Estimating water surface area at different flows using high-resolution multispectral digital imagery

This paper describes an application using high-resolution imagery (0.3 meter pixels) to obtain water surface areas at different flow rates on a 3.2 Kilometer long controlled bypass reach of the Catawba River close to Great Falls, South Carolina. The multispectral images were acquired using the USU airborne multispectral digital system during a 5-day period in November of 2004. Each flight was conducted at a different flow rate, once the flow reached steady state after adjustment of the control gates. The imagery from each flight was processed forming rectified mosaics of the entire reach that were cut using an overlay polygon covering the extent of the river channel and immediate banks. The imagery was classified using supervised classification techniques in order to extract the water surface area from the rectified mosaic. The water area totals were plotted against the steady state flow rates obtaining a very good relationship with a coefficient of determination of over 99%. This project showed the usefulness and cost effectiveness of airborne digital imagery taken under difficult lighting and sun-angle conditions.