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<br />I <br />I <br />I <br />.' <br />I <br />. <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />reducing the flooding along the railroad tracks and the split flows that previously occurred. Upstream of <br />Lamar Street, the flow is generally confined between the D&RGW railroad tracks and Ralston Road. <br /> <br />Reach R-2 (Sheets 10, 11, and 12, Stations 124 to 148) <br /> <br />This reach begins at the Pierce Street crossing and extends upstream to the Ralston Creek confluence with <br />Van Bibber Creek. Downstream of the Wadsworth bypass (SH121), the channel and the floodplain are <br />characterized by a grass channel with an apartment complex in both overbanks. Immediately upstream of <br />the SHI21, to approximately Wadsworth Boulevard, the channel is undersized and allows flows to spread <br />out in this area. <br /> <br />From Wadsworth Boulevard through to the confluence with Van Bibber Creek, the channel flows in a well- <br />maintained park-like grassed waterway. There are minor instances of flooding which exceed this channel's <br />capacity and floods adjacent streets and homes. <br /> <br />Reach R-3 (Sheets 8, 9, and 10, Sections 148 to 182 <br /> <br />This reach of Ralston Creek extends from the confluence with Van Bibber Creek upstream to the Ralston <br />Creek confluence with Leyden Creek. The hydraulic capacity of this reach is severely constricted by <br />encroachment into the floodplain by old residential development. In areas where encroachment has not <br />occurred on both sides of the channel, the open space areas have been developed as parkland. <br /> <br />Ralston Creek in this reach passes through various commercial, residential, and park properties. The <br />channel makes some sharp bends near Garrison Street and Brooks Drive. Farther upstream, the channel is <br />constricted as it passes through some back yards, causing a wide spread floodplain. The channel opens up <br />again near Oak Street at a park, reducing the floodplain width, but then is restricted again as it passes <br />through more residences near 68th A venue. Near the confluence with Leyden Creek, the creek passes <br />through another open park area, reducing the floodplain width. <br /> <br />Reach R-4 (Sheets 6, 7 and 8, Sections 182 to 215) <br /> <br />This reach begins at the confluence with Leyden Creek, extending upstream to Indiana Street. At the lower <br />end of this reach, residences encroach fairly closely on both sides of the channel, inundating many houses <br />just upstream and downstream of Ward Road. The channel then opens up to an open space area from just <br />upstream of Ward Road to Beech Street where the 100-year flow is fairly well defined. Upstream of Beech <br />Street to Indiana Street, the floodplain is generally contained within a larger open space area between the <br />residences. <br /> <br />Reach R-5 (Sheets 4, 5, and 6, Sections 215 to 236) <br /> <br />Reach R-5 extends from Indiana Street upstream to Quaker Street. The channel passes through both <br />residential and commercial properties. It also passes over two canals, the Farmer's High Line Canal and the <br />Croke Canal. Between these two canals is a golf course with ponds located on both sides of the channel. <br />The floodplain breaches its banks in this area and spreads out to the local ponds. The 100-year flow backs <br />up behind the Croke Canal, but is conveyed across the canal at a single location, as modified by the <br />Cottonwood West Industrial Park LOMR. The channel passes through residential areas near Quaker Street, <br />but the 100-year flow is fully contained within the channel. <br /> <br />Reach 6 (Sheets 2 and 3, Sections 236 to 249.5) <br /> <br />This is the uppermost reach for this report. It extends from Quaker Street upstream to the Arvada/Blunn <br />Reservoir. The residences are spread farther apart on both sides of the canal between the Church Ditch and <br />Quaker Street, allowing for more green area and less residential flooding impacts. There is very little <br />development upstream of the Church Ditch and higher flows in this area tend to escape the channel banks <br />and spread out to the south of the channel. At the Arvada/Blunn Reservoir outlet works, the 100-year flow <br />is limited to the reservoir outfall channel and the spillway area. Note that development n this area was <br />underway at time of printing. <br /> <br />LevdeD Creek <br /> <br />Reach L-l (Sheet 16, Sections 500 to 508) <br /> <br />This reach of Leyden Creek extends from the confluence of Ralston Creek upstream to the city limits of <br />Arvada. This reach passes through areas already developed with homes. The channel crosses Simms Street <br />and West 72nd Avenue. The 100-year flow overtops both of these street crossings. The crossing at West <br />72nd Avenue creates a backwater, which diverts flow from the channel into downstream properties. <br /> <br />Reach L-2 (Sheets 15 and 16, Sections 508 to 518) <br /> <br />This reach extends from the city limits of the City of Arvada to Alkire Street, including one street crossing <br />at West 75th Place. The channel is small, but clearly defined and more closely resembles the natural state. <br />Floodplain development consists of rural residential homes and some greenhouses in the vicinity of Alkire <br />Street. The Alkire Street crossing is inadequately sized to convey more than nuisance flows and results in <br />overtopping of the street and shallow flooding to the east of Alkire Street during larger events. <br /> <br />Reach L-3 (Sheets 14 and 15, Sections 518 to 531) <br /> <br />This reach of Leyden Creek extends from Alkire Street upstream to Leyden Lake. The channel in this reach <br />has steep grades with resulting high velocities. In general, the channel meanders across a relatively <br />undisturbed floodplain and local residences. Just above Alkire Street is the North Jeffco Park and <br />Recreation District's sports complex, which has encroached into the floodplain. There has been little <br />increase in the backwater at that crossing as a result of filling in the floodplain. In this reach, Leyden Creek <br />crosses the Croke Canal and the Farmer's High Line Canal and Indiana Street. <br /> <br />Leyden Lake is the upstream limit of this reach. The Leyden Lake spillway has recently been reconstructed <br />and a hold order by the State Engineer of Colorado has been removed. The lake now has a 100-year <br />detention volume of 753 ac-ft. The discharge from this lake during a 100-year flow is 373 cfs through its <br />outlet works. <br /> <br />4.6 Floodplain and Floodway Data <br /> <br />A floodplain delineation was performed using the methodologies described earlier in this section. The 100- <br />year floodplain for the existing channel configuration with future basin development, including the <br />detention capacity of the Arvada/Blunn reservoir and Leyden Lake, is depicted on the drawings in the <br />Appendix. <br /> <br />11 <br />