1

Alvanchi, A., Bajalan, Z. and Iravani, P. (2021), "Emission assessment of alternative dam 1 structure types, a novel approach to consider in new dam projects", Construction Innovation, 2 Vol. 21 No. 2, pp. 203-217. https://doi.org/10.1108/CI-08-2019-0074 3

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Emission Assessment of Alternative Dam Structure Types, a Novel 5

Approach to Consider in New Dam Projects 6

7

Abstract 8

Purpose: Dams require high-volume of construction materials and operations over the life cycle. Selecting 9

a proper type of dam structure can significantly contribute to the sustainability of dam projects. 10

Methodology: This research proposes a complementary fuel consumption and carbon dioxide (CO2) 11

emission assessment method for the alternative dam structure types to assist decision-makers in selecting 12

sustainable choices. Related equations are developed for two common earthen and rock-fill dam structures 13

types in Iran. These equations are then successfully applied to two real dam project cases where the 14

significance of the achieved results are assessed and discussed. 15

Findings: The achieved results of the case studies demonstrate a high deviation of up to 41.3% in CO2 16

emissions comparing alternative dam structure scenarios of earthen and rock-fill dam structures. This high 17

deviation represents an important potential for CO2 emission reduction considering the high volume of the 18

emission in large dam projects. 19

Originality: The life cycle emission assessment of the alternative dam structures, proposed in this research 20

as a novel complementary factor, can be used in the decision-making process of dam projects. The results 21

in this research identify high potential sustainability improvement of dam projects as a result of the proposed 22

method. 23

24

Keywords: Dam structure; life cycle assessment; energy consumption; carbon dioxide emission; dam 25

construction; sustainability 26

This author accepted manuscript is deposited under a Creative Commons Attribution Non-commercial 4.0 International (CC BY-NC) licence. This means

that anyone may distribute, adapt, and build upon the work for non-commercial purposes, subject to full attribution. If you wish to use this manuscript

for commercial purposes, please contact permissions@emerald.com.

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1- INTRODUCTION 27

The expected benefits of many new dam construction projects have been challenged as s result of their 28

adverse impacts on sustainability. Environmental impacts of dam projects on air, land, and water are 29

subjects of many past studies. There is an extensive history of analyzing heavy metals concentration 30

increase in different dams in Turkey (e.g., Karadede and Unlü 2000; Öztürk et al. 2008; Özdemir et al. 31

2010; Uysal et al. 2010; Çiçek et al. 2013). Wei (2009) investigated the adverse impacts of dam construction 32

on the purification capacity of the water stream. Bako et al. (2014) reported soil degradation as a result of 33

the dams’ water penetration and heavy metal containment in areas around the Zobe dam in Nigeria. Air 34

pollution as a result of green gas emission of decomposable materials in the reservoir was investigated in 35

several research efforts conducted in past several years (Tremblay et al. 2004; IRN 2007; Mendonça et al. 36

2012; Deemer et al. 2016; Fearnside 2016; and Song et al. 2018). 37

In another perspective to the environmental sustainability caused by dam projects, the dam structure type 38

is an important component that can affect the sustainability over different phases of its life cycle. Various 39

types of materials, including concrete, soil, masonry, wood, and steel, have been used in the dam structures. 40

The use of masonry, wood, and steel materials in dam structures returns to the past centuries (Jansen, 1983; 41

Reynolds, 1989; Yang et al., 1999). Currently, dams are commonly made of concrete and soil materials 42

(Youdeowei, 2019; ASDSO 2020; TBDS 2020). According to the Association of State Dam Safety 43

Officials (ASDSO 2020), at the first level, dam structures can be categorized into the embankment dams 44

and the concrete dams. At the second level, the embankment dams are divided into the earthen dams and 45

rockfill dams and the concrete dams are divided into gravity, buttress, and arch dams. Figure 1 illustrates 46

the classification of different dam structures and their typical schematic shapes. Only two studies were 47

found on the sustainability of dam structures, and both are performed in China. In a case study, Liu et al. 48

(2013) investigated life cycle emissions of rock-fill concrete and conventional concrete arch dam types. 49

The results indicated 55% of energy consumption and 64% of CO2 emission reduction in the rock-fill 50

concrete arch dam type compared to the conventional arch concrete dam type. Additionally, Zhang et al. 51

