The Challenges of Storm Water Management

Storm water is often treated as a nuisance rather than an important resource. While some runoff issues can cause extensive damage and health hazards, the accumulated water is also necessary for recharging the local water table. Without proper storm water management, local rivers can lose volume, wells can dry up, and waterways can become contaminated with chemicals and bacteria. Proper management is far more challenging than many civil engineers and business owners expect. Whether you’re dealing with storm water on a private or public property, here’s some of the many challenges you’ll face.

Uneven Distribution

When rainfall or flooding occurs, it’s never spread over an area in an equal way. Variations in local conditions will always lead to some areas receiving more water than others. Areas with a higher concentration of water impervious surfaces, like parking lots and roofs, contribute greater levels of runoff. This makes it challenging to build systems that collect and transport runoff away from streets and properties. If you use a standard approach to calculating average rainfall, some drains end up undersized while others are unnecessary or oversized. It’s important to use the finest points of rainfall data available for local areas to add the right number, and size, of catch basins to your storm water drainage system.

Unexpected Rainfall or Storm Surges

It’s hard to predict the weather, even for relatively short periods in the future. Considering most storm water systems are only overhauled and redesigned after a few decades of use, it’s essential to use the most accurate data and predication available for maximum possible rainfall. While some areas only call for using 25 or 50-year flood records to determine the largest possible amount of volume, that’s not enough data to create the safest possible urban system. 100-year flood records are better for sizing your system if there’s any chance of risk to private or public property due to overflow and flooding. Inaccurate rainfall records and predictions lead to undersized systems that flood eventually, even if it takes years for a major storm event to occur.

Importance of Recharging the Water Supply

If storm water is so difficult to manage, why can’t it just go into the ocean or any convenient river? Discharging water into local bodies of water does keep it in the cycle, but you won’t add any water back to the underground deposits this way. The local water table must recharge by absorbing moisture trickling through the particles of the soil. Gravity pulls moisture downward over time, filtering it naturally while keeping it safe for future use. Discharging the water into lakes and rivers will at least allow the water to seep through the soil of these local features, while water released into the ocean can take many years to return in the form of rainfall.

Strict Federal Regulations

Regardless of your state’s opinions about handling storm runoff and other forms of wastewater, the Environmental Protection Agency (EPA) has plenty of regulations that apply from the federal level. Ignoring the EPA regulations for storm water management will only result in high fees and costs for repairing your system. The National Pollutant Discharge Elimination System (NPDES) covers all the various levels of storm water regulations, helping you determine which rules and regulations apply to your particular project. These rules apply to both small municipal systems and construction sites disturbing between one and five acres. Projects larger than this are generally handled by engineers well-versed in federal permitting requirements, but smaller storm water systems still qualify for many restrictions.

Regional Variations

The local soil conditions around a specific storm water catch basin play a surprising role in how much water flows into the system. If a catch basin is surrounded by healthy soil covered by vegetation, most rainfall will absorb into the soil before it begins to run off and reach the basin. Drains in areas surrounded by bare compacted or clay soil won’t just experience high levels of runoff. Silt and sediment are also a problem in these cases, filling up the basins so they don’t work as intended and quickly overflow. Take into account any absorbent or impervious surfaces around the drainage area to properly size your catch basins.

Erosion and Soil Loss

Without erosion control equipment and techniques, storm water systems often fail due to filling up with silt and debris. Erosion removes healthy soil and depletes agricultural systems, destabilizes slopes and roads built above them, and costs millions of dollars a year to remedy and prevent. A few properly placed silt screens and some extra care given to vegetation can result in catch basins that stay clear year-round with minimal silt and sludge removal.

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