Hydrologic characteristics of HydroRock / systems Concept version

Petra Hulsman

August 7th, 2015

Table of Contents 1. Introduction ...... 1 2. Goal of this study ...... 1 3. Background information ...... 2 3.1. Application ...... 2 3.2. Characteristics ...... 2 3.3. Advantages and disadvantages ...... 3 4. Methodology of the experiments ...... 4 4.1. Physical characteristics of stonewool ...... 4 4.1.1. Density ...... 4 4.1.2. Maximum storage capacity and ...... 4 4.1.3. Influence of external loadings ...... 4 4.1.1. penetration ...... 4 4.1.2. Clogging of the geotextile ...... 5 4.1.3. Clogging of the stonewool ...... 5 4.2. Hydraulic characteristics of stonewool ...... 7 4.2.1. Retention capacity ...... 7 4.2.2. Infiltration capacity ...... 7 4.2.3. ...... 8 4.3. Water retention behaviour of HydroRock in ...... 9 4.3.1. Water retention behaviour in soil: Theoretical ...... 9 4.3.2. Water retention behaviour in soil: Lab experiment ...... 9 4.3.3. Water retention behaviour in soil: Field experiment ...... 12 5. Results of the experiments ...... 14 5.1. Physical characteristics of stonewool ...... 14 5.1.1. Density ...... 14 5.1.2. Maximum storage capacity and porosity ...... 14 5.1.3. Influence of external loadings ...... 14 5.1.4. Root penetration ...... 15 5.1.5. Clogging of the geotextile ...... 15 5.1.6. Clogging of the stonewool ...... 16 5.2. Hydraulic characteristics of stonewool ...... 17 5.2.1. Retention capacity ...... 17 5.2.2. Infiltration capacity ...... 18 5.2.3. Hydraulic conductivity ...... 18 5.3. Water retention behaviour of HydroRock in soil ...... 22 5.3.1. Water retention behaviour in soil: Theoretical ...... 22 5.3.1. Water retention behaviour in soil: Lab experiment ...... 23 5.3.2. Water retention behaviour in the soil: Field experiment ...... 29 6. Summary experiment results ...... 31 7. Conclusion ...... 33 8. Recommendation ...... 33 9. Literature ...... 34 Appendices ...... 35 1. Appendix ...... 36 2. Appendix ...... 37

1. Introduction The product HydroRock is made out of stonewool and geotextile. The company advertises that the material can retain and store large volumes of water. At the same time, the open structure would allow easy transmissivity of water through the stonewool and as such the manufacturer claims the material drains water effectively and sustainably. That is why it could be used to prevent local flooding or to separate rainwater runoff. More applications can be thought of in water management. An example for a rainwater separation and infiltration system is shown in Figure 1-1.

However, testing of the material for water management purposes have not been done yet. This is required to maximise the use of HydroRock. That is why this study aims at analysing and quantifying the hydraulic characteristics of this material.

Figure 1-1:Rainwater separation and infiltration system (Hydrorock International B.V.)

2. Goal of this study The goal of this study is to quantify the (long-term) hydraulic characteristics of stonewool in order to assess its suitability for the storage, drainage and infiltration of storm water runoff. The focus will be on the following aspects:

Simple physical characteristics 1. Density 2. Maximum storage capacity 3. Porosity 4. Influence of external loadings on the storage capacity and porosity 5. Root penetration 6. Clogging of the geotextile and stonewool

Water drainage capacity 1. Drain capacity of stonewool and HydroSand (a mixture of soil and loose stonewool; see section 3.2 for more information) 2. Hydraulic conductivity of stonewool and HydroSand

Water drainage behaviour in soil 1. Impact of HydroRock on the water drainage in the lab 2. Impact of HydroRock on the water drainage in the field

These aspects were evaluated by a series of short lab-tests in the Hydraulic laboratory of TU-Delft as a potential first step towards full scale long term field tests.

P. Hulsman HydroRock analysis Introduction | Page 1 3. Background information

3.1. Application Traditionally, stonewool is used as isolation material. However, stonewool can also be used to infiltrate and drain rainwater (Hydrorock International B.V.); in this case it is called HydroRock. Compared to the isolation rockwool, HydroRock is produced differently such that it is not water resistant as is the isolation material.

With HydroRock rainwater can be diverted into the soil where it is stored and drained at a later moment. As a result, flooding in urban areas could be prevented. In addition, droughts could be prevented as water is thought to be stored in the soil for a longer period and more water is led to the groundwater system. Moreover, storm water runoff could be drained separately preventing the overflow of combined sewer systems during heavy showers which would improve the water quality.

3.2. Characteristics The material stonewool is made of volcanic igneous rock such as basalt. To prevent the inflow of soil particles into the stonewool, it is surrounded with a geotextile. This combination of stonewool and geotextile is called HydroRock. In this study, two types of HydroRock are used (Hydrorock International B.V.):

- High density : 90% porosity, maximum load: 4000 kg/m3 - Standard density : 94% porosity, maximum load: 2000 kg/m3

The geotextile has a density of 120 g/m3. It is resistant and manufactured from cotton.

HydroSand is a mixture of soil and loose stonewool (see Figure 3-1). In our tests, two different types of soil are used: fine and silica flour M300; see Appendix for the sieve curve. This mixture contains 10% stonewool and 90% soil based on the weight.

Figure 3-1: Loose stonewool used in HydroSand mixtures

P. Hulsman HydroRock analysis Background information | Page 2 3.3. Advantages and disadvantages According to HydroRock International B.V., the use of HydroRock for the infiltration and drainage of rainwater has the following advantages and disadvantages:

Advantages: - Sustainable o 100% natural material o Lifetime of multiple decennia o Green alternative for infiltration crates o Resistant against root intrusion o Flora and fauna prosper on HydroRock - No connection to sewer system needed - Cheap

Disadvantages: - Possible clogging of geotextile through soil particles or - Conflict of interest: root resistant vs. vegetation growth

P. Hulsman HydroRock analysis Background information | Page 3 4. Methodology of the experiments

4.1. Physical characteristics of stonewool

4.1.1. Density 푚 To determine the density ρ, the dry weight was measured: 휌 = 푑푟푦 푉푡표푡 The total volume was equal to 15x15x15 cm3 = 3375 cm3 and 20x20x20 cm3 = 8000 cm3 for the standard and high density samples respectively.

4.1.2. Maximum storage capacity and porosity To determine the storage capacity S, the total volume and stonewool volume were measured. The latter was determined by putting it in water and measuring the resulting water level difference. 푉푝표푟푒 푉푡표푡−푉푠푡표푛푒푤표표푙 푆 = 푉푡표푡 − 푉푠푡표푛푒푤표표푙. With these volumes, also the porosity p was estimated: 푝 = = 푉푡표푡 푉푡표푡

4.1.3. Influence of external loadings To assess the influence of external loadings on high density stonewool, cyclic loading triaxial tests have been performed by the Geotechnical department at the Technical University Delft (Paassen et al., 2015). In these tests, a confined stress and static vertical stress were applied in addition to a dynamic vertical stress. The experiment characteristics were:

- Confined stress: 10 kPa to simulate soil horizontal forces at 75 cm below ground surface - Static vertical stress: 15 kPa to simulate soil vertical forces at 75 cm below ground surface - Dynamic vertical stress range: 15-25 kPa and 15-45 kPa to simulate traffic loads - Number of cycles: 500 or until no significant change in the deformation response was observed - Frequency: 0.1 Hz - Sample condition: Dry/Wet drained/Wet undrained

The results of these experiments indicated the permanent strain caused by the loading and the maximum strain before failure. These strains were used to assess the influence of these loadings on the storage capacity and porosity.

