Stormwater drainage systems must be built to handle more than the average rainy day. When they’re too small to manage rising volumes of water, the result isn’t just water pooling where it shouldn’t. The fallout includes pipe backups, road damage, and in worst cases, structural sinkholes.
Undersized systems are one of the leading causes of infrastructure failure in both commercial and residential areas, especially as storms become more intense and unpredictable.
The Illusion of “Good Enough”
Many systems function perfectly fine under normal weather conditions, giving a false sense of security. The problem appears when a storm dumps water across impervious surfaces like rooftops and parking lots, sending runoff toward storm drains at high velocity.
If the stormwater drainage system was never designed for this load, it quickly becomes overwhelmed. Storm drain covers and drain grates begin to overflow, and surface water spreads uncontrolled through streets and buildings.
Culverts That Can’t Keep Up
A culvert serves as a crucial pathway to move stormwater under roads and infrastructure. When undersized, culverts choke the flow, backing water up into roads and properties. Even if equipped with a culvert trash rack or trash rack, flow cannot exceed the system’s design limits.
Worse, this backup can cause pressurization and damage inside the pipe itself, leading to pipe joint separation or collapse — both precursors to sinkhole formation.
Detention Tanks Without the Right Capacity
Stormwater systems often rely on detention tanks to temporarily store water and slowly release it into downstream systems over a period of time. But if the detention tank is undersized or incorrectly modeled, it fills too quickly and spills over.
In areas without a backup plan or retention tank alternative, water floods streets and homes. The distinction between detention tank vs retention tank becomes critical in these scenarios. A properly engineered detention system can prevent surges in the sewer systems, but only when scaled correctly.
Subsurface Failures and Sinkholes
Excess water doesn’t just disappear — it finds weak points. When stormwater systems can’t accommodate high flow, water escapes the system and begins to erode soils around underground structures. Over time, this leads to subgrade washout and eventually, sinkholes.
Poor soil compaction, leaking joints, and inadequate protection of subsurface structures all contribute to the collapse. For municipalities, these failures often begin at overlooked points like stormwater drains, drain covers, or faulty pipe connections made without considering the long-term water load.
The Cost of Cutting Corners
Installing a smaller stormwater system might save upfront costs, but it often leads to high long-term expenses. The real costs show up as property damage, emergency repairs, lawsuits, and even public safety issues.
Proper stormwater management demands systems that can handle extreme weather events — not just average rainfall. That means factoring in the projected increase in stormwater runoff, the size and location of detention tanks, the use of durable materials like galvanized steel, and the importance of proper sizing across every component.
Undersized stormwater systems may seem like minor oversights, but they lead to major consequences. For long-term performance and safety, drainage infrastructure must be built with the future in mind — not just the budget.