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<br />capital cost for a specific size is interpolated from this function and the equi valent <br />annual cost is computed as the product of the capital cost and the capital recovery <br />factor for the appropriate discount rate. The annual cost of operation, mainte- <br />nance, and replacement is the product of the annual cost proportion and the <br />interpolated capital cost. The total annual cost of the reservoir is the sum of <br />these two costs, <br />In initial test applications of the technique to the Blue Waters Ditch studies <br />of the authorized East 5t, Louis and Vicinity Interior Flood Control Project, <br />it became apparent that for one component the "reservoir size" that was to <br />be determined was in actuality the lands that were to be acquired because <br />the "reservoir" embankment was sufficiently high so as to essentially contain <br />all floods. The embankment was in fact a large proposed highway fill. The <br />flow out of the reservoir would therefore pass only through the low level outlet <br />and thus the only variable to control the operation of the reservoir was the <br />capacity of the low level outlet. For this particular situation, a reservoir's operating <br />characteristics are specified uniquely by the outflow characteristics of the low <br />level outlet and the item regarding the reservoir that is to be optimized is the <br />"size" of the outlet. The reservoir performance is characterized as before except <br />it simply has no spillway and the dischargo coefficient for the low level outlet <br />is held constant and the area of the outlet opening is varied, .The cost charac- <br />terizations include a capital cost of outlet works function, and the reservoir <br />capital cost function which would be primarily the cost of acquiring the reservoir <br />site for the ponding level equivalent to a specified exceedence probability, taken <br />as the degree of protection in this case. This characterization will be necessary <br />for studying systems for urban areas that are protected by major levees, as <br />is typical in many local protection projects where pumping is necessary to remove <br />flood waters and the amount of ponding near the pumping facility is a function <br />of the size of the pumping facility. <br />Pumping Plant Characterization.-A pumping facility removes volume from <br />the system at a rate equal to the pumping capacity. The performance characteristics <br />of a pumping plant are .defined by an initial threshold water level at which <br />the pump is activated and the discharge capacity of the pumping facility, In <br />this analysis, it is assumed that water pumped from the system does not later <br />appear at other locations in the system. The cost of a pumping facility is computed <br />from a capital cost function and an associated capital recovery factor for <br />converting to equivalent annual cost, the annual operation, maintenance, and <br />replacement cost that is a proportion of the capital cost, and the annual power <br />cost. The power cost is 'adjusted if the volume to be pumped changes as the <br />system components sizes are being optimized. It can be demonstrated that despite <br />the pumping capacity, the power costs would not materially change if the volume <br />to be pumped does not change. The annual power costs are therefore adjusted <br />only for water that is removed from the system by diversions or other pumping <br />facilities. <br />Diversion Characterization,-A flow diversion transfers flow between locations <br />within or removes flow from the system. The performance characteristics are <br />defined by a threshold flow and a diversion capacity. The concept of the diversion <br />is indicated in Fig. 3 by showing the effect on a flood hydrograph. Flow diverted <br />at one location may be returned to the system at any downstream locationso that it is possible to characterize a facility that would bypass a portion <br /> <br />.1 <br />