A Conceptual Hydrogeological Model of the Gothenburg City Area with a Special Focus on Its Application to Determine Groundwater

UNIVERSITY OF GOTHENBURG Department of Earth Sciences Geovetarcentrum/Earth Science Centre

A conceptual hydrogeological

model of the Gothenburg city

area with a special focus on

its application to determine

groundwater recharge

- a feasibility study

Hannah Berg Johanna Engelbrektsson

ISSN 1400-3821 B957 Master of Science (120 credits) thesis Göteborg 2016

Mailing address Address Telephone Telefax Geovetarcentrum Geovetarcentrum Geovetarcentrum 031-786 19 56 031-786 19 86 Göteborg University S 405 30 Göteborg Guldhedsgatan 5A S-405 30 Göteborg SWEDEN Abstract Urban hydrogeology and its complexity are important to understand since half of the world’s population is living in urban areas which puts pressure on the environment and its water resources. Because groundwater can affect the ground stability, interact with urban constructions and is the primary water resource in many countries it is important to gain further knowledge of mechanisms controlling groundwater recharge in order to manage urban groundwater in a sustainable way. The aim of this study is to improve the knowledge of urban hydrogeology by creating a conceptual hydrogeological model of an area (Haga and Linné) in central Gothenburg (Sweden). The conceptual model was then used to evaluate groundwater recharge to the two main aquifer systems in Gothenburg; the upper, shallow unconfined and the lower one which is confined by a thick layer of marine clay. The study is designed as a feasibility study showing foremost the options and potentials to create and apply such a model and to evaluate the availability and usability of existing data available for this. The conceptual model is based on information gathered from authorities, literature studies, through interviews, and a questionnaire. The model is based on interpolated stratigraphical layers and potentiometric surfaces created using Kriging and Spline with barriers interpolation methods in Surfer® 11 and ArcMap 10.1. A numerical model was used to estimate direct groundwater recharge to the upper and lower aquifers based on infiltration coefficients of different land cover and soil type. In areas, generally close to bedrock outcrops, where the clay layer is thinner than 1.5 m the upper unconfined aquifer (mainly anthropogenic fill material) could be in contact with the lower confined aquifer (“friction material”, within this thesis a combination of gravel, sand and till). The main mechanisms of groundwater recharge to the lower aquifer appear to be from surface runoff from steep areas followed by infiltration in contact zones between bedrock and friction material, contribution of groundwater via fractured bedrock, leakage from water supply and sewage systems and other artificial infiltration and to a smaller degree vertical infiltration and lateral groundwater inflow from “outside” Gothenburg. The median groundwater recharge via direct recharge to the lower aquifer in Haga and Linné is estimated to be 59– 93 mm/year. Future research projects would benefit from better communication and collaboration between different companies and authorities regarding data management and data hosting which will enable better possibilities to handle information in a structured and more easily accessible way.

Sammanfattning Urban hydrogeologi och dess komplexitet är viktigt att förstå eftersom hälften av världens befolkning lever i en urban miljö vilket sätter press på miljön och dess vattenresurser. Eftersom grundvatten kan påverka markstabilitet, urbana konstruktioner och är i många länder också den främsta vattenresursen är det viktigt att få ytterligare kunskap om de mekanismer som styr grundvattenbildning för att kunna hantera urbant grundvatten på ett hållbart sätt. Syftet med denna studie är att förbättra kunskapen om urban hydrogeologi genom att skapa en konceptuell hydrogeologisk modell över ett område (Haga och Linné) i centrala Göteborg (Sverige). Den konceptuella modellen användes sedan för att utvärdera grundvattenbildning till de två huvudsakliga akvifersystemen i Göteborg; den övre grunda öppna och den undre som är sluten av ett tjockt lager av marin lera. Studien är utformad som en förstudie med avsikt att visa de alternativ och möjligheter som finns för att skapa och tillämpa en sådan modell och utvärdera tillgängligheten och användbarheten av den tillgängliga data som existerar. Den konceptuella modellen bygger på information som samlats in från myndigheter, genom litteraturstudier, intervjuer och en enkät. Modellen bygger på interpolerade stratigrafiska lager och potentiometriska ytor som skapats med Kriging- och ”Spline with barriers” interpoleringsmetoder i Surfer® 11 och ArcMap 10.1. En numerisk modell användes för att uppskatta grundvattenbildning genom direkt infiltration till den övre och undre akviferen genom att använda infiltrationskoefficienter för olika typer av markanvändning och jordarter. I områden, huvudsakligen när berggrundshällar, där lerlagret har en mäktighet på mindre än 1,5 m kan den övre öppna akviferen (huvudsakligen antropogent fyllnadsmaterial) vara i kontakt med den undre slutna akviferen (friktionsmaterialet, vilket i denna studie inkluderar grus, sand och morän). De huvudsakliga mekanismerna för grundvattenbildning till den undre akviferen verkar vara från ytavrinning från branta områden följt av infiltration i kontaktzoner mellan berggrunden och friktionsmaterial, tillskott av grundvatten genom sprickor i berggrunden, läckage från VA-ledningar och annan konstgjord infiltration och i mindre grad vertikal infiltration och tillströmning genom grundvattenflöde från ”utanför” Göteborg. Medianvärdet för grundvattenbildningen via direkt grundvattenbildning till den undre akviferen i Haga och Linné uppskattas vara 59 – 93 mm/år. Framtida forskningsprojekt skulle gynnas av bättre kommunikation och samarbete mellan olika företag och myndigheter för hantering av data och datavärdskap vilket skulle göra det möjligt att hantera information på ett mer strukturerat och lättillgängligt sätt.

Contents Abstract ...... 1 Sammanfattning ...... 2 1. Introduction ...... 5 1.1. General background and motivation ...... 5 1.2. Objective and aim ...... 5 1.3. Project outline ...... 6 2. Theoretical background – Hydrogeological elements ...... 7 2.1. Hydrological cycle with focus on groundwater ...... 7 2.2. Elements of the hydrological cycle related to water balance calculations ...... 9 2.3. Subsurface water with special focus on groundwater ...... 13 2.4. Urban hydrogeology ...... 20 2.5. Three-dimensional modelling ...... 22 3. Case study ...... 23 3.1. Geology and hydrogeology in Gothenburg ...... 23 3.2. Geotechnical challenges in Gothenburg ...... 24 3.3. Future climate ...... 25 3.4. Future projects in Gothenburg ...... 25 3.5. Description of the study area (Haga and Linné) ...... 26 3.6. Data hosting ...... 31 4. Methods and data ...... 34 4.1. Data sources ...... 34 4.2. Methods ...... 37 5. Results ...... 56 5.1. Compilation of available data ...... 56 5.2. Conceptual hydrogeological model ...... 67 5.3. Questionnaire and interviews with groundwater professionals ...... 86 5.4. Numerical model of groundwater recharge ...... 89 6. Discussion ...... 97 6.1. Discussion of uncertainties and limitations ...... 97 6.2. Thicknesses and positions of relevant hydrogeological formations in Gothenburg with special focus on the upper and lower aquifers ...... 99 6.3. Is the lower aquifer a continuous aquifer? ...... 101 6.4. Connections between the upper and lower aquifers...... 103

6.5. Mechanisms of recharge to the lower aquifer ...... 104 6.6. Climatic versus human impact on groundwater recharge ...... 107 6.7. A consistent hydrogeological model of Gothenburg? ...... 108 6.8. Availability, accessibility and usability of geological/hydrogeological data in Gothenburg 109 7. Conclusion ...... 111 8. Future studies ...... 112 9. Acknowledgement ...... 113 10. References ...... 114 11. Appendix ...... 119 11.1. Appendix 1 ...... 119 11.2. Appendix 2 ...... 123 11.3. Appendix 3 ...... 124 11.4. Appendix 4 ...... 125 11.5. Appendix 5 ...... 144 11.6. Appendix 6 ...... 145 11.7. Appendix 7 ...... 146 11.8. Appendix 8 ...... 147

1. Introduction

1.1. General background and motivation The interaction between urban development and groundwater is important to understand since urban environments can change groundwater recharge, groundwater flow dynamics, local water balances and contribute to contamination by metals and industrial compounds from industries (Lerner, 2002; Salvadore, Bronders, & Batelaan, 2015). Therefore, it is vital to understand the hydrogeological system and its relation to the urban structures in order to meet the environmental goals, suggest solutions to technical and environmental problems, address climatic change and other urban development challenges. Several tunnelling and infrastructure projects are in progress or planned in Sweden, e.g. the Western Link (Västlänken) project in Gothenburg. Such large scale infrastructure projects require a particular thorough investigation of the groundwater situation. A widely unsolved question is the mechanisms of groundwater recharge in urban areas (Lerner, 2002). In Gothenburg, deep valleys cut into the bedrock filled with a layer of thick clay characterises the geology. The clay layers separate an upper unconfined and a lower confined aquifer. This geological setup can cause a number of geotechnical challenges, including the risk of land subsidence and landslides. These risks are largely controlled by the hydraulic conditions in the system which in turn is controlled by human interference and naturally occurring groundwater recharge. Being able to determine groundwater recharge and understanding its mechanisms is thus an essential prerequisite to managing those risks.

The present project is partly a continuation of the master thesis by Ljungdahl (2015) and Albertsson (2014) and draws on the data they collected. To develop a further understanding about the stratigraphy and groundwater recharge in Gothenburg additional data was acquired and opinions from groundwater professionals were evaluated.

1.2. Objective and aim The overall aim of this thesis is to create a conceptual hydrogeological model of Gothenburg which in turn will be used to evaluate mechanisms of groundwater recharge to the lower aquifer. As there is a large number of data that could be used and much of this data is not immediately accessible and usable, the study will be designed as a feasibility study, showing foremost the options and potentials to create and apply such a model.

The main objectives of this thesis intend to:

• Create continuous contour maps of the thickness and position of relevant geological units in Gothenburg with special focus on the upper and lower aquifers. • Evaluate the availability and usability of geological/hydrogeological data collected within the time frame for this project. • Determine the opinions from groundwater and geotechnical professionals about mechanisms of groundwater recharge and on how a hydrogeological model should be designed to be feasible and applicable.

The main research questions are thereby:

• To what degree can the lower aquifer (friction material) be regarded as a continuous aquifer? • Where and how are the upper and lower aquifer connected? • What are the main mechanisms of recharge to the lower aquifer, how does it work, where are the recharge areas in Gothenburg located? • Is it possible to separate climatic from human impact on groundwater recharge? • Is it possible to create a consistent hydrogeological model of Gothenburg?

The underlying hypothesis is thereby that the mechanisms of groundwater recharge in the Gothenburg area are not yet completely understood and that the current opinions of how groundwater recharge in Gothenburg works do not adequately consider all potentially existing mechanisms.

1.3. Project outline This study was completed with guidance from Professor Roland Barthel at the University of Gothenburg. The thesis is based on data and information gathered from authorities, literature studies, through meetings and interviews with people working with hydrology/hydrogeology. The results are a stratigraphical model of the geological units and their thicknesses, a conceptual model of groundwater recharge mechanisms and potentiometric pressures of the lower aquifer which in turn make up the conceptual hydrogeological model. Also, a numerical model estimating the groundwater recharge and a compilation of the available data are produced. The results are mainly focussed on the area around Haga and Linné but are also further discussed in a wider context for the city of Gothenburg and other urban cities. Figure 1 shows a schematic workflow of this thesis. The blue boxes show the data sources that were used, and are presented in more detailed in section 4.1. The turquoise and green boxes show the results and are presented under section 5.

Figure 1. Workflow scheme of the thesis. The blue boxes illustrate the data used and the turquoise boxes show the obtained results. Some of the results are additionally used in order to compile further results, presented in the green boxes.

2. Theoretical background – Hydrogeological elements Hydrogeology is the study of the relationship between geological materials and processes with water (Fetter, 2001). Groundwater is defined as water located beneath earth’s surface which fills pore spaces and fractures in soil and bedrock formations and has a pore water pressure equal or higher than atmospheric pressure (Knutsson, Morfeldt, Dahlström, & Nicolson, 2002). This chapter starts with a brief general introduction of the hydrologic cycle and the components most relevant to this study. Next, the processes of groundwater recharge are explained in more detail and how groundwater behaviour in urban areas differs from rural environments.

2.1. Hydrological cycle with focus on groundwater Groundwater represents the underground part of the hydrologic cycle (Figure 2) which in turn describes the continuous movement of water on the earth (Fetter, 2001). It is therefore of great importance to understand the processes of the hydrologic cycle to be able to further understand the processes that effect groundwater and its properties.

As the name cycle implies there is no beginning or end of the transportation of water. The main driving forces of the cycle are solar energy and gravity (Knutsson et al., 2002). Solar energy causes water in liquid form to change to gas/vapour (evaporation). Therefore oceans and other water bodies can be considered as a starting point when explaining the hydrologic cycle where water evaporates from the water surfaces. The evaporated water can then under suitable atmospheric conditions form droplets (condensation), which can fall as precipitation or re-evaporise while still in the air. When precipitation falls on the ground the water can take several pathways back to the oceans, and during its course temporarily be stored in depression storages, like ice, snow and water bodies. Some of the precipitation will drain the land to a river, or some other form of stream channel, while other parts will infiltrate into the ground. In the uppermost part of the ground, called the vadose zone, soil pores contain both air and water (Figure 3). It is from this region the roots of plants can absorb water, and by transpiration from the plants water can become vapour again. Lateral water movement in the vadose zone is called interflow and it is possible for vapour in the vadose zone to migrate back to the surface again and evaporate. As mentioned before one of the driving forces in the hydrologic cycle is gravity. It acts on the extra water in the vadose zone so the water pulls downwards (gravity drainage) towards a point called capillary fringe and further to the zone of saturation. The capillary fringe is a zone in which the saturation is close to 100% because of capillary forces act on the water and holds it in place. The water table is the top of the zone of saturation and the water stored in this zone, as mentioned before, is called groundwater. Groundwater movement is called baseflow and it is together with overland flow sources of water for surface waters (pond, lake, oceans etc.). Magmatic water is also below the water table but the water is contained within magma chambers deep in the crust. Magmatic water forms when parts of the oceanic crust with water filled sediments are subducted. This process is slow in comparison to other process in the hydrologic cycle. Magmatic water can be returned to the earth’s surface again via magma eruption or sea floor vents.

Atmosphere (Water vapour)

Precipitation Precipitation Evaporation Evaporation Precipitation Evapotranspiration

Land surface Overland flow Lakes, ponds, Runoff Ocean (Ice, snow, streams & (Seawater) depression storage) rivers (Surface water)

r u

Vapo Infiltration movement

Vadose zone Interflow (Soil moister)

Rising magma in volcano magma Rising Capillary rise Gravity drainage Baseflow Zone of Saturation Subsea outflow (Groundwater)

Subduction Sea floor vent

Lithosphere (Magmatic water)

Figure 2. Schematic drawing of the hydrological cycle. The boxes represents water storage and the lines represents water movement, modified from Fetter (2001).

Figure 3. Classification of subsurface water, modified from Fetter (2001).

2.2. Elements of the hydrological cycle related to water balance calculations The hydrologic cycle is a central concept in hydrology but it is to schematic to allow quantitative calculations in e.g. a restricted area. The hydrologic equation (Eq.1) offers a way of quantifying the elements of the hydrologic cycle and further analysing the water budget for a defined area.

= ± (Eq.1)

The inflow to an area can be𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼 precipitation,𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜 surface𝑐𝑐 ℎand𝑎𝑎𝑎𝑎 𝑎𝑎𝑎𝑎𝑎𝑎groundwater𝑖𝑖𝑖𝑖 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 inflow from outside the area, artificial import of water (Fetter, 2001). Outflow can be evapotranspiration, evaporation from surface water, ground-water outflow, surface water runoff and export of water by artificial means. Changes in storage can be caused by volume changes in: surface water, snow and ice, water in the vadose zone, water on plants surfaces, groundwater, and other forms of temporary depression storages. With this in mind equation (Eq.1) can be rewritten to evaluate the water balance in an area:

+ = + + S (Eq.2)

𝑃𝑃 𝑄𝑄𝑖𝑖𝑖𝑖 𝐸𝐸𝐸𝐸 𝑄𝑄𝑜𝑜𝑜𝑜𝑜𝑜 ∆ where

P= Precipitation

Qin = Surface water and groundwater inflow to the area ET= Evapotranspiration (Evaporation and transpiration)

Qout = Surface water and groundwater outflow from the area ∆S= Changes in water storage

To be able to obtain actual values to use in this water balance equation (Eq.2) the different elements have to be quantified by different measuring methods (Svensson, 1984). The elements in equation

(Eq.2) measure the water flow in different formats (concentrated, different phases or inside other materials) and therefore the accuracy varies depending on the measuring techniques used.

2.2.1. Precipitation Precipitation can be in different forms and is one of the inflow elements in a water balance calculation. The amount of precipitation is often the controlling factor that restricts the amount of water available for the other processes in the hydrologic cycle, e.g. transpiration, evaporation, and infiltration. Precipitation is measured in mm per time unit where 1 mm corresponds to 1 l/m2 (Knutsson et al., 2002). Observations of volume, distribution and character over a long period of time with continuous measuring intervals from the same station are desirable for precipitations measurements. There are several factors (wind, topography, distance to the coast and time of the year) which affect the amount and distribution of precipitation (SMHI, 2013a).

In Sweden there are two (annual) precipitation maximums one on the western side of the south Swedish highland and the other one 10-20 kilometres from the Norwegian border in Norrland (Figure 4). The Swedish Meteorological and Hydrological Institute (SMHI) which is responsible to keep records of precipitation data has around 750 measuring stations in Sweden that measure precipitation (SMHI, 2012).

Figure 4. Annual precipitation in Sweden 1961-1990, from SMHI (2013a).

2.2.2. Evapotranspiration Evapotranspiration is the total amount of water that evaporates from ground or water surfaces and vegetation transpiration (Knutsson et al., 2002). Evaporation and transpiration measurements are not possible to separate in field conditions and are therefore measured together, often in mm per time unit. There is a difference between potential and actual evapotranspiration. Potential evapotranspiration is described by Thornthwaite (1944) as equal to “the water loss, which will occur if at no time there is a deficiency of water in the soil for the use of vegetation” while actual evapotranspiration is the amount of evapotranspiration that occurs under field conditions. The actual evapotranspiration can be determined by a lysimeter which is a field instrument that measures the amount of evapotranspiration released by vegetation and is calculated using the following equation (Eq.3).

= + + (Eq.3)

𝐸𝐸𝑇𝑇 𝑆𝑆𝑖𝑖 𝑃𝑃𝑅𝑅 𝐼𝐼𝑅𝑅 − 𝑆𝑆𝑓𝑓 − 𝐷𝐷𝐸𝐸 where

ET = the evapotranspiration for a period

Si = the volume of initial soil water

Sf = the volume of final soil water

PR = the precipitation into the lysimeter

IR = the irrigation water added to the lysimeter

DE = the excess moister drained from the soil

The actual evapotranspiration can also be estimated using the Pennman-Monteith equation which requires information about wind speed, daily mean temperature, solar radiation, and relative humidity (Beven, 1979). It is also possible to calculate a rough estimation of the actual evapotranspiration for areas with similar climate as Sweden only based on the annual average temperature with the Tamm’s formula (Tamm, 1959). If radiation and humidity data are available the method after Turc (1961) could also be used to calculate daily potential evapotranspiration. The Turc method is comprised of two equations depending on the relative humidity of the air. However, this method can only be used when the temperature is over zero degrees. For lower temperatures, the method after Ivanov (Wendling & Müller, 1984) could be used when estimating monthly evapotranspiration when the temperature is below zero.

In Sweden there are not any direct measurements of evaporation apart from research projects. Though, annual average evapotranspiration are calculated and in the south and middle parts of Sweden it is estimated to be 400-500 mm /year while it is below 100 mm/year in the mountain (fell) areas (Knutsson et al., 2002).

2.2.3. Discharge The water flow in or out from an area is the sum of surface flow, interflow and groundwater flow and is often measured in m3/s or l/s. Most of the water flow in and out from an area is in form of surface water and can therefore be measured direct from surface water bodies (Svensson, 1984). The specific discharge, measured in l/s/km2 or mm/year, for an area can be obtained by dividing the water flow by the current areas surface area.

SMHI has around 330 hydrological measuring stations in Sweden which measure discharge (the volume rate of water flow) (SMHI, 2015). The annual discharge in Sweden, calculated for the period 1961- 1990, varies between 1500 mm /year in the northern fell areas to 100 mm/year in the southern and eastern parts (Figure 5).

Figure 5. Annual discharge in Sweden between 1961-1990, from SMHI (2009).

2.2.4. Water storage Changes in water storage affects water balance calculations. Surface water can e.g. be stored as snow, ice, lakes, streams and other forms of surface water bodies (Fetter, 2001). Changes in water storage volume can be due to an increase or decrease in precipitation, evapotranspiration (evaporation), overland flow, runoff, infiltration to the vadose zone and outlets from sea floor vents to the oceans. Volume changes in the vadose zone can be caused by changes in infiltration, vapour movement, interflow and exchange with the zone of saturation (Grip & Rodhe, 2000). Groundwater storage

12 depends on how much water is drained from the vadose zone which in turn depends on the infiltration capacity of the surface. Groundwater storage also depends on how much of the water leaves the area due to the groundwater discharge into surface water bodies and on extraction by humans.

2.3. Subsurface water with special focus on groundwater Groundwater is, as mentioned before, a part of the hydrologic cycle and is the water contained in interconnected pores below the groundwater table (Fetter, 2001).

2.3.1. Aquifers An aquifer is a saturated water bearing geological formation from which groundwater can be extracted (Fetter, 2001). A confining layer has a little or no hydraulic conductivity (less than 10-2 darcy), which means that groundwater can move through these layers but with a slow rate. There are two kinds of aquifers, confined and unconfined (Figure 6). An unconfined aquifer is in direct contact with the atmosphere, no confining layers between the surface and the zone of saturation i.e. the hydrostatic pressure is the same as the atmospheric pressure (Knutsson et al., 2002). Recharge to an unconfined aquifer could be through downward infiltration from the unsaturated zone, upward seepage from underlying layers and lateral groundwater flow (Fetter, 2001). A confined aquifer is an aquifer overlain by a confining layer with significantly lower hydraulic conductivity. Therefore, a confined aquifer has a higher pressure than the atmospheric pressure. The potentiometric surface is the level to which the groundwater would rise in a well due to the pressure in the aquifer. Recharge to a confined aquifer can occur through areas where the aquifer crops out and leakage from the confining layers. To which level (pressure) the groundwater is in an aquifer can be measured with a piezometer which is a nonpumping well that measures the liquid pressure. A piezometer is open at the top and bottom and the water will rise in direct proportion to the total fluid energy at the point at which the bottom of the piezometer is open (Fetter, 2001).

Potentiometric surface Water table Unconfined aquifer

Confining layer

Confined aquifer

Confining layer

Figure 6. An upper unconfined and a lower confined aquifer with wells indicating where the potentiometric surface and water table are, modified from Fetter (2001); Knutsson et al. (2002).

2.3.2. Aquifer properties In a soil the movement of water is dependent on; porosity, specific yield, storativity, permeability, hydraulic conductivity and transmissivity which in turn can affect how much of the precipitation that will become groundwater (Fetter, 2001).

Porosity of a material describes how much of its volume are void spaces, i.e. is available to contain water. Total porosity (n) can be calculated by the following equation (Eq.4) (Domenico & Schwartz, 1998):

(Eq.4) = 𝑉𝑉𝑣𝑣 𝑛𝑛 𝑉𝑉𝑇𝑇 where

VV = the void volume

VT = the total volume of the material

The total and effective porosity can be calculated with equation (Eq.4).The total porosity is the total void space which is available for water. But since not all voids (pore spaces) in e.g. a soil are connected, water can be strongly bound to grain surfaces, and because flow velocity in very fine pores and the small edges of larger pores is reduced due to friction, effective porosity (also known as kinematic porosity) represents the volume water that can actually flow through divided by the total volume. Porosity is divided into two categories based on how the pore spaces formed (Fetter, 2001). Primary porosity describes pore openings formed when the sediment was deposited or the rock crystallized. While secondary porosity openings caused by processes e.g. weathering or fracturing which occurs after the rock or sediments are formed. For sediments porosity varies with how well the sediments are sorted, for well sorted sediments the porosity is higher than for sediments that are mixed (Table 1).

Table 1. Porosity ranges (%) for sediment, from Fetter (2001) .

