Laserfiche WebLink
_~_ <br />' S' I S H B AG R A, I N C s ~a s;s Union 81vd. <br />1 ' B I Engineering&Enviionmenta/Services lzkewood, Colorado <br />t~ U.S.A. 80228 <br />Phone: 303-763-8432 <br />February 17, 1993 Fax: 303989-5525 <br />Mr. John Lohr SHB AGRA Project E92-7075 <br />Southwest Portland Cement <br />P.O. Box 529 <br />Lyons, Colorado 80540 <br />RE: Haul Road Bridge Floodplain Analysis <br />Dowe Flats Project, Boulder County, Colorado <br />Dear Mr. Lohr: <br />Transmitted herewith is the report of our analysis of the impacts of construction of a bridge over <br />St. Vrain Creek for the proposed haul road from the Dowe Flats quarry to the cement plant. <br />The proposed haul road bridge is to be designed for use by 85 ton capacity mine trucks. The <br />bridge will be a two span structure with a total length of approximately 116 feet to span the <br />ordinary high water lines of the St. Vrain. The center pier will be established within the normal <br />channel of St. Vrain Creek, however the quantity of material placed and the surface area <br />disturbed are small. <br />The bridge location is at the downstream end of a section of the St. Vrain floodplain where the <br />100 year storm flow splits, with a portion of the total flow passing down an indistinct southern <br />channel flow area as defined by the current Boulder County floodplain mapping. Accordingly, <br />the impact of construction of the haul road bridge on the 100 year floodplain is to cause a slight <br />increase in the flow diverted to the southern flow channel. Results of this analysis predict the <br />surface water elevation in the northern or main channel of the St. Vrain will be slightly lower <br />than to that currently defined for the unaltered St. Vrain floodplain. The additional flow that <br />would be diverted to the southern channel area will cause a small (0.2 foot) increase in the water <br />surface elevation as a result of the very broad southern flow channel. <br />Should there be any questions concerning this report, we would be pleased to discuss them with <br />you. <br />-<, <br />Vice PreSidenf-~g-9¢ <br />Enclosures <br />:E. <br />AG RA <br />Earth & Environmen to/Group <br />