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<br />I <br />'ie <br />I <br />I <br />'I <br />I <br />I <br />I <br />I <br />-- <br />I <br />I <br />II <br />I <br />I <br />I <br />I <br />I. <br />I <br /> <br />CHA~TER I <br /> <br />INTRODUCTION <br /> <br />1 he purpose of this ehapter is to lay the groundwork for apPlication of the <br />concepts of open-ehannd flow, fluvial ')eomorphology, and river meehanics to the <br />design, maintenance, and related environmental problems associated with highway <br />crossings an<1 encroachments. <br />8asic definitions of terms and notations adopted for use herein have been <br />presented In the preceding section for '~asy use and rapid reference. Addition;]lly, <br />these Important terms and variables are defined and explained as they are <br />encountered, <br /> <br />1.1 ClASSIFICA TION OF RIVER CROSSINGS AND ENCROACHMENTS <br /> <br />1 here Is a wide variety of types uf rivers, river crossln']s and encroachments. <br />!Cncroachment Is any occupancy of~river and floodplain for hl'lhway use, lhe <br />objective herein Is to consider the fluvial, hydraulic, ']eolTlurphlc and envlronment;]l <br />aspects of hlqhway encroachments, includinq brldqe and culvert loeations, <br />alignments, 10nqltlJdlnal encroachments, stabili;:ation works and road approaches. <br />f_ncroach!l1ents usually present no problEl!TIs durinq normal staqes but require special <br />protection aqalnst. floods. Flood protection requirements vary from site to site. <br />Some bridges and culverts must accolllmodate the passage of livestock and farm <br />equipment underneath durlnl] periods uf low flow. Other bridges require low <br />embankments for aesthetic appeal, especially in populated areas. Still other bridlJes <br />re~uire shmt spans with lonl] approaches and numerous piers for economic reasons. <br />MI of these factors, and many more, COntribute to the difficulty In generali;:Ing the <br />design for all highway encroachments. <br />A classification uf encroachments based on prominent features Is helpful. <br />Classlfylnl] the regions requiring protectiun, the possible types uf protection, the <br />possible flow conditions, the possible channcl shapes, and the various geometric <br />conditions ilids the enqlneer In selecting the desll]n criteria fur the conditions he has <br />encountered. <br />