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Trench drains in walkways and roadways

A few weeks back, we took a look at a linear trench drain at an areaway at a well leading to an entry at a basement.

Today we are taking a look at different types of linear trench drain, generally above grade and at larger openings. Linear trench drains can be extremely useful whereas in the past, and historic times, only areaway drains were really practical options for draining smaller areas.

The outline for today’s article follows:

  1. Why Linear Trench Drains are Better.    
  2. Longer Lasting Materials
  3. Modular and Customizable Designs
  4. Improved Grate Designs.
  5. High-Performance Surface Treatments
  6. Efficient Water Filtration Systems
  7. Smart Drainage Systems.

A picture of a linear trench drain from over 50 years ago follows below. This isn’t exactly a historic element, but nor is it contemporary or modern. The grate, overall, has a lower percentage of area that allow passage of water through and into the drain, than modern drain grates.

cast iron linear trench drain

The cast iron linear drain shown in the photo above is over 50 years old, a bit of a hybrid between historic and contemporary drains.

Why Linear Trench Drains are Better

Linear trench trains have a higher volumetric capacity than areaway drains.  This matters because it is the maximum capacity that becomes critical before a drain is breached.  Breaching a drain can lead to flooding of a building interior so the damage can be possibly catastrophic. 

Because of both the overall larger surface area and the longer shape linear drains do not get clogged as easily as areaway drains.   For example, when a concentration of debris is deposited onto an area of a drain, with a circular areaway drain, that area is the entire drain and therefore the drain can easily become covered over and clogged. By comparison though with the linear trench drain, even if the area has the same size of debris deposited, water can still flow around to another section of the same linear trench drain.   Effectively, it would take a much greater amount of debris to cover the entirety of a linear trench drain than it would to cover the entirety of an areaway drain.  Linear drains can be built to adapt to the context of a grade or layout better than areaway drains which often require the modification of a larger portion of the surrounding grade / paving.

Essentially, for a areaway drain to serve relatively large area, the entire area has sloped directly to that single sole point.  Whereas, by comparison, with a linear trench drain, the drain can follow a roadway or pathway, for example, and the drain can still collect water that runs in towards that direction but the grade doesn’t necessarily have to slope so that they’re all areas feed specifically in that direction. In fact areaway drains can particularly collect water that is built up or amassed during very high points of volume during storms or above average precipitation, for example.

The trench drain in the picture below protects the garage area of this building from heavy water flows but may only capture a portion of the water that runs across the roadway. Particularly during the heaviest rains, water may run both directions from the crown of the roadway and follow the gutter of the street.

trench drain

The open end of this trench drain can collect water that flows with the direction of the street gutter during the heaviest of rainfalls.

Longer Lasting Materials

Initially, most areaway drain systems, in historic neighborhoods of DC, such as Capitol Hill, were built with cast iron components.  Cast iron is strong and somewhat resistant to oxidation, but it has low ductility and several limitations as a drain material.  By comparison, stainless steel has a much higher resistance to rust and oxidation.  Stainless steel however, didn’t become popularly used as a common building material until decades after the majority of historic buildings were built.

Cast iron is an alloy of iron that contains a higher proportion of carbon than steel, along with silicone and other elements. While cast iron is known for its strength and durability, it is susceptible to rusting when exposed to moisture and oxygen. The presence of carbon in cast iron can contribute to the formation of a protective layer of oxidation on the surface, which can act as a barrier against further corrosion. This layer may be referred to as a patina.   Steel or wrought iron, by comparison, will continue rusting, even after the surface rusts, they will rust all the way through.

Modular and Customizable Designs

In modern and contemporary times, many of the components of drain systems are made so that they can be expanded or modular yet semi-customizable to be interconnected with additional pieces to fit the length, configuration, and shape of the needed installation.  This is a big improvement over historic systems which did not allow for customization on site.  Instead, as an alternative to customization onsite, individual productions could be created to customize the mold to create a system tailored to the content of the construction.   This is an example of extreme customization.   Today though, systems can be tailored to a large extent using near readily available catalog components.

drain and grate

The drain and grate at this garage opening are set with an angle in the otherwise linear run of the drain.

angled miter

As you look closer, you can see that the grate, where joined at the angled miter are pieced together on-site not manufactured as one singular unit.

