Study on the Calculation Method of Carbon Emissions in the Construction Industry: Targeting Small River Maintenance Projects in Korea

Abstract

The construction industry, responsible for approximately 30% of global carbon emissions, is closely linked to national development, making carbon reduction challenging. While national development is of paramount importance, it is essential to prioritize individual projects and establish a direction for reducing carbon emissions. The starting point should involve calculating the carbon emissions for each project and comprehending their quantitative impact. In this study, we calculated the carbon emissions for a small river maintenance project aimed at disaster prevention in the construction industry in Yongin-si, Gyeonggi-do, Korea. The total carbon emissions generated by the small river maintenance project in the target area amounted to 2016.6 tonCO₂. By process, the embankment construction was responsible for 789.7 tonCO₂, while the revetment construction contributed 1226.9 tonCO₂. The analysis revealed that the carbon emissions generated by the small river maintenance project equated to 10.2 tonCO₂/km of river length. Additionally, we developed an equation by applying the double-log function model (log–log) to small river length and carbon emissions. The coefficient of determination for the calculation equation is 0.42, which may not yield highly precise results. However, it is believed that this equation will provide a rough estimate of the carbon emissions associated with the small river maintenance project.

1. Introduction

Climate change is a major problem facing human society, and impacts and damage will continue to occur worldwide [1,2]. Many countries are preparing various measures to reduce carbon emissions through the 1997 Kyoto Protocol and the 2015 Paris Agreement. According to the IEA (2021), the nationally determined contribution (NDC) to the Paris Agreement target is to reduce the emissions intensity of GDP by 35% by 2030 [3].

Various industries emit carbon, and among them, the construction industry emits about 33% of the world’s carbon every year [4,5,6,7,8]. Additionally, raw materials, construction, and building operations are among the largest sources of carbon emissions worldwide [2,9,10,11,12]. The construction industry is a major contributor to carbon emissions, and strategic controls are needed to address climate change [13,14,15]. In addition, urban development, a common element in construction projects, has a significant impact on carbon emissions due to the construction of roads, buildings, and facilities. The annual urbanization rate is expected to increase by 1.46% from 2015 to 2030 [16].

Global carbon dioxide emissions in 2021 are approximately 36 billion tons. Of these, carbon dioxide emissions from the construction sector account for approximately 40%. In the construction field, 30% of greenhouse gases are generated from raw material processing and 70% from building operations [17]. China’s building and construction industry is the most carbon-emitting industry, with emissions comparable to those of the entire Middle East or twice that of Africa [18,19,20]. An analysis of the spatial and temporal evolution of 30 regions in China from 2005 to 2019, using the Theil index, GIS techniques, and Moran’s I index, revealed that construction is one of the industries with the highest carbon emissions [21,22]. Additionally, it is suggested that rapid urbanization increases carbon emissions due to increases in energy consumption and the construction industry [23]. Since 2015, energy consumption in the construction industry has accounted for 25% to 33% of China’s total energy consumption [11,24,25,26]. In Europe, a method for calculating carbon emissions was presented by evaluating the fuel consumption process at construction sites. The analysis found that carbon emissions were relatively low in transportation, demolition, and construction, in that order. Based on the calculated carbon emissions, Austria implemented a carbon emissions taxation system [27,28].

Buildings are one of the major structures created by the construction industry. During the construction process of large-scale residential complexes, carbon emissions from high-rise buildings and villas account for approximately 84% of the total emissions [29]. Additionally, energy consumption continues to be required for operation even after the building is completed, and carbon emissions account for approximately 24% of the total emissions [30]. Some studies indicate that 12.6%, 85.4%, and 2% of carbon emissions occur at different stages of the building’s life cycle: construction, operation, and demolition [25,31,32,33,34,35,36,37,38]. It has been analyzed that carbon emissions have a ripple effect based on the spatial characteristics of the city, and building materials also make a significant contribution [39,40,41]. Cement, widely used in the construction sector, has been found to account for approximately 5% of global carbon emissions [42].

