Application and evaluation of LID facilities in sponge airport, China

According to the Boeing Current Market Outlook report, passenger traffic growth will continue to rise at an average of 4.1% between 2013 and 2032, while cargo traffic will grow at 5.0% (Airplanes 2013). The size and quantity of airports are quickly on the increase. Efforts to minimize harmful impacts on the environment already dominate the design, construction and operation of airports and airports are expected to be environmentally responsible. And most new or renovated airports are adopting environmental management programs (Carvalho et al. 2013; Jaiyeola 2017). The traditional airport construction mainly hardens the road surface, which destroys the original hydrological cycle around the airport. The short-term heavy rainfall brings huge pressure to the airport drainage network (Peng et al. 2020). Therefore, it is of great significance to explore the concept and application of the sponge airport for the development of airports in China. The United States proposed ‘Low Impact Development City and Green Buildings’. O'Hare International Airport has achieved 90%–95% rainfall emissions through the full greening of the roof (Li 2018). The Australia put forward ‘Water Sensitive Urban Design’ (Liu et al. 2016). Britain proposed ‘Sustainable Drainage Systems’, which mimic natural processes to manage floods (Gimenez-Maranges et al. 2020). Singapore's ‘source-process-end’ drainage system has multiple benefits. China's research started late. The Beijing Daxing International Airport adopted a secondary drainage system, the total capacity of rainwater collection facilities will reach 2.8 million cubic meters. According to statistics, since the airport opened, for more than seven months, the natural collected water in the airport has reached 700,000 square meters, and the sewage treatment rate and reclaimed water utilization rate have reached 100% (Zhang 2019). The sponge construction measures taken by Qingdao Jiaodong Airport include ecological roofing, permeable paving, concave green space and vegetative swale. Two-thirds of the GTC roof of the T3 terminal building of Beijing Capital International Airport is greened. In the construction of sponge airports, rainwater runoff control is realized by increasing the green area of airports, building large-capacity water storage facilities and green roofs, and emphasizing the treatment and reuse of rainwater resources.

Many achievements have been made in the study of LID facilities, including (1) the setting of LID parameters in different regions (Xu et al. 2016; Wang et al. 2019; Zhu et al. 2019), (2) sensitivity analysis of LID parameters (Weaver & Nachabe 2019; Madrazo-Uribeetxebarria et al. 2021), (3) optimizing LID layout (Hu et al. 2015; Chen et al. 2019; Gao et al. 2021) and (4) evaluation of LID control effect and so on (Cipolla et al. 2016; Wang et al. 2020; Ekmekcioglu et al. 2021). Through consulting the literature, it is found that the utilization rate of permeable pavement is highest, followed by bio-detention facilities and green roofs (Qin et al. 2013; Lei 2015; Li et al. 2016; Wu et al. 2017). The model of Kansas, USA, was built based on SUSTAIN (System for Urban Stormwater Treatment and Analysis Integration Model), and it was found that bio-detention facilities and permeable pavements can reduce the annual runoff by nearly 70% (Lee et al. 2012). Based on SWMM simulation and analysis of hydrological response of LID facilities in rainfall, it was found that the study area was still affected by floods after LID facilities renovation. The most reasonable LID facilities combination was bio-detention facility, permeable pavement and vegetative swale (Mei et al. 2018). The Reynoldsburg commercial parking lot in Ohio used a bio-detention facility and permeable pavement to complete the water permeability transformation of the parking lot. The study showed that the rainwater runoff depth of the transformed parking lot has been reduced by 47%, and the peak flow rate has been reduced by 56% (Tirpak et al. 2021). Permeable paving can not only replenish groundwater, but also reduce rainwater runoff. And study has shown that permeable pavement can serve as an effective pretreatment for stormwater harvesting schemes (Winston et al. 2020). LID facilities layout structure and layout area size both had an impact on urban rainfall runoff, and reasonable layout of LID can effectively alleviate urban waterlogging to a certain extent (Wu et al. 2021). An optimal combination of bioretention, subsurface infiltrating systems, rainwater harvested cisterns, and the porous pavements can reduce about 60% and 76.6% of in and out-of-village runoff, respectively (Jokar et al. 2021). The combination of green roofs, rainwater tanks, grass ditch and permeable pavements has the best reduction effect on runoff and pollutants concentration, and the combination of green roofs, rainwater tanks, rainwater gardens and permeable pavements has the best reduction effect on peak flow (Rong et al. 2021).The bioretention pond can not only effectively decrease rainwater runoff, increase rainwater infiltration and reduce the peak flowrate of rainwater runoff, but can also intercept certain amounts of the pollutants such as suspended particles, nutritious matters, heavy metals and so on (Xue et al. 2018). Different LID combination schemes are simulated based on the SWMM, the results show that the combination of green roofs, rain barrels, grass ditch and permeable paving has the best effect on reducing runoff. And the combination of green roofs, rain barrels, rain gardens and permeable pavement has the best effect on reducing peak flow (Rong et al. 2021).

