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<br />farm land. The channel shifted laterally toward the concave bank for as <br />much as 200 ft, putting this part of the farm land into the river channel. <br />A picture of the new concave channel bank taken after the flood is shown <br />in Fig. 6. <br /> <br />SlIlUu.nON AND RESULTS <br /> <br />The mathematical model FLUVIAL-ll was used to simulate river <br />channel changes in the San Dieguito River during the 1978 and 1980 <br />floods. Graf s equation (8) for bed-material load was used in computing <br />the sediment movement. Channel roughness in terms of Manning's n <br />was selected to be 0.035 in consideration of the channel irregularity and <br />minor vegetation growth; it was estimated to be 0.04 at the bridge cross- <br />ing. The combined duration of 140 hr for these two floods was computed <br />using 2,000 time steps. <br />Simulated results as presented in Figs. 1, 3, and 7-10 are described. <br />Changes in River Channel Configuration.-River channel changes, <br />including those in channel-bed profile, channel width, and lateral mi- <br />gration, as simulated by the computer model, are described herein. <br />Changes in the longitudinal channel-bed profile (see Fig. 7) are char- <br />acterized by aggradation in the borrow pits, erosion at higher grounds, <br />and the gradual formation of a more or less smooth channel-bed profile <br />at the end of the flood. In that process, considerable variation in the <br />longitudinal channel-bed elevation through the downstream portion of <br />the river reach is predicted at the peak flood as shown in Figs. 1 and 7, <br />The higher channel-bed elevations at Sections 45, 46, and 48 are asso- <br /> <br />_W..._4 <br />_'OS"'" <br /> <br /> <br />I: <br /> <br />I" _ <br />II" I <br />" I <br /> <br />I: <br /> <br />SlWl Dieguito River <br /> <br />:I'~--- <br /> <br />... <br /> <br />I " <br />I,,! <br />.. 20r ,---- <br />..I <br />-- <br />:~., ~ .. ......"" ., .. .. .. i .. " .. ""j:s <br />J :~ . =onG__OI t ._._____.::-:..-...:~~~+~~.-- ~,;:. ,.1 <br />J :'.-----..... ..- ..- '",_..,.- 12 <br /> <br />,,.,::1 '_ '-=i.., <br />1""1':::'-':--- ~- cO' ~uuuu.""! <br />1100 "!..':'!"!.----n...-..h-'o tOO ( <br />0: -..----.-.....--..--.~- .....10.!t <br />,.----- ~ <br />!";~Vl1";' ~.--.... ._co I"J <br />i ' .-- .,,:-:. 'J I ! <br />. -- <br />, T..... <br />, , <br />10-------;--4 3 4 --; - 6"- 7 IQlO . <br /> <br /> <br />-"'11"_...., <br />--...- <br /> <br />-. - <br /> <br />~"'<IIlII"'" <br /> <br />FIG. 7.-Slmullted and Measured Results <br />166 <br /> <br />15 <br />