Soil type Porosity (%) Well-sorted sand or gravel 25-50 Sand and gravel, mixed 20-35 Glacial till 10-20 Silt 35-50 Clay 33-66

Specific yield (Sy), is a ratio of the volume of water which will drain under the force of gravity in relation to the total volume of the material (e.g. sediment) under saturated conditions (Johnson, 1967). It is not a definitive value since the volume of water which will drain depends on several factors such as temperature, duration of the measurement, physical characteristics of the material, and mineral composition of the water. Specific yield (Sy) can be calculated with the following equation (Eq.5):

(Eq.5) = 𝑉𝑉𝑤𝑤𝑤𝑤 𝑆𝑆𝑦𝑦 𝑉𝑉𝑇𝑇 where

Vwd = the volume of water drained

VT = the total volume of the material

Specific yield can be measured with laboratory methods or in the field with pumping tests. Due to surface tensions sediments with lower average grain size will have lower specific yield than sediments with higher average grain size. Quite often, but without a clear physical explanation effective porosity is assumed to be equal to the specific yield of an unconfined aquifer.

Storativity, or storage coefficient, for an unconfined aquifer (see section 2.3.1) equals the specific yield. For a confined aquifer the change in its volume storage (the volume of water the aquifer takes in or releases) per unit area of the aquifer per unit change in head (Fetter, 2001). In a confined aquifer a small withdrawal decreases the potentiometric presure since the water released only corresponds to the volume change cause by compression of granular structures and expansion of the water (Knutsson et al., 2002).

Henry Darcy identified in the mid-1800s that the rate of water flow through a given material is in proportional relationship to the change of hydraulic gradient i.e. pressure drop between two points and that the quantity of flow depends on the properties of the media the water flows through together with the cross-sectional area of the medium (Fetter, 2001). This relationship is known as Darcy’s law (Eq.6):

(Eq.6) = ( ) 𝑑𝑑ℎ 𝑄𝑄 −𝐾𝐾𝐾𝐾 𝑑𝑑𝑑𝑑 where

Q = Discharge (volume/time) K= Hydraulic conductivity (distance/time) A= Cross-sectional area (units of area) dh/dl = Hydraulic gradient (dimensionless)

Permeability describes a sediment’s or a rock’s ability to let a fluid to pass through it (Knutsson et al., 2002). It is given as groundwater flow per time unit through a surface perpendicular to the flow direction when the hydraulic gradient is equal to one. The SI unit for permeability is m2. There are several factors which affect the permeability such as effective porosity, material properties, structures, stratigraphy and the amount of air captured in the material. If properties of the fluid passing through the material also are taken into consideration permeability is referred to as hydraulic conductivity (or coefficient of permeability) and is given in length per time (e.g. m/s or cm/s). The hydraulic conductivity (K) can be calculated with the following equation (Eq.7) which is a rearrangement of equation (Eq.6):

(Eq.7) = −( 𝑄𝑄 ) 𝐾𝐾 𝑑𝑑ℎ 𝐴𝐴 𝑑𝑑𝑑𝑑 where

Q = Discharge A= Area dh/dL = Hydraulic gradient

The hydraulic conductivity for clay and till is lower than compared to gravel or sand but the range of primary porosity is despite that higher for clay and till (Table 2). This is due to the fact that the pore spaces are not as well connected in clay and till sediments as they are in gravel and sand, hence lower hydraulic conductivity. Since permeability can be different in different directions transmissivity describes, under a certain gradient, a measurement of how much water can move through a layer, e.g. m2/s (Knutsson et al., 2002).

Table 2. Porosity and hydraulic conductivity, modified from Brown (1972)

Porosity Hydraulic Primary (%) Secondary* conductivity (m/s) Sediments Gravel 30-40 100 - 10-2 Coarse sand 30-40 10-1 - 10-4 Medium- fine 30-35 10-2 – 10-6 sand Silt 40-50 Occasional 10-7 – 10-9 Clay, till 40-55 Rare (mud cracks) 10-8 – 10-11 Crystalline rocks Granite, gneiss - Weathering and joints 10-2 – 10-11 etc. (decreasing with depth) *Rarely >10%

2.3.3. Infiltration The infiltration rate into a soil varies over time. For example, if there is a constant or increasing supply of water to the surface the infiltration rate will initially be rapid but after a while it starts to decrease and continue to do so over time (Figure 7). This was first identified by Horton (1933); (1941). The infiltration capacity is the maximum rate at which water can enter a soil under given conditions and is a function of the soil moister content since capillary forces between the soil particles decreases with increasing soil moisture. When the infiltration capacity is reached the water will cumulate in depression storages which with time can form overland flow.

Period of precipitation

Period of overland flow Period of infiltration

Rate (cm/h) Infiltration capacity

Time

Incremental precipitation rate Amount of infiltration Amount of depression storage Amount of overland flow

Figure 7. Increasing precipitation rate, amounts of infiltration, depression storage and overland flow, modified from Fetter (2001).

2.3.4. Pathways for precipitation to groundwater In De Vries and Simmers (2002) three ways of how rainwater reaches an aquifers in a rural environment is described: direct, localised and indirect. The classification is based on spatial distribution which means that precipitation that vertically infiltrates below the point of impact is termed direct whereas if water infiltrates after a short distance of lateral movement is called localised. Indirect recharge involves recharge from runoff into e.g. a river (Lerner, 2002). Direct recharge dominates in humid regions whereas in arid regions localised and indirect recharge is more common (Scanlon, Healy, & Cook, 2002).

2.3.5. Groundwater level fluctuations The changes in a groundwater level during a year are mainly due to seasonal weather variations and when the recharge occurs (Knutsson et al., 2002; Lång, 2009). All water that infiltrates into the ground does not become groundwater, some is lost through transportation from plants and some gets stuck if the field capacity is not reached (Knutsson et al., 2002). Field capacity is in the unsaturated zone the maximum amount of water a soil can hold against the pull of gravity (Fetter, 2001). Depending on the soil moisture content, drainable and effective porosity there can be a delay between the precipitation event and the change in groundwater level (Knutsson et al., 2002). This delay can be up to days in a

17 compact till and even months or up to one year in a more complex system with a deep-lying groundwater table. The groundwater table in shallow deposits in the southern and central parts of Sweden is lowest during the summer months due to high degree of evapotranspiration (Knutsson et al., 2002). In the northern parts of Sweden, the groundwater levels are lowest at the end of the winter due to frozen ground. The highest groundwater levels in Sweden are after the winter when the snow has melted and in the beginning of the autumn due to more precipitation. In Figure 8 changes of the groundwater table for different geological formations in similar environments is displayed. In large deposits with high specific yield (gravel) the amplitude of the groundwater level is small whereas in coarse sediment with low specific yield such as till the amplitudes can be up to meters. These differences in response times are due to permeability of the ground surface, thickness of the unsaturated zone and the size of the geological formation.

Figure 8. Groundwater level responses to comparable precipitation events in different geological formations, modified from Knutsson et al. (2002).

Short term fluctuations of the groundwater table can be caused by direct events such as cloudbursts, drought, transpiration, and changes in close by surface water bodies (Knutsson et al., 2002). Indirect events such as gravitational changes, earthquake, and changes in air pressure could also give rise to short-term fluctuations of the groundwater level.

2.3.6. Groundwater flow The flow of groundwater is controlled by the laws of thermodynamics and physics. There are three external forces acting on groundwater and the flow of it. Gravity pulling the water downward, external pressure from e.g. atmospheric pressure, and molecular attraction causing water to stick to solid surfaces (Fetter, 2001). Also, shear stress, normal stress, and viscosity are forces resisting the movement of water in the ground. Groundwater flow occurs when there is a difference in hydraulic

18 head, i.e. there is a hydraulic gradient (Domenico & Schwartz, 1998). It will generally have a vertical and a horizontal component. The direction of the horizontal component is generally perpendicular to the contour lines of the groundwater table (Conlon et al., 2005). By comparing water levels in nearby wells measuring at different depths in an aquifer it is possible determine the vertical component. On a regional scale in a unconfined homogenous aquifer the groundwater flow is downward at topographic high places (recharge zone) and upwards in topographic low areas (discharge zone) (Figure 9)(Fetter, 2001).

Discharge zone Recharge zone Discharge zone

Figure 9. Groundwater flow direction on regional scale in a unconfined homogenous aquifer in rural environments. Recharge zone located in high topographical places with vertical downward groundwater flow. Discharge zones in low- lying areas with vertical upward groundwater flow, from Fetter (2001).

2.3.7. Direct groundwater recharge The amount of groundwater recharge depends on how much water from the surface can infiltrate into the unsaturated zone and percolate downwards, below the groundwater table and down to the groundwater zone. How much of the water that reaches the surface and is available for infiltration depends on several factors such as what form the precipitation is in and its temporal distribution, terrain ruggedness, soil structures, soil type, surface conditions (e.g. if the ground is frozen), position of surface pressure and especially the soil layers and bedrocks water permeability. All these factors, apart from precipitation and terrain ruggedness, are dependent on properties of subsurface materials. In humid regions recharge is generally considered to occur in topographic highs and discharge in topographic lows while in arid alluvial – valley regions the recharge is concentrated in topographic lows (Scanlon et al., 2002).

2.3.8. Methods of quantifying groundwater recharge It is important to be able to quantify groundwater recharge when investigating groundwater withdrawal possibilities, planning constructions below the groundwater table, and when landfill sites should be located. Rough estimations can be done by considering precipitation, vegetation, topography and geology but for more quantitative estimations other methods are to be used (Knutsson et al., 2002). These methods can be divided depending on where the water movement in the groundwater system is studied: inflow, responses within the system, and discharge. Examples of inflow measurements are the use of natural and added tracers where the water movement in the unsaturated zone down to the water table can be observed. The method uses the average velocity of water particles and the water content in a defined distance in order to estimate the groundwater

19 recharge. Looking at responses within a groundwater system the recharge respectively the discharge in an unconfined aquifer can be estimated but the specific yield must be known for the stratigraphical layers within the fluctuation zone. A simple method in order to estimate the maximum groundwater recharge in an area is to look at the measured average discharge from e.g. a river. This method requires a well-defined catchment area with minor surface runoff. The methods vary in time resolution and measuring requirements (Knutsson et al., 2002).

2.4. Urban hydrogeology Today, approximately half of the world’s population is living in urban areas (United Nations, 2014) and 13% of the urban population today lives in coastal areas that are less than 10 m above sea level (McGranahan, Balk, & Anderson, 2007). According to the United Nations this trend will continue and by 2050 66 % of the world’s population is believed to live in an urban environment (United Nations, 2014). An increasing population puts pressure on the environment and its water resources as the need for water in urban areas is increasing simultaneously (Schirmer, Leschik, & Musolff, 2013). To cope with this demand surface and groundwater are often imported from outside the cities. Groundwater is today one of the primary water sources in many European countries such as Germany, Austria, Denmark, Hungary Belgium, Romania, Switzerland and former Yugoslavia but also in large cities in other parts of the world e.g. China, Libya, India, Saudi Arabia, Yemen and Tunisia (Zektser & Everett, 2000). However, if the groundwater is overexploited i.e. the extraction is greater than the recharge, it will cause falling groundwater levels which in turn can cause problems such as salt water intrusions, lowering of stream flow and lake levels, reduction of vegetation and land subsidence (Zektser, Loáiciga, & Wolf, 2005). Also, rising groundwater levels can cause problems such as flooded basements and tunnels and mobilised pollutants in unsaturated zones (Yang, Lerner, Barrett, & Tellam, 1999). Therefore, urban hydrology/hydrogeology and water management will have an increasing role to play in the sustainability of urban water, its quality and quantity (Niemczynowicz, 1999).

2.4.1. Urban hydrological cycle Groundwater recharge in urban areas compared to rural environments is very complex. The sources and pathways for groundwater recharge in urban areas are changed due to buildings, roads, other impervious surfaces and underground constructions as well as through leakage from water supply and sewage systems (Lerner, 2002; Schirmer et al., 2013), see Figure 10 for the changed pathways and routes. The two main sources of groundwater recharge in urban areas are precipitation and leakage from water supply and sewage systems (Yang et al., 1999). Surface coverings such as buildings and roads generally reduce infiltration of water into the ground while surface runoff is increased. In Newcomer, Gurdak, Sklar, and Nanus (2014) it is demonstrated that low impact development planning and best management practice have an influence on groundwater recharge since they increase groundwater recharge. The direct recharge can therefore be smaller but the indirect recharge due to leakage from water supply and sewage systems can in turn contribute and increase the groundwater recharge (Salvadore et al., 2015). Leakages of 20-25% from water supply and sewer systems are common in urban areas, but rates of 50 % are also reported (Lerner, 2002). Other influences which could contribute and increase the direct recharge are climatic changes e.g. reduced evapotranspiration, over-irrigation of green areas (Lerner, 1990) and artificial and near-natural storm water infiltration systems, which can delay and redirect surface runoff by e.g. keeping it in the soil and thereby increasing groundwater recharge (Göbel et al., 2004). Due to the complexity it is difficult to estimate groundwater recharge in urban areas.

Evapo- Precipitation Evaporation transpiration Consumptive Roofs use Surface Imported Surface Surface runoff water water water

Storm sewers Sewers Local Unsaturated Pickup in perched Unsaturated zone groundwater water tables zone Localised Direct Sewer Roof Infiltration Ground- Mains Irrigation Septic Sewer recharge recharge leakage soakways systems Ground- water leakage excess tanks leakage a) b) water

Figure 10. Pathways for precipitation and b) routes for water supply and sewage systems to recharge groundwater in urban areas, modified from Lerner (2002).

2.4.2. Methods of quantifying urban groundwater recharge To gain a better knowledge for the hydrological cycle and to identify groundwater recharge in an urban environment several approaches can be used, either by measuring individual components (e.g. direct recharge and leakage from water supply and sewage systems) or to have holistic approaches e.g. groundwater modelling (Lerner, 2002).

To be able to quantify the recharge the individual components contributing to the recharge have to be identified. On a local scale this means identifying every possible point of recharge and at a regional scale a more wide approach is used to demonstrate that individual sources have an impact on the recharge. A helpful tool in the initial process of identifying sources of groundwater recharge and understand the system is to create a primarily conceptual model of the system (Vázquez-Suñé, Carrera, Tubau, Sánchez-Vila, & Soler, 2010). The sources of groundwater recharge can then be identified by measuring potentiometric levels, concentration of solutes in the water or by setting up a water balance of the water supply (Lerner, 2002). In Vázquez-Suñé et al. (2010) potential recharge sources to the Barcelona city aquifers were evaluated using solute mass balances. In Lelliott, Bridge, Kessler, Price, and Seymour (2006) the use of a 3D geological model of quaternary deposits in Manchester (UK) demonstrated to be useful for groundwater management, particularly for the development of a recharge model. The authors emphasise the importance and potentials at an early stage in urban planning and introduced a 3D geological model to better inform strategic planning options, reclamation strategies and ground investigations. Precipitation and leakage from water supply and sewage systems are the two main source of recharge in an urban area but due to the complexity in an urban environment, e.g. infrastructures, it is difficult to estimate and quantify the recharge (Yang et al., 1999). Using a simple water-balance equation (Eq.8) to calculate recharge in urban area is probably not accurate enough since it is difficult to get good estimations of the different parameters (Lerner, 2002).

= + + (Eq.8)

𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸 𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 𝑅𝑅𝑅𝑅𝑅𝑅ℎ𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 Instead it is better to look at the different recharge components (direct and localised recharge from precipitation, water supply and sewage systems and storm-water infiltration systems) in an urban environment and estimate them (Lerner, 2002). In arid and semi-arid climates over-irrigation also contributes to the recharge.

By using a holistic approach, such as groundwater modelling, solute balances or piezometry, recharge in urban areas also can be estimated. These approaches estimate the total recharge and not all the individual components of urban recharge. The holistic methods have the advantage that they do not require as much data as the component methods do. In Yang et al. (1999) groundwater recharge to the a sandstone aquifer in Nottingham (UK) is estimated using a calibrated groundwater flow model together with calibrated solute balances for three conservative species.

Depending on what the aim of the study is, e.g. water-resource assessments or estimates for contamination transport, different recharge estimates are more or less suitable (Scanlon et al., 2002). Space/time scale, reliability and range of the estimates must be considered when choosing method.

2.5. Three-dimensional modelling Detailed information about the soil structure and bedrock became more important during the Industrial Revolution, in the 1800s and 1900s, when demands for agriculture, mining and urban planning developed. Geological information is often visualised in the form of maps and profiles and are traditionally presented in two dimensions. The purpose of a geological map is to, within an area, describe the soil and bedrock structure, i.e. also the depth, a third dimension. A geologist is used to interpret and understand the third dimension in a map but for others this can be difficult and complicated. Today, with the use of new technology, it is possible to create three-dimensional models that visualises the geology in a new way that is difficult or sometimes even impossible to produce with geological maps and profiles (Peterson, Jirner, Karlsson, & Engdahl, 2014). There are several 3D methods and software tools e.g. GSI3D (Geological Surveying and Investigation in 3D Dimensions) and SubsurfaceViewer®. In (Aldiss, Black, Entwisle, Page, & Terrington, 2012) the benefits of using a 3D model, in this case GSI3D, when constructing a new underground station in London is described. The software allows the geologist, with its knowledge, to decide whether to honour each data point or not. Also, new information can be added to the model at any time. The 3D model provides a better geological understanding of the ground and allows all parties concerned to better be able to visualise and control risks.

3. Case study

3.1. Geology and hydrogeology in Gothenburg Gothenburg is the second largest city in Sweden and is situated on the west coast at the outlet of Göta Älv. Göta Älv flows from Lake Vänern east of Vänersborg and splits into two branches at Kungälv, the northern part being Nordre Älv and the southern part keeping the name Göta Älv, to eventually flow into Kattegatt (Klingberg, Påsse, & Levander, 2006). The bedrock of Gothenburg is mostly Precambrian and consists of granites in the western part and gneisses in the eastern part and generally has a low hydraulic conductivity (Engdahl, Fogdestam, & Engqvist, 1999).

The majority of the quaternary sediments overlying the bedrock were deposited during and following the last glaciation in glaciomarine and marine environments and consists predominantly of clay (Stevens & Hellgren, 1990). During the deglaciation, several moraine systems were formed in the coastal areas in southwest Sweden e.g. the Göteborg Moraine being one of them (Larsen, Linge, Håkansson, & Fabel, 2012). The Göteborg Moraine stretches from Halland to Hisingen and constitutes major aquifers in some places (Hultén, 1997). Around 14 500 years ago the ice left the area which resulted in isostatic uplift and a gradual movement of the coastline to its present position. The isostatic uplift is still ongoing in the area at a rate of approximately 2 mm/year and the highest coastline remnants are about 100 m above the sea level today (Engdahl & Jelinek, 2013).

The stratigraphy in the central parts of Gothenburg shown in Figure 11 typically consists of till and/or glaciofluvial deposits overlaying the crystalline Precambrian bedrock (Hultén, 1997). In some areas these deposits extend up to the surface, permitting water to infiltrate (Stevens, Rosenbaum, & Hellgren, 1991). Covering the coarser sediments is glacial clay, with a thickness of as much as 100 m in some areas, and post glacial clay. In some places the glacial clay and the post glacial clay are separated by thin layers of sand (Norin, 2004). The uppermost part of the clay tends to be more silty and sandy which increases weathering and dry crust development (Stevens et al., 1991). On top of post glacial clay lies fill material which covers most parts of the city today and ranges in thickness from about seven meters in the harbour to less than half meters in areas where the soil cover is thin (Norin, Hultén, & Svensson, 1999). The composition of the fill material is rather heterogeneous and can consist of different material, e.g. gravel, sand, wood, glass, brick and macadam (Hultén, 1997).

Göta Älv with its tributaries is an important national resource and the use of the water is intense, the river provides the drinking water supply for about 700 000 people. Furthermore, Göta Älv is an important transport route and several industries use its water as cooling water or process water (Klingberg et al., 2006).

In central Gothenburg, two aquifers are identified, one unconfined upper and one confined lower aquifer, separated from each other by a thick layer of clay (Figure 11). The upper aquifer is located in the fill material and receives its water from precipitation and leaking water supply and sewage systems (Norin et al., 1999). According to Berntson (1983) the dry crust clay with its fractures is considered to be a part of the upper aquifer. Of the produced fresh water in Gothenburg about 13 million m3 (21%) is lost through leaking water pipes (Jakob Ljungquist, personal communication, 2015). The lower aquifer is artesian in some places and found in the till and glaciofluvial deposits underneath the clay and recharge occurs from precipitation and percolation through the hill slopes (Hultén, 1997). Stockholm and London are two examples of cities with similar geological conditions to those in

Gothenburg, where the aquifer in the fill material is separated from the underlying aquifer (Norin et al., 1999; Royse et al., 2012). The bedrock constitutes a fractured aquifer, but not all fractures are water-bearing because of tectonic stresses or other processes such as mineralisation (Hultén, 1997).

Figure 11. The geological setting in central Gothenburg. The line in the clay layer represents the boundary between the glacial and postglacial clay. In the fill material the upper aquifer is located and the lower aquifer can be found in the sand, glaciofluvial and till deposits, from Hultén (1997).

3.2. Geotechnical challenges in Gothenburg The city of Gothenburg has to cope with numerous geotechnical problems related to hydrology and hydrogeology. Gothenburg was built up during the past 400 years and many of the older buildings in the city are built upon the muddy areas along the Göta Älv. Many are built on wooden piles driven into the clay and as the city expanded and urbanised the bedrock hills on both sides of the river were used as well (Hultén, 1997). Urbanisation has a major impact on the groundwater system as it alters the pathways of groundwater, the travel time and causes the groundwater level to rise or fall as well as changing the groundwater quality. The use of different fill materials in Gothenburg is one approach in order to try and stabilise the ground and to raise the land above the water table. Drainage to pipes and tunnels leads to a lowering of the groundwater level and rotting of wooden piles which in turn can induce subsidence and cause breaking of fresh water pipes and sewers. As a result of this many houses and buildings around central Gothenburg are damaged (Hultén, 1997). Raising the groundwater locally by groundwater infiltration and replacing old piles are a few examples of how old buildings can be saved and reduce the risk of subsidence (Norin et al., 1999).

Clay sediments are often linked with different geotechnical challenges of which landslides are the most prominent problem existing in the area around Gothenburg, which can damage or destroy buildings and other infrastructure and even cause fatalities. Landslides can be triggered by human impact, however, these events are linked to chemical and physical changes in the clays that have taken place over a long period of time. Another problem is quick clay, a sensitive glaciomarine clay, which can, if

24 disturbed, transition from a solid to a liquid (Persson, 2014). The largest recent landslides occurred at Surte in 1950 and at Tuve in 1977 (Norin et al., 1999).

3.3. Future climate The Intergovernmental Panel on Climate Change (IPCC) has predicted that the global mean temperature will rise by 1.8-4.0 degrees Celsius by the end of the 21st century compared with the reference period 1961-1990. In Sweden, the temperature is assumed to rise more than the global mean. Compared to the reference period 1961-1990 the average temperature is predicted to rise by 3-5 degrees by the 2080s (SOU, 2007). Precipitation patterns will also change and the annual precipitation is estimated to increase by 10-30% by the end of the century (SMHI, 2007). The predicted sea level rise is assumed to be about 0.1 – 0.9 cm, taking isostatic uplift into account, affecting the southern parts of Sweden to a greater extent where the uplift is lower (SOU, 2007). A sea level rise together with wind under the right conditions may cause problems e.g. flooding in low-lying tunnels and roads such as the Tingstad and Göta tunnels in Gothenburg. Furthermore, 100-year floods are also predicted to increase, mostly in western Götaland and western Svealand (SOU, 2007).

Climate change increases the demand on management and planning for new infrastructure in Gothenburg and other urban cities in order to cope with existing problems as well as to prepare for those arising.

3.4. Future projects in Gothenburg Gothenburg is a city under development with a growing population and employment market and as a result of this traffic levels are increasing due to people travel longer distances. To be able to manage the city’s expansion in an efficient and sustainable way several tunnelling and infrastructure projects are in progress or planned (Göteborgs Stad, 2015b). These projects must also take into account the previously mentioned geotechnical challenges, see section 3.2.

