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Study dissects flooding fixes in Tree Streets District

June 16th, 2013 8:16 pm by Gary B. Gray

Study dissects flooding fixes in Tree Streets District


A Knoxville company handling the majority of the city’s storm water design and engineering has completed a drainage study of the Tree Streets District to determine how to control water flow and minimize flooding along the State of Franklin corridor from Buffalo Street to University Parkway. 


Don Mauldin, Lamar Dunn & Associates executive vice president and lead consultant/engineer, ran through the results at last week’s City Commission meeting. The main problem identified was that drainage pipes are not sized to properly accommodate runoff. However, should the four main identified projects be done, the total estimated cost to the city would be about $3.5 million.


Mauldin suggested the fixes be done in phases beginning with a portion of the Earnest Street project, which carries with it an estimated $210,000 price tag. This initial phase would bring new 54-inch pipe under State of Franklin Road that drains water to the south side of the road. The existing 30-inch pipe would remain and be used only to carry water away from the road.


The completed Earnest Street phase would run about $1 million.  


“This project will have significant immediate flood mitigation benefits by providing additional capacity to remove water from State of Franklin, mitigating the flood potential adjacent to the historic train depot, which is the proposed future location of Tupelo Honey Cafe,” he said.


 Additional drainage facilities also would be placed under State of Franklin and the railroad tracks.


“State of Franklin is a heavily traveled thoroughfare in Johnson City and the preference would be to avoid open cuts across the road if possible,” he said. “A new pipe system would extend between the existing buildings to Ashe Street. From Ashe Street, there would be a new drainage system with its spine along Earnest Street extending to Poplar Street.”


The study points out three additional areas of concern: Sevier Street, Watauga Avenue and the Harman Ice Company.


Storm water collects at the intersection of Sevier and State of Franklin and passes under State of Franklin in an 18-inch pipe that connects to Brush Creek, but the existing pipe is much too small to accept the volume of runoff. 


Mauldin proposed the installation of a 42-inch pipe from the existing manhole in Sevier to allow the pipe to discharge into the open channel of Brush Creek. This proposal has an estimated cost of $313,000.


Runoff from Watauga and storm water collection in that portion of State of Franklin also is in need of larger pipes. Two 6-foot by 4-foot box culverts have been proposed from the south side to the north side of State of Franklin, then under the railroad tracks and then parallel to the tracks and tying into Brush Creek.  


This plan is estimated to cost about $543,000.


Fixing flooding problems at Harman Ice Co. is the most expensive proposition, at about $1.6 million. Mauldin said when water levels rise in Brush Creek, the flap gates in this area are forced closed.


“When the gates close, the existing pipes have no flow, resulting in flooding,” he said. “The analysis is complex, because it is near impossible to accurately estimate or measure the amount of runoff that will flow through existing pipes before the flap gates close.”


The plan calls for a three-phase project in which 54-inch pipe would be installed from west of the company site to an area near Arrow Mechanical; installation of 66-inch pipe, or a 6-foot by 4-foot box culvert from Arrow Mechanical to Watauga Avenue; and installation of a 8-foot by 4-foot box culvert from Watauga to Brush Creek.


“The flooding at Harman Ice Company will not be relieved until the project is complete,” he said.   


The 285-acre area is located west of the Central Business District and east of the East Tennessee State University campus, bounded generally by University Parkway, Buffalo Street and State of Franklin Road. The area is primarily residential with commercial and light industrial along the district’s northern edge.  


Houses in the area are generally older homes on large lots. And because of the close proximity to ETSU, some of these homes have been converted to student-oriented apartments.


The southern boundary is a ridge top, but the topography flattens near the north end where businesses are located. There are no catch basins or pipes in the upper reaches of the area to collect runoff. There are catch basins in the lower reaches at street intersections that connect to pipe systems, and water from the entire area runs in to Brush Creek. 


The district has experienced periodic flooding at a handful of intersections, and the study revealed that many of the catch basins in the lower half of the drainage area are in poor condition. Combine this and the fact that there are few drainage facilities on the steeper terrain, and the result is high-velocity water flow, especially along the northbound streets to the lower areas. 


Meanwhile, “flap gates,” which release water from four main areas that then drain into the south side of Brush Creek, were found in the study to be roughly at the same height between the two sides of the road, resulting in blocked water flow. The study also revealed the Watauga Bridge is acting as a barrier for water to reach Brush Creek.

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