International Low Impact Development Conference 2023: Adaptation and Resilience for a Changing World

The City of Fayetteville has developed a Watershed Master Plan program that uses 1D and 2D riverine and collection system modeling to proactively identify and develop flood mitigation projects across the city. The multi-million-dollar Russell-Person Street Bridge and Stream Improvements project was a recommended result of this modeling work. The project mitigates flooding for a large, marginalized area of downtown Fayetteville, includes nature-based solutions, and serves as a capstone project for the Blounts Creek Watershed as well as the entire Watershed Master Plan program. Local leaders have supported grant initiatives and actively backed funding for the project. They understand that a comprehensive project and program that supports resiliency and equitably uses City resources must have inter-governmental and cross-departmental collaboration and public support.

The effect of climate change on the Mediterranean landscape requires environmental restoration projects based on interdisciplinary research methods that consider the integration of different evolving aspects mainly in urban contexts where the increase of severe rainfalls is significantly impacting citizen behaviour. Starting from a case study of Strada Statale 7 bis in South Italy (a boundary between four municipalities: Melito di Napoli, Sant'Antimo, Giugliano in Campania, and Aversa) in which flooding, since last twenty years, exposed the road system fragility, composed by a main road and its sidewalks to allow normal citizen activities. A multidisciplinary research group proposed an innovative re-design of the street aiming to improve the quality of life during stormwaters. This work explores the possibility of importing best practices from North America to Southern Italy and integrating them into the hydrological approaches suggested by Italian law for risk mitigation.

Municipalities in the United States have partnered with the private sector to address increasing environmental challenges posed by stormwater runoff. Low impact development (LID) can be used to establish green infrastructure assets, which can ultimately offer unique opportunities for social equity and workforce development. A sustainability triple-bottom-line framework was used to examine the clean water partnership (CWP), the first Community-Based Public Private Partnership (CBP3) in the US focused on implementing LID projects in Prince George’s County, MD. Results show that adopting a community-driven approach to delivering and maintaining stormwater infrastructure assets can provide long-term sustainable benefits to host communities. This study also highlights the role of outreach programs in enabling minority inclusion and workforce development, especially when it comes to delivering and maintaining green infrastructure assets.

Technology and design principles falling within the modern category of low impact development are not new methods, but are re-discoveries of old technological principles, retrofitted into the framework of modern infrastructure. Low impact development technologies first developed during the Neolithic Revolution are well-documented in historical and archaeological records. Since 10,000 BC, most of the world’s population lived in low-density rural areas, where LID technologies were readily implemented for convenience and survival. Around 4,000 BC, populations slowly migrated into densely populated areas, where new centralized infrastructure began to replace traditional LID technologies. Around 1,750, a significant shift in population concentration to urban areas occurred coinciding with the Industrial Revolution. During this time, centralized infrastructure designed to deal with the issues of urban living nearly replaced LID technologies. This paper examines mass urbanization as a catalyst and inhibitor of LID technology from the agricultural revolution to the beginning of the Industrial Revolution.

The Industrial Revolution sparked mass urbanization leading to ongoing migration trends toward urban areas. However, high-density populations pose a sustainability challenge for infrastructure, particularly with centralized water management systems historically relied upon by cities. With urbanization expanding, these systems are becoming overburdened, highlighting the need for more sustainable approaches. As a result of the environmental movement in the 1960s and 1970s, low impact development technologies emerged as a multifaceted and sustainable solution to address the limitations of conventional water management techniques. This study examines the historical and cultural context that revived traditional LID technologies in the mid-twentieth century to address sustainability concerns amid the continuing growth of mass urbanization.

The conventional approaches for flood mitigation can be divided into two categories, namely structure approaches and non-structural approaches. However, both measures have their limits, such as local-scale impact, high cost of implementation, and limited capability to address flood hazards financially. In order to overcome these limits, this paper demonstrates an effective framework of low impact development (LID) in preventing urban flooding at the watershed scale. A practical watershed in Houston, TX, was chosen as a case study. The strategies provided based on the framework shows the maximum potential for flood mitigation and improvement of rainfall-runoff performance. Furthermore, the placements of LID facilities maximize the benefits of flood reduction near to the flood control locations.