3.4.1. The West Sweden Agreement (Västsvenska paktetet) Politicians in West Sweden all agree that in order to make Gothenburg and West Sweden a growing region improvement to infrastructure is required, e.g. development of railways, public transport and roads. The West Sweden Agreement is a collaboration project between the City of Gothenburg, the West Götaland Region, the Gothenburg Region Association of Local Authorities, Region Halland, Västtrafik and the Swedish Transport Agency (Göteborgs Stad, 2013b). The project is estimated to cost SEK 34 billion. State funding finances half the cost (SEK 17 billion) and the remaining half is financed by the West Götaland Region, Region Halland and the City of Gothenburg together with income from congestion tax in Gothenburg (Trafikverket, 2014b). The West Sweden Agreement contains (Trafikverket, 2013b):

Improved public transport More roads in Gothenburg will have assigned bus lanes and 55 km of new bus lanes will be added to the 35 km that exist today. New commuter stations in Gamlestadstorget, Haga and Korsvägen and the Central Station in Gothenburg will be built. Furthermore, additional commuter car parks, bicycle paths and parking are also being built and extended. These projects are ongoing and will be completed in the coming years.

The West Link The West Link is the single largest investment in the West Sweden Agreement to relieve the heavy

25 pressure on the railway network in West Sweden. An 8 km long double railway track will be built of which 6 km through a tunnel. There will be three underground stations at Central Station, Haga and Korsvägen. This will make it easier for people to commute, reduce traffic in central Gothenburg, rail services can run more frequent and make travel times shorter. The estimated construction period for the West Link is between 2018-2028.

The new Göta Älv Bridge (Hisningsbron) The Göta Älv Bridge is today the most important public transport link over the river to Hisingen and is heavily trafficked. However, the bridge is in poor condition and needs to be replaced by a new bridge. The new bridge will be situated just east of the Göta Älv Bridge and give more room for increased public transport, be safer for cyclists and contribute to growth in central Gothenburg. The new Göta Älv Bridge is expected to be completed in 2020.

The Marieholm Tunnel The road tunnel under the Göta Älv will be located 600 meters to the east of the Tingstad Tunnel and will connect E20, E6, E45 and the Lundby by-pass. The new traffic tunnel will improve the accessibility for people, increase the capacity and reduce the vulnerability in the transport system. The Marieholm Tunnel is predicted to be open for traffic in 2020.

Gamlestaden – hub for public transport A new travel centre will be built at Gamlestadstorget creating a meeting place in the north-east part of Gothenburg and a hub for public transport where people can change between different types of public transport. The idea is to diversify the area around Gamlestadstorget with housing, offices, cultural and recreational activities and services. The new travel centre is scheduled to be completed by 2018.

Congestion tax Congestion tax is part of the West Sweden Agreement and is in operation since 1 January 2013. The intention of congestion taxes is to improve accessibility on the roads, contribute to a better environment and be a part in financing the investments in the West Sweden Agreement.

3.5. Description of the study area (Haga and Linné) The investigation areas of this study are the areas around Haga, Olivedal, Masthugget, Annedal and Änggården which are located in the borough Majorna-Linné in Gothenburg (Figure 12). Hereafter, the study area will be referred to as Haga and Linné. The area Haga and Linné was chosen for the reason that this thesis is a continuation of Ljungdahl (2015) and Albertsson (2014) master theses who conducted investigations in the area. Many investigations have been carried out around Haga and Linné and several groundwater level observation wells are located in the area. Furthermore, new and major infrastructure is planned in the region such as the West Link with an underground station located in Haga, making it an interesting area for further investigations.

A general description of the study area and the geological/hydrogeological and geotechnical situation in the area will be given in the following section.

Figure 12. Overview of the focus area Haga and Linné (black box) and its location in Gothenburg (Sweden).

The focus area Haga and Linné is located in the western part of central Gothenburg and has evolved over several centuries. The area Haga has been built up successively during the 17th and 18th century but it was not until the 1840s when new industries were established in Gothenburg the urban development expanded and densified in the area (Aronsson, 1991). The urban development of Linnéstaden and around Linnégatan occurred during the 1880s to the 1920s. In the past a stream, Djupedalsbäcken, ran along the valley towards Göta Älv where Linnégatan is located today. During the development of the area Djupedalsbäcken was made into a culvert at a depth of five meters and filled up with filling material with a thickness of up to 5-6 meters in some places (Bergström, 1981).

The focus area is characterised by low-lying clay filled valleys extending towards the Göta River valley and is surrounded by higher lying outcrop areas (Figure 13). The general soil stratigraphy of the study area consists of 1.5-3 m of fill material (Hultén, 1997), varying clay thicknesses with around 25- 30 m in the southern end of Linnégatan, close to Linnéplatsen (Aronsson, 1982) and a decrease in thickness

27 between Skansberget and Nordhemsberget to about 10 m. Further north, towards Järntorget, the clay thickness increases again with thicknesses of more than 60 m (Bergström, 1981). Around Haga the clay thickness is generally up to 10 m (Wassesnius, 1987) but greater thicknesses are found in the area (Aronsson, 1991). The friction material underlying the clay has in general a thickness of a few decimetres up to a few meters (Wassenius, 1987).

Figure 13. SGU's quaternary deposits map shows the distribution of soil types at or near the soil surface.

Two aquifers separated from each other by a layer of clay are defined, one upper aquifer located in the fill material above the clay and one lower aquifer located in the friction material underneath the clay. In some areas where the sediments are thinner the upper and lower aquifers are in contact with each other (Hultén, 1997). The groundwater flow generally occurs northward, from higher areas in the south towards the Göta Älv in the north (Stadsbyggnadskontoret, 2011).

The Office of City Planning (SBK) is responsible for the overall control of groundwater level measurements in Gothenburg and is divided into 6 larger areas (Figure 14), from which further subdivisions have been made in order to describe the catchment areas in the city (Trafikverket, 2013a).

The catchment area for the Haga-Linné is presented in Figure 15 and contains information about groundwater flow and assessed hydrogeological environments according to: 1 – Confined aquifer (friction material underneath clay), 2 – Unconfined (upper) and confined (lower) aquifer, 3 – Unconfined aquifer (friction material on bedrock) and 4 – Bedrock.

Figure 14. Groundwater observation wells (black points) included in the control program of groundwater level measurements in Gothenburg. The orange boxes display the six larger areas included in the control program from which further subdivisions have been made (Aqualog, 2010).

Precambrian crystalline bedrock, with thin or no soil cover > Type environment 4

Clay*, water-bearing friction layer (<2) may occur under clay > Type environment 1 or 2 Clay*, friction material of moderate thickness (2-5 m) under clay, confined aquifer, poor or no GW-resources (<1 l/s) Clay*, friction material of significant thickness (>5 m) under clay, confined aquifer, moderate GW-resources (1-5 l/s) Clay*, friction material of great thickness (>10 m) under clay, confined aquifer, good GW-resources (5-25 l/s) Sand and gravel**, unconfined aquifer, poor or no GW-resources (<1 l/s)

Sand and gravel**, unconfined aquifer, moderate GW-resources (1-5 l/s) Type environment 3 (mainly) Type 2 environment 1 or 2 as assessed Mainly Sand and gravel**, unconfined aquifer, good GW-resources (5-25 l/s) Water divide, assessed on the basis of the topography Water divide, SGU Groundwater level measuring points Groundwater level (median value), Gothenburg local height system Groundwater flow direction Approximate infiltration area * Including other fine-grained sediments, **Mainly glaciofluvial deposits

Figure 15. Subcatchment area Haga and Linné, modified from Stadsbyggnadskontoret (2011).

Subsidence in Haga and Linné has occurred due to lowering of groundwater levels which in turn can cause wooden foundations to rotten and decay, compaction of clay and fill material caused by external load and consolidation of clay (Aronsson, 1980; Hultén, 1997). Several houses in the focus area have been damaged due to uneven subsidence rates because of their position in the transition between clay and bedrock (Bergström, 1981). In some places the subsidence rate has been measured to up to 10-15 mm/year (Aronsson, 1980). Foundation reinforcement has been carried out over the years in the area, from 1930 and onwards, in order to save, stabilise and prevent new damages to buildings (Bergström, 1981). Several underground constructions and tunnels are located in the area around Haga-Linné which led to lower groundwater levels by several meters during the first half of the 1970s when most of the underground constructions where built. Since then the low groundwater levels have been compensated partly through permanent infiltration and by other additional groundwater infiltrations in the area (Banverket, 2005).

3.6. Data hosting The following sections briefly describe government agencies and other actors relevant for this thesis and what they are working with and what of kind of information they can provide. The data hosting is presented on the basis that it could be useful in investigations carried out in Gothenburg. The collected data and information used in this thesis are further described and explained in Table 3.

3.6.1. Geological Survey of Sweden (SGU) SGU is the national agency responsible to the Ministry of Enterprise, Energy and Communication (Näringsdepartementet) for matters concerning bedrock, soil and groundwater in Sweden. One of the most important tasks SGU has is to provide society with the geological information needed, for example with regards to sustainable supplies of natural resources, urban development and the environment but also in strengthening geological research in Sweden and bringing geological knowledge forward in schools and other social debates (SGU, 2015a). The information and data from SGU is stored and can be obtained from databases, maps, reports, publications and more. In SGU’s databases information about soil depth, depth to bedrock, geochemistry, groundwater and much more can be obtained. From SGU’s map generator maps of the bedrock, quaternary deposits, marine geology, geophysics, geochemistry and groundwater of Sweden can be produced and downloaded. SGU’s customer services can also help in order to find the information needed (SGU, 2015e). SGU is divided into five departments, mineral resources, mining inspectorate, geodata, physical planning and geohydrology (SGU, 2015d).

3.6.2. Office of City Planning in Gothenburg (SBK) The Office of City Planning in Gothenburg (SBK) is responsible to create a comprehensive plan for Gothenburg on a regular basis, make local plans which describe how and where new houses and other buildings can be built. Furthermore, the Office of City Planning is also responsible for building permits, maps, and aerial photographs. In their archive building permits from 1875 to today can be found as well as documents from National Land Survey of Sweden (Lantmäteriet), different types of maps, existing plans and much more (Göteborgs Stad, 2013a).

Large volumes of geodata, e.g. groundwater measurements, subsidence measurements, geotechnical investigations and boreholes are administered by the Office of City Planning and stored in databases and their archive (Göteborgs stad, 2014).

3.6.3. Department of Sustainable Waste and Water in Gothenburg (KOV) The department of sustainable waste and water in Gothenburg is a local authority and is responsible for producing and distributing safe drinking water, divert sewage water, clean and divert storm water and to take care of solid waste in the municipality in an efficient and sustainable way. The department works with the safety of water in several ways, e.g. risk analyses, water safety areas, regional plans and the protection of microbial influence and other substances (Göteborgs stad, 2015a).

3.6.4. Swedish Transport Administration (Trafikverket) The Swedish Transport Administration is a government agency with the responsibility for a long-term infrastructure planning of the transport systems for road, rail, aviation and shipping. A sustainable and efficient transport system is the Swedish Transport Administrations vision and collaboration and long- term infrastructure planning with regions and municipalities is needed to achieve this vision (Trafikverket, 2014a). The Swedish Transport Administration is the procurer of around half of all the geotechnical investigations conducted in Sweden, thus the main actor within this field. The Swedish Transport Administration has a geotechnical portal and a map viewer for internal use for planners and consultants. Geotechnical information requested from the Swedish Transport Administration is stored at the Swedish Transport Administration in different databases e.g. Chaos and IDA (SGU, 2014).

3.6.5. Swedish Meteorological and Hydrological Institute (SMHI) Swedish Meteorological and Hydrological Institute (SMHI) is a government agency operating under the Ministry of the Environment and Energy (Miljö- och energidepartementet). SMHI is responsible to manage and develop information on weather, climate and water which provides knowledge and decision-making data for public services, the private sector and the public. The goal is to contribute to increased social benefit, safety and a sustainable society. General forecasts, warnings about the weather, simulations, and analyses, statistics, and climate studies are a few examples of SMHI’s services. SMHI cooperates with agencies and organisations both on a national and international level on a daily basis and is representing Sweden in several international organisations. SMHI operations are funded in three main ways; by government funded operations, assignments from other government agencies and business operations on a commercial basis (SMHI, 2013b).

3.6.6. Consultants and contractors Consultant companies and contractors carry out the assignments/investigations they are given from the procurer e.g. the Swedish Transport Administration and the City of Gothenburg. The information from geotechnical investigations conducted by consultant companies and contractors can in many cases be more complete than the information at the procurer. Usually only the final product, report or model is handed to the procurer while the comprehensive data collected, used and experiences learned from different projects is merely available at the consultant companies and contractors (SGU, 2014).

3.6.7. Collaboration between actors and authorities An EU-directive called INSPIRE (Infrastructure for Spatial Information in Europe) started in 2007 and by 2019 the directive should be in full operation. The intention of the directive is to create an European Union spatial data infrastructure with the purpose of enabling better access to public geodata between different authorities (European Commission, 2015). The idea is that different member countries are going to be able to use, share and combine data without the need to change format or methods. In Sweden, the National Land Survey of Sweden has the responsibility for the implementation, organisation and support of INSPIRE (SGU, 2015c).

SGI, SGU, Swedish Transport Administration, the National Land Survey of Sweden, local governments and Swedish Civil Contingencies Agency (MSB) have together developed a map service “Geotechnical theme portal” (http://gis.swedgeo.se/startgsp/) where meta data related to projects can be found but contains no geological or geotechnical information. The meta data contains information about where the investigations have been conducted, who conducted the work and usually what type of work that has been performed (SGU, 2014).

3.6.8. Occurrence and management of data A large number of geological information gathered by external actors and government agencies during different projects, particularly in infrastructure developments, is at present not handled and stored in a structured way. Knowledge and experience is often linked to individuals and if that person leaves the job or retires the information can get lost (SGU, 2014). Geological and geotechnical data and information are available in different forms and by different actors with varying levels of detail and quality. Geotechnical investigations from the past 15 years are available in digital format, usually in GeoSuite/AutoGRAF, but older investigations are generally more scattered and much of the data is available only as paper prints (Öberg, Norén, & Wiberg, 2011).

According to the law SFS 1975:424, well protocols and written compilations of groundwater investigations in Sweden must be reported to SGU by the person responsible for the drilling or investigation (Sveriges Riksdag, 1975). This information is stored in the Wells Archive (Brunnsarkivet) and contains information about soil depth, drilling depth, stratigraphy, groundwater level and geographic location (SGU, 2015b). From personal communication with employees at SGU and consultant companies it is understood that well protocols from drilling are somewhat being submitted to SGU but information from groundwater investigations are rarely being submitted to SGU.

SGU was at the request of the Swedish Government in 2014 given the assignment to investigate, review and identify the possibilities to a greater extent gather and manage geological information collected from different actors and ensure that the information is of good quality and accessible in an easy way (SGU, 2014).

Therefore, it is of interest for this thesis to investigate and try to identify from where geological and especially hydrogeological information can be collected, what can be done with it and how this information can be made accessible to as many people as possible.

4. Methods and data This chapter is divided into two sections, data sources and methodology, the first section describes the datasets used in this thesis and from where they are obtained (Table 3) and the latter describes the methods used and the workflow in preparing and processing the data.

4.1. Data sources This section describes the datasets used in this thesis and from where it is obtained, see Table 3.

4.1.1. Geographical data Elevation data, property map and orthophoto (©Lantmäteriet [I2014/00696]) are provided from the National Land Survey of Sweden and quaternary deposits data is provided by SGU (©SGU [I2014/00696]) and obtained from Swedish University of Agricultural Sciences (Sveriges lantsbruksuniversitet).

4.1.2. Stratigraphical data The stratigraphical data with information about fill material, clay, friction material and bedrock is obtained from SGU, SBK’s databases, a surface map created by Lars-Gunnar Hellgren whom worked at SBK and old geotechnical investigations found in their archive and working material from COWI’s access database, ADA. The database, ADA, was established within a project for the Swedish Transport Administration.

4.1.3. Groundwater level data The groundwater level data were obtained from SBK who is responsible for the overall control of groundwater levels in Gothenburg and measurements from 437 groundwater observation wells around Gothenburg is stored in their database (Stadsbyggnadskontoret, 2013). The measuring periods and number of groundwater level measurements differ for different wells and can vary from a few months to decades. The longest groundwater time series observations started in the end of the 1960s. The groundwater level measurements are at present carried out by COWI 6 times/year in about 140 observation wells around Gothenburg. COWI is also responsible for data management, analysis and compilation of the groundwater level observations. In five groundwater observation wells, where the groundwater levels are considered to be relatively stable during a longer period, automatic data loggers were installed in end of 2011/early 2012 in order to monitor the groundwater level continuously (1x/h) and are considered as reference wells.

4.1.4. Climate data Precipitation and temperature data were obtained from SMHI for the period 1961-2014 and are measured at a daily basis. The data collected are from two measuring stations within the Gothenburg region, Göteborg A (N6399235, E321068) and Säve (N6408301, E314474). Primarily, data from the Göteborg A measuring station were used except during periods where no data exists for which data from the Säve measuring station were added. Humidity and radiation data were obtained from SMHI for the period 1991-2014, however, a few years are excluded due to incomplete time series. Also, evapotranspiration data from the Climate Research Unit, CRU, for the period 1961-2012 were obtained from Ljungdahl (2015).

4.1.5. Questionnaire and interviews with groundwater professionals Views, ideas and further information and data regarding groundwater recharge in urban areas and hydrogeological models were collected through interviews and questionnaires with groundwater professionals mainly working in Gothenburg. Further described in section 4.2.5.

4.1.6. Compilation of data sources used Table 3 displays an overview of the different data sources and information used in order to create the conceptual hydrogeological model. By combining known data e.g. boreholes and groundwater level measurements with “soft data” such as geological/hydrogeological knowledge and other previously interpreted information such as SGU’s quaternary deposits map about soil type and geotechnical investigations the conceptual hydrogeological model can be improved.

Table 3. Compilation of data sources used in order to create the individual components for the conceptual hydrogeological model and the numerical model of groundwater recharge. The information from the different actors and authorities are the latest existing data and information that was available to collect within the time frame of this thesis.

recharge

Data source Information used Bedrock surface Stratigraphyc) (a, b, Confirmed thicknessc of Potentiometric surface Groundwater Office of City Planning Borehole logs/Soundings X X Geotechnical investigations X X X Groundwater observation wells X X Lars- Gunnar Hellgren’s map X Geological Survey of Stratigraphical information (boreholes) X X X Sweden Wells X Quaternary deposits map (1:25 000–100 000) X* X* X Soil depth (map) X* Description to the map "Grundvatten- förekomster i Göteborgs kommun, X* K109" (Lång, 2009) COWI's ADA Database Borehole logs/Soundings X X X Swedish Meteorological Precipitation measurements and Hydrological Institute X Temperature X Global radiation X Average air humidity X National Land Survey of Orthophoto X Sweden Property map X Elevation data X X X Swedish Rail Järnvägsutredning Västlänken Administration (2005), Appendix 1 Map X* X* Department of sustainable Leakage from water supply systems waste and water X

Erik Sturkell Research material (Säröbanan) X X Questionnaire Infiltration coefficients X von Brömssen (1968) Infiltration coefficients X Wiles and Sharp (2008), Infiltration coefficients Misstear and Brown X (2002) *= Soft data

4.2. Methods This section describes the methods used and the workflow in preparing and processing the data, the compilation of available data, the hydrogeological model development and estimations of groundwater recharge. Before processing all data is converted into the common reference systems Swedish Reference Frame 1999 Transverse Mercator (SWEREF 99 TM) and the National Height System 2000 (RH 2000). The interpolation resolution is, if not stated otherwise, 10 x 10 m.

4.2.1. Compilation of available data A compilation of the geological/hydrogeological data available and manageable to collect within the time frame for this project is presented in section 5.1 and was done by contacting, meeting and interviewing government authorities, scientists, consultant companies, contractors and other people, with expertise knowledge in the matter. The data and information obtained are compiled and evaluated in order to be able to see if and how this data can be used and what efforts are required to make it accessible and usable. All the data and information collected within this thesis are not included in the conceptual hydrogeological model and the numerical model of groundwater recharge, see Table 3 for the data sources used.

4.2.2. Conceptual hydrogeological model development The interpolation process and calculations for the stratigraphical model are partly based on the steps described in Sundell, Rosén, Norberg, and Haaf (2015) and adjusted to fit the extent and limitations of this project. Surfer®11 which is a 3D visualisation, countering and surface modelling software was used to interpolate the bedrock surface and thickness of the stratigraphic layers with the Kriging interpolation method. The Kriging method is based on the assumption that the distance or direction between observation points reflects a spatial correlation which can be used to explain variations in the surface. To determine the output value for each location the Kriging method fits a mathematical function to all points within a specified radius or a specific number of points. The method requires the data used to have a normal distribution. In order to specify the spatial correlation between the observation points a variogram model is chosen from a set of mathematical functions which describes the spatial relationships. A variogram can also display the anisotropy of a variable within the area of interest (Johnston, Ver Hoef, Krivoruchko, & Lucas, 2001).

The potentiometric surfaces were produced in ArcMap 10.1 which is a geospatial processing program. All maps are visualised using ArcMap 10.1 and the hydrogeological model which is a combination of the bedrock surface and stratigraphic layers compiled in ArcScene 10.1, which is a 3D- visualisation program.

In order to create the stratigraphical part of the conceptual hydrogeological model some assumptions were made. The stratification in the focus area is conceptualised and is represented by four geological units. From the surface and downwards: fill material (a), clay (b), friction material (c) and the bedrock surface (Figure 16).

Figure 16. To the left, possible stratification in Gothenburg, modified from Hultén (1997) and Berntson (1983). To the right, conceptualised stratification used in the model.

Since the motivation of creating this model is foremost to evaluate the thickness and extent of the upper and lower aquifers, it was decided not to separate between glacial and postglacial clay or any material in between them. This is because clay generally acts as an almost impermeable layer (if not cracks and anthropogenic constructions exist in it) (Berntson, 1983). The fill material and the dry crust clay are represented in the model as one layer (fill material) since the dry crust clay often is anthropogenically reworked and mixed with the fill material. The gravel, sand and till (sandy) below the clay are also represented by one layer (friction material) because they can act as aquifers.

Another assumption made is that all three layers (fill material, clay and friction material) are present in the stratigraphic sequence if not soundings or boreholes confirm the opposite. This assumption leads to when there is a space between the lower boundary of the clay layer and the bedrock surface the space is interpreted as friction material. This is because the general view of the stratigraphy in the area is that there is a friction material present between the bedrock and the clay (Stevens & Hellgren, 1990). This can occur since input data to the model e.g. consists of soundings with the purpose of identifying solid ground below the clay. The soundings are therefore ended when they have reached friction material and/or bedrock.

4.2.2.1. Bedrock surface The bedrock surface is produced using Kriging interpolation with associated variograms. It is based on data described in section 4.1.2 and summarised in Table 3. The interpolation is performed in several steps to incorporate as much of the available data as possible. If only boreholes or other sorts of information that confirms the bedrock surface were to be used a lot of information would be lost. The bedrock surface would in some areas be interpolated as shallower than what boreholes containing information about the soil stratigraphy confirm it is (Figure 17).Therefore a combination of the minimum values of separate interpolations are selected. This produces a surface which is assumed to be closer to reality than the two interpolations would be separately. How this process is carried out is included in the description of the interpolation steps for the bedrock surface.

Figure 17. Illustration of how the bedrock surface is interpolated depending on how the data are included. The black arrows represent boreholes that either reach the bedrock surface or ends before reaching the bedrock surface. a) Shows an interpolation (red dashed line) based on boreholes confirming bedrock only. Interpolation b) (blue dashed line) is based on all available data. Picture c) displays the final surface (lime green line) which is a combination of the minimum level of both interpolation a) and b), from Sundell et al. (2015).

Management of data The data used in the interpolation of the bedrock surface can be divided into different categories based on how they are incorporated in the interpolation process:

• Boreholes, soundings or other sorts of observation points which confirm the bedrock surface (represented as red points in Figure 18). In this category bedrock outcrops interpreted from SGU’s quaternary deposits map (22 290 points) are also included but are represented by blue points. • All boreholes, soundings and observation points that either confirms the bedrock surface (1581 points) or ended before they have reached the bedrock surface (2508 points) (represented as green points in Figure 18). • Interpolation points were added to enhance the small valleys between the bedrock outcrops. These points (130 points) are constructed as a sub-step in the interpolation process (represented as grey points Figure 18).

Figure 18. Map over the focus area Haga and Linné displaying the interpolation points used for interpolating the bedrock surface.

Interpolation Using the Kriging interpolation method it is possible to create maps from unevenly distributed data and express trends which can occur in the data. The Kriging interpolation method was chosen since it takes the spatial variation into consideration. This statistical correlation that exists in the data is described by a variogram model which displays the change of spatial dependence of, for example, a random field of observation points. Appendix 1 shows the variogram models created for the observations confirming bedrock surfaces and for all the boreholes and soundings with stratigraphical information. For the data only confirming the bedrock surface the variogram model is expressed by an exponential model and for all the soundings and observations an exponential model is also representative. Appropriate variogram models were identified by iterative calculations.

