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I I I I I I I I I I I I I I I I I I I II. STUDY AREA DESCRIPTION Drainage Basin Characteristics Little Dry Creek, located in Adams and Jefferson Counties, is a left bank tributary to Clear Creek. From its origin in the hills about a mile and a half southwest of Standley Lake, the Little Dry Creek basin slopes southeastward to Clear Creek. The confluence is immediately downstream of the Colorado and Southern Railroad bridge over Clear Creek. The Little Dry Creek drainage basin is oblong in shape, approximately 9 miles long and 2.7 miles at the widest point. It drains 13.3 square miles. It rises at about elevation 5,650 feet above mean sea level and falls about 480 feet to elevation 5,170 feet in its 8 mile course. Just downstream from Sheridan Boulevard, Little Dry Creek is joined by the Shaw Heights Branch, a left bank tributary draining approximately 2.1 square miles. Two other tributaries draining a total of 2.1 square miles flow into Lake Arbor, a natural lake which acts also as a detention pond, before discharging into Little Dry Creek just upstream from Sheridan Boulevard, In the upper reaches, the Farmer's Highline Canal and Croke Canal intersect Little Dry Creek as they meander across the drainage basin. The Croke Canal carries storm runoff from nearby residential developments and a spill structure has been constructed at Little Dry Creek to separate storm from irrigation waters. The Farmer's Highline Canal presently has no flow separation structure at Little Dry Creek. Further upstream, minor dams for stock watering or irrigation have been constructed across the channel. The development status of the entire Little Dry Creek basin has been classified as "B" by the Denver Regional Council of Governments (DRCOG) in their 1971 Project REUSE, meaning the basin is not yet fully developed, but will become so in the immediate future. East of Sheridan Boulevard in Westminster and Adams County, the basin is now nearly fully developed with medium and high density residential areas on the hillsides and residential, commercial and industrial areas in the valley. West of Sheridan, residential development has occurred through(J'~t Arvada and is rapidly spreading into the unincor- porated areas of Jefferson County at the westernmost limits of the basin. With this development comes a significant increase in storm runoff. Study Reach Description Typical of South Platte River tributaries around Denver, the Little Dry Creek channel can contain only minor flows. Land development in the floodplains east of Sheridan Boulevard has severely encroached on the channel primarily because most n - I reaches of the channel are on private property. The channel has been further constricted by numerous culverts placed beneath roads, parking lots, and the Colorado and Southern Railroad tracks. From the confluence with Clear Creek in Reach 1, Little Dry Creek runs parallel to the Colorado and Southern Railroad to Federal Boulevard. The channel, although rustic in appearance, has been so extensively modified by man's activities that the historic channel has been obliterated. The dominating feature is the Colorado and Southern Railroad. Just downstream from Federal, the Colorado and Southern Railroad crosses Little Dry Creek on a fill with a 48" diameter culvert to pass stream flows. Three other corrugated metal pipe culverts placed beneath railroad sidings restrict the flow capacity of the channel. Floatable flood debris deposited at the entrance to all culverts and at channel obstructions in Reach 1 is evidence of the present restrictive flow conditions and general lack of maintenance. Upstream from Federal Boulevard in Reach 2, the channel meanders through residential and industrial properties. The channel is capable of conveying only minor storm flows and the floodplain is flat and wide. Only minor channel improvements have been made in Adams County and Westminster and the channel does not appear to be maintained. Numerous industrial sites in this reach have displaced the channel and runoff from these sites contains silt and other pollutants. Upstream from 72nd Avenue in Reach 3, the floodplain areas have been occupied by single and multi-family residences. The channel is lined with grasses and weeds. Use of the channel area for parks and recreational purposes is limited by chain link fences which isolate the channel area. There is evidence that children play along the creek banks nevertheless. The culverts placed at road crossings in this reach, although in good condition and protected with headwalls, are undersized for even the 5-year flood flows, Debris and other material present in the creek bed are indications that the channel receives little regular maintenance. Between Sheridan Boulevard and Wadsworth Boulevard in Arvada, recent residential development is present adjacent to the Little Dry Creek channel. This development has been controlled. A 100 foot right-of-way has been deeded to the City of Arvada and the channel is grass-lined and is utilized for neighborhood recreational pursuits. An 8-foot wide creekside trail provides access for maintenance and recreational purposes. To the north of Little Dry Creek and west of Sheridan Boulevard, two tributaries drain approximately 2.1 square miles and are detained by Lake Arbor before discharging into the main stem of Little Dry Creek in Reach 4 just west of Sheridan Boulevard. The land in this tributary area has rapidly developed and the tributary channels have been