SECTION 3 Site Investigations & Results C:\D Data\GWS C Drive\GWS\Client Files\1344 OGL - WKP\4 Deliverables\WKP Final Draft Report\June Report\WAI-985-000-REP-LC-0030. Final_Rev_0.docx 22 Table 4 Surface Water Flow Gaugings Location Jan-19 Jun-19 Sep-19 Jan-20 May-20 Aug-20 Dec-20 May-21 L/s L/s L/s L/s L/s L/s L/s L/s T-Stream West 44.3 60.8 252.9 28.8 23.6 144.0 56.4 50.5 T-Stream East 59.6 53.0 244.5 33.3 26.3 142.0 74.2 52.1 WKP3 79.6 85.8 424.5 52.5 36.9 267.0 95.3 83.5 WKP2 145.9 90.5 426.2 69.7 48.6 - 120.9 104.7 WKP1 - - - 90.8 68.2 - 164.0 143.2 Table 4 shows, the catchment is relatively flashy in response to rainfall. Based on the September 2019 high flow and May 2020 low flow measurements, there can be an order of magnitude change in the catchment flow rates seasonally. 3.7 Surface Water Dating During the December 2020, March 2021 and May 2021 surface water gauging events, contemporaneous samples were collected for radon dating and general chemistry. Samples were also collected from the standpipe piezometers and from accessible historical adits and shafts. The purpose of the dating was to better understand where groundwater inputs into surface waters are sourced. Figure 23 and Table 5 presents the results of the dating. The results of the dating are documented in a report prepared by GNS (July, 2021) and are summarised as follows. The dating has shown: • Where Rn <0.3 becquerel per litre (Bq/L) there is no groundwater inputs, between 0.3 to 0.5 Bq/L there is possible groundwater input and >0.5 Bq/L is a groundwater input. • Overall, the surface waters are young in age with 75% having Rn <0.5 Bq/L indicating limited deep groundwater input in the catchment. • There is a general inverse relationship between stream flows and Rn concentration with older water having smaller flow rates (Figure 24). • The warm spring is the dominant source of deep groundwater in the catchment and affects the age of the surface water at WKP3, WKP2 and WKP1. • Some deep groundwater is noted to discharge at the headwaters of the Teawaotemutu -Stream, Edmonds and Thompson sub-catchments. • Similarly deep groundwater is noted to discharge at the headwaters of the subcatchments on either side of the WKP catchment. • Tributaries X,W and U had comparatively high radon concentrations but have very low flows (<0.1 L/s).
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