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~_ --..~ TUTTLE APPLEGATE RINDAHL, INC. .= Consultants for Land and Resource Development Mr. John lloerfer• Mired Land Reclamation Divisior~ July 'c'c, 1988 Pabe 5 Re-establishing Ct~al Creek. in the nridd le .~P the post-mining channel is intentional. Coat Creek. has a nat t_iral tendency to meander and +~nce mining is c+~nrplet ed, it will cent inue to do so. Your• observation abo,_~t it beino_ difficult to peedici: the final location ;~f the stream is correct. General observations also can be made that it will probably assume zi c~~nfigur•ation with the same sinu~~sity. Coal Creek curr^ently meanders and occasionally erodes steep cut banks otn sides Of" the channel. This process will continue after mining is c~~ntplet ed. There is no reasonable measure that anyon P_ ca,•~, d~~ t,~ prevent this nat+_tr•al or•ocess, save out the Creek int,~ a r•ectangular• concrete channel. The bottom material will be c~~ntposed of sands, windblown silts, clays, and silty sands. This mat er•ial will be> cohesive. Str-eant sco,ar• has always ,~cc,ar•r•ed in this ar^ea regardless +~f the material in place. Flood flows thr•~~ugf~t the area ar•e as capable of nr~~ving sand bar•t ides as they are of moving the r•e,7ect fines. The mining and r•eclanration piar•~ will minimize er•osi~~n and sct~ur•!ng +~f dist,.~r•bed materials. Fiowever•, it is impossible to c,~ntoletely eliminate sc,~ur•int:;f even if mining in this area was not done at all. A concern abo,_tt creating gr•eater• runoff d,ar•ino a storm because of reduced per•nreability in the flo~~dDlain is valid. Localized flows will 6e sl it]ht ly increased. Fi,~wever•, it••, looking at the C~~al Creek basin can a regional level, the effect of the mining operation will 6e to reduce flood peak:.: dt~wnstr•eam in urbanl zed areas dur•inq rra~,~r• st t~rnts. The mining plan sh,~ws eioht Iocat ions where the channel is:: constricted by existing too•~graph is feat ur•es such as tree pockets. Mining upstream of these areas is creating ei larger v,~Iunre ~~f detent i~~n. The backwat er• created by the channel constrictions during a nta~or• flood will pr•od,acr:;> aoprox innately 66tR acre-feet ~~f additional storage. Enclosed is a c+~py of a Setter to the Urban Drainage and Flooc:i Cent r•ol Dist r•ict that discusses this b~~int. Their r•esot'+nse to this concern is concur•r•ence that an increase in storage;> appears r•easonab le. The locat i~~n L~f this pr•o~ect in the headwaters of C,~al Creek actually makes this increase it•i fioodplain storage beneficial t~~ the urban areas downstream.