How Important Are Those Fracture Zones? Scale Dependent Characteristics Revealed Through Field Studies and an Integrated Hydrological Model of a Mountain Headwater Catchment

Modeling groundwater flow in bedrock can be particularly challenging due to heterogeneities associated with fracture zones. However, fracture zones can be difficult to map, particularly in forested areas where tree cover obscures land surface features. This study presents the evidence of fracture zo...

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Autores principales:	Diana M. Allen, Alexandre H. Nott
Formato:	article
Lenguaje:	EN
Publicado:	Frontiers Media S.A. 2021
Materias:	fracture zone lineaments groundwater flow numerical modeling uncertainty headwater catchment Environmental technology. Sanitary engineering TD1-1066
Acceso en línea:	https://doaj.org/article/9ed60b5801274d06ab055b28eb3a6d29
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spelling	oai:doaj.org-article:9ed60b5801274d06ab055b28eb3a6d292021-12-02T10:11:24ZHow Important Are Those Fracture Zones? Scale Dependent Characteristics Revealed Through Field Studies and an Integrated Hydrological Model of a Mountain Headwater Catchment2624-937510.3389/frwa.2021.767399https://doaj.org/article/9ed60b5801274d06ab055b28eb3a6d292021-12-01T00:00:00Zhttps://www.frontiersin.org/articles/10.3389/frwa.2021.767399/fullhttps://doaj.org/toc/2624-9375Modeling groundwater flow in bedrock can be particularly challenging due to heterogeneities associated with fracture zones. However, fracture zones can be difficult to map, particularly in forested areas where tree cover obscures land surface features. This study presents the evidence of fracture zones in a small, snowmelt-dominated mountain headwater catchment and explores the significance of these fracture zones on groundwater flow in the catchment. A newly acquired bare earth image acquired using LiDAR identifies a previously undetected linear erosion zone that passes near a deep bedrock well at low elevation in the catchment. Borehole geophysical logs indicate more intense fracturing in this well compared to two wells at higher elevation. The well also exhibited a linear flow response during a pumping test, which is interpreted to reflect the influence of a nearby vertical fracture zone. The major ion chemistry and stable isotope composition reveal a slightly different chemical composition and a more depleted isotopic signature for this well compared to other groundwaters and surface waters sampled throughout the catchment. With this evidence of fracturing at the well scale, an integrated land surface – subsurface hydrologic model is used to explore four different model structures at the catchment scale. The model is refined in steps, beginning with a single homogeneous bedrock layer, and progressively adding 1) a network of large-scale fracture zones within the bedrock, 2) a weathered bedrock zone, and 3) an updated LiDAR-derived digital elevation model, to gain insight into how increasing subsurface geological complexity and land surface topography influence model fit to observed data and the various water balance components. Ultimately, all of the models are considered plausible, with similar overall fit to observed data (snow, streamflow, pressure heads in piezometers, and groundwater levels) and water balance results. However, the models with fracture zones and a weathered zone had better fits for the low elevation well. These models contributed slightly more baseflow (~14% of streamflow) compared to models without a weathered zone (~1%). Thus, in the watershed scale model, including a weathered bedrock zone appears to more strongly influence the hydrology than only including fracture zones.Diana M. AllenAlexandre H. NottFrontiers Media S.A.articlefracture zonelineamentsgroundwater flownumerical modelinguncertaintyheadwater catchmentEnvironmental technology. Sanitary engineeringTD1-1066ENFrontiers in Water, Vol 3 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	fracture zone lineaments groundwater flow numerical modeling uncertainty headwater catchment Environmental technology. Sanitary engineering TD1-1066
spellingShingle	fracture zone lineaments groundwater flow numerical modeling uncertainty headwater catchment Environmental technology. Sanitary engineering TD1-1066 Diana M. Allen Alexandre H. Nott How Important Are Those Fracture Zones? Scale Dependent Characteristics Revealed Through Field Studies and an Integrated Hydrological Model of a Mountain Headwater Catchment
description	Modeling groundwater flow in bedrock can be particularly challenging due to heterogeneities associated with fracture zones. However, fracture zones can be difficult to map, particularly in forested areas where tree cover obscures land surface features. This study presents the evidence of fracture zones in a small, snowmelt-dominated mountain headwater catchment and explores the significance of these fracture zones on groundwater flow in the catchment. A newly acquired bare earth image acquired using LiDAR identifies a previously undetected linear erosion zone that passes near a deep bedrock well at low elevation in the catchment. Borehole geophysical logs indicate more intense fracturing in this well compared to two wells at higher elevation. The well also exhibited a linear flow response during a pumping test, which is interpreted to reflect the influence of a nearby vertical fracture zone. The major ion chemistry and stable isotope composition reveal a slightly different chemical composition and a more depleted isotopic signature for this well compared to other groundwaters and surface waters sampled throughout the catchment. With this evidence of fracturing at the well scale, an integrated land surface – subsurface hydrologic model is used to explore four different model structures at the catchment scale. The model is refined in steps, beginning with a single homogeneous bedrock layer, and progressively adding 1) a network of large-scale fracture zones within the bedrock, 2) a weathered bedrock zone, and 3) an updated LiDAR-derived digital elevation model, to gain insight into how increasing subsurface geological complexity and land surface topography influence model fit to observed data and the various water balance components. Ultimately, all of the models are considered plausible, with similar overall fit to observed data (snow, streamflow, pressure heads in piezometers, and groundwater levels) and water balance results. However, the models with fracture zones and a weathered zone had better fits for the low elevation well. These models contributed slightly more baseflow (~14% of streamflow) compared to models without a weathered zone (~1%). Thus, in the watershed scale model, including a weathered bedrock zone appears to more strongly influence the hydrology than only including fracture zones.
format	article
author	Diana M. Allen Alexandre H. Nott
author_facet	Diana M. Allen Alexandre H. Nott
author_sort	Diana M. Allen
title	How Important Are Those Fracture Zones? Scale Dependent Characteristics Revealed Through Field Studies and an Integrated Hydrological Model of a Mountain Headwater Catchment
title_short	How Important Are Those Fracture Zones? Scale Dependent Characteristics Revealed Through Field Studies and an Integrated Hydrological Model of a Mountain Headwater Catchment
title_full	How Important Are Those Fracture Zones? Scale Dependent Characteristics Revealed Through Field Studies and an Integrated Hydrological Model of a Mountain Headwater Catchment
title_fullStr	How Important Are Those Fracture Zones? Scale Dependent Characteristics Revealed Through Field Studies and an Integrated Hydrological Model of a Mountain Headwater Catchment
title_full_unstemmed	How Important Are Those Fracture Zones? Scale Dependent Characteristics Revealed Through Field Studies and an Integrated Hydrological Model of a Mountain Headwater Catchment
title_sort	how important are those fracture zones? scale dependent characteristics revealed through field studies and an integrated hydrological model of a mountain headwater catchment
publisher	Frontiers Media S.A.
publishDate	2021
url	https://doaj.org/article/9ed60b5801274d06ab055b28eb3a6d29
work_keys_str_mv	AT dianamallen howimportantarethosefracturezonesscaledependentcharacteristicsrevealedthroughfieldstudiesandanintegratedhydrologicalmodelofamountainheadwatercatchment AT alexandrehnott howimportantarethosefracturezonesscaledependentcharacteristicsrevealedthroughfieldstudiesandanintegratedhydrologicalmodelofamountainheadwatercatchment
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How Important Are Those Fracture Zones? Scale Dependent Characteristics Revealed Through Field Studies and an Integrated Hydrological Model of a Mountain Headwater Catchment

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