Data sets and methods

River discharge data were sourced from Henderson & Diettrich (2007) . Mean annual discharge (m³/s) was converted to total annual discharge (m³/y) by multiplying mean flow by the number of seconds in a year (365 * 24 * 60 * 60).

Rainfall data were sourced from Average annual rainfall, 1972-2016, a gridded data set available for all of New Zealand. Total annual rainfall volume for each catchment was calculated by spatially intersecting the average annual rainfall raster with catchment subzones. Rainfall depth values (mm/y) were converted to volumetric units by multiplying by raster cell area, and volumes were summed across all cells within each catchment to produce total annual rainfall (m³/y).

The runoff ratio was then calculated as the ratio of total annual discharge to total annual rainfall volume.

Rock type, soil drainage classes and LSNAI categories are taken from Appendix H of thesis.

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Results map

Monitoring site AFN values.

Observed river SIN loads vs unattenuated loads (t/year)

sID Catchment SIN_t_y unatt_SIN_t_y attenuation
Ohura at Tokorima Whanganui 906 629 -0.44
Whanganui at Wades Landing Whanganui 3421 2980 -0.15
Whanganui at Te Rewa Whanganui 3864 3959 0.02
Makuri at Tuscan Hills Manawatu 121 141 0.14
Kumeti at Te Rehunga Manawatu 15 17 0.14
Whanganui at Pipiriki Whanganui 2735 3704 0.26
Whanganui at Te Maire Whanganui 1155 1597 0.28
Ongarue at Taringamotu Whanganui 605 890 0.32
Tiraumea at Ngaturi Manawatu 317 495 0.36
Whanganui at Cherry Grove Whanganui 338 553 0.39
Rangitikei at McKelvies Rangitikei 1300 2436 0.47
Mangahao at Ballance Manawatu 113 235 0.52
Turakina at ONeills Bridge Turakina 264 580 0.54
Manawatu at Upper Gorge Manawatu 1770 3897 0.55
Manawatu at Opiki Bridge Manawatu 2226 5238 0.58
Manawatu at Teachers College Manawatu 1892 4595 0.59
Mangatainoka at Brewery Manawatu 346 872 0.60
Mangatoro at Mangahei Road Manawatu 82 216 0.62
Rangitikei at Onepuhi Rangitikei 640 1757 0.64
Ohau at Gladstone Reserve Ohau 19 54 0.65
Whangaehu at Kauangaroa Whangaehu 549 1648 0.67
Tokiahuru at Junction Whangaehu 28 87 0.68
Mangatainoka at Larsons Road Manawatu 19 59 0.68
Oroua at Awahuri Bridge Manawatu 370 1164 0.68
Manawatu at Weber Road Manawatu 259 824 0.69
Hautapu at US Rangitikei River Conf Rangitikei 62 211 0.71
Raparapawai at Jackson Road Manawatu 29 100 0.71
Mangawhero at Pakihi Rd Bridge Whangaehu 61 216 0.72
Oroua at Almadale Slackline Manawatu 115 411 0.72
Manawatu at Hopelands Manawatu 482 1764 0.73
Rangitikei at Mangaweka Rangitikei 364 1358 0.73
Mangapapa at Troup Road Manawatu 12 47 0.74
Tokomaru River at Horseshoe bend Manawatu 8 35 0.77
Hautapu at Papakai Road Bridge Rangitikei 31 140 0.78
Pohangina at Mais Reach Manawatu 81 398 0.80
Whakapapa at Footbridge Whanganui 8 48 0.83
Hautapu at Alabasters Rangitikei 24 140 0.83
Mangawhero at Raupiu Road Whangaehu 104 744 0.86
Owahanga at Branscombe Bridge Owahanga 39 410 0.90
Rangitikei at Pukeokahu Rangitikei 36 464 0.92 
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