Underwater Utility Locating: Mapping Submerged Cable in Lake Ray Hubbard

With every new project, unique issues can arise that require a bit of innovation to solve. Oftentimes, engineers will need to think outside of the box to continue with their work. KCI was contracted to rise to the challenge and find solutions for a difficult subsurface utility engineering and underwater utility locating project in Texas.

The Texas Department of Transportation (TxDOT) is planning to widen the IH-30 main lane bridges crossing Lake Ray Hubbard. New frontage road bridges are also being added in order to alleviate congestion and provide greater access to proposed developments. However, existing communications cabling ran underwater alongside the route, and the exact location was unknown. During the previous widening effort, a contractor had accidentally cut the unmarked cable and caused widespread outages nearby, triggering the communications provider to lay new fiber optic lines across the lakebed. Ten years later a parallel cable was added. Hoping to avoid a similar outcome with the planned widening, TxDOT contracted KCI to locate and mark approximately 7,000 feet of submerged cable.

IH-30 Underwater Utilities Locating
With two active and one severed cable traveling along the bottom of Lake Ray Hubbard, utility location was paramount to completing the IH-30 bridge widening.

The Quality Level D engineering records available did not provide enough accuracy to commence design for the widening project. KCI performed Quality Level B subsurface utility designation adjacent to the bridge approaches to identify the alignment of the three utilities. After mapping the vaults and cabinets nearest to the shore, KCI crews utilized a Hydrovac to excavate test holes in heavy clay below the water table to confirm both horizontal location and vertical depth near the shoreline.

Underwater Utility Locating

Our underwater team mobilized from Maryland and worked with local SUE staff to source a multi-beam sonar device, which was then mounted to the firm’s dive boat. Engineers were hopeful that the sonar would return some data on the alignment of the cables during a bathymetric survey. They followed a grid pattern to map the lakebed. Other than a few locations where the cable was visible, the initial scan was inconclusive.

IH-30 Underwater Utilities Locating
A bathymetric survey of the anticipated alignment area was unable to accurately locate the three fiber-optic cables under years of silt.

Because they had anticipated that the cables would be difficult to identify, the team had a plan in place to dive along the alignment to visibly, if possible, and tactilely trace the cable and attach floating markers in 100-foot intervals. With submersible buoys not readily available, alternatives were considered, including the use of heavyweight balloons to mark locations, but the logistics and air supply required were not practical. In addition, the aggressive project timeline did not leave room for trial and error. Instead, our engineers demonstrated an uncommon mix of ingenuity and creativity in solving the challenge, proposing to fashion buoys by cutting pool noodles into two-foot intervals and tethering them along the alignment. A quick trip to a local retailer provided all the supplies needed with no delays in schedule.

Pool Noodle Infographic
By thinking outside the box, our team was able to successfully survey the underwater utilities by tying pool noodles to the submerged cable.

In placing the markers, divers had to contend with severe weather, extreme turbidity and low visibility while sifting through 20 years of silt settled on top of the utility lines. With years of experience in similar conditions, the team felt along the bottom to trace the alignment. Once complete, the outboard sonar unit was able to quickly pick up the exact location of the submerged cable, which sat at depths of up to 35 feet underwater. The markers were left in place tethered to the line to allow for contractors or other workers to easily locate the line in the future. The tetherings will last for several years, long enough for the design and construction to be completed. The marker material will not decompose in the water and poses no environmental hazard.

With our unique solution of tethering pool noodles along the alignment and mounting the sonar device to the bottom of our dive boat to map the submerged markers, TxDOT is now able to move forward with their improvement plans.

D. Scott Stockburger, PEVice President, Regional Practice Leader

D. Scott Stockburger, PE

The quick thinking of our engineers proved vital to completing this underwater utility locating task successfully. Once the bathymetric survey was completed, the alignment data was processed and overlaid in MicroStation against proposed bent locations to determine conflicts. It is assumed that drift of the utilities has not occurred from the original placement, although the concrete bags detailed in the proposed cable prints to anchor the line location could not be readily identified due to the buildup of silt over the previous 20 years. Despite the physical and logistic challenges, the final mapping was submitted to TxDOT under budget and ahead of schedule.