PROJ00455 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I I I I I I ! I I I I I engineering judgment and evaluation. The alternative with the highest total points is the most feasible alternative. A comparative evaluation matrix for each of the proposed alternatives is presented in Table 7.3. As can be seen from this table the tunnel alternative scored 33 and the pipeline 20. This indicates that the pipeline is generally more complex to design and construct, and has more permitting and right-{)f-way problems. 8.0 CONCLUSIONS AND RECOMMENDATIONS 8.1 Conclusions The results of the geological and tunnel site evaluation indicates that construction of a reliable tunnel adjacent to the existing tunnel is possible. Based on the comparative evaluation between the tunnel alternative and bypass pipeline, it appears that the proposed tunnel alternative is the most feasible plan for augmenting the existing pipeline system. This alternative presents fewer and less complicated construction and design considerations, and is easier to permit. For the following reasons the bypass alternative is believed to be less reliable than the tunnel alternative: a) The subsurface conditions along the pipeline present some risk of possible future movement and possible distress of the pipeline; b) The river crossings present adverse construction conditions such as unstable trenches, and the need for de-watering. Soft and unstable ground conditions present difficulty in pipeline installation and the pipe could be more prone to problems; c) The river crossings are susceptible to scour and undermining during the event of a major storm events; and d) During a major storm event the Colorado River and Plateau creek can undercut their banks which would cause pipeline failures outside of current scour and erosion zones . 8.2 Recommendations Based on the results of this amendment feasibility study, we recommend that the tunnel alternative be selected as the recommended alternative for augmentation of this portion of the water delivery 4S