3

(2015) investigated CO2 emissions of rock-fill and concrete gravity dam types in the Nuozhadu 52

hydroelectric dam, China. The rock-fill dam resulted in a 24% less CO2 emission than the concrete gravity 53

dam. 54

[Insert Figure 1 here] 55

These case studies identified the dam structure type as the main contributor to the CO2 emission and energy 56

consumption over the life cycle. The achieved results put forward the importance of the selection of the 57

proper dam structure type as a contributor to the sustainable development of the dam projects. In many dam 58

project cases, project owners have choices for the dam structure type, while volume and types of materials 59

used in each dam structure type can significantly change. Therefore, different levels of sustainability are 60

expected during the life cycle when different types of dam structures are selected. Traditionally, dam 61

structure alternatives are compared according to their financial, economic, technical, and environmental 62

assessments. Past research has identified the significant impact of the adopted dam structure type on the 63

resulting emissions. This significant impact, however, motivates this research to propose emission 64

assessment of the alternative dam structures as a new complementary factor in the dam project decision-65

making process. Complementary information received from this assessment becomes an important 66

determinant especially when achieved values of the conventionally evaluated factors are relatively close. 67

Applicability and validity of the proposed approach are investigated in two dam project cases in Iran, where 68

emissions from two commonly used dam structure types are assessed. First, the widely used dam structure 69

types are identified in Iran. Then, life cycle energy consumption and CO2 emission evaluation equations 70

are developed for the defined dam structure types. Next, the developed equations are used for the life cycle 71

emission assessment of the dam project cases. Finally, the significance of the results achieved is discussed 72

in the research, and their correspondence is demonstrated with past research. 73

2- COMMON DAM STRUCTURES TYPES IN IRAN 74

4

The semi-arid climate and the limited available water resources have triggered the construction of many 75

new dam projects in Iran. According to Iran Water Resource Management Co. (IWRMC 2018), currently, 76

more than 100 large dams are under construction, and more than 500 new dam projects are under-study in 77

Iran. Embankment dams are the most common dam structures in these projects. Two embankment dam 78

structures types of earthen dams with a clay core and rock-fill dams with a clay core are the main alternative 79

dam structures. Therefore, the focus of this investigation was set on the emission assessment of these two 80

alternative dam types. 81

3- LIFE CYCLE EMISSION EVALUATION OF EMBANKMENT DAM STRUCTURES 82

Emissions from embankment dam structures are mainly results of various material handling and mechanical 83

operations performed on the dam materials over the life cycles. An overall emission of a dam structure can 84

be estimated as a summation of the emissions separately estimated in production, construction, 85

maintenance, and removal phases. Diesel fuel is the main source of energy used in various equipment 86

involved in processing embankment dam materials in different phases of the dam projects. Therefore, 87

equivalent diesel fuel consumption can be used for representing energy consumption. This equivalency, 88

however, is subject to the diesel fuel properties and the performance of the equipment used for processing 89

dam materials. Staffell (2011) presents nine different sources that report on different energy density for 90

diesel fuel with a limited deviation of 2%. The average diesel energy density value of 35.94 Megajoule per 91

liter (or MJ/liter) (Staffell, 2011) was accounted for the development of the emission estimation equations. 92

In cases that other fossil fuel types are also consumed, an equivalent energy density value of those fuel 93

types can be used instead. For example, according to Staffell (2011), the average equivalent energy density 94

value for natural gas is 35.22 Megajoule per cubic meter (or MJ/ m3), for gasoline is 32.70 (MJ / liter) and 95

for coal is 25.75 Megajoule per kilogram (or MJ/ kg). 96

It is assumed that the adopted dam structure type has a negligible impact on the formation of other parts of 97

the dam project, including the dam reservoir and the hydro-power plant. Therefore, the developed equations 98

in this study only target the life cycle assessment (LCA) of the emissions created directly from the dam 99

5

structure. Emissions from other parts of the dam project are assumed equal and non-determinant in the 100

decision regarding the proper type of dam structure. Figure 2 represents the overall picture of the research 101

method. Further explanations about the emission estimation of the dam structure in different phases of a 102

dam project are provided in the rest of the section. 103

[Insert Figure 2 here] 104

3-1- Emission Estimation in the Production Phase 105

Clay, sand, and crushed rock are the main materials used in different types of embankment dams. Past 106

research efforts have estimated the emissions from the production of these materials according to the 107

regional conditions, as presented in Table 1. Emission coefficients of the construction materials, 108

representing the rate of emissions for the production of one kilogram of the material, is an output of these 109

research efforts. Table 1 presents energy consumption and CO2 emission coefficients estimated in these 110

research efforts conducted in different parts of the world. The energy consumption coefficients are 111

presented in the Megajoule of energy consumed per kilogram of materials produced (or MJ/kg). The CO2 112

emission coefficients are represented in kilograms of CO2 emission per kilogram of the materials produced 113

