Keeping storm water moving downhill can be a thankless job but failing to consider the effects of storm water on a project can often have disastrous results. Here are a few tips that reduce the risk of storm water management issues.
Appropriate Finished Floor Elevation
Propping up the floor elevation of your building is a quick and easy way to add some insurance to your development. Typically, about six inches is enough of a gap to keep storm water out of a traditionally designed building, though many industrial facilities will push that number upwards of four feet. Also consider the surrounding topography and any localized high spots when selecting a finished floor elevation. If your building is located in a “bowl”, propping the structure above the localized high spot will help runoff travel offsite before backing up into the building in a flood condition.
Consider Economic Upsizing of Pipes
The 500-year storm event is the new 100-year. It seems like larger storm events happen more frequently and engineers should take notice. Traditionally, a storm sewer is designed such that the frequent rain event, like a 2-year event stays in the pipe, and the larger events like a 100-year event flows through the property and to the public streets. Cost is always a big factor, but at ALJ we think of it as cheap insurance to upsize storm sewer size and slope to contain the larger event in the pipe. It’s better to err on the side of caution when possible.
We always keep in mind relative cost per pipe size and depth when designing with this philosophy. It’s only “cheap insurance” if upsizing has little relative cost. We’ve typically found the cutoff point to be between 18”- 24” pipes and depths of five or six feet; an increase in dollars per size and dollars per foot of depth takes a jump around these areas.
Ensure Owners are Aware of Maintenance Requirements for Green Infrastructure
Permeable pavers and their infiltrative siblings are prevalent nationwide, but there is still a lack of education surrounding maintenance of these best management practices. Be aware of your client and their maintenance capabilities when specifying infiltration-type drainage options versus less maintenance intensive options like hydrodynamic separators. The site may be perfectly suited for an infiltration basin, but if the owner does not have maintenance resources in place with the knowledge of how to maintain infiltration-type drainage systems, lean towards simpler options like separators.
Flooding has been a major issue across the country the past few years, none more so than with 2017’s Hurricane Harvey in our own backyard in Houston, TX. ALJ Lindsey has the experience and detailed knowledge to properly plan against flooding, give us a call.