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07i20i1990 10:31 FROM • TO • P.05 access road flattens near the intersection of Cedar Heights Drive. Conversations with th¢ guard house attendant indicated that runoff from basins HR-6 and HR-7 causes erosion damage and sedimentation on a fairly lrequent basis, Eventually Lhe sediments carried by the runo!! axb deposited in the Black Canyon Drainageway via the 5430 inch culvert. Erosion o£ the natural Swale downstream of the proposed HR-F culvert has caused sediment to be deposited within the Ceda Heights Drive street section. Tha runoff and sediment originating within basin HR-6 and the natural swale arc eventually deposited near the existing 24-inch culvert under Cedar Heights Drive approxi.mataly 400 feet south of the ~~roposed culvert "A" identified in the Obeying worth report. l Srdiment mainly consisting of rock Chips oaring in size from 1/~- inch to 1/2-inch have been deposited a]ong the quarry access road presumably by tii"~ operator of the quarry. This material can be found along the natural swale downstream of the HR-6 ba~cin and along the east side of the quarry access road. This material can ,~ also 1?e found at several locations along Cedar Heights Drive. Runoff from the HR-6 basin will continue to Carry this material to downstream areas until such time the material is removed yr otherwise stabilized. This material has apparently bean used to construct a truck ramp in the vicinity of the outlall paint ~f the HR-6 basin. Review of Alternative Qptions As a result of the preparation of the Obaring Wurth HR-6 Synder Quarry CAP and the subsequent review of this report by th~s MLRD, seven alternative drainage plans have been developed. A discussion of each follows. Option l: This option consists of the construction o£ a 24-inch culvert under the quarry access road at the outfdll point of the HR-6 basin. This culvert has the capacity to convey the 5-year flow under. the road and into the natural Swale., The overflow li.e., the )lows exceeding the 5-year discharge), are proposed '~`~n~Pd"~o be con'v~~+'e"d''Yn" a'roadside ditch aligned along the west side o! the quarry access road and outlall to the existing 84'/30-inch culvert. The total slow estimated to reach the 54/30-loon, culvert in a 100-year avant is 108 cubic feet per second 1cfs1. This exceeds the culvert capacity and would cause flow to overtop the roadway in the vicinity of the qua rd house. This option is in our opinion unacceptable since no provision for stabili~~ation of the natural Swale has been proposed. This concept implies that flow will be diverted from the historic flow path. Th~.s option would simply shift the existing aoneerns to another :location. The roadside Swale proposed for this option would have 2 A - ... ._.' .1'