Hydraulic Evaluation and Energy Optimization for a 134 Mile Integrated Raw Water Transmission System

The Tarrant Regional Water District (TRWD) and City of Dallas have partnered to explore the feasibility of an integrated raw water transmission system to meet future water needs in North Central Texas (TRWD and Dallas service areas). The Integrated Pipeline (IPL) project's ongoing planning and conceptual design phases involve multiple analyses such as operations, capital and life cycle costing, facility siting assessment, permitting and regulatory reviews, and hydraulic evaluation. With an ultimate goal of building a reliable and efficient transmission system, the final system configuration is continuing to evolve. The 134-mile long raw water transmission main pipeline ranges in diameter from 84-inch to 120-inch conveying water from the East Texas to West Texas regions with peak capacity projected at 347 million gallons per day (mgd). Pipe segments converging and diverging from the mainline constitute an additional 18 miles of transmission pipeline. The IPL will be integrated with 72-inch to 108-inch diameter existing transmission pipelines, which currently convey up to 247 mgd of water. A thorough hydraulic evaluation of several potential pipeline corridors was evaluated during the planning phase. Hydraulic evaluations developed and compared pipe sizing for peak flow conditions and capacity/power requirements for pumping stations. This information was fed into a basic decision matrix for various corridor options and combinations to narrow down to a preferred pipeline corridor. Several pumping configurations are being considered for the selected IPL corridor. The pumping facilities consist of three intake stations and two or three booster pump stations depending on the selection of the final system configuration. Various tunnel configurations are being analyzed in order to conserve pumping power and avoid high points and difficult construction areas along the pipeline corridor. The IPL will deliver water to various lakes and water treatment plants served by TRWD and Dallas. Energy optimization is an integral part of this transmission system as it involves pumping water over long distances using large diameter pipelines. Optimization of pipe sizing is being performed by comparing capital investment costs versus energy costs on a present worth/life cycle basis. Potential gravity operation is a possibility over a wide range of low flows using balancing reservoirs at high points and pump station bypass modes at low demand conditions are also being examined. Such potential power savings as well as operational benefit is incorporated in the hydraulic evaluation. Achieving IPL system redundancy, reliability, and operational flexibility in conjunction with the existing transmission system operation is a critical path forward. The hydraulic and operational aspects of achieving these goals will be explored in this paper.