By Gordon Whitaker
The increased severity and frequency of storms, combined with large amounts of development paving over more of our watersheds, requires that Chapel Hill make the best stormwater management decisions possible on every new project. This is especially the case where flooding already exists immediately downstream from an area where large areas of impervious surface are proposed to replace forested land. This is the case with the Lullwater Park concept plan.
The property proposed for development is atop a ridge, with drainage mostly to the south into the Cedar Fork of Booker Creek. Affected properties directly downstream include the existing multifamily townhouse and condominium communities at Coventry, Weatherstone and Kensington Trace. Already these neighborhoods and others downstream experience flooding following heavy rains.
Given the extensive impervious surface proposed to replace the current forest, stormwater collection on site will be required to prevent stormwater from leaving the property at high velocities, endangering the neighborhoods at lower elevations. The concept plan states: “Stormwater detention will be provided in multiple on-site underground detention systems, using best management practices.” However, the use of underground detention seems questionable, given the typology of the site.
While the concept plan recognizes the Resource Conservation Districts (RCDs) dotting the property, it does not provide adequate protection for them. Constructing underground stormwater reservoirs would seem to require RCD disturbance where buildings or paved parking are located directly adjacent to an RCD. The Lullwater Park concept plan shows proposed construction right to the edge, if not in, RCDs in several places.
Where and how water would be released from the underground storage facilities is also critical. All proposed development is above RCDs or neighboring properties. An area between Kensington Trace and Weatherstone adjacent to Weaver Dairy Road already sits in a designated floodplain. On the eastern side of Lullwater Park, one proposed parking lot is atop a steep bank just north of Coventry townhouses and apparently across an ephemeral stream. Another parking lot abuts the RCD. Where would any underground stormwater retention tanks release the stormwater they accumulate without flooding the RCD?
Another defect in the plan is the intensity planned for the narrow strip of land along the proposed new access street into the property from Weaver Dairy Road. This land slopes toward the Coventry neighborhood and Weaver Dairy Road. Heavy rains already flood the backyards of some Coventry townhouses. The proposed development would clear cut the forest on these slopes and replace them with a new street and tightly-packed townhouses surrounded by paved alleys/parking.
Without careful management of runoff from this narrow strip, stormwater will flood both the access street and the adjacent properties in Coventry and neighborhoods downstream. Where would any underground stormwater retention tanks in this section release the stormwater they accumulate if not into existing neighborhoods?
Adequate stormwater management is an essential part of any development at the headwaters of the Cedar Fork/Booker Creek watershed. The Town Council’s coming review on September 28, gives the Council an opportunity to stress the critical importance of stormwater management to developers.
Gordon Whitaker retired from the School of Government after teaching Public Administration at UNC for 39 years. He lives at Carol Woods.
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Well said, Professor Whitaker.