Faulty FEMA Floodplain Maps

From FEMA's Flood Map Service Portal, modified with my labels

The current FEMA Flood Hazard maps for Duharts Creek were set in 2007, with one 2013 addendum for the Target creek reconstruction at Tributary D-8 that ignores the added bioretention ponds, and with no changes yet to reflect the infill at the Tributary D-6 conjunction for the 2013 Starbucks coffee shop.  These maps are of data provided by and used by the City. And they are inaccurate, perhaps dangerously so, in the area immediately south of the parcel proposed for development.

Floodplain map provided me by City Stormwater Department, with my labels

The map simply ignores the effects of the house sitting at 402 Deerwood Drive directly across the creek, nor does it take into account the effect of the four-foot high retaining wall going 3/4 around that property (see closeup above), all along the Duharts Creek side and the Armstrong Creek side and to my family's property side at the south.  Those constructions, permitted in the flood plain by the City in the 1970s before a floodplain ordinance and intensive commercial developments upstream, have a major effect on water flow during significant flood events. [For the second time in just eighteen months, Duharts Creek hit 100-year flood event lines at this parcel on December 30, 2015 - watch the video below and see many other images from this event at our Facebook page.]

Duharts Creek/Lineberger Parcel Flood Event December 30, 2015

The increased runoff from those commercial developments along Duharts Creek has altered the ability of Armstrong Creek to drain out quickly, and the number and severity of floodplain events in the Armstrong Creek tributary's floodplain have increased, impacting the enjoyment and use of those properties. The "100-year floodplain" along Armstrong Creek certainly functions more like a ten-to-twenty year one now.  Below are two videos showing how a very heavy summer storm (four-inches in two hours - a volume that is high, but not a 100-year event) inundated that floodplain in the summer of 2014.  As part of a family that owns a 100-year floodplain, I'd rather City action not turn it into a regularly recurring swamp.

A spring shower view across my family's backyard, the "100-year floodplain" of Armstrong Creek, with creek at back of property; and same yard becoming fully flooded in summer 2014 in two YouTube videos below

Armstrong Creek is the "J-shaped" creek leading into the Lineberger parcel at upper center (from the USGS National Map website)

Armstrong Creek, Tributary D-4 on City/FEMA maps, drains a wide basin from Armstrong Circle at New Hope Road to major portions of the Sedgefield, Gardner Woods, and Gardner Park neighborhoods.  In the last forty years its storm flow has also increased, in part due to new runoff from the Armstrong Park Road extension south to New Hope Road and commercial developments along the northeast side of New Hope down to Redbud Drive.  In water volume, it is the largest single tributary to Duharts Creek.  Where it joins Duharts Creek adjacent to the southside Lineberger parcel and just yards from the confluence of Tributary D-3, the conjunction could be said to be the most sensitive to commercial intrusion of any in the county.

Water volume discharge rates for Duharts Creek and its tributaries (from NC Floodplain Mapping Program)

The 12-foot high retaining wall at the back of the proposed Lineberger development will sit across Duharts Creek from the unaccounted-for 4-foot high wall at 402 Deerwood, and at that creek's confluence with Armstrong Creek, altering water behavior during flood events.  Currently, the City's Stormwater Division does not have any measuring station for ongoing stream flow monitoring on either commercially developed Duharts or residential Armstrong Creeks.   Instead, cross-sections are shot on Duharts (see the FEMA map at top, and below) to monitor any changes in the stream channel.  Only one current cross-section is taken along the floodplain section of Armstrong Creek between Deerwood Drive and Pamela Street.  This area recently had storm channel work done by the City (with no notice to adjacent property owners across the creek) in an effort to mitigate erosion along the expanding creekbank that threatened to undermine several houses along Pamela Street.  Why does the City and FEMA not regularly collect stream flow and storm channel profile data along this important waterway?  Would it not be easier to get data to prevent problems rather than create problems due to the absence of accurate data?

Cross-sections to be monitored - but how often? and why not re-checked after each new floodplain construction?

I have asked if the City Stormwater Department has plans to correct and update its maps, and have been told there are none; but that they will continue to coordinate with FEMA to have this reach remodeled and resurveyed to current conditions. "Until that point, the maps and model are the best tool we have available, and are the only ones recognized by FEMA." By the way, FEMA says that a request for a letter of map revision (LOMR) to its floodplain maps must come from the "CEO of the municipality," i.e., in our case, the mayor - a developer who has announced the commercialization of this southside parcel as a top personal priority for 2015.

Our one-time neighbor, and friend of nature, E.C.

As a nine-year-old new to the neighborhood, I used to jump across Armstrong Creek, then three feet across with waist-high-deep banks, and dig out crawfish.  That same creek is now ten feet across in spots and has banks over my six-foot-tall head.   In the 1970s I explored Duharts Creek around the Lineberger parcel with a nature-lover you may know, Mountain Man Eustace Conway, who lived just down the street on Deerwood. There were minnows and turtles and crawdads in the creek then. Eustace, not surprisingly, wanted to explore much farther and deeper and snakier along the creek than I did.   Once a flood brought a massive alligator turtle into the neighbor's yard.  Habitat changes brought by infill development make me doubt there are any alligator turtles in Duharts now. I wonder what it would look like after this proposed development, or after the even heavier developments across I-85 that are proposed. I don't have the skills to model and mitigate those impacts (my son studying civil engineering at Vandy might one day).  

 
But I hope our decision-makers will at least have accurate data to do the modeling on which to base sound development decisions. I don't believe they currently do.

[7.12 update - some good news.  A neighbor along Rosemary Lane reports that her German shepherd found a snapping turtle in the creek recently - so maybe the summer's drought has let the stream environment get a little friendlier for wildlife.  With a few breaks from our intrusions, nature will try to repair itself.]