Comparative Analysis of Raw Water Transmission System Design with Field Hydraulic Testing: Hydraulic and Surge Startup Testing for a Raw Water Transmission System

Colorado Springs Utilities and other regional partners are currently constructing a new water delivery and treatment system known as the Southern Delivery System (SDS) in southern Colorado. A major component of SDS is a raw water transmission system that comprises approximately 50 miles of predominately 66-inch diameter pipeline and three large raw water pump stations with ultimate capacities ranging from 78 to 100 million-gallons-per-day (MGD). Major construction of the pump stations was completed in the fall of 2015, which was followed by extensive field hydraulic testing to verify the design and optimize operations. The first phase of field hydraulic testing recorded steady-state system hydraulic characteristics (i.e., system curves). Although this is common practice for large water transmission systems, for SDS, establishment of accurate system characteristics was a critical component of automatic control algorithms designed to select the most efficient combination of pumps and speeds for a given flow rate. The second phase of testing focused on the hydraulic transient (surge) mitigation system, which is a critical component of the raw water transmission system. The surge design was verified during startup testing by operating the system at various flow rates up to the peak capacity, followed by a simulated power outage that caused uncontrolled stopping of all pumps simultaneously. Data was recorded using high resolution pressure transmitters located at critical locations and compared to the design values. A final area of testing that is often overlooked is pump startup. In a long pipeline system, such as SDS, the system must overcome the inertia of water mass, which manifests as additional head resistance during pump startup. During field testing acceleration of the water was monitored from startup to steady-state to better understand the change in head resistance and associated hydraulic transients. This paper presents the results of field testing completed during the startup phase with a specific focus on how the results compared to detailed analyses completed during design of the system.