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<br />54 <br /> <br />. <br /> <br />site on the river system, such as a hydraulic structure location, is estimated <br /> <br />by comparing the meander characteristics of the specific site to the range <br /> <br />of meander characteristics of the river system. If the amplitude and radius <br /> <br />of curvature at the specific site are smaller than the average of the river <br /> <br />system, then the migration tendency will be small. However, if the amplitude <br /> <br />and radius of curvature are greater than the average of the river system, the <br /> <br />migration tendency will be greater. <br /> <br />When lateral migration potential is high, engineering control measures <br /> <br />to prevent failure of a structure are necessary. Two possible measures to <br /> <br />control lateral migration are bank stabilization and channelization. It is <br /> <br />important to mention again, that the estimation of lateral migration is a <br /> <br />qualitative engineering judgment based upon past and present river responses. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />3.10 Seepage Force <br />Seepage forces occur whenever there is inflow or outflow through the <br />bed material and banks of a channel formed in permeable alluvium. The in- <br />flow or outflow through the interface between water and channel wall depends <br /> <br />on the difference in pressure across the interface and the permeability of <br /> <br />the bed material. The seepage force acts to reduce or increase the effective <br /> <br />weight and stability of the bed and bank materials depending on inflow or <br />outflow. As a direct result of changing the effective weight, seepage force <br /> <br />can influence the form of bed roughness and the resistance to flow for a <br /> <br />given channel slope, channel shape, bed material, and discharge. <br /> <br />Seepage force may create an upward hydrostatic pressure on structures <br /> <br />(uplift). The magnitude and distribution of seepage forces in a foundation <br />and the amount of underseepage for a given coefficient of permeability can <br /> <br /> <br />be obtained from a flow net. The weighted-creep theory as developed by <br /> <br /> <br />Lane (1935) is suggested as a means for designing hydraulic structures on <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br />