4.1.1. Root penetration The HydroRock is applied in environments where vegetation grows. That is why roots could penetrate and therefore clog the geotextile. To test this possibility, plants were grown under three conditions (see Figure 4-1):

- Soil as reference situation - Standard density stonewool instead of soil - Soil restricted by geotextile

P. Hulsman HydroRock analysis Methodology of the experiments | Page 4

Figure 4-1: Picture of the experiment: Plant growth in soil restricted by geotextile, stonewool and soil under normal conditions

4.1.2. Clogging of the geotextile HydroRock is implemented in soil with both the inflow of stormwater and also groundwater. The stormwater is first directed to a settling tank to filter all coarse materials before flowing into the HydroRock. As a result, also suspended solids (SS) flows in the direction of the HydroRock and will be filtered out through the geotextile to prevent the inflow of particles in the stonewool. However, this may result in the clogging of the geotextile.

This possibility was tested by draining synthetic SS polluted water through the geotextile. This turbid water was circulated through the until the water became clear (see Figure 4-2). In this experiment, the following characteristics were applied: - Sample size o Diameter D : 4.4 cm

o Dry weight mdry : 0.22 g - Water was circulated o Volume : 7l o Duration : 46.75 hours o Speed : 200 ml/min - Water was polluted with a silica flour called Sikron M600 (Sibelco, 2006)

o D50 : 4 μm o Concentration : 100 mg/l o See Appendix for the sieve curve

Figure 4-2: Picture of the experiment: Clogging of the geotextile

4.1.3. Clogging of the stonewool Similar to the previous experiment, synthetic polluted water was circulated through standard density stonewool to assess whether this material captures small particles such as or sand. In this experiment, the following characteristics where applied:

- Sample size

P. Hulsman HydroRock analysis Methodology of the experiments | Page 5 o Diameter D : 4.4 cm o Height : 3.5 cm

o Dry weight mdry : 4.75 g - Water was circulated o Volume : 8l o Duration : 25 hours o Speed : 200 ml/min - Water was polluted with a silica flour called Sikron M600 (Sibelco, 2006)

o D50 : 4 μm o Concentration : 100 mg/l o See Appendix for the sieve curve

P. Hulsman HydroRock analysis Methodology of the experiments | Page 6 4.2. Hydraulic characteristics of stonewool

4.2.1. Retention capacity One of the functions of HydroRock is draining the excess precipitation which should take place fast enough. Otherwise the residual storage capacity is not sufficient to store and drain all the water of the next rain shower. This retention capacity is assessed by saturating a standard HydroRock sample and the HydroSand samples with water and measuring how fast this water leaves the material under gravity (see Figure 4-3).

Figure 4-3: Picture (left) and schematization (right) of the experiment: Drain capacity of standard density stonewool

4.2.2. Infiltration capacity Another important function of HydroRock is the infiltration of precipiation. Therefore, the infiltration capacity of HydroRock using high density stonewool was assessed. For this assessement, a sample was placed in a tube and clear water was pumped in the fibre direction such that the water level above this sample remained constant. The discharge in this case was used to determine the infiltration capacity.

Sample size: - Diameter D = 4 cm - Length L = 11.5 cm

Figure 4-4: Picture of the experiment: Infiltration capacity of high density stonewool

P. Hulsman HydroRock analysis Methodology of the experiments | Page 7 4.2.3. Hydraulic conductivity A sample was placed in the middle of a watertight box such that there were no preferential flows (see Figure 4-5). This sample was drained with a constant discharge using a Mariotte’s bottle. This discharge was estimated based on the speed of the volume decrease (ΔV) in the Mariotte’s bottle. The hydraulic conductivity k is equal to:

Δℎ 푄 = 푘 ∗ 퐴 ∗ Δ퐿 푄 Δ퐿 푘 = ∗ 퐴 Δℎ With Q the discharge [L3/T], A the cross-section of the sample [L2], ∆h the water level difference over the sample [L] and ∆L the flow length [L].

Experiment runs: 1. Clean water drained through the sample in the direction of the fibre 2. Clean water drained through the sample perpendicular to the direction of the fibre

Sample types used: 1. Standard stonewool without geotextile 2. Standard stonewool with geotextile 3. High density stonewool without geotextile 4. High density stonewool with geotextile

Figure 4-5: Picture of the experiment: Hydraulic conductivity of standard and high density stonewool

This experiment is repeated for HydroSand, with the same concept, but a different setup to be able to use smaller samples (see Figure 4-6).

Figure 4-6: Picture of the experiment: Hydraulic conductivity of HydroSand

P. Hulsman HydroRock analysis Methodology of the experiments | Page 8 4.3. Water retention behaviour of HydroRock in soil The effect of HydroRock on the water drainage in soil was analysed through measurements in the lab and on the field.

4.3.1. Water retention behaviour in soil: Theoretical The interaction between HydroRock and soil was assessed theoretically by comparing the water retention curves of stonewool and soil.

4.3.2. Water retention behaviour in soil: Lab experiment In the lab, HydroRock was placed in soil to assess the immediate response of HydroRock on the water drainage by observing the water level.

Setup description For this experiment, a watertight box was filled with fine sand and high density HydroRock (see Figure 4-8). While draining clean water through this box with a fixed discharge, the water level, soil moisture and electric conductivity were measured on several points in the soil and HydroRock (see Figure 4-7).

Measurements: - Water level in soil and HydroRock using water pressure devices - Soil moisture in soil and HydroRock using a θ-probe - Electric conductivity in HydroRock using CTD (conductivity, temperature, pressure) devices

This experiment was repeated several times changing the flow direction and angle of the box: - Experiment 1: Flow direction in the direction of the fibre (see Figure 4-7); inflow at the top simulating rainwater discharge (see Figure 4-10 a) o Experiment 1.1: Horizontal box o Experiment 1.2: Box sloped in the flow direction (5 %) o Experiment 1.3: Box sloped perpendicular to the flow direction (3%) - Experiment 2: Flow direction perpendicular to the fibre direction; inflow at the bottom simulating groundwater flow (see Figure 4-10 b) o Experiment 2.1: Horizontal box o Experiment 2.2: Box sloped in the flow direction (3%) o Experiment 2.3: Box sloped perpendicular to the flow direction (5%)

Box characteristics: - Size: 1.5 x 1 x 0.4 m3 (length x width x height); see Figure 4-7 - 4 closable holes to drain in two directions; see Figure 4-9 - Tubes covered with filter cloth at each hole to spread the inflow and outflow equally across the entire length/width; see Figure 4-9 - The bottom of the box was elevated with 6.4 cm above the lab floor and each opening was located 4.6 cm above the box floor.

P. Hulsman HydroRock analysis Methodology of the experiments | Page 9 Legend 6 5 15 15 Fine sand D2 CTD2 35 HydroRock 4 3 Diver location 70 100 θ - probe 42

2 1 D1 CTD1 8 15

15 32 18 20 65

32.5 32.5 10 10 65

150

Figure 4-7: Sketch of the experiment setup; mentioned dimensions are in [cm]: Top view and location of the divers and soil moisture measurements using a soil moisture probe (θ – probe)

Figure 4-8: Picture of the experiment: Box filled with fine sand and high density HydroRock including monitoring for the divers

Figure 4-9: Detail pictures of the experiment, from left to right: A) Closable inflow/outflow point, B) Tube covered with filter cloth spreading the water inflow/outflow equally over the entire width of the box, C) Tube covered with filter cloth spreading the water inflow/outflow equally over the width of HydroRock, D) High density HydroRock in the box, E) Monitoring for one of the divers

P. Hulsman HydroRock analysis Methodology of the experiments | Page 10

Figure 4-10: Types of water inflow: from the top for Experiment 1 (left) and from the bottom for Experiment 2 (right)

Soil characteristics For this experiment, very fine sand with a diameter of 125-250mm was used. This sand had the following characteristics:

- Grain size 125-250 μm (see Appendix for the sieve curve) - Density o Uncompressed  V = 250 cm3  m = 359 g  Hence: ρ = 1436 kg/m3 o Compressed  V = 250 cm3  m = 419.5 g  Hence: ρ = 1678 kg/m3 - Porosity o Uncompressed 3  Vtotal = 250 cm 3  Vwater = 109 cm 푉 푉  Hence: 푝 = 푝표푟푒 = 푤푎푡푒푟 = 0.44 푉푡표푡푎푙 푉푡표푡푎푙 o Compressed 3  Vtotal = 250 cm 3  Vwater = 102.9 cm 푉 푉  Hence: 푝 = 푝표푟푒 = 푤푎푡푒푟 = 0.41 푉푡표푡푎푙 푉푡표푡푎푙

In this experiment, the sand was merely spread over the bottom of the box; hence uncompressed. However, the compaction might have increased during the experiment as the box was filled with water and emptied repeatedly. Therefore, the actual density and porosity values in the box were between the uncompressed and compressed results.