Improved Grate Designs

In recent decades, grate design has been optimized to increase load-bearing capacity and increae water flow.   Every grate has a trade-off in this area. Grates with larger surface area of the base materials are stronger and can support a greater imposed load, while grates that have more open areas are generally weaker but can allow much better water flow.   There’s a careful balance between these 2 elements, and the point of optimization is based on being able to handle the  imposed loads of vehicle traffic and also allowing the maximum amount of water capacity.

Looking closely at an older cast iron drain cover you can see that this appears to be much stronger, from the position of supporting heavy loads of traffic, but the amount of water that can pass through the grade is decreased significantly because only a smaller portion of the area is perforated or open to allow water to flow into the drain body.

cast iron material for trench drain

Cast iron appears strong, yet has inherent limitations including the inability to undergo bending, stretching, or shaping through external force due to its weak tensile strength, which leads to fractures before any bending or distortion can occur.

High-Performance Surface Treatments

Application of advanced coatings and surface treatments to trench drains can help to to resist corrosion, reduce maintenance, improve longevity, and provide traction coatings to reduce slippage.   The traction to resist slippage mostly applies to foot traffic, but also applies to vehicle traffic as well, particularly where there is a transition in grade or angle of the roadway.

The options for surface treatments vary widely depending on the type of base material used for the drain and grate system.  Modern steel materials are often treated with a galvanization process which protects the substrate metal from oxidation and deterioration. There are two main types of galvanic treatments, the less expensive option is electro galvanization. Hot dip galvanization. By comparison, the hop-dip process requires submersion of the material in a bath of molten zinc liquid.   It’s difficult to hot dip galvanized large materials because particularly large beds are required to submerge variety large steel materials. This makes the hot dip process a bit more costly for large sections of drain grates, for example.

Hot-dip galvanization and electro-galvanization are both processes used to apply a protective zinc coating to steel or iron surfaces, but they differ in the way the zinc coating is applied. The key differences in the processes contribute to variations in the thickness, structure, and effectiveness of the zinc coating, which, in turn, affect the resistance to deterioration.  Hot-Dip Galvanization creates a zinc-iron alloy layer at the interface between the zinc coating and the base metal. This alloy layer provides a metallurgical bond, contributing to the durability and effectiveness of the coating.  Electro-Galvanization, in contrast, typically forms a pure zinc coating without the same degree of alloying with the base metal. The bond is generally less robust compared to hot-dip galvanization.

Hot-dip galvanization generally provides a more robust and thicker coating, along with the formation of a zinc-iron alloy layer, resulting in enhanced corrosion resistance and durability. This makes hot-dip galvanization particularly effective in applications where extended protection against deterioration is crucial, such as outdoor structures, marine environments, or industrial settings. However, electro-galvanization remains a viable and cost-effective option for many applications, especially when a thinner coating is acceptable, and a smoother finish is desired. The choice between the two processes depends on the specific requirements of the application and the environmental conditions the coated material will face.

By comparison, as a contemporary alternative to steel and metal grate systems, polycarbonate plastics are relatively strong. They can handle a relatively high degree of tensile strength resistance and have almost no commensurate deterioration related to moisture or exposure to water. Polycarbonate materials though, are highly susceptible to exposure to ultraviolet rays and therefore while they are better in some ways, have one inherent weakness which may render them less effective, in some cases.

galvanized steel grate

The picture above shows a galvanized steel great, is particularly great does not have to support vehicle loads, But it must support pedestrian foot traffic.

Polycarbonate is lightweight compared to steel, making it easier to handle and install in certain applications.

One of the significant weaknesses of polycarbonate is its susceptibility to UV degradation. Prolonged exposure to sunlight can lead to yellowing, loss of transparency, and reduced mechanical strength over time.  Polycarbonate surfaces are relatively soft and can be prone to scratching, which may affect their appearance and optical clarity.  While polycarbonate has a wide operating temperature range, extreme temperatures can affect its mechanical properties. It may become brittle in very cold conditions and soft in high-temperature environments.

To mitigate the effects of UV exposure, manufacturers often add UV stabilizers or coatings to polycarbonate products. UV-resistant polycarbonate formulations are available to address this weakness.  The choice between polycarbonate and traditional materials like steel depends on the specific environmental conditions of the application. If UV exposure is minimal, and impact resistance and moisture resistance are critical, polycarbonate may be a viable option.

In summary, while polycarbonate plastics offer several advantages, their vulnerability to UV degradation is a significant consideration. Properly addressing UV exposure through protective coatings or choosing UV-resistant formulations can help extend the lifespan and performance of polycarbonate materials in outdoor applications.