Traditional asset management has included gray (man-made) assets but the increasing interest in and use of green infrastructure necessitates an approach to asset management that integrates green and gray assets together in one asset management framework. This approach allows more holistic management of assets. It is important to understand why green assets should be incorporated within a gray asset management program, how to incorporate them, and some of the special considerations in incorporating green assets within the traditional approach. When green and gray are incorporated together there is the opportunity for significant benefits. Resources are available to help develop an integrated asset management program including an on-line green asset database and an on-line integrated asset management framework that can assist entities in creating their asset management programs.

Residential water consumption in city has positive correlation with population density, urbanization, and living standards. Therefore, water consumption in mega city such as Seoul, Busan, and Sejong in South Korea has increased. For a stable and efficient water supply, prediction of water consumption is important to design, construct, and operate water supply facilities. Common residential type in South Korea is large-scale apartments having more than 1,000 households. Water cost is divided into personal and public usage and imposed to households. Personal usage is used inside the households for living, however, public usage is cleaning and gardening. In this study, real-time water meters are installed in a large-size apartment located in Sejong and water usage patterns of households divided into weekday and weekend are analyzed. Also, the amount of public water usage in the apartment is measured. To reduce public water use, low impact development (LID) facilities are installed and the effect of LID facilities are evaluated. As a result, the peak of water consumption in a day occurs when preparing go to work and right after returning home. However, during the weekend, the maximum water consumption does not appear until almost noon. Using the measuring data, water consumption is predicted and supply schedule is proposed.

The present paper assesses the quickest and most inexpensive dredging measure for flood mitigation in Bangkok. To assess the performance gained from the accepted dredging practice, the existing Thammasat University Storm Sewer (TUSS) system in the greater area of the city has been adopted as a study SS system. Modeling of this TUSS system has been then established using a widely-used storm water management model (SWMM). Assuming various wasted-deposit depths ranging from 0 to 30% of pipe diameters for the dredging representation in the SWMM, results of model applications to the 1st and 2nd quartile storms for 25-year return period have shown that the dredged system manages the flooding better than the uncleaned one. The flooding volume, peak, and duration of the assessed system could be reduced up to 40, 55, and 73% of those for the based one. Further considerable decrease of these flooding properties would be also achieved if the existing system was restored to be the new one. Additionally, considering the 2nd quartile flooding hydrographs with multiple-peaked pattern is suggested for managing the inundation.

Underground chamber storage is a popular solution to meet stormwater detention, retention, and water quality requirements in urban settings, however little is known about the long-term viability of geotextiles used as filter fabric to remove stormwater-borne pollutants. Nationally recognized performance verification protocols such as the Washington State TAPE program and the New Jersey Department of Environmental Protection (NJDEP) protocols do not recognize buried filter fabric as an approved treatment solution due to maintenance and access concerns, however, these practices are still widely used across the United States. Issues such as clogging, biofouling, and operations and maintenance feasibility are not wholly understood and resolved. This research examines the long-term water quality performance and maintenance triggers of an underground chamber storage system with filter fabric. Pollutant removal trials were conducted in a laboratory setting per the NJDEP filtration protocol in two phases: the first using inorganic sediment per the protocol, the second phase with the addition of organic sediment and hydrocarbons. Adding hydrocarbons and organics have been demonstrated to clog filters up to 10× faster than with inorganic sediment alone and can better predict the long-term, in situ filter fabric response. Results suggest filter fabric may clog quickly if hydrocarbons and organics are present in stormwater. In the absence of performance verification under a recognized protocol, understanding the response of filter fabric to long term pollutant loading can better inform designers and regulators on how and when to use these devices.

