F’ville watershed changes mean bigger drain pipes, deeper ponds

The Feb. 6 vote by the Fayetteville City Council to create the Pye Lake Southern Tributary Special Watershed District was unanimous. The new ordinance will mean potentially more on-site stormwater storage, as needed, for future development.

The new watershed district provides the framework to help resolve issues with future stormwater runoff as additional property is developed in the Villages at Lafayette development and on the south side of Ga. Highway 54 east of Grady Avenue. If needed, future on-site stormwater storage would come in the form of larger and deeper detention ponds and stormwater drain lines with larger diameters, according to city Public Services Director Chris Hindman.

As pertains to current stormwater runoff, an evaluation is underway to determine if any action is required to deal with the current increased flow rate in the tributary that flows into Pye Lake, Hindman said.

Pye Lake is situated immediately south of Hood Avenue east of Ginger Cake Road.

In identifying the need to establish the Pye Lake Southern Tributary Special Watershed District, Hindman in a Jan. 6 letter said, “Concerned with the potential of increased stormwater runoff flows through the southern tributary that feeds into Pye Lake, staff had our engineering consultant perform an analysis of the southern watershed basin. Approximately 362 acres of property drains into the southern tributary with minimal detention ponds within the basin due to development occurring before ponds were required.”

The unnamed stream passes under Hwy. 54 approximately 1,100 feet east of Sharon Drive near The Villages residential development. The stream drains into Pye Lake which is located near the north end of Sharon Drive.

The watershed district includes The Villages development on the north side of Hwy. 54 and a large portion of land south of Hwy. 54 that extends east and south from the entire length of Grady Avenue to the east side of Ga. Highway 85.

Hindman said an analysis was completed in December 2012 which reviewed pre-development conditions, 1993 land cover conditions and 2010 land cover conditions to evaluate how the stormwater runoff flows have changed from pre-development time frame through the 2010 land cover conditions.

“Our consultant also looked at two different possible future land conditions with some potential upgrades to the existing ponds at the Villages subdivision and how that might change the stormwater runoff,” Hindman said.

Hindman said the results of the analysis shows the stormwater runoff has steadily increased from the pre-development conditions to the 2010 Land Cover conditions from 21.37 cubic feet per second to 149.34 cubic feet per second peak flow rate at the watershed outlet at Pye Lake.

“If the remaining properties are developed with the current zoning and land use classifications we estimate the potential future land use conditions will be 197.96 cubic feet per second peak flow rate at the watershed outlet and will be an increase of 48.62 cubic feet per second over the 2010 land cover flow rates,” said Hindman. “Through the analysis our consultant has concluded that significant changes need to be made in regards to future development to minimize the estimated flows from potential future development within the basin. Staff concurs and has worked with our consultant to create additional requirements for any new development within the basin.”

City staff recommended establishing the watershed district and imposing additional requirements on development within the district. The ordinance creating the watershed district would include flow levels up to a 100-year flood, Hindman said.

As for the increase in the flow rate seen over the past decade, Hindman said Integrated Science and Engineering is in process of evaluating the existing flow to determine if other action is needed.