The interpolation of the bedrock surface was carried out in several steps. For the first interpolation only observations confirming the bedrock surface was used, then a second interpolation containing all sounding with stratigraphic information was carried out. From these two interpolations the minimum elevation level were chosen. In addition to this and in order to enhance the narrow valleys extra interpolation points based on the combined elevation level of the bedrock surface were added to the layer containing all observation points and this layer was used again in a third interpolation. Then the minimum elevation level values from the second and third interpolation were used to produce a map of the depth to the bedrock from the surface level.

Together with the Kriging interpolation Surfer®11 generates an estimation standard deviation grid where the z value represents the difference between the actual grid values and the expected values. The standard deviation gives the prediction error for the given point. The minimum values from each standard deviation grid produced together with the interpolated surfaces in the second and third interpolation are chosen. This grid/surface is not integrated in the final bedrock surface but is displayed separately in section 5.2.1.1 and gives how much the z value could differ with distance from the interpolation points.

4.2.2.2. Stratigraphical layers Management of data The purpose with the interpolation is to create thickness maps for the stratigraphic layers in the model. The data used in the interpolation are given in Table 3 and displayed in Figure 19. From SGU’s quaternary deposits map additional interpolation points were added where till occurred at the surface. In these places the whole stratigraphy is interpreted as friction material since till, sand and gravel are deposited after (or during) an ice margin retreat and it is therefore not likely that other sediments occur in these areas, beside from fill material (Stevens et al., 1991). The soil thickness is limited by the surface elevation and the interpolated bedrock surface. This leads to a dependence between the soil thickness of the different layers, surface elevation and the bedrock surface. The layers are therefore related to each other and only soundings/boreholes which confirm both the boundary between fill material and clay, and clay and friction material are used in the interpolation. However, in areas where no clay is confirmed in the stratigraphy are also incorporated in the interpolation process. For boreholes/soundings not penetrating down to the bedrock surface a bedrock depth is assigned from the bedrock model created in section 4.2.2.1.

Figure 19. Map of the focus area displaying interpolation points used in the process of creating the stratigraphical thickness maps. The boreholes/soundings represented by black points are used in the interpolation using the Kriging method. The red points are boreholes/soundings that confirm the upper and lower boundary of the friction material and it is these points that the IDP interpolation is based on which is described later on in this section.

The thickness of the different soil layers are calculated based on the interpolation of the proportion of the given soil type in the sounding or borehole which then is multiplied by the total soil thickness. From the total soil thickness (Figure 20) the proportion of clay was calculated using (Eq.9)

(Eq.9) = + + 𝑏𝑏 𝑝𝑝𝑏𝑏 𝑎𝑎 𝑏𝑏 𝑐𝑐 where

pb = Proportion of clay of the total soil thickness a = Thickness of fill material (m) b = Thickness of clay (m) c = Thickness of friction material (m)

Further, the proportion of fill material of the remaining soil thickness (a + c) after the clay thickness is subtracted was calculated using (Eq.10)

(Eq.10) = + 𝑎𝑎 𝑝𝑝𝑎𝑎 𝑎𝑎 𝑐𝑐 where

pa = Proportion of fill of the remaining soil thickness a = Thickness of fill material (m) c = Thickness of friction material (m)

Figure 20. Simplified soil stratification used in the hydrogeological model.

Before the data are used for interpolation the proportion of both clay and fill material are converted to be represented by a normal distribution curve since the used interpolation method (Kriging) requires that the data are normally distributed.

Interpolation The interpolation based on the converted values obtained from equations (Eq.9) and (Eq.10) was performed using Kriging with appropriate variograms, see Appendix 1. The thickness of the clay was obtained by multiplying the proportion of clay by the total soil thickness. The thickness of the fill

43 material was calculated the same way by multiplying the proportion fill by the remaining soil thickness. The thickness of the friction material was then obtained by subtracting the thickness of the fill and clay layer from the total soil thickness.

In addition to the interpolations based on points confirming the upper and lower boundary of the clay layer an additional interpolation of the thickness of the friction material was performed using only boreholes/soundings confirming the upper and lower boundary of the friction material and observations where the friction material is absent, see Table 3 and Figure 19. The interpolation was performed using inverse distance to power (IDP). IDP is a weighted average interpolator which assigns values to unknown points by calculating weighted average of the values available at the known points (Heywood, 2010). This was used as a comparison to the thickness of the friction material created with the Kriging interpolation in order to show that if only boreholes confirming the upper and lower boundary of the friction material is used some information that could be useful, even if it does not contain the complete stratigraphy, would be neglected.

4.2.2.3. Potentiometric surface Because groundwater flows down gradient from high to low hydraulic head, potentiometric surface maps can be used to indicate the general direction and pattern of groundwater flow as well as potential infiltration areas to the confined aquifer. The data used in order to create the potentiometric surface maps are average values from the latest groundwater level measurements in the lower aquifer conducted between 2000-2014. Some of the observation wells are no longer in use today and the measuring period can vary between each groundwater observation well. Additionally, soft data (knowledge or already interpreted information) of groundwater levels obtained from the groundwater report related to the railway investigation for the West Link project (Banverket, 2006, 2007) and Lång (2009) were added in areas where little or no data exists. This was done in order to decrease the uncertainty for the interpolation of the potentiometric surface and incorporate existing hydrogeological knowledge. The Spline with Barriers tool in ArcMap 10.1 is a deterministic interpolator that is used to interpolate a grid surface from the groundwater level data obtained. Spline with Barriers uses a minimum curvature method when interpolating which estimates unknown values by bending a surface through known values, resulting in a smooth surface that passes through all known input points. This interpolation method was used instead of for example Kriging since it can handle interpolation within a restricted area. The input barrier features used are the bedrock outcrops located in the focus areas (central Gothenburg and Haga and Linné) which restricts the extent of the lower aquifer. Also, areas where no data exists are excluded from the interpolation. In the focus area Haga and Linné areas where the clay thickness is thinner than <1.5 m the potentiometric surface is removed due to the assumption that the lower aquifer is not confined in these areas. For central Gothenburg SGU’s quaternary deposits map was used to identify areas were the lower aquifer is assumed not to be confined i.e. areas where no clay is mapped.

A potentiometric surface map was created for a larger part of central Gothenburg based on 110 interpolation points of which 19 are soft data points. SGU’s quaternary deposits map is used to identify bedrock outcrops and used as input barrier features, see Table 3. The cell size for the interpolated grid is set to the default value (12.76 m). A potentiometric surface map was also produced for the area Haga and Linné (based on 56 interpolation points of which 9 are soft data points) where the input barrier feature used is the bedrock outcrops created in section 4.2.2.1 and with a cell size set to 10

(Figure 21). Contour lines were added to the potentiometric surface maps at a 2 m interval to display the pressure and in which direction the water is moving in the subsurface.

Furthermore, in order to see if the potentiometric surface follows the topography in the focus area the interpolated potentiometric surface was subtracted from the digital elevation model (ground surface).

Figure 21. Groundwater observation wells from the lower aquifer and infiltration/pumping wells in the focus area Haga and Linné. Groundwater wells marked with a black box around them are further analysed and described in section 4.2.2.4.

4.2.2.4. Groundwater level observations around infiltration wells In order to analyse if it is possible to separate the influence of human impact and urban development from climatic influences, groundwater level time series from the lower aquifer in an area northeast of Skansberget were analysed, GW1436, GW414, GW415, GW1929, GW1927, GW1926A, GW416, GWSK4 and GW1924 obtained from Ljungdahl (2015). The area was chosen because the potentiometric surface displayed deviant levels with respect to the surrounding potentiometric surface. Also, a known infiltration well is located nearby which is assumed to influence the potentiometric pressure. The influence of the infiltration well is assumed to have a radial extent in the lower aquifer. For each observation well a 10-year average of the groundwater level was calculated from 1970 – 2014 to display the general trend. Some time series are incomplete due to periods when no measurements were conducted. The levels were plotted against distance to the infiltration well to see changes within each groundwater observation well and how the potentiometric surface varies with distance and over time. In addition to this, complete time series of a few wells around Skansberget (GW1436, GW430 and GW435) are displayed and selected based on the proximity to known infiltration wells. The groundwater levels were normalised by subtracting the average groundwater levels and thereafter by dividing the groundwater level standard deviation for the same period (note that the period can vary between wells).

4.2.2.5. 3D-stratigrapghical model and cross sections In order to get a better visualisation of the stratigraphy in the Haga-Linné area and to display the thickness of the fill material, clay and friction material 3D-stratigraphical models were created based on the information produced in the stratigraphical part of the conceptual hydrogeological model. The 3D-models (block diagram and fence diagrams) were created following the steps explained in Carrell (2014) and visualised in ArcScene 10.1. The block diagram created covers the focus area and the two fence diagrams display selected profiles of the area, one in a 150 x 150 m grid and the other one following the two longest roads in the area (Linnégatan and Övre Husargatan) with profiles crossing them (Figure 22).

Six stratigraphical cross sections of the same profiles as the latter fence diagram (Figure 22) were created in the Haga and Linné area in order to display the boundaries and the thickness of the fill material, clay, friction material and the potentiometric surface. The cross sections were created in Surfer® 11 using the thicknesses and potentiometric surfaces created for the conceptual hydrogeological model.

Figure 22. The six profiles from which the 3D-stratigraphical model and cross sections were created.

4.2.3. Climatic input variables

4.2.3.1. Precipitation Precipitation is considered the main, and also the most reliable input for most groundwater recharge estimations. However, it is known that precipitation measurements can be erroneous. For that reason Alexandersson (2003) developed a correction of precipitation according to simple climatological principles done on mean values for the present standard normal period 1961-1990. There are three main types of errors which can affect and in most cases underestimate the precipitation: wind errors, adhesion and evaporation. By using a simple equation in Alexandersson (2003) based on measured precipitation, temperature, wind errors for rain and snow, a monthly mean evaporation value and an assumed adhesion value the “true” precipitation can be calculated. The measured average annual precipitation in Gothenburg for the period 1961-1990 was 758 mm/year and the corrected average annual precipitation was 872 mm/year (Figure 23). For the period 1991-2014 the measured average annual precipitation in Gothenburg is 911 mm/year and the corrected average annual precipitation was calculated in this study to be 965 mm/year using the correction model in Alexandersson (2003). The precipitation values used in order to calculate the groundwater recharge are the corrected average annual precipitation values 872 mm/year for the period 1961-1990 and 965 mm/year for the period 1991-2014.

Monthly precipitation 120 110 Measured 1961-1990 100 Corrected 1961-1990 90 Measured 1991-2014 80 Corrected 1991-2014 70 60 50 40 Precipitation (mm) Precipitation 30 20 10 0 Jan Feb Mar Apr May Jun Jul Aug Sep Okt Nov Dec Month

Figure 23. Monthly precipitation values (measured and corrected) for the periods 1961-1990 and 1991-2014. The blue columns with measured and corrected precipitation values are obtained from Alexandersson (2003). The light green columns with measured precipitation was obtained from SMHI and the darker green columns are the corrected values calculated in this study based on the correction model in Alexandersson (2003).

4.2.3.2. Evapotranspiration Evapotranspiration values were calculated using different empirical evapotranspiration models and equations (Eq.11), (Eq.12), and (Eq.13), see Table 4.

Tamm’s formula

= 221.5 + 29 (Eq.11) where 𝐸𝐸𝐸𝐸 𝑇𝑇

T = Annual average temperature (°C) ET = evapotranspiration (mm)

Tamm’s formula (Eq.11) is based on observations of annual precipitation, runoff and temperature from Sweden. It is obvious that that temperature is the crucial factor of determining the evapotranspiration using this method.

Turc method The method was developed for France and North Africa and is a radiation based evapotranspiration model (Turc, 1961). The equation (Eq.12) takes temperature, radiation and humidity into consideration in order to calculate the daily potential evapotranspiration. However, this method can only be used when the temperature is over zero degrees. The Turc method is comprised of two equations depending on the relative humidity of the air.

(Eq.12) = ( + ) + 15 𝑇𝑇 𝐸𝐸𝐸𝐸 𝑎𝑎 ∗ 𝐶𝐶 ∗ 𝑅𝑅𝐺𝐺 𝑏𝑏 ∗ where 𝑇𝑇

ET = Evapotranspiration after Turc (mm/day) T = Average temperature for the given time interval (°C) 3 RG = Global radiation (MJ/m /day) a = Parameter a = 0, 31 (m2/MJ/mm) b = Parameter b = 2,094 (MJ/m2/day)

50 = 1 + < 50 % 70 − 𝑅𝑅𝑅𝑅 𝐶𝐶 𝑅𝑅𝑅𝑅 = 1 50 % where 𝐶𝐶 𝑅𝑅𝑅𝑅 ≥

RH = Average air humidity (%)

Ivanov method The method is a temperature based evapotranspiration model that is developed to estimate evapotranspiration on a low temporal resolution. The method after Ivanov (Wendling & Müller, 1984)

49 can be used to estimate monthly or daily evapotranspiration when the temperature is below zero (Eq.13).

= 0.00036 (25 + ) (100 ) (Eq.13) where 2 𝐸𝐸𝐸𝐸 ∗ 𝑇𝑇 ∗ − 𝑅𝑅𝑅𝑅 ET = Evapostranspiration after Ivanov (mm/day) T = Average air temperature for the given time interval (°C) RH = Average air humidity (%)

The methods by Tamm (Tamm, 1959), Turc (Turc, 1961) and Ivanov (Wendling & Müller, 1984) are not specifically designed for calculating evapotranspiration in urban environments. The evapotranspiration calculated with Tamm’s formula (Eq.11) is 445 mm/year for the period 1961-1990 and 446 mm/year for the period 1991-2014. Using a combination of the Turc method (Eq.12) and the Ivanov method (Eq.13) the evapotranspiration for the period 1991-2014 is calculated to be 567 mm/year. The evapotranspiration values calculated with Tamm’s formula, the combined Turc and Ivanov methods and the evapotranspiration from CRU are used in order to calculate the groundwater recharge.

Table 4. Calculated evapotranspiration values for Gothenburg for the period 1961-2014.

Average annual evapotranspiration (mm/year) Period/Values Tamm (Eq.11) Turc & Ivanov (Eq.12)(Eq.13) CRU 1961-1990 445 - 554 1991-2014 466 567 549

4.2.4. Land cover and soil type The local catchment for the area around Haga-Linné was defined in ArcMap 10.1 using the elevation data and the hydrology tools: fill, flow direction, flow accumulation and watershed. The land cover and soil type in the catchment area were classified based on the National Land Survey of Sweden’s orthophoto and property map, stratigraphical information from the created hydrogeological model, Office of City Planning’s soil cover map created by Lars-Gunnar Hellgren and SGU’s quaternary deposits map into the following classes: buildings, impervious surfaces, asphalt coated surfaces and natural areas (soil type and bedrock outcrops), see Figure 24. Also, the focus area Haga and Linné was classified into the same classes as previously mentioned (Figure 25). Primarily, bedrock outcrops created for the hydrogeological model were used to determine the extent of the outcrops, however, in areas where boreholes/soundings were sparse and in areas outside the focus area (Haga and Linné) SGU’s quaternary deposits map was used to determine the bedrock outcrops. The soil cover was also split into a number of sub-classes based on soil type, where soils of the same character, e.g. glacial clay and postglacial clay were combined into one soil type. For the focus area the clay was divided into two classes: clay>150 cm and clay<150 cm, because clay with a thickness >150cm is considered to have almost no groundwater infiltration (Barkels & Parra, 2010). Thereafter, the areas for the different land cover and soil type classes within the whole catchment and the focus area Haga and Linné were calculated in ArcMap 10.1 (Table 5).

Figure 24. Land cover and soil type classification for the local catchment area. Note that the bedrock outcrops could be covered by a soil cover with a thickness of 0.5 m.

≤

Figure 25. Land cover and soil type classification for the focus area Haga and Linné. Note that the bedrock outcrops could be covered by a soil cover with a thickness of 0.5 m. The infiltration area to the lower aquifer is marked with a square pattern. ≤

Table 5. Size of the different land cover and soil cover areas in the catchment area (Figure 24) and focus area (Figure 25 and Appendix 2).

Catchment area Haga and Linné Haga and Linné Haga and Linné - Lower aquifer (Land cover & (Land cover & (Soil type) (Land cover & soil type) soil type) Soil type) Land cover/ Area Area Area Area Area Area Area Area soil type (km2) (%) (km2) (%) (km2) (%) (km2) (%) Buildings 0.872 14.3 0.813 21.1 - - 0.069 18.4 Asphalt 0.835 13.7 0.690 17.9 - - 0.072 19.3 Impervious surface 0.937 15.4 0.702 18.2 - - 0.059 15.9 Clay (Total) 0.810 13.3 0.486 12.6 1.965 51.0 0.094 25.4 <1.5m - - 0.094 2.4 0.248 6.4 0.094 25.4 >1.5 m - - 0.392 10.2 1.717 44.6 - - Sand 0.170 2.8 0.109 2.8 0.198 5.1 0.045 12.2 Till 0.107 1.8 0.038 1.0 0.087 2.3 0.033 8.8 Peat 0.048 0.8 ------Bedrock outcrops 2.302 37.9 1.013 26.3 1.600 41.6 - -

Total (area) 6.081 3.851 3.851 0.373

4.2.5. Questionnaire and interviews with groundwater professionals To gain further knowledge, ideas and views on groundwater recharge and the application and implementation possibilities in creating hydrogeological models in urban cities, e.g. in Gothenburg, a number of interviews with groundwater professionals at different consultant companies in Gothenburg were conducted. Additionally, an online questionnaire was sent to groundwater professionals working at consultant companies, public authorities and higher education facilities dealing with hydrology/hydrogeology in Gothenburg in May 2015, see Appendix 4. The questionnaire was sent to approximately 60 people, most of them working in the Gothenburg region, and includes questions about the upper and lower aquifers in Gothenburg and their continuation, groundwater recharge mechanisms, estimations of groundwater infiltration coefficients for different land cover and soil types and views on how a hydrogeological model could be structured and what should be included in such a model. The aim with the questionnaire is to determine what the general view on the groundwater situation in urban areas is among people working with hydrology/hydrogeology around Gothenburg and in Sweden.

23 people participated in the survey and the results were compiled with the built-in function in the questionnaire program and presented in graphs and tables. Questions regarding the lower aquifer, groundwater recharge and the hydrogeological model are further analysed and visualised in Excel and presented in section 5.3. The infiltration coefficients obtained from the questionnaire and used for the groundwater recharge estimation are given in the following section (4.2.6).

4.2.6. Numerical model of groundwater recharge In order to get a clearer, better validated and to possibly quantify the direct groundwater recharge a numerical model of groundwater recharge estimations was done. The input data used were yearly average precipitation, yearly average evapotranspiration, infiltration coefficients and percentages of different land cover and soil types and are further described.

Considering the land cover and soil type distribution within the local catchment and Haga and Linné a rough estimate of the direct groundwater recharge can be made based on assumptions about the potential groundwater recharge (infiltrations coefficients) of the different land cover and soil types (Eq.14). Also, an estimation of groundwater recharge in the Haga and Linné area was made based on soil type only (Appendix 2). An infiltration coefficient is how much of the effective precipitation that will infiltrate into the ground and become groundwater and how much that will become surface runoff.

(Eq.14) = ( ) 𝐴𝐴𝑖𝑖 𝑅𝑅 � ∗ 𝑃𝑃 − 𝐸𝐸𝐸𝐸 ∗ 𝐶𝐶𝑖𝑖 𝑖𝑖→𝑛𝑛 𝐴𝐴 where

R = Groundwater recharge [mm/year] A = Total area

Ai = Area of specific soil type P = Precipitation ET = Evapotranspiration

Ci = Infiltration coefficient

The infiltration coefficients used are mainly values obtained from the questionnaire together with values found in the literature. Also values from von Brömssen’s study in 1968 obtained from the study by Barkels and Parra (2010) are used in order to compare and evaluate the values obtained from the questionnaire. Infiltration coefficient values for asphalt, peat and buildings were obtained from Wiles and Sharp (2008), Misstear and Brown (2002) and Trafikverket (2013a) respectively and were used when estimating the groundwater recharge with values from both the questionnaire and von Brömssen (Table 6). Leakage from pipes and sewer systems (mainly pressurised) could be a potential source of additional recharge to the aquifer (mainly the upper aquifer) and can be added to the estimation of groundwater recharge. The addition of water from leaking water supply systems was calculated assuming the leakage is equally distributed across the city of Gothenburg (447.76 km2) (Statistiska centralbyrån, 2015), see Table 7.

Table 6. Infiltration coefficients obtained from the questionnaire, Wiles and Sharp (2008), Misstear and Brown (2002), Trafikverket (2013a) and Barkels and Parra (2010) and used for estimating the direct groundwater recharge. Q1: Lower quartile and Q3: Upper quartile. The land use/land cover with * have infiltration coefficient values found in the literature and are not derived from the questionnaire hence the same values are written in the Q1, Q2 and median columns.

Infiltration coefficients Questionnaire von Brömssen

Land use/land cover Q1 Q3 Median Mean Buildings* 0.00 0.00 0.00 - Asphalt* 0.32 0.32 0.32 - Impervious surface 0.05 0.10 0.08 - Clay 0.05 0.15 0.10 0.001 Clay< 1.5 m - - - 0.21 Sand 0.40 0.65 0.50 0.39 Till 0.20 0.38 0.30 0.23 Peat* 0.05 0.05 0.05 - Bedrock outcrops 0.10 0.26 0.11 0.26

Table 7.Size of Gothenburg and leakage from water supply systems in Gothenburg.

Size of Gothenburg and leakage from water supply systems Gothenburg municipality area (km2) 448 Leakage from water supply systems (km3) 0.013

5. Results In the following sections the results obtained within this thesis using the data and methods described in section 4 are presented.

5.1. Compilation of available data The following section presents a table with a compilation of the available geological/hydrogeological data, from a university student’s perspective, collected for this thesis (Table 8). Confidential data have not been included in this compilation. Furthermore, for each data host follows a short description of what data can be obtained and how the information can be used in geological and hydrogeological projects.

5.1.1. Office of City Planning, Gothenburg (SBK) The Office of City Planning manages large amounts of geotechnical and geographical data, mainly from the Gothenburg region and can be used in several different ways. Many of SBK’s products are available as PDF files for free at their archives. To gain access and use of other digital products as well as to convert between desired formats is at a charge. The data are usually delivered in the coordinate system SWEREF 99 1200 and the height system RH2000 and can be obtained by contacting SBK or downloaded from their website

5.1.1.1. Borehole logs Borehole logs are reported to SBK and contain information about the stratigraphy, strength of materials, density sensitivity, water content and cone liquid limits. All information is not always documented for all boreholes. Digital boreholes are delivered in Novapoint GeoSuite-format. This format cannot be opened at the University of Gothenburg and has to be converted into text file format (.prv) before it can be used in for example GIS programs. To be able to use information about the stratigraphy it has to be manually reviewed and classified. The database is continuously updated with new borehole data.

5.1.1.2. Ground surface infiltration classes Cloudburst modelling for Gothenburg was conducted by Sweco where ground surface infiltration classes were created. Cloudburst modelling is used to identify problem areas in existing built up areas, identify suitable and unsuitable areas for exploitation and identify the vulnerability of important public services and infrastructure. The coordinate system used for this model is SWEREF 99 1200, the height system RH2000 and can be opened in GIS programs. The land use is divided into two classes, hard surfaces (class 50) and soft surfaces (class 2), based on the “Urban Atlas” from the European Environment Agency (EEA) which hosts detailed maps and land cover information. Hard surfaces are for examples airports, construction sites, roads and railways and soft surfaces are surfaces such as agricultural areas, wetlands, green urban areas, water bodies and forests. The infiltration classes, 1 to 5, are based on SGU’s quaternary deposits map, where 1 is regarded as low and 5 as high. The information from the ground surface infiltration classes created may be used in order to locate potential groundwater infiltration areas.

5.1.1.3. Groundwater level measurements Groundwater level measurements are conducted in Gothenburg since 1970’s where information about the groundwater level and observation day is recorded. There are 437 observation wells stored in their database. However, many locations have not complete ground water level measurements from 1970’s until today or are measured at the same time or with the same measuring interval. Most of the

56 groundwater observation points are located in the lower aquifer. COWI is responsible for the groundwater level measurements today. The information is delivered in the coordinate system SWEREF 99 1200, height system RH200 and comes in the format as text files. Because the contents of the groundwater level measurements database is partially gathered from older data sources it can therefore contain uncertainties in terms, classifications etc. Also, measuring errors and misclassification can occur which is why an evaluation of the data quality has to be made before the data are used. The groundwater level measurements can be obtained by downloading it from http//:datagoteborg.se or by contacting SBK. Groundwater level measurements can be used in hydrogeological modelling e.g. analysing groundwater level trends.

