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I I I I I I I I I I I I I I I I I I I improved in some areas. As in the lower reaches, however, there ll!"e yet numerous places in Reach 4 and the tributary reaches where culverts with capacity insufficient for conveyance of the 100-yell!" flood have been installed. The northernmost tributary into Lake Arbor, Tributary "B", rises east of Church Lake and flows along 84th Avenue, through two small detention ponds, an irrigation lake, golf course, and behind residential properties before flowing into Lake Arbor, For the most part, the channel is improved and regularly maintained, Flowi~ into the west end of Lake Arbor is a small channel, Tributll!"Y "C," which follows the alignment of Pomona Drive before entering the Lake. This channel is entirely underground west of Wadsworth Boulevll!"d and has been improved as a grass-lined channel east of Wadsworth. In Reach 5, to the west of Wadsworth Boulevll!"d, residential development is rapidly spreading throughout the basin. This development'is being controlled by the land use regulations and ordinances of the City of Arvada. Where Little Dry Creek is concerned, developers have been required to provide 100 feet of public right-of-way and to upgrade the channel and all appurtenant structures to safely pass the 100-year flood. A detention dam and reservoir, Pomona Lakes 2 and 3 relocated, has been constructed just north of 80th Avenue at Pomona Drive to detain increased storm runoff due to the developments. The reservoir provides as much as 60 acre-feet of flood storage capacity, significantly reducing downstream flood peaks; see Figure III-2. Although now privately owned, this facility may soon be acquired by the City of Arvada. This detention reservoir, if publicly owned, could become an excellent multiple-use facili ty. Another major channel feature in Arvada's jurisdiction in Reach 5 is the flow separation structure located about 1/2 mile west of Kipling Street at the Croke Canal. Since residential developments in the basin ll!"e dischll!"ging stormwaters into the canal, a flow separating structure was constructed at the intersection of Li ttle Dry Creek and the canal to pass stormflows to the creek, see Figure III-2. Upstream from the Croke Canal, the floodplain is in unincorporated areas of Jefferson County and is in a natural state, for the most part. There are numerous small and medium sized ripll!"ian trees a!0ng the creek banks. The channel is cut off in several places by stock watering ponds or it. igation canals. Some flooding potential exists where culverts have been placed at Alkire Road and at the places where irrigation canals and pondS have been constructed, Shaw Heig'hts Tributary The Shaw Heights Tributll!"Y, which joins the main channel at 76th Avenue has been included in the Phase "B" analysis. This tributary drains approximately 2.1 square miles in n - 2 Adams County and Westminster. For the analysis, the tributary has been divided into the four reaches listed ell!"lier in the previous chapter. Reach AlA, extending from West 75th Avenue to West 80th Avenue, includes a short section of the main channel of Little Dry Creek between 75th Avenue and 76th Avenue. Because of the flooding situation at the confluence, improvement to this one block of the main channel should be considered at the same time as the lower reach of the tributary channel. The channel in Reach AlA suffers from the same problems present in Reach 3. Residential development has severely encroached into the floodplain and there is no visible evidence of regular channel maintenance. Culverts and headwalls are in satisfactory condition, but are inadequate for conveyance of flood flows. Multi-family residential structures have been constructed in the floodplain of Reach AlB. The channel is concrete lined in one section, in an underground conduit in another and unimproved in a short undeveloped section. In Reaches AlC and AID, the historic channel has been completely obliterated by residential development. Storm flows are conveyed from a small detention dam, just east of U. S. 36 by a 36" diameter concrete pipe which follows the back lot lines of residences in Reach AlC. Upstream from the detention pond, storm runoff is conveyed by streets and a limited underground collection system. All components of the major drainageway system in these two reaches are undersized and the flood damage potential severe.