Cary’s 2006 Stormwater Engineering Report

A 2006 engineering study identified major problems in Cary’s downtown storm water system. Not one was ever corrected.

The attached report is the starting point for anyone trying to understand how and why so many homes and cars are now being flooded in and around downtown Cary.

In 2006, in anticipation of major downtown development,  the Town of Cary commissioned the Dewberry and Davis engineering company to  evaluate 2006 flooding problems, future flood risks,  and recommend any  improvements needed to minimize flooding and to handle future development.

The study was for “downtown”, or more broadly what Cary calls its “Town Center” area, or TCAP.   It includes Swift Creek, Coles Branch and Walnut Creek.

The 2006 study identified grossly undersized storm water systems which did not meet Town guidelines.

“The results from the existing and future conditions analyses reveal that significant portions of the existing drainage system in the TCAP area do not meet the desired level of service or current design standards.

Numerous areas show the potential for roadway, property, and structure flooding, as well as other problems such as erosive velocities as a result of the undersized system.”

Yet Cary’s TCAP storm water system,  mostly built in the 1950’s and 60’s, has still not been upgraded to handle decades of new development in and around downtown.

A major cause  of flooding identified in the report,  are undersized culverts that run beneath road crossings. The report indicates many of these underpasses need to be 6 or 8 times larger.  When storm water cannot flow under a roadway, the road crossing acts as dam, backing up water into residents’ yards, cars, crawlspaces and homes.

A graphic from the Dewberry and Davis report shows the “dam” effect of the undersized Maynard Road crossing. This underpass is so small that it causes Swift Creek to backup like a lake during a storm.

It is important to keep in mind that  this report is now 11 years old and the Town Council  did not fund any of the critical storm water improvements the engineers identified.  Rather, the Staff and  Council have worsened the situation by aggressively approving roadways and high density developments,  which now further strain a  storm water system designed well over 50 years ago.


The report can be downloaded by clicking here.