5.1.1.4. Description of sub-catchment areas Hydrogeological descriptions for different areas in Gothenburg where information about e.g. groundwater flow, drainage dividers, aquifers, groundwater measurement points and assessed hydrogeological environments and can be obtained by contacting SBK. This information can be useful to review before a new investigation will begin and be used to compare results since it is a good summary of the hydrogeology in different areas in Gothenburg (Stadsbyggnadskontoret, 2011).

5.1.1.5. Subsidence measurements SBK’s subsidence database contains levelling data of objects around Gothenburg and includes 5362 ground levelling point measurements, measured in meters above sea level. Regular measurements are conducted since 1970s but some measurements were made as early as in the end of the 19th century. Measurements of subsidence can provide data and information about changes in land elevation and help to gain further knowledge of how groundwater drainage influences subsidence, especially in urban cities, and how this can be prevented (Albertsson, 2014).

5.1.1.6. Lars-Gunnar Hellgren’s soil cover map A detailed soil cover map of central Gothenburg created by Lars-Gunnar Hellgren whom worked at SBK. This map can be useful to review before a new investigation begins and to compare results with. The map is available at SBK on request.

5.1.1.7. Geotechnical investigations Geotechnical investigations are often carried out by different consultant companies in order to determine properties of bedrock and sedimentary deposits e.g. when constructing buildings. The geotechnical investigations stored at SBK are delivered as PDFs or as scanned photo copies. Copies of geotechnical investigations from SBK’s paper archive need to be collected from the actual archive and digital investigations can be sent by e-mail. From geotechnical investigations geological/hydrogeological and geotechnical information could be obtained such as groundwater levels, subsidence rates and soil thicknesses. The information from the investigations is often more specific and detailed since it is usually in a restricted area the investigation is carried out. The information in many older geotechnical investigations has to be digitised in order to be able to use e.g. borehole logs. Important to note is that older geotechnical investigations can have different height systems than what is used today. The database is continuously updated with new geotechnical investigations.

5.1.2. Geological Survey of Sweden (SGU) SGU provides information and data that can be obtained from their Web Map Services (WMS) or databases. The data are systematically arranged which makes it easy to create maps with their map

57 services or order data, maps, other publications and information from their databases. SGU provides both open data that are free to use and can be downloaded from their website and data that are available at a charge and requires contracts and licenses and are obtained by contacting SGU’s customer service. The open data are delivered in the format JSON (JavaScript Object Notation), CSV (Character-Separated Values) and sometimes as an image file. Data from SGU divided by geological topic can be obtained by contacting SGU’s customer service and are usually delivered in the standard format ESRI Shape and the coordinate system SWEREF 99 TM, which is easy to use in different GIS programs.

5.1.2.1. Bedrock data Bedrock data contain information about the bedrock e.g. bedrock chemistry, bedrock distribution, and bedrock quality. This information can be used as an important basis when planning for new constructions and buildings, geothermal energy extraction and in environmental questions.

5.1.2.2. Geophysical data Geophysical surveys can be used in order to map the bedrock, soil and groundwater as well as for other problems such as assessment of landslide risks and identification of contaminated areas. Geophysical data that can be obtained from SGU includes electromagnetic fields, gamma radiation, magnetic field data, rocks density and magnetic properties and gravitational information.

5.1.2.3. Geochemical data Geochemical data include for example information about the natural occurrence of different metals in the ground as well as the content of metals released through human activity, areas where gold exists or risk of naturally elevated levels of, for example, arsenic and cadmium.

5.1.2.4. Groundwater data Data and information about groundwater are important in the planning of new infrastructure, urban development and the public’s water supply among other things. Furthermore, groundwater data can be used in matters relating land use and spatial planning in general e.g. as a basis for environmental impact assessments and in the construction of roads and industries. SGU’s hydrogeological parameter database includes observations of stratigraphy, groundwater properties and probing methods gathered during SGU's groundwater mapping, 1:50 000. Also, SGU has a database of 9000 groundwater investigations of which 1000 is in digital form. In the Gothenburg area this database mainly contains information about the stratigraphy. Groundwater data includes:

Wells The well data contain information such as depth to bedrock, what it is used for and the capacity (l/h) of the well.

Map of Sweden’s groundwater resources in bedrock and soil (1:1 million) A generalised map based on several groundwater maps in different scales, ages and quality and therefore the accuracy of this map varies.

Aquifers The aquifer data contain information about groundwater in large reservoirs along eskers and in sedimentary bedrock with information of its groundwater flow direction, drainage dividers, size of the aquifers and estimated exploitation potential of groundwater.

Groundwater level monitoring The data include measured groundwater levels as well as information about the locations of the measurements within SGU’s groundwater network. Information obtained about soil type, topographical location and type of aquifer can be used and is important in order to assess groundwater level variation patterns. Groundwater level measurements are conducted by SGU since 1960 -70s. The measurement points closest to Gothenburg included in SGU’s national groundwater network are located in Kungälv, Lerum and Kungsbacka.

Springs The data contain information about the properties and locations of springs. Only a few springs exist in the Gothenburg area.

Environmental monitoring of groundwater, hydrochemical data The data come from monitoring at 1700 locations in Sweden, usually in observation wells and springs, and contains information about the location and results from analyses.

Monthly map of the groundwater situation in Sweden The map is based on groundwater levels from 330 observation wells within SGU’s groundwater network and is mainly addressed to people with private wells.

Water quality data of groundwater bodies The data include statistical compilations of water quality from national and regional monitoring programs and single observation surveys. Covers entire Sweden, divided by county.

5.1.2.5. Soil data The data include information about soil type and distribution, soil thickness (both information about depth to bedrock and minimum level of soil depth), landslides and properties such as genesis and grain size. This information can for example be used in urban planning and when to assess groundwater resources in an area. Data about soil thickness together with information about soil type are important in hydrogeological modelling.

5.1.2.6. Marine geological data The data contain information about soil types and distribution as well as an overview of the geological characteristics of the seabed. The information can be used as a basis for planning of marine constructions and in making decisions on the protection and exploitation of the seabed.

5.1.3. Swedish University of Agricultural Sciences (SLU) SLU has access to geodata from several authorities including the National Land Survey of Sweden, Swedish Maritime Administration (Sjöfartsverket), SGU and Statistics Sweden (SCB). Maps and geodata can be downloaded from the service Geodata Extraction Tool (GET) via http://www.slu.se/en/library/search/digitalmaps/. As a student at a university in Sweden you can use this service for free. When downloading datasets from SLU two coordinate systems can be selected from, SWEREF 99 TM and RT 90 2.5 gon V and the formats are in ESRI Shape and TIFF. All downloaded data are GIS compatible. Only information relevant to geology/hydrogeology was obtained but other information can also be collected from SLU.

5.1.3.1. Bedrock The bedrock data contain information about lithology and structural features which can be useful as e.g. an initial estimation of possible groundwater resources or in identifying water-bearing fractures.

Deformation zones, no distinction between brittle and ductile deformation, resolution 1:1 million. Bedrock outcrops, 1:50 000. Bedrock lines (dikes), age and rock type 1:50 000. Bedrock surface, rock type and age, 1:50 000. Bedrock structural lines, structural formations (lines and deformations) and lithologies, 1:50 000 and 1: 250 000. Tectonic fractures, only location of tectonic fracture zones are displayed, 1: 250 000.

5.1.3.2. Soil (type, depth, layer) The soil data contain information about soil thicknesses and soil types. This data can e.g. be used when making estimations about groundwater recharge via vertical infiltration based on soil type.

Quaternary deposits map 1:25 000 – 1:100 000, mapped soil type at a depth of 0.5 m. Soil thickness, soil thickness based on information from wells and stratigraphy. Soil type below 0.5 m, underlying the SGU mapped soil type (>0.5m), 1:25 000 till 1:100 000.

5.1.3.3. Groundwater The groundwater data contain information about groundwater resources, flow direction and withdrawal capacity in bedrock and soil layers which can be used in hydrogeological modelling, e.g. estimating groundwater recharge.

Groundwater resources in soil layers, 1:250 000 and 1: 1 million. Groundwater withdrawal capacity in bedrock, 1:250 000 and 1:1 million. Groundwater withdrawal capacity in soil layers, 1:50 000. Groundwater drainage dividers, 1:50 000. Groundwater flow direction, given in 1-360 °. Aquifers, 1:50 000.

5.1.3.4. Geographical information The geographic data contain information about elevation and an aerial overview of an area of interest. The data can be used when calculating surface runoff, identifying catchment areas, relate soil thickness in relation to topography and classifying land use.

Elevation data, with a 2x2 m resolution. Orthophoto, photo image. Property map, with information about different properties and topography.

5.1.4. Swedish Meteorological and Hydrogeological Institute (SMHI) Precipitation, temperature and humidity data were collected from SMHI through the Explorer SMHI’s data where climate observations and data with open access are available and easy to download. Radiation data could be downloaded from the Explorer SMHI’s data but only for a short period of time. Longer radiation measurements were obtained separately from SMHI’s webpage. Data from SMHI often require evaluation and processing of the data to make it usable for further analyses, due to incomplete continuity of the data and the difference in time series length. Data from SMHI together

60 with other hydrogeological data such as groundwater levels can be used for water balance calculations as well as groundwater recharge estimations.

5.1.5. Climate Research Unit (CRU) The Climate Research Unit is part of the University of East Anglia and is one of the leading institutions when it comes to the study of natural and anthropogenic climate change. On both a regional and global scale, CRU produces climate datasets of e.g. temperature, precipitation and pressure. Evapotranspiration data are obtained from CRU but not from CRU itself but as secondary information from Ljungdahl (2015). Data from CRU, as other meteorological and climatological data, could be used when evaluating hydrogeological questions.

5.1.6. PanGeo PanGeo is a collaborative project that started in 2011 and lasted for three years with the purpose to provide free ground instability data for many of Europe’s bigger cities. The data consist of satellite measurements of the ground, building movements and other geological information from National Geological Surveys. Information and data gathered during the PanGeo project are not evaluated and used in this thesis but could be used in order to investigate e.g. subsidence in cities (PanGeo, 2015 ).

5.1.7. Department of sustainable waste and water in Gothenburg Data about pipe failure statistics from the Department of sustainable waste and water were collected. The data include information about historical pipe failures, where the pipes are repaired but not replaced, and actual pipe failures, where the pipes are repaired and replaced. The format is in ESRI Shape and the coordinate system in SWEREF 99 1200. Also, through personal communication information about how much of the produced fresh water in Gothenburg is lost (21%) through leaking water pipes was obtained. Potentially the data obtained from the Department of sustainable waste and water in Gothenburg could be used in order to correlate broken pipe lines with groundwater levels.

5.1.8. COWI and other consultant companies COWI is conducting investigations regarding the West Link Project for the Transport of Administration. From a database created by COWI access to borehole log data were obtained, with data from both the West Link projects own geotechnical investigations and from soundings inventoried from SBK’s digital and analogue archives. The height system is RH2000 and the coordinate system is SWEREF 99 1200. This data can be used for stratigraphical modelling. COWI has contributed with data and information to this thesis but there are many other consultant companies in Gothenburg that could have similar data and information which could be obtained.

5.1.9. Swedish Transport of Administration (Trafikverket) The Swedish Transport of Administration is the host of several databases e.g. IDA and Chaos where geotechnical information and data are stored. For this thesis data from the Swedish Transport of Administration are not evaluated nor used. However, the Swedish Transport of Administration is the procurer of many investigations carried out by consultants and contractors the Swedish Transport of Administration holds several comprehensive reports regarding different geological/hydrogeological fields associated with infrastructure projects. This information can be useful to review before a new project will begin and when comparing results.

5.1.10. Swedish Geotechnical Institute (SGI) SGI is an expert government agency belonging to the Ministry of Environment working with tasks determined by the Government e.g. reducing risks for landslides and coastal erosion, effective soil works, climate adaption and remediation of contaminated land. Parts of SGI’s mapping and analysis can be found and obtained from the web and at www.geodata.se as a Web Map Services e.g. digital material related to the Göta Älv study. SGI is also the data host for Branschens Geotekniska Arkiv where geotechnical information, positions and drawings of boreholes are stored. SGI also has a literature database (SGI-Line) containing references to international geotechnical and geoenvironmental literature. The literature database is continuously updated. For this thesis information and data from SGI are not evaluated or used.

5.1.11. Libraries In libraries, especially different university libraries, papers, publications and research series concerning geology/hydrogeology can be found. At the Chalmers and Gothenburg university libraries some literature which could not be found on the internet was available.

Table 8. Compilation of available data collected/identified within the time frame of this master thesis and usable for future hydrogeological projects. Explanation of how to obtain the data is given in Table 9.

Data host Data Name Name of data Data source Format How to obtain the data Office of City Planning, Gothenburg Borehole logs SBK Text files or Novapoint Visit or E-mail GeoSuite - format Ground surface infiltration classes SBK Raster (or ESRI Shape) E-mail Groundwater level measurements COWI/SBK Text file (XML) E-mail or Download Description of subcatchment areas SBK PDF E-mail Subsidence measurements SBK Text file (XML) Visit or E-mail Lars-Gunnar Hellgren's soil cover map SBK PDF Visit or E-mail Geotechnical investigation SBK/Consultant PDFs or scanned photo Visit or E-mail companies copies Geological Survey of Sweden (SGU) Bedrock data SGU Standard format: ESRI E-mail Shape Geophysical data SGU Standard format: ESRI E-mail Shape Geochemical data SGU Standard format: ESRI E-mail Shape Groundwater data Wells SGU ESRI Shape (Points) or E-mail or Download (Open Text file (CSV or JSON) data) Sweden´s groundwater resources SGU ESRI Shape (Polygon) E-mail or Download in bedrock and soil (1:1 million) Aquifers SGU ESRI Shape or ESRI File E-mail Geodatabase (GDB) Groundwater level monitoring SGU Text file (CSVor JSON) E-mail or Download (Open data) Springs SGU ESRI Shape or Text file E-mail or Download (Open (CSV or JSON) data) Environmental monitoring of SGU Text file (CSV or JSON) E-mail or Download (Open groundwater chemistry data) 63 cont. of Table 8.

Data host Data Name Name of data Data source Format How to obtain the data Geological Survey of Sweden (SGU) Monthly map of the groundwater SGU JSON, PNG, JPG or GIF E-mail or Download (Open situation data) Water quality data of SGU JSON E-mail or Download (Open groundwater bodies data) Hydrogeological parameter SGU Text file (XML) E-mail database Groundwater investigation SGU/ Consultant PDFs or non-digital E-mail or Download (Login) database companies Soil data SGU Standard format: ESRI E-mail or Download (Login) Shape Marine geological data SGU Standard format: ESRI E-mail or Download (Login) Shape Swedish University of Agricultural Bedrock Sciences Deformation zones 1:1 million SGU ESRI Shape (Polylines) Download (Login) Bedrock outcrops (1: 50 000) SGU ESRI Shape (Polygons) Download(Login) Bedrock lines (dikes) (1: 50 000) SGU ESRI Shape (Polylines) Download(Login) Bedrock surface 1: 50 000 SGU ESRI Shape (Polygons) Download (Login) Bedrock structural lines (1:50 SGU ESRI Shape (Polylines) Download (Login) 000) and (1: 250 000) Tectonic fractures (1: 250 000) SGU ESRI Shape (Polylines) Download (Login) Soil Quaternary deposits map (1: 25 SGU ESRI Shape (Polygons) Download (Login) 000 - 1: 100 000) Soil thickness SGU ESRI Shape (Points) Download (Login) Soil type below 0.5 m (1: 25 000 - SGU ESRI Shape (Polygons) Download (Login) 1: 100 000)

64 cont. of Table 8.

Data host Data Name Name of data Data source Format How to obtain the data Swedish University of Agricultural Groundwater Sciences Groundwater resources in soil SGU ESRI Shape (Polygons) Download (Login) layers (1: 250 000 and 1: 1 million) Groundwater withdrawal SGU ESRI Shape (Polygons) Download (Login) capacity in the bedrock (1: 250 000 and 1: 1 million) Groundwater withdrawal SGU ESRI Shape (Polygons) Download (Login) capacity in soil layers (1: 50 000) Groundwater drainage dividers SGU ESRI Shape (Polyline) Download (Login) (1: 50 000) Groundwater flow direction SGU ESRI Shape (Points) Download (Login) Aquifers (1: 50 000) SGU ESRI Shape (Polygons) Download (Login) Geographic information Elevation data 2x2 m resolution National Land TIFF Download (Login) Survey of Sweden Orthophoto National Land TIFF Download (Login) Survey of Sweden Swedish Meteorological and Precipitation SMHI Text file (TXT) Download Hydrological Institute (SMHI) Temperature SMHI Text file (TXT) Download Humidity SMHI Text file (TXT) Download Radiation SMHI Text file (TXT) Download The Climate Research Unit (CRU) Evapotranspiration CRU Unknown Unknown PanGeo Subsidence measurements PanGeo Unknown Unknown Department of sustainable waste Pipe failure statistics Department of ESRI Shape E-mail and water sustainable waste and water 65

cont. of Table 8.

Data host Data Name Name of data Data source Format How to obtain the data COWI Borehole logs COWI (TR?) Access database E-mail Swedish Transport of Database of geotechnical information Swedish Unknown E-mail or Download (Login) Administration and data Transport of Administration Swedish Geotechnical Institute Geotechnical investigations SGI Unknown Download (swedgeo.se) (SGI) Literature database SGI Unknown Download (swedgeo.se) WMS service of geodata SGI Unknown Download (www.geodata.se) Geotechnical archive SGI Unknown Download (Login) (Branchens geotekniska arkiv) (http://bga.swedgeo.se/bga/) Library Papers, publications and research - Unknown - series concerning hydrogeology in Gothenburg

Table 9. Explanation of how to obtain the data given in Table 8.

Key to "How to obtain the data" Name Explanation Download Download from the data host's website as free (Open data) or sometimes an account is needed (Login.). E-mail Contact the data host via e-mail and ask for the required data. Visit First contact the data host via mail or phone and then collect the data from a given place (physical address).

5.2. Conceptual hydrogeological model In this section the conceptual hydrogeological model consisting of the stratigraphical model, potentiometric surfaces and 2D and 3D visualisation are presented. Opinions about mechanisms of groundwater recharge to the lower aquifer obtained through the questionnaires and interviews are also incorporated in the conceptual hydrogeological model but presented as a separate section (5.3).

5.2.1. Stratigraphy In this section the depth to the bedrock surface (soil thickness) and the thicknesses of the fill material, clay and friction material are presented using the methods explained in sections 4.2.2.1 and 4.2.2.2.

5.2.1.1. Bedrock The interpolated depth to the bedrock surface based on the methods described in section 4.2.2.1 is shown in Figure 26. The depth to the bedrock surface ranges from 0 to 94 m and is deepest along the valleys and towards Göta Älv where a maximum depth of 94 m is confirmed by boreholes. The valleys in the area are generally oriented in N-S, NNE-SSW and WNW-ESE directions. In large parts of the area the depth to bedrock is <5 m (57%).

The interpolated bedrock surface level uncertainty using the Kriging interpolation method is shown in Figure 27. From the figure it is clear that the uncertainty is smaller closer to boreholes and soundings compared to further away from them. According to this map the bedrock surface has an uncertainty in different areas that can vary between 0.5 – 15 m. Where the bedrock outcrops, the uncertainty can be assumed to be 0 m.

Figure 26. Interpolated depth to the bedrock surface in the focus area Haga and Linné using the Kriging interpolation method. Note the difference in the depth to bedrock interval.

Figure 27. Map of the interpolated bedrock level uncertainty in the focus area Haga and Linné obtained using the Kriging interpolation method. In the blue areas the uncertainty is the highest with an uncertainty of ±15 m.

5.2.1.2. Fill material The interpolated thickness of the fill material based on the methods described in section 4.2.2.2 is shown in Figure 28. The thickness of the fill material ranges from 0 to 15 m with larger thicknesses closer to Göta Älv and along the central parts of the valleys. Approximately 2/3 of the area has a fill material thickness of <2 m.

Figure 28. Interpolated thickness of fill material in the focus area Haga and Linné using the Kriging interpolation method. The two first meters are displayed in a different colour scheme.

5.2.1.3. Clay The interpolated thickness of the clay described in section 4.2.2.2 is shown in Figure 29. The thickness of the clay ranges from 0 to 82 m with the greatest thickness in the northern parts of the area close to Göta Älv and along the valleys greater thicknesses are also observed. In some places and often close to the bedrock outcrops the thickness of the clay is <1.5 m.

Figure 29. Interpolated thickness of clay in the focus area Haga and Linné using the Kriging interpolation method. Note the difference in the clay thickness interval, the first 1.5 m is displayed in a light yellow colour.

5.2.1.4. Friction material The interpolated thickness of the friction material (gravel, sand, and till) is described in section 4.2.2.2 is shown in Figure 30. The thickness of the friction material ranges from 0 to 16 m. The friction material is thickest along the central parts of the valleys and in the northern parts of the area. Approximately 40 % of the area has a friction material thickness of <1 m, generally occurring closer to bedrock outcrops and in narrow valleys.

Figure 30. Interpolated thickness of friction material in the focus area Haga and Linné using the Kriging interpolation method. Note the difference in the thickness interval of friction material in the first meter indicated by purple and pink.

5.2.1.5. Friction material (observations confirming friction material) The interpolated thickness of the friction material based on observation points confirming the upper and lower boundary of the friction material and described in 4.2.2.2 is shown in Figure 31. By comparing the IDP interpolation with the Kriging interpolation (Figure 30) the overall thickness of the friction material is less with the IDP interpolation than for the friction material interpolated with the Kriging method where respect to other stratigraphical layers are taken into consideration. No increasing thickness in the central parts of the valleys or closer to Göta Älv is observed (Figure 31). 47% of the friction material using the IDP interpolation method has a thickness of less than 1 m and 91% of the friction material has a thickness of less than 2 m hence greater thicknesses only occur in a few areas in the focus area.

Figure 31. The interpolated thickness of the friction material based on observations confirming the upper and lower boundary of friction material in the focus area Haga and Linné using the IDP interpolation. The first meter is displayed in purple.

5.2.2. Potentiometric surface In this section the potentiometric surfaces of the lower aquifer created for central Gothenburg and the focus area based on the method in section 4.2.2.3 are presented. This was done in order to identify potential infiltration areas and evaluate the continuity of the lower aquifer.

5.2.2.1. Central Gothenburg The potentiometric surface of the lower aquifer in central Gothenburg is shown in Figure 32. The general groundwater flow in the lower confined aquifer is from SSE to NNW, perpendicular to the potentiometric contour lines. In some areas close to bedrock outcrops the groundwater flow has a different direction. The highest measured groundwater level was 56 meters above sea level (m.a.s.l.) and is observed the south-central part of the focus area. There is a general decrease in the groundwater level towards Göta Älv where measured levels of around 0-2 m.a.s.l. are observed. Steeper gradients are observed in the narrow valleys in the area. A cone of depression is located in SW in the area close to a bedrock outcrop (Skansberget). Several infiltration and pumping wells are located in the area.

Figure 32. Potentiometric surface of the lower aquifer in central Gothenburg. The potentiometric contour lines have an interval of 2 m.

5.2.2.2. Haga and Linné The potentiometric surface of the lower aquifer for the Haga and Linné area is shown in Figure 33. The general groundwater flow in the lower confined aquifer is from south towards north. In some areas close to bedrock outcrops the groundwater flow has a different direction. The highest measured water level was 46 (m.a.s.l.) and is observed in the southern part of the area. There is a general decrease in the groundwater level towards Göta Älv where measured levels of around 0-2 m.a.s.l. are observed. A cone of depression is located in the central part of the area close to a bedrock outcrop (Skansberget) same as in (Figure 32). Several infiltration and pumping wells are located in the area.

Figure 33. Potentiometric surface of the lower aquifer in the focus area Haga and Linné. The potentiometric contour lines have an interval of 2 m.

5.2.2.3. Difference between the ground surface and potentiometric surface in the focus area In order to evaluate if the potentiometric surface of the lower aquifer follows the topography in the focus area the interpolated potentiometric surface was subtracted from the digital elevation model. The difference between the ground surface and potentiometric surface is presented in Figure 34. In approximately 70 % of the area the potentiometric surface is somewhere between 0 – 4 below the ground surface.

