Appendix C - Provisional Inflow Data Development - New and Watauga

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APPENDIX C – Provisional Inflow Data Development for the New and Watauga River Basins

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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 5 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 For gages that are no longer active, a drainage area adjustment of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.
• 03164000 New River near Galax, VA
• 03161000 South Fork New River near Jefferson, NC
• 3480000 Watauga River At Stump Knob, TN
• 03479000 Watauga River near Sugar Grove, 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.