Diver calibration The divers used in this experiment were calibrated in advance. During the calibration all divers were put in a water bucket with no water, then with a known water level. All devices were supposed to measure the same water depth. If this was not the case, then there was a certain offset. This procedure was repeated for different water

P. Hulsman HydroRock analysis Methodology of the experiments | Page 11 levels: 0 cm, 5 cm, 10 cm, 15 cm and 20 cm. In Table 4-1 the average offset is shown. Additionally, the water level data was shifted for each experiment separately such that the data corresponded with 0 cm water depth observations.

Table 4-1: Calibration results: average offset Diver number Diver location Offset A1 Atmosphere 0.50 D1 Soil upstream 1.31 D2 Soil downstream 0.85 CTD1 HydroRock upstream 0.93 CTD2 HydroRock downstream 1.25

4.3.3. Water retention behaviour in soil: Field experiment Additionally, the short term effect of HydroRock on the water drainage was assessed in the field. In Rotterdam, standard density HydroRock was placed about 6 months earlier. This gave the opportunity to observe the effects on a larger scale. Similar to the lab experiment, the water level were measured on several points throughout the field: two in the soil to measure groundwater levels (S1 and S2) and two in HydroRock at its top level to measure water levels during inflow (HR1) and outflow (HR2); see Figure 4-11 and Figure 4-12. The measurements of the different locations were then compared to each other.

Legend:

HydroRock 60 cm Soil

150 cm 20 cm

Water pressure 100 cm device

Figure 4-11: Sketch of the experiment layout (side view)

P. Hulsman HydroRock analysis Methodology of the experiments | Page 12

Figure 4-12: Sketch of the location of the measurement points (top view); water pressure devices were placed in HydroRock (HR1 and HR2) and in the soil (S1 and S2)

P. Hulsman HydroRock analysis Methodology of the experiments | Page 13 5. Results of the experiments

5.1. Physical characteristics of stonewool

5.1.1. Density As shown in Table 5-1, the observed average density was 73 kg/m3 and 114 kg/m3 for standard resp. high density stonewool.

Table 5-1: Results density ρ 3 Vtot [cm ] mdry [g] mdry [g] mdry [g] mdry,average ρavg ρavg [g] [g/cm3] [kg/m3] Standard 153 243.85 249.5 248.2 247.2 0.073 73 High density 203 892.98 925.6 - 909.3 0.11 114

5.1.2. Maximum storage capacity and porosity As shown in Table 5-2, the observed storage capacity was 3048.9 ml and 7143.7 ml and the average porosity 0.94 and 0.92 for standard resp. high density stonewool. The porosity of the standard sample was the same as the described product characteristics. However, for high density samples there was a difference: the observation was 92% instead of 90%.

Table 5-2: Results storage capacity S and porosity p 3 3 Vtot [cm ] Vstonewool [cm ] S [ml] p [-] Standard 3241.6 192.7 3048.9 0.94 High density 7762.4 618.7 7143.7 0.92

5.1.3. Influence of external loadings Based on the results of triaxial tests, the maximum strain was 0.15% under wet drained conditions. For this sample, the maximum strain before failure was 1.8% at 58 kPa. Assuming this strain merely compresses the pore volume, the influence on the density and porosity was assessed. As shown in Table 5-3, the storage capacity and density would decrease with only 2% under maximum deformation of ϵ = 1.8%. Thus, the influence of external loadings on HydroRock is negligible.

Table 5-3: Results influence of loading on storage capacity S, density ρ and porosity p for high density stonewool S [ml] ρ [kg/m3] p [-] Originally (ε = 0%) 7143.7 113.7 0.92 After ε = 0.15% deformation 7132.1 113.8 0.92 After ε = 1.8% deformation 7004.0 115.8 0.92

P. Hulsman HydroRock analysis Results of the experiments | Page 14 5.1.4. Root penetration The following was observed, 8 days after having planted the seeds; see Figure 5-1: - The leaves bloomed best if the seeds were planted in soil and were not restricted. At this point, the differences were very small though. - Roots of seedlings did not intrude well into standard density stonewool. - Roots grew through the geotextile.

Figure 5-1: Results plant growth after 8 days: growth under all three conditions (left), root penetration of seedlings into stonewool (middle), root penetration through the geotextile (right)

The following was observed, 10 days after having planted the seeds; see Figure 5-2: - The plants bloomed slightly better if the seeds were planted in soil and not in stonewool. - Roots of larger plants did intrude the stonewool.

Figure 5-2: Results root growth after 10 days: plant height under all three conditions (left), root penetration through stonewool and soil (right)

5.1.5. Clogging of the geotextile

Experiment results After having drained turbid water through the geotextile, the sample weighed 0.41 g. Hence, 0.19 g of silica flour was captured on the textile (see Figure 5-3). This was 31.24 g/m2. Initially, the water level above the sample was merely 2-3 mm larger than the level of the surrounding water. At the end of the experiment, this water level difference increased to 2-3 cm as a result of clogging. Hence, the specific resistance of the geotextile increased from about 0.025 h-1 to 0.38 h-1.

P. Hulsman HydroRock analysis Results of the experiments | Page 15

Figure 5-3: Results clogging of the geotextile: before (left) and after (right) draining the textile with synthetic polluted water

Experiment evaluation The following can be concluded: - Geotextile captured fine silica flour. - As indicated by the water level rise, the specific resistance of the geotextile increased from about 0.025 h-1 to 0.38 h-1. - Hence, the geotextile captured suspended sediment well.

5.1.6. Clogging of the stonewool

Experiment results After having drained synthetic polluted water through standard density stonewool, the sample weighed 5.01 g, hence 0.26 g of silica flour was captured (see Figure 5-4); which was 1.22 kg/m3. Initially, the water level above the sample was 3 mm larger than the level of the surrounding water. At the end of the Experiment, this water level difference increased to 4.3 cm. Hence, the specific resistance of the stonewool increased from about 0.038 h-1 to 0.54 h-1.

Figure 5-4: Results clogging of standard density stonewool: before (left) and after (right) draining the textile with synthetic polluted water

Experiment evaluation The following can be concluded: - Standard density stonewool captured fine silica flour. - As indicated by the water level rise, the specific resistance of the stonewool increased from about 0.038 h-1 to 0.54 h-1. - Hence, the standard density stonewool was very good in capturing suspended sediments.

P. Hulsman HydroRock analysis Results of the experiments | Page 16 5.2. Hydraulic characteristics of stonewool

5.2.1. Retention capacity

Experiment results A standard density stonewool sample was fully saturated and then drained by letting the water flow out under gravity. As a result, the weight decreased in time; see Figure 5-5. The sample weighed 243.6 g when it was dry. At the start of the experiment, the sampled weighed 2894.3 g and after 19 hours 2691.4 g which was a decrease of 8%. The weight of HydroSand decreased with about 10% or 25% within 1.5 min (see Figure 5-6). However, afterwards the weight remained constant. Do keep in mind that the sample sizes differed: 3 - Stonewool: 10x10x10 cm (cube) - HydroSand: 12 cm high with diameter of 3.3 cm (cylinder)

100%

99%

98%

97%

96%

relative relative weight 95%

94%

93% 0 50 100 150 200 250 300 t [min]

Figure 5-5: Results drain capacity of standard density stonewool under gravity: weight decrease as a function of time

100%

95%

90%

85% Fine sand

relative relative weight 80% M300

75%

70% 0 0,5 1 1,5 2 2,5 t [min]

Figure 5-6: Results drain capacity of HydroSand under gravity: weight decrease as a function of time

P. Hulsman HydroRock analysis Results of the experiments | Page 17 Experiment evaluation The following can be concluded: - Initially the weight decreased rapidly. - At a certain point, the weight decreases very slowly. - The standard density stonewool sample remained wet for a long time: The weight decreased with only 7% within almost a day at room temperature. Hence the available volume to store additional water increases very slowly after wetting. - The weight of HydroSand decreased more rapidly: 10% or 25% within 1.5 min depending on the soil type used.

