Streets concentrate much of the impervious surface in cities. The contemporary approach to drainage seeks to control water closer to where it falls, rather than simply carrying it away as quickly as possible.
The best drainage is not the one that simply removes water from the street faster. It is the one that manages the cycle without transferring risk to the next block or downstream.
Streets account for a significant share of impervious surfaces and, for that reason, participate directly in the formation and transport of surface runoff. For decades, the dominant principle was to capture rainfall and move it away quickly through gutters, curb inlets, storm drains, and channels. This infrastructure remains essential, but urbanization and greater climate variability expose the limits of a strategy based on transfer alone.
The contemporary approach seeks to control water closer to where it falls, distributing devices that infiltrate when the ground allows, store water temporarily, slow peaks, and safely deliver the excess to the conventional system. In Brazil, this vision gained regulatory backing with ANA Reference Standard No. 12/2025, which prioritizes source control, nature-based solutions, and green, blue, and gray infrastructure integrated with urban design considerations. This shift does not authorize standardized solutions: rain gardens and permeable pavements can fail due to inadequate sizing, clogging, low-permeability soil, or lack of maintenance, and they also do not eliminate events that exceed the design storm.
The street is at the center of the problem, and it can be at the center of the response
Streets, parking lots, and sidewalks interrupt part of the infiltration and rapidly connect large areas to the drainage network. The greater the impervious surface and the efficiency of that connection, the shorter the time between the start of rainfall and the arrival of the peak flow tends to be, even though topography, rainfall intensity, storm drain capacity, and basin occupation also condition the outcome. The roadway also concentrates a rare opportunity: it forms a continuous network of public space, follows the natural paths of runoff, and already receives periodic investment in paving, sidewalks, and tree planting. International references propose that the right-of-way be understood as water infrastructure, since road runoff carries sediments, metals, and petroleum derivatives, so that control close to the source benefits both water quantity and quality.
Draining is not only about conveying
The conventional system collects and transports volumes through gutters, curb inlets, pipes, and channels, and in many places it will continue to be the primary safety element. The problem appears when the entire strategy is reduced to increasing the speed of transfer: a project can relieve one stretch and raise flows in another, or create a false sense of protection in the face of events larger than the one designed for.
Sustainable urban drainage introduces a broader sequence: avoiding unnecessary imperviousness, controlling water at the source, attenuating and treating it in a distributed manner, and articulating everything with macro-drainage and risk management. Green and gray are not rival categories; international references use the idea of next-generation infrastructure to advocate for combinations capable of harnessing natural functions without giving up the reliability of built components.
A repertoire of solutions, not a catalog of parts
Rain gardens and bioretention cells receive water through openings in the curb and use vegetation and draining layers to store, filter, and, when permissible, infiltrate. Vegetated swales transport runoff at lower velocity; permeable pavements allow water to pass into a storage layer; plazas, parks, and grassed depressions can function as public space in daily life and as temporary storage during rainfall.
The typology alone does not define performance. Two visually similar rain gardens can have opposite responses due to the contributing area, inlet elevation, soil conductivity, or maintenance. The selection must arise from the required function, whether to reduce volume, limit peak flow, or protect a low point; without a measurable target, the device runs the risk of being landscaping presented as infrastructure.
Not every solution needs to, or should, infiltrate
Infiltration is valuable when the subsurface offers capacity and safety, but it is not a universal requirement.
Low-permeability soils, a shallow water table, geotechnical risk, or proximity to foundations can limit its application, and in areas with contaminated soil or groundwater, infiltrating runoff can mobilize contaminants; the environmental and hydrogeological assessment must precede the decision, especially in industrial corridors and redeveloped sites. In these situations, the response may be an impermeable cell with an underdrain, storage with controlled discharge, or retention for reuse. It is also necessary to evaluate the quality of the runoff: areas subject to spills or heavy loads require pre-treatment and access for sediment removal. Sustainability lies in adequacy to risk, not in the obligation to infiltrate at any cost.
The basin comes before the planter
Isolated interventions can resolve local occurrences, but their cumulative effect depends on location and connectivity: a device far from the main flow paths produces little benefit, and another at a critical point can be overloaded by a contributing area larger than anticipated. For this reason, the strategy begins by delineating basins and sub-basins, mapping elevations and low points, and locating vulnerable populations.
ANA Reference Standard No. 12/2025 determines that systems consider conditions close to those of pre-development and distributed attenuation. The Ministry of Cities Manual requires hydrodynamic analysis in situations funded by the federal government and consideration of downstream effects. The common message is clear: a good street project must respond to a hydrological logic larger than its physical limits.
ANA Reference Standard No. 12/2025 raises the level of the discussion
The standard approved by ANA Resolution No. 245/2025 defines green and blue infrastructure as part of public drainage services, with objectives such as minimizing the impacts of urbanization on the hydrological cycle and contributing to climate resilience. The design must prioritize nature-based solutions, without excluding gray infrastructure. The advance is relevant because it links innovation to operational responsibilities: the standard includes planning, construction, maintenance, and monitoring, and prioritizes devices harmonized with the landscape and multiple uses in parks and plazas. At the same time, it requires sizing for the design storm and overflow structures. Green infrastructure ceases to be an ornament and enters the service delivery cycle.
A method in five technical decisions
Deployment can occur in new urbanization, roadway requalification, or retrofit areas. At any scale, five decisions help separate a functional solution from a merely illustrative piece.
- Map the water and the risk. Delineate the contributing area, recognize surface paths, the existing network, low points, and the history of occurrences, distinguishing between ponding, flash flooding, and riverine flooding.
- Establish verifiable targets. Define the rainfall and scenarios, the restriction volume or flow, and the desired performance, making explicit what happens above the design capacity.
