International Low Impact Development Conference 2020: Setting the Vision for the Next Twenty Years

Rapid urban sprawl has led to tremendous changes in land surface characteristics and urban stormwater problems have become serious, including urban flooding, catchment pollution, and receiving waterbody damage. Compared to residential areas, industrial areas have more stormwater problems due to higher proportions of impervious area and industrial pollution. This paper draws on a catchment in Auckland, New Zealand, which contains a developing industrial area. This is a case study example to demonstrate the development of a water sensitive design (WSD) approach that provides a stormwater resilient environment for industrial areas. To identify WSD’s physical characteristics, possibilities and constraints, document, and digital data from publicly available government databases, were obtained and analysed. The assessment of environmental and social elements helped identify the benefits of industrial water sensitive development (IWSD) in the case study area. Green and blue space and the natural water cycle are key for IWSD and the assessment identified the multi-benefits of water and non-water aspects that WSD could bring to industrial areas. This could help to encourage various industrial stakeholders to identify objectives and prioritise the features that they would like a WSD project to deliver. A comparison of two types of industrial development in the study proves that the reasonable synergy of urban green and blue space and the natural water cycle in initial planning and design stages is important for WSD implementation. This approach offers industrial development a new concept for achieving a stormwater resilient industrial catchment and finally leads to a sustainable water environment.

Low impact development (LID) model of stormwater simulation is ordinarily difficult to implement because it needs a lot of parameters. To improve simulation accuracy, based on the similar effect to the characteristic of the outflow, a detention tank model has been proposed to substitute the LID model in the simulation in this paper. The detention volume and the diameter of outlet nozzle obtained by the results of simulation can provide performance criterion for other kinds of LID facilities. In order to verify the actual effect of the detention tank model of LID, three typical LID facilities were selected to carry out the equivalence experiment of LID detention capacity. For vegetative swales, permeable pavements, and rain gardens, a cross-over study was done with slope 1%, 3%, and 5% as well as the recurrence period of 1-, 5-, and 10-year, respectively. The Nash-Sutcliffe efficiency coefficients were above 0.75, and the mean value was 0.9. It is indicated that using the detention tank model instead of the LID model is feasible in stormwater simulation. Moreover, an evaluation example is given. For other types of LID which haven’t involved in this paper, the detention and runoff process are similar. Therefore, they can also be replaced by the detention tank model according to their inflow and outflow characteristics. With the promoted detention tank substitution model of LID, it can be applicated in the stormwater simulation as well as evaluation of LID facilities.

With the acceleration of the urbanization process, and the increase of the impervious surface area, the problems of urban waterlogging are becoming more and more serious. How to effectively reduce the frequency of urban rain and flooding and its impact and destruction has become a major problem in urban construction. This paper selects the area around Guangming Phoenix New City Park in Guangming District, Shenzhen, constructs regional rainfall runoff model by SWMM model, and simulates the operation of the existing drainage network and the degree of waterlogging under six types of rainstorm return period of 1a, 3a, 5a, 10a, 20a, and 50a. Consequently, on this basis, four kinds of low impact development (LID) measures including separating the placement of bioretention cells, green Roof, permeable paving, and rain barrels, and combined arrangement as the fifth schemes, are used to stimulate the reduction of the regional total runoff and total peak flow. By the comparison, in the current state of study, LID combination has the best effect in reducing the total runoff, followed by the bioretention cells, permeable paving, and rain barrels; green roof is the worst. In terms of reducing total peak flow and delaying the time of peak flow, LID combination is the best, followed by bioretention cells, permeable paving, and green roof; the worst is rain barrels. In basis of this to consider the problem of combining low impact development measures with the sponge city special plan. In the future, it is expected to inspire the construction of sponge cities in south coastal cities, especially the low impact development measures.

Stormwater storage depth is generally considered as an evaluation criteria of LID effectiveness. According to this, a kind of detention tank model could be employed as a substitute model of LID facilities in case that stormwater modeling data are inadequate. Fuzzy synthetic evaluation is applied to evaluate the catchments’ fitness to LID facilities, and the evaluation factors consist of natural environment conditions, geographical location, land use, and the construction time of the region, and so on. About 107 catchments in Torch District, Zhongshan, South China, are taken as examples which are divided into 5 categories. The storage depth of both existing conditions and LID facilities applied of these 5 kinds of catchments with relatively complete modeling data is calculated. The additional storage depth serving as evaluation criteria represents LID performance in runoff control. Lack of measured or empirical data, the object regions are studied on whether LID facilities could be substituted by the detention tank model with an appropriate orifice. It indicates that the storage depth (H) of the same type catchment with the best LID facilities is similar, and the average H of each type catchments is given. The outlet flowrate of LID facilities is in close agreement with the results of the detention tank model. Finally, the proposed method is applied into a practical case.

