuri River from 2006. In this section we report on this data to assess the longer-term nature of temperature within the river. Daily single temperature records show that temperature of the temperature ranges from 12.7⁰C to 30.4⁰C32. In-river temperatures from the four sites ranged from 7.9⁰C (sites OC2, OH3 and OH5) to 27.9⁰C (site OH5) and median values ranged from 14.8 (sites OC2 and OH3) to 15.9 (OH6) (Table 40). In-river temperatures rarely exceeded 25⁰C (occurring on only two occasions over the temperature record) but exceeded 20⁰C on several occasions (up to 117 occasions within the temperature record). The higher threshold temperatures exceedances occurred at the downstream sites at all temperature bands (>20⁰C up to >25⁰C) (Table 41). In-river temperature differences between sites above and below the discharge recorded by spot sampling on the same days are shown in Table 42. We note that there is a time-of-day sampling disparity on each daily record of 2-3 hours (that is the samples were not collected at the same time of day on each occasion). Temperature differences of >3⁰C occurred on only two occasions over the sample period, and >2⁰C on 21 occasions (Table 42). Table 40:. Summary statistics of discharge and in river water temperature (°C) in the Ohinemuri River. Site locations shown in Figure 14. Location Statistic Discharge (°C) OC2 (°C) OH3 (°C) OH5 (°C) OH6 (°C) Summary for all year temperature record Mean 21.9 15.3 15.4 16.1 16.3 Median 22.3 14.8 14.8 15.8 15.9 Minimum 12.7 7.9 7.9 7.9 8.5 Maximum 30.4# 24.5 24.8 27.9 25.8 n 1206 628 889 801 782 Sample period 2014-2018 20062021 20082021 20032021 20042021 Summary for critical summer temperature period (1 January to 30 March) Mean 19.3 19.2 20.1 20.6 Median 19.3 19.4 20.3 20.7 Minimum 13.5 13.5 13.9 13.8 Maximum 24.5 24.8 27.9 25.2 n 138 107 168 167 32 We note that the discharge temperature records show that temperature was elevated (40.6⁰C - 43.4⁰C) for 12 days during June 2018. As the temperature records during this time are clearly outliers, probably due to failure of temperature loggers, we have removed them from our data summary.
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