THE EFFECT OF NORTHRIDGE EARTHQUAKE ON LOS ANGELES WASTEWATER SYSTEM

The January 17, 1994 Northridge earthquake in the Los Angeles area caused substantial fluctuations in the influent flow to the Hyperion treatment plant (HTP), lasting almost a full day after the quake. Four reasons for these fluctuations have been identified: 1. The seismic wave momentarily displaced a portion of the influent wastewater collection system; 2. The HTP barscreens were twice blinded by the arrival of debris such as rags and grease shaken loose in that portion of the system; 3. The Los Angeles Glendale Wastewater Treatment Plant (LAG) upstream of HTP came offline and resumed treatment twice; 4. The Donald C. Tillman Wastewater Treatment Plant (DCT), which is even further upstream and near the epicenter, came off-line and resumed service once. The timing of these events relative to the flow fluctuations at HTP must be understood in terms of both surface wave (celerity) and normal flow velocity. These results provide insight into the hydrodynamics of a large collection system that could be useful in the design, testing and analysis of such systems, particularly with regard to storm surges. This presentation describes the successive events, their interpretation, and the methodology of the analysis.