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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . Bosley Wash Drainage Master Plan I.'" , '~. -" '. ".. -' . Phase 2:dAlternative Drainage Facility Evaluation improve undersized channels and culverts in critical areas and to purchase ROWs to facilitate the future construction of critical detention facilities. Channel improvements within the Watershed include improvements to the Stub Ditch drainage channel. This includes the enlargement of the channel to carry 50 cfs. These improvements consist of channel excavation and embankment construction. In combination, this prevents the overtopping of the channel and the subsequent flooding of properties above the Government Highline Canal. There are limited additional areas where channel improvements are needed, primarily in conjunction with culvert improvements at select locations along the channel parallel to F % Road. Generally, these culvert improvements consist of the addition of another 48-inch diameter culvert parallel to the existing crossing at SIX driveway locations along the road. Ai1 alternative is the complete replacement of the existing crossings with a new 60-inch crossing. Finally, additional culvert improvements include the enlargement of the crossing at Hwy 6/UPRR. Here, it is proposed that a 36-inch parallel culvert be added to the existing culvert. Because of the nature of this crossing and the critical need to maintain traffic on both the roadway and the railroad, this culvert installation will need to be constructed by means of a bore. This alternative also relies on the crossings at G Road and the Government Highline Canal to control flow rates downstream and subsequently control the flood hazard. This reliance is intended to be temporary, being critical only until long term flood storage facilities are in place. To facilitate the implementation of flood storage in the future, this recommendation includes the acquisition of storage sites to control runoff generated above 1-70. The purchase of lands in the Reservoir A location and the location of Reservoir M&N is proposed. The cost of construction of these facilities is prohibitive at this time, but having the property allows the construction in the future without undo risk of conflicting demands such as development. It also controls the cost risk associated with inflation or property value escalation. The cost of these structural improvements, including land acquisition for the areas of future flood storage, is estimated to be $422,000. This represents the capital cost of the facilities, the cost of land, and the cost of any incidental construction such as roadway .~~. ,;,.;,,:,~ ,I" ,~~. ;i~'~,;,~j;}~ Page 22 /~--...... ~ ',Y' lill.