The picture below shows an example of a polycarbonate drain grate.  The top upper surface of the grate is covered with an embedded texture surface, iitger uniting silica or aluminum oxide, similar to a sangmdpaper, to provide texture and prevent pedestrian slippage.

polycarbonate drain

Efficient Water Filtration Systems

Integration of advanced filtration systems within trench drains to improve water quality by capturing debris and pollutants has improved in recent years.  Often, in many parking lots, to achieve  environmental credits related to construction, as imposed or promoted by municipalities, gutters are often installed which go to a tree base which allows water to run through the area below the base of the tree and also some potentially are filtered before water returns to the natural drain points such as the Anacostia River.  Environmental damage to the Anacostia River from paved area runoff has decreased significantly in recent decades.   In fact, there are currently projects,  in tge planning stages, which will both celebrate and further develop on the revitalization of the Anacostia River to bring a mixed retail and other type elements to neighborhoods along the river which have been food deserts and lacked variety of services for many decades.

Water filtration systems are not typically integrated directly into linear trench drains. Linear trench drains are primarily designed for the efficient conveyance of surface water, capturing runoff from paved or landscaped areas and directing it to a proper drainage system. However, there are related components and systems that may be used in conjunction with linear trench drains to address water quality concerns.

While not traditional water filtration systems, separators and sediment traps are components that can be installed upstream of a drainage system, including linear trench drains. They help to capture and settle out sediments and pollutants, preventing them from entering the drainage network.  In some sustainable drainage systems (SuDS) or green infrastructure designs, bioswales or vegetated channels may be used alongside linear trench drains. These features help filter and treat water through natural processes, promoting the removal of pollutants through vegetation and soil.  Bioswales are not often found in the middle of the concrete urban jungle, but they are used along parkland, for example.  

And while bioswales are not highly common in the middle of the urban concrete jungle, permeable paving, by comparison has become extremely popular, even in the middle of the city urban environment.  In certain applications, permeable pavers may be installed along with linear trench drains. These pavers allow water to infiltrate through the surface and into the ground, promoting natural filtration. Infiltration basins or underground systems may be used to enhance water quality by allowing water to percolate through soil layers.  While not integrated directly into trench drain, removable inserts or filtration devices may be added to the outlet points of the drain system. These devices can capture debris and prevent it from entering the downstream drainage system.

It’s important to note that the primary function of linear trench drains is to manage surface water runoff efficiently, and they are not designed as advanced water treatment systems. For more comprehensive water filtration needs, dedicated stormwater treatment systems or detention/retention basins with specific filtration elements may be employed. These systems are designed to remove pollutants and contaminants from stormwater before it is discharged into natural water bodies or municipal sewer systems.

unprotected garage

This garage entry connects directly to the main part of the building, so it’s not just a garage space being protected from water backup and or flooding, it’s also an extremely expensive interior space.

Historic masonry upkeep and preservation

To properly maintain, repair, and care for these historic buildings, a knowledge, interest and understanding of historic building principles is required.  Here in Washington DC, historic masonry buildings are extremely expensive and the amount of financial loss caused by improper repointing and low quality construction is staggering.   However, in addition to the direct financial value of the property, there is also a cultural loss when historic buildings are damaged. By comparison, consider neighboring poor cities, when historic buildings are damaged, it’s not just the loss of value to the property owner, there’s also a loss to all inhabitants and visitors of a city, present and future, who care about architecture, history, and culture.

We encourage all of our clients, and all readers of this article and to our blog in general, to prioritize the historic built environment of Washington DC and neighborhoods such as Capitol Hill, Dupont Circle, and Georgetown and become educated on on the difference between proper historic preservation versus improper work which leads to significant damage to the historic fabric of a building.

From a conservation and preservation perspective, several approaches can be taken to improve conditions related to deteriorated historic brick masonry. Primarily, lime mortar brick joints and low temperature fired soft red clay bricks should be inspected and checked on a routine maintenance schedule, either seasonally or at least annually.   If brick masonry is kept in good condition, the life of embedded wood elements can be significantly extended.  Hire a professional contractor which specializes, understands and appreciates historic construction elements and buildings.

You can learn a lot more on our blog.  Feel free to check it out.  If you have questions about the historic masonry of your building in Washington DC, contact us or fill out the webform below and drop us a line.  We will be in touch if we can help.