(or kg CO2/ kg). Expectedly, regional conditions, such as quarry material properties and production 114

methods, have contributed to the values achieved in the energy consumption coefficients. Value ranges are 115

seen for emission coefficients of similar construction materials as presented in Table 1. Here, especially 116

high deviation is seen between production emission coefficients of the naturally extracted aggregates and 117

mechanically produced aggregates. For example, Reddy and Jagadish (2003) reported zero energy 118

consumption for natural sand. However, the energy consumption coefficient of mechanically produced sand 119

material was reported up to 0.10 Megajoule per kilogram (Ndiaye, 2001). Limited deviations are, though, 120

observed for the emission coefficients of the aggregates produced by similar methods, e.g., the mechanical 121

operations. 122

[Insert Table 1 here] 123

6

Earthmoving equipment, such as shovels, loaders, and dozers, are involved in the material production 124

process of embankment dams. Currently, the prevalent fuel consumed in the earthmoving equipment is 125

diesel. However, other types of fuels might be consumed, such as natural gas and gasoline. Furthermore, 126

electrical equipment is also involved in the production processes of materials, such as electric motors and 127

pumps used in conveyors and crushers. It should be noted that electricity is not a primary source of energy. 128

According to IEA (2019), the majority source of electricity generation comes from fossil fuel, including 129

coal, natural gas, and oil. Since many mines are located in remote areas, far from main electricity lines, 130

many of them directly use diesel-generators on-site for generating electricity. In such cases, the consumed 131

diesel need to be estimated and added to the diesel fuel consumed in the other equipment. If electricity is 132

generated from other sources of energy, they also need to be accounted for. Equations 1 estimates diesel 133

consumption in the production phase according to the material weight, energy consumption coefficient for 134

the material production, and the diesel energy density value of 35.94 MJ / liter (Staffell, 2011). Similar 135

equations need to be used in cases that other fossil fuel types are consumed by replacing diesel energy 136

density value of 35.94 MJ/liter with the related fuel energy density values. Equation 2 estimates the CO2 137

emission of the material production based on the weight of the material and its CO2 emission coefficient in 138

the production phase. Adopting emission coefficients of each construction material from the coefficients 139

estimated based on the prevalent material production techniques in the region increases the accuracy of the 140

result. Average values need to be adopted in case emission coefficients are not available for the specific 141

region. 142

Diesel (liter) = 𝑀𝑎𝑡𝑒𝑟𝑖𝑎𝑙 𝑤𝑒𝑖𝑔ℎ𝑡 (𝑘𝑔) × 𝐸𝑛𝑒𝑟𝑔𝑦 𝑐𝑜𝑛𝑠𝑢𝑚𝑝𝑡𝑖𝑜𝑛 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 𝑜𝑓 𝑡ℎ𝑒 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙 (

𝑀𝐽

𝑘𝑔 𝑜𝑓 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙)

35.94 (𝑀𝐽

𝑙𝑖𝑡𝑟𝑒 𝑜𝑓 𝑑𝑖𝑒𝑠𝑒𝑙)

(1) 143

CO2 (kg) = 𝑀𝑎𝑡𝑒𝑟𝑖𝑎𝑙 𝑤𝑒𝑖𝑔ℎ𝑡 (𝑘𝑔) × 𝐶𝑂2 𝑒𝑚𝑖𝑠𝑠𝑖𝑜𝑛 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 𝑜𝑓 𝑡ℎ𝑒 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙 (𝑘𝑔 𝑜𝑓 𝐶𝑂2

𝑘𝑔 𝑜𝑓 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙) (2) 144

3-2- Emission Estimation in the Construction Phase 145

The massive material movement is the main source of emission in the construction phase. Various 146

operations done in this phase can be divided into three different parts, including 1) land preparation, 2) 147

7

material transportation, and 3) material placement. In the land preparation operation, land clearing and 148

excavation is done by different earthmoving equipment to reach the required depth. Then, loaders load 149

different dam materials on the hauling trucks and haul materials from material quarry sites to the dam site. 150

