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<br />11 <br />I: <br />I <br />I <br />I <br />I <br />I <br />I' <br />I' <br />1 <br />I <br />I' <br />I <br />I <br />I <br />I <br />1 <br />1 <br />1 <br /> <br />the cost of travel that could be allocated to a gage visit is not always <br /> <br />the same. <br /> <br />Because of these complexities, the technique used in this study <br /> <br />takes as the network manager's decision variables, the number of times that <br /> <br />a particular route of travel is used during the year. A route is defined as <br /> <br />a set of one or more gages and the least cost travel that takes the hydro- <br /> <br />grapher from his home base to each of the gages and back to base. A <br /> <br />route, therefore, will have associated with it an ~~pected cost for travel <br /> <br />and an expected cost of servicing each stream gage visited along the way. <br /> <br />In a network of more than a few stream gages there are a great many feasible <br /> <br />routes when one considers all possible combinations of gages. However, <br /> <br />many of these by the nature of their locations and the connecting road <br /> <br />system will be impractical. Therefore, the first step in the analysis is <br /> <br />to choose a set of practical routes that might stand a chance of being used <br /> <br />in the final solution and to evaluate the unit costs associated with each <br /> <br />route. This practical set will contain routes to gages that are in close <br /> <br />proximity or that lie along a not too devious route; it will also contain, <br /> <br />as individual routes, the path to and from each stream gage with that gage <br /> <br />as the lone stop so that the individual needs of a streamgage can be <br /> <br /> <br />considered in the absence of stops at other gages. <br /> <br /> <br />The second step in the procedure is to determine any special requirements <br /> <br /> <br />for visits to each of the gages. For example, the recording equipment <br /> <br />at a gage may not have the capacity to operate longer then 65 days; such <br /> <br />a gage would then have to be visited at least six times per year. Another <br /> <br />type of constraint can result from auxiliary uses of the streamflow data; <br /> <br />water quality samples, for example, might be required monthly entailing <br /> <br />12 visits to the station each year. <br />9 <br />