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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 /> <br />Structure 7 - Owl Creek/Branch Split. The purpose of the Structure is to apponion flows <br />between the main Owl Creek Lateral and the Branch, a west side lateral. The relatively new <br />existing structure appears to have been designed for a 60% (0 40% split between the main <br />Owl Creek and the Branch Lateral. Under current operations, the maximum flow is estimated <br />to be 200 cfs in the main ditch. and 60 cfs in the Branch. The existing Structure appears to <br />have been built within the past 10 years. and is good physical condition. Because of <br />measurement problems, the existing Structure should either be removed entirely before <br />instaIIing a new structure; or it should be significantly modified, as described below. <br /> <br />The structure is located on a relatively straight reach of me lateral. so thal approach <br />conditions are generally good; however. the structure alignment is skewed with respect to the <br />channel; and downsrream conditions are urumitable for measurement on the Branch side. The <br />main channel is generally stable upstream from the structure, and marginally unstable <br />downstream. Erosion prmection downstream of the Strucrure is curremly inadequate. both <br />with respect to configuration and material - bank protection and energy management seem <br />to work at cross-purposes. Plunge pools at both discharge points should be configured to <br />provide bank prOtection. energy management, and a smooth transition to the downstream <br />conditions. Those objectives can be largely achieved by proper riprap sizing and placemem <br />below either a new structure or a reconfigured existing structure. <br /> <br />The alternative considered was to repair/modify the existing structure. The dimensions of <br />the existing Structure appear to be such that it could be modified to improve the flow <br />characteristics. This would require the installation of a ramp in each side to rum the structure <br />into a Replogle tlume. and modifying the walls on the branch side to provide a more unifonn <br />transition of the flow. Some riprap and bedding material would need to be imponed to the <br />site. and any existing broken concrete riprap should be funher broken up such that the <br />maximum dimension is no greater than 3 times the minimum dimension. Riprap should be <br />hand-placed over bedding material to specified comours to provide the previously memioned <br />hydraulic objective. <br /> <br />The existing structure has a 16.0 foot throat for the Owl Creek side and a 9.0 foot throat on <br />the Branch side. There is no drop through lhe structure on either side. The strocrure could <br />be modified by installing new 8-inch walls on the Branch side (Q provide for a proper <br />transition of tlow around the 45 degree rum. The installation of a 2.0 foot ramp on lhe <br />Branch side and a 1.0 foot ramp on the Owl Creek side would be required to rum the <br />structure into a Replogle tlume to provide for accurate flow measuremnts. The flow capacity <br />for the Owl Creek side would be 200 cfs at a head of 3.0 feet and a 60 cfs on the Branch side. <br /> <br />The details for [be modified flume are shown on Figure 5. <br /> <br />Structure 8 - Branch TurnoutlDrop. The purpose of the structure is to deliver water to two <br />right-side head ponds which serve cemer-pivots. The existing structure appears to have been <br />modified on at least three previous occasions. Under currem operations. the maximum flow <br />is estimated to be 15 cfs in the Branch and a total of 3 cfs to both of the rum-outs. The <br /> <br />Owl Creek Feasibility <br /> <br />Page 9 <br />