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I I I I I I I I I I I I I I I I I I I concrete pipe described previously. The culvert beneath West 80th is to be enlarged and right-of-way acquisition will be necessary for all new major drainage construction in this tributary. In Reach AlA, where the Shaw Heights Tributary joins the main channel, a grass- lined channel parallels 76th Avenue for about 1,000 feet. Upstream, only slight reshaping of the channel is required to incorporate the improved channel into the master plan for the proposed Wolff Run Park. A maintenance road is required from the enlarged culvert at 80th Avenue to Wolff Run Park. Some modifications are required to contain the 100 year flood along Tributaries "B" and "C", Sheets 26 through 28. On Tributary B, the existing concrete-lined outlet channel from Lake Arbor and culvert beneath 80th Avenue are both to be enlarged to effectively convey the 100-year flood. An improved grass lined channel is proposed to conduct the 100-year flows from Chase Drive to the Lake Arbor Inlet. The culvert and culvert inlet beneath Wadsworth Boulevard at Pomona Drive on Tributary "C" are also to be improved, mitigating the ponding effect west of Wadsworth. The selected plan for Reaches 4 and 5, in Arvada and Jefferson County, calls for continued floodplain regulation and management. Developers in Reach 4, Sheets 9 through 12, have been required by the City of Arvada to provide public right-of-way along the drainage channel. The present channel is grass-lined and has capacity adequate for conveyance of the 100-year flood. Although some culverts are undersized in Reach 4, there is not enough potential flood damage to warrant their enlargement on the basis of economics. Development is forthcoming to the upper section of Reach 5 in Jefferson County, Sheets 1 through 9, which is currently in a predominantly natural state. Flow separation structures are proposed at Church Ditch and Farmers Highline Canal, Sheets 4 and 5, respectively, to ensure that the storm runoff does not overburden these canals. In all of the study reaches of Little Dry Creek, it is necessary to regulate the existing 100-year flood plain until improvements are made, after which time the 100-year flood plain can be revised. All residents in and adjacent to the 100-year flood plain should be informed of the flood hazard area delineation and encouraged to purchase flood insurance. Cost estimates for the selected plan are listed in Table I-I by jurisdiction, and are further detailed in Section V and on a sheet by sheet basis in the Drawings. I - 3 Table I-I JURISDICTIONAL COST BREAKDOWN SUMMARY Jurisdiction City of Jefferson City of Adams Item Arvada County Westminster County Channel Improvements $ 227,700 $ 0 $ 2,026,100 $ 1,338,500 Street Improvements 154,600 0 1,270,100 770,400 Utility Relocations 11,200 0 318,600 191,800 Subtotals 393,500 0 3,614,800 2,300,700 25% Contingency* 98,400 0 903,700 575,200 Total Construction Costs 491,900 0 4,518,500 2,875,900 Right-of-Way Acquisition 58,000 0 317,800 634,300 Present Worth- Operations and Maintenance** 142,000 14,100 520,200 288,200 Total Improvement Costs 691,900 14,100 5,356,500 3,798,400 * Includes cost for Fiscal, Legal, and Administrative Fees, Engineering, Surveying, Construction Inspection, and Construction Contingencies. ** Based on capitalized annual costs over a 50-year period using a 6-5/8 percent annual interest rate.