5.2.2. Infiltration capacity The discharge needed to obtain a constant water level above a high density stonewool sample was 2.1∙10-3 m/s. Hence, the infiltration capacity of high density stonewool was 2.1∙10-3 m/s and the specific resistance 18.5 s-1.

5.2.3. Hydraulic conductivity

Experiment results The results for the hydraulic conductivity when draining water in the fibre direction are noted in Table 5-5 and plotted in Figure 5-8. See Table 5-6 and Figure 5-9 for the results when draining water perpendicular to the fibre direction. These tables include the average value, standard deviation and measurement error. The standard deviation was calculated over 10 values and for the total measurement error, inaccuracies of 0.1 cm in the water level difference and discharge were taken into account (see formula below). The experiments were repeated for different water level/sample height ratios.

Calculation of the measurement error ε:

휖 = 휖Δℎ + 휖Q

Δℎ 푄 Δ퐿 푄 = 푘 ∗ 퐴 ∗ → 푘 = ∗ Δ퐿 퐴 Δℎ ΔV 퐶 ∗ Δ퐻 푄 = = Δ푡 Δ푡

Δℎ = Δℎ푚푒푎푠푢푟푒푑 ± 0.1 푐푚; Δ퐻 = Δ퐻푚푒푎푠푢푟푒푑 ± 0.1푐푚

퐶 ∗ (Δ퐻푚푒푎푠푢푟푒푑 ± 0.1푐푚) 1 Δ퐿 푄 1 휖Q = ∗ ∗ ; 휖Δℎ = ∗ Δ퐿 ∗ Δ푡 퐴 Δℎ 퐴 Δℎ푚푒푎푠푢푟푒푑 ± 0.1 푐푚

P. Hulsman HydroRock analysis Results of the experiments | Page 18 On average the hydraulic conductivity was found to be lower for the high density samples. Also, it was found that the influence of the geotextile was not negligible. This experiment was repeated with coloured water to observe the water flow within stonewool. As can be seen in Figure 5-7 , the water level increased significantly within the stonewool due to suction.

For HydroSand the hydraulic conductivity was estimated with the falling head permeability test. As shown in Table 5-4, the hydraulic conductivity for HydroSand was smaller than for stonewool regardless of the soil type. Also, the addition of stonewool increased the hydraulic conductivity; this increase was larger for silica flour than fine sand. -7 -4 -11 As reference, typically the hydraulic conductivity of fine sand is 2∙10 - 2∙10 m/s and clay 1∙10 - 4.7∙10-9 m/s (Domenico et al., 1990).

Table 5-4: Hydraulic conductivity for soil and HydroSand using two different types of soil: fine sand and silica flour M300 Soil type Soil (100%) HydroSand: soil (90%) + stonewool (10%) -4 -4 Fine sand 4∙10 m/s 5∙10 m/s Silica flour M300 8∙10-7 m/s 2∙10-4 m/s

Figure 5-7: Experiment result: Water flow through standard density stonewool using red coloured water

P. Hulsman HydroRock analysis Results of the experiments | Page 19 Table 5-5: Results hydraulic conductivity when draining water in the fibre direction: average value Table 5-6: Results hydraulic conductivity when draining water perpendicular to the fibre direction: -3 -3 kavg, standard deviation σ, measurement error ε in [10 m/s] average value kavg, standard deviation σ, measurement error ε in [10 m/s] High density Standard density High density Standard density

Stonewool 96% filled: kavg = 2.0 (σ = 0.5, ε = 1.0) 77% filled: kavg = 7.4 (σ = 0.4, ε = 1.5) Stonewool 85% filled: kavg = 2.3 (σ = 0.3, ε = 0.7) 82% filled: kavg = 8.4 (σ = 0.4, ε = 2.0) 48% filled: kavg = 2.8 (σ = 0.2, ε = 0.2) 38% filled: kavg = 4.9 (σ = 0.5, ε = 0.6) 51% filled: kavg = 3.2 (σ = 0.2, ε = 0.9) 54% filled: kavg = 8.2 (σ = 0.5, ε = 1.5) Stonewool 93% filled: k = 1.4 (σ = 0.1, ε = 0.3) 77% filled: k = 6.7 (σ =0.3 , ε = 1.5) avg avg Stonewool 85% filled: k = 2.8 (σ = 0.4, ε = 0.6) 86% filled: k = 8.0 (σ= 0.3, ε = 1.6) with geotextile 62% filled: k = 1.9 (σ = 0.1, ε = 0.6) 66% filled: k = 5.0 (σ = 0.0, ε = 1.8) avg avg avg avg with geotextile 50% filled: k = 3.6 (σ = 0.3, ε = 1.0) 53% filled: k = 9.1 (σ = 0.4, ε =1.8) (=HydroRock) 24% filled: k = 3.0 (σ = 0.3, ε = 0.2) 43% filled: k = 5.1 (σ = 0.5, ε = 0.8) avg avg avg avg (=HydroRock) 18% filled: kavg = 6.3 (σ = 0.7, ε = 0.3)

Figure 5-8: Results hydraulic conductivity draining water in the fibre direction Figure 5-9: Results hydraulic conductivity draining water perpendicular to the fibre direction

Experiment numbers (water flow in fibre direction): 1. High density, stonewool, 96% filled 7. Standard density, stonewool, 77% filled 2. High density, stonewool, 48% filled 8. Standard density, stonewool, 38% filled Experiment numbers (water flow perpendicular to fibre direction): 3. High density, HydroRock, 93% filled 9. Standard density, HydroRock, 77% filled 1. High density, stonewool, 85% filled 6. Standard density, stonewool, 82% filled 4. High density, HydroRock, 62% filled 10. Standard density, HydroRock, 66% filled 2. High density, stonewool, 51% filled 7. Standard density, stonewool, 54% filled 5. High density, HydroRock, 24% filled 11. Standard density, HydroRock, 43% filled 3. High density, HydroRock, 85% filled 8. Standard density, HydroRock, 86% filled 12. Standard density, HydroRock, 18% filled 4. High density, HydroRock, 50% filled 9. Standard density, HydroRock, 53% filled

P. Hulsman HydroRock analysis Results of the experiments | Page 20 Experiment evaluation The following can be concluded: - High density vs. standard stonewool samples High density stonewool samples had a smaller hydraulic conductivity than standard stonewool: 2.0∙10-3 m/s resp. 7.4∙10-3 m/s for high density resp. standard samples when draining water in the fibre direction and with near-saturation stonewool samples. As a reference, the hydraulic conductivity of coarse sand is 9∙10-7 - 6∙10-3 m/s (Domenico et al., 1990). - Water flow direction The hydraulic conductivity was slightly larger when draining water perpendicular to the fibre direction: o Water flow in fibre direction o Water flow perpendicular to fibre direction . Standard sample 7.4∙10-3 m/s . Standard sample 8.4∙10-3 m/s . High density sample 2.0∙10-3 m/s . High density sample 2.3∙10-3 m/s However, this difference was within the error range and was therefore not significant. Hence, the hydraulic conductivity seemed similar in both directions. - Geotextile The addition of geotextile slightly decreased the hydraulic conductivity for standard and high density samples when draining water in the fibre direction. This suggested the textile had a smaller hydraulic conductivity. o Standard density sample o High density sample . Stonewool 7.4∙10-3 m/s . Stonewool 2.0∙10-3 m/s . HydroRock 6.7∙10-3 m/s . HydroRock 1.4∙10-3 m/s Suspended sediment clogging the geotextile can however decrease the hydraulic conductivity significantly. - HydroSand HydroSand is a mixture of stonewool and soil: 10% of the weight is stonewool. Its hydraulic conductivity was: o 5∙10-4 m/s and 4∙10-4 m/s (HydroSand resp. pure soil using fine sand) o 2∙10-4 m/s and 8∙10-7 m/s (HydroSand resp. pure soil using silica flour M300) Typically the hydraulic conductivity of fine sand is 2∙10-7 - 2∙10-4 m/s and clay 1∙10-11 - 4.7∙10-9 m/s (Domenico et al., 1990).

