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<br />Critical velocity for Dso bed material size, mls <br />Critical velocity for D90 bed material size, mls <br />Q/A., mls <br />Average velocity of flow zone below the top of the footing, mls <br />Approach velocity when particles at a pier begin to move, mls <br />Maximum average velocity in the cross section at Qmax' mls <br />Velocity ratio <br />Shear velocity in the upstream section, mls <br />(tip) = (gytSJ)Y. <br />Volume of water in the tidal prism between bigh and low tide levels, m3 <br />Bottom width of the bridge less pier widths, or overbank width (set back distance less pier widths, <br />m <br />= Topwidth of the scour hole from each side of the pier of footing, m <br />WI Bottom width of the upstream main channel, m <br />W 2 Bottom width of tbe main channel. in the contracted section less pier widths, m <br />(J) Fall velocity of the bed material of a given size, mls <br />Y Depth of flow, m, This depth is used in the Neill's and Larson's equation as the upstream channel <br />depth to determine V c' <br />Depth of flow in the contracted bridge opening for estimating a median stone diameter, Dso, m <br />Amplitude or elevation of the tide above mean water level, m, at time t <br />Average depth of flow on the floodplain, m <br />Distance from the bed to the top of the footing, m <br />Existing depth of flow, m <br />Depth of pier scour, m <br />Average scour depth, m <br />Depth of contraction scour, m <br />Average depth in the upstream main channel or on the floodplain prior to contraction scour, m <br />Depth of flow directly upstream of the pier, m <br />Depth of flow at the abutment, on the overbank or in the main channel for abutment scour, m <br />Average depth in the contracted section (bridge opening) or on the overbank at the bridge, m <br />A verage depth under lower cord, m <br />Vertical offset to datum, m <br />Average bed shear stress at the contracted section, Pa or N/m' <br />Critical bed shear stress at incipient motion, N/m' <br />Unit weight of water (9800 N/m3) <br />Density of water (1000 Kgim3) <br />Density of sediment (quartz, 2647 kgim3) <br /> <br />V.so <br />V.90 <br />V. <br />Vr <br />Vi <br />Vmax <br /> <br />VR <br /> <br />V. <br /> <br />VOL <br />W <br /> <br />Ya <br />Yr <br />Yo <br />Yps <br />Ys <br />Ys. <br />Yt = <br /> <br />Y2 = <br />Z <br />"[2' to <br />t. <br />y <br />P <br />Ps <br /> <br />LIST OF SYMBOLS (continued) <br /> <br />= <br /> <br />= <br /> <br />= <br /> <br />= <br /> <br />= <br /> <br />xi <br />