Spreading, watering, and compacting are major activities done by different construction equipment during 151

material placement operation. In this operation, various layers of earthen and rock-fill dam structures are 152

built such as core, shell, filter, and drain. The majority of the emission in the construction phase is the result 153

of diesel fuel combustion in the mobile earthmoving equipment engines. Therefore, first, the volume of 154

diesel fuel consumption in the construction equipment engines is estimated for estimating emission in the 155

construction phase. The resulting CO2 emission is then estimated based on the volume of the consumed 156

diesel fuel. 157

In regards to the fuel consumption estimation method, construction equipment can be divided into two 158

groups: material hauling trucks and on-site material handling equipment (RazaviAlavi 2010). While for the 159

hauling trucks rate of the diesel fuel consumption is estimated per kilometer of the hauling distance, the 160

rate of diesel fuel consumption for the on-site equipment is estimated based on the hours of operation. 161

Equation 3 presents the diesel consumption of the hauling trucks traveling between the dam construction 162

site and a specific source of the material. Here, diesel consumption is estimated based on the number and 163

distance of round trips between the material source and the dam site, and the average diesel consumption 164

rate of the hauling trucks. Overall, the diesel fuel consumption of the hauling trucks is estimated as the 165

summation of the estimated fuel consumption for different materials supplied from various sources. 166

Equation 4 presents the diesel consumption of on-site equipment, performing a specific type of material 167

handling activity. The total operating hours of specific equipment is estimated by dividing the volume of 168

the handled material over the hourly rate of the material handling operation of the equipment. Furthermore, 169

according to USEPA (2015), every liter of diesel fuel combustion in construction equipment emits 2.697 170

kg of CO2. This factor is used in Equation 5 for estimating equivalent CO2 emission of the diesel fuel 171

consumed in different on-site mobile construction equipment. 172

8

𝐷𝑖𝑒𝑠𝑒𝑙 𝐶𝑜𝑛𝑠𝑡𝑢𝑚𝑝𝑡𝑖𝑜𝑛 𝑜𝑓 𝑡ℎ𝑒 𝐻𝑎𝑢𝑙𝑖𝑛𝑔 𝑇𝑟𝑢𝑐𝑘𝑠 (𝑙𝑖𝑡𝑒𝑟) = 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑇𝑟𝑖𝑝𝑠 × 𝑅𝑜𝑢𝑛𝑑 𝑇𝑟𝑖𝑝 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (𝑘𝑚) ×173

𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝐷𝑖𝑒𝑠𝑒𝑙 𝑐𝑜𝑛𝑠𝑢𝑚𝑝𝑡𝑖𝑜𝑛 𝑟𝑎𝑡𝑒 (𝑙𝑖𝑡𝑒𝑟

𝑘𝑚 ) (3) 174

𝐷𝑖𝑒𝑠𝑒𝑙 𝐶𝑜𝑛𝑠𝑡𝑢𝑚𝑝𝑡𝑖𝑜𝑛 𝑜𝑓𝑡ℎ𝑒 𝑂𝑛𝑠𝑖𝑡𝑒 𝑀𝑎𝑡𝑒𝑟𝑖𝑎𝑙 𝐻𝑎𝑛𝑑𝑙𝑖𝑛𝑔 𝐸𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡 (𝑙𝑖𝑡𝑒𝑟) =𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑠𝑜𝑖𝑙(𝑚3)

𝐸𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡 𝑜𝑝𝑒𝑟𝑎𝑡𝑖𝑜𝑛 𝑟𝑎𝑡𝑒 (𝑚3

ℎ)

×175

𝐷𝑖𝑒𝑠𝑒𝑙 𝑐𝑜𝑛𝑠𝑢𝑚𝑝𝑡𝑖𝑜𝑛 𝑟𝑎𝑡𝑒 (𝑙𝑖𝑡𝑒𝑟

ℎ𝑜𝑢𝑟) (4) 176

CO2 (kg) = 𝐷𝑖𝑒𝑠𝑒𝑙 𝑐𝑜𝑛𝑠𝑢𝑚𝑝𝑡𝑖𝑜𝑛 𝑖𝑛 𝑒𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡 (𝑙𝑖𝑡𝑒𝑟) × 2.697 (𝑘𝑔 𝑜𝑓 𝐶𝑂2