Permeable pavements offer an alternative to conventional low impact development (LID) stormwater control measures. A project is undertaken in San Antonio, TX, evaluate the environmental benefits of permeable pavements in parking lot areas placed over the Edwards Aquifer recharge zone. It involved four permeable parking lot surfaces, namely permeable asphalt, plastic grid pavers, permeable interlocking concrete pavers, and permeable concrete. In addition, a conventional (i.e., impermeable) asphalt concrete parking lot was considered to serve as the control for the experiment. Each parking lot had space for 8 cars, a granular base layer storage for handling a 50-year rain event, a drainage system directing the water to manholes from where it could be sampled. Instrumentation involved water samplers and water volume flow meters. Moreover, the surface infiltration rate was monitored to evaluate potential clogging. The water samples were tested for total and volatile suspended solids, metals, pH, conductivity, polycyclic aromatic hydrocarbons, bacteria, and temperature. A system to monitor the number of cars parked utilizing security cameras.

The Federal District of Brazil (DF) is located at the top of a plateau with occurrence of springs and small rivers. With the aim of restoring natural hydrological processes, modified by urbanization, and preserving water resources, which tend to suffer major impacts with increasing urban drainage flows, LID devices (low impact developments), and infrastructure such as detention or retention ponds have been proposed in DF. The stormwater monitoring group from Unversidade de Brasília (UnB), Maplu group, conducts studies monitoring, and performing hydrological simulations in several urban areas of DF. In this paper the main contributions of these studies are presented, showing the importance of applying LID devices, as well as the relevance of using hydraulic-hydrological simulations. The results found reinforce the idea that LID devices applied at the source are effective in reducing flood volumes and peak flows for frequent rainfall events. On the other hand, detention ponds may be necessary to reduce peak flows for longer return time rainfall events, but, because they are usually installed at the end of the drainage network, they do not always help mitigate flooding points.

Stormwater controls in urban environments that use plants are being promoted as green infrastructure. To better understand these controls and their relationship to the environment, soil fauna extraction was performed on a variety of stormwater controls from urban locations including rain gardens and detention basins. Urban wooded areas were also used for background comparisons. Additional metrics including bulk density, loss on ignition (LOI), and soil moisture were also performed on samples. Several ecological indices were calculated and statistically tested. Three groupings were identified for 27 samples collected over a two-year period: background (8), rain gardens (13), and other stormwater controls (6). Statistical testing of these groupings by the Shapiro-Wilk W test indicated several indices were considered parametric. A one-way analysis of variance of the number of taxa and the Shannon diversity index was considered significant (p< 0.05). Comparisons of sample enumerations and indices to the other soil metrics measured were poorly correlated. Specifically, analysis of organic matter to number of fauna or derived indices, while expected to, did not show a linearly increasing correlation; cited literature indicated that maximum organic content may not coincide with maximum fauna observations and further, the fauna extraction method used may have confounded this analysis.

Through its Green Continuum: Streets design guidelines (“The Continuum”), the City and County of Denver is implementing lower-impact low impact development on public projects in the right-of-way. The suite of green infrastructure tools outlined in the Continuum are intended to mitigate both stormwater runoff and urban heat island leading to cleaner, cooler, and more beautiful streets. The stormwater management approach is one of runoff reduction: infiltrating smaller, more frequent rain events carrying first flush pollutants into many shallow, pervious areas. This differs from the conventional, volume-based approach that has been in the city’s MS4 permit for decades. However, a “Runoff Reduction” pathway was added to Denver’s most recent MS4 permit that makes the control measures in the Continuum better suited for regulatory compliance. These control measures include shallow landscapes with no formal inflow/outflow, flow-through bioretention with little depression storage, and infiltration-only bioretention facilities. These proceedings will describe an Excel-based calculator that can aid in designing green infrastructure for regulatory compliance. The proceedings will include an overview of the runoff modeling and post-processing that underpins the calculator. This analysis includes development of regression equations that predict runoff with inputs available during design (e.g., soil classification, run-on ratio, geometry, etc.). The regression equations predicted runoff within 0.01 in. for a 0.6 in. design storm event in over 84% of 220,000 random green infrastructure configurations. While the calculator is developed for Denver’s regional climate and requirements, the proceedings offer a method for other municipalities looking to incorporate runoff reduction practices on right-of-way projects.

