Planning Support Services for San Francisco's Auxiliary Water Supply System (AWSS)

Abstract

The 1906 San Francisco earthquake (magnitude 7.8) is considered to be one of the most severe earthquakes in US history. Approximately 80 percent of San Francisco’s (City’s) total loss was caused by the fires following the earthquake (ATC, 2005). The earthquake and resulting fires caused approximately 3,000 deaths and destroyed nearly 28,000 buildings. The domestic water system was severely damaged, sustaining more than 300 breaks on water mains and 23,000 breaks on service connections. There was virtually no water available for firefighting. A study was conducted in 1908 to evaluate the need for a dedicated water system for firefighting in the City. Construction of an independent fire protection system, known as the Auxiliary Water Supply System (AWSS), was implemented to be used as the secondary defense against fires in the event the potable water system fails. This paper describes the process to select and recommend a Preferred Program Alternative which optimizes benefits from repairs and improvements to the AWSS, given the potential for seismic activity in the area. Level of Service (LOS) performance goals were targets selected by San Francisco Public Utilities Commission (SFPUC) decision makers against LOS criteria metrics by which performance of the AWSS and the benefits of the Improvement Program (Program) were measured. Performance of the AWSS with regard to the LOS criteria was measured using various modeling tools including hydraulic modeling, reliability modeling, and geotechnical analyses. The LOS criteria recommended to SFPUC for development of the AWSS program was Water Delivery Reliability, measured both Citywide and in defined geographic areas called Fire Response Areas (FRAs). LOS Performance Objectives were selected for development of the Program Alternatives with a minimum for each FRA and a resulting minimum average for San Francisco as a whole. A condition and needs assessment was performed, projects were identified and sized utilizing the hydraulic and reliability modeling tools developed for the project. Selected projects were grouped into program alternatives, with the Preferred Program selected by an analytical hierarchy process.