In general, LID facilities have advantages in restoring the natural hydrological cycle, but there is less research on the application of LID facilities in sponge airport construction. This paper studies the application and effect of LID facilities in airports. On the base of existing construction theories and experiences, the airport hydrological conditions, the special needs of each functional area of the airport and the construction goals of the LID facility, this study designs a LID facility application program suitable for this airport. This study also constructs a SWMM model to simulate and analyze the application effect of LID facilities in the airport. The research results of this study provide a reference for the construction of a LID facility at the airport, and provide a theoretical reference for planning and construction of LID facilities at airports in China.

It is not only necessary to plan the construction of the sponge airport scientifically and reasonably, but also to ensure the feasibility of construction, so that the airport can cope with extreme rainstorm weather and ensure efficient and safe operation of the airport.

• (1)

  Pay attention to protecting the ecological environment. First, it is necessary to increase the area ratio of regional greening and improve the problem of poor rainwater infiltration caused by many buildings and hardened pavement. Secondly, initial rainwater pollution problems should be paid more attention, and rainwater can be preliminary purified by designing methods such as infiltration facilities to reduce rainwater pollution.

• (2)

  Rational and full utilization of resources. For example, Lyon, France, advocated the management of rainwater according to local conditions, its full use of its own terrain to collect rainwater, and it has achieved collection without drainage pipes. For areas with well-developed natural water systems, it is necessary to make full use of the natural water systems to realize rainwater storage without destroying natural water systems, such as Liupanshui Wetland Park.

• (3)

  Rainwater is solved on the spot. Solving rainwater on the spot, instead of transferring rainwater to the downstream area, can not only alleviate downstream drainage pressure, but also help restore the water environment in this area.

• (4)

  LID facilities are suitable for local hydrological conditions. For areas with heavy rainfall, attention should be paid to the stagnation, discharge and purification of rainwater. The areas with less rainfall and relatively scarce water resources should pay attention to the infiltration and reuse of rainwater. In areas with high groundwater level and poor water permeability, the use of infiltration facilities should be reduced, and rainwater retention and purification should be emphasized (Zhuo et al. 2018). That is, plan and select LID facility combinations according to local conditions, and reasonably determine the control indicators for low-impact development (Ministry of Housing & Urban-Rural Development 2014).

In addition, each functional zone of the airport has special requirements, which makes it impossible for the airport to completely copy conventional buildings in sponge construction. When planning LID facilities for the airport, on the one hand, it should meet the needs of flood control and drainage, foundation waterproofing and bird damage prevention. On the other hand, it is necessary to ensure that the initial rainwater flows into the downstream rainwater system after being treated.

The construction of LID facilities at airports should aim at restoring the pre-development hydrological conditions and meet the needs of flood control and drainage at airports. The control objectives of LID facilities planning and construction mainly include total runoff, peak volume, runoff pollution, rainwater resource reuse (Ministry of Housing and Urban-Rural Development, 2014) and waterlogging prevention (Table 1).

In general,the technical route and frame of this study is shown in Figure 1.

LID facilities have remarkable effects in terms of stormwater control (Lee et al. 2012; Winston et al. 2020; Jokar et al. 2021; Tirpak et al. 2021), regional groundwater replenishment (Du et al. 2019), rainwater purification (Wu et al. 2018; Xue et al. 2018), rainwater reuse, environmental beautification, and so on. It not only helps the regional hydrological mechanism to be closer to the pre-development state, but also has certain ecological value, social value and economic value. The hydrological and water quality control effect of LID facilities is influenced not only by natural conditions such as weather, climate and soil, but also by its own structural characteristics. The application effects of each LID facility are summarized (Table 2). The runoff reduction rate of bio-detention facility is 50%–97%, the peak volume reduction rate is 20%–90%, and the TSS removal rate is 55%–100% (Li & Davisa 2009; Xu et al. 2017; Jiang et al. 2018). The runoff reduction rate of green roof is 70%–90%, the peak volume reduction rate is 88.9% (Berndtsson et al. 2006; Carpenter & Kaluvakolanu 2011). The runoff reduction rate of permeable pavement is 40%–90%, the peak volume reduction rate is 28%–56%, and the TSS removal rate is 58%–94% (Fach & Geiger 2005; Ahiablame et al. 2012).

