Halff Associates provides full service to our water utility clients, from the assessment and modeling of existing infrastructure to the design of pipelines and facilities. For the San Jacinto River Authority (SJRA), Halff developed a hydraulic model of the Highlands Canal System to identify opportunities to improve the efficiency of the canal system. The hydraulic modeling was utilized to determine whether siphons and other hydraulic structures could be removed, where the channel embankment could be improved or raised, and where operation and maintenance budgets should be prioritized. Halff’s hydraulic modeling presented SJRA with viable alternatives to optimize their system.
SJRA canal system study
The SJRA operates and maintains the Highlands Canal System. The canal system was originally constructed in the early 1940s as part of the war effort and was turned over to the SJRA in 1945 at the war’s conclusion. The 27-mile system includes three canals that are located in east Harris County and deliver raw water from Lake Houston and the Trinity River. The system also includes a 1,400-acre staging reservoir and pump stations on Lake Houston and the Coastal Water Authority (CWA) canal that provide raw water to industrial, public water supply and agricultural customers pursuant to long-term water supply contracts. SJRA is currently contracted to deliver more than 80 million gallons per day (MGD) of water to its customers.
The Highlands Canal System currently contains various water-control and utility crossing structures consisting of 49 siphons, 17 culverts and bridge structures as well as a small number of control gates. The siphons are used to facilitate the low-head transfer of water under road crossings, utilizing the hydraulic head of the system. Levees are used along the canals to increase capacity and maintain hydrologic independence.
In 2013, SJRA recognized the need to study the conditions of the canal system as a component of developing a Capital Improvements Program for system improvements. Halff participated in the Highlands System Evaluation to study the current conditions of each of the three canals. The assessment included an evaluation of the current capacity conditions of the canals; hydraulic structures and levee conditions; water quality analysis; field survey of the siphons/structures; bathymetry; digital terrain development; detailed canal hydraulic modeling; and conceptual improvement recommendations. Halff prepared a HEC-RAS hydraulic model in steady and unsteady states to evaluate the hydraulic capability of the canals and the hydraulic structures. The hydraulic model included the 70 siphons/ structures along the canal system. The unsteady RAS model was calibrated to measure flows and headlosses to recreate existing conditions and evaluate existing and anticipated flow demand scenarios. The use of an unsteady hydraulic analysis allowed for the modeling of gates, pumps, storage volumes and interaction with the reservoir. The study identified areas of deficiencies in the canal system, though no improvement alternatives were recommended.
In 2015, Halff conducted an alternative analysis of the Main and South Canals. The study included an evaluation of the potential capacity of these canals, hydraulic structures and levee conditions, detailed canal hydraulic modeling and conceptual improvement recommendations. The HEC-RAS hydraulic model was used to evaluate the hydraulic capacities of the canals and structures. An analysis was conducted to identify improvement alternatives for levee repair; siphon/structure maintenance, rehabilitation, improvements or replacement; sediment removal; and operation optimization.
The study equipped SJRA with information to refine the capital improvements plan based on costs, constructability and consequence of failure. Halff assisted SJRA with developing a preliminary schedule of projects to maximize the capacity of the canals. The SJRA used the schedule and opinions of costs to update its Capital Improvements Projects list.
The alternative analysis determined that the limiting factor to increased flow capacity in the entire system was the upstream 3 miles of the Main Canal located from the Lake Houston Pump Station to Siphon 6. This area contains three siphons that were constructed in the 1940s and limit the capacity. Halff is creating a PER to remove these siphons and improve the levees along this stretch of canal. These improvements will increase the overall capacity and reliability of the entire canal system.
Halff is fully invested in sharing valuable information that can help our clients solve immediate issues and plan for the future through innovation and smarter solutions. Hydraulic modeling is a key Halff service, and our water resource professionals stay up-to-date on the latest computer programs and techniques. We consider hydraulic modeling to be an important tool for our clients and as such provide training opportunities each year. Upcoming class lists are featured on our website (www.halff.com) and Facebook page (https://www.facebook.com/HalffAssociates/). If Halff can assist your team with a water resources issue, please call Executive Vice President Jessica Baker, PE, CFM, PMP, at (214) 217-6692.
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Texas Regional Stormwater Conference
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Jan. 14, 2021