First-generation extensive green roof systems included only vegetation, growing media, and drainage materials. However, these simple systems can be too heavy for roofs that were not originally intended to support green infrastructure, and the growing media may not provide adequate stormwater detention to meet desired flooding mitigation targets. Today, many commercial green roof manufacturers and suppliers aim to increase the retention and detention provided by green roofs by using lightweight growing media alternatives. This study evaluates the hydrologic impacts of generic vegetated roof assemblies (VRA) that use ultra-lightweight and soilless materials—fleece, mineral wool, and a combined reservoir-detention system—throughout a complete growing season under the natural rainfall conditions in Toronto, Ontario. Discharge from test beds was continuously measured from July to November 2022 and compared to discharge produced by a conventional green roof assembly and an impervious roof covered with stone ballast. The total rainfall for the monitoring period was 219.2 mm, and the stone control retained 48% (105.4 mm). The green roofs improved retention, retaining an additional 73–95 mm of rainfall depending on the roof assembly. All green roofs provided some detention and decreased peak discharge. The extent of detention provided ranged substantially based on the VRA, particularly for large rain events. All green roofs drastically reduced peak flow, averaging greater than 95% regardless of the assembly. The best-performing system (combined reservoir-detention) retained 95% of all received rainfall, reduced peak flows by 98%, and had the greatest discharge delay (9.6 hrs) and duration (15 hrs). This work demonstrates that detention layers improve the hydrologic performance of a green roof system to varying degrees.

Inadequate stormwater infrastructure, rapid urbanization, and climate change are the three main drivers of intense flooding. This situation is worse in coastal areas where the effects of climate change are more severe and result in high-intensity storms and a rise in sea level. Houston, as a coastal city, is one of the most susceptible areas in terms of flooding and highly suffers from the negative effects of intense flooding, especially in its vulnerable communities such as Kashmere Gardens and Trinity/Houston Gardens. These communities have been suffering frequent flooding due, in part, to inadequate stormwater infrastructure. Implementation of green stormwater infrastructure (GSI) strategies is a viable solution for stormwater management and can provide environmental, economic, and social benefits especially when optimally designed and constructed. In this study, different GSI implementation strategies are tested using the Environmental Protection Agency National Stormwater Calculator (EPA SWC), a screening tool with the ability to assess the runoff volume reduction resulting from the implementation of GSI. Four of the most appropriate strategies (permeable pavement, rain garden, green roof, rain barrel) are selected based on their potential in runoff reduction and community interest. Several maps are generated for these four types of GSI strategies after defining appropriate site selection criteria which represent the potential placement of GSI strategies.

Low impact developments (LID), by definition and by the term, should allow land development projects to reduce their impact on the environment. Vegetation that includes grasses, trees, shrubs, and other types of plants is often used to achieve the desired goal by mimicking what happens in natural environments. It is used so much that green infrastructure (GI) is now interchangeable with LID. However, plants are often under stress and consequently die. Replacing dead plants has been a the standard operation. When LID/GI components are incorporated into projects, people use the mature state of the selected plants in their calculations. That may include the reduction of stormwater runoff due to the retention and absorption by the leaves, barks, and roots, the amount of pollutants that plants pull out of the stormwater, the amount of pollutants break down by microbials in the soil, the rate of evapotranspiration, the infiltrated rate through the healthy soil that is home for plant roots, microbials, and beneficial insects. If the plants are constantly being replaced and never reach their mature state, then it is not a “Low” impact development. Indeed, it can be very high considering not only the LID/GI do not function as designed, but the replanting process increases the pollution/emissions and maintenance costs. This study is to look into the fundamentals of the LID/GI systems, identify the main stress sources (water for almost everywhere and deicing salt only for northern climates and coastal areas), provide a solution that can reduce the casualties of the plants in these systems, and actually reduce the impact of LID/GI projects.

