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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 />The outlet works consists of a cast In -place concrete, modified horseshoe shaped <br />conduit, The outlet end of the conduit empties Into an open masonry flume that <br />discharges Into the creek channel approximately 126 feet downstream of the dam, <br />The outiet has no energy dissipation structure, The outlet conduit is approxl- <br />mately 600 feet In overall length and has mlnlmal slope. The outlet works Is in <br />good condition and no rehabilitation work Is being considered at this time. <br /> <br />2. Problem Areas, The primary problem at the Mountain Home Reservoir Is the <br />inadequate spillway in conjunction with inadequate freeboard on the dam for the <br />spillway size, FOllowing Is a general list of deficiencies, <br /> <br />1. Inadequate spillway size in conjunction with the avallable freeboard <br />to allow filling to the maximum decreed gage height. <br />2, Poor condition of the spillway control section. <br />3, Seepage at the toe of the main dam. <br />4. Potential for sliding of the basalt blocks to the south of the <br />spillway If flood flows saturate the underlying silts and clays. <br /> <br />Due to the deficiencies of the emergency spillway, the State Engineer has placed <br />a restriction on the dam requiring storage be limited to Gage Height 87,6 feet <br />rather than the maximum storage of Gage Height 100 feet. Because of the <br />current storage restriction, the owner Is potentially loslng 7,361 acre-feet of <br />storage per year, The restr~ctions at tl1..is ~ tlme<!() J!ot_~ll,t!y~ffec! tl:le <br />operation of th" "ystem; however,_.the.Jpst s!~rage could be .s.1.&rt.1.flcl!.ntln a dry <br />year due to a reduction in potential carryover. Another concern is the potential <br />for another entity toffle on the' ro.st storage-and challenge their water right. <br /> <br />3. Proposed Improvements, In order to restore the reservoir to full utilization, <br />It is necessary to reconstruct and replace the spillway and increase the <br />freeboard on the dam. The crest of the dam must be raised approxlmately 3 to <br />16 feet, depending on the spillway option chosen, to provide adequate freeboard; <br />riprap and rlprap bedding must be placed on the upstream slopes where the dam <br />Is raised; a toe drain should be installed at the downstream toe of the dam to <br />control the underseepage; and, the spillway must be sized such that It will pass <br />a minimum of 76% of the probable Maximum Flood (PMF) as required by the State <br />Engineer's office for a Class I, large size dam as outlined In Rule 6 of The Rules <br />And Regulations For Dam Safety And Dam Construction. <br /> <br />A more detailed description of the proposed improvements and structural plans is <br />included in the remainder of this chapter, <br /> <br />A.2, STRUCTURE PLANS <br /> <br />1. Spillway, The primary reason for this study was to determine the <br />alternatives avallable for the construction of an adequate emergency spillway. <br />Three types of emergency spillways were contemplated at three different <br />locations. The pIan view on Figures V-2 shows the location of the three <br />alternatives to be considered throughout the remainder of this study, <br /> <br />Emergency Spillway Alternative No. 1. Alternatlve No, 1 is a spillway excavat- <br />ed into the south (left) abutment area of the main dam as shown on Figures V-2 <br /> <br />PAGE V-3 <br />Chapter V - Mountain Home Reservoir <br />