As further development is planned in downtown Wylie, council debated drainage additions that could mitigate current issues, such as pooling water after storms.
The results of a recent drainage study were presented during a work session as part of the Tuesday, April 25, council meeting. To solve the issue, four options with a combination of aboveground and underground detention options were presented across a few areas downtown.
Gabriela Bell, a project manager with Huitt-Zollars, presented the findings to council highlighting a shortage of drainage options downtown. Specifically, in areas along the southern portions of Ballard Avenue, there are slow surface flows meaning that water tends to pond after a storm.
There is not a high risk of further development adversely affecting parts of Ballard Avenue because most of the area is largely built out.
“The impact that you’re going to see is at the surface level,” Bell said. “The extent of the flooding is more significant here. We’re not getting that water farther downstream, we’re just allowing it to pond to a greater extent in this area.”
However, in areas near Brown Street and State Highway 78, there is more at risk if action is not taken to address substantial surface flows.
“Without any mitigation measures in place, [it] will adversely affect that property because of the additional impervious cover that we can expect with future development of the downtown area,” Bell said.
The first option presented would implement a surface detention pond in the proposed development at the intersection of Brown Street and SH 78 with three underground detention areas near Marble Street, underneath a proposed parking lot of Birmingham Street and in the southern portions of Ballard Avenue. Of the sites, the one near Birmingham Street would have the lowest capacity, but the three others will likely hold around 1 million gallons of stormwater.
The total cost for the first option is $7.3 million with a $460,000 design fee.
The second option was significantly different, proposing the construction of several reinforced concrete boxes underneath downtown roads to collect stormwater. The only continuity was the underground containment near Birmingham Street.
“This one might not be as ideal due to the amount of infrastructure required to have the equivalent amount of storage that is required,” Bell said. “If we were to store that same volume under the street, we would need about 2,800 linear feet of 10 feet by 5 feet concrete boxes.”
The options cost was $17.4 million and a $1.15 million design fee.
The third option would maintain the Ballard Avenue and Birmingham Street underground detention areas while converting the Marble Street underground area into a shared aboveground space with a detention pond in the Brown Street development.
The cost for the third option would be $5.6 million with a $340,000 design fee. The fourth option was the same as the third with one modification: adding vertical walls that would take the cost to $6.1 million with a $370,000 design fee.
Council took no action but directed staff to keep working with area partners, such as the North Texas Municipal Water District, to discuss potential conservation and detention options.
For the full story, see the May 3 issue of the Wylie News.