𝑙𝑖𝑡𝑒𝑟 𝑜𝑓 𝑑𝑖𝑒𝑠𝑒𝑙) (5) 177

3-3- Emission Estimation in the Operation and Maintenance Phase 178

Various operation and maintenance activities are performed during the long life span of the dams. However, 179

the focus of this research is on the dam structure and only related operation and maintenance activities to 180

the dam structure are of concern. The majority of the operation and maintenance activities, such as the 181

reservoir’s dredging, the reservoir’s vegetation control, and the hydroelectric generator operation, are done 182

regardless of the dam structure type. Concerning the studied dam structure types, i.e., the embankment dam 183

types, control of vegetation is an activity required during the operation and maintenance phase. Control of 184

the vegetation requires special attention for the dams located on the humid climates with high annual rainfall 185

and dense vegetation coverage. In general, different techniques such as bowing and the use of herbicides 186

are used for controlling the vegetation. The volume of materials used and handled during these activities, 187

however, are quite low compared to the construction phase. Furthermore, the majority parts of Iran lies in 188

the semi-arid regions with low vegetation coverage. Therefore, limited care is expected to control the 189

vegetation coverage of the dams in the country. In another perspective, errors that occurred during the 190

design and construction can cause problems in the dam structure during the operation and maintenance 191

phase. Here, crack, erosion, and seepage issues are sample problems. In such cases, maintenance activities 192

might get quite extensive. This study, however, does not capture the risk of possible mistakes made during 193

the design and construction of dams. No corrective maintenance activities are considered in the research. 194

Therefore, the resulting emissions from the dam structure were considered relatively minimal in the 195

operation and maintenance phase compared to the production and construction phases. 196

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3-4- Emission Estimation in the Removal Phase 197

Various dam removal strategies might be considered depending on the dam-site condition. Recycling 198

materials, using them in other construction projects (Mulder 2007), and using a portion of them for the 199

restoration of the dam area (USSD 2015) are among the options. Different removal strategies can create a 200

different volume of emissions. For embankment dams, however, if original borrow areas of dam materials 201

are available, they are usually the best choices to place dam removal materials (Hepler 2013; USSD 2015). 202

For the emission estimation, unless other strategies are indicated, it can be considered that materials 203

removed from a dam structure are placed into their original borrow locations. In such a case, dam materials 204

are excavated from the dam structure and loaded on the hauling trucks to be hauled to their original quarries. 205

Equations 3, 4, and 5 can be respectively used for estimating diesel fuel consumption of the hauling trucks, 206

the diesel fuel consumption of the on-site earthmoving equipment, and the resulting CO2 emissions. 207

4- CASE STUDY 1: ROUDBAR DAM 208

Roudbar dam is located on the Roudbar River in Lorestan province, Iran, with a reservoir capacity of 228 209

million cubic meters. Its crest has a length of 185 meters, a width of 720 meters, and a height of 155 meters. 210

Construction of this rock-fill dam started in 2003, its partial operation commenced in 2016, and it became 211

fully operational in mid-2017. The high level of river sedimentation in this dam has limited its predicted 212

service life to 50 years. In this case study, life cycle emissions of the actual scenario of the rock-fill dam 213

with a clay core and the alternative scenario of the earthen dam with a clay core were studied. Information 214

required in the actual scenario of the rock-fill dam were collected from the project owner, Iran Water and 215

Power Resources Development Co. The alternative dam structure was analyzed and designed by the 216

research team based on the information received from the project owner. Figure 3 represents schematic 217

views of the actual scenario of the rock-fill dam and the alternative dam scenario of the earthen dam of the 218

Roudbar dam case. 219

[Insert Figure 3 here] 220

10

According to the field study from material sources in the region, regular mechanical operations, including 221

excavation, crushing, and screening operations were performed in the production of the dam materials. The 222

energy consumption coefficient of 0.056 MJ/kg and the CO2 emission coefficient of 0.0045 kg CO2/kg 223

estimated by Ghanbari et al. (2017) in Iran was adopted for the mechanical production of the sand materials. 224

