Appendix C - Provisional Inflow Data Development - French Broad

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APPENDIX C – Provisional Inflow Data Development for the French Broad River Basin

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The current methodology for developing model inflow data does not lend itself well to frequent updates that will be necessary for real-time forecasting using OASIS in position analysis mode. The current methodology requires a large amount of input gage data
(using 21 active gages in the basins); impairments from reservoir operations, water supply, wastewater returns, and agricultural withdrawals; correction to negative inflows that could otherwise cause model infeasibility; filling-in of missing gage data; and scaling of gains to ensure that filled-in data for gages with missing data preserves the known volume of flow at downstream gages. Obtaining impairment data alone (which are
necessary to unimpair the gage flows) is the most time-intensive part of the updating process. Hazen has developed a simplified, provisional procedure that will enable weekly or monthly updates to be made, later overridden by periodic annual updates using the
current methodology. It is meant to provide a representative inflow to key points in the basin. The downloading of data and calculations for the provisional update are handled automatically within the GUI from the History tab. To simplify the update as much as possible, the procedure eliminates the need for most
impairments and the concern over negative inflows that could lead to model infeasibility. The assumption is that most of the net impairments (withdrawals – discharges) in the basin are small and occur within a reach and therefore are not likely to have much effect on the natural inflow. The following active gages are used to estimate provisional inflows for the basin. For gages that are no longer active, a drainage area adjustment of
the nearest gage from this list is used.
• 03439000 French Broad River at Rosman, NC
• 03441000 Davidson River near Brevard, NC
• 03443000 French Broad River at Blantyre, NC
• 03446000 Mills River near Mills River, NC
• 03447687 French Broad River near Fletcher, NC
• 0344894205 North Fork Swannanoa River near Walkertown, NC
• 03450000 Beetree Creek near Swannanoa, NC
• 03451500 French Broad River at Asheville, NC
• 03453000 Ivy River near Marshall, NC
• 03453500 French Broad River at Marshall, NC
• 03454500 French Broad River at Hot Springs, NC
• 03456100 West Fork Pigeon River at Bethel, NC
• 03456500 East Fork Pigeon River near Canton, NC
• 03456991 Pigeon River near Canton, NC
• 03459500 Pigeon River near Hepco, NC
• 03460000 Cataloochee Creek near Cataloochee, NC
• 03463300 South Toe River Near Celo, NC
The simplified procedure is detailed in the processor file update_record.1v file contained
in the model database. As noted, all data acquisition and calculations are automatically done within the model from the History tab in the model (instructions are detailed in the available OASIS PowerPoint tutorials). The user should do a manual QA/QC check on the downloaded data before updating the record.