Taking the east working area of the airport as an example, which is located on the northern coast of China (Figure 2). The climate in this airport is characterized by a typical warm temperate semi-humid continental monsoon climate, with hot and rainy summers, cold and dry winters. The annual precipitation is 500–700 mm. In this study, the drainage network design data (Figure 3), the elevation data and the CAD drawing data of this airport are combined to accurately divide the sub-catchment areas of the airport study area. The SWMM model of this airport east working area is constructed. The area can be generalized into 819 sub-catchments, including 871 nodes, 872 pipelines and 4 reservoirs.

t—— rainfall duration, min;

P——design return period, year.

The rainfall pattern is expressed by peak coefficient r (the ratio of the peak time to the rainstorm time). The design rainstorm process with return period P = 3a, P = 5a, P = 10a, peak coefficient r = 0.375 and rainstorm duration of 120 min are calculated (Figure 4).

The east work area of the airport mainly includes the parking lot, the access road, the public area and other work areas. In addition, most of the roof rainwater of the terminal building is collected by the eastern rainwater system while the rest is collected by the flying area rainwater system. The east work area covers an area of 1,842,500 square meters, which is mainly divided into two parts according to the position of the outlet. The total catchment area corresponding to the outlet 1 is 663,200 square meters. The total catchment area corresponding to the outlet 2 is 930,000 square meters. The land use types in the east work area of this airport include green areas, pool, parking, buildings and road, as shown in Figure 5. However, in the actual operation of the airport, the area corresponding to outlet 1 is prone to water accumulation and other problems. The catchment area of outlet 1 is selected as the research area for the effect of LID layout in the east work area.

The different functional zones of the east wok area have different requirements for rainwater runoff control. The roof area of the terminal is large, and its initial runoff pollution concentration is high. The demand for water resources in the terminal building is also large. Thus, the rainwater runoff control of the terminal should pay attention to rainwater purification and reuse. The roof of other buildings besides the tower can increase the proportion of greening area by realizing roof greening. The traffic flow of the parking lot and its entrance and exit is large. The rainwater runoff control will directly affect the convenience and safety of passengers entering and leaving in the airport. At this time the rapid discharge and seepage of rainwater should be emphasized. Depressions with abundant plants can be built in public green spaces to achieve water storage, at the same time it can also enhance the green landscape effect of the airport. The specific application of LID facilities in different functional zones is shown in Figure 6.

The value of the LID parameters in the model is mainly determined according to the SWMM user manual and existing research results (Table 3).

The LID facilities application plan (Figure 5) in the east work area of the airport has already shown that the LID facilities can be deployed in different functional areas. Considering that the more types of LID facilities, the more unfavorable the construction. Therefore, three types of facilities with excellent control effects, namely permeable pavement, roof greening and biological retention facilities, were selected to improve the rainwater regulation ability of the east work area in this airport. According to the different proportion combinations, three different layout schemes were designed (Table 4). Due to the small proportion of green roof area, 80% of the layout ratio of green roof will not be changed when designing LID combination scenarios. The permeable pavement and bio-detention facility use 70 and 50% as the standard floating fixed steps length respectively, and then combining to obtain each scenario. Since 10% is selected as the fixed step size, the simulation results of key node J-1 are not obviously different, so the fixed step size is modified to 20%.

According to Figure 5, there are two outfalls in this area. Based on the simulation analysis of the SWMM model, it is found that the drainage capacity of the rainwater pipe network in the area corresponding to outlet 2 is better. Therefore, it is of representative significance to lay out LID facilities in the area corresponding to outlet 1. The node J-1(as shown in Figure 3) is a typical node. The runoff process of node J-1 (Figure 7) are drawn under different design rainstorm recurrence periods for each LID facility combination deployment scenario based on simulation results. It can be clearly seen that the LID facilities combination has a certain control effect on design rainstorm with different return periods. As the proportion of LID facilities increases, the control effect of LID combination is enhanced. With the increase of rainfall intensity, the control effect of LID facilities combination gradually weakens, which indicates that LID facilities can only alleviate the problem of runoff retention caused by moderate and light rain. The results also show that these three LID measures affect the runoff generation process more, rather than the confluence process of the river basin. This means these three LID measures are more suitable as source measures for rainwater control rather than process measures (Yang et al. 2018).

The simulation results of total runoff, peak volume and peak present time of the three LID scenarios under the designed rainstorms with different return periods are as follows (Table 5, Figure 8).

