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<br />. <br /> <br />A copy of the Approval Letter for Alternative No.3, which was prepared by the State Engineer's office and <br />dated November 6, 200 I, is shown in Appendix B, <br /> <br />Alternate No.4, which is very similar to Alternate No, 3 with the exception of increasing the embankment <br />height by approximately 2 feet and modifYing the existing concrete structure in the spillway, is the most <br />preferred alternative since it would provide the owner with a stable embankment and increase the storage <br />capacity of the reservoir by approximately 40 percent with very few modifications, It should be noted that <br />the plans and specifications for this alternative have not yet been submitted or approved by the State <br />Engineer's office as of this date, <br /> <br />Alternative No,S was ruled out as it would substantially increase the cost of the project, as well as <br />significantly increase the time required to complete the construction, with little added benefit, <br /> <br />. <br /> <br />Selected Alternatives <br /> <br />Alternative No, 4 is the selected alternative for this project since it will allow the owner to increase the <br />reservoir storage from 250 acre-feet to approximately 350 acre-feet with only a few minor modifications <br />and an increase in the project budget of 10 percent However, it should be noted that this alternative, which <br />is very similar to Alternative No, 3 with the exception of the modifications to the final height of the dam <br />and modifications to the spillway structure, has not yet been submitted to or approved by the State <br />Engineer's office, Therefore, at a minimum the owner would like to complete Alternative No, 3 and then <br />complete the enlargement of the reservoir and embankment after it has been approved by the State <br />Engineer's office, <br /> <br />. <br /> <br />Alternative No, 3 consists of repairing/reconstructing the embankment and the construction of a new outlet <br />structure along the south side of the embankment The failed materials situated along the upstream slope of <br />the embankment will be removed and replaced with properly compacted on-site clays, Based on the <br />information obtained from the Geotechnical Investigation completed by NWCC, Inc, it appears that the <br />upstream portion of the existing embankment was placed directly over the topsoil materials, This condition <br />probably led to or was one factor in the slope failure in this area, In addition, it does not appear that a <br />cutoff trench/keyway was constructed beneath the embankment Therefore, prior to replacing the fill <br />materials all of the existing topsoil materials will need to be removed and a positive cutoff trench/keyway <br />will be constructed into the underlying claystone bedrock materials, The on-site clays, which will be <br />excavated from the east end of the reservoir, will then be placed and compacted in this area so that the final <br />slope configuration of the upstream face is 3.5 (horizontal) : I (vertical), Prior to placing the fill materials, <br />the upstream end of the existing outlet pipe will be exposed and the entire pipe will be filled with concrete, <br /> <br />The existing fill materials being removed from the upstream face of the embankment and having a suitable <br />moisture content will be placed and compacted along the downstream face of the embankment The <br />downstream face of the embankment is currently at a 2 (horizontal) : I (vertical) configuration and needs to <br />be at a 2,5 (horizontal) : I (vertical) configuration to meet the State Engineer's minimum requirements, <br />Prior to placing the fill materials in this area, all of the topsoil and vegetation will be removed and the new <br /> <br />. <br /> <br />Martin Cull Dam Rehabilitation Feasibility Study <br /> <br />May 2002 <br /> <br />Page 3 <br />