P. Hulsman HydroRock analysis Results of the experiments | Page 21 5.3. Water retention behaviour of HydroRock in soil

5.3.1. Water retention behaviour in soil: Theoretical The water retention curve of stonewool obtained from RockWool B.V. was compared with the typical curves for soil (see Figure 5-10, Figure 5-11 and Figure 5-12). The pF value is an indication for the suction pressure h in soil or stonewool: pF = log(-h) with h in [cm]. For high pF values, pF > 2, the moisture content of most was larger than of stonewool. For low pF values, pF < 1.7, the stonewool however retained over 11% of water. Hence, under wet conditions a lot of water is stored in the stonewool before it is drained or infiltrated into the soil.

This water retention curve is in contrast with own lab experiments on the retention capacity; see section 5.2.1. Based on lab experiments, the soil moisture is about 0.86 at pF = 2 which is the field capacity. According to the water retention curve, the soil moisture is much lower: about 0.1. This difference might a result of differences measuring technique or sample material. For the water retention curve raw material is used instead of stonewool used for HydroRock.

Figure 5-10: Typical water retention curve of four different soil types (Savenije, 2010)

Water retention curve stonewool 7 6 5

4 pF 3 2 1 0 0 0,2 0,4 0,6 0,8 1 θ

Figure 5-11: Water retention curve of standard density stonewool

P. Hulsman HydroRock analysis Results of the experiments | Page 22 Water retention curve stonewool 2

1,5

pF 1

0,5

0 0 0,2 0,4 0,6 0,8 1 θ

Figure 5-12: Water retention curve of standard density stonewool

5.3.1. Water retention behaviour in soil: Lab experiment In the lab, high density HydroRock was placed in fine sand to assess the immediate response of HydroRock on the water drainage by observing the water level. This experiment was repeated multiple times changing the flow direction or the slope:

Experiment 1: Flow direction in the direction of the fibre (see Figure 5-13) Experiment 1.1: Horizontal box Experiment 1.2: Box sloped in the flow direction (5 %) Experiment 1.3: Box sloped perpendicular to the flow direction (3%) Experiment 2: Flow direction perpendicular to the fibre direction (see Figure 5-14) Experiment 2.1: Horizontal box Experiment 2.2: Box sloped in the flow direction (3%) Experiment 2.3: Box sloped perpendicular to the flow direction (5%)

Each experiment consisted of two parts: water inflow and drainage. The water inflow part of the experiment started under dry conditions whereas the drainage part started under completely saturated conditions. In both parts of the experiment, the boundary condition downstream was a fixed water level hout (see Figure 5-13 right and Figure 5-14 right). If this water level was lower than 10 cm relative to the lab floor, then there was free flow as this was the outflow level. The water level in the box was measured relative to the lab floor. The upstream boundary condition was the inflow Qin. In Table 5-7, an overview of the individual experiment runs is given.

The soil moisture was found to be about 0.4 at the end of the water inflow or drainage test run; hence no significant difference was observed between a fully saturated or drained fine sand. This was probably due to the small soil depth (20cm) compared to the capillary rise capacity of fine sand which is about 40 cm (Kasenow, 2001).

In the next section, the individual experiments are compared with each other. See Appendix for the results and analyses individual experiments.

P. Hulsman HydroRock analysis Results of the experiments | Page 23

A’ Legend Qout Fine sand A A’ D2 CTD2 HydroRock Qin Diver location

hout D1 CTD1 10 cm

Qin A

Figure 5-13: Sketch of the experiment setup: Experiment 1 top view (left) and cross-section AA’ (right)

Legend

Fine sand

HydroRock D2 CTD2 B B’

Qout Qin Diver location

B’ B hout Qin D1 CTD1 10 cm

Figure 5-14: Sketch of the experiment setup: Experiment 1 top view (left) and cross-section BB’ (right)

Table 5-7: Overview experiment runs

Experiment name Test duration Qin [l/min] hout [cm] Flow duration [min] Experiment 1.1 Water inflow + EC 4h 0.61 12.5 51 Experiment 1.1 Water drainage 1h 0 4 - Experiment 1.2 Water inflow + EC 4.1h 0.35 12.5 102 Experiment 1.2 Water drainage 2h 0 0 - Experiment 1.3 Water inflow + EC 4.1h 0.35 12.5 115 Experiment 1.3 Water drainage 2h 0 4 - Experiment 2.1 Water inflow 2.75h 0.35 4 - Experiment 2.1 Water drainage 2.25h 0 4 - Experiment 2.2 Water inflow 2.33h 0.35 4 - Experiment 2.2 Water drainage 3.58h 0 4 - Experiment 2.3 Water inflow 2.25h 0.35 0 - Experiment 2.3 Water drainage 1.75h 0 0 -

P. Hulsman HydroRock analysis Results of the experiments | Page 24 Experiment comparison Water levels The experiments were compared with each other focusing on the water depths measured in HydroRock at CTD1 (see Figure 5-15). In all experiments, the boundary conditions were the same except for the inflow in Experiment 1.1.

During water inflow Focusing on Experiment 1, the water level increased most rapidly in Experiment 1.1 probably due to the larger inflow Qin. In general, the water level increased slower in Experiment 2 where the water first flowed through fine sand before reaching the HydroRock. Overall, the water depth increase varied between 1 cm (Experiment 2.2) and about 15 cm (Experiment 1.1). The final water depth varied between 2 cm (Experiment 2.2) and 15 cm (Experiment 1.1) even though the downstream boundary condition was the same.

During water drainage In general, the water level initially decreased slowly followed by an extremely rapid decrease. The slow decrease reflected the decline of the water level in saturated zone. As soon as the entire saturated zone was drained, the capillary zone was drained very rapidly resulting in an extremely fast decrease in the water level measurements. The water depth decrease varied between 18 cm (Experiment 1.2) and 20 cm (Experiment 1.1 and 2.2).

Water inflow

20

E 1.1 15 E 1.2 10 E 1.3 5

E 2.1 water depth[cm]water 0 E 2.2 0:00 0:15 0:30 0:45 1:00 E 2.3 time [hour:min]

Water drainage

25

20 E 1.1 15 E 1.2 10 E 1.3

5 E 2.1 water depth[cm]water 0 E 2.2 0:00 0:15 0:30 0:45 1:00 E 2.3 time [hour:min]

Figure 5-15: Comparison of the water level measured at CTD1 for each experiment

P. Hulsman HydroRock analysis Results of the experiments | Page 25 Electric conductivity In Experiment 1 during the water inflow part, a salt plume was drained through the system and the conductivity (EC) was measured. During Experiment 1.2 and 1.3, the peak in the electric conductivity decreased by a factor of 25 and 60 resp. whereas it decreased merely by a factor 1.5 during Experiment 1.1. This dilution of the salt water was caused by dispersion due to different flow accelerations and lateral flow (see Figure 5-16). This dispersion was strengthened by the slopes in Experiment 1.2 and 1.3 causing an extreme dilution.

Figure 5-16: Schematization of later flow in the box (top view)

Through the lateral flow, salt water flowed into the soil. While filling the box such that it was completely saturated, this salt water flowed to the downstream point completing its circulation. This was observed by the increase in electric conductivity (EC) at CTD2; see where the water level and EC was plotted for Experiment 1.2 during the water inflow, filling to obtain complete saturation and drainage.