However, no direct estimation was found for the embodied energy of the clay and the crushed rock materials 225

in the county. According to the field survey from the material production sources in the region, crushing 226

and screening were the main mechanical activities performed during the production phase of the consumed 227

aggregates. The average values of the identified emission coefficients for mechanically produced clays and 228

crushed rock (presented in Table 1) were accounted for estimating emission values of clay and crushed 229

rock. Energy consumption coefficients of 0.08 MJ/ kg for the clay and 0.04 MJ/ kg for the crushed rock 230

and CO2 emission coefficients of 0.0064 kg CO2/ kg for the clay and 0.0032 kg CO2/ kg for the crushed 231

rock were assumed. 232

The dam’s site distance to different material production plants and the weight of materials were collected 233

from the project documents according to Table 2. Almost all the materials were hauled by 20-ton hauling 234

trucks. The construction operation details of both dam structure types were obtained from direct field 235

observations and interviews with the experts in the dam construction company. Operation rates of different 236

construction equipment in dams were extracted from the survey done on the embankment dam’s equipment 237

in Iran by RazaviAlavi (2010). The diesel consumption rates of the construction equipment were estimated 238

based on the field survey conducted on the construction site. Table 3 represents the main assumptions 239

related to the equipment used in the dam project. Figure 4 summarizes the estimation results. 240

[Insert Table 2 here] 241

[Insert Table 3 here] 242

[Insert Figure 4 here] 243

11

The achieved results suggest 34.3% fewer emissions in the actual scenario of the rock-fill dam than the 244

earthen dam. In both scenarios, material production is responsible for the majority of emissions followed 245

by the construction and removal phases. 246

5- CASE STUDY 2: KARKHEH DAM 247

Karkheh dam is located on the Karkheh River in Khuzestan province, Iran. It is the largest dam in the 248

country with a reservoir capacity of more than 7 billion cubic meters. Its crest has a length of 3030 meters, 249

a width of 1100 meters, and a height of 127 meters.The construction of this earthen dam started in 1992 250

and finished in 2006. The service life of this dam is estimated to more than 130 years. Here again, the 251

sedimentation rate in the reservoir is the main contributor to the dam’s service life. The research team 252

analyzed and designed the alternative dam structure of the rock-fill dam with clay based on the project’s 253

information. Figure 5 represents schematic views of the actual scenario of the earthen dam and the 254

alternative dam scenario of the rock-fill dam for the case. 255

[Insert Figure 5 here] 256

The material production method and construction equipment were fairly similar to ones used in the Roudbar 257

project; similar assumptions were considered for the material production and the productivity of various 258

equipment. Table 4 presents the distances of different material sources and the amount of material supplied 259

from each source. Figure 6 presents a summary of the estimated emissions in different phases of the 260

project’s life cycle. 261

[Insert Table 4 here] 262

[Insert Figure 6 here] 263

Although in this case, the earthen dam was the actual dam type, the rock-fill dam scenario resulted in 41.3% 264

fewer emissions than the earthen dam. Figure 6 presents the total emissions and the emission portion of 265

different dam project phases. Achieved results reasonably followed a similar trend to the Roudbar dam. 266

12

6- DISCUSSION AND FINDINGS 267

Investigations conducted in this research represented considerable deviations in the emissions of the 268

alternative embankment dam structure type over the life cycle. The rock-fill dam resulted in 34.5% fewer 269

emissions in the Roudbar case and 41.3% fewer emissions in the Karkheh dam compared to the earthen 270

dam type. A main contributing factor to this saving can return to the less volume of materials used in the 271

rock-fill dam than the earthen dam. The high emission deviation in different dam structure types achieved 272

in this research conforms with the high emission deviations achieved for different dam type alternatives in 273

the past research (Liu et al., 2013; Zhang et al., 2015). Figure 7 presents emission reduction in the rock-fill 274

dam type compared to the earthen over the life cycle in both cases. Every life cycle phase of the dam 275

projects contributes to emission saving. In both cases, additional emission savings were observed in the 276

production phase. This additional reduction was due to the low mechanical activities involved in the 277

production of crushed rock, as the main material used in the rock-fill dam type, compared to the sand 278

material, the main material in the earthen dam type. 279

[Insert Figure 7 here] 280

In both conducted case studies, emission in the production phase was relatively higher than the construction 281

phase (see Figures 4 and 6). This trend was also seen in the results reported in the past. Figure 8 presents 282

the relative CO2 emission shares of the production and construction phases reported in the past research 283

efforts and the current research. It was seen that the emission share of the production phase was higher in 284

the concrete-based dam types than the embankment dams due to the high embodied energy of the concrete 285

material. Emissions achieved in the production phase of the rock-fill dams in the current research, with 68% 286

and 61% shares, represented a relatively lower share than the case studied by Zhang et al. (2015), with 83% 287

share. The majority of emissions in the production phase of the case studied by Zhang et al. (2015) was also 288

returned to the concrete materials used in the electro-power generation facilities. However, since dam 289

structure types had a limited impact on the specifications of other components, such as the reservoir and 290

the electro-power generator, emissions from these components were not accounted for in the current 291