The RainScapes program of the Montgomery County, MD, Department of Environmental Protection has developed and deployed a cost-effective and flexible set of tools in the toolbox of BMPs used to meet the County MS4 permit goals. In just over 10 years, with minimal staff, the program has overseen the addition of nearly 11 acres of RainScapes LID projects which control runoff from over 32 impervious acres. The program is achieving the fiscal promise of LID to be a cheaper than conventional means to manage stormwater in a retrofit environment. The multi- pronged approach provides technical guidance, training of professionals and the public, and continuous marketing both in person and on social media. RainScapes projects solve site level stormwater problems while providing a host of co-benefits that provide property owners with relief from increased lot to lot drainage in developed landscapes at a cost that the County can afford.

The purpose of this paper would be to study both the cost and hydraulic effectiveness of the rain gardens in New York City. In 2012, New York City started to use rain gardens throughout the city as a cost effective method to reduce the water flowing into the sewer system. The rain gardens initially have a higher upfront cost, with some contracts averaging $40,000 per rain garden, compared to the standard practice of piping or detention tanks but the maintenance cost will save in the long term. The current New York City sewer system also overflows during huge rain events so decreasing the amount of water or detaining some of it will help reduce the overflow and allow the system to last longer. Since 2012, there have been over thousands of rain gardens planted and still thousands more that will be constructed this upcoming spring. New York City Department of Environmental Protection has estimated that the first 90 rain gardens planted in Gowanus would be able to absorb over 8 million gallons of water each year. Over the last few years, there have been several design changes to help make them easier to construct and to allow for more stormwater collection. These changes, such as new types of rain gardens, allows the city to place rain gardens in more areas, reducing the amount of impervious area and replacing it with pervious area. The types of rain gardens that New York City currently uses are standard, green-strips, infiltration basins, and stormwater green street (SGS) all differ by their dimensions, siting criteria, amount of filtration, and detention rates. The green-strips are used for areas where there is limited room due to their reduced width. Infiltration basins are used for areas with lots of entrances because they can be designed with concrete tops for people to walk on. SGS are used in the streets where there is adequate space for them (very rare). The rain gardens not only help with increasing pervious area but they also help with water quality, helping remove nitrogen from the water before releasing it in to the sewer system. There have been several studies of areas with high chances of flooding due to the poor state of the sewer infrastructure with how much flooding they have. Recently, there have been rain gardens installed in these areas (such as Jamaica, Queens) and the amount of flooding will be measured to see how much the rain gardens have helped with the reduction of flooding. Knowing the amount of rainfall for each of the storms will also help in estimating the amount of inflow into the rain gardens. NYCDEP has several excel sheets available to calculate nitrogen removal and stormwater detention which can be compared to the experimental data from the field.

In the progress of urbanization, the natural permeable underlying surface is transformed into impervious underlying surface, which increases the surface runoff. Meanwhile, the overland flow is transformed into pipe flow with the construction of drainage system, which artificially organizes the confluence process. In order to reduce the impact of urbanization construction, the idea of low impact development (LID) has been widely recognized, which emphasizes the infiltration and storage functions of urban underlying surface through green facility construction. Runoff reduction effect of LID has been widely studied, but there is a lack of research on the runoff regulation capacity of drainage system in the LID construction region. We used a case study watershed in Beijing, China, in which LID facilities are widely implemented. The drainage system in this watershed is about two-year return period, the pipe network density is 5.90 km/km², and the storage volume is 12.6 thousand m³/km² (equals to 12.6 mm depth of runoff). Through the simulation analysis of Storm Water Management Model (SWMM), it can be found that before the implementation of LID practices, the drainage system can reduce the total and peak of surface runoff by 31.2% and 60.8%, respectively. And along with the increase of rainfall return period, the reduction effect of total volume decreased from 41.7% to 17.3%, while the reduction effect of peak flow had a slow upward trend. After LID construction, the reduction effect of total and peak flow changed to 34.3% and 56.9%, respectively. This study provides an insight into the regulation capacity of the drainage system in a LID construction region, which can expand the knowledge of urban stormwater management and LID evaluation.