Methods for measuring and evaluating carbon emissions in the construction field are being explored in many studies, including assessments of asphalt, exhaust gas, and energy consumption [43,44,45,46]. These studies argue for the need for quantitative management of carbon emissions generated in the construction sector [19,47,48,49]. Quantitative calculation of carbon emissions can serve as a standard for carbon reduction. Given that the construction field is a sector with high carbon emissions, it underscores the importance of alternative approaches to carbon reduction and suggests effective carbon reduction methods based on the construction stage and building life cycle [18,19,50,51,52]. Carbon emissions must be reduced during the design and operation process, and research on low-carbon construction projects is also underway [11,53,54,55,56,57,58].

The construction industry includes businesses engaged in construction activities such as civil engineering, architecture, equipment, and facilities, as well as businesses involved in the installation, maintenance, and repair of facilities and structures. However, previous studies on carbon emissions in the construction industry have primarily analyzed integrated carbon emissions at the national or regional level. Furthermore, a standardized carbon emissions calculation method was developed to establish quantitative standards and emphasize the importance of carbon reduction. While there have been studies on carbon emissions by country, region, city, etc., there has been a lack of analysis of detailed projects within the construction industry. Additionally, no research has been conducted to calculate carbon emissions for projects such as the installation and maintenance of facilities or structures. In the construction industry, small river maintenance projects, which involve the installation of facilities and structures, are projects aimed at disaster prevention through the installation of structures such as levees or revetments in small rivers. Disaster management is a field that generates a significant amount of carbon emissions as it falls within the construction industry, so it is imperative to establish a carbon reduction plan. However, there is currently no standard for the total carbon emissions associated with small river maintenance projects, and a calculation method has not been established. Therefore, this study aims to develop an evaluation method by investigating the calculation methods used in the construction industry to assess the carbon emissions of small river improvement projects. We aim to evaluate the carbon emissions in the field of disaster prevention projects through the developed carbon emissions calculation method for small river maintenance projects.

2. Materials and Methods

2.1. Estimation Method of Carbon Emissions in the Construction Industry

In Korea, guidelines have been developed for calculating carbon emissions in the construction industry. The Ministry of Land, Infrastructure and Transport issued guidelines in 2012 for carbon emissions calculation for various facilities, including roads, railways, buildings, ports, dams, river maintenance, and urban regeneration. These guidelines outline the carbon emission calculation process for each facility and provide carbon dioxide emission coefficients for raw materials, materials, equipment, and more, measured in tonCO₂/unit. The carbon dioxide emission factors in MOLIT (2012) were derived from the national Life Cycle Inventory Database (LCI DB), developed in accordance with ISO 14044 procedures and the IPCC 4th report [59].

The carbon emissions calculation process for the river maintenance sector comprises four stages. In river maintenance projects, data for calculating carbon emissions is collected, and material inputs for each process are quantified. Furthermore, energy consumption associated with equipment used during the process is calculated to determine the overall carbon emissions. For energy consumption related to input materials and equipment for each process, we applied the carbon dioxide emissions values specified in the guidelines for calculating carbon emissions by facility. Additionally, the Ministry of Land, Infrastructure and Transport utilized the 2021 construction standard calculation for work volume per hour for each piece of equipment [60]. The carbon emission calculation process for the small river maintenance project is illustrated in Figure 1.

The guidelines for calculating carbon emissions by facility provide equations for calculating carbon emissions based on material inputs for each process, energy consumption due to equipment usage for each process, carbon emissions resulting from material inputs, and carbon emissions arising from equipment usage. The material input for each process is determined by Equation (1), energy consumption due to equipment usage is calculated using Equation (2), carbon emissions resulting from material inputs are calculated through Equation (3), and carbon emissions arising from equipment usage are determined using Equation (4).

