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I I I I '1 I I I I I I I I I I I I I I completely developed, ond the drainageway has been replaced by a storm sewer system designed for the lower frequency storms (less than a 5-year return interval). A 48" RCP along Irma Drive, a 48" RCP along Muriel Drive, and a 24" RCP combine ond increase to 0 60" RCP at an existing junction box at approximately channel Station 41 +00. The 60" RCP then increases to a 72" CMP somewhere between the junction box and the discharge point above the Union Pacific Railroad crossing. The proposed improvements in the reach include the following: (I) A gross-lined channel throughout the reach. (2) The construction of a two 4' x 6' RCBC culverts under Leroy Drive. (3) The construction of two 4' x 6' RCBC culverts under the roilroad spur. (4) The existing storm sewer system will serve as the low flow channel through the reach. The proposed improvements will greatly reduce the flood plain in the reach, and the cost of the improvement is to be the responsibility of the developer of the property. 17. Drawing TN-2 (Sheet 22 of 30), Tributory N, Station 30+00 to 0+00, Grange Hall Creek Confluence The channel in this reoch vories from a narrow, incised channel with a steep, longitudinal slope to a low flow channel with brood overbonk flow areo. The storm flows up to the 100-yeor recurrence interval flood are contained within the channel area. A 72" CMP storm sewer discharges to a gully ponding area then crosses the railrood in another 72" CMP culvert (presently submerged and silted). There are presently no proposed improvements below the Union Pacific Roilroad dike except for limited channelization work. Immediotely below the railroad crossing some chonnelization work (about 400') is proposed to improve the channel ond insure thot the 72" CMP culvert under the Union Pacific Roilroad crossing will function and not silt in as before. The existing 72" CMP culvert will be cleaned out and all debris and silt will be removed. Above the Union Pacific Roilroad crossing on improved, grass-lined channel is proposed. No trickle channel is proposed because the existing 72" CMP will take care of the low flows. In addition, two 4' x 6' reinforced concrete box culverts are proposed for crossing the existing railroad spur. 18. Drawing TNE-I (Sheet 23 of 30), Tributary NE, Station 52+30 to 30+00 The channel in this reach above York Street consists mainly of a broad surface flow area without a defined low flow channel. The main channel below York Street in some places is narrow and incised with a steep, longitudinal slope. There are two private ponds without formal spillways in the lower end of the channel reach. Overtopping the railroad embankment and 112th Avenue occurs at the upstream end of the reach and, therefore, a secondary flood plain also occurs olong both sides of 112th Avenue. Tributary NE crosses the railroad in two 60" CMP's and York Street in a 12" CMP and an 18" x 29" CMPA. The flood plain is determined to a degree by the flow limitation fro"n the 60" CMP culvert under the railroad and is broad and shallow. The overtopping of the railroad embankment and 112th Avenue allows storm runoff to flow in the gener~1 easterly direction along 112th Avenue and the flow returns to the main chonnel of T ributory NE at the 112th Avenue crossing. The improvements in this reach are designed to completely remove the area along 112th Avenue from the 100-year flood plain. The improvements in this reach are as follows: (I) (2) An improved, grass-lined chonnel between the railroad and York Street. Included are four 3' concrete check drop structures to control erosion in the reach. A berm west of the railroad near 112th Avenue to prevent any storm water flows from overtopping 112th Avenue. 19