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Groundwater Resources Potential in Hard Rock Terrain: A Multivariate Approach
KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
2014 (English)In: Ground Water, ISSN 0017-467X, E-ISSN 1745-6584Article in journal (Refereed) Published
Abstract [en]

Groundwater resources are limited and difficult to predict in crystalline bedrock due to heterogeneity and anisotropy in rock fracture systems. Municipal-level governments often lack the resources for traditional hydrogeological tests when planning for sustainable use of water resources. A new methodology for assessing groundwater resources potential (GRP) based on geological and topographical factors using principal component analysis (PCA) and analysis of variance (ANOVA) was developed and tested. ANOVA results demonstrated statistically significant differences in classed variable groups as well as in classed GRP scores with regard to hydrogeological indicators, such as specific capacity (SC) and transmissivity. Results of PCA were used to govern the weight of the variables used in the prediction maps. GRP scores were able to identify 79% of wells in a verification dataset, which had SC values less than the total dataset median. GRP values showed statistically significant correlations using both parametric (using transformed datasets) and non-parametric methods. The method shows promise for municipal or regional level planning in crystalline terrains with high levels of heterogeneity and anisotropy as a hydrogeologically and statistically based tool to assist in assessing groundwater resources. The methodology is executed in a geographic information systems environment, and uses often readily available data, such as geological maps, feature maps and topography, and thus does not require expensive and time-consuming aquifer tests.

Place, publisher, year, edition, pages
John Wiley & Sons, 2014.
Keywords [en]
Coastal aquifer, Crystalline rock, Fracture, Geographic information system (GIS), Principal Component Analysis (PCA)
National Category
Environmental Management Other Environmental Engineering Remote Sensing Geology Oceanography, Hydrology and Water Resources Other Earth and Related Environmental Sciences Geosciences, Multidisciplinary
Identifiers
URN: urn:nbn:se:kth:diva-151298DOI: 10.1111/gwat.12265ISI: 000360758100009Scopus ID: 2-s2.0-84940744630OAI: oai:DiVA.org:kth-151298DiVA, id: diva2:747548
Note

Updated from Manuscript to published Article. QC 20150218

Available from: 2014-09-17 Created: 2014-09-17 Last updated: 2019-08-29Bibliographically approved
In thesis
1. Water supply in hard rock coastal regions: The effect of heterogeneity and kinematic porosity
Open this publication in new window or tab >>Water supply in hard rock coastal regions: The effect of heterogeneity and kinematic porosity
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Water resources in hard rock terrain are difficult to characterize due to heterogeneity and anisotropy in the fracture network, low porosities and limited recharge volumes available during the summer season. Three methods were developed and evaluated in order to assist in water supply planning. A groundwater resources potential index was estimated using multivariate statistics, where physical and geological variables were classified using Analysis of Variance and Fisher's Least Significant Difference tests according to their effect on hydraulic properties. Principal component analysis was used to assign weights to the different classed variables. Classes and weights were used to produce an index referred to as groundwater resources potential (GRP), which correlated significantly with well data. Nearly 80% of the wells with less than median specific capacity values also had GRP values at those locations of zero or lower. Non-stationary variance was observed in specific capacity sub-samples taken from the Geological Survey of Sweden's well archive, despite homogeneous geology and topography. Spatial statistical analyses showed that spatial correlations were weak in well archive samples, implying that regional approximations based on sparse point data are highly error prone. Kinematic porosity estimated using superficial fracture measurements correlated significantly with well archive data. However, low correlation coefficients indicated that well data is likely not a suitable method for predicting water supply characteristics. This approach is an efficient method which shows promise in preliminary estimations of groundwater storage in heterogenic terrains. A groundwater balance model which describes seasonal groundwater storage changes was created in order to better approximate the groundwater situation often found in Swedish urbanized and semi-urbanized hard rock terrains. The model was based on a water budget approach at the pixel scale, and allows for approximation of well extraction which is not uniformly distributed in space. The model showed that in specific regions groundwater extraction may lead to severe decreases in groundwater level, where these impacts may not otherwise be expected. Dry season modelling with 10% increased evapotranspiration showed that in several areas groundwater reservoir depletion may be influenced by more than 50%.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. p. xii, 31
Series
TRITA-LWR. LIC, ISSN 1650-8629 ; 2014:03
Keywords
Coastal aquifer; Crystalline rock; Water balance; Geographic information systems; Water supply planning
National Category
Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-143647 (URN)978-91-7595-071-6 (ISBN)
Presentation
2014-04-16, V3, Teknikringen 76, 2tr, KTH, Stockholm, 13:15 (English)
Opponent
Supervisors
Note