Material input for each process = Workload (unit) × Material input quantity for standard quantity-per-unit cost (ton, m³, m, etc./unit)(1)

Energy consumption for each process = Workload (unit) × Equipment usage time per unit workload (h/unit) × Fuel efficiency(L/h)(2)

Carbon emissions from material input(tonCO₂) = Material input (unit) × Carbon emission coefficient of materials (tonCO₂/unit)(3)

Carbon emissions from equipment use (tonCO₂) = Energy usage(unit) × Net calorific value (kcal/unit) × Carbon emission coefficient of materials for energy (tonC/kcal) × Oxidation rate (%) × 44/12 (tCO₂/tC)(4)

2.2. Establishment of the Carbon Emissions Process for Small River Maintenance Projects

In this study, our objective is to establish a carbon emissions process for small river maintenance projects in Yongin-si, Gyeonggi-do, which is one of the cities, counties, and districts in Korea. In Korea, the Small River Maintenance Act mandates that each city, county, and district formulate a comprehensive small river maintenance plan every 10 years. Yongin-si, Gyeonggi-do, is home to a total of 124 small rivers with a combined length of 196.89 km (see Figure 2) [61].

The small river maintenance comprehensive plan provides approximate values for area, volume, and construction quantities related to small river maintenance projects. By examining the construction details for each small river within the project, common representative construction types were selected, as shown in Table 1. The small river maintenance project involves several main processes, including embankment construction, revetment construction, structure construction, appurtenant work, overhead expenses, and compensation expenses. Embankment construction and revetment construction focus on building river embankments, while structure construction entails installing various facilities. Appurtenant work, overhead expenses, and compensation expenses cover supplementary construction and operational costs essential for executing a small river maintenance project. The quantity calculation for each process within the small river maintenance project provides an initial overview of unit prices, units, quantities, and construction costs.

For structure construction, the plan includes the number of drainage culverts, drainpipes, as well as the area and length of bridges, weirs, and drop structures. Additionally, the appurtenant work specifies the number of auxiliary facilities, while overhead expenses and compensation costs are presented in terms of monetary amounts. To calculate carbon emissions, the quantities of materials and equipment input are multiplied by the carbon generation intensity associated with each unit. Consequently, this study aims to calculate carbon emissions for embankment construction and revetment construction, as these processes allow us to verify the quantities of materials and equipment used in various stages of small river maintenance projects.

2.3. Calculation of Material and Equipment Input for Each Process

2.3.1. Embankment Construction

Embankment construction comprises a total of five stages (Table 1). Embankment, Useful Embankment, Sandy Soil, and Side Grading do not require additional materials and utilize excavators among the equipment. The process of cutting slopes along small rivers involves the use of vegetation and equipment for tasks like attaching nets, installing and dismantling mechanical equipment, and applying squirt and paste. Vegetation is excluded from carbon emissions calculations, while the equipment used includes generators and cranes for attaching nets, cranes for installing and disassembling mechanical equipment, and generators, truck-mounted cranes, and dump trucks for spraying.

The quantity of excavators used in embankment construction is determined based on the slope protection process specified in the 2021 Construction Standard Quantity (MOLIT) [60]. When calculating the excavator’s hourly workload, we consider coefficients for volume conversion, work efficiency, bucket capacity, and cycle time adjustments based on the characteristics of the construction area. However, due to the numerous variables involved in considering the characteristics of all small rivers, we apply standard values typically used for general small river maintenance work.

For embankment construction along small rivers, a bucket coefficient of K = 0.98 is applied, assuming slightly hard soil types such as sand, normal soil, and clay. Work efficiency is assumed as E = 0.75, considering normal, disturbed, sandy, and sandy soil conditions. A one-cycle time is assumed to be a 135° rotation, with a bucket capacity of 0.8 m³, and we use a cm = 20 s for cycle time calculations.

(5)$\mathrm{Q}=\frac{3600\times \mathrm{q}\times \mathrm{k}\times \mathrm{f}\times \mathrm{E}}{\mathrm{c}\mathrm{m}}$

Here, Q: hourly workload(m³/h), q: bucket capacity (m³), f: volume conversion coefficient, E: work efficiency, K: bucket coefficient, cm: one cycle time (s).

