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Memorandum to CWCB Page 4 <br /> equipment averages ten years. Therefore, in order to continue using the present system to collect and <br /> transmit basic stream flow data, all sets of electronic equipment must be replaced approximately every 10 <br /> years. Since DWR operates over 450 total sets of DCP equipment this equates to an average of about 45 <br /> replacements per year. <br /> This new standard for faster transmission rates for sending data from the stream gages to the central <br /> computer has greatly improved the'real-time'nature of the system. With new high data rate DCPs in <br /> operation,data transmission changes from once every four hours to every hour. The cost of new DCPs <br /> with the new radios is$2,700. To replace antennas, batteries,gage height sensors,solar panels,wiring, <br /> grounding equipment, etc., the total cost per site averages$4200. <br /> Flood Hardening/High Flow Measurement Sustainabillty at Existing Stream Ganes <br /> In 2001, a committee of representatives of DWR, CWCB and the USGS evaluated and ranked, using <br /> a set of flood warning/monitoring criteria, all satellite monitoring stream gages throughout the State. <br /> This ranking has identified prioritized sites where flood-hardening projects would be useful in flood <br /> warning and notification. The cost to modify many of these gages to withstand flood events varies <br /> considerably. Each site is being evaluated for required modifications to flood harden the gage. Flood <br /> hardening, by definition, allows for stream flow data to continue to be transmitted during a flood event. <br /> Flood hardening prevents the need to develop a plan to remove all equipment from stream gages prior to <br /> their destruction by floods. While this equipment removal saves equipment costs,this does not allow for <br /> data transmission during flood events to emergency managers and the public. <br /> Flood hardening involves moving or modifying the existing stream gages so that they can continue to <br /> operate during flood events. Some times it may be necessary to add a second gage at the site on higher <br /> ° ground so that the low flows needed for accurate water administration can be measured and the high flows <br /> of floods also can be measured. Another form of flood hardening involves rebuilding the stream channel <br /> so that accurate data will continue to be available during the flood. Often the stream channel becomes <br /> scoured or modified to the point that existing relationships between stage and discharge are no longer <br /> valid at high flow. Even if the stage data continues to be available, it is of little or no value in determining <br /> the flow of the river. <br /> High flow measurement capability varies from gage to gage. High flow discharge measurements at <br /> DWR stream gages are important for maintaining/updating the high flow portion of the gage's stage- <br /> discharge relationship. This calibration consequently improves the accuracy of high flows reported at <br /> the gage(s). High flows at stream gages are measured from cableways at the gage or from nearby <br /> • up-or downstream bridges. Cableways at DWR stream gages are given a detailed inspection each <br /> four years. During the past 4 years many cableways, primarily because of age, have been found to <br /> need replacement of key components of the cableway system. High flow measurement sustainability <br /> projects address such identified cableway design/safe use issues. These may include replacement of <br /> cable, improvements to the cable anchorage system, replacement of A-frame components, <br /> replacement of cable cars, etc. Alternatively, existing cableways found to have design or safe use <br /> deficiencies are, under certain site conditions, being replaced with bank-operated cableways. High <br /> flow measurements are facilitated with new technology measuring equipment:Acoustic Doppler <br /> Current Profilers (ADCPs). This technology provides for more rapid, safer, and often more accurate <br /> measurement of stream flow. DWR is employing this technology to help verify and extend the middle <br /> and upper ranges of the stage-discharge relationship at key gages. <br /> • <br />