The use of magnesium chloride deicer on pervious concrete may be harmful to its mechanical properties. However, carbonation of the cementitious materials might increase its resistance to MgCl₂ attack. Previous studies evaluated the efficacy of using carbonate laden water, specifically sodium bicarbonate solution treatments on pervious concrete, to accelerate the carbonation process and perhaps increase the material’s resistance to MgCl₂ impacts. In this paper, 43 pervious concrete cylindrical specimens were subjected to 10 days of treatment with either a 3.3% concentrated NaHCO₃ solution or tap water, as a control. After treatment the compressive strength, and elastic modulus were tested. For half the specimens these mechanical property tests were tested a few days after treatment, and for the other specimens the tests were conducted two months later. Therefore, age after treatment became an additional independent variable. The NaHCO₃ treatment seemed to decrease the early tested specimens’ compressive strength, but the same type of treatment appears to increase the material’s compressive strength values, if tested 2 months later. No statistically significant changes in elastic moduli were noted. These results might imply that the sodium bicarbonate treatment may need to be combined with an aging process, even after the treatment application, in order to be effective in terms of gain in compressive strength, but more research is needed, especially in order to verify the effectiveness of the treatment with respect to the resistance to MgCl₂ deicer attacks.

Stormwater infiltration systems, such as permeable pavement systems, are strategies for runoff reduction and flood mitigation, especially within urban environments, but there are still unknowns as to their efficacy in regions with low infiltration rates in the subgrade soils. This research developed a model for the infiltration of underground stormwater infiltration beds based on a percolation constant (k_p) and used the model on field data from two sites with soils that have low saturated hydraulic conductivity, one in Pullman, Washington, and one in Beaumont, Texas. The model was converted into a linear function and the data in Pullman fit this well. At the Beaumont site, the linear behavior diverged when the water in the infiltration bed was level with ponded water on the surrounding grounds, implying groundwater head impacts. In Beaumont, the infiltration rates had decreased after one year of measurement prompting interest in further long-term studies. The relationship between measured percolation rates (k_p) versus saturated hydraulic conductivity (K_H) was explored at these two sites and from the literature on other urban underground infiltration systems such as onsite wastewater treatment systems (OWS). These systems may function in urban areas where the soil has low saturated hydraulic conductivity, but the systems may be affected by partially saturated conditions in the surrounding area, and the percolation constant is typically much higher than the saturated hydraulic conductivity.

Low impact development (LID) techniques have been widely applied as stormwater control measures (SCMs) across the United States. LID SCMs aim to mimic the pre-development hydrologic patterns in order to restore the natural water cycle. Bioretention basins are one of the most common LID SCM, which take the advantage of soil retention capacity to infiltrate water back into the ground. The composition of the bioretention media significantly controls the system’s performance. Previous study performed in a lab using column and synthetic stormwater showed that the use of manufacture sand made of limestone provided improvement in the removal of heavy metals and phosphorous. To test how the limestone sand would perform on a full scale, a LID testbed was implemented at the University of Texas at San Antonio (UTSA). The testbed is composed of six parallel cells that receive the same amount of influent and discharge the effluent into a drainage system or allow water to infiltrate. Three different types of plants along with three different soil mixtures including the traditional sand media are being tested. Target water quality pollutants are suspended solids, heavy metals, and nutrients. This study is part of a long-term implementation and monitoring project that not only evaluates the system performance, but also answers the question of whether LID techniques’ capital and maintenance costs exceed those of the traditional designs.