13

research. The achieved result highlighted the determinant role of material production in the overall 292

emission. 293

[Insert Figure 8 here] 294

7- SUMMARY AND CONCLUSION 295

Regardless of the significant impacts of dam structure types, emission assessment of dam structures is not 296

normally performed during the feasibility and initial planning stages of dam construction projects. This 297

research proposed the incorporation of the emission assessment of alternative dam structures in the 298

feasibility and planning stages of dam construction projects. Implementation of emission assessment for 299

two dam cases in Iran represented high deviations in the life cycle emission of alternative dam structures 300

types with the possible emission saving up to 41.3%. 301

This research introduced life cycle emissions of the dam structure type as a complementary decision factor 302

to the traditionally accounted factors such as financial, economic, technical, and environmental factors. 303

Extensive studies are performed in different aspects of the dams before the implementation of every large 304

dam project. The adopted dam structure type is one of the main outputs of these studies. High emission 305

deviations between alternative dam types can justify additional efforts required for the dam structure 306

emission assessments in cases that the alternative dam structure types are available. In this perspective, this 307

investigation aimed to raise awareness regarding how emission assessments of dam projects can improve 308

the dam’s sustainability without compromising the project objectives. The emission assessment results can 309

be analyzed in conjunction with the results of the technical and financial assessments to decide about the 310

most viable dam structure. In this research, only evaluation equations for earthen and rock-fill dam structure 311

types were developed. However, similar steps taken for these two dam types can be expanded to other 312

applicable dam structure types, such as conventional concrete, roller compacted concrete, and earth rock-313

fill. Although the proposed LCA method in the research was applied for dam construction projects in Iran, 314

14

no reservations were assumed in the developed evaluation method. Similar steps taken in this research can 315

be followed for the life cycle emission assessment of dam structure cases in other parts of the world. 316

ACKNOWLEDGMENT 317

We would like to express our appreciation to Dr. Hesam Fouladfar from Iran water and power resources 318

development Co. who supported us in collecting data on the case studies. We also thank Mr. Mohammad 319

Bisadi, who helped us during the initial data collection. 320

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19

Table 1. Energy consumption and CO2 emission coefficients of soil materials reported in the literature 427

Source Soil Material Energy Consumption

Coefficient (MJ/kg)

CO2 Emission

Coefficient (kg CO2/kg) Production method

Clay 0.070 0.0023

Mechanical production

operations used in New

Zealand

Sand 0.1000 0.0076

Alcorn, 2003 General

Aggregate 0.0400 0.0017

River

Aggregate 0.0300 0.0011

Virgin Rock 0.0600 0.0022

Reddy and

Jagadish, 2003

Sand 0.000 - Use of natural sand and

crushed rock in India Crushed Rock 0.010 -

Ndiaye et al.,

2005 Sand 0.060 0.004

Mechanical production

operations used in

Senegal

Hammond and

Jones, 2011

Sand 0.081 0.0048 – 0.0051 According to the fuel

consumption data in

material production

plants in the UK Crushed Rock 0.083 0.0048 – 0.0052

Magwood, 2014

Clay and Sand

(General

Aggregate)

0.083 0.0052

General mechanical

production operation in

North America

Milijan, 2015 Clay 0.087 -

Mechanical production

operations used in

Estonia

Ghanbari et al.,

2017

Sand and

gravel 0.056 0.0045

Mechanical production

operations used in Iran

428

429

20

Table 2. Roudbar dam site distance to different material sources 430

Material Source Weight

(million tons)

Distance

(km)

Ro

ck-f

ill

da

m

Clay Source 1 2.13 8

Sand Source 2 1.45 6

Crushed rock Source 3 12.7 4.5 Total 16.3

Ea

rth

en

da

m Clay Source 1 2.13 8

Sand Source 2 18.8 6

Total 21.0

431

432

21

Table 3. Main assumption used in the calculation of construction phase 433

Equipment operation rate (m3/ hour) Equipment fuel consumption rate

Dozer (crawl, 105 HP, bucket 2 m3) 85 40 (liter / hour)

Grader (180 HP, blade 3.66x0.61 m) 280 25 (liter / hour)

