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I v 111-6 I I Simms Street will have the existing pipe replaced with two structural steel plate arches and the existing Ward Road bridge will have its structure opening area increased. LEYDEN CREEK WITHIN THE CITY LIMITS OF ARVADA - Station 0+00 to 44+00 I RALSTON CREEK FROM XENON STREET TO INDIANA STREET - Station 306+00 to 384+00 A grass-I ined channel is to be used for the entire length of Leyden Creek within the Arvada city limits. Currently, there is a grass-lined channel upstream of station 20+00, which will have its capacity increased by providing minor grading and selective brush removal. To accomplish the master plan recommendations along the remainder of this reach a grass-l ined channel is to be built from station 0+00 to station 20+00, For the 100-year flow this new channel has an average velocity of 8 feet per second, a base width of 63 feet, an overbank depth of flow of 4 feet, and 4 to I side slopes. I The master plan improvements for this reach of channel are given on Sheets 13 and 14. These improvements will contain the 100-year flood in the proposed channel and will alleviate the overtopping of Simms Street and Ward Road dur- ing a 100-year event- I I A nonstructural modified channel is to be used for this reach of Ralston Creek. Due to the minimal damage potential of this area, no erosion pro- tection measures will be provided to the channel. Simms Street will have the existing box culvert replaced with a 60-foot long bridge and the existing West 72nd Avenue bridge will have its structure opening area increased by a minimum of 33 percent. This can be accomplished by adding a new bay to the structure, or by excavating the channel beneath the existing bridge or a combination of both. Transitions to the existing channel will be provided upstream and downstream of the improved structures. I The master plan improvements for this reach of channel are presented on Sheets 10 through 13. RALSTON CREEK FROM INDIANA STREET TO QUAKER STREET - Station 384+00 to 444+00 The master plan improvements for this reach of channel are presented on Sheets 39 and 40. These improvements will decrease the area of the flood plain in this reach and will alleviate the overtopping of West 72nd Avenue and Simms Street during a 100-year event. I A nonstructural modified channel is to be used in this reach of Ralston Creek. Rock side channel spillways sized for the 100-year flow will be located on the east banks of the Croke Canal and the Farmers Highline Canal. These side channel spillways will help protect the canals from being breached during design events. I LEYDEN CREEK FROM THE ARVADA CITY LIMITS TO ABOVE ALKIRE STREET - Station 44+00 to 92+00 I This reach of channel has several private roads and driveways that are assumed to wash out. A nonstructural modified channel is to be used for this reach of Leyden Creek. The West 75th Place roadway embankment will be armored to protect it from being washed out and three 6.08 feet x 4.58 feet structural plate steel pipe arches will be installed to convey low flows under the roadway. I No improvements are proposed for Indiana or Quaker Streets. The existing roadways are close to meeting the criteria of the Urban Drainage and Flood Control District for the present flows, Due to the minimal damage potential of the area, no erosion protection will be provided to the channel. This reach of channel has two small pond embankments and three private driveways that will be washed out. Because there is no rldverse effect to the flood hazard from the private facilities, master plan improvements are not provided. I The master plan improvements for this reach of channel are given on Sheets 6 th rough 10. I RALSTON CREEK FROM QUAKER STREET TO STATE HIGHWAY 93 - Station 444+00 to 578+60 The Alkire Street crossing will have the existing pipe replaced with a 50-foot long bridge sized to carry the 100-year flow of 2,450 cfs. The existing channel capacity in the vicinity of the bridge will be increased to handle the higher discharge. The addition of this bridge will alleviate the present overtopping of Alkire Street during the 100-year discharge and will de- crease the area of the flood plain in this reach. Due to the minimal damage potential of this area, no erosion protection measures will be provided to the channel in the master plan, The master plan improvements for this reach of channel are presented on Sheets 36,37,38 and 39, I A nonstructural modified channel is to be used in this reach of Ralston Creek. Two structural steel pipe arches will replace the existing pipe at State Highway 93. Transitions to the existing channel will be provided upstream and downstream of these structures. I This reach of channel has several private roads and driveways that are assumed to wash out- I The master plan improvements for this reach of channel are given on Sheets I through 6. These improvements wi 11 decrease the flood plain in the vicinity of the new structures and will alleviate the overtopping of Colorado Highway 93. Dur to the minimal damage potential of the area, no erosion protection measures will be provided to the channel. I I