A physical and mathematical model used in the third tier of the California Department of Water Resources ' Urban Levee Geotechnical Evaluations Program Erosion Screening Process (ESP) is described. It has been developed and calibrated based on the results of Erosion Function Apparatus (EF A) test results of California river and levee soil samples, confirming the relationships re lating general soil classification to erosion resistance as a function of water-induced shear stresses. The model is used to assess erosion during normal andlor flood conditions for combined wind and current loads. An example calculation using the method is provided.

The elastic response spectrum provides the engineer with two important elements of the seismic structural response: intensity and frequency content. However, this approach does not provide information on the phasing, number of occurrences of the maxima, and duration. This paper uses the Short Time Response Spectrum (STRS) methodology to evaluate ground motion time history characteristics and their implications to engineering analyses. The STRS provides a TimePeriod-Intensity representation of structural response to ground motions and compatible measures of earthquake duration. Thus, the STRS captures not only the maximum amplitude and frequency content of the earthquake motion but also its time evolution.

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The California Department of Water Resources ' Urban Levee Geotechnical Evaluations Program is evaluating urban levees in the Sacramento and San Joaquin river systems. A three-tiered Erosion Screening Process (ESP) has been developed to qualitatively assess the current risk of erosion failure on a levee's waterside slope. Erosion is caused mainly by a weakened geometric levee cross section or poor initial construction coupled with high flow velocity and/or wave action. Levees are evaluated through this three-tiered screening process until the erosion risk potential is determined. Each of the tiers progressively increases in detail. Tier one assesses overall geometry, fetch length, and historical performance. In the second tier, assessments are performed to evaluate the levee ' s surface resistance to velocity and wave shear stress. Also, field reconnaissance verifies expected levee performance and look for signs of erosion or unstable conditions. In the third tier, the ESP analyzes levee geometry, river geometry, soil and vegetation types, wind-wave impacts and river velocity impacts to categorize levee reaches into a high, medium, or low erosion risk.

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