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Hazards of Gre"t F lood~ The effects Of the Intormodi<ltoReglondl and Star>dard Project Flood~ wora analyzed to determine the flood potential for each stream. The analysis was made using bridge and valley cross 56Ctions which ware surveyad In 1967 and 1968. The water surface profll<:lS lIere determined using bilckwatercot'l'lputatlons ernploylng tha Standard Step Mothod. Thehaad lossesat1'hebridgeand large culvertswtlrecomputadusingdatil in "HydraulIcs of Bridge Waterways" published by the U.S. Department of Commerce. Weir and submerged walr flow was used with the above whenever water overtopped any portion of the roadways. The small culverts were considered blocked by debris, orcarryingonlya small portion of the large floods making their effect on the profile Insignificant. Severo I of the SMII oldE>r brldgE>s would have e><:tremely high velocities through them and were considered to have faIled during the Standard Project Flood. I I were u~ed to make the study. The locations of the reference points ",..." shown on both the "Floooed Areas" plJtes and the "Prof i Ie" olates. A tabulation of reference point data 15 provided In tables following the text. The tabu lations ShOw the elevation~ 01 the 5treambod, thelntermedidteReglonal FlooddndstandJrdPrQjec1' Flood. A Ledring i5alsoprovided which shows the orillntiltion thaf fhecross:>ecfionwo.Jldhavethroughthereforeocepolnt. In the reach of Lena GulCh be1'lIeen reference points 62 and 76, the rIOrm<l1 ch~nnel is "long the s<.>uthtlrn edge of the va Iley with the channel banks being highor than the floodway 1'0 tho north. An unusual situation is created by floods like the Intermediate Regional Flood. Theseflood"aterSQverflowthllleftbankandtrJvel norfh to the lower flood"ay Jrea. This crossover areJ is indicated by a cross-b~tching On plate 26. As the floodwaters accumulate, enoughhaJd is built\.lptoc<luseagradu<ll flo" to fhe east which again joins the stredm in the vicinity ot refgrence point 76. Floods of the magnitude of the Standard Project Flood inundate thn entire area. Flood depths In th i S arM will be sha Ilow, and in 50'11e ca~8S the flows lIill bo containod in dltche5 or sw~les through the area. However, the E>~tire JreJ l~ shown J~ boing ~ubject to overland flood~ Ing beeau~e of the numerou~ Idctors whiCh Cdn ~Iter tho floll patterns of 5hJ 110" f load I ng. The I ntcrmcdlate Re~ ion.:J I and Stanoard Project flO<Xl profiles show toe tfoadcondiflons in the floodwavand Jronot representatlveotfheprotileinthenormal channel which would be higher. (See ~]ate 30.) Thee><:tentoffloodlng is shown On the "FIO<Xled Area" plates for each stream (sea i nde", m~p plate I). Flood outl1nes were detennined from the cross section survey and lJ.S. G""I<><Jical Surve y quadr;,nglemaps to show the general ar9<lS subject to flooding. For any spccificsltuatlon, whereaccurllCy Is needed It will be MCeSSary to take the appropriate flO<Xl elevation from the profll..s and locafe by survey Its corresponding ground elevlltion on the flood plain. Water surface profiles for the Int,m"edlatG Regional and Sfandard f>roject Floods are shown on the "Profile" plates which follow 1'he "Flooded Are"" plates tor each stream. TM prr>tlle<; <;how the depths ot flooding in the channel and theelevatlonofthewatcr surfaces Over the adjaeGnt flood plain. The "Cross Section"pl<ltes portray the channel and valley characteristics besides showing the depths of overbdnk floodlnq. Reference points have beGn provided to locate flood elevaflons at Intervals along the streams. The referonce points coincide with the location ot the surveyea cross SOC1',ons wll'ch " "