Approximately 60% of all streams in the conterminous U.S. are ephemeral or intermittent. In the southwestern U.S., they make up more than 80% of all water courses. While dry during most of the year, ephemeral streams (also called arroyos) episodically convey runoff and sediment following intense summer storms. Arroyos provide a wide range of ecological functions such as habitat and hydrologic connectivity. Perhaps less notably, they also furnish ecosystem goods and services important for human well-being: groundwater recharge, water quality benefits, and recreation, to name just a few examples. Despite their vast spatial extent, dryland watersheds, and the arroyo systems they support have received less attention compared to their perennial counterparts. Under natural conditions, arroyos are in a state of dynamic equilibrium between sediment supply and transport. This equilibrium is disrupted by urbanization. In urban areas, impervious cover causes increased surface runoff. This, in turn, increases the magnitude and frequency of runoff events. At the same time, imperviousness prevents erosion, and runoff from municipal areas carries little sediment. Increased discharge and decreased sediment supply lead to channel degradation. In the past, runoff from urbanizing areas was often treated as a nuisance, and arroyos were seen as having one sole purpose: to get rid of stormwater as fast and efficiently as possible. This short-sighted view of ephemeral systems overlooks the multitude of ecosystem services they provide. Channel degradation has a profound negative impact on the welfare of dryland watersheds and the people that inhabit them. This study examines one arroyo in central New Mexico where urbanization-induced stressors have led to substantial degradation. Engineered elements designed to increase channel stability have had the opposite effect and exacerbate the problem. Important ecosystem services provided by the stream are identified, and possible restoration strategies are discussed. This example demonstrates that low impact development in a semi-arid setting requires rethinking of traditional engineering approaches.

This paper describes the development of a complex modeling system used for planning, design, and evaluation of sponge city construction projects in Zhenjiang City, Jiangsu Province, China. This modeling system adapts two models to simulate hydrology and pollutant (point source and non-point source) transport in watersheds. SWMM is used for urban watersheds and HSPF is used for rural watersheds. Another two models are used for receiving waters. HEC-RAS is used to simulate hydraulics and water quality in one-dimensional rivers and EFDC is selected to simulate three-dimensional hydrodynamics and water quality in three rivers and Jinshan Lake. This paper discusses the coupling process between watershed models and receiving water models, as well as calibration and confirmation for each sub-model. Finally, this study uses TMDL (total maximum daily load) process for this modeling system to evaluate the performance of water quality improvement in receiving waters after LID (low impact development) projects implementation. Effect of sponge city construction projects on water quality improvement in receiving waters is analyzed from modeling results and further pollution control work is suggested for the next-phase task of sponge city construction.

Chinese central government started the “ Sponge City” Initiative (SCI) in 2014 to offset the adverse impacts of urban developments and to tackle many water-related problems. Five years into the program, hundreds of cities have started SCI with more than three million acres of land to be retrofitted/developed to meet SCI goals by 2030. By emphasizing stormwater management practices with “ natural solutions,” many positive results have been achieved while the long-term success gained more and more focuses. Two major challenges include operation and maintenance (O&M) and stormwater fees. Major O&M challenges including: (1) shortage of O&M regulations and standards; (2) limited experience in large scale and under various conditions; (3) training for different groups; (4) PPP specific concerns; (5) department coordination; (6) public motivation of adoption; (7) ownership issues; (8) documentation during planning, design, and construction; (9) O&M monitoring and evaluation, etc. This study discussed the O&M challenges in financial, technical, and management aspects. Selected cases, such as O&M in Chizhou pilot cities, is used as examples. Moreover, the long-term funding stream for SCI is also very important. Since most private sectors are lack of interest in investing in Sponge City projects, stormwater fees may be an important source to financially support the on-going large-scale constructions as well as intensive O&M needs. This research studied the implementation of stormwater fee in the U.S. and compared the readiness of a stormwater fee system in China. The (1) fee coverage, (2) amount, (3) calculation method, (4) public readiness, (5) establishment of the fee structure, and (6) possible obstructions are discussed.

The Bioinfiltration Traffic Island (BTI) is a bioinfiltration rain garden that was retrofitted off an existing traffic island in 2001. Having been monitored since 2003, the BTI has quantitative hydrological data collected for the past 15 years, making it a very valuable dataset for an in-depth analysis of the performance of the site. The initial analysis comprises of a high-resolution analysis of rainfall event frequency along with resulting performance at the bioinfiltration rain garden. All rainfall events within the 15 years of collected data was discretized in to 2.5 mm, 2-h bins. The binned rain events were then analyzed using a mass balance approach to understand how the different hydrological elements contribute to the ability of the site to treat incoming stormwater runoff. Each component of the hydrological cycle within the BTI will be studied in detail and over different types of rain events. The second part of the analysis focuses on assessing the intensities of each of the recorded storms to understand its influence on the performance of the rain garden. Preliminary results show that, between 2003 and 2018, there were 1,202 recorded events, and 82% of them were less than 25 mm. Approximately 16% of all observed events resulted in substantial overflow. The overall analysis provides lessons into system components and aims to understand the interaction of the different hydrological elements within the rain garden. The objective is to use the findings in designing green Infrastructure systems that can be optimized in their ability to manage and treat incoming stormwater.

