City of Round Rock BCRWWS Drainage Improvements
Erosion Control Solutions in Round Rock
Back in 2000, under Contract 6 of the Brushy Creek Regional Wastewater System (BCRWWS), a 72-inch diameter wastewater line in Round Rock was constructed by open-cut excavation through the overburden soils into the limestone. When the line was installed, the trench was backfilled by conventional methods, using a granular backfill, topsoil, and seeding. The finished grade was set to create a level pasture area instead of following original ground contours descending to Brushy Creek. In the Contract 6 section, the alignment of the wastewater line coincided with a depression that conveyed floodwater runoff from upland areas.
Over time, floodwater eroded the overbank and washed backfill into the creek exposing the saw cut limestone. The grading at the Contract 21 site had not been restored to original ground contours at completion of the project; instead, the finished grade filled a portion of the Brushy Creek floodplain.
KFA was contracted to review the erosion problems located at both sites and provide a Preliminary Engineering Report (PER) with two restoration options. The first alternative consisted of limestone blocks which are used throughout Austin on stream channel bank stabilization projects and were locally available from a nearby quarry. In this application, where they would function as channel spillway, the potential for erosion behind the blocks was a concern.
KFA and the City selected the second alternative, a stepped-spillway constructed with gabions whose elevation coincided with the natural limestone layer. The gabion’s larger typical size and ability to be tied together allow them to resist significantly more lateral movement than the limestone blocks and their construction cost is approximately 25 percent less expensive. The flood flow is designed to cascade over a series of three-foot “waterfalls,” providing significant energy dissipation along its length. The steps were located at roughly the same elevations as the original limestone ledges, matching a more natural channel configuration. The Contract 21 site was graded to restore the floodplain to the pre-project topographic contours.
Our KFA team produced a technical memorandum, final construction plans, and cost estimate for both sites. We also provided construction administration services, including reviewing submittals and pay applications and responding to RFIs.
Construction was completed in 2011. This project provided a cost-effective solution for the City of Round Rock to fix the erosion issue caused by floodwater runoff.