The different LID scenarios have a weakening effect on the total runoff, peak present time and peak volume under the design rainstorm with different return periods. For high-frequency rainstorm that occurs once in three years and once in five years, the degree of runoff process weakening increases with the enlarging of the LID ratio in the study area. When the layout ratio of LID facilities is the largest, the maximum reduction rate of total runoff and peaking volume is 30.89% and 25.58%, and the peak present time delay rate is up to 28.57% (Table 5). When the layout ratio of LID is smallest, the minimum reduction rate of total runoff and peaking volume is 12.11% and 13.94%, and the peak present time delay rate is down to 12.05% (Table 5). For low-frequency rainstorms that occur once-in-a-decade, the degree of runoff process weakening in the study area increases with the enlarging of the LID ratio. But the overall reduction effect is not obvious (Yang et al. 2018), especially the effect of delaying the peak present time is very limited. This is because, in the deployed LID facilities, only the bio-detention facility has a good rainwater retention effect, and the total area of the bio-detention facility is small. When the layout ratio of LID is largest, the maximum reduction rate of total runoff and peaking volume is 17.96% and 14.95%, and the peak present time delay rate is up to 6.12% (Table 5). When the layout ratio of LID facilities is smallest, the minimum reduction rate of total runoff and peaking volume is 9.09% and 8.81%, and the peak present time delay rate is down to 2.04% (Table 5). Among them, there is a 46,500 square meters difference between the largest proportion and the smallest proportion of permeable pavement. The area of the bio-detention facility varies by 46,300 square meters. Some research results show that for shorter return-period storms, reduction in peak flow and runoff volume achieved by combining these measures is up to 66.2% and 49.4%, respectively, while the reduction in runoff volume is only 11.5% and no considerable reduction in peak flow was achieved for extreme floods (Chang et al. 2016). And the reduction rate of rainwater facilities for the total runoff of rainfall in different return periods will decrease with the increase of the return period of rainfall, and the reduction rate is 37.76%–47.25% (Zhang et al. 2021). Due to the special needs of airport functional zones and the large proportion of impervious areas, the results of this study are different from other studies. Furthermore, the difference in the layout area of LID facilities is also the reason for the different results.

In summary, there is no obvious reduction effect of LID facilities under low-frequency rainstorms (Yang et al. 2018). However, the investigation found that the parking lot area of the airport is prone to waterlogging under low-frequency heavy rain. Therefore, it cannot ensure the safe operation of the parking lot only relying on LID facilities under low-frequency heavy rain. Now, taking the parking lot area as an example, three working conditions are designed, and the flood control effect of the three working conditions in the parking lot under the once-in-decade rainfall scenario is analyzed. The specific contents of each working condition include: working condition 1, only changes the diameter of the open channel (to 1.3 times of the original pipe diameter). Working condition 2, only deploys LID facilities (refer to scenario 3). And working condition 3 is a combination of the first two conditions. The simulation results show that the number of overflow nodes in working conditions 1,2 and 3 are decreased by 7,8 and 13, respectively under the once-in-a-decade rainfall. Therefore, there is no significant control effect on rainstorms and floods only relying on increasing the amount of grey infrastructure or laying LID facilities under low-frequency rainstorms.

This paper studies the design and application of LID facilities for sponge airports, and analyzes the reduction rate of LID facilities using the SWMM model. The planning and an appropriate LID facilities layout scheme should be adopted at sponge airports according to the main problems of airports in different regions.

• (1)

  Based on the construction theory and achievements of typical cases at home and abroad, this study discusses the principles and goals of sponge airport construction, and then designs suitable LID facilities according to the application effect of various LID facilities and the actual conditions of the airport. The airport is located in an area that has abundant rainfall in summer months, and there are many farmlands and rivers around the airport. Therefore, the construction of LID facilities should emphasize the infiltration, storage, drain of rainwater, and the use of natural water.

• (2)

  LID facilities mainly emphasize the source control of rainwater, which has good runoff control effect when dealing with high-frequency rainfall, and can effectively reduce the total runoff, peak volume and delay the peak present time. LID facilities are also of great significance for flood control in airports.

• (3)

  LID facilities can only alleviate the problem of runoff retention caused by small and moderate rain, with limited control effect on heavy rain. In order to cope with the frequent occurrence of extreme rainstorms in recent years, LID facilities should be used in conjunction with rainwater pipelines, pumping stations and reservoirs (Chang et al. 2016) to form a rainwater drainage system of source reduction-process control-terminal control and storage to ensure the safe operation of the airport and reduce the risk of airport flood disasters.

Different from conventional buildings, each functional zone of the airport has special requirements, which makes it impossible for the airport to completely copy conventional buildings in sponge construction. Therefore, the application of LID facilities in airports still need further exploration and research. In addition, how to build a scientific and reasonable index system evaluating the application and determining the best deployment ratio of airport LID facilities still need further research.

This study was funded by [Tianjin Municipal Education Commission Scientific Research Plan Project] grant number [2019KJ125].

The authors wish to thank the anonymous reviewers for their comments and suggestions and people who have supported this study.

We declare that we have no financial and personal relationships with other people or involved with any organization or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this paper.

All relevant data are included in the paper or its Supplementary Information.