Six years after Hurricane Harvey ravaged the Bayou City and overwhelmed its flood protection measures, flooding remains an ever-present threat to Houston-area communities. According to Harris County, the city’s flood plain is expanding – a fact reflected in its newest flood plain maps. That means the risk of severe flooding is also expanding across the city.

All cities tend to experience increased flooding because they’re covered in impermeable materials – asphalt and some forms of concrete – that do not absorb water. However, that doesn’t mean pavement can’t serve as a flood control measure on its own. With the right drainage structures in place, commercial properties can fortify themselves against floodwaters and stay dry when the next major rain event arrives.

The Cost of Not Investing in Better Drainage in Houston

Water can cause extreme damage to commercial properties as it pools and flows. During a major flooding event, the rate at which water may cause damage is impressive – in a bad way. For example, during a high-intensity flood event, the following may occur on commercial properties:

• Soil erosion – When runoff courses through a property at top speed, it carries plenty of topsoil sediment with it. This topsoil erosion will kill off vegetation and worsen future flooding, as a result. That means worse water damage in the future.
• Foundation and structural damage – If storm waters reach the property’s buildings, it can cause damage to floors, carpets, drywall, and other water-sensitive items. Remediation and replacement costs can be extreme.

  Further, if water pools around the building’s foundation, it will cause foundation-adjacent soils to expand and shift, placing major stresses on the foundation and potentially causing early failure. Again, the expenses associated with repair and replacement may be extreme.

• Pavement damage – Other pavement structures, including parking lots and roads, may also sustain damage if they are exposed to standing water for long. If water infiltrates through surface layers, asphalt and concrete paving may experience subsidence (caving in) that leads to total base failures. Replacement may be the only solution if this occurs.
• Loss of supplies or material – Floods may also wipe out onsite material stocks, inventory, fixtures, vehicles, and other high-value assets or inputs. This will add to the final flood bill.
• Pests – Standing water will also attract a variety of pests, including mosquitos and rodents. In addition to being a nuisance, pests can also bring health-related hazards to the property.

How Drainage Structures Protect Houston Properties Against Severe Floods: A High-Level Summary

When it rains in urban areas, the goal is to capture the water and direct it through sanitary, safe channels until it reaches a natural source. This could be a lake, a river, a reservoir, or the ocean itself, but the objective is the same: Get flood waters out of the city and back to nature.

Cities use various flood control structures to make this happen. We’ll address the most important ones in detail, but they’re all connected to the same storm drain network that runs under city streets. Curb inlets, catch basins, culverts and more all feed into this system, which runs separate from the city’s sewage infrastructure. In other words, storm water and sewage don’t mix.

The goal for pavement contractors is to ensure the property is connected to this system and able to access the city’s municipal flood control system. That starts with the drainage structure basics – drains, inlets and catch basins.

Storm Drains, Curbs and Catch Basins: Structures That Every Commercial Property in Houston Should Have in Place

Pavement contractors are experts in curb, inlet, and storm drain construction. Together, these structures are responsible for capturing runoff and funneling it along road edges and into catch basins. There, the floodwaters can be safely channeled through the city’s stormwater system.

Storm drains, curbs, and basins are fundamental parts of any property’s flood control measures. Here is a quick summary of each component:

• Curbs – Curbs can be formed by hand or with the use of a specialized curb installer. In either case, curbs are typically made from waterproofed concrete and are effective at channeling street runoff into inlets and catch basins. To be optimally effective, curbs must be sloped and jointed properly. This requires attention to detail during forming, pouring, sawcutting, and curing.
• Inlets – Inlets are built into the curb system and serve as ingress points for captured runoff. Inlets must also be sloped properly to draw water in, and they must be carefully spaced to promote optimal drainage.
• Catch basins – Catch basins are the part of the storm drain that sits at the bottom of the inlet. They’re responsible for temporarily capturing large amounts of runoff and metering its flow using a small outlet at the basin’s bottom. Catch basins are, perhaps, the most labor-intensive part of the project and require extensive excavation to install.

  It’s important for commercial properties to have enough catch basins in place and to ensure they are properly constructed to prevent obstructions from clogging them.

For commercial applications, the best construction material for the above structures is concrete. If mixed with silicas, crystalline materials or petroleum derivatives, concrete can be made waterproof and withstand constant water exposure. Further, some waterproofing admixtures can improve the concrete’s compressive strength and its hydraulic (flow) efficiency.

Retention Ponds and Detention Ponds: Additional Flood Control Projects for Larger Houston Properties

On some larger commercial properties, retention and detention ponds can provide a reliable way to contain large amounts of stormwater. Both generally do the same thing – reduce the volume of runoff that flows from the property by capturing it and “buffering” against potentially destructive flows.

There are subtle differences, though, between retention and detention ponds, so here’s a closer look at each:

• Retention ponds – Retention ponds are wet ponds, so unlike detention ponds, they are designed to hold a permanent store of water during and between rain events. In this way, retention ponds can serve a double purpose – controlling runoff and boosting the property’s value with an attractive amenity. Also, unlike detention ponds, retention ponds may rely on nothing but evaporation for outflow purposes, so flow rates are much slower out of a retention pond, compared to detention ponds.
• Detention ponds – Detention ponds are sometimes referred to as dry ponds because they’re designed to empty out between rain events. By doing so, commercial properties can avoid standing water while still having the capacity to handle heavy runoff. Since detention ponds are designed to empty quickly between rains, they are installed with an outlet system that typically includes a riser and culvert. Together, these concrete structures meter outflow, which helps control flow rates further down the drainage network.

Culverts: Necessary for Protecting Houston Roads While Facilitating Efficient Drainage

Culverts are a situational flood control structure, as they’re purpose-built to direct runoff under roads, bridges, walkways, and other frequently used structures. They may be constructed from corrugated metal, polymer or concrete, and the latter is preferred for commercial applications, as concrete provides superior strength and hydraulic efficiency – which are important considerations for commercial-scale applications.

The culvert installation process is second nature for experienced contractors and includes the following:

• Determining slope, diameter, and length – The first step may be the most important, as it involves planning the culvert project. Altogether, this means establishing an effective slope for the culvert (working with the natural slope is recommended), as well as measuring out the proper length and diameter. This is an engineering concern, so reputable contractors will rely on their engineering expertise on staff to develop the right culvert dimensions.
• Excavating the area around the culvert – Once the right culvert is selected and brought to the project site, it’s time to excavate the ground around the installation area. The minimum recommended excavation area is 6 inches around the culvert’s circumference.
• Laying down a layer of base sand – With the area excavated, the construction team will then lay down a layer of sand that will sit under the culvert. This sand provides excellent loading stability and is also easy to compact.
• Placing the culvert and backfilling around it – Once the sand and the culvert is placed, the area around and on top of the culvert is backfilled, sometimes with material from the site, or using aggregate mixes that also provide good loading stability and compaction potential.
• Compacting the topsoil and adding vegetation – With the culvert installed and the site backfilled, all that’s left is to place and compact the topsoil that will sit on top of the culvert. This ensures the culvert remains in place and that traffic can pass over the top of the culvert safely. The contractor may also add vegetation around the newly installed culvert to improve soil stability further.

Stay Above the Flood in Houston and You May Avoid Expensive Remediation Costs

Houston property owners are all too familiar with the risks and consequences of severe flooding. Foundation and structural damage, loss of valuable materials, safety hazards and other impacts can add up to a budget-crippling remediation bill.

However, flood-related damage is somewhat avoidable. An expert pavement contractor in Houston is the team to call, as they can install various flood control structures with high quality materials and processes that ensure long-term stormwater control.