Cutting Slope was referenced based on the slope protection hole installation standard in the 2021 Construction Standard Test (MOLIT) [60]. The installation standard for attachment nets is 0.2 h for a 50 kW generator and 0.05 h for a 5-ton crane per 10 m². The quality standard for installing and dismantling mechanical equipment was established at 4 h per 5-ton crane. The quality standard for squirt and paste application is 0.51 h for a 50 kW generator, 5-ton truck-mounted crane, and 6-ton dump truck per 10 m².

Table 2 displays the quantities of materials and equipment required for each type of embankment construction. For cutting and filling, equipment input for 1 m³ was calculated at 0.0137 h, based on a 0.6 m³ excavator. Regarding the installation of attachment nets on the cutting slope, the input amount was calculated as 0.02 h for a 50 kW generator and 0.005 h for a 5-ton crane. For the installation and dismantling of mechanical equipment, an input amount of 0.04 h was calculated for a 5-ton crane. As for squirt and paste application, the input amount of 0.051 h remains the same for a 50 kW generator, 5-ton truck-mounted crane, and 6-ton dump truck per 10 m².

2.3.2. Revetment Construction

Revetment construction offers a range of construction methods that vary depending on the type and design of the revetment. However, in the case of most small rivers, the primary methods employed include precast concrete block installation, stone pitching, and vegetation mat. The input quantities for each process within revetment construction were derived from the 2021 Construction Standard Quantity (MOLIT). The slope protection process aligns with precast concrete block installation, stone construction aligns with stone pitching, and river revetment aligns with vegetation mat installation.

In the precast concrete block installation method, concrete is used as the primary material, and a 5-ton crane (tire) serves as the equipment. Based on 1 m², the input quantity of concrete was computed to be 0.375 tons, while based on 1 m³, the input quantity for the 5-ton crane (tire) was calculated as 0.09 h. Assuming a concrete thickness of 15 cm, approximately 0.15 m³ of concrete are estimated for each 1 m².

The stone pitching method typically involves manual labor and the use of an excavator. In the case of manual labor, it was excluded from the carbon emissions calculation due to its absence from the report. Taking into account that an excavator requires additional manpower during working hours and that equipment does not operate continuously, the input quantity for a 0.6 m³ excavator was calculated as 0.25 h/m². For vegetation mat installation, the input quantity for a 0.6 m³ excavator was determined as 0.031 h/m². Table 3 provides details regarding the quantities of materials and equipment input for each process within revetment construction.

3. Results

3.1. Standards for Calculating Carbon Emissions by Process

To calculate carbon emissions within the small river maintenance project, the quantities of materials and equipment input for each process were established in Section 2.3. The carbon emissions for the small river maintenance project were computed based on the guidelines for calculating carbon emissions for river maintenance facilities published by MOLIT in 2012 [59]. Table 4 provides information on the carbon emissions associated with materials and equipment for each process as outlined in the report. Concrete stands out with the highest carbon emissions at 346 tonCO₂/m³, while cranes exhibit the lowest carbon emissions at 13.28 tonCO₂/h. Carbon emissions for the equipment sector were presented within the range of 13.28 tonCO₂/h to 26.56 tonCO₂/h.

The carbon emissions associated with the materials and equipment used throughout the entire small river maintenance project are detailed in Table 5. When the same equipment was applied to multiple processes, carbon emissions were calculated consistently. Embankment, Useful Embankment, Sandy Soil, and Side Grading for Embankment construction were uniformly assessed, resulting in a carbon emission rate of 0.364 tonCO₂/m³ for a 0.6 m³ excavator. The carbon emissions for Cutting Slope ranged from 0.066 kgCO₂/m² to 1.062 kgCO₂/m², varying by process. In the case of revetment construction, concrete materials exhibited a carbon emission rate of 51.9 tonCO₂/m³, while equipment emissions ranged from 0.823 kgCO₂/m² to 1.195 kgCO₂/m³, depending on the specific process.

