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<br />VII-4 <br /> <br />feature of 156th Avenue Is that the bridge be constructed On a skew so <br />that the alignment of 156th Avenue Is straightened. jl.1 I earth work and <br />drops associated with both bridges on Sheet 6 have bee,n Included under high- <br />way costs in Section VIIJ. It will be necE,ssary to construct a spur dike <br />on the east sIde of the i56th Avenue bridge. Due to hydraulic constraints, <br />It Is not feasible to carry the low flow channel s.ho1Nn In the detail on <br />Sheet 6 through the bridge. It Is recommended in Instances such as this <br />that a raised foot path be constructed and that the low flow channel bench <br />downstream of the bridge be rlprapped. ThE' presence of the bench wi 11 <br />serve a dual purpose In that the bench will be essentIally a flow spreader <br />and energy dlssipatoras well as a dry surface for pedestrian travel. <br /> <br />The culvert crossing east of 144th AVE'nue shown on Sheet 9 Is to be <br />replaced with a new bridge meeting the hydr'aullc c:rlte,rla of an arterial. <br />I t will be necessary to ra Ise the road~ray 'lOd low..,r the channe 1 invert to <br />meet these criteria. <br /> <br />As presently constructed, North Washington Street and 136th Avenue <br />will be overtopped In excess of allowable c:rlter1.,I. In addition, the <br />presence of the German Ditch headgate placErs an elevation ccmstralnt which <br />must be met. What Is proposed Is: <br /> <br />I. A new brIdge On North Washington Street be constrUlcted with a width of <br />190 feet. <br /> <br />2. A geometric channel be constructed with a capo,lclty of 1300 cfs before <br />being overtopped. <br /> <br />3. The existing German Ditch bridge crossing North Wa.shlngton Street be <br />retained and the existIng head gate be used with an overflow Into the <br />proposed geometric channel. <br /> <br />4. Relocation of the German Ditch headgate to the, east bank of the geo- <br />metric channel approximately 400 feet nlJrth of 136th Avenue. The <br />German DItch flows are to be carrIed In the old Big Dry Creek ai Ign- <br />ment to the North Washington Street ditch crossing!. <br /> <br />5. Replace the newly constructed 136th Avenue bridge with II new bridge <br />ISO feet wide, or add a suffIcient number of new bays to the exIsting <br />bridge to achIeve the same effect. <br /> <br />6. A low berm be constructed for flood-proofing of ex.lstlng buildings. <br /> <br />With the proposed Improvements, North l~ashlnSlton Street will not be <br />overtopped except by Wave action, and i36th Avenue will meet overtoppIng <br />criterIa. <br /> <br />The bridges at Interstate 25 are adequoBte hydraulically and suitable <br />for the Intended vehicular use. There are no changes proposed for the <br />