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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bosley Wash Drainage Master Plan r , ~,. ~.. -~ , ' _P~a~e 2: Alternative Drainage Facility Evaluation the site of Reservoir M&N is also important. This reservoir helps control the upper portion of the basin and manages to reduce the hazard of overtopping of the Stub Ditch drainage channel. This reduction in flow, and the reduction in overtopping hazard, serves to reduce the flood hazard downstream significantly. The Reservoir M&N site will provide storage of 37 AF. In combination, these storage facilities reduce flow sufficiently ,to make the enlargement of crossings at G-Road and the Government Highline Canal unnecessary. Channel improvements within the Watershed include improvements to the Stub Ditch drainage channel. This includes the enlargement of the channel to convey 50 cfs. These improvements consist of chan~el excavation and embankment construction. In combination, this prevents the overtopping of the channel and the subsequent flooding of properties above the Government Highline Canal. The remainder of the channel downstream of the junction with the Stub Ditch drainage channel is generally adequate. There are limited areas where improvements are needed, consisting primarily of culvert improvements at select locations along the channel. Generally, these consist of the addition of another 48-inch diameter culvert parallel to the existing crossing. An alternative is the complete replacement of the existing crossings with a new 60-inch ' crossing. This alternative also requires the enlargement of the culvert at the UPRR/Highway 6 crossing. 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. The cost of these structural improvements, including land acquisition for the detention facilities, is estimated to be $2.5 million. This represents the capital cost of the facilities, the cost of land, and the cost of any incidental construction such as roadway repairs or utility relocation. Table 1 presents a tabular summary of the costs of the improvements associated with this alternative. EiL~::',-:;':;:~:'''12diTi ~~:L:;-'::::;:i~~~lS:'.:.." : >~(~:'rd~li ,;~~ (~; {h:~~~;~:~;'; . - 0-;'7'",<'<";''''''- ^ Page 18 ;-,-...... ~ ,,~ @l.