In situations where surface stormwater management is more difficult, underground stormwater retention can be an alternative. This system of underground vaults and pipes can direct water run off below the ground and can allow stormwater to be redirected to natural waters or guided back into the ground surface. An underground system can offer some stormwater relief when there is limited land available for traditional management. There are drawbacks, however, such as cost and the requirement of experienced and specialized engineers, but it is an option in a pinch.
Although the first glance at the cost may seem staggering, these underground stormwater vaults definitely have some benefits;
- Reduction of stormwater runoff flow.
- More control over the release of water.
- Good option for high density areas, or areas where land is prohibitively expensive.
- Quick and efficient installation with prefabricated parts.
- Potential for a long life span.
- Increased level of public safety and health over open ponds or other above ground storage.
- Insulation from freezing.
- Aesthetically pleasing to public in that such systems are out-of-sight and thus out-of-mind.
It is important to plan ahead when considering this type of solution, as there are factors that may not be obvious when you are used to regular above ground retention. The system design and installation require the input of city planners and engineers to maintain proper specifications, especially when handling storm events. Underground stormwater storage will also require regular and often costly maintenance to keep inlets clean and trapping gates free of debris. Without this regular maintenance sediment could trap the system or get flushed downstream into native waters.
Underground stormwater management can be used when land costs, land shapes, and limited space does not allow for traditional Best Management Practices (BMPs). Although costly, it does offer water conservation benefits when water tables are low. When planned adequately, underground water systems can last for decades and offer some communities a reliable water control system.