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surface profiles were determined using backwaterccrnputatlons employing the Standard Step method. The bridge head losses were computed using data presented in "Hydraulics of BridgeWater'.ay s" publIshed by the U.S. O<ll'ar-tmentofCorrY11<lrce. WeIr and submerged weir equations were used in conjunction with the above whenever water overtoppedanYl'or-tlonsoftherOildways. SeverllloftheS/llall bridges were considered Incal'able of withstllndlng these greater flOO<Js and were assumed to bowashed out for the I'urposeof the computations. The extent of flooding is shown On the "Flooded Are,," plates for each stream (see Ind<lx map on plate I). Flood outlines were determined from the cross sectIon surveys and available U.S. Geological Survey quadrangle mapping to show general areas subject to flooding. ForanyspQClflcsltua-tlon, where accuracy Is needed, it will be necessary to take the apl'roprla-te flood elevation from the profIles and locate by su~ey i-ts corresponding ground elevation on the flood plain. Water surface profiles for the Intermediate Regional and Standard Project Floods are snown on the "Profile" plates which follow the ''Flooded Area" plates for <lach stream. The prof I les show the depths of flooding In the channel and the elevations of the water surfaces over the adjacent flood plain. Til.. "CrossSactlon" plates portray thecnannel and valley characteristics besides showing tho dep-ths of overbank flooding. Reference points have been provided to pinpoint flood elevations at Intervals along the streams. The reference points coincide with the location of the surveyed cross sections Which were used to make the study. The locations of the reference points are shown on both the "Flooded Areas" plates and the"Profile" plates. Tables8and9,followingthetext, provide the pertinent informa tlon. The tabulation shows the elevations of -the streambed and the Standard Project and Intermediate Regional Floods, and the bearing of a , , 23 rel~rence line which, when drawn through the reference point, shows where the llood elevations are ~pplicablc. Roads crossing the reference line t~nd to alter flood depths which may be higher upstream and lower downstream. This study shows that there are large areas of flood plain upstre3ln frC<11 the confluence of 80ulderana South Boulder Creeks whi ch areno"t inundated by the Intermediate Regional Flood. Several factors Should be considered before development 01 these areas. First, they are In the flood plain and may be fiooded again, as portions were floodad in 1894 and 1938. The Standard Project Flood, Illustrated in this report, shows the areas that could be flOOded again. Secondly, Shallow flooding may occur eIther frorn local runoff or because of a temporary constriction which would dlvar-t floodwaters out of the channel onto these areas. New Construction Should be placed on flil several feet above the flood plain. The existing swales or drai~ge coursosmustbemalntalned. They may be developed by minor altering of grades but drainage should bec:ontinuous from one property_to th e next. Bu Ildl ngs upstream of roadw;:,ys shoe Id ~e olaced on 1 III ~bove the elevation of the roadways. Roads tend to constrict flows especially If debris becomes lodged In the bridge openings. To summarize, shallow flooding Can be expected on those broad flat portions of the flood plilinwhlch lie outside of the Intermediate Regionai Flood and COn- structionprilctices5hould be adopted which will avoid damages f rom the shallow flooding. W<lrnlng The destructive force 01 the last moving floodwaters may create damages even more severe than the damages from Inundation. Buildings may be undermined. walls caved In, bridge abutments wilshed out, and trailer houses swept aw;o.y. Don't risk your lifeor resources on a oetagalnst nature. STAYOOT OF THE FLO',)[J KAZAR!l AREAS. "