3.2. Development of Carbon Emissions Calculation Equation for Small River Maintenance Projects

The established standards for calculating carbon emissions for each process within the small river maintenance project were applied to a total of 124 small rivers. The analysis revealed a cumulative carbon emissions total of 2016.6 tonCO₂ generated through the small river maintenance project in Yongin-si, Gyeonggi-do (see Figure 3). In Yongin-si, Gyeonggi-do, 96.8% of small rivers have lengths of 3 km or less, and 78.7% exhibit carbon emissions of 20 tonCO₂ or less. The highest carbon emissions were observed in Minjegungcheon, with 90.1 tonCO₂, while the lowest carbon emissions were recorded in Daechigaecheon, totaling 0.42 tonCO₂. It was noted that carbon emissions resulting from small river maintenance projects tended to increase as the length of the small rivers increased.

The carbon emissions for each process were calculated to be 789.7 tonCO₂ for embankment construction, primarily involving land construction, and 1226.9 tonCO₂ for revetment construction, primarily associated with the installation of revetment facilities (refer to Table 6). The average carbon emissions per 1 km of small rivers were 10.2 tonCO₂, with embankment construction accounting for 4.0 tonCO₂ and revetment construction totaling 6.2 tonCO₂. The average carbon emissions for a single small river amounted to 16.0 tonCO₂, with embankment construction contributing 6.3 tonCO₂ and revetment construction resulting in 9.7 tonCO₂.

Regarding Carbon Emissions by Construction Type Along the Length of Small Rivers, the average carbon emissions per river and per 1 km were analyzed, as illustrated in Table 7. Carbon emissions by construction type, based on the length of small rivers, peaked at 699.7 tonCO₂ within the 1 km to 2 km range. However, even though the number of small rivers in the 2 km to 3 km range is one-third that of the 1 km to 2 km range and the total length is 27.3 km, carbon emissions were estimated at 618.6 tonCO₂. The analysis of average carbon emissions per river and per 1 km revealed that carbon emissions generally increased with river length, except in the range of 0 km to 1 km. Surprisingly, despite the increase in river length from 0 km to 1 km to 1 km to 2 km, both the average carbon emissions per river and per kilometer decreased.

The carbon emissions resulting from the small river maintenance project and the characteristics of each process concerning the length of the small river were analyzed (see Figure 4). Across all processes, there was a tendency for the carbon emissions to increase as the length of the small river extended. However, the variation in carbon emissions depending on the length of the small rivers was substantial, making it challenging to derive a suitable regression equation. The all-logarithmic (log–log) function model was employed to establish the relationship between carbon emissions and the length of the small river.

An equation for calculating carbon emissions based on the length of small rivers within small river maintenance projects was proposed. The calculation equation relating small river length and carbon emissions is presented as Equation (6), with a Coefficient of Determination analyzed at 0.42. Additionally, individual carbon emission calculation equations were proposed for each process. The calculation equation linking small river length and carbon emissions for embankment construction is expressed in Equation (7), with a coefficient of determination analyzed at 0.38. Similarly, the calculation equation for small river length and carbon emissions for revetment construction is provided as Equation (8), with a coefficient of determination determined to be 0.46. These carbon emissions calculation equations for each process within the small river maintenance project highlight the trend of carbon emissions increasing with the length of the small river. However, in terms of accuracy, the coefficient of determination for each process was approximately 0.42, rendering it challenging to rely on quantitative calculation equations. Consequently, the findings from this study are expected to serve as a qualitative indicator of the carbon emissions generated by the small river maintenance project, facilitating the estimation of rough values.

(6)$\mathrm{Y}=0.62+1.05\times \mathrm{X}$

(7)$\mathrm{Y}=0.28+1.00\times \mathrm{X}$

(8)$\mathrm{Y}=0.03+1.18\times \mathrm{X}$

Here, X is log (small stream length (m)), Y is log (carbon emissions (kgCO₂)).

