UCLA Civil and Environmental Engineering

We are working towards developing risk assessment tools for levees to identify conditions that correlate with ground failure rates. Our initial data set is from the 2007 M_w6.6 Niigata Chuetsu-oki earthquake in Japan. Liquefaction-induced ground failure is a major source of levee damage in this case, so groundwater elevation is expected to be a critical factor affecting damage locations. What we seek is the water level in or beneath the levees themselves along the full length of the study region, which encompasses approximately 110km of levees. The available data includes river water levels (generally below the levee toe) and groundwater levels within levees measured from boreholes. Our approach, which is applied along the full length of the study region, is first to establish the river water elevation (RWE) both at the time of the earthquake and at the time of subsurface exploration in the levees, and second to establish the differential between levee ground water elevation (LGWE) and RWE at the exploration time. Each step presents challenges due to sparse and incomplete data. Once the above relations are established, the LGWE is taken as the sum of RWE on the earthquake date and the differential. Comparing the result to damage reports indicates that levee segments with LGWE higher than the levee base elevation have approximately nine times higher damage rates than those with deeper ground water.