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I I I I channel passes under two driveways to commercial properties, through relatively large box culvert bridges. Upstream of these structures, the channel aligmnent is through a combination residential/light industrial property. The existing natural channel in this area has been severely encroached by these properties and is blocked by accumulated natural and man-made debris, No major drainage improvements have been constructed in this reach. Several commercial developments have been constructed along this reach south of U.S. Highway 40. The developments contribute to increased runoff from the basin, low- through a small narrow and choked with debris and vegetation. The drainageway passes density residential development just downstream of S, Golden Road, to Orion Street. South Golden Road L-6 I I Amoco Gas Station driveway to the outlet of the culvert under Zeta Outlet of the culvert under the Street. L-ll I The existing channel in this reach is shallow and grass-lined between the Amoco Station driveway and the culvert under West Street. Upstream of West Street, a short section of natural channel connects the downstream with the outlet of the culvert under the East Tincup Village Campground The culvert under the campground is more than 600 feet long. The channel between the East Tincup Village culvert and the Zeta Street culvert is a deep natural section with steep banks and a rocky bottom. The banks through this stretch of channel show signs of severe erosion. No improvements have been made in this reach since the previous Master Plan. Trailer Park on Mt. Vemon Orion Street to the downstream end of Mountain Side Mobile Estates Road. L-7 I Outlet of culvert under Zeta Street to the confluence with Apex Gulch. L-I2 The drainageway in this reach passes through an open-space area recently purchased by Jefferson County Open Space. This area is mostly natural fields with small spring-fed ponds located near the middle of the fields. The channel through this reach is on the far north and runs adjacent to Mount Vernon Road. The existing channel is deeply incised with some evidence of severe bank erosion. Large well-established deciduous trees line the channel banks through this reach, No improvements have been constructed in this reach since the previous Master Plan. I I The only improvement in this reach is to the culvert under Zeta Street. The culvert is a 60-inch diameter conugated metal pipe with a 90-degree bend near the outlet. A concrete floodwall has been constructed downstream of the outlet to provide erosion protection, retain the bank materials and eliminate channel overtopping during high flow. The wall extends from the culvert outlet downstream to another 90-degree turn in the channel. Downstream end of Mountain Side Mobile Estates Trailer Park on Mount Vernon Road to the outlet of the 6th Avenue culvert. L-8 I Confluence with Apex Gulch to the upstream end of the study area. The channel in this reach is largely unimproved. Two culvert crossings have been improved since the previous Master Plan. The improved culvert crossings are at the Mobile Premix Quarry driveway and the access road to the south of the Mobile Premix driveway. Both crossings have enlarged culvert capacity and riprap erosion protection on the upstream and downstream faces No improvements have been constructed in this reach since the previous Master Plan. The drainageway through this reach meanders through mostly residential properties. Some commercial property is also immediately adjacent to the channel just upstream of South Golden Road. The existing natural channel varies in character from fairly well-incised and steep-banked to very shallow grass-lined. The channel passes under three streets upstream of South Golden Road Oth Street, Orchard Street, and Orion Street. The culverts at these locations are undersized and partially filled with sediment. L-13 The Mountain Side Mobile Estates Trailer Park was under development at the time of the previous Master Plan. No improvements have been made for flood control purposes. However, the channel in this reach has been relocated to the north side of the trailer park and is severely encroached by the trailer park. The existing channel is narrow and has inadequate capacity for other than very low flows. Various materials such as concrete slabs have been placed along the channel banks in an effort to stabilize them. I I I limits Improvements in this reach are primarily in the area of Heritage Square. An additional channel crossing has been added for a driveway to access new buildings on the west edge of Heritage Square. A 24-inch diameter conugated metal pipe was installed under the driveway to convey Apex Gulch flows. This culvert is quite undersized. Apex Gulch from the confluence with Lena Gulch to the study A-I end of the concrete channel At the time the previous Master Plan was completed, the concrete lined channel upstream of 6th Avenue did not exist and the existing channel was a natural unimproved section of limited capacity In addition to construction of the rectangular concrete-lined section, a business complex was built to the west of the channel. Fill was placed prior to construction to elevate the commercial structures above the floodplain. The concrete channel has adequate capacity for up to the IOO-year flow, although due to its limited freeboard and curved aligmnent, some overflow of the channel walls during very high flows is expected. Outlet of 6th Avenue culvert to the upstream L-9 I I P-l I of the improved to the outlet Pleasant View Tributary from the confluence with Lena Gulch channel. The drainageway in this reach consists of an open grassy swale. No clearly defined channel exists from the confluence with Lena Gulch upstream to the end of an improved upstream channel. This 5 Amoco Gas Station driveway. The Highway 40 side of U.S of the culvert under the is adjacent to the north to the outlet The existing channel through this reach End of the concrete channel L-lO I I