Figure 5-17: Water level and electric conductivity during Experiment 1.2. Part 1: Water inflow; Part 2: Filling of the box until it was completely saturated; Part 3: Water drainage

P. Hulsman HydroRock analysis Results of the experiments | Page 26 Flow duration and specific resistance With the electric conductivity, the flow duration for a distance of 70 cm was determined. This duration is equal to the time difference between the peaks in conductivity upstream and downstream. The flow duration was used to calculate the average speed and flow Qavg in the HydroRock and the specific resistance. The specific resistance c is equal to:

푘 푐 = Δ퐿

Δℎ 푄 = 푘 ∗ 퐴 ∗ = 푐 ∗ 퐴 ∗ Δℎ Δ퐿

푄 푐 = 퐴 ∗ Δℎ

As shown in Table 5-8, the average flow was found to be slightly lower than the inflow Qin due to the water that -5 -1 -5 -1 was retained in the HydroRock. The specific resistance varied between 3.44∙10 s and 5.11∙10 s . This resistant was largest in Experiment 1.1 where there was no slope whereas it decreased in Experiment 1.2 and 1.3 where slopes were added. Hence, the addition of a slope caused an acceleration of the average flow through HydroRock regardless of the slope direction.

Table 5-8: Results on the flow duration, average speed, average flow, hydraulic conductivity and specific resistance for Experiment 1

Type Qin Flow Average Average flow Hydraulic Specific [l/min] duration speed [l/min] conductivity resistance [min] [mm/s] [m/s] [s-1] Experiment 1.1 0.61 51 0.23 0.50 3.58∙10-3 5.11∙10-3 Experiment 1.2 0.35 102 0.11 0.13 2.41∙10-3 3.44∙10-3 Experiment 1.3 0.35 115 0.10 0.10 2.59∙10-3 3.70∙10-3

P. Hulsman HydroRock analysis Results of the experiments | Page 27 Experiment evaluation Flow direction in fibre direction - During water inflow o The water level increased within 5 - 10 min in HydroRock up to 15 cm. The response in the soil was noticed after 1 - 2 min. o The flow duration was between 51 min and 115 min depending on the inflow and slope. With this duration, the hydraulic conductivity was estimated to be 2.59∙10-3 - 3.58∙10-3 m/s and the specific resistance 3.44∙10-3 - 5.77∙10-3 s-1. The addition of a slope caused an decrease this resistance regardless of the slope direction. o During Experiment 1.2 and 1.3, the peak in the electric conductivity decreased by a factor of 25 and 60 resp. whereas it decreased merely by a factor 1.5 during Experiment 1.1. This dilution of the salt water was caused by circulation through the soil which was strengthened by the slopes in Experiment 1.2 and 1.3. - During drainage o In general, the water level initially decreased slowly followed by an extremely rapid decrease. The slow decrease reflected the decline of the water level in saturated zone. As soon as the entire saturated zone was drained, the capillary zone was drained very rapidly resulting in an extremely fast decrease in the water level measurements. o The water level decreased within 15 - 25 min in HydroRock up to 20 cm. The response in the soil was noticed after 1 - 2 min.

Flow direction perpendicular to fibre direction - During water inflow o In general, the water level increased slower than when the flow direction was in the fibre direction. In this case, the water first flowed through fine sand before reaching the HydroRock. o The water level increased within about 15 - 30 min in HydroRock up to 11 cm. The response in the soil was noticed after 1 - 2 min. o Despite the constant boundary conditions, the water level decrease upstream in HydroRock varied between 1 cm and 11 cm and the final water level between 10 cm and 16 cm. - During drainage o In general, the water level initially decreased slowly followed by an extremely rapid decrease. The slow decrease reflected the decline of the water level in saturated zone. As soon as the entire saturated zone was drained, the capillary zone was drained very rapidly resulting in an extremely fast decrease in the water level measurements. o The water level decreased within 20 - 25 min in HydroRock up to 20 cm. The response in the soil was noticed after 1 - 2 min.

Diver drift off For each experiment, the water level data was shifted for each experiment separately such that the data corresponded with 0 cm water depth observations. This shift is called the drift off of the diver and is presented in Table 5-9.

P. Hulsman HydroRock analysis Results of the experiments | Page 28 Table 5-9: Diver drift off for each experiment D1 D2 CTD1 CTD2 Experiment 1.1 Inflow 3.40 4.62 0.04 1.59 Experiment 1.1 Drainage 3.96 5.67 0.49 2.08 Experiment 1.2 Inflow 4.59 8.47 2.78 4.95 Experiment 1.2 Drainage 4.25 5.70 1.01 2.99 Experiment 1.3 Inflow & Drainage 3.30 2.60 6.85 5.07 Experiment 2.1 Inflow 3.55 4.73 0.06 1.51 Experiment 2.1 Drainage 3.99 4.45 0.08 2.46 Experiment 2.2 Inflow & Drainage 3.05 1.72 6.71 5.12 Experiment 2.3 Inflow & Drainage 4.07 5.24 0.46 2.10

5.3.2. Water retention behaviour in the soil: Field experiment In the field, the groundwater level, water level in HydroRock and precipitation were from June 17th to August 5th. The water level data in the HydroRock was excluded in this analysis because of its poor quality; no difference was found between wet and dry conditions regardless of the weather suggesting too low water levels to be observed. The precipitation and groundwater level data are plotted in Figure 5-18.

During the month July, the groundwater level was observed to increase for each storm. This increase was more significant at Location 1 which is located close to the stormwater runoff inflow into HydroRock; see also the sketch in Figure 5-13. At Location 2, the increase was more damped. This suggested a water flow from HydroRock into the soil.

Figure 5-18: Precipitation and groundwater level data relative to ground level

P. Hulsman HydroRock analysis Results of the experiments | Page 29

Figure 5-19: Sketch of field experiment: location of the water pressure devices at Location 1 (L1) and Location 2 (L2) relative to the HydroRock. The red arrows indicate the stormwater inflow into the HydroRock and the outflow from HydroRock into the soil

P. Hulsman HydroRock analysis Results of the experiments | Page 30 6. Summary experiment results In this section a summary is given of all the experiment results. These were conducted in the lab using tap water at a temperature of about T=20° unless stated differently.

Influence of loading External loadings such as car traffic had an insignificant effect on the stonewool. The strain caused by a typical load of 15-45 kPa was 0.15% under drained conditions whereas the stonewool had a maximum strain of 1.8% at 58 kPa shortly before it collapsed.

Root penetration Roots of seedlings did not intrude well into stonewool; however roots do penetrate when the plants are larger. Roots did penetrate the geotextile as well.

Clogging The geotextile and stonewool both suffered from clogging by synthetic suspended sediment polluted water using silica flour called Sikron M600.

Retention capacity During a drainage experiment, initially the weight decreased rapidly. The maximum observed decrease was 8% for stonewool, 10% for HydroSand using silica flour M300 and 25% using fine sand. At a certain point, all the water that can be drained through gravity had flown out of the sample. The rest of the water remained in the sample; hence the available volume to store additional water decreased significantly. However, according the water retention curve obtained from Rockwool B.V., water can be drained under gravity out of stonewool up to a soil moisture of 10%.

Infiltration capacity The infiltration capacity was estimated based on the maximum discharge flowing vertically through high density stonewool such that the water level above the sample remained constant. This capacity was about 2.1∙10-3 m/s and the specific resistance 18.5 s-1.

Hydraulic conductivity High density samples had a smaller hydraulic conductivity than standard samples. HydroSand had a significantly smaller hydraulic conductivity. - High density stonewool : 1.4 - 3.0 ∙10-3 m/s - Standard stonewool : 5.0 - 7.4 ∙10-3 m/s - HydroSand : 5∙10-4 m/s and 4∙10-4 m/s (HydroSand resp. pure soil using fine sand) 2∙10-4 m/s and 8∙10-7 m/s (HydroSand resp. pure soil using silica flour M300)

As a reference, the hydraulic conductivity of coarse sand is 9∙10-7 - 6∙10-3 m/s, of fine sand 2∙10-7 - 2∙10-4 m/s and clay 1∙10-11 - 4.7∙10-9 m/s. The hydraulic conductivity when draining stonewool in the fibre direction was similar to when water was drained perpendicular to the fibre direction. The addition of geotextile to the stonewool slightly decreased the hydraulic conductivity for standard and high density samples suggesting the textile had a smaller hydraulic conductivity. The hydraulic conductivity for HydroSand was smaller than for stonewool in all tested cases and larger than the soil used for the HydroSand mixture. This increase was larger for silica flour than for fine sand.

