Habitat Assessment Using A Coupled Surface Water-Groundwater Flow and Heat Exchange Model for the Braided Ngaruroro River in Hawke's Bay, New Zealand
Abstract/Contents
- Abstract
- Braided rivers are highly biodiverse environments owing to the wide variety of hydraulic habitats that they possess. However, the natural division of flow during braiding leads to low discharge and overheating in braids when subjected to reduced summertime flows and high temperatures. In the absence of anthropogenic disturbances, these rivers mitigate extreme temperatures through an intimate subsurface network of groundwater flow, particularly in high conductivity beds and aquifers like that of the Lower Ngaruroro River in Hawke’s Bay, New Zealand. Through a feedback cycle of infiltration and groundwater spring discharge, the river is able to maintain ecologically favorable river temperatures, even in easily heated, low-flow braids. In this study, groundwater abstraction was shown to diminish the river’s self-cooling capabilities. Not all groundwater-fed braids were found to be equally vulnerable to such decreases – in fact, some zones of thermal refugia were resilient against even extreme levels of groundwater abstraction (causing up to 75% losses in river discharge). In contrast, surface water abstraction was found to promote cooler temperatures in localized, spring-fed thermal refugia, albeit at the expense of reach-wide hydraulic habitat suitability. To gauge the impacts of abstraction on the ecological community, the habitat preferences of two sensitive but valuable species native to the Ngaruroro River - the mayfly (sp. Deleatidium) and torrentfish (sp. Cheimarrichthys fosteri) - were used in the formulation of composite habitat suitability indices. While the temperature-sensitive mayfly experienced a reduction in habitat quality during groundwater abstraction due to increased water temperatures, the more selective hydraulic preferences of the torrentfish resulted in a steeper decline in its high quality habitats during both surface water and groundwater abstraction. Under current climate conditions, optimizing for species hydraulic preferences alone appeared to provide the best outcome for the Lower Ngaruroro River’s ecological community.
Description
| Type of resource | text |
|---|---|
| Date created | August 2020 |
Creators/Contributors
| Author | Tan, Benjamin Z.W. |
|---|---|
| Primary advisor | Gorelick, Steven M. |
| Advisor | Freyberg, David L. |
| Degree granting institution | Stanford University, Earth System Science |
Subjects
| Subject | School of Earth Energy & Environmental Sciences |
|---|---|
| Subject | braided river |
| Subject | groundwater |
| Subject | habitat |
| Genre | Thesis |
Bibliographic information
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- User agrees that, where applicable, content will not be used to identify or to otherwise infringe the privacy or confidentiality rights of individuals. Content distributed via the Stanford Digital Repository may be subject to additional license and use restrictions applied by the depositor.
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- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
Preferred citation
- Preferred Citation
- Tan, Benjamin Z.W. (2020). Habitat Assessment Using A Coupled Surface Water-Groundwater Flow and Heat Exchange Model for the Braided Ngaruroro River in Hawke's Bay, New Zealand. Stanford Digital Repository. Available at: https://purl.stanford.edu/dc677gr4409
Collection
Master's Theses, Doerr School of Sustainability
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- bentzw@stanford.edu
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