Numerous shallow depressions in Lubbock called playas can become little lakes, holding normal rainfall. However, in bigger storms, they can form a chain reaction of overflow runoff from playa lake to playa lake, and finally into normally dry stream beds that overflow into the river drainage system. Storm sewer construction in Lubbock is more expensive than in some other areas because the uplift of the Yellowhouse canyon rim necessitates a deep cut, sometimes in rock; because of the extra expense of tunneling under railroad tracks; and because the extremely flat grade of the terrain dictates larger pipe sizes to carry the water at these flat grades.
The City of Lubbock chose Parkhill and a partner firm to design a storm drainage relief system for 12 playa lakes to control stormwater runoff. The standing water on some streets could take as many as 120 days to abate. Extensive hydrological and hydraulic computer model simulations were performed for the design. Computer modeling included the use of HEC-2, WSP, TR-20, HEC-1 and adICPR. Geopak was used for conversion of surveys to a three-dimensional drawing format and export of MicroStation CADD files.
Before the improvements were completed, the affected areas by the freeway experienced significant flooding that lingered for weeks. Great engineering started with knowledgeable people tackling complex problems. The team dedicated to this project were all detailed-oriented. It started with getting the correct field information. Accurate topography was essential. New aerial photographs and ground contours took considerable time on the timeline front end. Meanwhile, the team obtained detailed field topography of the existing playas. The team spent extraordinary effort in the design to carefully model the watershed, select the improvements, analyze the anticipated results, and then double check the model and results again. Confident with the design, the team prepared very detailed drawings and specifications to clearly describe the expected results.
In some areas, it was more efficient in that era to use a machine called a boat, upper left, to create cast-in-place concrete pipe, an efficient, economical and durable product. Concrete is placed inside the tray on top to create a concrete pipe, then the pipe is pushed to the back concave form to harden and dry, in a continuous process. The front part of the machine is used in creating the outside of the pipe, and the back part is used to create the inside of the pipe. The bottom right photo shows the view from inside the boat looking out into the trench.
Marsha Reed, P.E., former Senior Civil Engineer with the City of Lubbock, Texas, said she was impressed with the pipe material selections, and how those materials interacted according to the construction methods used. “This greatly aided resolving the constructability issues,” she said.