Columbus studies drainage issues

Published 9:10 am Thursday, June 30, 2011

The Town of Columbus now has a study of storm water drainage issues throughout the downtown area.
Columbus Town Council met Thursday, June 16 and reviewed the study, which was completed recently with grant funding.
Billy Lee and Alwyn Smith, with Withers & Ravenel, met with council and detailed the town’s problem areas.
Columbus applied for funding for the study in 2008 with the N.C. Clean Water Management Trust Fund (CWMTF). The town was approved for $50,000 of funding in 2009, but the state funding was suspended in 2010. The funding was released this year, with the town’s match being $5,700.
Lee said Withers & Ravenel mapped the town’s storm water system and looked at opportunities to make water quality improvements. The town plans to use the study to apply for more grant funding in the future to make improvements to the system.
Withers & Ravenel completed a geographic information system (GIS) map of the town’s system and then looked at the performance of the system to determine where water is backing up and how those problem areas can be fixed.
Some problem areas include erosion issues at the N.C. Department of Transportation site, just above White Oak Creek, the engineers said. They noted that ditches in the area are undersized for the amount of flow they are getting.
“Currently, most of the runoff is generated from the highly impervious downtown area,” states the results section of the study. “This runoff is routed directly to storm drains to control flooding, but creates erosive flows during storms. There is evidence of scour in drainage ditches throughout the area, but it is most pronounced in the main drainage ditch that conveys stormwater from downtown into White Oak Creek. The high degree of impervious surface area in downtown, coupled with steep slopes and a lack of detention, creates a situation where even small storms create high stormwater flows conveyed at erosive velocities.
“Establishing rain gardens and detaining devices to capture and slow down runoff in downtown is probably the lowest cost method to improve flooding and erosion concerns. The conventional, more expensive approach would be to dig up and replace stormwater pipes and ditches.”
Locations that were identified where light landscaping could be added to slow down drainage and decrease erosion were the courthouse lawn, the veteran’s park area, in front of the post office and behind the parking lot of the post office.
Lee and Smith also said the town’s sewer easement through the town could be converted to a trench, but that would be expensive.
Areas around the post office were identified as good areas for rain gardens.
Smith said other ways to reduce storm water include limiting or reducing impervious surface areas, using cisterns and rain barrels at downspouts to slow water down, to encourage the creation of rain gardens and to retrofit roadside ditches with low impact development methods.
Smith said Columbus next needs to identify the two sites it is most interested in investigating for drainage improvement possibilities. Withers & Ravenel will prepare a detailed investigation, report the findings and pursue other grant funding to pay for the drainage improvements.

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