4. Discussion

The increase in carbon dioxide emissions due to the impacts of climate change prompted the establishment of a global carbon neutrality goal, beginning with the Kyoto Protocol in 1997. Many countries have joined the carbon neutrality agreement and are actively working to reduce carbon emissions. Among various industries contributing to carbon emissions, the construction sector accounts for approximately 33% of the world’s total [22,23,24,46,47]. While the construction industry is essential for national development, it generates significant carbon emissions during construction, maintenance, and demolition activities. The construction industry encompasses diverse projects, including urban development, road infrastructure, social facilities, and disaster prevention structures. However, prior research primarily focused on carbon emissions from the construction industry as a whole or examined the life cycle of buildings [11,13,14,15,24,25,26,31,32,33,34,35,36,37,38]. Additionally, some studies have been conducted to evaluate CO₂ emissions due to the impact of fertilizers in rivers located near agricultural fields [62].

In this study, we analyzed carbon emissions generated by small river maintenance projects for disaster prevention within the construction industry, targeting administrative districts in Korea. In Korea, there are 22,093 designated small rivers nationwide, with the country’s 229 administrative districts managing an average of approximately 100 small rivers each [63]. Although these small rivers are typically less than 3 km long and have an average width of 2 m, they are often located in mountainous areas with rapid rainwater runoff. As larger river maintenance projects have been completed since the 1990s, small rivers have increasingly experienced significant disasters. Small river maintenance projects at the administrative district level commenced in 2000, with plans for secondary maintenance projects currently in progress.

Upon reviewing previous domestic and international studies, it became evident that carbon emissions standards for various disaster prevention projects had not been extensively researched. In this study, we established carbon emissions calculation standards specifically for small river maintenance projects among various disaster prevention initiatives. As of 2021, Korea’s total carbon emissions amounted to 679 million tonCO₂, with the construction industry contributing 258 million tonCO₂, or 38% of the total. This proportion of carbon emissions generated by the construction industry aligns with rates observed in other countries [2,4,5,11,14,26,30,58]. The total carbon emissions resulting from the small river maintenance project in Yongin-si, Gyeonggi-do, were calculated at 2016.6 tonCO₂. When applied on a national scale, the carbon emissions generated by small river maintenance projects within the construction industry for each administrative district amount to approximately 0.179%.

In this study, we developed calculation equations linking small river length and carbon emissions for small river maintenance projects. By applying these equations, the estimated carbon emissions generated by maintenance projects for all 22,093 small rivers nationwide sum up to 353,593 tonCO₂. This figure represents 0.14% of the total carbon emissions produced by the construction industry. It is worth noting that the carbon emissions calculations in this study exclude structures such as weirs and bridges within the small rivers. If carbon emissions from these structures are incorporated through subsequent research, it is expected that both the accuracy of the proposed calculation equations and the total carbon emissions estimation will improve. Furthermore, considering that, as of 2021, only approximately 40% of the small river maintenance projects have been completed, future efforts to implement eco-friendly processes aimed at reducing carbon emissions could contribute to achieving the national carbon neutrality goal.

In this study, we specifically analyzed carbon emissions resulting from small river maintenance projects within the context of disaster prevention initiatives in the construction industry. The study was conducted in Yongin-si, Gyeonggi-do, an administrative district in Korea, and encompassed 124 small rivers. The analysis of total carbon emissions in the administrative district was carried out by applying standards for calculating the input of materials and equipment for each process within the small river maintenance project. Currently, the construction industry has established carbon emissions calculation standards based on material and equipment input. However, for structure construction, only the number of existing drainage culverts or the length of drop holes has been presented and is excluded from carbon emissions calculations.

