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I I I I I I I I I I I I I I I I I I I & City 0/ Littleton ~~~ ~o.,-_ -;'.' 0' ~.. Massey Dr2W ard S)CD (Sourh) Milp Dralf"lageway PlannwlQ UpdatE" Conceplual Des,ign Report February 2006 1.0 Introduction 1.1 Authorization . Wherever possible. provide public use and access trails within the corridors of existing and proposed drainageways to provide maintenance access and for active and passive public recreation. This report is part of a study co-sponsored by Urban Drainage and Flood Control District (UDFCD), Jefferson County and the City of Littleton. The Agreement Regarding Major Drainageway Planning for Massey Draw and SJCD (South) Drainageways Update (Agreement No. 03-08.06) was executed on December 8. 2003. Addendum No.1 subsequently amended the agreement to include a Flood Hazard Area Delineation (FHAD) Study. Addendum No.1 was executed on January 2,2004. Addendum No.2, executed June 16, 2004, amended the agreement to include additional topographic surveying. Addendum No.3, executed July 21,2004, amended the agreement to include additional investigation and analyses related to the June 27, 2004 flash flood on Massey Draw. The Notice to Proceed for Phase B was dated April 11, 2005. . Consider the needs for new and upgraded roadway crossings when such crossings are practicable, affordable and add significant value in relation to the cost. 1.3 Planning Process The hydrologic models were prepared and calibrated to approximate flow rates from previous studies. The model results were presented in the Hydrology Study dated April 2004. When the hydrology was accepted, problem areas were identified using the model results and field observations. Alternatives were developed for each reach to address the identified problems and presented to the project sponsors at progress meetings. Based on input from the sponsors, the alternatives were refined and presented in the Alternative Evaluation Report dated February 2005. 0\ The project sponsors reviewed the recommendations in the Alternative Evaluation Report. Direction to proceed with the conceptual design of the Selected Plan was received on April 11, 2005. The Selected Plan is shown on Figure B-2 Progress meetings were held to review the progress of the project and obtain input from the project sponsors and other attendees. Meetings were held on Initial kick-off meeting with project sponsors Project overview for attending agencies, information request for land use and existing culverts Reviewed preliminary hydrology Hydrology review, discussion of problem areas Hydrology comparison, discussion of preliminary alternatives Hydrology report was distributed, observations from watershed tour with Jefferson County Predicted road overtopping, observations of problems on Foothills Park & Recreation District properties Additional mapping needs, alternatives evaluation criteria June 27, 2004 flooding Discussion of parallel hydrology model, Meadow Ranch alternatives Phase B kick-off meeting Reviewed draft Phase B drawings Reviewed Deer Creek Golf Course improvements, golf course tour . Water quality protection and enhancement. The meeting minutes are included in Appendix C. . Preservation of the natural character of the drainageways and their natural resource. Public meetings were help on October 19, 2004 and April 5, 2005 at Falcon Bluffs Middle School. Fliers announcing the date and location were mailed to the residents in the watershed. 45 to 60 people attended the meetings. The purpose of the first meeting was to present the alternatives and to 1.2 Purpose and Scope The project study area consists of the Massey Draw and SJCD (South) watersheds and is presented in Figure 1. Except for the North Tributary of SJCD (South), both watersheds were originally studied in 1979. The study results were presented in a report titled Major Drainageway Planning, Massey Draw & North Tributary, SJCD (South) 6200 & Tributaries (Original Plan, Reference 1). The North Tributary of SJCD (South) was studied in 1976 and the results were presented in the major drainageway planning study for SJCD (North)-Basin 6100 (Reference 2), The North Tributary of SJCD (Soufh) is included in the scope of the masterplan update. Since the Original Plan was prepared, the Ken Caryl Ranch area west of the hogback (and C-470) has been developed, the Natural Resources Conservation Service (NRCS), formerly Soil Conservation Service, produced more detailed soils maps that indicated substantially lower infiltration rates west of the hogback, and new hydrologic modeling methodologies have been adopted. The combination of these factors resulted in significantly increased flow rates at the hogback. In 1982, the Massey Draw hydrology was updated, which resulted in the 100-year flows being increased from 23 percent to 211 percent at various points along Massey Draw. In addition, Jefferson County, UDFCD, and private developers have constructed drainage improvements. January 7, 2004 January 28, 2004 February 18, 2004 March 2, 2004 March 31,2004 April 27, 2004 The purpose of the Massey Draw and SJCD (South) Major Drainageway Planning Update is to reflect the revised hydrology and the drainage improvements that have been constructed, and to identify future drainageway improvements that are needed. The Phase B report presents the conceptual design of the selected plan. The goals and objectives are to: May 19, 2004 June 9, 2004 July 8, 2004 August 27, 2004 . Minimize flood-related damages to public infrastructure and private property; April 26, 2005 May 26, 2005 June 8. 2005 . Balance the drainageway and stream stability solutions to provide multiple benefits. as much as is feasible, that include: . Water quantity resources protection. 1-1