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<br />50 <br /> <br />Assume a velocity of 5.0 feet per second and cillculate the impact load for normal and spe- <br />cial impact conditions. <br /> <br />Normal impact load: the normal impact load is a 1,000 pound mass traveling at the <br />velocity of flow. <br /> <br />FI = MV <br />t <br />F, ~ WV <br />gt <br />= 1,000(5.0) <br />(32.2)(1 ) <br /> <br />M=W <br />g <br /> <br />= 155 Ibs acting on anyone foot square surface of the submerged area <br />normal to the flow. <br /> <br />Special impact load, the special impact load i~ 100 pounds per foot of length normal to the <br />flow, Assume the structure is 70 feet wide. <br /> <br />FJ = MV <br />t <br /> <br />M=W <br />g <br /> <br />~ WV <br />gt <br /> <br />W ~ 100 Ibs/ft x 70 ft <br /> <br />= 7,000(5.0) <br />32.2(1) <br /> <br />~ 7,000 Ibs <br /> <br />~ 1,087 Ibs acting on a one foot wide strip the length of the structure. <br /> <br />FI ~ impact load (Ibs) <br /> <br />M ~ mass [Ibs,sec' ] <br />ft <br />W = weight (Ibs) <br /> <br />g ~ acceleration of gravity (ft/sec') <br /> <br />6.5 Erosion forces <br /> <br />6.5.1 General <br /> <br />Erosional forces along channel banks and fill embankments are greatly dependent on the <br />direction of flow in relation to the embankment and the magnitude of the velocity, During <br />flooding conditions, the direction of flow can change significantly due to the volume of water <br />and diversion due to obstructions. Also during flooding, velocities are significantly increased <br />and thus the potential for erosion is great. <br /> <br />Another important erosional condition that OCCurs during flooding is local scour. Local scour <br />is generally caused by reduction in flow area inducing an increase in flow per unit width <br />which results in higher velocities. This reduction in flow area or increase in velocity will occur <br />at the corners of structures, at piers, piles and walls and along embankments that come in <br />contact with the flow. <br /> <br />6.5.2 Application <br /> <br />Erosion and local scour should be a concern fOr all structures located in the flood plain, <br />Another major concern for structures located close to the channel is bank erosion. However, <br />bank erosion and protection are not within the scope of this manual and the reader is <br />