Figure 34. Difference between the digital elevation model (ground surface) and potentiometric surface in the focus area (Figure 33). Positive values indicate areas where the potentiometric surface is below the ground surface and negative values indicate areas where the potentiometric surface is above the ground surface (artesian). Note the difference in the interval.

5.2.3. Groundwater level observations In order to analyse if it is possible to separate the influence of human impact and urban development from climatic influences, groundwater level time series from the lower aquifer in the focus area were analysed, described in section 4.2.2.4. Also, groundwater level time series from Ljungdahl (2015) are presented in section 5.2.3.2.

5.2.3.1. Groundwater level observations around infiltration wells The groundwater levels (potentiometric pressure) for the observation wells around Skansberget are shown in Figure 35, for names and locations see Figure 21. The general trend is that observation wells (northeast of Skansberget) located closer to the infiltration well have lower groundwater levels and with distance from the infiltration well the groundwater level increases in the observation wells. The groundwater levels in each groundwater observation well increases with each 10-year interval, except from GW415, GW416 and GWSK4. The three observation wells (GW1436, GW414 and GW 415) closest to the infiltration well show a large increase in groundwater levels during 1980-1989 to 1990-1999 relative to the following time intervals. In observation well GW1436 close to the infiltration well a rapid increase in the groundwater level in 1995 is observed (Figure 36). This increase can also be observed in wells nearby but not as prominent.

Potentiometric level Infiltration well Distance from infiltration well (m) GW1929 GW1926A GWSK4 1 GW1436 GW414 GW415 GW1927 GW416 GW1924 0 0 20 40 60 80 100 120 140 -1 -2 -3 -4 1970-1979 -5 1980-1989 -6 -7 1990-1999 -8 2000-2009 Potentiometric pressure (m.a.s.l) pressure Potentiometric -9 2010-2014 -10

Figure 35. Groundwater levels (potentiometric pressure) between 1970-2014 with a 10-year interval in wells with increasing distance from an infiltration well located northeast of Skansberget.

Figure 36. Normalised groundwater level time series for GW1436, in the lower aquifer. Observations between 1982-2013. The groundwater levels were normalised by subtracting the average groundwater levels and thereafter by dividing the groundwater level standard deviation for the same period (note that the period can vary between wells). For precipitation reference, see Figure 39.

Between 1974-1975 infiltration occurred to the west of Skansberget (Appendix 3) which correlates with changes of the groundwater levels in wells close by during this period e.g. GW430 and GW435 (Figure 37 and Figure 38).

Figure 37. Normalised groundwater level time series for GW430, in the lower aquifer. Observations between 1969-2008. The groundwater levels were normalised by subtracting the average groundwater levels and thereafter by dividing the groundwater level standard deviation for the same period (note that the period can vary between wells). For precipitation reference, see Figure 39.

Figure 38. Normalised groundwater level time series for GW435, in the lower aquifer. Observations between 1973-2008. The groundwater levels were normalised by subtracting the average groundwater levels and thereafter by dividing the groundwater level standard deviation for the same period (note that the period can vary between wells). For precipitation reference, see Figure 39.

5.2.3.2. Groundwater level observations from Ljungdahl (2015) All groundwater level time series and results in this section (5.2.3.2) are from Ljungdahl (2015). The observation wells which the groundwater level times series come from (lower aquifer) are located in the focus area (Figure 21) and the groundwater level time series are normalised (Figure 39). In GW252 no correlation between groundwater level and precipitation since mid-1990 is observed.

According to Ljungdahl (2015) the groundwater levels respond quickly to changes in precipitation, with only a few months delay. The influences of artificial (human) impact observed in the groundwater level time series were removed. In observation wells GW431, GW433 and GW435 there are high groundwater levels around 1975 which is interpreted to be a result of groundwater infiltration.

Figure 39. Normalised groundwater time series compared to precipitation. Influences of artificial impact observed in the groundwater level time series were removed, marked in grey. The response of groundwater levels to changes in precipitation is quick with only a few months delay, from Ljungdahl (2015).

5.2.4. 3D-stratigraphical model In order to get a better visualisation of the stratigraphy in Haga and Linné and to display the thickness of the fill material, clay and friction material 3D-stratigrapghical models were created based on the thickness maps using the Kriging interpolation method, see section 5.2.1.1 - 5.2.1.4.

The block diagram (Figure 40) and the fence diagrams (Figure 41 and Figure 42) covering various aspects of the focus area display all geological units produced with the Kriging interpolation. Clay constitutes the largest part of the total sediment thickness in areas with greater sediment thicknesses. The assumption that all geological units are present in the stratigraphical sequence is shown in the 3D- model hence the fill material appears to cover the entire focus area, however, with varying thickness.

Figure 40. Block diagram of the focus area Haga and Linné displaying the four geological units: Fill material (grey), clay (yellow), friction material (blue) and bedrock (red). The block diagram has the same extent as the focus area Haga and Linné.

Figure 41. Fence diagram of the focus area Haga and Linné displaying the four geological units: Fill material (grey), clay (yellow), friction material (blue) and bedrock (red). The fence diagram has the same extent as the focus area Haga and Linné with a 150 x 150 m spacing between each line.

Figure 42. Fence diagram of the focus area Haga and Linné displaying the four geological units: Fill material (grey), clay (yellow), friction material (blue) and bedrock (red). The fence diagram displays the six stratigraphical profiles with the same position as in Figure 22.

5.2.5. Cross sections The cross sections display the topography, stratigraphical thicknesses, levels of the geological units combined with potentiometric surfaces (Figure 43a-f) with the corresponding positions of the profiles 1 – 6 seen in Figure 22. Profiles 1 and 2 runs in a S – N direction, following the two main roads in the focus area (Linnégatan and Övre Husargatan). Profiles 3 – 6 runs in a W – E direction, crossing profiles 1 and 2. In profile 1, between 190 – 240 m and 1150 – 1280 m in the profile, the thickness of the fill material increases as the thickness of the friction material decreases. In general the potentiometric surface is close to the ground surface in all profiles but in some places a deviation in the potentiometric surface is observed, e.g. between 500 – 650 m in profile 1 and 575 – 650 in profile 4.

Figure 43. a-c) Cross sections displaying the four geological units and the potentiometric surface. Note the different interval between the x- and y-axis and the different distances between the profiles (x-axis).

cont. Figure 43. d-f) Cross sections displaying the four geological units and the potentiometric surface. Note the different interval between the x- and y-axis and the different distances between the profiles (x-axis).

5.3. Questionnaire and interviews with groundwater professionals The complete questionnaire with answers is shown in Appendix 4. The questionnaire was sent to approximately 60 people of whom 23 people answered. In this section only answers regarding the lower aquifer, groundwater recharge and the hydrogeological model are presented. Also, interviews were conducted with groundwater professionals to gain further knowledge, ideas and views on urban hydrogeology, groundwater recharge and the application and implementation possibilities of creating hydrogeological models in urban cities.

5.3.1. Lower aquifer To the question “Is the lower aquifer in Gothenburg continuous?” 17% answered that they believe that the lower aquifer in Gothenburg is continuous while 83% believe that it is discontinuous (Figure 44). However, the general view is that the lower aquifer is continuous in large parts of Gothenburg but with a varying thickness, hence some areas are not well-connected and/or separated by e.g. bedrock structures and therefore the lower aquifer is not considered to be continuous.

Is the lower aquifer in Gothenburg continuous?

4 (17%) Yes No 19 (83%)

Figure 44. Results from the question "Is the lower aquifer in Gothenburg continuous?” based on answers from the questionnaire.

5.3.2. Infiltration coefficients The answers to the question “Estimate the infiltration coefficient of different land cover/soil type in different environments as % of precipitation” are compiled in Table 10. A compilation of the median, lower (Q1) and upper (Q3) quartile values of infiltrations coefficients for different land cover and soil types are presented. The infiltration coefficients obtained varies considerably in minimum and maximum values hence why the lower and upper quartiles are chosen and used hereafter. The coarser sediments show a higher infiltration coefficient than finer sediments.

Table 10. Infiltration coefficients based on the answers from the questionnaire: median values (bold), and range from lower to upper quartile (in brackets).

Urban Cultivated land Woodland environment Impervious surface 0.08 (0.05-0.10) X X Clay X 0.10 (0.05-0.15) X Silt X 0.20 (0.15-0.41) X Sand X 0.52 (0.34-0.75) 0.50 (0.40-0.65) Gravel X 0.71 (0.45-0.83) 0.61 (0.50-0.80) Till X X 0.30 (0.20-0.38) Bedrock X X 0.11 (0.10-0.26)

5.3.3. Groundwater recharge to the lower aquifer A schematic illustration of the main mechanisms of groundwater recharge to the lower aquifer and the frequency of answers to the question “What are the main mechanisms of groundwater recharge to the lower aquifer in Gothenburg?” is shown in Figure 45 and Figure 46. The respondents were to rank 4 alternative recharge mechanisms. According to the answers the main mechanism of groundwater recharge to the lower aquifer is from surface runoff from steep areas followed by infiltration in contact zones between bedrock and friction material, followed by (in decreasing order of importance) contribution of groundwater to the lower aquifer via fractured bedrock, vertical infiltration (direct recharge) and lateral groundwater inflow from “outside” Gothenburg. Also, additional water from supply and sewage systems could contribute to the groundwater recharge, mentioned in the comment box in the questionnaire, but was not listed as an option of mechanism of groundwater recharge to the lower aquifer.

Figure 45. A schematic figure of the main mechanisms of groundwater recharge to the lower aquifer in Gothenburg. 1) Contact zones between bedrock and friction material, 2) Addition of groundwater through fractured bedrock, 3) Vertical infiltration (direct recharge), 4) Lateral groundwater inflow from “outside” Gothenburg and 5) Addition of water from water supply and sewage systems.

Mechanisms of groundwater recharge to the lower aquifer, Gothenburg 14

12 1. Contact zones between bedrock 10 and friction material 2. Fractured bedrock 8

6 3. Vertical infiltraiton 4 Number of of Number answers

2 4. Outside Gothenburg 0 This is the Plays a Plays a Plays a Does not main major role certain role minor role occur mechanism Degree of importance Figure 46. Mechanisms of groundwater recharge to the lower aquifer in Gothenburg based on the answers from the questionnaire (graded according to importance). 1) Contact zones between bedrock and friction material, 2) Addition of groundwater through fractured bedrock, 3) Vertical infiltration (direct recharge), 4) Lateral groundwater inflow from “outside” Gothenburg.

According to the opinions of the questionnaire respondents the groundwater recharge to the lower aquifer would be 100 mm/year in median within an interval of 66 – 137 mm/year (lower to upper quartile) of the average annual precipitation Figure 47 and Table 11.

Groundwater recharge to the lower aquifer 6

Number of of Number answers 1

mm/yr

Figure 47. Histogram of values for groundwater recharge to the lower aquifer provided by the participants of the questionnaire.

Table 11. Groundwater recharge to the lower aquifer in Gothenburg based on the answers from the questionnaire showing the number of answers, average values, standard deviation, coefficient of variation (CV), minimum value (Min), lower quartile (Q1), median (Q2), upper quartile (Q3) and maximum value (Max).

Groundwater Number recharge to the of Avg. lower aquifer answers value Std.Dv. CV Min Q1 Q2 Q3 Max mm/year 23 140.1 136 97.1 % 16 66 100 137 584

5.3.4. Hydrogeological model In Table 12 the answers of how a hydrogeological model should be structured and what should be included are presented. Respondents were to choose from a list of options. In Table 12 these options are ranked according to the frequency with which they were mentioned. The three most important attributes a model should have are: easy to update, easy to extract data from and good visualisation possibilities. From the questionnaire it has emerged that most respondents consider a conceptual hydrogeological model to be made as easy as possible regarding the problem to be solved i.e. does not have to cover large areas, be very detailed or contain all available data.

Table 12. Ranking of the options of how a hydrogeological model should be structured and what the model should contain according to the answers in the questionnaire (1 – Most important and 10 – Least important).

Structure and content of a hydrogeological model 1 Easy to update the model 2 Easy to extract data from the model 3 Visualisation options 4 Easy to add new data to the model 5 Useful for all issues relating to geology and groundwater 6 Interaction with various types of software such as groundwater modelling program 7 Cover the entire Gothenburg area 8 Easy to use, no special skills in software program needed 9 Contain all available data 10 It should be as detailed as possible

5.4. Numerical model of groundwater recharge The numerical model was created in order to estimate the direct groundwater recharge via vertical infiltration based on infiltration coefficients, land cover/soil type and area for the local catchment area around Haga and Linné, the focus area and the lower aquifer within the focus area. The infiltration coefficients, area and percentage of land cover/soil type for respectively area are given in Table 13. Also, infiltration coefficients obtained from von Brömssen’s study obtained from Barkels and Parra (2010) are included in the table and used as a comparison.

Of the 62 million m3 produced fresh water in Gothenburg approximately 13 million m3 (21%) is lost through leakage. It is unknown where and how much of this water that contributes to groundwater recharge but if the total volume would be equally distributed over Gothenburg the contribution of water through leakages would potentially be 29 mm/year.

In the following sections of groundwater estimations (Table 14, Table 16, Table 18, and Table 20) note the increase in precipitation from the normal reference period 1961-1990 to today.

Table 13. Infiltration coefficients, percentage of area for different land use/land cover.

Infiltration coefficients Area (%) Questionnaire von Brömssen Catchment area Haga and Linné Haga and Linné Haga and Linné - (Land cover & (Land cover & (Soil type) Lower aquifer

Land use/From Q1 Q3 Median Mean soil type) soil type) (Land cover & soil type) Buildings 1 - - 0.00 0.00 14.3 21.1 - 18.4 Asphalt 2 - - 0.32 0.32 13.7 17.9 - 13.9 Impervious surface 0.05 0.10 0.08 0.08 15.4 18.2 - 15.9 Clay (Total) 0.05 0.15 0.10 - 13.3 12.6 51.0 25.4 Clay < 1.5m - - - 0.21 - 2.4 6.4 25.4 Clay > 1.5m - - - 0.001 - 10.2 44.6 - Sand 0.40 0.65 0.50 0.39 2.8 2.8 5.1 12.2 Till 0.20 0.38 0.30 0.23 1.8 1.0 2.3 8.8 Peat3 - - 0.05 0.05 0.8 - - - Bedrock outcrops 0.10 0.26 0.11 0.26 37.9 26.3 41.6 - Total area (km2) 6.081 3.851 3.851 0.373

1 Trafikverket (2013a) 2 Wiles and Sharp (2008) 3 Misstear and Brown (2002) 90

5.4.1. Catchment area The local catchment area for the area around Haga and Linné is 6.081 km2. The land cover is dominated by anthropogenic constructions (buildings, asphalt and impervious surfaces) and bedrock outcrops which constitutes 43.5% and 37.9% respectively. The remaining area constitutes of different quaternary deposits (18.7%). The median groundwater recharge via vertical infiltration according to (Eq.14) is 42 - 65 mm/year but due to different input parameter values (precipitation, evapotranspiration and infiltration coefficients) the calculated recharge could be between 35 – 101 mm/year (Table 14). The volume of the groundwater recharge is calculated to be between 2.1E+05 and 6.1E+05 m3/year (Table 15).

Table 14. Values of precipitation, evapotranspiration and potential direct groundwater recharge intervals for the local catchment area around Haga and Linné.

Groundwater recharge - Catchment area (Land cover & soil type) Precipitation Evapotranspiration Groundwater recharge (mm/year)

(mm/year) (mm/year) Q1 Q3 Median von Brömssen 8721 4453 48 87 56 73 (1961-1990) 5544 35 64 42 54 9652 4663 55 101 65 85 (1991-2014) 5675 44 81 52 68 5494 46 84 54 71 1 Corrected precipitation value for the reference period 1961-1990 from Alexandersson (2003) 2 Corrected precipitation value for the period 1991-2014 calculated using the correction model in Alexandersson (2003) 3 Tamms’ formula (Eq.11) 4 CRU (Ljungdahl, 2015) 5 Turc and Ivanov methods (Eq.12) and (Eq.13)

Table 15. Groundwater recharge median, Q1 and Q3 values and volumes for the local catchment area for the area around Haga and Linné.

Groundwater recharge rates and volumes mm/year m3/year

Q1 Min 35 2.1E+05

Q3 Max 101 6.1E+05 Median Min 42 2.6E+05 Max 65 4.0E+05

5.4.2. Haga and Linné The focus area Haga and Linné is 3.851 km2. Estimations of groundwater recharge for the focus area are conducted using two methods; the first method based on land cover and soil type and the second method is based on soil type only, described in section 4.2.4.

For the first method 57.3% of the area constitutes of anthropogenic constructions (artificial materials), 26.3% of bedrock outcrops and 16.4% of quaternary deposits of which 2.4% is clay with a thickness of less than 1.5 m. The median groundwater recharge via vertical infiltration according to (Eq.14) is 41 – 65 mm/year but due to different input parameter values (precipitation, evapotranspiration and infiltration coefficients) the calculated recharge could be between 36 – 92 mm/year (Table 16). The

91 volume of the groundwater recharge is calculated to be between 1.4E+05 and 3.5E+05 m3/year (Table 17).

Table 16. Values of precipitation, evapotranspiration and potential direct groundwater recharge intervals for the Haga and Linné area.

Groundwater recharge - Haga and Linné (Land cover & soil type) Precipitation Evapotranspiration Groundwater recharge (mm/year)

(mm/year) (mm/year) Q1 Q3 Median von Brömssen 8721 4453 48 79 58 68 (1961-1990) 5544 36 59 41 50 9652 4663 56 92 65 79 (1991-2014) 5675 45 74 52 63 5494 47 77 54 66 1 Corrected precipitation value for the reference period 1961-1990 from Alexandersson (2003) 2 Corrected precipitation value for the period 1991-2014 calculated using the correction model in Alexandersson (2003) 3 Tamms’ formula (Eq.11) 4 CRU (Ljungdahl, 2015) 5 Turc and Ivanov methods (Eq.12) and (Eq.13)

Table 17. Groundwater recharge median, Q1 and Q3 values and volumes for the Haga and Linné area.

Haga and Linné mm/year m3/year

Q1 Min 36 1.4E+05 Q3 Max 92 3.5E+05 Median Min 41 1.6E+05 Max 65 2.5E+05

In Figure 48 the numerical model of direct groundwater recharge estimation for the focus area Haga and Linné based on land cover and soil type is summarised. The part contribution of groundwater recharge for each land cover/soil type, effective precipitation and surface runoff are presented as well as the input parameters of precipitation and evapotranspiration.

Figure 48. Summarised numerical model of the direct groundwater recharge estimation in the focus area Haga and Linné. The climatic input variables used are described in section 4.2.3. Note that the values are rounded.

The second method based on soil type only is described in section 4.2.4. Using this method the focus area constitutes of 41.6% bedrock outcrops and 58.4% quaternary deposits of which 6.4% is clay <1.5 m, 44.6 % is clay >1.5 m, 5.1% is sand and 2.3% is till. The median groundwater recharge via vertical infiltration according to (Eq.14) is 41 - 64 mm/year but due to different input parameter values (precipitation, evapotranspiration and infiltration coefficients) the calculated recharge could be between 29 - 113 mm/year (Table 18). The volume of the groundwater recharge is calculated to be between 1.1E+05 and 4.4E+05 m3/year (Table 19).

Table 18. Values of precipitation, evapotranspiration and potential direct groundwater recharge intervals for the Haga and Linné area based on soil type only.

Groundwater recharge - Haga and Linné (Soil type) Precipitation Evapotranspiration Groundwater recharge (mm/year)

(mm/year) (mm/year) Q1 Q3 Median von Brömssen 8721 4453 39 97 55 63 (1961-1990) 5544 29 72 41 47 9652 4663 46 113 64 73 (1991-2014) 5675 37 90 51 59 5494 38 94 54 61 1 Corrected precipitation value for the reference period 1961-1990 from Alexandersson (2003) 2 Corrected precipitation value for the period 1991-2014 calculated using the correction model in Alexandersson (2003) 3 Tamms’ formula (Eq.11) 4 CRU (Ljungdahl, 2015) 5 Turc and Ivanov methods (Eq.12) and (Eq.13)

Table 19. Groundwater recharge median, Q1 and Q3 values and volumes for the Haga and Linné area based on soil type only.

Haga and Linné (Soil type) mm/year m3/year

Q1 Min 29 1.1E+05 Q3 Max 113 4.4E+05 Median Min 41 1.6E+05 Max 64 2.5E+05

5.4.3. Haga and Linné (lower aquifer) The infiltration area for the lower aquifer, derived from the interpolated clay thicknesses where clay is <1.5 m, is 0.372 km2 and constitutes of 53.6% anthropogenic constructions, 25.4% clay <1.5 m, 12.2% sand and 8.8% till. The median groundwater recharge via vertical infiltration according to (Eq.14) is 59 – 93 mm/year but due to different input parameter values (precipitation, evapotranspiration and infiltration coefficients) the calculated recharge could be between 47 -114 mm/year (Table 20). The volume of the groundwater recharge is calculated to be between 1.8E+04 and 4.3E+04 m3/year (Table 21).

Table 20. Values of precipitation, evapotranspiration and potential direct groundwater recharge intervals to the lower aquifer in the Haga and Linné area.

Groundwater recharge to the lower aquifer in Haga and Linné (Land cover & soil type) Precipitation Evapotranspiration Groundwater recharge (mm/year)

(mm/year) (mm/year) Q1 Q3 Median von Brömssen 8721 4453 64 98 80 84 (1961-1990) 5544 47 73 59 62 9652 4663 74 114 93 98 (1991-2014) 5675 59 91 75 78 5494 62 95 78 81 1 Corrected precipitation value for the reference period 1961-1990 from Alexandersson (2003) 2 Corrected precipitation value for the period 1991-2014 calculated using the correction model in Alexandersson (2003) 3 Tamms’ formula (Eq.11) 4 CRU (Ljungdahl, 2015) 5 Turc and Ivanov methods (Eq.12) and (Eq.13)

Table 21. Groundwater recharge median, Q1 and Q3 values and volumes to the lower aquifer in the Haga and Linné area.

Haga and Linné – Lower aquifer mm/year m3/year

Q1 Min 47 1.8E+04 Q3 Max 114 4.3E+04 Median Min 59 2.2E+04 Max 93 3.5E+04

In Figure 49 the numerical model of groundwater recharge estimations to the lower aquifer based on land cover and soil type is summarised. The part contribution of groundwater recharge for each land cover/soil type, effective precipitation and surface runoff are presented as well as the input parameters of precipitation and evapotranspiration.

Figure 49. Summarised numerical model of the direct groundwater recharge estimation to the lower aquifer in the focus area Haga and Linné. The climatic input variables used are described in section 4.2.3. Note that the values are rounded and that the clay thickness is not proportional to the scale axis.

6. Discussion In this section the objectives and research questions brought up in the introduction will be discussed and compared in a wider context for the city of Gothenburg and other urban cities as well as in relation to previous studies and other findings. Also, information and opinions obtained from the interviews conducted and the questionnaire sent out to groundwater professionals is kept in mind throughout the discussion. Furthermore, an evaluation of data hosting will be made and limitations and uncertainties will be discussed.

6.1. Discussion of uncertainties and limitations

6.1.1. Compilation of available data The compilation of data does not contain all the geological/hydrogeological data that exists, but the data available and manageable to collect within the time frame for this project. The data were collected with the overall aim to be useful in creating the conceptual hydrogeological model created for this thesis. Because the majority of the data was obtained from secondary sources it is possible that conceptualisations and interpretations have already been made and could have been collected with different purposes than for this study the quality and validation of the data can not be guaranteed. There are other possibilities and applications for the data and what it can be used for than what is suggested in section 5.1. Also, the availability and file format of the data is based on how the authors of this thesis obtained the data. Hence, other approaches of how to obtain the data may be required.

6.1.2. Stratigraphical data All stratigraphical data obtained for this thesis are obtained from secondary sources. These datasets were often compiled with other purposes than creating a geological model, therefore, the level of details, descriptions and geological interpretations vary widely. Moreover, using secondary information from external sources, there is always a possibility of misinterpretations, misclassifications and subjective assumptions that could be inherited to new projects. It also has to be taken into account that boreholes are not located at the best possible positions i.e. evenly distributed over the area.

A major problem results from the fact that classifications and geological boundaries used by external data sources do not always match the classifications needed to fulfil the objectives of this study. The purpose of this study was to evaluate the upper and lower aquifers. Therefore, the stratigraphy was conceptualised into four geological units: fill material, clay, friction material and bedrock. In reality the stratigraphy is more complex and heterogeneous and therefore there is a risk that the thickness of the stratigraphic layers could be over- or underestimated.

