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and maintenance costs by about $30,000 once every 10 years. <br />Alternative 3 <br />Advantages <br />- Provides precise flow control with a larger flow capacity compared to Alternative <br />2. <br />- Preserves the existing schematic of two parallel valves. <br />Disadvantages <br />- Would be the most expensive to construct. <br />- Does not provide redundancy in flow control for gate repairs or back up closure. <br />- Relies on the unknown structural integrity of the existing concrete bulkhead. If the <br />bulkhead were to fail, it would result in draining the reservoir in an uncontrolled <br />manner. <br />- Requires reservoir drawdown and stream diversion. <br />Alternative 3A <br />Advantages <br />- Provides precise flow control with a larger flow capacity compared to Alternative <br />2. <br />- Preserves the existing schematic of two parallel valves. <br />- Provides a means to dewater for valve maintenance. <br />- Work could be performed under full or partial reservoir head, eliminating the need <br />to drain the reservoir. <br />Disadvantages <br />- Construction requires a barge and lift with divers. <br />- Bulkhead closure may require crane and divers and will increase routine operation <br />and maintenance costs by about $30,000 once every 10 years. <br />Conclusions <br />- Flow control with throttling can be provided at either the upstream intake end of the outlet works <br />or at the mid - section of the dam: <br />- Slide gate on the upstream end of the outlet works. <br />- Knife gate valves at mid - section in the location of the existing valves. <br />- A bulkhead could be added to provide an upstream control if mid - section flow control is selected. <br />The bulkhead provides redundancy in case of emergency and allows for dewatering for outlet <br />inspection and valve and tunnel maintenance. It also reduces construction costs by allowing the <br />work to be performed without drawing down the reservoir. Due to the shape and condition of the <br />intake, other methods to plug the intake for construction were not feasible. <br />- Existing pipes require lining if mid - section valves are used. Steel is appropriate for liner pipe <br />because of installation conditions, sediment laden flows, and potentially high flow velocities. <br />- Underwater construction with a barge would cost less than constructing in the dry. The high cost <br />for dry construction comes from building access over the sediment, stream diversion, and potential <br />fines for sediment release. <br />