P. Hulsman HydroRock analysis Summary experiment results | Page 31 Water retention behaviour in the soil Water flow in the fibre direction: During water inflow, the water level in HydroRock increased within 5 - 10 min up to 15 cm. The soil response followed within 1 - 2 min. The flow duration in the HydroRock was 51 - 115 min for a distance of 0.7 m. With this flow duration, the average speed was found to be 0.23 - 0.10 mm/s, the hydraulic conductivity 2.41∙10-3 - 3.58∙10-3 -3 -3 -1 m/s and the specific resistance 3.44∙10 - 5.11∙10 s . The addition of a slope caused an decrease this resistance regardless of the slope direction. The salt concentration decreased significantly as water circulated through the soil; this circulation was strengthened by the box slopes. While draining the completely saturated system, the water level decreased within 15 - 25 min up to 20 cm. The soil response followed within 1 - 2 min. In general, the water level initially decreased slowly followed by an extremely rapid decrease. The slow decrease reflected the decline of the water level in saturated zone. As soon as the entire saturated zone was drained, the capillary zone was drained very rapidly resulting in an extremely fast decrease in the water level measurements.

Water flow perpendicular to the fibre direction: During water inflow, the water level in HydroRock increased within 15 - 30 min up to 11 cm. The soil response followed within 1 - 2 min. In general, the water level increased slower than when the flow direction was in the fibre direction. In this case, the water first flowed through fine sand before reaching the HydroRock. While draining the completely saturated system, the water level decreased within 20 - 25 min up to 20cm. The soil response followed within 1 - 2 min. Also in this case, the water level initially decreased slowly followed by an extremely rapid decrease.

P. Hulsman HydroRock analysis Summary experiment results | Page 32 7. Conclusion The goal of this study was to assess the suitability of HydroRock for the storage, drainage and infiltration of storm water runoff. This was done by conducting a series of lab experiments in the Hydraulic laboratory of TU-Delft as a potential first step towards full scale long term field tests. Based on these experiments the following can be concluded:

Infiltration The infiltration capacity of HydroRock was comparable with the one of coarse sand. This infiltration occurred after the retention capacity was exceeded. Hence, this material was suitable for the infiltration of storm water runoff into the soil.

Buffering and drainage HydroRock had a large porosity, storage capacity and a large soil moisture content with low pF values. Based on the water retention curve from previous studies done by RockWool B.V., this storage capacity decreased significantly after saturation as stonewool retains over 11% of water for pF < 1.7. Based on own lab experiments, stonewool retained about 86% of water at pF ≈ 2 which is at field capacity. Therefore, it was suitable for the storage of storm water runoff for a single shower and not consecutive storms within a short time period.

The hydraulic conductivity of HydroRock was comparable with the one of coarse sand; thus this material was suitable for the drainage of storm water runoff within stonewool. However, only if the maximum retention capacity of stonewool was exceeded, water was drained into the soil.

In all cases, external loads such as car traffic did not influence the characteristics of HydroRock. This material captured suspended sediments well and roots could grow in HydroRock. This may decrease the infiltration and drainage capacity on the long run.

8. Recommendation In this study, it is found that HydroRock captured suspended sediments well and root growth in that material was possible. For further studies it is recommended to perform long term experiments in order to assess the influence of clogging. These experiments should be conducted both in the lab and in the field. During such experiments, it is recommended to measure the inflow into HydroRock as also the water levels in within HydroRock at its bottom level.

When implementing HydroRock, it is recommended to pay special attention to the location regarding the height relative to the groundwater level in order to obtain a good balance between the buffering and drainage of storm water runoff.

P. Hulsman HydroRock analysis Conclusion | Page 33 9. Literature Domenico, P. A., & Schwartz, F. W. (1990). Physical and chemical : Wiley.

Hydrorock International B.V. HYDROROCK the green label in water management. Retrieved May 2015, from www.hydrorock.nl

Kasenow, M. (2001). Applied Ground-water and Well Hydraulics.

Paassen, L. A. v., Pham, V. P., & Greeuw, G. (2015). Cyclic Triaxial Loading and Hydraulic Conductivity Tests on Rockwool. Technical University Delft.

Savenije, H. H. G. (2010). Hydrologie.

Sibelco. (2006). SIBELCO. Retrieved June 2015, from www.sibelco.be

P. Hulsman HydroRock analysis Literature | Page 34 Appendices

Appendices

P. Hulsman HydroRock analysis Appendices | Page 35 1. Appendix Soil characteristics

Table 1-1: Characteristic diameters of silica flour (Sibelco, 2006) Silica flour Silica flour Unit Method M300 M600 control-sieve 1.8 0.004 % Alpine > 40 μm D10 3 2 μm Malvern MS 2000 D50 17 4 μm Malvern MS 2000 D90 40 9 μm Malvern MS 2000 D50 14 3 μm Malvern MS X

Sieve curve: fine sand (Silica sand S60) 100 90

80 70 60 50 40 30 Percentfiner [%] 20 10 0 0 50 100 150 200 250 300 350 400 Grain size

Figure 1-1: Sieve curve of fine sand (Sibelco, 2006)

P. Hulsman HydroRock analysis Appendix | Page 36 2. Appendix Results of lab tests on the water retention behaviour of HydroRock in the soil

Experiment 1.1: Flow direction in the direction of the fibre, horizontal box During water inflow (see Figure 2-2 a): - The water level increases with 11-16 cm within about 10 min in HydroRock and soil. This increase occurred first in the HydroRock, then within about 1 min in the soil. - During stationary flow, the water level was largest at the inflow point (CTD1). In the soil, the water level upstream was 1 cm larger than downstream. At CTD2, the water level was 4 cm larger than the downstream boundary condition. - The flow duration was 51 min (see Figure 2-1); hence the average speed was 0.23 mm/s, the average flow through the HydroRock 0.50 l/min and the specific hydraulic conductivity 5.11∙10-5 s-1.

During water drainage(see Figure 2-2 b): - The water level decreased with about 21 cm within about 25 min in HydroRock and soil. It decreased rapidly first in the HydroRock and within about 1 min it started decreasing in the soil.

Experiment 1.1: EC

140

120

100 80 60

EC EC [mS/cm] 40 20 0 0:00 0:30 1:00 1:30 2:00 2:30 3:00 3:30 4:00 4:30 time [hour:min]

Upstream Downstream

Figure 2-1: EC during water inflow (Experiment 1.1)

P. Hulsman HydroRock analysis Appendix | Page 37 Experiment 1.1: Water inflow 25

20

[cm] Soil (D1) 15 Soil (D2) level 10 HydroRock (CTD1)

water 5 HydroRock (CTD2) 0 Box bottom level 0:00 0:15 0:30 0:45 t [hour:min]

Experiment 1.1: Water drainage 30

25

20 Soil (D1) 15 Soil (D2)

10 HydroRock CTD1) water level level water [cm] 5 HydroRock (CTD2) 0 Box bottom level 0:00 0:15 0:30 0:45 1:00 1:15 t [hour:min]

Figure 2-2: Water level during water inflow and drainage (Experiment 1.1)

P. Hulsman HydroRock analysis Appendix | Page 38 Experiment 1.2: Flow direction in the direction of the fibre, sloped box (5%) During water inflow (see Figure 2-4 a): - The water level increases with 7-8 cm within about 7 min in HydroRock and soil. This increase occurred first in the HydroRock, then within about 1 min in the soil. - During stationary flow, the water level was about 3 cm larger upstream than downstream in both HydroRock and the soil. The water level was slightly larger in the HydroRock than in the soil. At CTD2, the water level was 4.5 cm lower than the downstream boundary condition. - The flow duration was 102 min (see Figure 2-3); hence the average speed was 0.11 mm/s, the average discharge 0.13 l/min and the specific hydraulic conductivity 3.44∙10-5 s-1. Downstream, the conductivity was much lower than upstream suggesting large dilution due to a large inflow into the soil.