In recent decades, many cities in China and across the world have been suffering from the flooding and rainwater waterlog problems. Campus, being regarded as the innovation base and green hub of cities, could play significant role not only for the mitigation of stormwater problems but also for the environmental education. Since 2009, campus of Tsinghua University in Beijing has been used as a lab for stormwater management teaching and research, and it was titled Sponge Campus Initiatives after the concept of Sponge City was widely adopted. During the past 10 years, in total over 30 innovative design case study were proposed in Tsinghua campus and 4 of them were realized. These works demonstrated rich innovative design considerations combining water issues with benefits such as campus history, social life, landscape aesthetic, community regeneration, and environmental education. Before these pioneering and frontier works there was no such way in Chinese universities and education programs. Besides, this decade of teaching in the course of landscape hydrology has borne rich academic fruits, including papers, books, and awards of national and international levels. The most recent one is the 2019 ASLA Students Excellent Award and the 2019 Finalist of the Landscape Innovation Award of Landscape Institute of U.K. with the research of “ Monitoring Design: Stormwater Management Process Visualization and Evaluation” of Shengyin Yuan. This paper intends to introduce the development of landscape hydrology course and Sponge Campus Initiatives in Tsinghua University showing the way to combine campus stormwater management and landscape planning and design.

Over the last decade, there has been a tremendous increase in the usage of AI technologies for hydrological and hydraulic modelling on the application of water resource management. In early model stage, AI methods were used primarily for prediction and forecasting, utilizing quantitative data. With SCADA and sensor applications with internet of things (IOT), AI technologies have increasingly been used for the incorporation of qualitative and subjective information into real time monitoring. With rapid calculation of model results and decision support systems (the AI process), the drainage system can control hydrological devices such as pumps, valves, or gates to adjust or control the flow rate of a drainage system as well as urban drainage ability to model complex hydrological systems in an integrated fashion. There are three parts to the AI applications on blockchain water platform (BWP). From the upstream of BWP, sensors and meters will be able to collect hydrological data such as rain gauge, flowrate, pressure in pipes, and key indicators of water quality. This information will input into hydrological and hydraulic modelling, many engineering modelling software have been used for predicting flow with the scenario analysis. The engineer will be able to run the model 24/7 to collect data from the studying watershed. With continuous updated results, they will be able to obtain real time monitoring. Finally, through the results from the modelling system, operation procedure, drainage analysis, and the decision support system (DSS), control devices such as pumps, valves, and gates will have the ability to be controlled wirelessly. The AI process will allow the urban stormwater drainage to optimize their operation and produce the most efficient results for urban drainage. With this approach, AI will link the sensor data by internet of things (IOT) into the model with model analysis. The overall benefits of using AI storm water management include an increase of energy efficiency, a decrease in flood risks, and a decrease in cost. The system is operating in both Guam, U.S., and southern China, since spring 2018.

The city of Johannesburg’s latest stormwater management by-laws encourage the use of sustainable drainage systems (SuDS) and rainwater harvesting (RWH) is one of the proposed SuDS options for residential complexes. Also, RWH is an essential element of effective water conservation where stormwater is utilised to augment water supply. However, the exploitation of this additional water resource in the City to date is very limited. This paper seeks to illustrate the extent to which RWH reduces post-development peak flows and corresponding reduction in domestic water demand. A rainwater harvesting system was designed for a 7.15 ha site in Soweto, Johannesburg. The proposed development will alter current and natural drainage patterns of the site as approximately 59% of the total surface area will be made impermeable. The proposed RWH system reduced the post-development peak runoff flow by 25%. Additionally, an annual saving of 13.8% of the water required for toilet flushing was achieved.

The increase in impervious surfaces accompanying urban development in the recent decade has caused an increase in the volume of stormwater runoff and pollutant loads flowing downstream to receiving waters. In response to increased volumes of impaired stormwater runoff, there is a growing use of stormwater best management practices (BMPs) in urban areas. As such, there is a need to monitor the concentration and load of pollutants that enter receiving streams. This monitoring aids in decision-making to improve the efficiency of the BMPs in already use. In addition, monitoring may provide a case for increasing the number of BMPs to reduce the pollutants entering downstream and improving the efficiency of the existing BMPs. The purpose of this study is to evaluate stormwater runoff quality in various creeks in the city of Charlotte based on precipitation, to forecast future conditions and the associated needs for BMPs.