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<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 />
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