During water drainage(see Figure 2-4 b): - The water level decreased with 18-21 cm within about 16 min in HydroRock and soil.

Experiment 1.2: EC

140 5

120 4 100 80 3 60 2 40 1

20 EC [mS/cm]EC upstream

0 0 EC downstream[mS/cm] 0:00 0:30 1:00 1:30 2:00 2:30 3:00 3:30 4:00 time [hour:min]

Upstream Downstream

Figure 2-3: EC during water inflow (Experiment 1.2)

P. Hulsman HydroRock analysis Appendix | Page 39 Experiment 1.2: Water inflow 14

12

10 Soil (D1) 8 Soil (D2) 6 HydroRock (CTD1)

4 HydroRock (CTD2) water level level water [cm] 2 Box bottom level CTD1, D1 0 Box bottom level CTD2, D2 0:00 0:15 0:30 0:45 time [hour:min]

Experiment 1.2: Water drainage

25

20 Soil (D1) 15 Soil (D2) 10 HydroRock (CTD1) HydroRock (CTD2)

water level level water [cm] 5 0 Box bottom level CTD1, D1 0:00 0:15 0:30 0:45 1:00 1:15 Box bottom level CTD2, D2 time [hour:min]

Figure 2-4: Water level during water inflow and drainage (Experiment 1.2)

P. Hulsman HydroRock analysis Appendix | Page 40 Experiment 1.3: Flow direction in the direction of the fibre, sloped box (3%) During water inflow (see Figure 2-6 a): - The water level increases with 4-7 cm within about 7 min in HydroRock and soil. This increase occurred first in the HydroRock, then within about 1-2 min in the soil. - During stationary flow, the water level was largest at the inflow point (CTD1). In the soil, the water level upstream was 0.8 cm larger than downstream. At CTD2, the water level was 6 cm lower than the downstream boundary condition. - The flow duration was 115 min (see Figure 2-5); hence the average speed was 0.10 mm/s, the average discharge 0.10 l/min and the specific hydraulic conductivity 3.70∙10-5 s-1. Downstream, the conductivity was much lower than upstream suggesting large dilution due to a large inflow into the soil.

During water drainage(see Figure 2-6 b): - The water level decreased with 19-21 cm within about 12 min and 20 min in HydroRock resp. soil; hence the decrease occurred faster in HydroRock than in the soil. It decreased rapidly first in the HydroRock and within about 1 min it started decreasing in the soil.

Experiment 1.3: EC

140 2,5

120 2 100 80 1,5

60 1 40 0,5

EC [mS/cm]EC upstream 20 EC EC downstream[mS/cm] 0 0 0:00 1:00 2:00 3:00 4:00 5:00 time [hour:min]

Upstream Downstream

Figure 2-5: EC during water inflow (Experiment 1.3)

P. Hulsman HydroRock analysis Appendix | Page 41 Experiment 1.3: Water inflow

10 Soil (D1)

8 Soil (D2)

6 HydroRock (CTD1)

4 HydroRock (CTD2)

water level level water [cm] 2 Box bottom level D1, D2 0 0:00 0:15 0:30 0:45 1:00 time [hour:min]

Experiment 1.3: Water drainage 25 Soil (D1)

20 Soil (D2) 15

10 HydroRock (CTD1)

water level level water [cm] 5 HydroRock (CTD2) 0 0:00 0:15 0:30 0:45 1:00 Box bottom level D1, D2 time [hour:min]

Figure 2-6: Water level during water inflow and drainage (Experiment 1.3)

P. Hulsman HydroRock analysis Appendix | Page 42 Experiment 2.1: Flow direction perpendicular to the fibre direction, horizontal box During water inflow (see Figure 2-7 a): - The water level increased with 7-11 cm within about 25-30 min in HydroRock and soil. This increase occurred first in the HydroRock, then within about 1 min in the soil. - During stationary flow, the water level was about 4 cm larger in HydroRock than in soil. At CTD2, the water level was 5 cm higher than the downstream boundary condition.

During water drainage (see Figure 2-7 b): - The water level decreased with about 19 cm within about 22 min in soil and HydroRock. It decreased rapidly first in the soil and after about 1-2 min it started decreasing in the HydroRock.

Experiment 2.1: Water inflow

20

15

[cm] Soil (D1)

10 Soil (D2) level HydroRock (CTD1) 5 water HydroRock (CTD2) 0 Box bottom level 0:00 0:30 1:00 1:30 2:00 2:30 3:00 time [hour:min]

Experiment 2.1: Water drainage 30

25

[cm] 20 Soil (D1)

15 Soil (D2) level 10 HydroRock (CTD1)

water 5 HydroRock (CTD2) 0 Box bottom level 0:00 0:15 0:30 0:45 1:00 1:15 1:30 1:45 time [hour:min]

Figure 2-7: Water level during water inflow and drainage (Experiment 1.2)

P. Hulsman HydroRock analysis Appendix | Page 43 Experiment 2.2: Flow direction perpendicular to the fibre direction, sloped box (3%) During water inflow (see Figure 2-8 a): - The water level increased with about 1.5 cm within about 15 min in HydroRock. - There was no water level difference in the soil whereas it increased in HydroRock. The reason might be the small water level increase of 1.5 cm in HydroRock instead of about 10 cm in for example Experiment 2.1. In the soil, this water level increase is smaller than in HydroRock and in this case so small that it is not measureable anymore. - During stationary flow, the water level was 3 cm larger in HydroRock than in soil. At CTD2, the water level was 8.5 cm lower than the downstream boundary condition.

During water drainage (see Figure 2-8 b): - The water level decreased with 19-21 cm within about 25 min in soil and HydroRock. It first decreased gradually for 20 min, then rapidly.

Experiment 2.2: Water inflow 5 Soil (D1)

4 Soil (D2) 3 HydroRock (CTD1) 2 HydroRock (CTD2) Box bottom level D1, D2 water level level water [cm] 1 0 Box bottom level CTD1, CTD2 0:00 0:30 1:00 1:30 2:00 2:30 time [hour:min]

Experiment 2.2: Water drainage 25 Soil (D1) 20 Soil (D2) 15 HydroRock (CTD1) 10 HydroRock (CTD2)

water level level water [cm] 5 Box bottom level D1, D2 0 Box bottom level CTD1, CTD2 0:00 0:15 0:30 0:45 1:00 1:15 time [hour:min]

Figure 2-8: Water level during water inflow and drainage (Experiment 2.2)

P. Hulsman HydroRock analysis Appendix | Page 44 Experiment 2.3: Flow direction perpendicular to the fibre direction, sloped box (5%) During water inflow (see Figure 2-9 a): - The water level increased with 9-12 cm within about 45 min in HydroRock and with 4.5-9 cm within about 40-45 min in soil. This increase occurred first in the HydroRock, then within about 2-5 min in the soil. - During stationary flow, the water level was about 4 cm larger in HydroRock than in soil. At CTD2, the water level was similar to the downstream boundary condition.

During water drainage (see Figure 2-9 b): - The water level decreased within about 15-20 min in soil and HydroRock. It decreased rapidly first in the soil and after about 1 min it started decreasing in the HydroRock.

Experiment 2.3: Water inflow 16

14 Soil (D1)

12 Soil (D2) 10 8 HydroRock (CTD1) 6 HydroRock (CTD2)

4 water level level water [cm] 2 Box bottom level CTD1, D1 0 Box bottom level CTD2, D2 0:00 0:15 0:30 0:45 1:00 1:15 1:30 1:45 time [hour:min]

Experiment 2.3: Water drainage 25

20 Soil (D1) 15 Soil (D2)

10 HydroRock (CTD1) HydroRock (CTD2) water level level water [cm] 5 Box bottom level CTD1, D1 0 Box bottom level CTD2, D2 0:00 0:15 0:30 0:45 1:00 1:15 1:30 1:45 2:00 time [hour:min]

Figure 2-9: Water level during water inflow and drainage (Experiment 2.3)

P. Hulsman HydroRock analysis Appendix | Page 45