Rainfall recharge models of the Heretaunga Plains

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White, P.A.; Tschritter, C.; Westerhoff, R.; Lovett, A. 2014 Rainfall recharge models of the Heretaunga Plains. Lower Hutt, N.Z.: GNS Science. GNS Science report 2013/50 42 p.

Abstract: Hawke’s Bay Regional Council (HBRC) is currently reviewing water resources in the Heretaunga Plains as part of the Greater Heretaunga/Ahuriri Catchment Area plan change process. As rainfall recharge is a key component of water resources in the region, GNS Science has completed an assessment of rainfall recharge to groundwater in the Heretaunga Plains and the Ahuriri Estuary catchments. This work has been completed as a component of the National Institute of Water and Atmospheric Research (NIWA) Waterscape programme. Three rainfall recharge models (SOILMOD, Rushton and the genetic program) were applied to assess rainfall recharge on a daily basis between 1972 and 2006. Inputs to the model were generated from estimates of climate and soil properties. Daily rainfall and potential evapotranspiration values were derived from NIWA’s Virtual Climate Station Network (VCSN), and soil profile available water was derived from Landcare Research’s soils database. Daily rainfall recharge was estimated in five zones: zone 1 (the unconfined area of the Heretaunga Plains); zone 2 (the confined Heretaunga Plains aquifer located south of the Ngaruroro River, including Hastings City); zone 3 (the confined Heretaunga Plains aquifer located north of the Ngaruroro River, including parts of Napier City); zone 4 (the Ahuriri area, including Bay View) and zone 5 (south of the Tukituki River near the coast, including the Te Awanga coastal strip). Average modelled rainfall recharge between 1972 and 2006 for all zones was 2.7 m3/s (SOILMOD), 2.2 m3/s (Rushton) and 1.6 m3/s (genetic program). Rainfall recharge estimates by the SOILMOD and Rushton models were similar, aside from zone 2 where significant runoff was calculated using the Rushton model. Modelled rainfall recharge is highly variable. For example, modelled rainfall recharge ranged from approximately 100 to 500 mm/yr at Bridge Pa in the unconfined zone, and rainfall recharge through heavy soils may be zero in dry years. Rainfall recharge is also highly seasonal, with zero rainfall recharge typical of the summer months. (auth)