The old Francisco Reservoir was a 4.5-acre eyesore of an unused public open space in the heart of San Francisco. Built in 1859, the reservoir was decommissioned in 1940 and sat vacant for a further 79 years until 2019 when construction began. This project was born from the combined desire to convert a dilapidated structure into an environmentally friendly park system. From 2008 to present day, 14 design agencies, 26 community support organizations, 27 local companies, and dozens of volunteers joined to create a unique, urban park landscape in this underutilized, dilapidated public space. The design team utilized a system in which stormwater is collected, stored, treated, and recycled. This design included a storage system that could support an aboveground park system and an underground collection system that will reutilize stormwater to irrigate the park’s community garden and grass fields, and for use in flushing public toilets. This presentation will address and highlight the complexities and successes of this project, the opportunity to design more effective systems, and the details associated with a complex stormwater management system in the hope that others will replicate this success on future projects.

Pervious concrete is currently used in pavements and structures related to the drainage of pavements. In this study four pervious concrete mix designs that incorporate fly ash and blast furnace slag were investigated for their potential use in structural vertical green walls. Properties tested included compressive and flexural strength, permeability, and effect on plant growth. The objective was to develop a pervious concrete mix with adequate strength for constructing structurally independent vertical wall units and that provides a favorable environment for plants. Three of the four mix designs tested had adequate strength and were able to support plant growth. A combination of Portland cement, fly ash, and blast furnace slag resulted in the most workable of the mixes.

The objective of this study is to adapt a rainfall simulator that allows controlling input of different rain intensities to later evaluate the hydrological response of SUDS (sustainable urban drainage systems) through output hydrographs. A rain simulator was built at the National Hydraulics Laboratory–UNI. The simulator consists of a 1 HP pump that drives water through a 3/4 in. piping system, towards a system of 6 FullJet 1/4HH–14WSQ sprinklers distributed symmetrically. The rain catchment area is approximately 18 m² with a variable slope from 0% to 50%. Through calibration tests, it was proven that the rain simulator can produce rainfall intensities of 59.4 to 74.6 mm/h with errors of 0.1 to 1%. The coefficient of uniformity of the intensities was from 69 to 71% with an average droplet diameter of 2.30 to 2.52 mm. According to the results of the parameters of coefficient of uniformity and droplet size, the rain simulator has been properly calibrated.

The Allegheny County Sanitary Authority (ALCOSAN) serves an area that spans approximately 310 square miles across 83 municipalities, including the City of Pittsburgh, Pennsylvania. ALCOSAN recently adopted a clean water plan (CWP) to improve and protect the water quality of the region's streams and rivers by controlling combined sewer overflows (CSOs) and eliminating sanitary sewer overflows (SSOs). The CWP is part of a Federal Consent Decree (CD) to comply with the United States Environmental Protection Agency's CSO Control Policy. The CWP is made up of several components including preventing excess water from entering the sewer systems. As part of its green stormwater infrastructure (GSI) and source control (SC) program, ALCOSAN released Controlling the Source that lays out a consistent framework for evaluating GSI/SC in the Pittsburgh region. A key component involves identifying cost-effective and impactful GSI/SC projects capable of reducing sewer overflows to improve water quality. Overflow reduction efficiencies (OREs) were developed throughout the service area using automated modeling techniques to represent different GSI/SC techniques, varying implementation levels, and different system conditions. OREs provide a hydraulically-informed estimate of the relative overflow impacts of projects in different areas, so that effort and attention can be focused in those areas with the greatest potential overflow benefits. To complement the OREs, a GIS-based constraints analysis was performed to provide a geospatially-informed estimate of areas where GSI potential may be limited and/or costlier based on mapped physical and environmental constraints. Individual constraints such as shallow bedrock and slopes were assigned a range of constraint scores based the relative impact to GSI and then overlaid and summed. By targeting areas/sites with high OREs and lower levels of constraints, practitioners have powerful planning-level tools to identify projects most likely to be feasible, cost-effective, and impactful. Using these tools, ALCOSAN identified and evaluated almost 200 potential GSI opportunities. The opportunities were ranked and prioritized based on capture potential and implementation feasibility. Detailed concept plans for 60 of the higher ranked sites were developed and incorporated in discussions with municipalities as a tool to incentivize GSI project implementation in response to public comments received during the development of the CWP.