5. Conclusions

In this study, we examined carbon emissions resulting from small river maintenance projects within the realm of disaster prevention initiatives in the construction industry. Our research focused on Yongin-si, Gyeonggi-do, an administrative district in South Korea, encompassing 124 small rivers. We analyzed the total carbon emissions generated in this administrative district by employing established standards for calculating the material and equipment inputs for each phase of small river maintenance projects. Presently, standards for calculating carbon emissions in the construction field are based on material and equipment inputs. However, for structural construction, the calculation of carbon emissions only takes into account the number of existing drainage culverts or the length of drop structures and excludes other aspects.

The total carbon emissions stemming from the small river maintenance project situated in Yongin-si, Gyeonggi-do, amounted to 2016.6 tonCO₂. Within this, embankment construction contributed 789.7 tonCO₂, while revetment construction accounted for 1226.9 tonCO₂. The overall carbon emissions resulting from the small river maintenance project were calculated at 10.2 tonCO₂/km for every 1 km of river length. Carbon emissions, when analyzed according to the lengths of small rivers, revealed figures of 16.1 tonCO₂/km for 0 km to 1 km, 7.8 tonCO₂/km for 1 km to 2 km, 11.6 tonCO₂/km for 2 km to 3 km, 11.6 tonCO₂/km for 3 km to 4 km, and 18.4 tonCO₂/km for 4 km to 5 km.

Through the analysis of small river length and carbon emissions characteristics, we developed an equation based on the double-logarithmic function model. This calculation equation estimates carbon emissions according to the small river route and is presented for the entire process, embankment construction, and revetment construction, respectively. The coefficient of determination for this calculation equation is 0.42, which may limit the precision of the results, but it should enable a rough estimation of carbon emissions from small river maintenance projects. We anticipate that the carbon emissions calculations derived from this study can serve as evidence of the viability of disaster prevention projects within the field of disaster management or as foundational data for carbon neutrality initiatives.

Author Contributions

Conceptualization, Y.S. and J.J.; methodology, Y.S.; software, J.J.; validation, Y.S., J.J. and M.P.; formal analysis, M.P.; investigation, Y.S.; resources, J.J.; data curation, Y.S.; writing—original draft preparation, Y.S.; writing—review and editing, J.J.; visualization, Y.S.; supervision, M.P.; project administration, M.P.; funding acquisition, Y.S. All authors have read and agreed to the published version of the manuscript.

Data Availability Statement

This data is analyzed based on a book report and has not been published on the site.

Conflicts of Interest

The authors declare no conflict of interest.

Footnotes

Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Figures and Tables

Figure 1. Flowchart of the carbon emissions calculation process in the construction industry [59,60].

Figure 2. Study area.

Figure 3. Carbon emissions from small river maintenance projects.

Figure 4. Double log function analysis of carbon emissions from small rivers.

Table 1

Examples of representative processes of small river maintenance projects.

Process	Unit	Process	Unit
1. Embankment construction		3. Structure construction
(1-1) Embankment	m3	(3-1) Drainage culvert	ea
(1-2) Useful Embankment	m3	(3-2) Drainpipe	ea
(1-3) Sandy soil	m3	(3-3) Bridge	m2
(1-4) Cutting Slope	m2	(3-4) Weir and Drop structures	m
(1-5) Side grading	m2	4. Appurtenant work	Form
2. Revetment construction		5. Overhead expenses	Form
(2-1) Precast concrete block installation	m2	6. Compensation expense	m2
(2-2) Stone pitching	m2
(2-3) Vegetation mat	m2

Table 2

Material and equipment input for embankment construction.

Process		Unit	Material	Input(ton)	Equipment	Input(h)
Embankment		m3	-	-	0.6 m3 excavator	0.0137
Useful Embankment		m3	-	-	0.6 m3 excavator	0.0137
Sandy soil		m3	-	-	0.6 m3 excavator	0.0137
Cutting Slope	Installation of attachment nets	m2	-	-	50 kW generator5-ton crane	0.020.005
	Installation and dismantling of mechanical equipment		-	-	5-ton crane	0.04
	Squirt and paste		Vegetation	-	50 kW generator5-ton truck-mounted crane 6-ton dump truck	0.0510.0510.051
Side grading		m2	-	-	0.6 m3 excavator	0.009

Table 3

Material and equipment input for revetment construction.

