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<br />E. Step 2. Evaluate Hydraulic Conditions. <br /> <br />1. Channel bed slope increased by subsidence, <br /> <br />2. Manning's n. <br /> <br />. 0.02 main channel <br />. 0.04 overbank area <br /> <br />3. Knowledge of basic hydraulic conditions (velocity, flow depth, etc.) <br />for various flood events is essential to completion of a quantitatively <br />based Level 2 analysis. Hydraulic information is often required for <br />both the main channel and the overbank areal (e.g., contraction scour <br />analysis). Application of the Continuity Equation to the 1995 <br />flood peak on L.os Gatos Creek indicated the followin!~ average <br />hydraulic parameters: <br /> <br />Flow depth <br />Average velocity <br /> <br />y'" 6,1 m (<~O ft) <br />V := 3.4 m/s (11.3 ftIs) <br /> <br />4. Backwater at the bridge extended more than 609 m (2,000 feet) <br />upstream. <br /> <br />F. Step 3: Bed and bank material analysis. <br /> <br />1. Erodibility or stability of a channel depends on the size of particles <br />in the channel bed and banks. Additionally, knowledge of particle <br />size is necessanJ for Level 2 sediment analyses. <br /> <br />2. Bed material at Los Gatos gagll~ (1.5 miles upstream from bridge), <br /> <br />. <br /> <br />Depths 0,15 to 0.91 m (0,5 to 3.0 feet) D50 = 0.34 mm <br />Depths 0,91 to 2.13 m (3,0 to 7,0 feet) 050 = 0,70 mm <br />Clay hard pan layer <br /> <br />. <br /> <br />. <br /> <br />5,7 <br />