Roller compactor (155 HP, 10 ton) 120 15 (liter / hour)

Sheep foot roller compactor (155

HP, 12 ton) 100 15 (liter / hour)

Water truck (19000 liter) 95 25 (liter / hour)

Truck (20 ton) 0.4 (liter /km) 434

435

22

Table 4. Karkheh dam site distance to different material sources 436

Material Source Weight (M ton) Distance (km)

Ro

ck-f

ill

da

m

Clay Source 1 5.25 12

Sand Source 2 2.59 1.5

Crushed rock

Source 2 1.81 1.5

Source 3 2.94 2.5

Source 4 10.1 6

Source 5 8.19 7

Source 6 5.48 9 Total 36.3

Ea

rth

en d

am

Clay Source 1 5.25 12

Sand

Source 2 4.41 1.5

Source 3 7.18 2.5

Source 4 35.7 6

Source 5 3.31 7

Total 55.8

437

438

23

Earthen

Embankment

Rockfill

Dam

Structure

Types

Gravity

Concrete Buttress

Arch

Figure 1. Classification of the dam structures types and their schematic views 439

440

CoreSandy gravel Sandy gravel

CoreRock-fill Rock-fill

Co

ncr

ete

24

441

442

443

Figure 2. Fossil fuel consumption and CO2 emission over the dam structure life cycle 444

445

CO2

Emission

Fuel

Consumption

Maintenance Construction

Production Removal

25

446

447

448

449

a. The actual scenario ( rock-fill dam with clay core) 450

451

b. The alternative scenario (earthen dam with a clay core) 452

Figure 3. Schematic views of the actual and alternative dam scenarios of Roudbar dam case 453

454

Clay Core

Rock-fill Rock-fill

15

5 m

720 m

Clay CoreSandy gravel Sandy gravel

15

5 m

15 m

1020 m

26

455

456

457 Figure 4. Life cycle* emission results of alternative scenarios in Roudbar dam 458

* Resulting emissions from the operation and maintenance phase of the studied alternative dam structure types were 459 found minimal compared to other phases and were not reported consequently. 460

461

Production

Production

Construction

Construction

Removal

Removal

Rock-fill Earthen

a. Diesel consumption

60.8(million litres)

39.9(million litres)

20%

27%

56%

25%

53%

19%

Production

Production

Construction

Construction

Removal

Removal

Rock-fill Earthen

b. CO2 emission

170 (million kg)

111 (million kg)

20%

26%

24%

18%

58%

54%

27

462

a. The actual scenario (earthen dam with a clay core) 463

464

b. The alternative scenario (rock-fill dam with clay core) 465

466

Figure 5. Schematic views of the actual and alternative dam scenarios of Karkheh dam case 467

468

Clay Core

Sandy gravelSandy gravel

12

7 m

12 m

1100 m

Clay Core

Rock-fill Rock-fill

12

7 m

12 m

28

469

470

471 Figure 6. Life cycle* emission results of alternative scenarios in of Karkheh dam 472

* Resulting emissions from the operation and maintenance phase of the studied alternative dam structure types were 473 found minimal compared to other phases and were not reported consequently. 474

Production

Production

Construction

Construction

Removal

Removal

Rock-fill Earthen

a. Diesel consumption

176 (million litres)

104(million litres)

23%

31%

52%

29%

46%

19%

Production

Production

Construction

Construction

Removal

Removal

Rock-fill Earthen

b. CO2 emission

491 (million litres)

288 (million litres)

23%

30%

53.5%

28%

47%

18.5%

29

475

Figure 7. Emission reduction of different phases in the rock-fill dam compared to the earthen dam 476

477

Life cycle, 41.3%

Life cycle, 34.5%

30

68%

70%

61%

65%

91%

85%

90%

83%

32%

30%

39%

35%

9%

15%

10%

17%

478

Reference/ Dam case type Production share Construction share

Current research/ Roudbar, rock-fill

Current research/ Roudbar, earthen

Current research/ Karkheh, rock-fill

Current research/ Karkheh, earthen

Liu et al., 2013/ Conventional concrete arch

Liu et al., 2013/ Rock-fill concrete arch

Zhang et al., 2015/ Concrete gravity*

Zhang et al., 2015/ Rock-fill*

* The case is a hydroelectric dam 479

Figure 8. Relative CO2 emission shares of the production and construction phases achieved for dam 480

projects in different research efforts 481

482

483

484