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Show PART VIII TECHNOLOGICAL ADVANCEMENTS Large-scale tests performed or sponsored by the Bureau of Reclamation indicate a capability of reducing lake evaporation losses by 8 to 14 percent at an operational cost of about $60 to $70 per acre- foot. Future improvements in techniques and the efficiency of opera- tion may reduce costs to a point where such operations would be justified for municipal and industrial uses. Flow Measurement Techniques Instrumentation in hydrology has developed greatly within the past few decades. Electronic circuitry is being adapted to replace mechanical equipment for measuring stages and velocities. Such devices as the optical current meter (for reading very high surface velocities without physical contact with the water) and the sonic velocity meter (for continuous recording of average velocity on a cross-channel line) help us gather streamflow data that has been difficult or impossible to collect. Equipment to measure tracer materials can help to determine the diffusing and mixing properties of waterways and to measure the rate of movement of delimited masses of water. Unmanned installations (quality of water monitoring stations) that can sample streamflow and record the concentration of sediment and of many solutes are being operated at sites of special interest. Such equipment must be improved and brought into more general use. Laboratory studies of the use of dam crests, bridge constrictions and other waterway structures as measuring devices have been made, but more such studies are needed. There is also great need for sensors of water level, water depth, and streamflow that can operate without direct contact with the water itself, in order to reduce vulnerability to damage. Techniques and equipment for determining the directions and rates of underground flow are as yet poorly developed, and the changes in chemical quality of water during its residence underground are as yet inadequately understood. There may be advances in the use of tracer substances to determine the nature of underground flow, and there is need for more complete metering of withdrawals from ground water. Greatly refined measurements of all the surface components of the hydrologic budget are necessary to determine the recharge to ground water. There will undoubtedly be advances in the technology of inter- pretation of cores and well logs, in seismic exploration, and perhaps in completely new methods of determining the nature of aquifer charac- teristics. Advancements in these fields (study of the hydrologic budget and study of aquifers), and in the application of methods already known but as yet considered too costly for use in hydrology, together would greatly increase our knowledge of the underground regimen of water. 33 |