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C150109 Feasibility Study
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C150109 Feasibility Study
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Last modified
8/10/2011 9:47:21 AM
Creation date
2/21/2008 2:17:00 PM
Metadata
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Template:
Loan Projects
Contract/PO #
C150109
Contractor Name
Larimer and Weld Irrigation Company, The
Contract Type
Loan
Water District
2
County
Weld
Bill Number
MC3
Loan Projects - Doc Type
Feasibility Study
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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />This alternative, although less expensive initially than the replacement alternative, has several <br />disadvantages when compared to the third alternative. The structures will be patched and <br />repaired, but will have a shorter life span than a new structure. We would estimate the structures <br />would most likely be ready for complete replacement in approximately 30 to 40 years. The new <br />structures would be expected to last on the order of 100 years with repair on the gates and controls <br />requirc~d every 25 years. The repaired structure would utilize the same method of checking the <br />ditch by using stop logs which is difficult and dangerous on this size of ditch. No improvements <br />in operational efficiency can be achieved with the repaired alternative using stop logs for the <br />checks. The addition of gates to the old structures is not feasible due to the condition of the <br />structure walls and the lack of reinforcing steel in the' walls and slab. <br /> <br />Alternative #3 <br /> <br />This alternative consist of a total replacement of the existing structures with a concrete structure <br />which; incorporates energy management features to control downstream erosion; and, utilizes <br />Obemleyer pneumatically operated gates. The gates are controlled by a programable PCL unit <br />that allows onsite or remote operation. The gates can be programmed to hold a certain backwater <br />elevation or a certain discharge over the gate. Power is supplied to the control unit by solar cells <br />and the gates are opened and closed by a 12-volt DC powered air pump. The system can be <br />operated remotely, but will not be configured to do so at this time. <br /> <br />The proposed new check structures would be similar in configuration to the two checks built in <br />2002. Those checks have a critical-flow throat in a rectangular constricted section, with upstream <br />stilling wells and air-operated Obermeyer gates to control the upstream water surface elevation. <br />Gate operation is automatic, with power supplied by photo-voltaic collectors through storage <br />batteries. For hydraulic energy management, the downstream sections of the checks have a plunge <br />pool stilling basin, with either a solid or a dentated end sill (dependent on sub-elevation of the <br />plunge: pool floor). Water exits the structures in a trapezoidal cross-section that approximates the <br />downstream ditch cross-section, A downstream riprap apron, which varies in length from 10 to <br />40 feet, provides downstream erosion protection. An engineering drawing showing thl~ plan and <br />section details of the structures is included in Appendix B of this report. <br /> <br />Sizing of the check structures is based on linear variation of design discharge with canal length; <br />between 1000 cfs at Lee Lake to 200 cfs at the outfall to the Owl Creek Lateral. <br /> <br />The check structures considered for replacement are listed in Table 3. The width and height of <br />the structure is listed and the estimated cost of each structure is provided in the table. <br /> <br />The cost of the check structures are based on the actual cost of three structures that were finished <br />in the spring of 2002. The cost breakdown of the three structures completed are shown in Table <br />4. The cost of the structures in Table 3 were estimated based on a cost per foot price of $5,100 <br />based on the information shown in Table 4. <br /> <br />Larimer & Weld Feasibility Study <br /> <br />Page 10 <br />
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