6.1.3. Groundwater level observations The potentiometric surface maps were created using average values from the latest groundwater level measurements conducted between 2000-2014, i.e. some of the observation wells are no longer in use today or the measuring period can vary between each groundwater observation well. Therefore, the potentiometric surface maps might not represent the actual groundwater level of today.

The groundwater observations wells are not evenly distributed over the area which leads to an increase in uncertainty of the potentiometric surface with distance to the wells. To be able to make good and reliable maps of groundwater levels or/and potentiometric levels, groundwater level observations made in the aquifer of interest must be done. Because groundwater levels can change

97 with time, all the readings should be done within a short period of time, preferably during the same day.

6.1.4. Meteorological data The precipitation data obtained from SMHI are from two different measuring stations with two different types of gauges in use, Göteborg A and Säve, which means that the precipitation and other factors such as temperature and wind may vary between the locations but also within the city of Gothenburg. Due to incomplete time series of the meteorological data obtained (precipitation, temperature, radiation and humidity) the data must be used with this knowledge. Also, the meteorological data used in this thesis are not measured in the focus area or with a sufficient time resolution or spatial resolution which is desirable when estimating groundwater recharge in urban areas (Schilling, 1991). Different methods of estimating the potential evapotranspiration requires different climatic input variables which is why there is inconsistency in the results estimated by various methods (Fisher & Pringle III, 2013). Therefore, three different methods and one dataset (Tamm’s formula, Turc and Ivanov method and evapotranspiration data from CRU) were used to estimate the potential evapotranspiration in this study in order to gain a representative interval with the data that has been available and manageable to collect within the time frame for this project. The reliability of the evapotranspiration data from CRU, obtained from Ljungdahl (2015) is unknown to the authors.

6.1.5. Numerical model of groundwater recharge The numerical model of groundwater recharge only estimates the potential recharge through direct infiltration and not the actual/total groundwater recharge. Several assumptions were made in order to create the numerical model of groundwater recharge. The input parameter values used for estimating the groundwater recharge are meteorological data (see previous section) and land cover and soil type classification. As urban cities constantly are changing available maps and digital elevation models used for classification of different land cover and identification of catchment areas could be outdated which in turn could affect the estimations of groundwater recharge. However, in the focus area no major changes of the land cover have occurred during the investigation period of 1960’s until today. The different land cover and soil type classifications are considered to have the same infiltration coefficient within each class, however, these can differ e.g. the infiltration coefficient for asphalt can vary with age where new asphalt is more permeable than older (Viman, 2005).

6.2. Thicknesses and positions of relevant hydrogeological formations in Gothenburg with special focus on the upper and lower aquifers In this section the contour maps of the thicknesses and positions of the stratigraphical layers relevant to the conceptual hydrogeological model are discussed. A special focus is on the upper and lower aquifers. The results from the stratigraphical model are compared with existing results and literature regarding Gothenburg.

Bedrock The total soil thickness is limited by the ground surface and the bedrock surface. It is therefore of great importance to get as good as possible estimation of the position of the bedrock surface since the elevation of the ground surface is well-known. The uncertainty of the bedrock level is between 0.5 – 15 m i.e. the bedrock surface could differ with ±15 m in some places which in turn will affect the total soil thickness and individual layers. The uncertainty is smaller closer to boreholes/soundings and increases with distance. Comparing the soil thickness with SGU’s soil thickness (Appendix 5) there is a difference. Especially in narrow valleys and where no data is available, SGU interprets greater soil thicknesses compared to the depth to bedrock (soil thickness) produced in this thesis. On the other hand, closer to Göta Älv and around Linnéplatsen SGU interprets the soil thickness to be thinner. The difference is assumed to be due to different amounts of interpolation points in certain areas. Also, SGU uses geophysical data and information about fracture zones in order to enhance greater soil depths in these areas. Furthermore, different interpolation methods are used when creating the depth to bedrock (soil thickness) (Daniels & Thunholm, 2014). In areas with high density of interpolation points the soil thickness estimated for the stratigraphical model is believed to better represent a more accurate soil thickness than SGU’s depth to bedrock map. This since more site specific knowledge about the soil thickness is included those areas. On the other hand, SGU’s map is probably closer to reality in areas with fewer input data/interpolation points since SGU includes other information than borehole data only.

Fill material In densely urbanised environments great thicknesses of fill material is often observed. The fill material is heterogeneous and is a product of the development of the city. The uncertainty of the interpolated fill thickness increases with distance from the interpolation points. The thickness of the fill material has the same general trend and spatial distribution in thickness but it has a higher resolution than the map in Hultén (1997), who presented a generalised map of the fill material in Gothenburg (Appendix 6). The main difference between the spatial interpolation produced within this thesis and the map presented by Hultén (1997) is the generally greater thicknesses of the fill material. In this study the overall thickness varying between 0 – 15 m was determined, whereas in Hultén (1997) the estimated thickness varies between 1 – 7 m in central Gothenburg. An urban environment can change groundwater levels, flow patterns, pathways and sources of recharge. The occurrence of groundwater in the fill material (upper aquifer) is restricted by the influence and drainage of water supply and sewer systems (Lerner, 2002). Therefore, the groundwater table is generally found 2 m below the ground surface (Bergström, 1981; Hultén, 1997) which means that groundwater is not always present in the fill material. This lowering of the groundwater table can e.g. cause rotting of wooden piles which in turn can have economic consequences.

Clay The thickness of the clay correlates well with Lars-Gunnar Hellgren’s soil cover map and the hydrogeological map from Banverket (2006) (Appendix 7 and Appendix 8). All maps display great thicknesses along the valleys and towards Göta Älv, where thicknesses of >50 m are observed. Furthermore, the clay thickness in Haga and Linné is previously examined in Albertsson (2014) and Ljungdahl (2015) and these studies support the general trend and thickness of the interpolated thickness of the clay. The main difference is the position of the clay layer in the stratigraphy which is due to the incorporation of the fill material in this study. The clay layer is assumed to act as an aquitard in places with thickness of >1.5 m (Berntson, 1983) and separates the upper unconfined aquifer in the fill material and the lower confined aquifer in the friction material. Great clay thicknesses together with a fluctuating groundwater level and great overburden can lead to subsidence which is a major concern in many urban cities around the world e.g. Jakarta, New Orleans and Bangkok (Erkens, Bucx, Dam, De Lange, & Lambert, 2014).

Friction material The thickness of the friction material created for the stratigraphical model with the Kriging interpolation and the thickness of the friction material using the IDP interpolation method do not correlate well. The thickness map produced with the Kriging interpolation method generally displays greater thicknesses than with the IDP interpolation method, see Figure 30 and Figure 31. This is assumed to be due to the different interpolation methods used and that the thickness of the friction material produced with the Kriging interpolation incorporates more interpolation points. The main purpose of creating a map of the thickness of the friction material based on points confirming the upper and lower boundaries is to show the difference when only considering one stratigraphical layer at a time rather than considering the stratigraphy as a whole, where both the lower boundary of the clay and the bedrock surface are included. In areas where the friction material is thin e.g. <1 m the groundwater flow in the lower aquifer can be restricted due to a lower transmissivity.

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6.3. Is the lower aquifer a continuous aquifer? The stratigraphical part of the hydrogeological model was created with the assumption that the thickness of the friction material is restricted by the lower boundary of the clay layer and the bedrock surface. This assumption leads to the presence of friction material in the entire focus area if not boreholes confirm the opposite. This is a result of calculations of the interpolated depth to bedrock (soil thickness) and interpolated thicknesses of fill material and clay. The friction material forms the lower aquifer and according to Figure 30 this friction material is present in the entire focus area. However, because there is an uncertainty in the position of the bedrock surface level the thickness of the friction material can also vary i.e. the thickness of the friction materiel could either be thicker or thinner.

In large parts of the focus area (40 %) the interpolated friction material has a thickness of < 1 m which means that the transmissivity in these areas would be considerably lower than in areas with thicker friction material, assuming that hydraulic conductivity is homogenous for the entire aquifer. A lower transmissivity would lead to a restricted groundwater flow. It can be assumed that the transmissivity in some places would be as low that the lower aquifer has to be regarded as non-continuous even though the friction material, according to the interpolation results, is present in the entire area.

As the result of the interpolation of aquifer thickness carried out in this study yield ambiguous results, it was compared to results from pumping tests conducted close to Lisebergsgaraget (2005), Korsvägen, Skansen Lejonet (2013) and in Haga (2014). These pumping tests were performed in order to investigate the hydrogeological conditions such as the hydraulic conductivity and transmissivity for the lower aquifer, the connection between the lower aquifer and fractures in the bedrock and indirect measurements of groundwater recharge (Trafikverket, 2013a). From the investigations in these areas it was concluded that small extractions of water from the lower aquifer generates lowering of groundwater levels (potentiometric pressure) in a large area extending up to 1 km in certain directions. The small extraction over a short period of time together with the large influence area indicates a high transmissivity in certain areas.

According to the results of the interpolation, the friction material is very thin in places, indicating interruptions in the aquifer. Also, the interpolated potentiometric surface for both central Gothenburg and for the focus area display strong changes (from flat to steep gradients) in some areas and often coincides with places where the friction material is thin. These steep gradients also support the idea that the lower aquifer has disruptions in its continuity. However, pumping tests conducted in other investigations in Gothenburg show that a small extraction from the lower aquifer results in lowering of groundwater levels in large areas which could indicate either a continuous lower aquifer and/or high hydraulic contact between the lower aquifer and the bedrock. The groundwater time series analysis in Ljungdahl (2015) display a rapid decrease in groundwater level around 1984. The observation wells were this is observed are located in different parts of the Haga and Linné area but all display the same trend. This indicates that the lower aquifer is to a certain degree continuous in these areas.

According to the questionnaire and interviews conducted within this thesis the general view among groundwater professionals regarding the continuity of the lower aquifer (friction material) is that the lower aquifer does not underlie the clay in entire Gothenburg or is completely continuous but it is continuous in large parts. This is in agreement with the results from the interpolated thickness map of

101 the friction material, the potentiometric surface maps and previously conducted investigations in Gothenburg.

Based on the results in this study the friction material is regarded as continuous in large parts of the Haga and Linné area but with a varying thickness, hence the continuity of the lower aquifer is restricted by this and the hydraulic properties and interfaces of the material and is therefore not always continuous. These results are in agreement with the finding from previous studies. As shown by the studies of Trafikverket (2013a) one way of evaluating how continuous the lower aquifer is to conduct pumping tests over a longer period of time.

The area investigated in this study does not cover the entire area of the city of Gothenburg. It is, however, assumed that the findings with respect to the continuity of the lower aquifer in the city of Gothenburg show similar characteristics as in the focus area. This assumption is mainly based on the opinions of groundwater professionals in Gothenburg, which are also those who mostly have been working with questions regarding the lower aquifer, who believes that the lower aquifer is continuous in large parts of the city but with disruptions in some areas. Also, the potentiometric surface map covering central Gothenburg display similar characteristics as the one in the focus area where the interpolated thickness of the friction material is known.

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6.4. Connections between the upper and lower aquifers From the conceptual hydrogeological model created with the associated cross sections and thickness maps the main contact between the upper and lower aquifer is where the friction material outcrops at the surface and where the clay separating the fill and friction material is < 1.5 m i.e. where the infiltration/recharge areas to the lower aquifer are located (Figure 29). These areas are generally located in the contact zones between the bedrock outcrops and the quaternary deposits in the focus area.

Fractures can occur in the top part of the clay in the stratigraphy due to stress release and weathering (Hight, McMillan, Powell, Jardine, & Allenou, 2003) and can therefore only contribute to the connection between the upper and lower aquifer at small clay depths. With increasing depth the clay acts as an aquitard. Hence, fractures in the clay do not enable a contact between the upper and lower aquifer in places with greater clay depths (Berntson, 1983). Similar results are observed in Wraysbury, close to London in the UK, which has a similar hydrogeological setting as Gothenburg were a clay layer is separating an upper (unconfined) and a lower (confined) aquifer. Joints and fractures are predominately observed in the top 2.5 m of the clay layer hence there is no connection between the aquifers in this way at greater depths (Skempton, Schuster, & Petley, 1969).

Other possible connections and pathways between the upper and lower aquifer are groundwater observation wells, boreholes/soundings and underground constructions (Banverket, 2005; Shanahan, 2009). To what degree and where these connections influence the contact between the aquifers in the focus area are uncertain and not further investigated within this thesis. One way to investigate this could be by using groundwater modelling, see section 8.

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6.5. Mechanisms of recharge to the lower aquifer In this section the main mechanisms of groundwater recharge to the lower aquifer is discussed as well as where the recharge areas in Gothenburg are located and how it works.

According to De Vries and Simmers (2002) there are three pathways for how precipitation enters the ground and contributes to groundwater in rural environments: direct, localised and indirect. However, in an urban environment the surface and subsurface processes are even more complex than in a rural environment and more pathways can exist. As an initial step of understanding groundwater recharge in urban areas this conceptual division of direct, localised and indirect pathways for precipitation to groundwater is a good start. In this study only the direct recharge is estimated but the influences of the other ways are considered and discussed.

The estimation of direct recharge in this study was performed on the basis of infiltration coefficients. The infiltration coefficients obtained from the questionnaire sent out to groundwater professionals are within the same range as the values obtained from von Brömssen’s (1968) study in Barkels and Parra (2010). The groundwater recharge estimated in Haga and Linné using the method based on soil type only is larger than when using the method taking both land use and soil type into account. The median groundwater recharge via direct recharge based on land cover and soil type is 41 - 65 mm/year but due to different input parameter values (precipitation, evapotranspiration and infiltration coefficients) the calculated recharge could be between 36 - 92 mm/year. Based on soil type only the median groundwater recharge is 41 - 64 mm/year but could range between 29 - 113 mm/year due to the previously mentioned reasons. The difference in the recharge estimation range could be explained by urban environments changing the land use e.g. more paved and impervious surfaces and therefore increasing the surface runoff and reducing the direct recharge (Haase, 2009; Vázquez-Suñé, Sánchez- Vila, & Carrera, 2005). However, this reduce in direct recharge is often compensated by indirect recharge via pluvial soakaways from paved surfaces and roofs and/or localised recharge where water moves horizontally a short distance before infiltrating e.g. runoff from bedrock outcrops and impervious surfaces (Saether & De Caritat, 1996). Also, an urban environment generates a decrease in evapotranspiration due to less green areas and more paved surfaces which can give an increase in available water for groundwater recharge (Schirmer et al., 2013). Even though the two methods of estimating direct groundwater recharge gives similar estimations the method based on land cover and soil type is believed to be more representative. This because the method better shows where precipitation actually can infiltrate and contribute to groundwater recharge e.g. where buildings are located no water is believed to infiltrate.

In addition to precipitation, leakage from water supply and sewage systems is the main source of groundwater in urban areas. A leakage of 20-25% from the pipeline networks is common in urban areas, but rates of 50 % are also reported. This means that there is an extra source of water that could be available for recharge which in some cases can be larger than the direct recharge from precipitation, e.g. Hong Kong (Lerner, 2002). In Gothenburg approximately 21% of the produced fresh water is lost through leakages which could be a possible addition to the recharge. Where and how much of the water lost through leakages that actually becomes groundwater is unknown because the pipeline network can also act as a drainage system in an urban environment (Boukhemacha, Gogu, Serpescu, Gaitanaru, & Bica, 2015).

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In Trafikverket (2013a) the groundwater recharge based on land cover in Korsvägen is estimated to be approximately 150 mm/year of which 10 mm/year is from water supply and sewage systems but due to uncertainties the groundwater recharge could be in the interval 70-290 mm/year. The total groundwater recharge estimation from Trafikverket (2013a) is greater than the direct recharge estimations for the focus area Haga and Linné. This supports the idea that there are other mechanisms than direct recharge which contributes to groundwater recharge in the area such as leakages from water supply and sewage systems, infiltration wells, indirect and localised recharge.

According to the majority of opinions expressed in the questionnaire the main mechanisms of groundwater recharge to the lower aquifer is from surface runoff from steep areas followed by infiltration in contact zones between bedrock and friction material, contribution of groundwater to the lower aquifer via fractured bedrock and to a smaller degree vertical infiltration (direct recharge) and lateral groundwater inflow from “outside” Gothenburg. The median recharge to the lower aquifer in Gothenburg is 100 mm/year according to the questionnaire.

How much of the groundwater recharge that actually can reach the lower aquifer depends on the presence of a continuous upper aquifer and the gradient and hydraulic contact between the upper and lower aquifer. The connection between the upper and lower aquifer is restricted by clay layers, and they are mainly in contact when the clay is <1.5 m, hence there is a potential direct recharge to the lower aquifers in these areas. These recharge areas, with clay thicknesses <1.5 m, generally coincides with the margin areas close to bedrock outcrops. Also, areas with high potentiometric pressure, often located close to bedrock outcrops, could indicate possible infiltration areas. The median groundwater recharge via direct recharge to the lower aquifer in Haga and Linné in these areas is estimated to be 59 – 93 mm/year but due to different input parameter values the calculated recharge could be between 47 -114 mm/year. It is difficult to estimate how much of the potential groundwater recharge that actually becomes groundwater and reaches the lower aquifer due to the previously mentioned reasons and because pipeline networks can act as drainage networks in urban environments. On the other hand, there is also the possibility that additional water to the lower aquifer besides precipitation can come from indirect and localised recharge as well as infiltration wells and possibly leakage from water supply and sewage systems.

Several infiltration wells are located in the focus area which could contribute to the groundwater recharge. In Banverket (2005) and Trafikverket (2013a) the hydraulic contact between the friction material and bedrock is discussed. The addition of groundwater to the lower aquifer is there described to be controlled by the vertical percolation at the margins of valleys and to smaller degree the contact with hydraulic zones in the bedrock. This is in agreement with the results from the questionnaire that hydraulic fracture zones in the bedrock have an influence and is a possible mechanism of addition of groundwater to the lower aquifer. Vertical addition of groundwater from the overlying clay to the lower aquifer and lateral groundwater inflow from “outside” Gothenburg is not considered to be important mechanisms of addition of groundwater to the lower aquifer neither in the results from the questionnaire or in Banverket (2005) or Trafikverket (2013a).

Trafikverket (2013a) estimated groundwater recharge to the lower aquifer in a restricted area in Gothenburg to be 5 – 40 mm/year using a solute mass balance. Ljungdahl (2015) estimated the direct recharge in Gårda to be 8.5 – 38 mm/year based on infiltration coefficients for different soil types. The median recharge from the questionnaire sent out in this study is 100 mm/year. Finally, the direct

105 groundwater recharge determined in this thesis using the methods described in section 4.2.6 is estimated to be 41 – 65 mm/year. The estimation from the questionnaire may be based on guessing rather than on actual experiences and calculations. It is however interesting to see, that groundwater professionals in Gothenburg tend to estimate higher recharge rates than what different calculation methods yield. According to the literature it is not unusual that recharge estimations based on different methods differ widely (Scanlon et al., 2002). It proves that estimating groundwater recharge, especially in a confined aquifer, is complex and filled with several uncertainties and assumptions (Schirmer et al., 2013). This conclusion is unsatisfactory but it may very well that a clearer picture of urban recharge in Gothenburg can not be obtained without much more complex and expensive measures. Depending on the aim of the study different approaches for estimating groundwater recharge are suitable e.g. measuring/estimating individual components such as direct recharge, localised recharge, water supply and sewage system and storm-water infiltration systems. Also, a more holistic approach could be used in order to measure/estimate the total groundwater recharge in an area.

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6.6. Climatic versus human impact on groundwater recharge An urban environment, which is a product of human activity, changes the groundwater recharge for example with impervious surfaces reducing the direct recharge (Schirmer et al., 2013). This can be observed in the different ranges of potential groundwater recharge estimations for the focus area when the two different methods are used based on both land cover and soil type and soil type only.

One way of observing human impact on groundwater recharge could be to look at groundwater level time series. In groundwater time series from observation wells GW430 and GW435 it is possible to identify human impact on groundwater recharge where a sharp increase and decrease in groundwater levels between 1974-1975 can be observed. This coincides with known infiltration well activities in the area. In well GW1436 a slow decrease of the groundwater level is observed from the installation of the well to 1995 where a sharp increase occurs. From 1995 and thereafter the groundwater level is higher and stable. This could indicate either that an infiltration well is installed close by or a very rapid recovery from a previous extraction. The first is considered to be more likely since there is an infiltration well close to the observation well. This general trend of rising groundwater levels is also observed in the surrounding observation wells northeast of Skansberget. The increase in groundwater levels can be explained by either that an infiltration well is located close by or a very rapid recovery from a previous extraction. With the data and information presented in this thesis short-term individual events of human influence can be identified. Also, from the obtained data and information regarding water supply and sewer systems it is not possible to identify how much of this contributes to groundwater recharge.

In Ljungdahl (2015) it is concluded that groundwater levels in the lower aquifer in Gothenburg have a fairly quick response time to changes in precipitation and that it is possible to separate artificial influences from the fluctuations in precipitation if the time series are long enough. The rising trend in groundwater levels observed in several observation wells are discussed to either to be caused by an increase in precipitation or that the levels are recovering from previous extractions. Ljungdahl also discussed that groundwater observations close to underground constructions display less correlation between groundwater level fluctuations and fluctuations in precipitation as seen in GW252. The increase in direct recharge between the two different periods 1961-1990 and 1991-2014 calculated in this study is interpreted as a response to climatic changes and not by human impact because an increase in precipitation between these two periods also occurs.

To quantify how much of the groundwater that actually has an anthropogenic origin (leakage from water supply and sewage systems) a more holistic approach such as the calibrated solute balancing in combination with groundwater flow model described in Yang et al. (1999) could be used.

Since much of the information regarding human impact i.e. locations of pumping or infiltration wells or quantities of groundwater that are infiltrated or extracted is confidential the influences of these activities are not further investigated.

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6.7. A consistent hydrogeological model of Gothenburg? Creating hydrogeological models often requires conceptualisations of the complex subsurface which means that all available information is not presented or included. However, conceptual models are valuable in order to understand how systems and processes work and to ease and improve the data collection, organisation and processing (Bredehoeft, 2005). Often hydrogeological models are developed in order to understand basic principles or to solve practical problems which usually limits the models extension. For example, in Kerl, Runge, Tauchmann, and Goldscheider (2012) a conceptual hydrogeological model of the city of Munich was developed in order to estimate the aquifer’s geothermal potential but further investigations regarding groundwater temperatures, heat transport modelling and numerical groundwater flow is required in order to quantify the geothermal potential. In Boukhemacha et al. (2015) a conceptual hydrogeological model in a restricted area in Bucharest, Romania is created with the purpose of studying urban groundwater flow. The model takes urban infrastructure elements such as sewer systems, subway tunnels and water supply network into consideration. In Voss (2005) “future hydrogeology” subjects concerning potential development in different aspects of hydrogeology is summarised and discussed based on several authors experience and personal opinions. It is concluded that hydrogeology is not a representative quantitative science and its models and estimations are only hypotheses that seldom can be proven and should be treated accordingly.

According to the questionnaire a hydrogeological model does not have to be able to answer or solve every hydrogeological problem, contain all available data, cover large areas or be very detailed but it should rather be made as easy as possible regarding the problem to be solved, be easy to update and extract data from and have good visualisation possibilities.

The hydrogeological model created in this study for the focus area Haga and Linné is a conceptual model of the stratigraphy and groundwater levels (potentiometric surface). Also, a numerical model of groundwater recharge was done. It would be possible to “upscale” this model in a similar way done in this thesis to the size of Gothenburg if sufficient data is available i.e. boreholes/soundings and groundwater levels are available and if the data is consistently distributed. However, a model like this will have limited possibilities to answer “all” hydrogeological questions since certain features are not included, e.g. the heterogeneity of the fill and friction material, the postglacial sand layer separating the glacial and postglacial clay. A model capable answering “all” hydrogeological questions requires vast amounts of data, high resolution of details and knowledge to handle and work with such a model.

Therefore, a model covering entire cities with similar conceptualisations made and characteristics as in this thesis would probably be mostly useful as an initial step in understanding the geology/hydrogeology of an area but not when answering specific research questions at a smaller scale.

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6.8. Availability, accessibility and usability of geological/hydrogeological data in Gothenburg From the information and data compiled within this thesis it is clear that a large amount of data exists and could be used in urban hydrogeology research. However, this data and information is hosted by different actors and authorities and are in different formats and not always easily accessible or usable. Therefore, it is difficult to get an overview of all relevant data for a project.

