Hydraulic Transient Considerations in Conceptual Design

Abstract

Control of hydraulic transients is of critical importance in the design of transmission pipelines. While horizontal alignment is a key element of conceptual design, there are issues related to vertical alignment which affect not only steady state hydraulics but also the transient characteristics of the pipeline. In the work summarized in this paper, the author developed horizontal and vertical alignments for a 48-inch raw water transmission line from a lake intake structure to a water treatment plant 27,000 linear feet distant. Steady state and transient hydraulic models were then developed from the preliminary alignments and the baseline condition was established. Full power pump trip transients were modeled and simple surge control options were evaluated to form the baseline. Modified vertical alignments were then developed to evaluate the transient characteristics of the pipeline with a tunneled section in place of a relatively high near-surface pipe segment. It was found that the tunnel option reduced the size of the hydro-pneumatic surge tank, but did not eliminate the need for it. While the control of hydraulic transients is not the only consideration in the determination of vertical alignment, it should be a major consideration and can be a source of value engineering. TRANSMISSION SYSTEM OVERVIEW The system modeled in the current study is based on a conceptual design for a proposed raw water pumping station and transmission pipeline. Raw water withdrawn from a lake intake structure is conveyed to the day pond of a water treatment plant in this design. The model is greatly simplified and strictly conceptual in nature. Table 1 summarizes the relevant properties of the piping system as modeled.