QC 20140331

Available from: 2014-03-31 Created: 2014-03-26 Last updated: 2015-02-18Bibliographically approved
2. Groundwater resources in hard rock coastal terrains: Insights into heterogeneity and spatial variability
Open this publication in new window or tab >>Groundwater resources in hard rock coastal terrains: Insights into heterogeneity and spatial variability
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Challenges regarding water security in hard rock coastal regions with limited soil cover are: a seasonal absence of recharge during times of peak residency, heterogeneity and variability of the fracture network, close proximity to saline water sources and spatially inconsistent storage and extraction. In areas where it is not feasible to connect residents to municipal water systems, a better understanding of the resilience of reservoirs is needed. The purpose of this study is to investigate and describe the spatial nature of hydraulic data in these types of terrains and present several novel GIS-based groundwater tools with the intent of increasing local water security and aiding in sustainable water resources management. Methods used in this study include groundwater balance modelling and conceptual groundwater storage modelling, as well as a combination of parametric and non-parametric statistical methods such as ANOVA, PCA, correlation and semivariogram analyses. Specific capacity estimates from the Geological Survey of Sweden’s well archive grouped by age or rock type showed very little autocorrelation and in assumed homogeneous geological regions showed statistically significant differences when arbitrarily grouped along a lineament. Estimates of kinematic porosity based on surface fracture data were found have statistically significant correlations with the well data. A GIS-based multivariate prediction tool for assessing Groundwater Resources Potential (GRP) was found to have statistically significant correlations with well data. The GRP method was then combined with a conceptual groundwater storage model and was subsequently found to have statistically significant correlations with chloride concentrations in well quality tests. The storage model was found to have a spatially-dependent sensitivity, meaning that different assumptions within the model had varying effects on the model depending on the geological settings. Incorporating the storage model into a spatial groundwater balance model was then compared with groundwater level time series data over a period of two years, where it was found to have a good explanative capacity and RMSE values of the storage ratio (0.06 to 0.34). Additionally, a soil depth model was developed, tested and found to produce promising results in regions with frequent rock outcrops, where up to 86% of estimates were within 2 m of actual soil depths. Conclusions from this study illustrate the need for a spatial approach to groundwater resources in these types of terrains, and demonstrate a strong potential of several new tools for quantity, capacity and vulnerability estimates to increase water security in a changing climate.

Abstract [sv]

Utmaningar för grundvattenförsörjning i kustnära områden med litet jordtäcke inkluderar begränsad grundvattenbildning under sommarsäsongen när behoven av vatten är som störst, heterogenitet i vattenflöde, närhet till saltvattenkällor samt heterogen lagring och uttag. I områden där det inte är möjligt att ansluta boende till kommunala VA-system behövs en bättre förståelse av magasinens uthållighet för att tillgodose vattenbehoven under nuvarande och ändrade klimatförhållanden. Syftet med forskningen har varit att undersöka det rumsliga beteendet hos hydraulisk data och att öka kunskapen om grundvattnets sårbarhet i kustnära områden med kristallin berggrund och tunna jordlager samt att utveckla verktyg för att beräkna vattenuttag och användning i dylika områden. Projekten har bedrivits med hjälp av GIS-verktyg, parametriska och icke-parametriska statistiska metoder såsom ANOVA, PCA, variogramsanalyser och korrelationsanalyser, samt modellering med grundvattenbalanser och grundvattenlagring.

Brunnsdata från borrade brunnar, grupperade efter ålder och berggrundstyp visade på svag rumslig korrelation. I områden med en antagen geologisk homogenitet hittades statistiskt signifikanta skillnader i brunnkapacitetsdata vid slumpmässig gruppering längs ett lineament. Uppskattningar av kinematisk porositet baserad på ytliga sprickmätningar har visat statistiskt signifikanta korrelationer med brunnskapacitet. Ett multivariat prediktionsverktyg (GRP) för bedömning av områden med god utvinningskapacitet har utvecklats och visade statistiskt signifikanta korrelationer med kapaciteten från existerande brunnar.

GRP-metoden kombinerades sedan med en konceptuell grundvattenmagasinsmodell som visade statistiskt signifikanta korrelationer med kloridhalter tagna från ett brunnskemiarkiv. Magasinsmodellen visade sig ha en rumsligt beroende känslighet, vilket innebar att olika antaganden inom modellen, bland annat avseende geologiska egenskaper i terrängen, hade varierande effekt på modellresultaten. En grundvattenbalansmodell har också utvecklats i GIS och jämförts med verkliga tidserier av grundvattennivå över en tvåårsperiod, med RMSE-värden varierande mellan 0,06 till 0,34. Som hjälp för att beräkna magasineringen i jordlager har en jorddjupsmodell utvecklats och testats vilken visade god överensstämmelse med existerande borrhål i områden med kristallint berg och stor berghällfrekvens.

Slutsatserna från dessa studier ger stöd till behovet av att ta hänsyn till det rumsliga förhållandet hos grundvattenresurserna i områden med kristallin berggrund och visar hur den rumsliga variationen kan beskrivas. Ökad kunskap om den rumsliga variationen kan ge möjlighet att utveckla förbättrade uppskattningar av grundvattenresurserna vilket i sin tur kan leda till bättre användning av befintliga vattenresurser. Dessutom har ett flertal nya verktyg utvecklats för potentiella beräkningar av kvantitet, kapacitet och sårbarhetsanalyser för grundvattenresurserna vilka kan användas för att analysera vattensäkerheten vid olika klimat- och markanvändningsscenarier.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. p. 45
Series
TRITA-ABE-DLT ; 1932
Keywords
Crystalline Rock, Groundwater Balance, Kinematic porosity, Groundwater Recharge, Water Security, Coastal Aquifer
National Category
Water Engineering Environmental Management Environmental Sciences
Research subject
Land and Water Resources Engineering
Identifiers
urn:nbn:se:kth:diva-256317 (URN)978-91-7873-272-2 (ISBN)
Public defence
2019-09-20, F3, Lindstedtsvägen 26, Stockholm, 14:00 (English)
Opponent
Supervisors
Funder
The Geological Survey of Sweden (SGU), 60-1640/2007Swedish Research Council Formas, 2017-01504
Note

QC 20190830

Available from: 2019-08-30 Created: 2019-08-29 Last updated: 2019-08-30Bibliographically approved

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