It proves to be a problem that large projects are usually controlled by a project group and when the project is completed the group dissolves whereby much of the control and knowledge about the geological information gathered during the project will be lost. That information is stored by an actor does not always mean that it is commonly known and available to use in new projects (SGU, 2014). Confidential information such as tunnels and underground constructions or other information from an ongoing project, e.g. West Link project could be a problem to handle if all geotechnical and geological information would be stored in one place easily accessible to the public. Furthermore, a consultant company may not want to share their knowledge and information with other consultant companies since their knowledge is what they are selling.

During the process of acquiring, organising and applying the data used in this study, the authors have identified the following options for improving data handling and storage:

• If actors, authorities, consultants and other people dealing with geological/hydrogeological and geotechnical information decided on a standardised format for how the data should be collected, reported and stored as well as making it easily accessible over the internet many would benefit from this. • It would be good to use a format that is not dependent on commercial software. • It would be good to conduct follow ups, controls and expansion of the already existing law concerning how well protocols and groundwater investigations should be reported and to incorporate geotechnical investigations in some way. • If the information and data would be stored in a structured way in databases easy to access and understand it would reduce the cost for research, geotechnical and hydrogeological/geological investigations by avoiding drilling at the same place twice i.e. the extent of new investigations can be reduced. • Data and information in the databases should be easy to add, extract, conceptualise and process. This would provide faster access and reduced costs for management and retrieval of information and shortened investigation time. • A common data server at universities where data and information could be stored and be easily accessible for students, researches and the public.

From interviews with groundwater professionals it has become clear that most respondents are in agreement about the need for a more structured and easily accessible way of handling geological/hydrogeological data. As it is today the start of a new project where geological/hydrogeological information and data are required often has to start with collecting and organising the data from beginning rather than using already existing data. The Office of City Planning has a vision for the City of Gothenburg to be a good example regarding the use of geodata and geographical information and the way that it is handled and stored. The aim is to make geodata available, user-friendly and economically beneficial. The Office of City Planning has together with other

109 administrations and companies within the city produced an internal local geological/geotechnical database called Geologgen where an overall view of the geological data available in the various administrations within the City of Gothenburg (Jeansson, 2010).

Better communication and collaboration between different companies and authorities within a city but also between cities regarding data management and data hosting will enable better possibilities to handle information in a structured and more easily accessible way. This would make it possible for future projects to use the large amounts of data and information when making it more available and beneficial.

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7. Conclusion An urban environment changes the nature of groundwater and is more complex than rural environments. The sources and pathways for groundwater recharge in urban areas are changed due to buildings, roads, other impervious surfaces and underground constructions as well as through leakage from water supply and sewage systems.

The main conclusions from this study related to the mechanisms of groundwater recharge are:

• The lower aquifer forms a continuous layer in large parts of Gothenburg but the continuity is restricted by the varying thickness (0-16 m) of the friction material. • The upper unconfined and lower confined aquifers in the focus area are interpreted to be in contact where the clay thickness is <1.5 m. Areas of thin clay thickness usually coincide with areas located in the contact zones between the bedrock outcrops and quaternary deposits. • Four main mechanisms to the lower aquifer are identified (in decreasing order of importance): surface runoff from steep areas followed by infiltration in contact zones between bedrock and friction material i.e. where the clay thickness is <1.5 m, contribution of groundwater via fractured bedrock, vertical infiltration (direct recharge) and lateral groundwater inflow from “outside” Gothenburg. • Other mechanisms of groundwater recharge such as leakage from water supply and sewage systems and other artificial infiltration could not be confirmed within this study but could be identified in future projects using other methods e.g. a holistic approach. • Short-term individual events of human influence can be identified in groundwater time series.

With respect to the options and potentials to create a conceptual hydrogeological model for the Gothenburg area it is concluded that:

• A model covering entire cities with similar conceptualisations made and characteristics as in this thesis would probably be most useful as an initial step in understanding the geology/hydrogeology of the Gothenburg area but it has to be clear that such a model could not be applied answering specific research questions at a smaller scale. • Future research projects would benefit from better communication and collaboration between different companies and authorities regarding data management and data hosting which will enable better possibilities to handle information in a structured and more easily accessible way. • The compilation of available data compiled within this thesis could be a first step of handling data and information in a more structured way.

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8. Future studies For future studies of urban hydrogeology/geology further development of the conceptual hydrogeological model created in this thesis could be a step to gain a further understanding of urban environments and its effects on hydrogeology. In order to identify potential sources of groundwater recharge water balances and numerical models could be applied. This knowledge can further be used to develop estimations of groundwater recharge by estimating all individual components such as direct, indirect, localised (e.g. precipitation, surface runoff and fractures in the bedrock) and leakage from water supply and sewage systems. Most generally it is recommended to use a holistic approach comprising groundwater modelling, piezometry or/and solute mass balances, tracer experiments and isotopical studies to quantify groundwater recharge. These approaches could improve the knowledge and understanding in Gothenburg specifically and urban hydrogeology in general.

In order to evaluate the continuity and hydraulic properties of the lower aquifer the performance of more specifically targeted pumping tests would be useful. Also, a more comprehensive investigation of the upper aquifer and its composition, groundwater levels and connection to the lower aquifer would be of interest to evaluate since it could have an influence of groundwater recharge to the lower aquifer. The lack of time series of groundwater observations in the upper aquifer forms a great obstacle for understanding the hydrogeology of Gothenburg.

In all of these suggestions of future studies it would be a good to a have a continued contact with groundwater professionals through meetings, interviews and questionnaires since groundwater in an urban environment is a complex system and varies between different cities. This way, researchers can make better use of existing information and groundwater professionals could benefit more from the experiences published on an international level.

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9. Acknowledgement Firstly we would like to thank our supervisor prof. Roland Barthel for providing us with the project and all the great support along the way. We want to thank our examiner Anne Hormes for constructive comments and the examination of the report. We would like to thank everyone that in some way contributed to our thesis with time, answering our questionnaire and providing data. A special thanks to Magnus Liedholm (Sweco), Niklas Blomquist (Stadsbyggnadskontoret), Johanna Ljungdahl (Stadsbyggnadskontoret), Jonas Sundell (Chalmers/COWI) Anders Blom (Sweco), Bengt Åhlén (Trafikverket), Jakob Ljungquist (Kretslopp & Vatten), Patrik Lissel (WSP), Ezra Haaf (Göteborgs universitet/COWI) and Lars-Ove Lång (SGU) for answering all our questions and giving us great inputs to improve our report. We would also like to thank our opponents Stina Ranjer and Erik Alsteryd for constructive critic. Next we would like to thank our lovely classmates, friends and family for always being there for us and having the patience to put up with us during this past year. Last but not least, Hannah Blomgren and Marika Sunesson, thank you for always being the amazing friends you are, you rock!

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11. Appendix

11.1. Appendix 1 Variogram model displaying an experimental and a fitted variograms in six directions for the bedrock interpolation based on boreholes confirming the bedrock surface. The fitted variogram is represented by an exponential model (blue line).

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Variogram model displaying an experimental and a fitted variograms in six directions for the bedrock interpolation based on all boreholes containing stratigraphic information (either confirming the bedrock surface or only containing stratigraphic depth information). The fitted variogram is represented by an exponential model (blue line).

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Variogram model displaying an experimental and a fitted variograms in six directions for the fill interpolation based the interpolation points given in section 4.2.2.2. The fitted variogram is represented by an exponential model (blue line).

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Variogram model displaying an experimental and a fitted variograms in six directions for the clay interpolation based on the interpolation points given in section 4.1.2. The fitted variogram is represented by a nugget effect and an exponential model (blue line).

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11.2. Appendix 2 This map is a combination of SGU’s quaternary deposits map (SGU, 2015e), Lars-Gunnar Hellgren’s soil cover map and the bedrock surface created for the hydrogeological model. This is used for estimating the groundwater recharge in the Haga and Linné area based on soil type only. Soils of the same character, e.g. glacial clay and postglacial clay are combined into one soil type.

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11.3. Appendix 3 The figure below displays pressure levels (potentiometric surface) in the lower aquifer in September 1974 as well as locations of tunnels and an infiltration well to the west of Skansberget (Bergström, 1981). Also, the location of the stream Djupedalsbäcken before it was made into a culvert is marked in the figure.

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11.4. Appendix 4 Questions and answers from the questionnaire sent out to groundwater professionals, mainly working in Gothenburg. The questionnaire was sent to approximately 60 people of whom 23 answers were obtained. Note that in some questions not all 23 people answered and in question 10 c) and f) some people answered the question twice.

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1. Välj Din huvudsakliga yrkesroll

Yrkesroll Antal svar Handläggare (på myndighet) av 1 (4.3%) frågor som inbegriper hydrologi/hydrogeologi Beställare/-ombud (oavsett 1 (4.3%) organisationsform) av tjänster inom hydrologi/hydrogeologi Akademiker, t ex 4 (17.4%) utbildningsansvarig/forskare inom hydrologi/hydrogeologi Konsult och/eller entreprenör 15 (65.2%) Summa 23 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Välj Din huvudsakliga 3.7 0.9 23.7% 1.0 3.5 4.0 4.0 5.0 yrkesroll

2. Välj Ditt huvudsakliga arbetsområde

Arbetsområde Antal svar Vattenförsörjningsprojekt 11 (47.8%) (kvantitet och kvalitet) Infrastrukturprojekt 8 (34.8%) (sättningsproblematik till följd av t ex sponter, vägar och tunnlar) Naturresursprojekt (t ex 0 (0.0%) dagbrott, gruvor och sandtäkt) Forskningsprojekt där frågor 4 (17.4%) som rör hydrologi /hydrogeologi ingår Om annat, specificera 0 (0.0%) Summa 23 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Välj Ditt huvudsakliga 1.9 1.1 58.8% 1.0 1.0 2.0 2.0 4.0 arbetsområde

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3. När Du tänker på grundvattenbildning, tänker du främst på:

Typ av grundvattenbildning Antal svar Infiltration av nederbörd i marken 5 (21.7%) Tillströmning av vatten till en 16 (69.6%) grundvattenakvifer Om annat, specificera 2 (8.7%) - Dock är akvifer alltid innehåller grundvatten enl. definition - Allt som bidrar till grundvattenbildning Summa 23 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil När Du tänker på grund- 1.9 0.5 29.3% 1.0 2.0 2.0 2.0 3.0 vattenbildning, tänker du främst på

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4. När Du tänker på grundvattenbildning i Göteborg, tänker du främst på:

Grundvattenbildning i Göteborg Antal svar Grundvattenbildning i det s.k. övre 2 (8.7%) magasinet (fyllnadsmaterial) Grundvattenbildning i det s.k. 14 (60.9%) nedre magasinet (friktionsmaterial) Om annat, specificera 7 (30.4%) - Båda delarna - båda ovan - Nybildning till övre magasin samt vidare strömning till undre magasin - båda! - Båda - båda - Båda Summa 23 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil När Du tänker på grund- 2.2 0.6 27.0% 1.0 2.0 2.0 3.0 3.0 vattenbildning i Göteborg, tänker du främst på

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5. Den genomsnittliga årliga nederbördsmängden i Göteborg är omkring 800mm. Hur stor (i mm) tror du den genomsnittliga årliga grundvattenbildningen till den nedre akviferen i Göteborg är?

mm/år Antal svar 0 - 80 11 (47.8%) 81 - 161 7 (30.4%) 162 - 242 1 (4.3%) 243 - 323 2 (8.7%) 324 - 404 1 (4.3%) 405 - 485 0 (0.0%) 486 - 566 0 (0.0%) 567 - 647 1 (4.3%) 648 - 728 0 (0.0%) 729 - 809 0 (0.0%) Summa 23 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil mm/år 140.1 136.0 97.1 16.0 66.0 100.0 137.0 584.0

6. Ser du den nedre akviferen i Göteborg som ett sammanhängande lager som finns överallt under leran Välj Ditt huvudsakliga arbetsområde:

Svar Antal svar Ja 4 (17.4%) Nej 19 (82.6%) Summa 23 (100.0%)

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7. Vi antar att det finns fyra olika sätt som grundvattenbildning till den nedre akviferen (friktionsmaterial) kan ske genom. Vilka av dem tycker du är viktigast (gradera alternativen)?

a) Vertikal infiltration

Betydelse Antal svar Det här är det huvudsakliga 2 (11.1%) sättet Det spelar en stor roll 2 (11.1%) Det spelar en viss roll 6 (33.3%) Det spelar nästan ingen roll 5 (27.8%) Det här förekommer inte alls 3 (16.7%) Summa 18 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Vertikal infiltration 3.3 1.2 37.4% 1.0 3.0 3.0 4.0 5.0

130 b) Genom uppsprucket berg

Betydelse Antal svar Det här är det huvudsakliga 0 (0.0%) sättet Det spelar en stor roll 12 (63.2%) Det spelar en viss roll 5 (26.3%) Det spelar nästan ingen roll 2 (10.5%) Det här förekommer inte alls 0 (0.0%) Summa 19 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Genom uppsprucket berg 2.5 0.7 28.2 % 2.0 2.0 2.0 3.0 4.0

c) Avrinning av ytvatten och markvatten från branta områden

Betydelse Antal svar Det här är det huvudsakliga 12 (60.0%) sättet Det spelar en stor roll 3 (15.0%) Det spelar en viss roll 5 (25.0%) Det spelar nästan ingen roll 0 (0.0%) Det här förekommer inte alls 0 (0.0%) Summa 20 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Avrinning av yt-vatten 1.7 0.9 53.0% 1.0 1.0 1.0 2.5 3.0 och mark-vatten från branta områden

131 d) Grundvattenbildning sker utanför Göteborg

Betydelse Antal svar Det här är det huvudsakliga 3 (15.0%) sättet Det spelar en stor roll 1 (5.0%) Det spelar en viss roll 2 (10.0%) Det spelar nästan ingen roll 11 (55.0%) Det här förekommer inte alls 3 (15.0%) Summa 20 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Grundvattenbildning sker 3.5 1.3 36.5 % 1.0 3.0 4.0 4.0 5.0 utanför Göteborg

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8. Använd graderingsskalorna nedan för att ange din uppskattning av grundvatteninfiltrationsfaktorn i % av nederbörd. T ex: Om du anger "50%“ som infiltrationsfaktor för "sand" på "skogsmark" så betyder det att 50% av all nederbörd som faller under ett år på sand i skogsmark infiltreras och blir grundvattenbildning. a) Urban miljö

Hårdgjord yta Antal 0 – 10 15 (78.9%) 11 – 21 2 (10.5%) 22 - 32 2 (10.5%) 33 – 43 0 (0.0%) 44 – 54 0 (0.0%) 55 – 65 0 (0.0%) 66 – 76 0 (0.0%) 77 – 87 0 (0.0%) 88 – 98 0 (0.0%) 99 – 109 0 (0.0%) Summa 19 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Hårdgjord yta 9.6 6.9 71.1% 0.0 5.0 8.0 10.0 26.0

133 b) Odlingsmark

Lera Antal svar 0 – 10 13 (61.9%) 11 – 21 4 (19.0%) 22 - 32 1 (4.8%) 33 – 43 3 (14.3%) 44 – 54 0 (0.0%) 55 – 65 0 (0.0%) 66 – 76 0 (0.0%) 77 – 87 0 (0.0%) 88 – 98 0 (0.0%) 99 – 109 0 (0.0%) Summa 21 (100%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Lera 13.6 12.7 93.7% 1.0 5.0 10.0 15.0 40.0

Silt Antal svar 0 – 10 5 (22.7%) 11 – 21 9 (40.9%) 22 - 32 1 (4.5%) 33 – 43 2 (9.1%) 44 – 54 4 (18.2%) 55 – 65 1 (4.5%) 66 – 76 0 (0.0%) 77 – 87 0 (0.0%) 88 – 98 0 (0.0%) 99 – 109 0 (0.0%) Summa 22 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Silt 25.4 17.2 69.9% 0.0 15.0 20.0 40.5 55.0

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Sand Antal svar 0 – 10 1 (4.5%) 11 – 21 1 (4.5%) 22 - 32 4 (18.2%) 33 – 43 2 (9.1%) 44 – 54 4 (18.2%) 55 – 65 2 (9.1%) 66 – 76 2 (9.1%) 77 – 87 6 (27.3%) 88 – 98 0 (0.0%) 99 – 109 0 (0.0%) Summa 22 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Sand 53.2 23.9 44.9 5.0 34.0 52.0 75.0 85.0

Grus Antal svar 0 – 10 1 (4.5%) 11 – 21 1 (4.5%) 22 - 32 1 (4.5%) 33 – 43 3 (13.6%) 44 – 54 1 (4.5%) 55 – 65 3 (13.6%) 66 – 76 2 (9.1%) 77 – 87 5 (22.7%) 88 – 98 4 (18.2%) 99 – 109 1 (4.5%) Summa 22 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Grus 63.9 28.0 43.8% 0.0 45.0 70.5 82.5 100

135 c) Skogsmark

Antal svar Sand 0 – 10 2 (9.1%) 11 – 21 0 (0.0%) 22 - 32 2 (9.1%) 33 – 43 4 (18.2%) 44 – 54 4 (18.2%) 55 – 65 4 (18.2%) 66 – 76 3 (13.6%) 77 – 87 3 (13.6%) 88 – 98 0 (0.0%) 99 – 109 0 (0.0%) Summa 22 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Sand 50.6 22.0 43:4% 0.0 40.0 50.0 65.0 80.0

Grus Antal svar 0 – 10 1 (4.8%) 11 – 21 0 (0.0%) 22 - 32 1 (4.8%) 33 – 43 2 (9.5%) 44 – 54 2 (9.5%) 55 – 65 6 (28.6%) 66 – 76 3 (14.3%) 77 – 87 2 (9.5%) 88 – 98 3 (14.3%) 99 – 109 1 (4.8%) Summa 21 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Grus 63.0 23.7 37.7% 10.0 50.0 61.0 80.0 100

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Morän Antal svar 0 – 10 2 (9.5%) 11 – 21 5 (23.8%) 22 - 32 7 (33.3%) 33 – 43 3 (14.3%) 44 – 54 1 (4.8%) 55 – 65 2 (9.5%) 66 – 76 0 (0.0%) 77 – 87 1 (4.8%) 88 – 98 0 (0.0%) 99 – 109 0 (0.0%) Summa 21 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Morän 31.7 19.4 61.3% 10.0 20.0 30.0 38.0 87.0

Berg Antal svar 0 – 10 10 (50.0%) 11 – 21 4 (20.0%) 22 - 32 3 (15.0%) 33 – 43 3 (15.0%) 44 – 54 0 (0.0%) 55 – 65 0 (0.0%) 66 – 76 0 (0.0%) 77 – 87 0 (0.0%) 88 – 98 0 (0.0%) 99 – 109 0 (0.0%) Summa 20. (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Berg 17.7 12.1 68.4% 5.0 10.0 10.5 26.0 40.0

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9.Tycker du att infiltration i marken och grundvattenbildning är samma sak?

Tycker du att infiltration i marken och Antal svar grundvattenbildning är samma sak Ja 1 (4.3%) Nej 22 (95.7%) Summa 23 (100.0%)

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10. Vad är viktigt för dig vid utformning och innehåll för en hydrogeologisk modell över Göteborg? Gör en gradering av följande påståenden där 1 är väldigt viktigt och 4 inte alls är viktigt. a)Den måste vara så detaljerad som möjligt

Den måste vara så detaljerad Antal svar som möjligt 1 väldigt viktigt 1 (4.3%) 2 viktigt 6 (26.1%) 3 mindre viktigt 14 (60.9%) 5 oviktigt 2 (8.7%) Summa 23 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Den måste vara så 2.7 0.7 25.1% 1.0 2.0 3.0 3.0 4.0 detaljerad som möjligt

b) Den ska innehålla all data som finns

Den ska innehålla all data som Antal svar finns 1 väldigt viktigt 3 (13.0%) 2 viktigt 8 (34.8%) 3 mindre viktigt 11 (47.8%) 5 oviktigt 1 (4.3%) Summa 23 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Den ska innehålla all data 2.4 0.8 32.4% 1.0 2.0 3.0 3.0 4.0 som finns

139 c) Den ska vara användbar för alla frågeställningar som berör geologi och grundvatten

Den ska vara användbar för Antal svar alla frågeställningar som berör geologi och grundvatten 1 väldigt viktigt 4 (17.4%) 2 viktigt 11 (47.8%) 3 mindre viktigt 9 (39.1%) 5 oviktigt 0 (0.0%) Summa 24 (104.3%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Den ska vara användbar 2.2 0.7 32.7% 1.0 2.0 2.0 3.0 4.0 för alla frågeställningar som berör geologi och grundvatten

d) Den ska vara enkel att använda, utan speciella kunskaper i programvaror

Den ska vara enkel att använda, Antal svar utan speciella kunskaper i programvaror 1 väldigt viktigt 5 (21.7%) 2 viktigt 9 (39.1%) 3 mindre viktigt 6 (26.1%) 5 oviktigt 3 (13.0%) Summa 23 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Den ska vara enkel att 2.3 1.0 42.3% 1.0 2.0 2.0 3.0 4.0 använda, utan speciella kunskaper i programvaror

140 e) Det ska vara enkelt att extrahera data från modellen

Det ska vara enkelt att Antal svar extrahera data från modellen 1 väldigt viktigt 9 (39.1%) 2 viktigt 9 (39.1%) 3 mindre viktigt 5 (21.7%) 5 oviktigt 0 (0.0%) Summa 23 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Det ska vara enkelt att extrahera 1.8 0.8 42.6% 1.0 1.0 2.0 2.0 3.0 data från modellen

f) Det ska vara enkelt att lägga till ny data i modellen

Det ska vara enkelt att lägga till Antal svar ny data i modellen 1 väldigt viktigt 6 (26.1%) 2 viktigt 15 (65.2%) 3 mindre viktigt 4 (17.4%) 5 oviktigt 0 (0.0%) Summa 25 (108.7%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Det ska vara enkelt 1.9 0.6 33.3% 1.0 2.0 2.0 2.0 3.0 att lägga till ny data i modellen

141 g)Visualiseringsmöjligheter

Visualiseringsmöjligheter Antal svar 1 väldigt viktigt 7 (30.4%) 2 viktigt 13 (56.5%) 3 mindre viktigt 3 (13.0%) 5 oviktigt 0 (0.0%) Summa 23 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Visualiseringsmöjligheter 1.8 0.7 35.6% 1.0 1.0 2.0 2.0 3.0

h) Samspel med olika typer av programvaror t.ex. grundvattenmodelleringsprogram

Samspel med olika typer av Antal svar programvaror t.ex. grundvattenmodelleringsprogram 1 väldigt viktigt 5 (21.7%) 2 viktigt 9 (39.1%) 3 mindre viktigt 9 (39.1%) 5 oviktigt 0 (0.0%) Summa 23 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Samspel med olika typer av 2.2 0.8 35.8% 1.0 2.0 2.0 3.0 3.0 programvaror t.ex. grundvattenmodelleringsprogra m

142 i) Enkelt att uppdatera

Enkelt att uppdatera Antal svar 1 väldigt viktigt 11 (47.8%) 2 viktigt 9 (39.1%) 3 mindre viktigt 3 (13.0%) 5 oviktigt 0 (0.0%) Summa 23 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Enkelt att uppdatera 1.7 0.7 43.2% 1.0 1.0 2.0 2.0 3.0

j) Den ska täcka hela Göteborgsområdet

Den ska täcka hela Antal svar Göteborgsområdet 1 väldigt viktigt 4 (17.4%) 2 viktigt 10 (43.5%) 3 mindre viktigt 8 (34.8%) 5 oviktigt 1 (4.3%) Summa 23 (100.0%)

Medel- Standard- Variations- Min Undre Media Övre Max värde avvikelse koefficient kvartil n kvartil Den ska täcka hela 2.3 0.8 35.8% 1.0 2.0 2.0 3.0 4.0 Göteborgsområdet

143

11.5. Appendix 5 SGU’s soil thickness map (classified).

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11.6. Appendix 6 Thickness of fill material, modified from Hultén (1997).

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11.7. Appendix 7 Lars-Gunnar Hellgren’s soil cover map of the Haga and Linné area. The map displays depth to bedrock and thicknesses of fill material, clay and friction material. Note that the entire focus area is not presented in this map.

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11.8. Appendix 8 Hydrogeological investigation conducted for the West Link project in Gothenburg. The different soil types, wells, groundwater observation wells, pressure levels and infiltration and groundwater drainage/pumping wells is presented in the map (Banverket, 2006).

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