Process	Unit	Material	Input(m3)	Equipment	Input(h)
Precast concrete block installation	m2	Concrete	0.15	5-ton crane	0.09
Stone pitching	m2	-		0.6 m3 excavator	0.25
Vegetation mat	m2	-		0.6 m3 excavator	0.031

Table 4

Carbon emissions of materials and equipment.

Materials and Equipment	Unit	Carbon Emissions(kgCO2/Unit)
concrete	m3	346
0.6 m3 excavator	h	26.56
50 kW generator	h	22.66
5-ton crane	h	13.28
5-ton truck-mounted crane	h	13.28
6-ton dump truck	h	20.83

Table 5

Standards for calculating carbon emissions by process.

Process		Unit	Materials and Equipment	Carbon Emissions(kgCO2/Unit)(A)	Input Amount by Process(h/Unit)(B)	Carbon Emissions(kgCO2/Unit)(C = A × B)
(1) Embankment construction
Embankment		m3	0.6 m3 excavator	26.56 h	0.0137	0.364
Useful Embankment		m3	0.6 m3 excavator	26.56 h	0.0137	0.364
Sandy soil		m3	0.6 m3 excavator	26.56 h	0.0137	0.364
Cutting Slope	Installation of attachment nets	m2	50 kW generator	22.66 h	0.02	0.453
			5-ton crane	13.28 h	0.005	0.066
	Installation and dismantling of mechanical equipment		5-ton crane	13.28 h	0.04	0.531
	Squirt and paste		5-ton crane	22.66 h	0.051	1.156
			5-ton truck-mounted crane	13.28 h	0.051	0.677
			6-ton dump truck	20.83 h	0.051	1.062
Side grading		m2	5-ton crane	13.28 h	0.04	0.531
(2) Revetment construction
Precast concrete block installation		m2	5-ton crane	13.28 h	0.09	1.195
		m3	concrete	346 m3	0.15	51.900
Stone pitching		m2	0.6 m3 excavator	26.56 h	0.25	6.640
Vegetation mat		m2	0.6 m3 excavator	26.56 h	0.031	0.823

Table 6

Carbon emissions from small river maintenance projects.

Process	Number of Small River (n)	River Length (km)	CarbonEmissions(tonCO2)	Average Carbon Emissions per 1 km (tonCO2/km)	Average Carbon Emissions per Small River (tonCO2/n)
Embankment construction	124	196.89	789.7	4.0	6.3
Revetment construction			1226.9	6.2	9.7
sum			2016.6	10.2	16.0

Table 7

Carbon emissions by construction type for small river length.

Content		River Length					Average(Sum)
		0~1 km	1~2 km	2~3 km	3~4 km	4~5 km
small River	Number of small River (n)	38	60	24	3	1	(124)
	River length (km)	30.8	89.2	61.9	10.7	4.3	(196.89)
Carbon emissions(tonCO2)	sum	495.5	699.7	618.6	124.0	78.8	2016.6
	Embankment construction	281.8	229.2	211.9	42.0	24.9	789.7
	Revetment construction	213.7	470.4	406.9	82.0	53.9	1226.9
Average carbon emissions per small river (tonCO2/n)	sum	13.1	11.7	25.8	41.3	79.0	16.0
	Embankment construction	7.4	3.8	8.8	14.0	25.0	6.3
	Revetment construction	5.6	7.8	17.0	27.3	54.0	9.7
Average carbon emissions per 1 km (tonCO2/km)	sum	16.1	7.8	10.0	11.6	18.4	10.2
	Embankment construction	9.2	2.6	3.4	3.9	5.8	4.0
	Revetment construction	6.9	5.3	6.6	7.7	12.6	6.2

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