- Investigate the local constraints. Characterize the soil, permeability, water table, geotechnics, topography, accessibility, and interferences.
- Integrate typologies and gray infrastructure. Select devices according to function, and provide for pre-treatment, drains, overflows, and safe surface routes.
- Design the operation from the outset. Define the responsible party, inspection frequency, sediment handling, cost, and indicators, with triggers for system correction.
Drainage, mobility, and landscape must fit within the same cross section
The roadway space is contested. A sidewalk extension or planter may be needed for accessibility, tree planting, a bike lane, and drainage all at once. Inserting a device without an integrated design can narrow the clear path or hide pedestrians; conversely, a corner extension can house bioretention, a median can store water, and a plaza can function as temporary storage.
Multifunctionality requires a safety hierarchy. Inlets must capture water without creating traps for wheels or canes; edges must be perceptible; vegetation cannot compromise visibility. The urban benefit appears when the hydraulic solution improves, or at least preserves, circulation and everyday experience.
What international experiences teach
International references systematize principles of bioretention, cooperation among transportation, public works, and water agencies, and evaluation of street performance. Their greatest merit is not offering a ready-made design, but placing different departments before the same space, recommending documented pilot projects and maintenance planning.
Projects by large international consultancies demonstrate the passage from device to network. In Mansfield, in the United Kingdom, one of these consultancies used territorial analysis to distribute thousands of sustainable drainage solutions, with an announced capacity to capture up to 58 thousand cubic meters and reduce risk for 90 thousand people. In Sibu, in Malaysia, another international team describes an extreme rainfall plan that connects wetlands, streets prepared as corridors, and sports spaces capable of temporarily storing water. These examples should not be copied without translation: rainfall regime, soil, legislation, and municipal capacity vary, and the transferable lesson is methodological, selecting solutions based on spatial data, working as a network, and measuring performance.
Co-benefits must be demonstrated
Green infrastructure can expand vegetative cover, reduce heat exposure, create habitat, and enhance public space, strengthening the economic case because a single investment serves more than one urban policy.
International references recommend that nature-based solutions be evaluated by effectiveness, biodiversity, and adaptation over time. The discourse of multiple benefits, however, does not replace evidence. Planting vegetation does not guarantee a meaningful reduction in peak; permeable pavement does not remain permeable without management of fines. Targets and indicators must separate hydraulic performance, water quality, and life-cycle cost, so that real benefits are not hidden within a generic sustainability narrative.
The counterpoint: green infrastructure can also fail
Common failures begin in the details: an inlet at the wrong elevation, a contributing area larger than calculated, an inadequate substrate, or the absence of a drain. After delivery, sediments can obstruct openings and responsibilities can end up divided among agencies. A green system without an operational routine loses capacity in a less visible way than a burst pipe, but no less importantly.
There are also physical limits: distributed devices are useful for frequent rainfall, but extreme events can exceed their capacity. The city must acknowledge controlled failure, indicating where the excess will go and protecting critical routes. Promising that rain gardens will “prevent floods” is technically inadequate without modeling and a scenario; the defensible statement is more precise, the solution can reduce a certain share of risk under defined conditions.
What this means for developments and urban projects
New developments alter cover, topography, and discharge points. Hydrological studies, drainage designs, and Neighborhood Impact Studies must evaluate how the lot and its interface with the street contribute to the basin, and whether the discharge and elevations are compatible with the network and with the downstream areas. Solutions on the facade or in the public space can complement control on the lot, provided that their operation and ownership are defined.
In requalifications, opportunities arise when drainage is coordinated with pavement replacement, sidewalks, and tree planting, reducing rework. Pilot projects are useful when they have a baseline and a scaling plan. The objective should not be to install the largest number of devices, but to build a network that continues to function after the opening.
Conclusion
The street that also drains represents a change in logic. Instead of treating rainfall as a volume to be removed immediately, the design recognizes that part of it can be intercepted, stored, and slowed before reaching storm drains and watercourses, reducing pressure on the system and opening space to combine resilience, landscape, and urban quality. This shift does not eliminate conventional engineering; it requires more engineering and more integration. The advance of ANA Reference Standard No. 12/2025 places Brazil on a course consistent with international practice. The city will not stop coexisting with intense rainfall, but it can redesign its streets so that they no longer merely receive the problem and instead participate in the solution.
Technical and framing note
This article is technical and informative in nature. It does not constitute a hydrological or hydraulic study, a drainage design, a construction specification, a geotechnical or hydrogeological assessment, a mobility plan, an environmental opinion, or a guarantee of flood reduction. The selection and sizing of devices must consider the applicable legislation, the Drainage Master Plan, municipal requirements, basin conditions, and technical responsibility. Foreign references are used as good practices, not as models for automatic application in Brazil.
Sources consulted: Brazilian Law No. 11.445/2007 (National Basic Sanitation Guidelines); ANA (Resolução No. 245/2025 and Norma de Referência No. 12/2025, and its guidance manual for implementation); Ministério das Cidades (Manual da Ação 00TK, Drenagem Urbana Sustentável, PPA 2024-2027, and the Caderno Temático on Urban Stormwater Drainage and Management) (link pending validation); NACTO (Urban Street Stormwater Guide); USEPA (Green Infrastructure and Municipal Handbook: Green Streets); World Bank (Integrating Green and Gray and A Catalogue of Nature-Based Solutions for Urban Resilience); IUCN (Global Standard for Nature-based Solutions); international technical publications on green infrastructure and sustainable drainage. The text and diagrams of this article are original syntheses by LZ Ambiental.
LZ Ambiental develops hydrological studies and urban projects that integrate basin, drainage, elevations, land use, mobility, and risk. Sustainable solutions begin with understanding the path of the water and are confirmed by the capacity to operate and respond over time.
